Title of Invention

METHOD OF SYNTHESIZING HIGHER-MOLECULAR ALCOHOL

Abstract

The present invention provides a production method with which polymeric alcohols having an even number of carbon atoms such as 1-butanol, hexanol, octanol and decanol, and a mixture of these are efficiently collected through clean processes with the use of ethanol as a raw material. By using calcium phosphate-based compounds such as hydroxyapatite Ca10(PO4)6(OH)2, tricalcium phosphate calcium monohydrogen phosphate CaHPO4-(0~2)H2O, calcium diphosphate octacalcium phosphate Ca8H2(PO4)65H2O, tetracalcium phosphate Ca4(PO4)2O and amorphous calcium phosphate Ca3(PO4)2nH2O, preferably hydroxyapatite, as a catalyst, using ethanol as a starting material, and setting a contact time at 0.4 second or longer, polymeric alcohols are produced from ethanol.

Full Text

This invention relates to method of synthesizing higher-molecular alcohol TECHNICAL FIELD The present invention relates to a method for producing polymeric alcohols from ethanol with the use of calcium phosphate-based catalysts. BACKGROUND ART Polymeric alcohols such as butanol (C4H9OH), hexanol (C6H13OH), octanol (C8H17OH), decanol (C10H21OH) are currently synthesized by the oxo method using propylene obtained from petroleum as a raw material. However, crude oil prices had exceeded 50 dollars/barrel in 2004, and the soaring prices of propylene as a raw material led to the rising production cost of polymeric alcohols, resulting in the worsening of profitability. Further, in case of the oxo method, it is necessary to use deadly carbon monoxide as a raw material in addition to propylene, and the method is a high-pressure reaction and complicated, therefore, it has become a factor for rising the production cost. Furthermore, in the oxo method, in case of butanol synthesis reactions for example, 2 moles of carbon dioxide, which is a global warming substance, are produced as a side product per 1 mole of butanol. Consequently, this method is unpreferable in view of global environmental conservation as well. CH3CH=CH2 (propylene) + 3CO (carbon monoxide) + 2H2O (water) → C4H9OH (butanol) + 2CO2 (carbon dioxide) (1) As for methods for synthesizing 1-butanol from ethanol, there are literatures regarding MgO catalysts ("Dimerisation of ethanol to butanol over solid-base catalysts" A. S. Ndou, N. plint, N. J. Coville, Applied catalysis A: General, 251, p. 337-345 (2003)) and zeolite (ZSM-5) catalysts on which alkali metals are supported ("Bimolecular Condensation of Ethanol to 1-Butanol Catalyzed by Alkali Cation Zeolites" C. Yang, Z. Meng, J. of Catalysis, 142, p. 37-44 (1993)), however, they are not industrially suitable because of their low selectivity. In addition, though a method for synthesizing 1-butanol with the use of calcium phosphate-based catalysts (International Publication No. WO99/38822) has been already disclosed, due to the high reaction temperature of this synthesis method, which is as high as 350 to 450°C, the method has problems such as: the selectivity of 1-butanol is low; it is necessary to repeat a catalyst regeneration treatment frequently because of the rapid degradation of catalytic property; the durability of devices is decreased; a fuel cost required for maintaining the reaction temperature is increased. Patent Document 1: International Publication No. WO99/38822 Non-Patent Document 1: "Dimerisation of ethanol to butanol over solid-base catalysts" A. S. Ndou, N. plint, N. J. Coville, Applied catalysis A: General, 251, p. 337- 345 (2003). Non-Patent Document 2: "Bimolecular Condensation of Ethanol to 1-Butanol Catalyzed by Alkali Cation Zeolites" C. Yang, Z. Meng, J. of Catalysis, 142, p. 37-44 (1993). DISCLOSURE OF THE INVENTION AN OBJECT TO BE ATTAINED BY THE INVENTION The object of the present invention is to provide a production method with which polymeric alcohols having an even number of carbon atoms such as 1-butanol, hexanol, octanol and decanol, and a mixture of these are efficiently collected through clean processes, with the use of ethanol as a raw material. MEANS FOR ATTAINING THE OBJECT Ethanol, which is a starting material of the process of the present application, is currently