Title of Invention	PROCESS FOR PRODUCING ACRYLIC ESTER
Abstract	A process for producing an acrylic ester with excellent economic efficiency, which can eliminate the conventional problems to maintain the stable quality and the low unit consumption of raw materials, in the process for producing an acrylic ester using acrylic acid containing high-boiling acid components influencing the loss in quality and the unit consumption of raw materials, and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms, as raw materials, and using a strongly acidic cation exchange resin as a catalyst. In such a process for producing an acrylic ester, a crude acrylic ester withdrawn from the bottom of a low-boiling separation column is supplied to a rectifying column, a rectified acrylic ester is taken out from the top of the rectifying column, while a high-boiling substance containing an acrylic ester, which is withdrawn from the bottom of the rectifying column, is supplied to a high-boiling separation column and/or a thin-film evaporator to separate it into an acrylic ester component and a high-boiling substance, and the separated acrylic ester component is taken out as a distillate and supplied to the low-boiling separation column for its recovery.

Title of Invention

PROCESS FOR PRODUCING ACRYLIC ESTER

Abstract

A process for producing an acrylic ester with excellent economic efficiency, which can eliminate the conventional problems to maintain the stable quality and the low unit consumption of raw materials, in the process for producing an acrylic ester using acrylic acid containing high-boiling acid components influencing the loss in quality and the unit consumption of raw materials, and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms, as raw materials, and using a strongly acidic cation exchange resin as a catalyst. In such a process for producing an acrylic ester, a crude acrylic ester withdrawn from the bottom of a low-boiling separation column is supplied to a rectifying column, a rectified acrylic ester is taken out from the top of the rectifying column, while a high-boiling substance containing an acrylic ester, which is withdrawn from the bottom of the rectifying column, is supplied to a high-boiling separation column and/or a thin-film evaporator to separate it into an acrylic ester component and a high-boiling substance, and the separated acrylic ester component is taken out as a distillate and supplied to the low-boiling separation column for its recovery.

