Title of Invention

"A PROCESS OF PRODUCING TEREPTHALIC ACID"

Abstract A process of producing terepthalic acid comprising the following steps (A) to (D): (A) oxidizing p-xylene with molecular oxygen in a solvent composed of acetic acid in the presence of a catalyst of the kind such as hereindescribed to obtain tetraphthalic acid containing 4-carboxybezaldehyde, (B) subjecting the resulting tetraphthalic acid slurry to a solid-liquid separator and subjecting the tetraphthalic acid slurry to solid-liquid separation into a tetraphthalic acid cake and a mother liquor composed mainly of acetic acid, (C) washing the resulting tetraphthalic acid cake with a washing liquid of the kind such as hereindescribed, and (D) a drying step of evaporating and removing the attached liquid remaining in the tetraphthalic acid cake after washing to obtain tetraphthalic acid crystal characterized in that: the finely divided tetraphthalic acid crystal to be entrained in a discharge gas produced by the drying step containing a solvent vapor generated by the evaporation and removal is brought into contact with acetic acid or water and recovered in a recovery device, and a part or the whole of this recovered material is sent to said step (A).
Full Text
This invention relates to a process of producing an aromatic carboxylic acid

In general, crude terephthalic acid obtained by oxidizing p-xylene or the like is obtained in the state of a cake containing acetic acid as a solvent by a solid-liquid separation step and then dried, thereby obtaining crude terephthalic acid as a product. Also, by dissolving this crude terephthalic acid in water, reducing an impurity, and after crystallization, subjecting to a solid-liquid separation step, purified terephthalic acid is obtained in the state of a cake containing water. By drying this purified terephthalic acid in the cake form, purified terephthalic acid as a product is obtained.
And, in all of these cases, a dryer is used for drying. In drying by this dryer, the evaporated solvent such as acetic acid and water is entrained in a flow of a ventilating gas to be used in the foregoing dryer and discharged out the dryer.

However, in many cases, a solid composed of finely divided terephthalic acid is intermixed in the gasified solvent having been discharged out the foregoing dryer. If this solid is discarded as it is, a lowering of the productivity in the respective steps is brought, and there may be the case where the treatment of this solid becomes a problem.
Now, this invention is aimed to recover a solid contained in a discharge gas in a drying step and design to reuse it.
This invention is to solve the preceding problem by a process of producing an aromatic carboxylic acid including the following steps (A) to (D):
(A) an oxidation step of oxidizing an alkyl aromatic compound with molecular oxygen in a solvent composed mainly of acetic acid in the presence of a catalyst to obtain an aromatic carboxylic acid,
(B) a solid-liquid separation step of subjecting the resulting aromatic carboxylic acid slurry to solid-liquid separation into an aromatic carboxylic acid cake and a mother liquor composed mainly of acetic acid,
(C) a washing step of washing the resulting aromatic carboxylic acid cake with a washing liquid, and
(D) a drying step of evaporating and removing the attached
liquid remaining in the aromatic carboxylic acid cake
after the washing to obtain an aromatic carboxylic acid crystal, wherein the aromatic carboxylic acid crystal to be entrained in a discharge gas containing a solvent vapor generated by the evaporation and removal is brought into contact with a liquid and recovered in a recovery device, and a part or the whole of this recovered material is sent to the foregoing step (A) .