synthesized through the conversion of sugars obtained from sugarcanes, beets, etc., by a fermentation method. Recently, a technique for synthesizing ethanol from biomass, agricultural and forestry residues, has been established, and a striking increase in the production of ethanol can be expected in future. As a result, it is expected that the production cost of ethanol will be lowered to the level comparable to that of crude oil. In fact, it is said that the production cost of ethanol is about 10 yen/1 in Brazil, an advanced country in terms of ethanol, and this is comparable to or less expensive than the international crude oil prices. Therefore, it is considered that by adopting the process of the present application, polymeric alcohols, less expensive than those obtained by using the oxo method, can be obtained. With regard to the method for synthesizing polymeric alcohols according to the present application, the raw material is only ethanol, and the reaction proceeds easily at normal pressure. Further, the side product of the synthesis reaction of polymeric alcohols is only water (see the reaction equations described below). Thus, unlike the oxo method, the present process does not use harmful substances and is a reaction at normal pressure, therefore, it is possible to lower the cost of safety management of plants, and the cost of plant construction, and to reduce the production cost of polymeric alcohols. In addition, the present process is a global environment-friendly, clean process because the side product of the present reaction is only water, while carbon dioxide is produced as a side product in the oxo method. Overall reaction equations of major synthesis reactions of polymeric alcohols are described below. 2C2H5OH (ethanol) -» C4H9OH (1-butanol) + H2O (water) (2) 3C2H5OH (ethanol) -> C6H13OH (hexanol) + 2H2O (water) (3) 4C2H5OH (ethanol) -+ C8H17OH (octanol) + 3H2O (water) (4) 5C2H5OH (ethanol) -» C10H21OH (decanol) + 4H2O (water) (5) Based on the ratio of synthesis amounts of these polymeric alcohols, it is considered that the synthesis reactions of polymeric alcohols from ethanol, catalyzed by calcium phosphate-based catalysts, are consecutive reactions of ethanol. It is therefore considered that polymeric alcohols having an even number of carbon atoms such as butanol having 4 carbon atoms, hexanol having 6 carbon atoms, octanol having 8 carbon atoms and decanol having 10 carbon atoms are synthesized from ethanol having 2 carbon atoms. Provided that polymeric alcohols mentioned above are synthesized as a result of the consecutive reactions of ethanol, the above-mentioned reactions (3) to (5) are described as the following equations (6) to (8). C4H9OH (1-butanol) + C2H5OH (ethanol) -» C6H,13OH (hexanol) + H2O (water) (6) C6H,3OH (hexanol) + C2H5OH (ethanol) -» C8H17OH (octanol) + H2O (water) (7) C8H17OH (octanol) + C2H5OH (ethanol) -» C1,0H21OH (decanol) + H2O (water) (8) The present inventors have pursued their keen studies for the effect of contact times in ethanol conversion reactions, and as a result, have found that the above- mentioned polymeric alcohols can be synthesized in a highly selective manner by contacting ethanol with a calcium phosphate-based catalyst for a contact time of 0.4 second or longer. With regard to the relationship between the contact times and the selectivity of reactants in catalytic reactions, it is common that as the contact time is prolonged, the selectivity of a single substance is decreased because the condensation polymerization of raw materials and multiple reactions take place. In the process of the present application, however, the selectivity of polymeric alcohols can be improved by prolonging the contact time to 0.4 second or longer at an arbitrary temperature. With regard to the relationship between the contact times and the abundance ratios of polymeric alcohols, consecutive reactions of ethanol proceeded as the contact time was prolonged, and alcohols with larger molecular weight were synthesized. This is attributed to the fact that these polymeric alcohols are reaction intermediates in ethanol conversion reactions catalyzed by hydroxyapatite catalysts. BRIEF DESCRIPTION OF DRAWINGS [Fig. 