Full Text	PROCESS FOR PRODUCING ACRYLIC ESTER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for producing an acrylic ester, and more particularly, to a process for producing an acrylic ester from acrylic acid and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms using a strongly acidic cation exchange resin. 2. Description of the Related Art Acrylic esters can be produced from acrylic acid and various alcohols, for example, as disclosed in Japanese Patent Laid-open Publication No. Shou 52-57116, by an esterification reaction using a homogeneous catalyst such as sulfuric acid or phosphoric acid, or alternatively, for example, as disclosed in Japanese Patent Laid-open Publications Nos. Hei 2-279655 and Hei 3-52843, by an esterification reaction using a heterogeneous catalyst such as a strongly acidic cation exchange resin. In the continuous production of an acrylic ester, there have heretofore been carried out operations in which acrylic acid and an alcohol are esterified in a reactor using a catalyst such as an inorganic acid, e.g. , sulfuric acid or phosphoric acid, or a strongly acidic cation exchange resin, the resulting reaction liquid is supplied to a low-boiling separation column to separate it into a high-boiling substance composed mainly of a generated acrylic ester and a low-boiling component composed mainly of an unreacted alcohol, acrylic acid, and generated water, and an acrylic ester is collected from the former high-boiling substance and circulated to the reaction system. In a process using an inorganic acid such as sulfuric acid or phosphoric acid as an esterification catalyst (e.g., see Japanese Patent Laid-open Publication No. Shou 52-57116), the use of a highly corrosive inorganic acid has no other choice to select an anti-corrosive material for apparatus, which causes problems that the apparatus becomes expensive and the waste liquid treatment to make an inorganic acid contained in the waste liquid harmless becomes highly costly. In an esterification reaction using an ion exchange resin, there is no drawback that will be involved when an inorganic acid is used as an esterification catalyst. As for acrylic acid to be used as a raw material, acrylic acid purified to remove low-boiling impurities and high-boiling impurities is used, the production cost of acrylic acid rises due to the removal of high-boiling impurities, and therefore, the use of unpurified acrylic acid would become advantageous. However, when acrylic acid containing a high-boiling acid component is used as a raw material, unfavorable polymerization reaction and side reaction occur, facilities such as piping systems are clogged by polymers, the unit consumption of acrylic acid or an alcohol increases, and the quality of a product is deteriorated. Thus, in Japanese Patent Laid-open Publication No. 2003-171347, there is proposed a countermeasure that the concentration of impurities such as maleic acid, B-acryloxypropionic acid (i.e., a dirtier of acrylic acid), furfural, and benzaldehyde is restricted to a specific concentration or lower. Of these high-boiling impurities, in particular, high-boiling acid components such as maleic acid and β-acryloxypropionic acid can easily be removed from waste oil in the production of an ester using a low-boiling alcohol having 4 or less carbon atoms as a raw material, thereby causing no particular problem. However, in the production of an ester using an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms as a raw material, it is difficult to separate high-boiling acid components, which has remarkable influences on the loss in quality of a product and the deterioration of the unit consumption of the main raw material, and which requires uneconomical operation, thereby causing serious problems. In particular, β-acryloxypropionic acid is generated during the storage after the acrylic acid production process, and therefore, the control of temperature and the like during the storage are sometimes required, which makes it difficult to maintain the stable quality and the low unit consumption of raw materials in the production of an acrylic ester. SUMMARY OF THE INVENTION Under these circumstances, it is an object of the present invention to provide a process for producing an acrylic ester with excellent economic efficiency, which can eliminate the conventional problems to maintain the stable quality and the low unit consumption of raw materials, in the process for producing an acrylic ester using acrylic acid containing high-boiling acid components such as maleic acid and β-acryloxypropionic acid influencing the loss in quality and the unit consumption of raw materials, and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms as raw materials, and using a strongly acidic cation exchange resin as a catalyst. The present inventors have made various studies, and as a result, they have found the following facts to complete the present invention: in the production of an acrylic ester from acrylic acid and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms using a strongly acidic cation exchange resin, the yield of a product acrylic ester can be improved without lowering the quality of a product and the amount of waste oil can be reduced to improve production efficiency by supplying the bottom liquid of a rectifying column, in which a crude acrylic ester is rectified, to a high-boiling separation column and/or a thin-film evaporator to separate it into an acrylic ester component and a high-boiling substance, and by taking out the separated acrylic ester component as a distillate and supplying it to the low-boiling separation column for its recovery; and further, an acrylic ester can be produced at the lower unit consumption of raw materials, while maintaining the stable quality of a product, by mixing all or part of the distillate from the high-boiling separation column and/or the thin-film evaporator with water to carry out the extraction treatment of high-boiling acid components. In particular, the application of the extraction treatment is also effective for reducing the burdens on the purification of raw material acrylic acid and the storage management by making it possible to expand the width of high-boiling acid component content in acrylic acid which can be used in the production of an acrylic ester from acrylic acid influenced markedly by high-boiling acid components such as maleic acid and β-acryloxypropionic acid, and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms. That is, the present invention provides a process for producing an acrylic ester by supplying acrylic acid and an aliphatic or alicvclic alcohol having from 5 to 8 carbon atoms to an esterification reactor to cause an esterification reaction using a strongly acidic cation exchange resin as a catalyst in the reactor, the process comprising supplying an obtained reaction product to a low-boiling separation column to distill an alcohol, acrylic acid, and water from a top of the low-boiling separation column, and separating them into a water phase and an organic phase containing the alcohol and acrylic acid, the organic phase being circulated as a circulated liquid to the reactor, supplying a crude acrylic ester, which is withdrawn from a bottom of the low-boiling separation column, to a rectifying column, taking out a rectified acrylic ester from a top of the rectifying column, and supplying a high-boiling substance containing an acrylic ester, which is withdrawn from a bottom of the rectifying column, to a high-boiling separation column and/or a thin-film evaporator to separate it into an acrylic ester component and a high-boiling substance, the separated acrylic ester component being taken out as a distillate and supplied to the low-boiling separation column for its recovery. The process for producing an acrylic ester according to the present invention preferably further comprises, before the distillate taken out from the high-boiling separation column and/or the thin-film evaporator is supplied to the low-boiling separation column for its recovery, mixing all or part of the distillate with water to extract and remove a high-boiling acid component contained in the distillate into a water phase, and supplying an obtained organic phase to the low-boiling separation column for its recovery. For the extraction and removal of the high-boiling acid component, a process wastewater generated in a step of producing an acrylic ester can preferably be used. The process wastewater may include reaction water generated in the esterification reaction and/or steam drain exhausted when a steam ejector is used for reducing pressure in a pressure reduction step included in a step of producing an acrylic ester. The ratio of water to be used to extract and remove the high-boiling acid component, relative to the distillate taken from the high-boiling separation column and/or the thin-film evaporator, may preferably be within a range of from 0.5:1 to 2.0:1, more preferably from 0.8:1 to 1.5:1, by mass ratio. In the process for producing an acrylic ester according to the present invention, the acrylic acid to be used as a raw material is acrylic acid containing high-boiling acid components such as maleic acid and β-acryloxypropionic acid, for example, acrylic acid containing from 10 to 5,000 ppm of maleic acid and/or from 10 to 5,000 ppm of β-acryloxypropionic acid, preferably acrylic acid containing from 10 to 500 ppm of maleic acid and/or from 10 to 3,600 ppm of β-acryloxypropionic acid. According to the present invention, in the production of an acrylic ester using acrylic acid and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms as raw materials and using a strongly acidic cation exchange resin as a catalyst, the yield of an acrylic ester can be improved without lowering the quality of a product by the effective separation of the acrylic ester from high-boiling acid components influencing the quality of a product and the unit consumption of raw materials. In the extraction treatment of high-boiling acid components, process wastewater generated in a step of producing an acrylic ester, including reaction generated water, can be used as extraction water, and therefore, there is no need to introduce fresh water, from the outside of the system, leading to an increase in the amount of wastewater. Further, the application of the extraction treatment of high-boiling acid components makes it possible to separate and remove, by an inexpensive method, high-boiling acid components difficult to be separated, and to use low-purity acrylic acid containing relatively great amounts of high-boiling acid components, as well as makes it easy to carry out the storage management of acrylic acid as a raw material, thereby making it possible to broaden the accepted range of raw material acrylic acid which can be used in the production of an acrylic ester from acrylic acid and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms. For these reasons, the present invention can provide a process for producing an acrylic ester with very excellent economic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing one example of the production process, which is preferred for carrying out the production process of the present invention and is the production process used in Examples 1, 2, and 5. FIG. 2 is a schematic diagram showing another example of the production process, which is preferred for carrying out the production process of the present invention and is the Production orocess used in Examples 3, 4, and 6. FIG. 3 is a schematic diagram showing the production process used in Comparative Examples 1, 2, and 3 . DETAILED DESCRIPTION OF THE INVENTION The process for producing an acrylic ester according to the present invention (hereinafter referred to simply as "the production process of the present invention" in some cases) is a process for producing an acrylic ester by supplying acrylic acid and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms to an esterification reactor to cause an esterification reaction using a strongly acidic cation exchange resin as a catalyst in the reactor, the process comprising supplying an obtained reaction product to a low-boiling separation column to distill an alcohol, acrylic acid, and water from the top of the low-boiling separation column, and separating them into a water phase and an organic phase containing the alcohol and acrylic acid, the organic phase being circulated as a circulated liquid to the reactor, supplying a crude acrylic ester, which is withdrawn from the bottom of the low-boiling separation column, to a rectifying column, taking out a rectified acrylic ester from the top of the rectifying column, and supplying a high-boiling substance containing an acrylic ester, which is withdrawn from the bottom of the rectifying column, to a high-boiling separation column and/or a thin-film evaporator to separate it into an acrylic ester component and a high-boiling substance, the separated acrylic ester component being taken out as a distillate and supplied to the low-boiling separation column for its recovery. In this case, all or part of the distillate from the high-boiling separation column and/or the thin-film evaporator may preferably be mixed with water to extract and remove a high-boiling acid component contained in the distillate into a water phase, and an obtained organic phase is supplied to the low-boiling separation column for its recovery. In the production process of the present invention, acrylic acid containing high-boiling acid components such as maleic acid and β-acryloxypropionic acid, even if it is, for example, acrylic acid containing from 10 to 5,000 ppm of maleic acid and/or from 10 to 5,000 ppm of β-acryloxypropionic acid, and even if it may preferably be acrylic acid containing from 10 to 500 ppm of maleic acid and from 10 to 3,600 ppm of β-acryloxypropionic acid as shown in Examples described below, can be used as a raw material. Incidentally, high-boiling acid components contained in acrylic acid can be analyzed by, for example, gas chromatography. As an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms (hereinafter referred to simply as "the alcohol" in some cases), there can be mentioned, although not particularly limited thereto, so long as an acrylic ester can be formed using a strongly acidic cation exchange resin, for example, 2-ethylhexanol and cyclohexanol. Such an alcohol may be linear or branched. Further, an unreacted alcohol recovered from the low-boiling separation column after the esterification reaction is circulated and recycled. In the production process of the present invention, a strongly acidic cation exchange resin is used as a catalyst for esterification reaction. In the case of a strongly acidic cation exchange resin, a porous or gel type resin can be used, and a porous type resin may preferably be used. In particular, when a low-purity acrylic acid is used, a porous type resin having excellent resistance to organic contamination may preferably be used. As a porous type strongly acidic cation exchange resin, for example, there may preferably be used those which have a degree of cross-linking of from 2% to 16%, a porosity of from 0.1 to 1.0 mL/g, and an average pore diameter of from 10 to 60 nm, specific examples of which are C-26C (available from Duolite International Co.), PK-208, PK-216, PK-228 (available from Mitsubishi Chemical Corporation), MSC-1, 88 (available from The Dow Chemical Company), Amberlyst-16 (available from Rohm and Haas Company) , SPC-108, and SPC-112 (available from Bayer AG). The esterification reaction is carried out by monitoring the conversion of acrylic acid through analyzing the compositions of an inlet liquid and an outlet liquid in the reactor, and adjusting the reaction temperature so that the conversion of acrylic acid becomes substantially constant. The conversion of acrylic acid may preferably be within a range of from -5% to +5%, more preferably from -3% to +3%, based on the conversion of acrylic acid in the steady state reached after the start of operation. The esterification reaction may preferably be carried out within a range of from 50°C to 100°C, more preferably from 70°C to 100°C, although depending on the intended esterification reaction. Further, the esterification reaction is carried out in a liquid phase, and the type of reaction may be on a fluid or fixed bed. In the esterification reaction, a polymerization inhibitor can be used as applied in ordinary cases. Examples of the polymerization inhibitor may include hydroquinone, methoxyhydroquinone, phenothiazine, hydroxylamine, and phenylenediamine. Incidentally, the effect of a polymerization inhibitor can further be enhanced when the esterification reaction is carried out in the presence of molecular oxygen. The thus obtained esterification reaction product is supplied to a low-boiling column for its distillation, and substantially all the amount of high-boiling substance composed mainly of a generated acrylic ester is withdrawn from the bottom of the low-boiling separation column and supplied to a rectifying column for its distillation, thereby obtaining a product acrylic ester as a distillate from the top of the rectifying column. On the other hand, from the top of the low-boiling separation column, low-boiling components composed mainly of an unreacted alcohol, unreacted acrylic acid, and generated water are distilled and condensed to separate them into a water phase and an organic phase composed mainly of an alcohol and acrylic acid. The organic phase is circulated as a circulated liquid to the reactor. On the other hand, the water phase may be discarded as wastewater or may be recycled as process wastewater. To allow the esterification reaction to proceed smoothly, it is advantageous to decrease the amounts of acrylic ester and water and to increase the amounts of alcohol and acrylic acid in the composition of a circulated liquid. Therefore, as for the circulated liquid, although depending on the intended acrylic ester and reaction conditions, the total amount of alcohol and acrylic acid may preferably be 50% by mass or higher, more preferably 60% by mass or higher, and the concentration of water may preferably be 5% by mass or lower, more preferably 2% by mass or lower. Further, the amount of circulated liquid to be circulated to the reactor is not preferred when it is too high or too low because of an increase in the amount of catalyst necessary for the esterification reaction. The amount of circulated liquid may suitably be from 1 to 5 times the total amount of alcohol and acrylic acid newly supplied. A polymerization inhibitor can also be used in the low-boiling separation column. Examples of the polymerization inhibitor may include the same as exemplified regarding the esterification reaction. In the same manner as described above, the effect of a polymerization inhibitor can be enhanced when the operation of the low-boiling separation column is carried out in the presence of molecular oxygen. A high-boiling substance containing an acrylic ester is withdrawn from the bottom of the rectifying column and supplied to a high-boiling separation column, and an acrylic ester component is recovered from the top of the high-boiling separation column. The high-boiling substance withdrawn from the bottom of the high-boiling separation column may be discharged as waste oil, or may be further introduced into a thin-film evaporator to recover an acrylic ester, after which it may be discharged as waste oil. On the other hand, an acrylic ester in the distillate from the high-boiling separation column and/or the thin-film evaporator is supplied to the low-boiling separation column for its recovery. All or part of the distillate from the high-boiling separation column and/or the thin-film evaporator is mixed with water to extract and remove high-boiling acid components such as maleic acid and β-acryloxypropionic acid contained together with an acrylic ester in the distillate into a water phase, and the organic phase is supplied to the low-boiling separation column to recover the acrylic ester. At this time, the distillate from the high-boiling separation column may be supplied without any treatment to the low-boiling separation column, and all or part of the distillate from the thin-film evaporator may be mixed with water to carry out an extraction treatment. In this way, the extraction treatment of high-boiling acid components can reduce the amount of waste oil without increasing the amount of acid components contained in the product acrylic ester. Further, it can expand the accepted range of raw material acrylic acid. In this case, low-purity acrylic acid containing relatively great amounts of high-boiling acid components, for example, even acrylic acid containing from 10 to 5,000 ppm of maleic acid and/or from 10 to 5,000 ppm of β-acryloxypropionic acid, can be used as a raw material, and as shown in the following Examples, acrylic acid containing from 10 to 500 ppm of maleic acid and from 10 to 3,600 ppm of β-acryloxypropionic acid can preferably be used as a raw material. Incidentally, as water to be mixed with all or part of the distillate, a process wastewater generated in a step of producing an acrylic ester may preferably be used. Examples of the process wastewater may include reaction water generated in the esterification reaction and steam drain exhausted in the case of using a steam ejector to reduce pressure in a pressure reduction step included in a step of producing an acrylic ester. In this way, the cost for wastewater treatment is not increased because of no increase in the amount of wastewater by making use of wastewater discharged from a step of producing an acrylic ester without introducing fresh water from outside the system. Further, the ratio of water to be used to extract and remove the high-boiling acid components relative to the distillate from the high-boiling separation column and/or the thin-film evaporator may preferably be within a range of from 0.5 to 2.0, more preferably from 0.8 to 1.5, by mass ratio. The production process of the present invention will be described below in more detail by reference to accompanying FIGs. 1 and 2. The production process of the present invention comprises supplying a high-boiling substance containing an acrylic ester, which is withdrawn from the bottom of a rectifying column, to a high-boiling separation column and/or a thin-film evaporator to separate it into an acrylic ester component and a high-boiling substance, the separated acrylic ester component being taken out as a distillate and supplied to a low-boiling separation column for its recovery. At this time, all or part of the distillate from the high-boiling separation column and/or the thin-film evaporator is mixed with water to extract and remove high-boiling impurities in the distillate into a water phase, and the obtained organic phase is supplied to the low-boiling separation column for its recovery. Therefore, the production process of the present invention is not limited to the production processes shown in FIGs. 1 and 2, and can be carried out by adding appropriate modifications and/or changes to these production processes unless such modifications and/or changes depart from the purport of the present invention. FIG. 1 is a schematic diagram showing one example of the preferred production process to carry out the production process of the present invention. This production process is characterized in that high-boiling acid components are decreased from the bottom liquid of a rectifying column 600 using a high-boiling separation column 700 and a thin-film evaporator 800 in a portion designated as "A", and then all or part of the distillate containing an acrylic ester separated and recovered is circulated to a low-boiling separation column 500. Acrylic acid is supplied through a line 1 to an esterification reactor 100 filled with a strongly acidic cation exchange resin. An alcohol is also supplied through a line 2 and a distillation column 200 to the reactor 100. An alcohol and reaction water are distilled out and introduced through a line 4 into the decanter 300. In the decanter 300, a water phase and an organic phase composed mainly of an alcohol are separated. Then, part of the organic phase is supplied through a line 5 to the esterif icat ion reactor 100, and the residue of the organic phase is sent through a line 6 as waste oil to a waste-oil treatment step. On the other hand, the water phase is stored through a line 7 in a process wastewater tank 400, and sent through a line 8 as wastewater to an alcohol recovery step or a wastewater treatment step. An esterification product containing a generated ester, unreacted acrylic acid, an unreacted alcohol, and generated water is supplied through a line 9 from the reactor 100 to the low-boiling separation column 500 for its distillation. The bottom liquid of the low-boiling separation column 500 contains substantially all the amount of acrylic ester, and is supplied through a line 10 to the rectifying column 600. The top liquid of the low-boiling separation column 500 contains unreacted acrylic acid, an unreacted alcohol, and generated water, and discharged through a line 11 to separate into a water phase and an organic phase composed mainly of acrylic acid and an alcohol. Then, part of the organic phase is circulated as a circulated liquid through a line 12 to the esterification reactor 100, and the residue of the organic phase is circulated as reflux through a line 13 to the low-boiling separation column 500. On the other hand, the water phase is sent through a line not shown in the figure as wastewater to an alcohol recovery step or a wastewater treatment step. The acrylic ester supplied to the rectifying column 600, after rectified, is discharged from the top of the rectifying column 600 through a line 14; part thereof becomes a finished product through a line 15, and the residual part is circulated as reflux through a line 16 to the rectifying column 600. The bottom liquid of the rectifying column is a high-boiling substance containing high-boiling acid components such as maleic acid and β-acryloxypropionic acid together with a small amount of acrylic ester, and is supplied through a line 17 to the high-boiling separation column 700. The top liquid of the high-boiling separation column 700 (referred to as "distillate" in some cases) contains the acrylic