Fig. 1 is a flow diagram to show an embodiment according to this invention, including a production step of crude terephthalic acid (first production step) and a production step of high-purity terephthalic acid (second production step); and
Fig. 2 is a schematic view to show the relationship between a dryer and a recovery device according to this invention.
Incidentally, with respect to the reference numerals and signs in the drawings, 1 denotes an oxidation reactor; 2 and 13 denote a crystallization tank; 3 and 14 denote a solid-liquid separator; 4 and 15 denote a dryer; 5 and 16 denote a recovery device; 11 denotes a mixing tank; 12 denotes a hydrogenation reactor; 21 denotes a solvent component removal device; 22 denotes a conduit; 23 denotes a spray device; A denotes an alkyl aromatic compound; B denotes a solvent; C, D and K denote an aromatic
The present invention relates to JP10-291956 describes that a gas obtained by an adsorption treatment or a filtration treatment of an exhaust gas discharged from a production process (mainly, a reactor) for producing an aromatic carboxylic acid is used as a carrier gas for transporting a dried aromatic carboxylic acid. However, JP 10-291956 neither describes nor suggests that an aromatic carboxylic acid crystal to be entrained in a discharge gas is brought into contact with a liquid and recovered in a recovery device and a part or the whale of this recovered material is sent to a reactor.
JP2002-128726 describes a process for producing carboxylic acids with an imide compound as a catalyst. However, JP2002-128726 is silent about an exhaust gas from a dry step and neither describes nor suggests that an aromatic carboxylic acid crystal to be entrained in a discharge gas is brought into contact with a liquid and recovered in a recovery device and a part or the whole of this recovered material is sent to a reactor.
Accordingly, the present invention is clearly different from the cited references and the present invention is not easily expected from the cited references.
carboxylic acid slurry; E and L denote an aromatic carboxylic acid cake; F and M denote a separated mother liquor; G denotes an aromatic carboxylic acid crystal; H denotes an aqueous medium; I denotes a solution; J denotes a reduction treated liquid; N denotes a high-purity aromatic carboxylic acid crystal; P and Q denote a discharge gas; R and S denote a liquid; and X and Y denote a recovered slurry.