1] Fig. 1 is a graph showing the relationship between the contact times and the selectivity of polymeric alcohols in Table 1. [Fig. 2] Fig. 2 is a graph in which the part between the contact times of 0.0 and 1.0 second in Fig. 1 is enlarged. [Fig. 3] Fig. 3 is a graph showing the analytical results obtained by GC-MS. [Fig. 4] Fig. 4 is a graph showing the relationship between the reaction temperatures and the selectivity of 1-butanol. BEST MODE OF CARRYING OUT THE INVENTION As calcium phosphate-based catalysts, the followings are known: hydroxyapatite Ca1o(PO4)6(OH)2, tricalcium phosphate Ca3(PO4)2, calcium monohydrogen phosphate CaHPO4-(0~2)H2O, calcium diphosphate Ca2P2O7, octacalcium phosphate Ca8H2(PO4)5H2O, tetracalcium phosphate Ca4(PO4)2O, amorphous calcium phosphate Ca3(PO4)2-nH2O, etc. Though hydroxyapatite is generally indicated by the stoichiometric composition mentioned above, it is characterized in that it can form an apatite structure even though it does not meet the stoichiometric composition. Such hydroxyapatite with non-stoichiometric composition can be indicated by: Ca1o-z(HPO4)z(PO4)6-z(OH)2.z-nH2O {0 The present invention is designed to produce the polymeric alcohols mentioned above efficiently by using these calcium phosphate-based catalysts to optimize the reaction conditions, in other words, the contact time and the reaction temperature. In the present invention, a method for producing calcium phosphate-based compounds used as catalysts is not particularly limited, and the catalysts can be synthesized by publicly known synthesis methods such as the solid phase reaction (dry method), the precipitation reaction (wet method), the solid phase reaction (wet method), and the hydrothermal synthesis method. For example, hydroxyapatite is synthesized as follows: solutions of calcium salt and phosphate salt at prescribed concentrations are added dropwise, while adjusting its pH, to an aqueous solution being stirred; precipitated products are recovered, washed, dried, ground, and calcinated if necessary, and used as a raw material of catalysts. As the calcium salt used, Ca(OH)2, Ca(NO3)2 are preferred, and as the phosphate salt used, ammonium phosphate salt is preferred. The Ca/P molar ratio of hydroxyapatite can be controlled by controlling the mixing ratio of salts as raw materials and the synthesis conditions. For instance, when the aqueous solution is adjusted to be basic with ammonia water, etc., at a time of synthesis, the Ca/P molar ratio will be higher, and when the aqueous solution is adjusted to be neutral or weakly acidic with dilute acid, the Ca/P molar ratio will be lower. In addition, hydroxyapatite whose Ca/P molar ratio is controlled can be obtained also by mixing calcium phosphate-based catalysts whose Ca/P molar ratios are known and then calcinating them in a water atmosphere. In case hydroxyapatite is used as a catalyst, the Ca/P molar ratio is adjusted to 1.4 to 1.8, preferably, 1.5 to 1.7, and the calcination temperature and the calcination atmosphere are selected in accordance with the purposes. At that time, it is preferred that the specific surface area of the catalyst is 2 m2/g or larger. Catalytically, the control of the Ca/P molar ratio in calcium phosphate-based catalysts means to control the types and the distribution densities of solid acid sites and solid base sites, which are active sites on the catalyst surface. Here, the intensity and the amount of acid sites and base sites can be assessed by NH3-TPD (Temperature Programmed Desorption) and CO2-TPD, or pyridine adsorption, indicator method, etc. In addition, as for methods for controlling the acidity and the basicity of the catalyst surface, a method to support a metal thereon is generally known. For example, by supporting dehydrogenation reaction accelerating-metals typically including Ni, Zn, Cu, Pd or Pt on hydroxyapatite, the same effect as that of the increase in the Ca/P molar ratio, in other words, the increase in the solid basicity is obtained. Further, in case of hydroxyapatite, by supporting dehydration reaction accelerating-metals typically including Al, the same effect as that of the decrease in the Ca/P molar ratio, in other words, the