ester separated and recovered, and all or part of the top liquid is circulated through a line 18 and the line 9 to the low-boiling separation column 500. The high-boiling substance containing high-boiling acid components such as maleic acid and β-acryloxypropionic acid is sent from the bottom of the thin-film evaporator 800 through a line 21 to a waste-oil treatment step. In the production process shown in FIG. 1, the high-boiling separation column 700 and the thin-film evaporator 800 are used to separate and recover the acrylic ester contained in the bottom liquid of the rectifying column 600; however, it is not necessary to use both of them, and for example, it is possible that, using only the high-boiling separation column 700, the top liquid of the high-boiling separation column 700, containing the acrylic ester separated and recovered, is circulated to the low-boiling separation column 500, and the bottom liquid of the high-boiling separation column 700, containing high-boiling acid components such as maleic acid and β-acryloxypropionic acid, is sent as waste oil to a waste-oil treatment step; or using only the thin-film evaporator 800, a distillate containing the acrylic ester separated and recovered is withdrawn from the top of the thin-film evaporator 800 and circulated to the low-boiling separation column 500, and a residual liquid containing high-boiling acid components such as maleic acid and [3-acryloxypropionic acid is discharged from the bottom of the thin-film evaporator 800 and sent as waste oil to a waste-oil treatment step. In such a production of an acrylic ester, esterification reaction is carried out so that the conversion of acrylic acid is always kept constant, and therefore, the composition of an esterification product is stable and the operation conditions of the low-boiling separation column 500 are also kept stably. That is, the operation temperature of the low-boiling separation column 500 is constant, and the composition and amount of the organic phase to be circulated as a circulated liquid to the esterification reactor 100 are both constant. FIG. 2 is a schematic diagram showing another example of the preferred production process to carry out the production process of the present invention. This production process is characterized in that a high-boiling acid substance containing an acrylic ester, which is withdrawn from the bottom of the rectifying column 600, is supplied to a high-boiling separation column 700 and a thin-film evaporator 800 in a portion designated as "A" to separate it into an acrylic ester component and a high-boiling substance, the separated acrylic ester component being taken out as a distillate, and all or part of the distillate is mixed with water in a portion designated as "B" to extract and remove high-boiling acid components in the distillate into a water phase, the obtained organic phase being supplied to the low-boiling separation column 500 for its recovery. Further, this production process is the same as the production process shown in FIG. 1 up to the stage of reducing high-boiling acid components from the bottom liquid of the rectifying column 600 using the high-boiling separation column 700 and the thin-film evaporator 800, that is, except for a portion designated as "B". Therefore, there will be described herein a step of extracting and removing high-boiling acid components contained in the top liquid of the high-boiling separation column 700 (referred to as "water extraction step" in some times). In FIG. 2, the same equipments as in FIG. 1 are designated by the same numbers. All or part of the top liquid of the high-boiling separation column 700 is supplied through a line 22 and a line 2 3 to an extraction tank 900. At this time, it is supplied to the extraction tank 900 after being mixed in the line 23 with wastewater from the process wastewater tank 400. In the extraction tank 900, high-boiling acid components such as maleic acid and β-acryloxypropionic acid are extracted and removed into a water phase. Then, an organic phase containing an acrylic ester is circulated through the line 24 and the line 9 to the low-boiling separation column 500. On the other hand, the water phase containing high-boiling acid components such as maleic acid and β-acryloxypr'opionic acid is sent through a line 25 as wastewater to a wastewater treatment step. As water to be used to extract and remove high-boiling acid components, any water discharged in the production process may be used, although it is not particularly limited, and process water generated in the production process of an acrylic ester, including reaction water, may preferably be used. In the production process shown in FIG. 2, the step of extracting, with water, all or part of the top liquid of the high-boiling separation column 700 is carried out in a portion designated as NXB"; however, all or part of the top liquid of the high-boiling separation column 700 may be circulated without any treatment to the low-boiling separation column 500, and only for the distillate from the thin-film evaporator 800, the step of extracting, with water, all or part of the distillate may be carried out in a portion designated as "B" . In FIGs. 1 and 2, the mixing ratio of wastewater from the process wastewater tank 400 to be used to extract and remove high-boiling acid components, relative to the distillate from the high-boiling separation column 700 or the thin-film evaporator 800, i.e., the distillate containing an acrylic ester separated and recovered, may preferably be within a range of from 0.5 to 2.0, more preferably from 0.8 to 1.5, by mass ratio. When the mixing ratio is within this range, high-boiling acid components can efficiently be extracted and removed into a water phase, and an acrylic ester from which high-boiling acid components have sufficiently been removed can be circulated to the low-boiling separation column 500. EXAMPLES The present invention will be described below in more detail by way of Examples, but the present invention is not limited to the following Examples. The present invention can be put into practice after appropriate modifications or variations within a range meeting the gists described above and later, all of which are included in the technical scope of the present invention. > To the esterification reactor 100 shown in FIG. 1 were supplied 400 kg/h of acrylic acid containing from 10 to 50 ppm of maleic acid and from 100 to 500 ppm of β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol, and 1,590 kg/h of a recovered alcohol liquid, and after 20 days of operation, the reaction was carried out at a reaction temperature of 85°C and a conversion of acrylic acid of 50%, thereby giving a product acrylic ester at a yield of 990 kg/h from the top of the rectifying column 600. At this time, 25 kg/h of waste oil was discharged from the bottom of the thin-film evaporator 800, and 115 kg/h of the distillate from the high-boiling separation column 700 was circulated to the low-boiling separation column 500. The acid components contained in the obtained product acrylic ester were in an amount of from 25 to 35 ppm (in terms of acrylic acid) . The measurement of acid components in the product acrylic ester was carried out by the titration of acid components (the same shall apply hereinafter). The results are shown in Table 1. > To the esterification reactor 100 shown in FIG. 1 were supplied 400 kg/h of acrylic acid containing from 10 to 50 ppm of maleic acid and from 100 to 500 ppm of β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol, and 1,590 kg/h of a recovered alcohol liquid, and after 230 days of operation, the reaction was carried out at a reaction temperature of 100°C and a conversion of acrylic acid of 50%, thereby giving a product acrylic ester at a yield of 965 kg/h from the top of the rectifying column 600. At this time, 50 kg/h of waste oil was discharged from the bottom of the thin-film evaporator 800, and 90 kg/h of the distillate from the high-boiling separation column 700 was circulated to the low-boiling separation column 500. The acid components contained in the obtained product acrylic ester were in an amount of from 25 to 35 ppm (in terms of acrylic acid). The results are shown in Table 1. > To the esterification reactor 100 shown in FIG. 2 were supplied 400 kg/h of acrylic acid containing from 10 to 50 ppm of maleic acid and from 100 to 500 ppm of β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol, and 1,590 kg/h of a recovered alcohol liquid, and after 20 days of operation, the reaction was carried out at a reaction temperature of 85°C and a conversion of acrylic acid of 5 0%, thereby giving a product acrylic ester at a yield of 1,000 kg/h from the top of the rectifying column 600. At this time, 15 kg/h of waste oil was discharged from the bottom of the thin-film evaporator 800, and 125 kg/h of the distillate from the high-boiling separation column 700 and 140 kg/h of wastewater from the wastewater tank 400 were mixed and supplied to the extraction tank 900 shown in FIG. 2. The water phase was removed as wastewater, and the organic phase containing an acrylic ester was circulated to the low-boiling separation column 500. The acid components contained in the obtained product acrylic ester were in an amount of from 25 to 35 ppm (in terms of acrylic acid). The results are shown in Table 1. > To the esterification reactor 100 shown in FIG. 2 were supplied 400 kg/h of acrylic acid containing from 10 to 50 ppm of maleic acid and from 100 to 500 ppm of β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol, and 1,590 kg/h of a recovered alcohol liquid, and after 230 days of operation, the reaction was carried out at a reaction temperature of 100°C and a conversion of acrylic acid of 50%, thereby giving a product acrylic ester at a yield of 997 kg/h from the top of the rectifying column 600. At this time, 18 kg/h of waste oil was discharged from the bottom of the thin-film evaporator 800, and 125 kg/h of the distillate from the high-boiling separation column 700 and 140 kg/h of wastewater from the wastewater tank 400 were mixed and supplied to the extraction tank 900 shown in FIG. 2. The water phase was removed as wastewater, and the organic phase containing an acrylic ester was circulated to the low-boiling separation column 500. The acid components contained in the obtained product acrylic ester were in an amount of from 25 to 35 ppm (in terms of acrylic acid). The results are shown in Table 1. > To the esterification reactor 100 shown in FIG. 3 were supplied 400 kg/h of acrylic acid containing from 10 to 50 ppm of maleic acid and from 100 to 500 ppm of β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol, and 1,590 kg/h of a recovered alcohol liquid, and after 20 days of operation, the reaction was carried out at a reaction temperature of 85°C and a conversion of acrylic acid of 50%, thereby giving a product acrylic ester at a yield of 815 kg/h from the top of the rectifying column 600. At this time, 200 kg/h of waste oil was discharged from the bottom of the rectifying column 600, The acid components contained in the obtained product acrylic ester were in an amount of from 25 to 35 ppm (in terms of acrylic acid). The results are shown in Table 1. > To the esterification reactor 100 shown in FIG. 3 were supplied 400 kg/h of acrylic acid containing from 10 to 50 ppm of maleic acid and from 100 to 500 ppm of β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol, and 1,590 kg/h of a recovered alcohol liquid, and after 230 days of operation, the reaction was carried out at a reaction temperature of 100°C and a conversion of acrylic acid of 50%, thereby giving a product acrylic ester at a yield of 615 kg/h from the top of the rectifying column 600. At this time, 400 kg/h of waste oil was discharged from the bottom of the rectifying column 600. The acid components contained in the obtained product acrylic ester were in an amount of from 25 to 35 ppm (in terms of acrylic acid). The results are shown in Table 1. > To the esterification reactor 100 shown in FIG. 1 were supplied 400 kg/h of acrylic acid containing from 100 to 500 ppm of maleic acid and from 500 to 3,600 ppm of β-acryloxypropionic acid, 740 kg/h of 2-ethyl- hexanol, and 1,590 kg/h of a recovered alcohol liquid, and after 230 days of operation, the reaction was carried out at a reaction temperature of 100°C and a conversion of acrylic acid of 50%, thereby giving a product acrylic ester at a yield of 975 kg/h from the top of the rectifying column 600. At this time, 40 kg/h of waste oil was discharged from the bottom of the thin-film evaporator 800, and 90 kg/h of the distillate from the high-boiling separation column 700 was circulated to the low-boiling separation column 500. The acid components contained in the obtained product acrylic ester were in an amount of from 220 to 280 ppm (in terms of acrylic acid). The results are shown in Table 1. > To the esterification reactor 100 shown in FIG. 2 were supplied 400 kg/h of acrylic acid containing from 100 to 500 pm of maleic acid and from 500 to 3,600 ppm of β-acryloxypropionic acid, 740 kg/h of 2-ethyl- hexanol, and 1,590 kg/h of a recovered alcohol liquid, and after 230 days of operation, the reaction was carried out at a reaction temperature of 100°C and a conversion of acrylic acid of 50%, thereby giving a product acrylic ester at a yield of 997 kg/h from the top of the rectifying column 600. At this time, 18 kg/h of waste oil was discharged from the bottom of the thin-film evaporator 800, and 125 kg/h of the distillate from the high-boiling separation column 700 and 140 kg/h of wastewater from the process wastewater tank 400 were mixed and supplied to the extraction tank 900 shown in FIG. 2. The water phase was removed as wastewater, and the organic phase containing an acrylic ester was circulated to the low-boiling separation column 500. The acid components contained in the obtained product acrylic ester were in an amount of from 35 to 50 ppm (in terms of acrylic acid). The results are shown in Table 1. > To the esterification reactor 100 shown in FIG. 3 were supplied 400 kg/h of acrylic acid containing from 100 to 500 ppm of maleic acid and from 500 to 3,600 ppm of β-acryloxypropionic acid, 740 kg/h of 2-ethyl- hexanol, and 1,590 kg/h of a recovered alcohol liquid, and after 230 days of operation, the reaction was carried out at a reaction temperature of 100°C and a conversion of acrylic acid of 50%, thereby giving a product acrylic ester at a yield of 845 kg/h from the top of the rectifying column 600. At this time, 170 kg/h of waste oil was discharged from the bottom of the rectifying column 600. The acid components contained in the obtained product acrylic ester were in an amount of from 150 to 170 ppm (in terms of acrylic acid) . The results are shown in Table 1. As can be seen from Table 1, in Examples 1 and 2, the yield of a product acrylic ester was able to be kept high in such a manner that when an acrylic ester was produced using the production process shown in FIG. 1, a high-boiling substance containing an acrylic ester, which was withdrawn from the bottom of a rectifying column, was supplied to a high-boiling separation column and/or a thin-film evaporator to separate it into an acrylic ester component and a high-boiling substance, and the separated acrylic ester component was taken out as a distillate and supplied to a low-boiling separation column for its recovery, thereby decreasing the loss of an acrylic ester from waste oil. At this time, no problem was caused on the quality of a product. Further, in Examples 3 and 4, when an acrylic ester was produced using the production process shown in FIG. 2, a high-boiling substance containing an acrylic ester, which was withdrawn from the bottom of a rectifying column, was supplied to a high-boiling separation column and/or a thin-film evaporator to separate it into an acrylic ester component and a high-boiling product, and the separated acrylic ester component was taken out as a distillate, all or part of which was mixed with water to extract and remove high-boiling acid components such as maleic acid and β-acryloxypropionic acid contained together with an acrylic ester in the distillate into a water phase, the water phase being discharged as wastewater, and the organic phase being supplied to a low-boiling separation column to recover an acrylic ester. In Examples 3 and 4 including a step of water extraction, it became possible to further decrease the loss of an acrylic ester from waste oil and improve the yield of a product acrylic ester, compared with those of Examples 1 and 2, without deteriorating the quality of a product. In the production of an acrylic ester controlling the constant conversion of acrylic acid, the reaction temperature is raised with extending the duration of using a strongly acidic cation exchange resin accordingly, in which case the amount of high-boiling acid components such as β-acryloxypropionic acid influencing the quality of a product increases, and therefore, it becomes necessary to make a response by increasing the amount of waste oil to maintain the quality of a product acrylic ester. However, according to the conditions of Example 4 into which a step of water extraction was introduced, the stable quality of a product acrylic ester and the stable yield of a product were able to be obtained without remarkably increasing the amount of waste oil from the early period of reaction in Example 3. The yield of a product under conditions of a high reaction temperature was quite noticeable as compared with Example 2 and Comparative Example 2. In contrast, in Comparative Examples 1 and 2, when an acrylic ester was produced using the production process shown in FIG. 3, the bottom liquid of a rectifying column was subjected as waste oil without any treatment to a step of waste treatment, and therefore, although the amount of high-boiling acid components contained in the product acrylic ester obtained as part of the top liquid of the rectifying column did not change as compared with Examples 1 to 4, the yield of a product acrylic ester was remarkably decreased as compared with Examples 1 to 4, and the amount of waste oil was remarkably increased as compared with Examples 1 to 4 . From these facts, it can be understood that the loss of an acrylic ester from waste oil can be decreased and the yield of a product acrylic ester can be increased, without deteriorating the quality of a product acrylic ester, by supplying the bottom liquid of a rectifying column to a high-boiling separation column and/or a thin-film evaporator, separating and taking out, as a distillate, an acrylic ester remaining in the bottom liquid of the rectifying column from a high-boiling substance, and supplying the distillate to a low-boiling separation column for its recovery; and further, that a decrease in the loss of an acrylic ester from waste oil can more stably be achieved to improve production efficiency, by introducing a step of water extraction in which all or part of the distillate from the high-boiling separation column and/or the thin-film evaporator is mixed with water generated in the production process to extract and remove high-boiling acid components into a water phase, which is discharged as wastewater, and a organic phase is supplied to the low-boiling separation column to recover an acrylic ester. Further, in Example 5, an acrylic ester was produced in almost the same manner as described in Examples 1 and 2 using the production process shown in FIG. 1, except that a low-purity acrylic acid was used as a raw material. Although the amount of high-boiling acid components contained in the product acrylic ester was great, in spite of using a low-purity acrylic acid as a raw material, the yield of a product acrylic ester and the amount of waste oil were at about the same level as those in Examples 1 and 2. Further, in Example 6, an acrylic ester was produced in almost the same manner as described in Examples 3 and 4 using the production process shown in FIG. 2, except that a low-purity acrylic acid was used as a raw material. In spite of using a low-purity acrylic acid as a raw material, the yield of a product acrylic ester was increased as compared with Example 5, and the amount of waste oil was remarkably decreased as compared with Example 5, both of which were by no means inferior to Examples 3 and 4 using a relatively high-purity acrylic acid as a raw material. In contrast, in Comparative Example 3, an acrylic ester was produced in almost the same manner as described in Comparative Examples 1 and 2 using the production process shown in FIG. 3, except that a low-purity acrylic acid was used as a raw material. The yield of a product acrylic ester was remarkably decreased as compared with Examples 5 and 6, and although the amount of high-boiling acid components contained in the product acrylic ester was smaller than that in Example 5, it was very great as compared with Example 6, and the amount of waste oil was remarkably increased as compared with Examples 5 and 6. From these facts, it can be understood that the loss of an acrylic ester form waste oil can be suppressed on a low level, without deteriorating the quality of a product acrylic ester, to improve production efficiency and achieve the stable production, even when low-purity acrylic acid containing great amounts of high boiling acid components such as maleic acid and β-acryloxypropionic acid is used as a raw material, or even when relatively high-purity acrylic acid is used as a raw material, by introducing a step of water extraction in which the bottom liquid of a rectifying column is supplied to a high-boiling separation column and/or a thin-film evaporator, an acrylic ester remaining in the bottom liquid of the rectifying column is taken out as a distillate through separating a high-boiling substance, all or part of the distillate is mixed with water generated in the production process to extract and remove high-boiling acid components into a water phase, which is discharged as wastewater, and an organic phase is supplied to a low-boiling separation column to recover an acrylic ester. As described above, the production process of the present invention makes it possible to stably achieve a large reduction in the production cost of an acrylic ester. The present invention provides a process for producing an acrylic ester using acrylic acid containing high-boiling acid components, such as maleic acid and β-acryloxypropionic acid, influencing the loss in quality of an acrylic ester and the unit consumption of raw materials, and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms, as raw materials, and a strongly acidic cation exchange resin as a catalyst, which process is excellent from an economical point of view because it can eliminate the conventional problems to maintain the stable quality and the low unit consumption of raw materials, and which process makes a great contribution to the filed of acrylic ester production. We Claim: 1. A process for producing an acrylic ester by supplying acrylic acid and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms to an esterif ication reactor to cause an esterification reaction using a strongly acidic cation exchange resin as a catalyst in the reactor, the process comprising supplying an obtained reaction product to a low-boiling separation column to distill an alcohol, acrylic acid, and water from the top of the low-boiling separation column, and separating them into a water phase and an organic phase containing the alcohol and acrylic acid, the organic phase being circulated as a circulated liquid to the reactor, supplying a crude acrylic ester, which is withdrawn from the bottom of the low-boiling separation column, to a rectifying column, taking out a rectified acrylic ester from the top of the rectifying column, and supplying a high-boiling substance containing an acrylic ester, which is withdrawn from the bottom of the rectifying column, to a high-boiling separation column and/or a thin-film evaporator to separate it into an acrylic ester component and a high-boiling substance, the separated acrylic ester component being taken out as a distillate, mixing all or part of the distillate with water to extract and remove a high-boiling acid component contained in the distillate into a water phase, and supplying an obtained organic phase to the low-boiling separation column for its recovery. 2. The process according to claim 1, wherein water to be used to extract and remove the high-boiling acid component is a process wastewater generated in a step of producing an acrylic ester. 3. The process according to claim 1 or 2 , wherein a ratio of water to be used to extract and remove the high- boiling acid component, relative to the distillate taken from the high-boiling separation column and/or the thin- film evaporator, is within a range of from 0.5:1 to 2.0:1 by mass ratio. 4. The process according to any one of claims 1 to 3, wherein acrylic acid to be used as a raw material in the process for producing an acrylic ester comprises from 10 to 5,000 ppm of maleic acid and/or from 10 to 5,000 ppm of β- acryloxypropionic acid. ABSTRACT OF THE DISCLOSURE PROCESS FOR PRODUCING ACRYLIC ESTER A process for producing an acrylic ester with excellent economic efficiency, which can eliminate the conventional problems to maintain the stable quality and the low unit consumption of raw materials, in the process for producing an acrylic ester using acrylic acid containing high-boiling acid components influencing the loss in quality and the unit consumption of raw materials, and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms, as raw materials, and using a strongly acidic cation exchange resin as a catalyst. In such a process for producing an acrylic ester, a crude acrylic ester withdrawn from the bottom of a low-boiling separation column is supplied to a rectifying column, a rectified acrylic ester is taken out from the top of the rectifying column, while a high-boiling substance containing an acrylic ester, which is withdrawn from the bottom of the rectifying column, is supplied to a high-boiling separation column and/or a thin-film evaporator to separate it into an acrylic ester component and a high-boiling substance, and the separated acrylic ester component is taken out as a distillate and supplied to the low-boiling separation column for its recovery.