This invention will be described below in detail.
In general, the process of producing an aromatic carboxylic acid according to this invention comprises a first production step of oxidizing an alkyl aromatic compound to produce an impurity-containing aromatic carboxylic acid and a second production step of reducing the impurity of the impurity-containing aromatic carboxylic acid obtained in the first production step and after crystallization, subjecting to solid-liquid separation to produce a purified aromatic carboxylic acid.
Here, examples of the foregoing alkyl aromatic compound include p-xylene; examples of the foregoing impurity include 4-carboxybenzaldehyde; and examples of the foregoing aromatic carboxylic acid include terephthalic acid.
The foregoing first production step is constructed of
the following steps as shown in Fig. 1.
(A) An oxidation step of sending and mixing an alkyl
aromatic compound A and a solvent B composed mainly of
acetic acid in an oxidation reactor 1 and oxidizing the
alkyl aromatic compound A with molecular oxygen in the
foregoing solvent B in the presence of a catalyst to
obtain an aromatic carboxylic acid;
(A') An optional crystallization step of sending the resulting aromatic carboxylic acid slurry C to a crystallization tank 2 and subjecting to crystallization by pressure-release and cooling to crystallize the aromatic carboxylic acid dissolved in a mother liquor;
(B) A solid-liquid separation step of sending the
resulting aromatic carboxylic acid slurry D to a solid-
liquid separator 3 and subjecting to solid-liquid
separation into an aromatic carboxylic acid cake and a
mother liquor F composed mainly of acetic acid;
(C) A washing step of washing the resulting aromatic carboxylic acid cake with a washing liquid; and
(D) A drying step of evaporating and removing the attached liquid remaining in the aromatic carboxylic acid cake E after the washing to obtain an aromatic carboxylic acid crystal G.
The aromatic carboxylic acid slurry C formed by the foregoing step (A) contains the foregoing impurity as an oxidation intermediate.
purified aromatic carboxylic acid N.
In all of the foregoing first production step and second production step, in the dryer 4 or 15, a scattered, finely divided aromatic carboxylic acid crystal is entrained in the discharge gas P or Q containing a solvent vapor generated by the evaporation and removal. By sending this discharge gas P or Q to a recovery device and brining it into contact with a liquid R or S the foregoing finely divided aromatic carboxylic acid crystal is recovered. A part or the whole of the aromatic carboxylic acid crystal as the recovered material is sent to the foregoing step (A) or mixing tank 11 as shown by I or I' in Fig. 1. In this way, the scattered, finely divided
whereby it is possible to design to provide it for reuse.
As the foregoing recovery device, a recovery device 5 or 16 using the foregoing liquid R or S as shown in Fig. 1 can be enumerated.
The recovery device 5 or 16 using the foregoing liquid R or S is a device of spraying this liquid R or S into the foregoing discharge gas P or Q, thereby adsorbing the finely divided aromatic carboxylic acid in the foregoing discharge gas P or Q onto the foregoing liquid R or S and recovering it. As the liquid R or S to be used at this time, it is preferable that the respective solvent is used. Specifically, an aliphatic carboxylic acid such
as acetic acid or water is preferable as the liquid R or S In particular, an aliphatic carboxylic acid such as acetic acid is more preferably used as the liquid R, and water is more preferably used as the liquid S. By using such liquids, no problem occurs even when the recovered material is returned to the oxidation step or dissolution step as described later.
As the foregoing recovery device 5 or 16 using the liquid R or S, an adsorption column can be employed. Examples of this adsorption column include a liquid dispersion type absorption column in which the liquid R or S is dispersed in the discharge gas P or Q and a gas dispersion type absorption column in which inversely, the discharge gas P or Q is dispersed in the liquid R or S.
Examples of the foregoing liquid dispersion type absorption column include a packed column, a spray column, a cyclone scrubber, and a venturi scrubber. Also, examples of the foregoing gas dispersion type absorption column include plate columns such as a tray column and a wet plate column and a jet scrubber.
The aromatic carboxylic acid crystal as the recovered material, which is recovered by the foregoing recovery device 5 or 16 becomes in the slurry state. A part or the whole of the aromatic carboxylic acid slurry as the recovered material is sent to the foregoing step (C) or solid-liquid separator 14 as shown by II or II' in Fig. 1
and can be used as a washing liquid or suspending and washing liquid. A washing discharge liquid (not shown) formed by this washing can be sent to the step (A) or mixing tank 11. In this way, the scattered, finely divided aromatic carboxylic acid crystal by the dryer 4 or 15 can be returned to the aromatic carboxylic acid cake E or L and can be recovered. Incidentally, the suspending and washing liquid as referred to herein means a liquid that is slurried and used for suspension and washing for the purpose of washing the aromatic carboxylic acid cake E or L.
Further, in the case where the solvent B or aqueous medium H that is used in each of the production processes as described previously is used as the liquid R or S, a part of a recovered slurry X or Y may be used as the foregoing liquid. In this way, it is possible to reduce the amount of a new liquid to be used.
Now, in the first production step, the separated mother liquor F to be separated by the solid-liquid separator 3 contains the solvent B and a trace amount of the aromatic carboxylic acid. By returning this separated mother liquor F to the foregoing oxidation step, it is possible to design to recover and reuse both of the solvent B and the aromatic carboxylic acid.
Also, in the second production step, the separated mother liquor M to be separated by the solid-liquid
separator 14 contains the solvent H, a reduced material (p-toluic acid) of the foregoing impurity, and the aromatic carboxylic acid. With respect to this separated mother liquid M, by depositing the foregoing aromatic carboxylic acid and the foregoing reduced material each having been dissolved therein and recovering and removing the deposit and returning the resulting secondary separated mother liquor or other mother liquor having been subjected to demineralization of water to the foregoing dissolution step, it is possible to design to recover and reuse the solvent H.
As the foregoing dryer, a rotary dryer using a ventilating gas as shown in Fig. 2 can be enumerated. As a route through which the foregoing ventilating gas passes, a circulation route wherein the ventilating gas passes through the foregoing recovery device 5 or 16 from the foregoing dryer 4 or 15 and again returns to the dryer 4 or 15. More specifically, there is formed a circulation rough shown by a flow III, wherein the ventilating gas passes through the foregoing recovery device 5 or 16 from the foregoing dryer 4 or 15, then passes through a solvent component removal device 21, and returns to the foregoing dryer 4 or 15. Examples of this ventilating gas include inert gases such as a nitrogen gas.
The foregoing ventilating gas has a flow following the foregoing circulation route, and the solvent vapor as
the foregoing discharge gas is sent to the foregoing
recovery device 5 or 16 from the foregoing dryer 4 or 15
following the foregoing circulation route together with
the foregoing ventilating gas. And, the ventilating gas
after the recovery treatment in the foregoing recovery
device 5 or 16 is sent to the solvent component removal
device 21. After removing the entrained solvent component
by cooling, condensation, and other operations, the
resulting ventilating gas is returned to the dryer 4 or 15
and again sent to the foregoing recovery device 5 or 6 together
with the foregoing discharge gas.
Also, a spray device 23 of spraying the foregoing liquid can be provided on the way of a conduit 22 constructing a route wherein a flow of the foregoing ventilating gas goes to the foregoing recovery device 5 or 16 from the foregoing dryer 4 or 15. When the foregoing liquid is sprayed by this spray device 23, at least a part of the aromatic carboxylic acid crystal entrained in the foregoing discharge gas can be adsorbed onto the foregoing liquid and recovered, whereby the foregoing aromatic carboxylic acid can be prevented from attachment to an inner wall of the conduit 22.
As described previously, an aliphatic carboxylic acid such as acetic acid or water is preferable as the liquid to be used at this time. Further, a part of the recovered material to be recovered in the foregoing recovery device
can also be used as the foregoing liquid.
Also, when a portion of the foregoing conduit 22 in the side of the foregoing recovery device 5 or 16, that is, a portion thereof in the side connecting to the foregoing recovery device 5 or 16, is inclined downwardly towards the foregoing recovery device 5 or 16, the liquid R or S to be sprayed in the foregoing spray device 23 can be sent into the foregoing recovery device 5 or 16, and hence, such is preferable.
At this time, an angle of inclination (0 in Fig. 2) of the foregoing portion of the conduit 22 is preferably from 30 to 60° upwardly against the horizontal plane. When the angle of inclination is less than 30°, there may be the case where the flow of the liquid to be sprayed in the foregoing spray device 23 into the foregoing recovery device 5 or 16 becomes slow and is retained within the conduit 22. On the other hand, when it exceeds 60°, since
the range where the liquid R or S is spread within the
conduit 22 is limited, the efficiency is liable to lower.
In the case where an inclination is provided in the foregoing portion of the foregoing conduit 22, it is preferred to provide the foregoing spray device 23 in such a manner that it can be sprayed towards the recovery device 5 or 16 in the portion of the conduit 22 wherein the conduit 22 is bent, whereby the foregoing inclination is provided. In particular, it is preferable that the

