Crude terephthalic acid methyl esterification reaction catalyst and preparation method and application thereof

Abstract

The invention discloses a crude terephthalic acid methyl esterification reaction catalyst as well as a preparation method and application thereof. The crude terephthalic acid methyl esterification reaction catalyst comprises a composite carrier and polyferric sulfate loaded on the composite carrier, the composite carrier is formed by compounding a modified H-ZSM-5 molecular sieve and titanium dioxide through a hydrothermal reaction; the modified H-ZSM-5 molecular sieve is prepared by treating an H-ZSM-5 molecular sieve with an organic acid solution and then roasting the treated H-ZSM-5 molecular sieve; in the composite carrier, the mass ratio of the modified H-ZSM-5 molecular sieve to titanium dioxide is (1: 1)-(5: 1); the mass ratio of the composite carrier to the polymeric ferric sulfate is (95: 5)-(99: 1). The composite catalyst of the H-ZSM-5 molecular sieve treated by the organic acid, the titanium dioxide and the polyferric sulfate is used as the catalyst for preparing the dimethyl terephthalate by methyl esterification of the crude terephthalic acid, so that the catalyst has excellent catalytic performance, basically has no corrosion to equipment and has few byproducts in the process.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a crude terephthalic acid methyl esterification reaction catalyst, a preparation method and application thereof. Background Art

[0002] Terephthalic acid is the largest dicarboxylic acid in production. In the current industrial production of terephthalic acid, p-xylene (PX) is used as a raw material, and under appropriate temperature and pressure conditions, crude terephthalic acid (CTA) is obtained by oxidation under the catalytic action of a Co / Mn / Br catalyst system. However, as an industrial raw material, CTA often contains a small amount of impurities such as p-carboxybenzaldehyde (4-CBA), which will seriously affect the downstream production of purified terephthalic acid (PTA). Dimethyl terephthalate (DMT) is an important chemical raw material intermediate, and one of the important raw materials for producing dimethyl terephthalate is purified terephthalic acid. Generally, p-carboxybenzaldehyde in crude terephthalic acid needs to be converted into other compounds through hydrorefining, and then impurities are removed through crystallization separation and purification to obtain purified terephthalic acid. The catalyst used in the hydrorefining process is a commercial palladium carbon (Pd / C) catalyst, which is a precious metal catalyst with high cost, and the conversion rate of hydrorefining is only about 90%. Therefore, it is of great significance to develop a catalyst for directly and efficiently catalyzing the conversion of crude methyl terephthalate to dimethyl terephthalate.

[0003] CN104072374A discloses a method for preparing dimethyl terephthalate. The method uses purified terephthalic acid and methanol as reaction raw materials and concentrated sulfuric acid as a catalyst to prepare dimethyl terephthalate, and the purity of the obtained dimethyl terephthalate is 99.8-99.9%. However, the method uses concentrated sulfuric acid as a catalyst, which is highly corrosive to the equipment and has high requirements on the equipment material; at the same time, the acid-containing wastewater generated by the method has a large pollution to the environment and the sewage treatment cost is high; in addition, the by-product dimethyl sulfate generated by the method is a highly toxic substance and is extremely unsafe.

[0004] CN102219689A discloses a method for producing dimethyl terephthalate. The method first uses alkali reduction wastewater as a raw material to prepare terephthalic acid with a water content of 40-60%, then purifies and dries the obtained terephthalic acid, and uses it together with methanol as a reaction raw material to prepare dimethyl terephthalate under the catalytic action of tin, zinc and antimonide. However, the metal catalyst is easily converted under high temperature and high pressure conditions, which makes it difficult to recover the catalyst and separate and purify the product; and a certain amount of monomethyl p-dibenzoate is produced in the process. Due to the high boiling point of monomethyl p-dibenzoate, it is easy to cause blockage problems in the subsequent separation and purification process.

[0005] Based on the above existing needs and deficiencies in the prior art, there is an urgent need to develop an efficient, environmentally friendly catalyst with high selectivity for the target product for use in the preparation of dimethyl terephthalate from crude methyl terephthalate. Summary of the invention

[0006] The present invention aims to overcome the above problems existing in the prior art and provides a catalyst for the methylation reaction of crude terephthalic acid, a preparation method thereof and an application thereof. The composite catalyst of H-ZSM-5 molecular sieve treated with organic acid, titanium dioxide and polyferric sulfate is used as a catalyst for the methylation of crude terephthalic acid to produce dimethyl terephthalate. The catalyst has excellent catalytic performance, is substantially non-corrosive to equipment and produces few by-products in the process.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a crude terephthalic acid methyl esterification reaction catalyst, including a composite carrier and polyferric sulfate loaded on the composite carrier; the composite carrier is composited by a modified H-ZSM-5 molecular sieve and titanium dioxide through a hydrothermal reaction; the modified H-ZSM-5 molecular sieve is formed by calcining the H-ZSM-5 molecular sieve after being treated with an organic acid solution; in the composite carrier, the mass ratio of the modified H-ZSM-5 molecular sieve and the titanium dioxide is 1:1 to 5:1; the mass ratio of the composite carrier to the polyferric sulfate is 95:5 to 99:1.

