WO2008044895A1

WO2008044895A1 - The process of isolating methyl-4-formylbenzoate and dimethylterephtalate

Info

Publication number: WO2008044895A1
Application number: PCT/KR2007/005005
Authority: WO
Inventors: Jae Suk Koh; Woo Sun Kim; Young Kab Yu
Original assignee: Sk Energy Co., Ltd.
Priority date: 2006-10-13
Filing date: 2007-10-12
Publication date: 2008-04-17
Also published as: JP5246516B2; JP2010505945A; CN101522605B; CN101522605A; KR100814597B1

Abstract

Disclosed is a method of isolating and recovering methyl-4-formylbenzoate (MFB) and dimethyl terephthalate (DMT) at high purity from a mixture of byproducts produced in a process of producing DMT from p-xylene as a starting material through oxidation and esterification reactions. In the method, methyl-4-formylbenzoate (MFB) included in the byproduct mixture is isolated at high purity by converting it into an acetal compound through reaction with alcohol, and DMT is isolated and recovered from the byproduct mixture from which the MFB has been removed. The method does not generate sulfur dioxide gas, which is noxious and corrodes equipment, and in addition, it alleviates economic and environmental problems associated with the use of an excessive amount of solvent and the generation of wastewater.

Description

[DESCRIPTION] [Invention Title]

THE PROCESS OF ISOLATING METHYL-4-FORMYLBENZOATE AND DMETHYLTEREPHTHALATE [Technical Field]

The present invention relates to a method for isolating and recovering methyl-4- formylbenzoate and dimethyl terephthalate from a mixture of byproducts produced in a process of producing dimethyl terephthalate, and more particularly to a method for isolating and recovering each of methyl-4-formylbenzoate (hereinafter, referred to as "MFB") and dimethyl terephthalate (hereinafter, referred to as "DMT") at high purity from byproducts of a DMT production process, which include MEB, DMT, methyl-p-toluate (hereinafter, referred to as "MPT"), etc. [Background Art]

MFB is a white crystal having an aldehyde odor and is readily dissolved in acetone, toluene, methylene chloride and the like. It is used as a raw material for producing fluorescent whitening agents, aromatic agents and the like and as a raw material for producing high-value- added materials such as p-aminobenzoate.

A conventional method for preparing such MFB is shown in Reaction Scheme 1 below: [Reaction Scheme 1]

Terephthal aldehyde 4-Formylbenzoate MFB As shown in Reaction Scheme 1, according to the prior conventional method, MFB is synthesized by converting terephthal aldehyde to p-formylbenzoic acid in the presence of a sulfuric acid catalyst, and then adding methanol thereto in the presence of an acid catalyst. However, this process has shortcomings in that terephthal aldehyde is an expensive starting material, additional treatment for removing sulfuric acid after the preparation of 4-formylbenzoic acid is required, leading to a reduction in yield in the isolation and purification step, and the use of a catalyst is required in the methanol addition reaction so as to increase the cost of producing the desired compound.

In connection with this, Korean Patent Laid-Open Publication No.2003-70824 discloses a method for preparing p-aminobenzoic acid from a mixture of byproducts of a DMT production process, but does not disclose a method for isolating MFB and DMT as the main components of the byproducts at high purity.

As an improvement over the method of said Korean Patent Laid-Open Publication, Korean Patent Application No. 2004-13412 (granted to SK Corp., Korea) discloses a method for isolating and recovering MFB and DMT from methyl-4-formylbenzoate (MFB), dimethyl terephthalate (DMT), methyl-p-toluate (MPT) and methyl benzoate (MBZ), which are reaction byproducts of a process of producing DMT from p-xylene as a starting material through oxidation and esterification reactions. As shown in Reaction Scheme 2 below, said Korean Patent Application discloses a method of isolating MFB, in which MFB is allowed to react with sodium bisulfite (Na₂S₂O₅) so as to be converted to an MFB sodium salt: [Reaction Scheme 2]

CH₃O₂C — P \ — CHO +Na₂S₂O₅ +^■ CH₃O₂C — / \ — CH(OH)NaSO₃

MFB sodium salt

M^FB

However, in the method according to said Korean Patent Application No. 2004-13412, there are problems in that the use of sodium bisulfite generates a large amount of sulfur dioxide gas, which corrodes process equipment and adversely affects the safety of workers, and the use of excess amounts of water and a solvent leads to an increase in the cost of producing MFB. Also, there are shortcomings in that, because water and a solvent are used in amounts at least eight times the weight of initial MBF and at least two times the weight of initial MFB, respectively, in order to isolate MFB at high purity, the production cost of MFB is high, and a large amount of wastewater is generated, thus causing environmental problems. [Disclosure] [Technical Problem] Accordingly, the present inventors have conducted various studies to solve the above- described problems occurring in the prior art and, as a result, have found that, when MFB contained in a byproduct mixture of the DMT production process is converted into an acetal compound by reacting it with alcohol, DMT and MFB can be isolated and recovered at high purity from the byproduct mixture, thereby completing the present invention. Therefore, it is an object of the present invention to provide a method of isolating and recovering both MFB and DMT, which are highly useful, from byproducts, generated in a DMT production process, at high purity through a simple purification process at low cost.