spray device 23 is placed in the upstream side as far as possible within the range where the liquid R or S does not fall down into the dryer 4 or 15. In this way, the recovery efficiency of fine powders of the foregoing conduit 22 by the liquid to be sprayed by the foregoing spray device 23 is more enhanced.
With respect to a ratio of the amount of the foregoing liquid to be used to the amount of the foregoing discharge gas P or Q to be treated, the amount of the foregoing liquid is from 1 to 10 kg, and preferably from 3 to 6 kg per m3 of the foregoing discharge gas P or Q in the standard state (at 0 °C and 0.1013 Pa (1 atm)). When the amount of the foregoing liquid is less than 1 kg, there may be the case where the finely divided aromatic carboxylic acid in the discharge gas P or Q cannot be sufficiently recovered, On the other hand, when it exceeds 10 kg, in comparison with the recovery efficiency of the finely divided aromatic carboxylic acid in the discharge gas P or Q, the amount of the liquid to be used increases so that a problem of the post-treatment tends to occur.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing
from the spirit and scope thereof.
This application is based on a Japanese patent application filed January 8, 2003 (Japanese Patent Application No. 2003-002141), the entire contents thereof being hereby incorporated by reference.
INDUSTRIAL APPLICABILITY>
According to this invention, since a solid composed of an aromatic carboxylic acid contained in a discharge gas is recovered by a recovery device, it is possible to return the recovered solid to an oxidation step or use it as a washing liquid in a solid-liquid separation step and return the solid to a cake. Thus, the solid composed of an aromatic carboxylic acid can be returned to the major step of producing an aromatic carboxylic acid and then reused, whereby not only it is possible to enhance the yield, but also it is possible to inhibit a treatment for the discard.