[0008] The present invention uses H-ZSM-5 molecular sieve, titanium dioxide and polyferric sulfate as a catalyst for the reaction of methyl esterification of terephthalic acid to dimethyl terephthalate. Unrefined crude terephthalic acid can be used as a reaction raw material, eliminating the refining process of terephthalic acid and reducing production costs. The catalyst of the present invention exhibits excellent catalytic performance in the process of catalyzing the methyl esterification of crude terephthalic acid to dimethyl terephthalate, and the crude terephthalic acid conversion rate and dimethyl terephthalate selectivity can reach more than 98%. In addition, the catalyst of the present invention is substantially non-corrosive to equipment and does not produce acid-containing wastewater and toxic byproducts.

[0009] When the H-ZSM-5 molecular sieve, titanium dioxide and polyferric sulfate are compounded, the H-ZSM-5 molecular sieve is first treated with an organic acid and roasted. The acid treatment can effectively remove non-stock aluminum species in the pore channel of the H-ZSM-5 molecular sieve, and play a role in dredging the pore channel; at the same time, the acid treatment can also expand the pores of the H-ZSM-5 molecular sieve to a certain extent, so that the active sites in the pore channel participate more in the methylation reaction. Then the modified H-ZSM-5 molecular sieve is mixed with titanium dioxide for hydrothermal reaction to obtain a composite carrier. Compounding under hydrothermal conditions can promote the uniform mixing of the two at the micrometer or even nanometer scale. It is beneficial to improve the active sites of the catalyst. Finally, the polyferric sulfate is loaded on the composite carrier, which can further improve the catalytic activity of the catalyst in the reaction of preparing dimethyl terephthalate by methylation of crude terephthalate.

[0010] Preferably, the mass ratio of the modified H-ZSM-5 molecular sieve to titanium dioxide is 1:1 to 3:1.

[0011] Preferably, the silicon-aluminum ratio in the H-ZSM-5 molecular sieve is 30 to 120. When the silicon-aluminum ratio is within this range, the catalyst can have better catalytic performance for the reaction of preparing dimethyl terephthalate from crude methyl terephthalate.

[0012] Preferably, the organic acid solution is one or a combination of two or more of citric acid solution, oxalic acid solution, tartaric acid solution, acetic acid solution, malic acid solution, and succinic acid solution; the concentration of the organic acid solution is 0.001 to 0.5 mol / L, and the mass ratio of H-ZSM-5 molecular sieve to the organic acid solution is 1:5 to 1:100.

[0013] Preferably, the calcination temperature after the organic acid treatment is 400-600° C., and the calcination time is 2-8 hours.

[0014] Preferably, the titanium dioxide is one or both of anatase titanium dioxide and diamond titanium dioxide.

[0015] In a second aspect, the present invention provides a method for preparing the above-mentioned crude terephthalic acid methyl esterification reaction catalyst, comprising the following steps: (1) mixing H-ZSM-5 molecular sieve with an organic acid solution, stirring the reaction, filtering, washing, drying, and then calcining the product to obtain a modified H-ZSM-5 molecular sieve; (2) mixing the modified H-ZSM-5 molecular sieve and titanium dioxide to obtain a mixed powder; mixing the mixed powder with deionized water, stirring evenly, and then performing a hydrothermal reaction; filtering and drying the product to obtain a composite carrier; (3) dissolving polyferric sulfate in an organic solvent to form an impregnation solution; impregnating the composite carrier in the impregnation solution and then drying to obtain the crude terephthalic acid methyl esterification reaction catalyst.

[0016] Preferably, the stirring reaction temperature in step (1) is 25-90° C., and the stirring time is 10-120 min; the drying temperature is 80-120° C., and the drying time is 2-15 h.

[0017] Preferably, in step (2), the mass ratio of the mixed powder to deionized water is 1:2 to 1:50; the hydrothermal reaction temperature is 50 to 90° C., and the hydrothermal reaction time is 2 to 10 h; the drying temperature of the product is 80 to 120° C., and the drying time is 2 to 15 h.