Full Text

PROCESS FOR PRODUCING ACRYLIC ESTER
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing
an acrylic ester, and more particularly, to a process for
producing an acrylic ester from acrylic acid and an aliphatic
or alicyclic alcohol having from 5 to 8 carbon atoms using a
strongly acidic cation exchange resin.
2. Description of the Related Art
Acrylic esters can be produced from acrylic acid and
various alcohols, for example, as disclosed in Japanese Patent
Laid-open Publication No. Shou 52-57116, by an esterification
reaction using a homogeneous catalyst such as sulfuric acid or
phosphoric acid, or alternatively, for example, as disclosed
in Japanese Patent Laid-open Publications Nos. Hei 2-279655 and
Hei 3-52843, by an esterification reaction using a
heterogeneous catalyst such as a strongly acidic cation
exchange resin.
In the continuous production of an acrylic ester, there
have heretofore been carried out operations in which acrylic
acid and an alcohol are esterified in a

reactor using a catalyst such as an inorganic acid, e.g. ,
sulfuric acid or phosphoric acid, or a strongly acidic
cation exchange resin, the resulting reaction liquid
is supplied to a low-boiling separation column to
separate it into a high-boiling substance composed
mainly of a generated acrylic ester and a low-boiling
component composed mainly of an unreacted alcohol,
acrylic acid, and generated water, and an acrylic ester
is collected from the former high-boiling substance and
circulated to the reaction system.
In a process using an inorganic acid such as
sulfuric acid or phosphoric acid as an esterification
catalyst (e.g., see Japanese Patent Laid-open
Publication No. Shou 52-57116), the use of a highly
corrosive inorganic acid has no other choice to select
an anti-corrosive material for apparatus, which causes
problems that the apparatus becomes expensive and the
waste liquid treatment to make an inorganic acid
contained in the waste liquid harmless becomes highly
costly.
In an esterification reaction using an ion
exchange resin, there is no drawback that will be
involved when an inorganic acid is used as an
esterification catalyst. As for acrylic acid to be
used as a raw material, acrylic acid purified to remove

low-boiling impurities and high-boiling impurities is
used, the production cost of acrylic acid rises due to
the removal of high-boiling impurities, and therefore,
the use of unpurified acrylic acid would become
advantageous. However, when acrylic acid containing
a high-boiling acid component is used as a raw material,
unfavorable polymerization reaction and side reaction
occur, facilities such as piping systems are clogged
by polymers, the unit consumption of acrylic acid or
an alcohol increases, and the quality of a product is
deteriorated. Thus, in Japanese Patent Laid-open
Publication No. 2003-171347, there is proposed a
countermeasure that the concentration of impurities
such as maleic acid, B-acryloxypropionic acid (i.e.,
a dirtier of acrylic acid), furfural, and benzaldehyde
is restricted to a specific concentration or lower.
Of these high-boiling impurities, in particular,
high-boiling acid components such as maleic acid and
β-acryloxypropionic acid can easily be removed from
waste oil in the production of an ester using a
low-boiling alcohol having 4 or less carbon atoms as
a raw material, thereby causing no particular problem.
However, in the production of an ester using an
aliphatic or alicyclic alcohol having from 5 to 8 carbon
atoms as a raw material, it is difficult to separate

high-boiling acid components, which has remarkable
influences on the loss in quality of a product and the
deterioration of the unit consumption of the main raw
material, and which requires uneconomical operation,
thereby causing serious problems. In particular,
β-acryloxypropionic acid is generated during the
storage after the acrylic acid production process, and
therefore, the control of temperature and the like
during the storage are sometimes required, which makes
it difficult to maintain the stable quality and the low
unit consumption of raw materials in the production of
an acrylic ester.
SUMMARY OF THE INVENTION
Under these circumstances, it is an object of the
present invention to provide a process for producing
an acrylic ester with excellent economic efficiency,
which can eliminate the conventional problems to
maintain the stable quality and the low unit
consumption of raw materials, in the process for
producing an acrylic ester using acrylic acid
containing high-boiling acid components such as maleic
acid and β-acryloxypropionic acid influencing the loss
in quality and the unit consumption of raw materials,
and an aliphatic or alicyclic alcohol having from 5 to