Another object of the present invention is to provide an efficient process, which significantly relieves a problem of high cost caused by the use of an excessive amount of solvent in the prior suggested isolation method (Korean Patent Application No. 2004-13412), significantly reduces the amount of water that is added, thus relieving economic and environmental problems caused by the generation of a large amount of wastewater, and does not generate sulfur dioxide gas, which is noxious and corrodes equipment. [Technical Solution] To achieve the above and other objects, the present invention provides a method for isolating and recovering each of MFB and DMT from a mixture of reaction byproducts, produced in a process of producing DMT from p-xylene as a starting material through oxidation and esterification reactions, the method comprising the steps of:

(a) adding alcohol to a mixture of reaction byproducts, including MFB, DMT, MPT and MBZ, stirring the alcohol solution, and filtering the stirred solution to recover highly pure DMT as a solid;

(b) adding an acid to the filtrate of step (a) to convert MFB into an acetal compound;

(c) filtering the reaction material resulting from the step (b) at a temperature between - 15 ^°C and 20 ⁰C to recover the remaining DMT as a solid; (d) distilling and recovering the alcohol from the filtrate of step (c), and adding water and an organic solvent to the remaining material to convert the acetal compound into MFB; and

(e) filtering the reaction material resulting from the step (d) to obtain highly pure MFB as a solid.

[Advantageous Effects] The inventive method for isolating and recovering MFB and DMT is an efficient process, which significantly relieves a problem of high cost caused by the use of an excess amount of solvent in the prior process of isolating and recovering MFB and DMT by treating a mixture of byproducts, generated in producing DMT from p-xylene as a starting material through oxidation and esterification reactions, significantly reduces the amount of water that is added, thus relieving economic and environmental problems caused by the generation of a large amount of wastewater, and does not generate sulfur dioxide gas, which is noxious and causes corrosion of the equipment. [Best Mode]

Hereinafter, the present invention will be described in further detail. As described above, the present invention provides a method of isolating and recovering highly useful, highly pure MFB and DMT from a byproduct mixture of the DMT production process, which includes MFB, DMT, MPT and MBZ, through a simple purification process at low cost.

The composition of byproducts generated in DMT production processes can be varied depending on the conditions of the DMT production processes. Byproducts produced in a DMT production process, which employ the liquid-phase oxidation reaction of p-xylene, contain a significant amount of p-formylbenzoic acid, which is an intermediate product for terephthalic acid

(hereinafter referred to as "TPA"). In a process in which p-formylbenzoic acid is converted into

DMT through an esterification reaction with an excess of methanol, a mixture of byproducts, comprising 50-90 wt% of MFB, 5-30 wt% of DMT, 1-8 wt% of methyl-p-toluate (MPT) and 0.1-

3 wt% of methylbenzoate (MBZ), is obtained.

In the present invention, in order to isolate and recover each of MFB and DMT at high purity from reaction byproducts, produced in a process of producing DMT from p-xylene as a starting material through oxidation and esterification reactions, alcohol is first added to a byproduct mixture of the DMT production process, preferably, comprising 50-90 wt% of MFB, 5-30 wt% of DMT, 1-8 wt% of MPT and 0.1-3 wt% of MBZ. Then, the alcohol solution is stirred, such that only DMT is present as a solid in high purity in the reaction material. The reaction material is filtered to isolate pure DMT as a solid.

The alcohol that is added to the byproducts may be a C₁-C₁₀ alcohol, such as methanol, ethanol, propanol, isopropanol or butanol, and the amount of alcohol added is preferably 50-300 parts by weight, and more preferably 150-250 parts by weight, based on 100 parts by weight of initial MFB. If the amount of alcohol added is less than 50 parts by weight, the recovery rate of

MFB will be reduced, and if it is more than 300 parts by weight, DMT will be dissolved, thus reducing the purity of the MFB product. Then, an acid is added to the filtrate to convert MFB into an acetal compound. The conversion reaction is shown in, for example, Reaction Scheme 3 below: [Reaction Scheme 3]

₃

Methyl-4-Formylben2oate Benzaldethyde dialkyl-4-acetate Methyl-4-Formylbenzoate wherein R is a C₁-C₁₀ alkyl group. The acid that is added is preferably an acid having a pH of less than 6, such as hydrochloric acid (HCl), nitric acid (HNO₃), sulfuric acid (H₂SO₄), p- toluenesulfonic acid or acetic acid (CH₃COOH). The amount of acid added is preferably 0.01-

30 parts by weight, and preferably 0.1-3 parts by weight, based on 100 parts by weight of initial

MFB. If the amount of acid added is less than 0.01 parts by weight, the reaction of conversion into acetal will not be complete, and if it exceeds 30 parts by weight, the generation of wastewater in a subsequent neutralization step will be excessive, leading to a reduction in economic efficiency.