[0018] Preferably, the concentration of the impregnation solution in step (3) is 0.05-0.5 mol / L; the composite carrier is immersed in the impregnation solution for 5-24 h; the drying temperature is 80-150° C., and the drying time is 2-15 h.

[0019] In a third aspect, the present invention provides an application of the above crude terephthalic acid methyl esterification reaction catalyst in the esterification reaction of crude terephthalic acid and methanol to produce dimethyl terephthalate, wherein the mass fraction of terephthalic acid in the crude terephthalic acid is above 90%.

[0020] Preferably, the mass ratio of methanol to crude terephthalic acid during the reaction is 2:1 to 6:1; the mass of the crude terephthalic acid methyl esterification reaction catalyst is 2 to 6% of the mass of the crude terephthalic acid.

[0021] Preferably, the reaction temperature for the esterification of crude terephthalic acid with methanol to produce dimethyl terephthalate is 150-300° C., the reaction pressure is 1-10 MPa, and the reaction time is 2-10 h.

[0022] Therefore, the present invention has the following beneficial effects: (1) The present invention uses H-ZSM-5 molecular sieve, titanium dioxide and polyferric sulfate as a catalyst for the reaction of methyl terephthalate to dimethyl terephthalate, and can use unrefined crude terephthalic acid as a reaction raw material, thereby eliminating the refining process of terephthalic acid and reducing production costs; (2) The catalyst of the present invention exhibits excellent catalytic performance in the process of catalyzing the conversion of crude terephthalic acid methyl ester to dimethyl terephthalate, and the crude terephthalic acid conversion rate and dimethyl terephthalate selectivity can reach more than 98%; (3) When the catalyst provided by the present invention is used to catalyze the production of dimethyl terephthalate from crude methyl terephthalate, it is substantially non-corrosive to equipment and does not produce acidic wastewater and toxic by-products. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with specific implementation methods.

[0024] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art.

[0025] Overall embodiment: A crude terephthalic acid methyl esterification reaction catalyst comprises a composite carrier and polyferric sulfate loaded on the composite carrier; the composite carrier is composited by a modified H-ZSM-5 molecular sieve and titanium dioxide through a hydrothermal reaction; the modified H-ZSM-5 molecular sieve is formed by calcining the H-ZSM-5 molecular sieve after being treated with an organic acid solution; in the composite carrier, the mass ratio of the modified H-ZSM-5 molecular sieve to the titanium dioxide is 1:1-5:1; and the mass ratio of the composite carrier to the polyferric sulfate is 95:5-99:1.

[0026] As a specific implementation manner, the mass ratio of the modified H-ZSM-5 molecular sieve to titanium dioxide is 1:1 to 3:1.

[0027] As a specific implementation manner, the silicon-aluminum ratio in the H-ZSM-5 molecular sieve is 30-120; preferably, the silicon-aluminum ratio in the H-ZSM-5 molecular sieve is 40-100.

[0028] As a specific implementation, the organic acid solution is one or a combination of two or more of citric acid solution, oxalic acid solution, tartaric acid solution, acetic acid solution, malic acid solution, and succinic acid solution.

[0029] As a specific implementation, the concentration of the organic acid solution is 0.001-0.5 mol / L; preferably, the concentration of the organic acid solution is 0.1-0.2 mol / L.

[0030] As a specific implementation manner, the mass ratio of H-ZSM-5 molecular sieve to organic acid solution is 1:5 to 1:100; preferably, the mass ratio of H-ZSM-5 molecular sieve to organic acid solution is 1:10 to 1:50.

[0031] As a specific implementation manner, the calcination temperature after the organic acid treatment is 400-600° C., and the calcination time is 2-8 hours; preferably, the calcination time is 4-6 hours.

[0032] As a specific implementation, the titanium dioxide is one or both of anatase titanium dioxide and diamond titanium dioxide; the particle size of the titanium dioxide is 50 to 1000 nm.

[0033] The method for preparing the crude terephthalic acid methyl esterification reaction catalyst comprises the following steps: (1) mixing H-ZSM-5 molecular sieve with an organic acid solution, stirring the reaction, filtering, washing, drying, and then calcining the product to obtain a modified H-ZSM-5 molecular sieve; (2) mixing the modified H-ZSM-5 molecular sieve and titanium dioxide to obtain a mixed powder; mixing the mixed powder with deionized water, stirring evenly, and then performing a hydrothermal reaction; filtering and drying the product to obtain a composite carrier; (3) dissolving polyferric sulfate in an organic solvent to form an impregnation solution; impregnating the composite carrier in the impregnation solution and then drying to obtain the crude terephthalic acid methyl esterification reaction catalyst.