8 carbon atoms as raw materials, and using a strongly
acidic cation exchange resin as a catalyst.
The present inventors have made various studies,
and as a result, they have found the following facts
to complete the present invention: in the production
of an acrylic ester from acrylic acid and an aliphatic
or alicyclic alcohol having from 5 to 8 carbon atoms
using a strongly acidic cation exchange resin, the
yield of a product acrylic ester can be improved without
lowering the quality of a product and the amount of waste
oil can be reduced to improve production efficiency by
supplying the bottom liquid of a rectifying column, in
which a crude acrylic ester is rectified, to a
high-boiling separation column and/or a thin-film
evaporator to separate it into an acrylic ester
component and a high-boiling substance, and by taking
out the separated acrylic ester component as a
distillate and supplying it to the low-boiling
separation column for its recovery; and further, an
acrylic ester can be produced at the lower unit
consumption of raw materials, while maintaining the
stable quality of a product, by mixing all or part of
the distillate from the high-boiling separation column
and/or the thin-film evaporator with water to carry out
the extraction treatment of high-boiling acid

components. In particular, the application of the
extraction treatment is also effective for reducing the
burdens on the purification of raw material acrylic
acid and the storage management by making it possible
to expand the width of high-boiling acid component
content in acrylic acid which can be used in the
production of an acrylic ester from acrylic acid
influenced markedly by high-boiling acid components
such as maleic acid and β-acryloxypropionic acid, and
an aliphatic or alicyclic alcohol having from 5 to 8
carbon atoms.
That is, the present invention provides a process
for producing an acrylic ester by supplying acrylic
acid and an aliphatic or alicvclic alcohol having from
5 to 8 carbon atoms to an esterification reactor to cause
an esterification reaction using a strongly acidic
cation exchange resin as a catalyst in the reactor, the
process comprising supplying an obtained reaction
product to a low-boiling separation column to distill
an alcohol, acrylic acid, and water from a top of the
low-boiling separation column, and separating them
into a water phase and an organic phase containing the
alcohol and acrylic acid, the organic phase being
circulated as a circulated liquid to the reactor,
supplying a crude acrylic ester, which is withdrawn

from a bottom of the low-boiling separation column, to
a rectifying column, taking out a rectified acrylic
ester from a top of the rectifying column, and supplying
a high-boiling substance containing an acrylic ester,
which is withdrawn from a bottom of the rectifying
column, to a high-boiling separation column and/or a
thin-film evaporator to separate it into an acrylic
ester component and a high-boiling substance, the
separated acrylic ester component being taken out as
a distillate and supplied to the low-boiling separation
column for its recovery.
The process for producing an acrylic ester
according to the present invention preferably further
comprises, before the distillate taken out from the
high-boiling separation column and/or the thin-film
evaporator is supplied to the low-boiling separation
column for its recovery, mixing all or part of the
distillate with water to extract and remove a
high-boiling acid component contained in the
distillate into a water phase, and supplying an
obtained organic phase to the low-boiling separation
column for its recovery. For the extraction and
removal of the high-boiling acid component, a process
wastewater generated in a step of producing an acrylic
ester can preferably be used. The process wastewater

may include reaction water generated in the
esterification reaction and/or steam drain exhausted
when a steam ejector is used for reducing pressure in
a pressure reduction step included in a step of
producing an acrylic ester. The ratio of water to be
used to extract and remove the high-boiling acid
component, relative to the distillate taken from the
high-boiling separation column and/or the thin-film
evaporator, may preferably be within a range of from
0.5:1 to 2.0:1, more preferably from 0.8:1 to 1.5:1,
by mass ratio.
In the process for producing an acrylic ester
according to the present invention, the acrylic acid
to be used as a raw material is acrylic acid containing
high-boiling acid components such as maleic acid and
β-acryloxypropionic acid, for example, acrylic acid
containing from 10 to 5,000 ppm of maleic acid and/or
from 10 to 5,000 ppm of β-acryloxypropionic acid,
preferably acrylic acid containing from 10 to 500 ppm
of maleic acid and/or from 10 to 3,600 ppm of
β-acryloxypropionic acid.
According to the present invention, in the
production of an acrylic ester using acrylic acid and
an aliphatic or alicyclic alcohol having from 5 to 8
carbon atoms as raw materials and using a strongly

acidic cation exchange resin as a catalyst, the yield
of an acrylic ester can be improved without lowering
the quality of a product by the effective separation
of the acrylic ester from high-boiling acid components
influencing the quality of a product and the unit
consumption of raw materials. In the extraction
treatment of high-boiling acid components, process
wastewater generated in a step of producing an acrylic
ester, including reaction generated water, can be used
as extraction water, and therefore, there is no need
to introduce fresh water, from the outside of the system,
leading to an increase in the amount of wastewater.
Further, the application of the extraction treatment
of high-boiling acid components makes it possible to
separate and remove, by an inexpensive method,
high-boiling acid components difficult to be separated,
and to use low-purity acrylic acid containing
relatively great amounts of high-boiling acid
components, as well as makes it easy to carry out the
storage management of acrylic acid as a raw material,
thereby making it possible to broaden the accepted
range of raw material acrylic acid which can be used
in the production of an acrylic ester from acrylic acid
and an aliphatic or alicyclic alcohol having from 5 to
8 carbon atoms.

For these reasons, the present invention can
provide a process for producing an acrylic ester with
very excellent economic efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing one example
of the production process, which is preferred for
carrying out the production process of the present
invention and is the production process used in
Examples 1, 2, and 5.
FIG. 2 is a schematic diagram showing another
example of the production process, which is preferred
for carrying out the production process of the present
invention and is the Production orocess used in
Examples 3, 4, and 6.
FIG. 3 is a schematic diagram showing the
production process used in Comparative Examples 1, 2,
and 3 .
DETAILED DESCRIPTION OF THE INVENTION
The process for producing an acrylic ester
according to the present invention (hereinafter
referred to simply as "the production process of the
present invention" in some cases) is a process for
producing an acrylic ester by supplying acrylic acid

and an aliphatic or alicyclic alcohol having from 5 to
8 carbon atoms to an esterification reactor to cause
an esterification reaction using a strongly acidic
cation exchange resin as a catalyst in the reactor, the
process comprising supplying an obtained reaction
product to a low-boiling separation column to distill
an alcohol, acrylic acid, and water from the top of the
low-boiling separation column, and separating them
into a water phase and an organic phase containing the
alcohol and acrylic acid, the organic phase being
circulated as a circulated liquid to the reactor,
supplying a crude acrylic ester, which is withdrawn
from the bottom of the low-boiling separation column,
to a rectifying column, taking out a rectified acrylic
ester from the top of the rectifying column, and
supplying a high-boiling substance containing an
acrylic ester, which is withdrawn from the bottom of
the rectifying column, to a high-boiling separation
column and/or a thin-film evaporator to separate it
into an acrylic ester component and a high-boiling
substance, the separated acrylic ester component being
taken out as a distillate and supplied to the
low-boiling separation column for its recovery.
In this case, all or part of the distillate from
the high-boiling separation column and/or the

thin-film evaporator may preferably be mixed with water
to extract and remove a high-boiling acid component
contained in the distillate into a water phase, and an
obtained organic phase is supplied to the low-boiling
separation column for its recovery.
In the production process of the present invention,
acrylic acid containing high-boiling acid components
such as maleic acid and β-acryloxypropionic acid, even
if it is, for example, acrylic acid containing from 10
to 5,000 ppm of maleic acid and/or from 10 to 5,000 ppm
of β-acryloxypropionic acid, and even if it may
preferably be acrylic acid containing from 10 to 500
ppm of maleic acid and from 10 to 3,600 ppm of
β-acryloxypropionic acid as shown in Examples
described below, can be used as a raw material.
Incidentally, high-boiling acid components contained
in acrylic acid can be analyzed by, for example, gas
chromatography.
As an aliphatic or alicyclic alcohol having from
5 to 8 carbon atoms (hereinafter referred to simply as
"the alcohol" in some cases), there can be mentioned,
although not particularly limited thereto, so long as
an acrylic ester can be formed using a strongly acidic
cation exchange resin, for example, 2-ethylhexanol and
cyclohexanol. Such an alcohol may be linear or

branched. Further, an unreacted alcohol recovered
from the low-boiling separation column after the
esterification reaction is circulated and recycled.
In the production process of the present invention,
a strongly acidic cation exchange resin is used as a
catalyst for esterification reaction. In the case of
a strongly acidic cation exchange resin, a porous or
gel type resin can be used, and a porous type resin may
preferably be used. In particular, when a low-purity
acrylic acid is used, a porous type resin having
excellent resistance to organic contamination may
preferably be used. As a porous type strongly acidic
cation exchange resin, for example, there may
preferably be used those which have a degree of
cross-linking of from 2% to 16%, a porosity of from 0.1
to 1.0 mL/g, and an average pore diameter of from 10
to 60 nm, specific examples of which are C-26C
(available from Duolite International Co.), PK-208,
PK-216, PK-228 (available from Mitsubishi Chemical
Corporation), MSC-1, 88 (available from The Dow
Chemical Company), Amberlyst-16 (available from Rohm
and Haas Company) , SPC-108, and SPC-112 (available from
Bayer AG).
The esterification reaction is carried out by
monitoring the conversion of acrylic acid through

analyzing the compositions of an inlet liquid and an
outlet liquid in the reactor, and adjusting the
reaction temperature so that the conversion of acrylic
acid becomes substantially constant. The conversion
of acrylic acid may preferably be within a range of from
-5% to +5%, more preferably from -3% to +3%, based on
the conversion of acrylic acid in the steady state
reached after the start of operation.
The esterification reaction may preferably be
carried out within a range of from 50°C to 100°C, more
preferably from 70°C to 100°C, although depending on
the intended esterification reaction. Further, the
esterification reaction is carried out in a liquid
phase, and the type of reaction may be on a fluid or
fixed bed.
In the esterification reaction, a polymerization
inhibitor can be used as applied in ordinary cases.
Examples of the polymerization inhibitor may include
hydroquinone, methoxyhydroquinone, phenothiazine,
hydroxylamine, and phenylenediamine. Incidentally,
the effect of a polymerization inhibitor can further
be enhanced when the esterification reaction is carried
out in the presence of molecular oxygen.
The thus obtained esterification reaction product
is supplied to a low-boiling column for its