increase in the solid acidic feature is obtained. Therefore, the acidity/basicity of the surface of hydroxyapatite catalysts can be changed also by supporting such metals thereon instead of changing the Ca/P molar ratios. In addition, a plurality of metals can be supported together for the purpose of the synergistic effect or the improvement of durability. Metals to be supported together include, for example, transition metals such as Zn, Co, Cr, Mo, W, Fe, Ni, Cu, Mn, Ti, V, Ga, Zr, Nb, Cd, In, Sn, Sb, Pb, La, Ce, Eu and Y; or noble metals such as Pt, Pd, Rh, Au, Ir, Ru and Ag; and alkali metals or alkali earth metals such as Ba, Na, K, Li, Sr, Ca, Mg, Cs and Rb. In some cases, oxides or sulfides of these metals can also be used. These substances are used in a range of 0.05 to 70 mol% on the basis of calcium in calcium phosphate-based catalysts. In the present invention, when polymeric alcohols and mixtures thereof are synthesized from ethanol as a raw material, a calcium phosphate-based catalyst to be used, control of the acidity and the basicity of the catalyst surface (for instance, the Ca/P molar ratio of the calcium phosphate-based catalyst), and reaction conditions (contact time, reaction temperature, pressure, etc.) are appropriately selected in order to increase the selectivity of desired polymeric alcohols. The calcium phosphate-based catalysts adjusted as described above can be used in any forms, for example, in a form of granules, powders, etc., and also can be used after they are formed into an arbitrary form such as spheres, pellets, honeycombs, as needed, and dried and calcinated. The calcium phosphate-based catalysts can be supported on conventional carriers well known to a person skilled in the art such as alumina, silica, alumina-silica,, zeolite, and clay mineral. Calcination is conducted at 200°C to 1200°C, preferably at 400°C to 700°C. The reaction temperature of the present application, suitable for synthesizing polymeric alcohols by contacting ethanol with a calcium phosphate-based catalyst, is usually selected preferably from a range of 150°C to 450°C, more preferably 200°C to 350°C. Though there is a means of maintaining the selectivity of polymeric alcohols high even when the temperature is 150°C or lower, yield is lowered and economic efficiency is worsened, due to the low conversion rate of ethanol. Further, in case the temperature is 450°C or higher, though the conversion rate of ethanol is increased, the selectivity of polymeric alcohols is lowered, unwanted reaction products are increased and there emerge a new problem of disposal of these products, and also economic efficiency is worsened. The contact time of the present application is usually 0.4 second or longer. It is preferred that the time is 0.6 second or longer. When the time is shorter than 0.4 second, synthesis yield is lowered and economic efficiency is worsened, due to the low selectivity of polymeric alcohols and the low conversion rate of ethanol. In case the reaction is conducted in a low temperature range, a batch reactor, which is equivalent to infinitely large contact time, can be also used to increase the conversion rate of ethanol. In the reaction conducted in a high temperature range, when the contact time is prolonged, other reactions are increased and the selectivity of polymeric alcohols is decreased. The reaction to synthesize polymeric alcohols from ethanol is an exothermic reaction. Consequently, when the high yield of polymeric alcohols is set as a target, temperature rise inside a reaction tower caused by heat of reaction, becomes prominent. As a result, there emerge problems such as a decrease in the selectivity of polymeric alcohols caused by the emergence of other reactions including ethanol decomposition reactions, deterioration of catalysts caused by catalyst temperature rise, and a decrease in the durability of reactors. Therefore, in case of reactions to synthesize polymeric alcohols from ethanol, it is more suitable for industrialization to set high selectivity as a goal than to pursue high yield. However, provided that a system for removing heat of reaction is introduced into a reaction tower, such limitation is not