[0034] As a specific implementation manner, the temperature during the stirring reaction in step (1) is 25 to 90° C., and the stirring time is 10 to 120 min; preferably, the temperature during the stirring reaction is 50 to 90° C., and the stirring time is 30 to 90 min.

[0035] As a specific implementation, the drying temperature in step (1) is 80-120° C., and the drying time is 2-15 hours; preferably, the drying time is 6-12 hours.

[0036] As a specific implementation, in step (2), the mass ratio of the mixed powder to deionized water is 1:2 to 1:50; preferably, the mass ratio of the mixed powder to deionized water is 1:5 to 1:25.

[0037] As a specific implementation manner, the hydrothermal reaction temperature in step (2) is 50-90° C., and the hydrothermal reaction time is 2-10 h; preferably, the hydrothermal reaction time is 4-6 h.

[0038] As a specific implementation manner, the drying temperature of the product in step (2) is 80 to 120° C., and the drying time is 2 to 15 hours; preferably, the drying time is 6 to 12 hours.

[0039] As a specific implementation, the concentration of the impregnation solution in step (3) is 0.05-0.5 mol / L; preferably, the concentration of the impregnation solution is 0.1-0.2 mol / L.

[0040] As a specific implementation, in step (3), the composite carrier is immersed in the immersion liquid for 5 to 24 hours; preferably, the immersion time is 8 to 16 hours.

[0041] As a specific implementation, the drying temperature in step (3) is 80-150° C., and the drying time is 2-15 hours; preferably, the drying time is 6-12 hours.

[0042] As a specific implementation, the organic solvent in step (3) is one or a combination of two or more of ethanol, ether, chloroform and carbon tetrachloride.

[0043] Embodiment 1: A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 60 was uniformly mixed with 100 g of 0.1 mol / L citric acid solution, stirred at 60° C. for 60 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 90° C. for 12 h, and calcined at 500° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) The modified H-ZSM-5 molecular sieve obtained in step (1) was mixed with 5 g of anatase titanium dioxide (particle size of 100 nm) to obtain a mixed powder; the mixed powder was added to 150 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 60° C. for 5 h, filtered, and the obtained solid was dried at 110° C. for 12 h to obtain a composite carrier; (3) Dissolve polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the composite support to make the content of polyferric sulfate in the catalyst 3 wt %. After impregnation at room temperature for 12 h, the obtained catalyst preparation sample is dried at 120° C. for 12 h to obtain the crude methyl terephthalate reaction catalyst.

[0044] Embodiment 2: A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 90 was uniformly mixed with 100 g of 0.1 mol / L oxalic acid solution, stirred at 70° C. for 70 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 110° C. for 12 h, and calcined at 550° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) The modified H-ZSM-5 molecular sieve obtained in step (1) is mixed with 2 g of anatase titanium dioxide (particle size of 150 nm) to obtain a mixed powder; the mixed powder is added to 200 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 80° C. for 5 h, filtered, and the obtained solid is dried at 110° C. for 12 h to obtain a composite carrier; (3) Dissolve polyferric sulfate in ether to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the composite support to make the content of polyferric sulfate in the catalyst be 1 wt %. After impregnation at room temperature for 12 h, the obtained catalyst preparation sample is dried at 110° C. for 12 h to obtain the crude methyl terephthalate reaction catalyst.

[0045] Embodiment 3: A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 85 was uniformly mixed with 150 g of 0.1 mol / L citric acid solution, stirred at 80° C. for 60 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 110° C. for 10 h, and calcined at 550° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) The modified H-ZSM-5 molecular sieve obtained in step (1) was mixed with 10 g of diamond-type titanium dioxide (particle size of 100 nm) to obtain a mixed powder; the mixed powder was added to 200 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 70° C. for 5 h, filtered, and the obtained solid was dried at 110° C. for 10 h to obtain a composite carrier; (3) Dissolve polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the composite carrier to make the content of polyferric sulfate in the catalyst be 5 wt %. After impregnation at room temperature for 15 h, the obtained catalyst preparation sample is dried at 100° C. for 14 h to obtain the crude methyl terephthalate reaction catalyst.