distillation, and substantially all the amount of
high-boiling substance composed mainly of a generated
acrylic ester is withdrawn from the bottom of the
low-boiling separation column and supplied to a
rectifying column for its distillation, thereby
obtaining a product acrylic ester as a distillate from
the top of the rectifying column.
On the other hand, from the top of the low-boiling
separation column, low-boiling components composed
mainly of an unreacted alcohol, unreacted acrylic acid,
and generated water are distilled and condensed to
separate them into a water phase and an organic phase
composed mainly of an alcohol and acrylic acid. The
organic phase is circulated as a circulated liquid to
the reactor. On the other hand, the water phase may
be discarded as wastewater or may be recycled as process
wastewater.
To allow the esterification reaction to proceed
smoothly, it is advantageous to decrease the amounts
of acrylic ester and water and to increase the amounts
of alcohol and acrylic acid in the composition of a
circulated liquid. Therefore, as for the circulated
liquid, although depending on the intended acrylic
ester and reaction conditions, the total amount of
alcohol and acrylic acid may preferably be 50% by mass

or higher, more preferably 60% by mass or higher, and
the concentration of water may preferably be 5% by mass
or lower, more preferably 2% by mass or lower. Further,
the amount of circulated liquid to be circulated to the
reactor is not preferred when it is too high or too low
because of an increase in the amount of catalyst
necessary for the esterification reaction. The amount
of circulated liquid may suitably be from 1 to 5 times
the total amount of alcohol and acrylic acid newly
supplied.
A polymerization inhibitor can also be used in the
low-boiling separation column. Examples of the
polymerization inhibitor may include the same as
exemplified regarding the esterification reaction.
In the same manner as described above, the effect of
a polymerization inhibitor can be enhanced when the
operation of the low-boiling separation column is
carried out in the presence of molecular oxygen.
A high-boiling substance containing an acrylic
ester is withdrawn from the bottom of the rectifying
column and supplied to a high-boiling separation column,
and an acrylic ester component is recovered from the
top of the high-boiling separation column. The
high-boiling substance withdrawn from the bottom of the
high-boiling separation column may be discharged as

waste oil, or may be further introduced into a thin-film
evaporator to recover an acrylic ester, after which it
may be discharged as waste oil. On the other hand, an
acrylic ester in the distillate from the high-boiling
separation column and/or the thin-film evaporator is
supplied to the low-boiling separation column for its
recovery.
All or part of the distillate from the
high-boiling separation column and/or the thin-film
evaporator is mixed with water to extract and remove
high-boiling acid components such as maleic acid and
β-acryloxypropionic acid contained together with an
acrylic ester in the distillate into a water phase, and
the organic phase is supplied to the low-boiling
separation column to recover the acrylic ester. At
this time, the distillate from the high-boiling
separation column may be supplied without any treatment
to the low-boiling separation column, and all or part
of the distillate from the thin-film evaporator may be
mixed with water to carry out an extraction treatment.
In this way, the extraction treatment of high-boiling
acid components can reduce the amount of waste oil
without increasing the amount of acid components
contained in the product acrylic ester. Further, it
can expand the accepted range of raw material acrylic

acid. In this case, low-purity acrylic acid containing
relatively great amounts of high-boiling acid
components, for example, even acrylic acid containing
from 10 to 5,000 ppm of maleic acid and/or from 10 to
5,000 ppm of β-acryloxypropionic acid, can be used as
a raw material, and as shown in the following Examples,
acrylic acid containing from 10 to 500 ppm of maleic
acid and from 10 to 3,600 ppm of β-acryloxypropionic
acid can preferably be used as a raw material.
Incidentally, as water to be mixed with all or part
of the distillate, a process wastewater generated in
a step of producing an acrylic ester may preferably be
used. Examples of the process wastewater may include
reaction water generated in the esterification
reaction and steam drain exhausted in the case of using
a steam ejector to reduce pressure in a pressure
reduction step included in a step of producing an
acrylic ester. In this way, the cost for wastewater
treatment is not increased because of no increase in
the amount of wastewater by making use of wastewater
discharged from a step of producing an acrylic ester
without introducing fresh water from outside the
system.
Further, the ratio of water to be used to extract
and remove the high-boiling acid components relative

to the distillate from the high-boiling separation
column and/or the thin-film evaporator may preferably
be within a range of from 0.5 to 2.0, more preferably
from 0.8 to 1.5, by mass ratio.
The production process of the present invention
will be described below in more detail by reference to
accompanying FIGs. 1 and 2. The production process of the
present invention comprises supplying a high-boiling
substance containing an acrylic ester, which is withdrawn
from the bottom of a rectifying column, to a high-boiling
separation column and/or a thin-film evaporator to
separate it into an acrylic ester component and a
high-boiling substance, the separated acrylic ester
component being taken out as a distillate and supplied
to a low-boiling separation column for its recovery.
At this time, all or part of the distillate from the
high-boiling separation column and/or the thin-film
evaporator is mixed with water to extract and remove
high-boiling impurities in the distillate into a water
phase, and the obtained organic phase is supplied to
the low-boiling separation column for its recovery.
Therefore, the production process of the present
invention is not limited to the production processes
shown in FIGs. 1 and 2, and can be carried out by adding
appropriate modifications and/or changes to these

production processes unless such modifications and/or
changes depart from the purport of the present
invention.
FIG. 1 is a schematic diagram showing one example
of the preferred production process to carry out the
production process of the present invention. This
production process is characterized in that
high-boiling acid components are decreased from the
bottom liquid of a rectifying column 600 using a
high-boiling separation column 700 and a thin-film
evaporator 800 in a portion designated as "A", and then
all or part of the distillate containing an acrylic
ester separated and recovered is circulated to a
low-boiling separation column 500.
Acrylic acid is supplied through a line 1 to an
esterification reactor 100 filled with a strongly
acidic cation exchange resin. An alcohol is also
supplied through a line 2 and a distillation column 200
to the reactor 100. An alcohol and reaction water are
distilled out and introduced through a line 4 into the
decanter 300. In the decanter 300, a water phase and
an organic phase composed mainly of an alcohol are
separated. Then, part of the organic phase is supplied
through a line 5 to the esterif icat ion reactor 100, and
the residue of the organic phase is sent through a line

6 as waste oil to a waste-oil treatment step. On the
other hand, the water phase is stored through a line
7 in a process wastewater tank 400, and sent through
a line 8 as wastewater to an alcohol recovery step or
a wastewater treatment step.
An esterification product containing a generated
ester, unreacted acrylic acid, an unreacted alcohol,
and generated water is supplied through a line 9 from
the reactor 100 to the low-boiling separation column
500 for its distillation. The bottom liquid of the
low-boiling separation column 500 contains
substantially all the amount of acrylic ester, and is
supplied through a line 10 to the rectifying column 600.
The top liquid of the low-boiling separation column 500
contains unreacted acrylic acid, an unreacted alcohol,
and generated water, and discharged through a line 11
to separate into a water phase and an organic phase
composed mainly of acrylic acid and an alcohol. Then,
part of the organic phase is circulated as a circulated
liquid through a line 12 to the esterification reactor
100, and the residue of the organic phase is circulated
as reflux through a line 13 to the low-boiling
separation column 500. On the other hand, the water
phase is sent through a line not shown in the figure
as wastewater to an alcohol recovery step or a

wastewater treatment step.
The acrylic ester supplied to the rectifying
column 600, after rectified, is discharged from the top
of the rectifying column 600 through a line 14; part
thereof becomes a finished product through a line 15,
and the residual part is circulated as reflux through
a line 16 to the rectifying column 600. The bottom
liquid of the rectifying column is a high-boiling
substance containing high-boiling acid components such
as maleic acid and β-acryloxypropionic acid together
with a small amount of acrylic ester, and is supplied
through a line 17 to the high-boiling separation column
700.
The top liquid of the high-boiling separation
column 700 (referred to as "distillate" in some cases)
contains the acrylic ester separated and recovered, and
all or part of the top liquid is circulated through a
line 18 and the line 9 to the low-boiling separation
column 500. The high-boiling substance containing
high-boiling acid components such as maleic acid and
β-acryloxypropionic acid is sent from the bottom of the
thin-film evaporator 800 through a line 21 to a
waste-oil treatment step.
In the production process shown in FIG. 1, the
high-boiling separation column 700 and the thin-film

evaporator 800 are used to separate and recover the
acrylic ester contained in the bottom liquid of the
rectifying column 600; however, it is not necessary to
use both of them, and for example, it is possible that,
using only the high-boiling separation column 700, the
top liquid of the high-boiling separation column 700,
containing the acrylic ester separated and recovered,
is circulated to the low-boiling separation column 500,
and the bottom liquid of the high-boiling separation
column 700, containing high-boiling acid components
such as maleic acid and β-acryloxypropionic acid, is
sent as waste oil to a waste-oil treatment step; or using
only the thin-film evaporator 800, a distillate
containing the acrylic ester separated and recovered
is withdrawn from the top of the thin-film evaporator
800 and circulated to the low-boiling separation column
500, and a residual liquid containing high-boiling acid
components such as maleic acid and [3-acryloxypropionic
acid is discharged from the bottom of the thin-film
evaporator 800 and sent as waste oil to a waste-oil
treatment step.
In such a production of an acrylic ester,
esterification reaction is carried out so that the
conversion of acrylic acid is always kept constant, and
therefore, the composition of an esterification

product is stable and the operation conditions of the
low-boiling separation column 500 are also kept stably.
That is, the operation temperature of the low-boiling
separation column 500 is constant, and the composition
and amount of the organic phase to be circulated as a
circulated liquid to the esterification reactor 100 are
both constant.
FIG. 2 is a schematic diagram showing another
example of the preferred production process to carry
out the production process of the present invention.
This production process is characterized in that a
high-boiling acid substance containing an acrylic
ester, which is withdrawn from the bottom of the
rectifying column 600, is supplied to a high-boiling
separation column 700 and a thin-film evaporator 800
in a portion designated as "A" to separate it into an
acrylic ester component and a high-boiling substance,
the separated acrylic ester component being taken out
as a distillate, and all or part of the distillate is
mixed with water in a portion designated as "B" to
extract and remove high-boiling acid components in the
distillate into a water phase, the obtained organic
phase being supplied to the low-boiling separation
column 500 for its recovery. Further, this production
process is the same as the production process shown in