When the reaction material converted into the acetal compound as described above is maintained at low temperature, the remaining DMT is deposited as a crystal. The remaining

DMT is recovered as a solid at high purity through filtration. The filtration is preferably carried out at a temperature between -15 ⁰C and 20 ^°C, and more preferably between -5 ^°C and 3 ⁰C. If the filtration temperature is below -15 °C , the acetal compound will be crystallized, leading to a significant reduction in recovery rate, and if it is above 20 ^°C, DMT will be dissolved, resulting in a decrease in the purity of MFB.

Herein, the reason why DMT is recovered at the lowered temperature after the acetalization reaction is because, if the temperature is high, the dissolution of DMT will be increased, so that the content of DMT in the MFB product will be increased, thus reducing the purity of the MFB product.

From the filtrate from which the remaining DMT has been isolated as described above, the alcohol is recovered by distillation. To the remaining material, water and a non-aromatic solvent are added, and the acetal compound, for example, benzaldehyde dialkyl-4-acetate, as shown in Reaction Scheme 3, is converted into MFB in the presence of an acid catalyst.

Herein, the amount of water added is preferably 50-300 parts by weight, and more preferably 150-200 parts, based on 100 parts by weight of initial MFB. The non-aromatic solvent that is used in the conversion reaction is preferable to a solvent containing an aromatic component, because the acetal compound has low solubility in the non-aromatic solvent. Also, it is preferably a non-aromatic hydrocarbon solvent having 3-12 carbon atoms. The amount of solvent added is preferably 50-300 parts by weight, and more preferably 100-200 parts by weight, based on 100 parts by weight of initial MFB. If the amount of solvent added is less than 50 parts by weight, crystals will rapidly form in the acetal-to-MFB conversion reaction, and thus the purity of the MFB product will be reduced due to impurities, and if it exceeds 300 parts by weight, the production cost of MFB will be increased due to the excessive use of the solvent, thus reducing economic efficiency. When the acetal compound is converted into MFB through the above reaction, MFB is present as a solid. MFB is recovered as a solid through filtration, and other impurities, such as MPT and MBZ, are isolated and removed with the solvent. From the recovered solid MFB, the solvent and water are removed, thus obtaining a highly pure MFB product. [Mode for Invention] Hereinafter, the present invention will be described in further detail with reference to the following examples. It is to be understood, however, that these examples are illustrative only, and the scope of the present invention is not limited thereto. Example 1 200 parts by weight of methanol was added to 100 parts by weight of a mixture, comprising about 63 wt% of MFB, about 30 wt% of DMT, about 6 wt% of MPT, about 1 wt% of MBZ and a trace amount of impurities, which were byproducts of the DMT production process. The methanol solution was stirred at 25 ^°C for 0.5 hours. After completion of the stirring, only DMT remained as a solid, and the stirred solution was filtered to recover DMT as a solid. The solid DMT was washed with methanol, and the DMT thus obtained had a weight of 27.4 g and a purity of 99.4%.

To the filtrate, 0.2 parts by weight of hydrochloric acid (HCl) was added, and the solution was stirred for 2 hours to convert MFB into benzaldehyde dimethylacetal-4-acetate. When the reaction material converted into benzaldehyde dimethylacetal-4-acetate was maintained at -2 "C, the remaining DMT was deposited as a solid. The reaction material was filtered at - 2 ^°C to recover the remaining DMT as a solid. The deposited DMT was washed with methanol, and the DMT thus obtained had a weight of 2.1 g and a purity of 98.5%.

From the filtrate, methanol was recovered by distillation, and 63 parts by weight of heptane and 63 parts by weight of water were added to the remaining material. The solution was stirred at 70 ^°C for 4 hours. After completion of the reaction, the reaction solution was cooled to 25 ^°C and filtered to recover the produced MFB as a solid. The produced MFB was recovered by drying at 50 °C, and the recovered MFB had a weight of 39.2 g and a purity of 98.9%.