applied. It is possible to react ethanol efficiently by contacting ethanol with a catalyst directly in the gas phase or in the presence of an inert carrier gas such as nitrogen or helium. At that time, a reactive gas such as hydrogen or hydrocarbon may be added to the carrier gas in order to maintain the catalytic activity. With regard to reaction forms in a reaction tower, any method such as a batch method, a continuous method, a fixed bed, a moving bed, a fluidized bed or a slurry bed can be used, and the reaction can be conducted at normal pressure or under pressure. In case of polymeric alcohol synthesis reactions, carbons are precipitated on the catalyst surface due to prolonged period of use, and this may result in a decrease in the ethanol conversion rate and changes in the nature of reactions. In such case, a regeneration treatment, wherein a catalyst is heated in oxygen atmosphere, is periodically conducted. The activity of the catalyst can be restored by this treatment. Consequently, in case of reaction conditions under which a lot of carbons are precipitated on catalysts, a plant operated in accordance with the above-mentioned system, in which a catalyst regeneration apparatus is incorporated, is effective. Polymeric alcohols thus obtained can be separated and purified with the use of conventionally used separation and purification methods, for example, rectification, microporous membrane separation, extraction, and adsorption. A catalyst was synthesized as follows. With regard to the obtained powder, a powder X-ray diffractometer M18XHF22 manufactured by MacScience was used for the crystal structure, and SA3100 manufactured by COLTER and an X-ray fluorescence spectrometer RIX1000 manufactured by Rigaku Denki Kogyo Co., Ltd. were used for the measurement of the specific surface area and the Ca/P molar ratio, respectively. [Example 1] Preparation of catalyst A solution prepared by dissolving 225.2 g of calcium nitrate: Ca(NO3)2-4H2O in 5.0 liters of distilled water and a solution prepared by dissolving 78.87 g of ammonium phosphate: (NH4)2HPO4 in 3.0 liters of distilled water were added dropwise to aqueous ammonia of which pH had been adjusted to 9 to 11 under a nicrogen atmosphere, and the resultant mixture was stirred for one day. Subsequently, the mixture was filtrated, washed with water, and dried to obtain a powder. Ion-exchange water was added to the obtained powder, and the resultant mixture was crushed for 48 hours with a ball mill. The slip thus obtained was matured and dried at 140°C in an oven. The resultant powder was calcinated in the air at 600°C for 2 hours to obtain a powdery catalytic composition whose Ca/P molar ratio was 1.64. [Example 2] Evaluation of catalytic property A fixed bed gas flow catalytic reactor was used as a reactor. The powdery catalyst was formed into tablets of 14 to 26 mesh. The tablets were filled in a reaction tube in an amount in accordance with the contact time, and a thermal dehydration treatment was conducted as a pretreatment under carrier gas (1% Ar/He-based; flow 112 ml/min) atmosphere, at 500°C for 30 minutes. After the pretreatment, the tablets were reacted at normal pressure under the conditions of ethanol concentration of 16 vol%, carrier gas flow 112 ml/min (total flow 134 ml/min). In case of the polymeric alcohol synthesis experiment, the reaction temperature was fixed at 300°C, and the contact time was in a range of 0.02 to 29.4 seconds. In the optimization experiment of 1-butanol synthesis conditions, the contact time was fixed at 1.0 second, the ethanol concentration was 8.1%, and the reaction temperature was in a range of 150 to 500°C. A gas chromatography mass spectrometer (GC-MS) was used for the identification of the components of the reaction gas, and a gas chromatography (GC) (detector: FID) was used for the measurement of the ethanol conversion rate and the selectivity of the synthetic gas. At that time, for the purpose of calculating the selectivity of ethanol as a raw material, butanol, hexanol, octanol and decanol, carbon molar response correction factors of 0.70, 0.85, 0.90, 0.93 and 0.94 were used, respectively. Ethanol conversion rate (%) = (number of moles of carbon