FIG. 1 up to the stage of reducing high-boiling acid
components from the bottom liquid of the rectifying
column 600 using the high-boiling separation column 700
and the thin-film evaporator 800, that is, except for
a portion designated as "B". Therefore, there will be
described herein a step of extracting and removing
high-boiling acid components contained in the top
liquid of the high-boiling separation column 700
(referred to as "water extraction step" in some times).
In FIG. 2, the same equipments as in FIG. 1 are
designated by the same numbers.
All or part of the top liquid of the high-boiling
separation column 700 is supplied through a line 22 and
a line 2 3 to an extraction tank 900. At this time, it
is supplied to the extraction tank 900 after being mixed
in the line 23 with wastewater from the process
wastewater tank 400. In the extraction tank 900,
high-boiling acid components such as maleic acid and
β-acryloxypropionic acid are extracted and removed
into a water phase. Then, an organic phase containing
an acrylic ester is circulated through the line 24 and
the line 9 to the low-boiling separation column 500.
On the other hand, the water phase containing
high-boiling acid components such as maleic acid and
β-acryloxypr'opionic acid is sent through a line 25 as

wastewater to a wastewater treatment step. As water
to be used to extract and remove high-boiling acid
components, any water discharged in the production
process may be used, although it is not particularly
limited, and process water generated in the production
process of an acrylic ester, including reaction water,
may preferably be used.
In the production process shown in FIG. 2, the step
of extracting, with water, all or part of the top liquid
of the high-boiling separation column 700 is carried
out in a portion designated as NXB"; however, all or part
of the top liquid of the high-boiling separation column
700 may be circulated without any treatment to the
low-boiling separation column 500, and only for the
distillate from the thin-film evaporator 800, the step
of extracting, with water, all or part of the distillate
may be carried out in a portion designated as "B" .
In FIGs. 1 and 2, the mixing ratio of wastewater
from the process wastewater tank 400 to be used to
extract and remove high-boiling acid components,
relative to the distillate from the high-boiling
separation column 700 or the thin-film evaporator 800,
i.e., the distillate containing an acrylic ester
separated and recovered, may preferably be within a
range of from 0.5 to 2.0, more preferably from 0.8 to

1.5, by mass ratio. When the mixing ratio is within
this range, high-boiling acid components can
efficiently be extracted and removed into a water phase,
and an acrylic ester from which high-boiling acid
components have sufficiently been removed can be
circulated to the low-boiling separation column 500.
EXAMPLES
The present invention will be described below in
more detail by way of Examples, but the present
invention is not limited to the following Examples.
The present invention can be put into practice after
appropriate modifications or variations within a range
meeting the gists described above and later, all of
which are included in the technical scope of the present
invention.
>
To the esterification reactor 100 shown in FIG.
1 were supplied 400 kg/h of acrylic acid containing from
10 to 50 ppm of maleic acid and from 100 to 500 ppm of
β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol,
and 1,590 kg/h of a recovered alcohol liquid, and after
20 days of operation, the reaction was carried out at
a reaction temperature of 85°C and a conversion of
acrylic acid of 50%, thereby giving a product acrylic

ester at a yield of 990 kg/h from the top of the
rectifying column 600. At this time, 25 kg/h of waste
oil was discharged from the bottom of the thin-film
evaporator 800, and 115 kg/h of the distillate from the
high-boiling separation column 700 was circulated to
the low-boiling separation column 500. The acid
components contained in the obtained product acrylic
ester were in an amount of from 25 to 35 ppm (in terms
of acrylic acid) . The measurement of acid components
in the product acrylic ester was carried out by the
titration of acid components (the same shall apply
hereinafter). The results are shown in Table 1.
>
To the esterification reactor 100 shown in FIG.
1 were supplied 400 kg/h of acrylic acid containing from
10 to 50 ppm of maleic acid and from 100 to 500 ppm of
β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol,
and 1,590 kg/h of a recovered alcohol liquid, and after
230 days of operation, the reaction was carried out at
a reaction temperature of 100°C and a conversion of
acrylic acid of 50%, thereby giving a product acrylic
ester at a yield of 965 kg/h from the top of the
rectifying column 600. At this time, 50 kg/h of waste
oil was discharged from the bottom of the thin-film
evaporator 800, and 90 kg/h of the distillate from the

high-boiling separation column 700 was circulated to
the low-boiling separation column 500. The acid
components contained in the obtained product acrylic
ester were in an amount of from 25 to 35 ppm (in terms
of acrylic acid). The results are shown in Table 1.
>
To the esterification reactor 100 shown in FIG.
2 were supplied 400 kg/h of acrylic acid containing from
10 to 50 ppm of maleic acid and from 100 to 500 ppm of
β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol,
and 1,590 kg/h of a recovered alcohol liquid, and after
20 days of operation, the reaction was carried out at
a reaction temperature of 85°C and a conversion of
acrylic acid of 5 0%, thereby giving a product acrylic
ester at a yield of 1,000 kg/h from the top of the
rectifying column 600. At this time, 15 kg/h of waste
oil was discharged from the bottom of the thin-film
evaporator 800, and 125 kg/h of the distillate from the
high-boiling separation column 700 and 140 kg/h of
wastewater from the wastewater tank 400 were mixed and
supplied to the extraction tank 900 shown in FIG. 2.
The water phase was removed as wastewater, and the
organic phase containing an acrylic ester was
circulated to the low-boiling separation column 500.
The acid components contained in the obtained product

acrylic ester were in an amount of from 25 to 35 ppm
(in terms of acrylic acid). The results are shown in
Table 1.
>
To the esterification reactor 100 shown in FIG.
2 were supplied 400 kg/h of acrylic acid containing from
10 to 50 ppm of maleic acid and from 100 to 500 ppm of
β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol,
and 1,590 kg/h of a recovered alcohol liquid, and after
230 days of operation, the reaction was carried out at
a reaction temperature of 100°C and a conversion of
acrylic acid of 50%, thereby giving a product acrylic
ester at a yield of 997 kg/h from the top of the
rectifying column 600. At this time, 18 kg/h of waste
oil was discharged from the bottom of the thin-film
evaporator 800, and 125 kg/h of the distillate from the
high-boiling separation column 700 and 140 kg/h of
wastewater from the wastewater tank 400 were mixed and
supplied to the extraction tank 900 shown in FIG. 2.
The water phase was removed as wastewater, and the
organic phase containing an acrylic ester was
circulated to the low-boiling separation column 500.
The acid components contained in the obtained product
acrylic ester were in an amount of from 25 to 35 ppm
(in terms of acrylic acid). The results are shown in

Table 1.
>
To the esterification reactor 100 shown in FIG.
3 were supplied 400 kg/h of acrylic acid containing from
10 to 50 ppm of maleic acid and from 100 to 500 ppm of
β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol,
and 1,590 kg/h of a recovered alcohol liquid, and after
20 days of operation, the reaction was carried out at
a reaction temperature of 85°C and a conversion of
acrylic acid of 50%, thereby giving a product acrylic
ester at a yield of 815 kg/h from the top of the
rectifying column 600. At this time, 200 kg/h of waste
oil was discharged from the bottom of the rectifying
column 600, The acid components contained in the
obtained product acrylic ester were in an amount of from
25 to 35 ppm (in terms of acrylic acid). The results
are shown in Table 1.
>
To the esterification reactor 100 shown in FIG.
3 were supplied 400 kg/h of acrylic acid containing from
10 to 50 ppm of maleic acid and from 100 to 500 ppm of
β-acryloxypropionic acid, 740 kg/h of 2-ethylhexanol,
and 1,590 kg/h of a recovered alcohol liquid, and after
230 days of operation, the reaction was carried out at
a reaction temperature of 100°C and a conversion of

acrylic acid of 50%, thereby giving a product acrylic
ester at a yield of 615 kg/h from the top of the
rectifying column 600. At this time, 400 kg/h of waste
oil was discharged from the bottom of the rectifying
column 600. The acid components contained in the
obtained product acrylic ester were in an amount of from
25 to 35 ppm (in terms of acrylic acid). The results
are shown in Table 1.
>
To the esterification reactor 100 shown in FIG.
1 were supplied 400 kg/h of acrylic acid containing from
100 to 500 ppm of maleic acid and from 500 to 3,600 ppm
of β-acryloxypropionic acid, 740 kg/h of 2-ethyl-
hexanol, and 1,590 kg/h of a recovered alcohol liquid,
and after 230 days of operation, the reaction was
carried out at a reaction temperature of 100°C and a
conversion of acrylic acid of 50%, thereby giving a
product acrylic ester at a yield of 975 kg/h from the
top of the rectifying column 600. At this time, 40 kg/h
of waste oil was discharged from the bottom of the
thin-film evaporator 800, and 90 kg/h of the distillate
from the high-boiling separation column 700 was
circulated to the low-boiling separation column 500.
The acid components contained in the obtained product
acrylic ester were in an amount of from 220 to 280 ppm

(in terms of acrylic acid). The results are shown in
Table 1.
>
To the esterification reactor 100 shown in FIG.
2 were supplied 400 kg/h of acrylic acid containing from
100 to 500 pm of maleic acid and from 500 to 3,600 ppm
of β-acryloxypropionic acid, 740 kg/h of 2-ethyl-
hexanol, and 1,590 kg/h of a recovered alcohol liquid,
and after 230 days of operation, the reaction was
carried out at a reaction temperature of 100°C and a
conversion of acrylic acid of 50%, thereby giving a
product acrylic ester at a yield of 997 kg/h from the
top of the rectifying column 600. At this time, 18 kg/h
of waste oil was discharged from the bottom of the
thin-film evaporator 800, and 125 kg/h of the
distillate from the high-boiling separation column 700
and 140 kg/h of wastewater from the process wastewater
tank 400 were mixed and supplied to the extraction tank
900 shown in FIG. 2. The water phase was removed as
wastewater, and the organic phase containing an acrylic
ester was circulated to the low-boiling separation
column 500. The acid components contained in the
obtained product acrylic ester were in an amount of from
35 to 50 ppm (in terms of acrylic acid). The results
are shown in Table 1.

>
To the esterification reactor 100 shown in FIG.
3 were supplied 400 kg/h of acrylic acid containing from
100 to 500 ppm of maleic acid and from 500 to 3,600 ppm
of β-acryloxypropionic acid, 740 kg/h of 2-ethyl-
hexanol, and 1,590 kg/h of a recovered alcohol liquid,
and after 230 days of operation, the reaction was
carried out at a reaction temperature of 100°C and a
conversion of acrylic acid of 50%, thereby giving a
product acrylic ester at a yield of 845 kg/h from the
top of the rectifying column 600. At this time, 170
kg/h of waste oil was discharged from the bottom of the
rectifying column 600. The acid components contained
in the obtained product acrylic ester were in an amount
of from 150 to 170 ppm (in terms of acrylic acid) . The
results are shown in Table 1.