Example 2

200 parts by weight of ethanol was added to 100 parts by weight of a mixture comprising about 63 wr% of MFB, about 30 wt% of DMT, about 6 wt% of MPT, about 1 wt% of MBZ and a trace amount of impurities, which were byproducts of the DMT production process. The ethanol solution was stirred at 25 ^°C for 0.5 hours. After completion of the stirring, only DMT remained as a solid, and the stirred solution was filtered to recover DMT as a solid. The solid DMT was washed with methanol, and the DMT thus obtained had a weight of 25.1 g and a purity of 99.6%. To the filtrate, 0.2 parts by weight of hydrochloric acid (HCl) was added, and the solution was stirred for 2 hours to convert MFB into benzaldehyde dimethylacetal-4-acetate. When the reaction material converted into benzaldehyde dimethylacetal-4-acetate was maintained at -2 °C, the remaining DMT was deposited as a solid. The reaction material was filtered at - 2 °C to recover the remaining DMT as a solid. The deposited DMT was washed with ethanol, and the DMT thus obtained had a weight of 1.8 g and a purity of 99.1 %.

From the filtrate, ethanol was recovered by distillation, and 63 parts by weight of heptane and 63 parts by weight of water were added to the remaining material. The solution was stirred at 70 ^°C for 4 hours. After completion of the reaction, the reaction solution was cooled to 25 °C and filtered to recover the produced MFB as a solid. The produced MFB was recovered by drying at 50 ^°C, and the recovered MFB had a weight of 36.8 g and a purity of 98.1%.

Example 3

MFB was recovered in the same manner as in Example 1, except that the same amount of Exelsol 670 (SK Corp., Korea) was used instead of heptane. In this case, the recovered DMT had a purity of 99.4% and a weight of 29.8 g, and the recovered MFB had a purity of 98.8% and a weight of 39.9 g.

Example 4

MFB was recovered in the same manner as in Example 1, except that the same amount of p-toluenesulfonic acid was used instead of hydrochloric acid. In this case, the recovered DMT had a purity of 99.5% and a weight of 29.5 g, and the recovered MFB had a purity of 99.0% and a weight of 40.5 g.

Claims

[CLAIMS] [Claim 1 ]

A method for isolating and recovering each of methyl-4-formylbenzoate (MFB) and dimethyl terephthalate (DMT) from a mixture of byproducts, produced in a process of producing DMT from p-xylene as a starting material through oxidation and esterification reactions, the method comprising the steps of:

(a) adding alcohol to a mixture of reaction byproducts, including MFB, DMT, methyl-p- toluate (MPT) and methyl benzoate (MBZ), stirring the alcohol solution, and filtering the stirred solution to recover DMT as a solid; (b) adding an acid to the filtrate of step (a) to convert MFB into an acetal compound;

(c) filtering the reaction material resulting from the step (b) at a temperature between - 15 ^°C and 20 ^°C to recover the remaining DMT as a solid;

(d) recovering the alcohol from the filtrate of step (c) by distillation, and adding water and an organic solvent to the remaining material to convert the acetal compound into MFB; and (e) filtering the reaction material resulting from the step (d) to isolate solid-phase MFB.

[Claim 2]

The method of Claim 1, wherein the reaction byproducts in the step (a) include 50-90 wt% of MFB, 5-30 wt% of DMT, 1-8 wt% of MPT and 0.1-3 wt% of MBZ.

[Claim 3] The method of Claim 1, wherein the alcohol in the step (a) is an alcohol having 1-10 carbon atoms.

[Claim 4]

The method of Claim 1 or 3, wherein the amount of alcohol added in the step (a) is 50- 300 parts by weight based on 100 parts by weight of initial methyl-4-formylbenzoate (MFB).

[Claim 5] The method of Claim 1, wherein the acid in the step (b) is an acid having a pH of less than 6, which is selected from hydrochloric acid (HCl), nitric acid (HNO₃), sulfuric acid (H₂SO₄), p- toluenesulfonic acid and acetic acid (CH₃COOH).

[Claim 6] The method of Claim 1 or 5, wherein the amount of acid added in the step (b) is 0.01-30 parts by weight based on 100 parts by weight of initial methyl-4-formylbenzoate (MFB). [Claim 7]

The method of Claim 1, wherein the amount of water added in the step (d) is 50-300 parts by weight based on 100 parts by weight of initial methyl-4-formylbenzoate (MFB). [Claim 8]

The method of Claim 1, wherein the organic solvent in the step (d) is a non-aromatic hydrocarbon solvent having 3-12 carbon atoms. [Claim 9]

The method of Claim 1 or 8, wherein the amount of organic solvent added is 50-300 parts by weight based on 100 parts by weight of initial methyl-4-formylbenzoate (MFB). [Claim 10]

The method of Claim 1, wherein the acetal compound is benzaldehyde dialkylacetaM- acetate.