in 1-ethanol/total number of moles of carbon) x 100 Selectivity of 1-butanol (%) = (number of moles of carbon in 1-butanol/total number of moles of carbon) x 100 * The selectivities of hexanol, octanol and decanol are calculated in a same manner as in the case of 1-butanol. Selectivity of polymeric alcohols (%) = selectivity of 1-butanol + selectivity of hexanol + selectivity of octanol + selectivity of decanol. The results of the experiment are shown in Table 1, Fig. 1, and Fig. 2 (an enlarged view of the part between the contact times of 0.0 and 1.0 second in Fig. 1). [Table 1] (Table Removed) Table 1 shows the relationship between the contact times and the selectivity of polymeric alcohols when the ethanol conversion experiment was conducted with the use of a hydroxyapatite catalyst at an ethanol concentration of 16% and at a reaction temperature of 300°C. The selectivity of 1-butanol reached its maximum value at the contact time of 1.34 seconds, and decreased when the contact time was longer than that. The selectivity of decanol, octanol and hexanol were low, in this order. Up to the contact time of 29.4 seconds, each of selectivity was increased as the contact time was prolonged. Though the selectivity of polymeric alcohols was very low, 2.4% at the contact time of 0.02 second, it rapidly increased as the contact time was prolonged, and it exceeded 60% at the contact time of 0.4 second. Further, when the contact time was 0.6 second or longer, the selectivity of polymeric alcohols was very high as 70% or more, which is a value advantageous for industrialization. [Example 3] Example of analysis by gas chromatography mass spectrometer (GC-MS) The ethanol conversion experiment was conducted with the use of a hydroxyapatite catalyst at an ethanol concentration of 16%, for a contact time of 1.78 seconds and at a reaction temperature of 300°C, and an analysis was conducted with GC-MS. The results are shown in Fig. 3. The peaks of 1-butanol, hexanol (2 types: iso and normal), octanol (2 types: iso and normal), and decanol (3 types: iso and normal) can be observed at the retention times of 8.5 minutes, 13 to 14 minutes, 17 to 18 minutes, and 20 to 22 minutes, respectively. It can be seen from this result that polymeric alcohols having 4 or more and an even number of carbon atoms are synthesized selectively. [Example 4] Evaluation of reaction temperature and the selectivity of 1-butanol The ethanol conversion experiment was conducted with the use of a hydroxyapatite catalyst at an ethanol concentration of 8.1%, for a contact time of 1.0 second. In addition, a same ethanol conversion experiment, except that the contact time 12 was changed to 0.3 second, was conducted for comparison. The results are shown in Fig. 4. As a result that synthesis properties of 1-butanol at the contact times 1.0 second and 0.3 second were compared, the selectivity of 1-butanol at the contact time of 1.0 second was higher than that of 1-butanol at the contact time of 0.3 second by about 12% at maximum. When the reaction temperatures at the maximum values were compared, the temperature at the contact time of 1.0 second was lower than that at the contact time of 0.3 second by about 75°C. INDUSTRIAL APPLICABILITY The catalyst according to the method of the present application can be produced at a low cost and easily, and moreover, is stable to reactions and regeneration treatments. With the catalyst, it is possible to efficiently obtain polymeric alcohols from ethanol by selecting reaction temperatures and contact times. WE CLAIM: 1. A method for synthesizing one or more high molecular alcohol having 6 or more and an even number of carbon atoms, comprising contacting ethanol with hydroxyapatite for a contact time of 0.6 second or longer and at 150 to 450°C . 2. A method for synthesizing 1-butanol at a selectivity of 70.3% or more, comprising contacting ethanol with hydroxyapatite for a contact time of 0.6 second or longer, and at 200°C or more to less than 350°C, wherein the hydroxyapatite does not support a metal. 3. A method for synthesizing one or more high molecular alcohol substantially such as herein described.

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