We claim:
1. A process of producing terepthalic acid comprising the following steps
(A) to (D):
(A) oxidizing p-xylene with molecular oxygen in a solvent composed of acetic acid in the presence of a catalyst of the kind such as hereindescribed to obtain tetraphthalic acid containing 4-carboxybezaldehyde,
(B) subjecting the resulting tetraphthalic acid slurry to a solid-liquid separator and subjecting the tetraphthalic acid slurry to solid-liquid separation into a tetraphthalic acid cake and a mother liquor composed mainly of acetic acid,
(C) washing the resulting terepthalic acid cake with a washing liquid of the kind such as hereindescribed, and
(D) evaporating and removing the attached liquid remaining in the tetraphthalic acid cake after washing to obtain tetraphthalic acid crystal characterized in that:
the finely divided terepthalic acid crystal to be entrained in a discharge gas produced by the drying step containing a solvent vapor generated by the evaporation and removal is brought into contact with acetic acid or water and recovered in a recovery device, and a part or the whole of this recovered material is sent to said step (A).
2. The process of producing terepthalic acid as claimed in claim 1, wherein said recovered material is in the slurry state, a part or the whole of this recovered material is used as the washing liquid in said step (C), and a washing discharge liquid obtained in the step (C) is sent to the step (A).
3. The process of producing terepthalic acid as claimed in claim 1, wherein said liquid is acetic acid and/or water.
4. The process of producing terepthalic acid as claimed in claim 1, wherein the amount of said liquid to be used is from 1 to 10 kg per m3 of said discharge gas (in the standard state).
5. The process of producing terepthalic acid as claimed in claim 1,
wherein a part of the recovered material to be recovered in said recovery device is recycled as said liquid.
6. The process of producing terepthalic acid as claimed in claim 1, wherein said alkyl aromatic compound is p- xylene, and said aromatic carboxylic acid is terepthalic acid.

Documents:

2742-delnp-2004-abstract.pdf

2742-delnp-2004-claims.pdf

2742-delnp-2004-complete specification (as filed).pdf

2742-delnp-2004-complete specification (granted).pdf

2742-DELNP-2004-Correspondence-Others-(22-09-2009).pdf

2742-DELNP-2004-Correspondence-Others-(25-06-2010).pdf

2742-delnp-2004-correspondence-others.pdf

2742-delnp-2004-correspondence-po.pdf

2742-delnp-2004-description (complete).pdf

2742-delnp-2004-drawings.pdf

2742-delnp-2004-form-1.pdf

2742-delnp-2004-form-19.pdf

2742-delnp-2004-form-2.pdf

2742-DELNP-2004-Form-3-(22-09-2009).pdf

2742-DELNP-2004-Form-3-(25-06-2010).pdf

2742-delnp-2004-form-3.pdf

2742-delnp-2004-form-5.pdf

2742-delnp-2004-gpa.pdf

2742-delnp-2004-pct-301.pdf

2742-delnp-2004-pct-304.pdf

2742-delnp-2004-petition-137.pdf

2742-delnp-2004-petition-138.pdf


Patent Number 242410
Indian Patent Application Number 2742/DELNP/2004
PG Journal Number 35/2010
Publication Date 27-Aug-2010
Grant Date 25-Aug-2010
Date of Filing 17-Sep-2004
Name of Patentee MITSUBISHI CHEMICAL CORPORATION
Applicant Address 33-8, SHIBA 5-CHOME, MINATO-KU, TOKYO 108-0014, JAPAN
Inventors:
# Inventor's Name Inventor's Address
1 MASARU NISHIO C/O MCC PTA INDIA CORPORATION, 22, CAMAC STREET, BLOOK-C KOLKATA, INDIA
2 KATSUHIKO FUKUI C/O MITSUBISHI CHEMICAL CORPORATION, 580 OOKAGA 3-CHOME, MATSUYAMA-SHI, EHIME 791-8057, JAPAN
3 HIRONORI OOGI C/O MCC PTA INDIA CORPORATION, 22, CAMAC STREET, BLOOK-C KOLKATA, INDIA
PCT International Classification Number C07C 51/265
PCT International Application Number PCT/JP2003/016466
PCT International Filing date 2003-12-22
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2003-002141 2003-01-08 Japan