As can be seen from Table 1, in Examples 1 and 2,
the yield of a product acrylic ester was able to be kept
high in such a manner that when an acrylic ester was
produced using the production process shown in FIG. 1,
a high-boiling substance containing an acrylic ester,
which was withdrawn from the bottom of a rectifying
column, was supplied to a high-boiling separation
column and/or a thin-film evaporator to separate it
into an acrylic ester component and a high-boiling
substance, and the separated acrylic ester component
was taken out as a distillate and supplied to a
low-boiling separation column for its recovery,
thereby decreasing the loss of an acrylic ester from
waste oil. At this time, no problem was caused on the
quality of a product.
Further, in Examples 3 and 4, when an acrylic ester
was produced using the production process shown in FIG.
2, a high-boiling substance containing an acrylic ester,
which was withdrawn from the bottom of a rectifying
column, was supplied to a high-boiling separation
column and/or a thin-film evaporator to separate it
into an acrylic ester component and a high-boiling
product, and the separated acrylic ester component was
taken out as a distillate, all or part of which was mixed
with water to extract and remove high-boiling acid

components such as maleic acid and β-acryloxypropionic
acid contained together with an acrylic ester in the
distillate into a water phase, the water phase being
discharged as wastewater, and the organic phase being
supplied to a low-boiling separation column to recover
an acrylic ester. In Examples 3 and 4 including a step
of water extraction, it became possible to further
decrease the loss of an acrylic ester from waste oil
and improve the yield of a product acrylic ester,
compared with those of Examples 1 and 2, without
deteriorating the quality of a product. In the
production of an acrylic ester controlling the constant
conversion of acrylic acid, the reaction temperature
is raised with extending the duration of using a
strongly acidic cation exchange resin accordingly, in
which case the amount of high-boiling acid components
such as β-acryloxypropionic acid influencing the
quality of a product increases, and therefore, it
becomes necessary to make a response by increasing the
amount of waste oil to maintain the quality of a product
acrylic ester. However, according to the conditions
of Example 4 into which a step of water extraction was
introduced, the stable quality of a product acrylic
ester and the stable yield of a product were able to
be obtained without remarkably increasing the amount

of waste oil from the early period of reaction in Example
3. The yield of a product under conditions of a high
reaction temperature was quite noticeable as compared
with Example 2 and Comparative Example 2.
In contrast, in Comparative Examples 1 and 2, when
an acrylic ester was produced using the production
process shown in FIG. 3, the bottom liquid of a
rectifying column was subjected as waste oil without
any treatment to a step of waste treatment, and
therefore, although the amount of high-boiling acid
components contained in the product acrylic ester
obtained as part of the top liquid of the rectifying
column did not change as compared with Examples 1 to
4, the yield of a product acrylic ester was remarkably
decreased as compared with Examples 1 to 4, and the
amount of waste oil was remarkably increased as
compared with Examples 1 to 4 .
From these facts, it can be understood that the
loss of an acrylic ester from waste oil can be decreased
and the yield of a product acrylic ester can be increased,
without deteriorating the quality of a product acrylic
ester, by supplying the bottom liquid of a rectifying
column to a high-boiling separation column and/or a
thin-film evaporator, separating and taking out, as a
distillate, an acrylic ester remaining in the bottom

liquid of the rectifying column from a high-boiling
substance, and supplying the distillate to a
low-boiling separation column for its recovery; and
further, that a decrease in the loss of an acrylic ester
from waste oil can more stably be achieved to improve
production efficiency, by introducing a step of water
extraction in which all or part of the distillate from
the high-boiling separation column and/or the
thin-film evaporator is mixed with water generated in
the production process to extract and remove
high-boiling acid components into a water phase, which
is discharged as wastewater, and a organic phase is
supplied to the low-boiling separation column to
recover an acrylic ester.
Further, in Example 5, an acrylic ester was
produced in almost the same manner as described in
Examples 1 and 2 using the production process shown in
FIG. 1, except that a low-purity acrylic acid was used
as a raw material. Although the amount of high-boiling
acid components contained in the product acrylic ester
was great, in spite of using a low-purity acrylic acid
as a raw material, the yield of a product acrylic ester
and the amount of waste oil were at about the same level
as those in Examples 1 and 2.
Further, in Example 6, an acrylic ester was

produced in almost the same manner as described in
Examples 3 and 4 using the production process shown in
FIG. 2, except that a low-purity acrylic acid was used
as a raw material. In spite of using a low-purity
acrylic acid as a raw material, the yield of a product
acrylic ester was increased as compared with Example
5, and the amount of waste oil was remarkably decreased
as compared with Example 5, both of which were by no
means inferior to Examples 3 and 4 using a relatively
high-purity acrylic acid as a raw material.
In contrast, in Comparative Example 3, an acrylic
ester was produced in almost the same manner as
described in Comparative Examples 1 and 2 using the
production process shown in FIG. 3, except that a
low-purity acrylic acid was used as a raw material. The
yield of a product acrylic ester was remarkably
decreased as compared with Examples 5 and 6, and
although the amount of high-boiling acid components
contained in the product acrylic ester was smaller than
that in Example 5, it was very great as compared with
Example 6, and the amount of waste oil was remarkably
increased as compared with Examples 5 and 6.
From these facts, it can be understood that the
loss of an acrylic ester form waste oil can be suppressed
on a low level, without deteriorating the quality of

a product acrylic ester, to improve production
efficiency and achieve the stable production, even when
low-purity acrylic acid containing great amounts of
high boiling acid components such as maleic acid and
β-acryloxypropionic acid is used as a raw material, or
even when relatively high-purity acrylic acid is used
as a raw material, by introducing a step of water
extraction in which the bottom liquid of a rectifying
column is supplied to a high-boiling separation column
and/or a thin-film evaporator, an acrylic ester
remaining in the bottom liquid of the rectifying column
is taken out as a distillate through separating a
high-boiling substance, all or part of the distillate
is mixed with water generated in the production process
to extract and remove high-boiling acid components into
a water phase, which is discharged as wastewater, and
an organic phase is supplied to a low-boiling
separation column to recover an acrylic ester.
As described above, the production process of the
present invention makes it possible to stably achieve
a large reduction in the production cost of an acrylic
ester.
The present invention provides a process for
producing an acrylic ester using acrylic acid
containing high-boiling acid components, such as

maleic acid and β-acryloxypropionic acid, influencing
the loss in quality of an acrylic ester and the unit
consumption of raw materials, and an aliphatic or
alicyclic alcohol having from 5 to 8 carbon atoms, as
raw materials, and a strongly acidic cation exchange
resin as a catalyst, which process is excellent from
an economical point of view because it can eliminate
the conventional problems to maintain the stable
quality and the low unit consumption of raw materials,
and which process makes a great contribution to the
filed of acrylic ester production.

We Claim:
1. A process for producing an acrylic ester by supplying
acrylic acid and an aliphatic or alicyclic alcohol having
from 5 to 8 carbon atoms to an esterif ication reactor to
cause an esterification reaction using a strongly acidic
cation exchange resin as a catalyst in the reactor, the
process comprising supplying an obtained reaction product
to a low-boiling separation column to distill an alcohol,
acrylic acid, and water from the top of the low-boiling
separation column, and separating them into a water phase
and an organic phase containing the alcohol and acrylic
acid, the organic phase being circulated as a circulated
liquid to the reactor, supplying a crude acrylic ester,
which is withdrawn from the bottom of the low-boiling
separation column, to a rectifying column, taking out a
rectified acrylic ester from the top of the rectifying
column, and supplying a high-boiling substance containing
an acrylic ester, which is withdrawn from the bottom of the
rectifying column, to a high-boiling separation column
and/or a thin-film evaporator to separate it into an
acrylic ester component and a high-boiling substance, the
separated acrylic ester component being taken out as a
distillate, mixing all or part of the distillate with water
to extract and remove a high-boiling acid component
contained in the distillate into a water phase, and
supplying an obtained organic phase to the low-boiling
separation column for its recovery.

2. The process according to claim 1, wherein water to
be used to extract and remove the high-boiling acid
component is a process wastewater generated in a step of
producing an acrylic ester.
3. The process according to claim 1 or 2 , wherein a
ratio of water to be used to extract and remove the high-
boiling acid component, relative to the distillate taken
from the high-boiling separation column and/or the thin-
film evaporator, is within a range of from 0.5:1 to 2.0:1
by mass ratio.
4. The process according to any one of claims 1 to 3,
wherein acrylic acid to be used as a raw material in the
process for producing an acrylic ester comprises from 10 to
5,000 ppm of maleic acid and/or from 10 to 5,000 ppm of β-
acryloxypropionic acid.

ABSTRACT OF THE DISCLOSURE

PROCESS FOR PRODUCING ACRYLIC ESTER
A process for producing an acrylic ester with
excellent economic efficiency, which can eliminate the
conventional problems to maintain the stable quality
and the low unit consumption of raw materials, in the
process for producing an acrylic ester using acrylic
acid containing high-boiling acid components
influencing the loss in quality and the unit
consumption of raw materials, and an aliphatic or
alicyclic alcohol having from 5 to 8 carbon atoms, as
raw materials, and using a strongly acidic cation
exchange resin as a catalyst. In such a process for
producing an acrylic ester, a crude acrylic ester
withdrawn from the bottom of a low-boiling separation
column is supplied to a rectifying column, a rectified
acrylic ester is taken out from the top of the rectifying
column, while a high-boiling substance containing an
acrylic ester, which is withdrawn from the bottom of
the rectifying column, is supplied to a high-boiling
separation column and/or a thin-film evaporator to
separate it into an acrylic ester component and a
high-boiling substance, and the separated acrylic
ester component is taken out as a distillate and
supplied to the low-boiling separation column for its

recovery.

Documents:

00954-kol-2007-abstract.pdf

00954-kol-2007-assignment.pdf

00954-kol-2007-claims.pdf

00954-kol-2007-correspondence others 1.1.pdf

00954-kol-2007-correspondence others.pdf

00954-kol-2007-description complete.pdf

00954-kol-2007-drawings.pdf

00954-kol-2007-form 1.pdf

00954-kol-2007-form 2.pdf

00954-kol-2007-form 3-1.1.pdf

00954-kol-2007-form 3.pdf

00954-kol-2007-form 5.pdf

00954-kol-2007-pa.pdf

954-KOL-2007-(09-09-2011)-ABSTRACT.pdf

954-KOL-2007-(09-09-2011)-AMANDED CLAIMS.pdf

954-KOL-2007-(09-09-2011)-AMANDEDPAGES OF SPECIFICATION.pdf

954-KOL-2007-(09-09-2011)-DRAWINGS.pdf

954-KOL-2007-(09-09-2011)-EXAMINATION REPORT REPLY RECIEVED.pdf

954-KOL-2007-(09-09-2011)-FORM 1.pdf

954-KOL-2007-(09-09-2011)-FORM 2.pdf

954-KOL-2007-(09-09-2011)-FORM 3.pdf

954-KOL-2007-(09-09-2011)-OTHERS.pdf

954-KOL-2007-ASSIGNMENT.pdf

954-KOL-2007-CORRESPONDENCE 1.1.pdf

954-KOL-2007-CORRESPONDENCE 1.2.pdf

954-KOL-2007-CORRESPONDENCE.pdf

954-KOL-2007-EXAMINATION REPORT.pdf

954-KOL-2007-FORM 13.pdf

954-KOL-2007-FORM 18 1.1.pdf

954-kol-2007-form 18.pdf

954-KOL-2007-FORM 3.pdf

954-KOL-2007-FORM 5.pdf

954-KOL-2007-GRANTED-ABSTRACT.pdf

954-KOL-2007-GRANTED-CLAIMS.pdf

954-KOL-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

954-KOL-2007-GRANTED-DRAWINGS.pdf

954-KOL-2007-GRANTED-FORM 1.pdf

954-KOL-2007-GRANTED-FORM 2.pdf

954-KOL-2007-GRANTED-SPECIFICATION.pdf

954-KOL-2007-OTHERS.pdf

954-KOL-2007-PA 1.1.pdf

954-KOL-2007-PA.pdf

954-KOL-2007-PRIORITY DOCUMENT.pdf

954-KOL-2007-REPLY TO EXAMINATION REPORT.pdf

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Patent Number

255709

Indian Patent Application Number

954/KOL/2007

PG Journal Number

12/2013

Publication Date

22-Mar-2013

Grant Date

18-Mar-2013

Date of Filing

02-Jul-2007

Name of Patentee

NIPPON SHOKUBAI CO., LTD.

Applicant Address

1-1, KORAIBASHI 4-CHOME, CHUO-KU, OSAKA-SHI, OSAKA

Inventors:

#	Inventor's Name	Inventor's Address
1	HARAMAKI HIDEFUMI	C/O NIPPON SHOKUBAI CO., LTD., 992-1, AZA NISHIOKI, OKINOHAMA, ABOSHI-KU, HIMEJI-SHI, HYOGO
2	MATSUI MANABU	C/O NIPPON SHOKUBAI CO., LTD., 992-1, AZA NISHIOKI, OKINOHAMA, ABOSHI-KU, HIMEJI-SHI, HYOGO

PCT International Classification Number

C07C67/03; C07C69/54; C08G65/332

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	JP2006-190889	2006-07-11	Japan