[0046] Embodiment 4: A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 90 was uniformly mixed with 140 g of 0.1 mol / L citric acid solution, stirred at 80° C. for 60 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 110° C. for 12 h, and calcined at 550° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) The modified H-ZSM-5 molecular sieve obtained in step (1) was mixed with 5 g of anatase titanium dioxide (particle size of 150 nm) to obtain a mixed powder; the mixed powder was added to 180 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 70° C. for 5 h, filtered, and the obtained solid was dried at 100° C. for 12 h to obtain a composite carrier; (3) Dissolve polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the composite carrier to make the content of polyferric sulfate in the catalyst be 3 wt %. After impregnation at room temperature for 12 h, the obtained catalyst preparation sample is dried at 100° C. for 10 h to obtain the crude methyl terephthalate reaction catalyst.

[0047] Embodiment 5: A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 80 was uniformly mixed with 120 g of 0.1 mol / L citric acid solution, stirred at 70° C. for 70 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 110° C. for 10 h, and calcined at 550° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) The modified H-ZSM-5 molecular sieve obtained in step (1) was mixed with 5 g of diamond-type titanium dioxide (particle size of 200 nm) to obtain a mixed powder; the mixed powder was added to 180 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 75° C. for 4 h, filtered, and the obtained solid was dried at 100° C. for 12 h to obtain a composite carrier; (3) Dissolve polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the composite carrier to make the content of polyferric sulfate in the catalyst be 3 wt %. After impregnation at room temperature for 18 h, the obtained catalyst preparation sample is dried at 115° C. for 10 h to obtain the crude methyl terephthalate reaction catalyst.

[0048] Comparative Example 1 (H-ZSM-5 molecular sieve is not modified with organic acid): A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 60 and 5 g of anatase titanium dioxide (particle size of 100 nm) were mixed to obtain a mixed powder; the mixed powder was added to 150 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 60° C. for 5 h, filtered, and the obtained solid was dried at 110° C. for 12 h to obtain a composite carrier; (2) Dissolve polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the composite carrier to make the content of polyferric sulfate in the catalyst be 3 wt %. After impregnation at room temperature for 12 h, the obtained catalyst preparation sample is dried at 120° C. for 12 h to obtain the crude methyl terephthalate reaction catalyst.

[0049] Comparative Example 2 (H-ZSM-5 molecular sieve and titanium dioxide are not compounded by hydrothermal treatment): A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 60 was uniformly mixed with 100 g of 0.1 mol / L citric acid solution, stirred at 60° C. for 60 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 90° C. for 12 h, and calcined at 500° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) mixing the modified H-ZSM-5 molecular sieve obtained in step (1) with 5 g of anatase titanium dioxide (particle size of 100 nm) to obtain a composite carrier; (3) Dissolve polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the composite support to make the content of polyferric sulfate in the catalyst 3 wt %. After impregnation at room temperature for 12 h, the obtained catalyst preparation sample is dried at 120° C. for 12 h to obtain the crude methyl terephthalate reaction catalyst.

[0050] Comparative Example 3 (without adding H-ZSM-5 molecular sieve): A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 5 g of anatase titanium dioxide (particle size of 100 nm) was added to 150 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 60° C. for 5 h, filtered, and the obtained solid was dried at 110° C. for 12 h to obtain a carrier; (2) dissolving polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly dropping the impregnation solution onto the carrier to make the content of polyferric sulfate in the catalyst be 3 wt %. After impregnation at room temperature for 12 h, the obtained catalyst preparation sample was dried at 120° C. for 12 h to obtain the crude methyl terephthalate reaction catalyst.

[0051] Comparative Example 4 (without adding titanium dioxide): A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 60 was uniformly mixed with 100 g of 0.1 mol / L citric acid solution, stirred at 60° C. for 60 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 90° C. for 12 h, and calcined at 500° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) adding the modified H-ZSM-5 molecular sieve obtained in step (1) to 150 g of deionized water, stirring evenly, loading into a polytetrafluoroethylene reaction kettle, heating at 60° C. for 5 h, filtering, and drying the obtained solid at 110° C. for 12 h to obtain a carrier; (3) Dissolve polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the carrier to make the content of polyferric sulfate in the catalyst be 3 wt %. After impregnation at room temperature for 12 h, the obtained catalyst preparation sample is dried at 120° C. for 12 h to obtain the crude methyl terephthalate reaction catalyst.

[0052] Comparative Example 5 (without adding polyferric sulfate): A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 60 was uniformly mixed with 100 g of 0.1 mol / L citric acid solution, stirred at 60° C. for 60 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 90° C. for 12 h, and calcined at 500° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) The modified H-ZSM-5 molecular sieve obtained in step (1) is mixed with 5 g of anatase titanium dioxide (particle size of 100 nm) to obtain a mixed powder; the mixed powder is added to 150 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 60° C. for 5 h, filtered, and the obtained solid is dried at 110° C. for 12 h to obtain the crude methyl terephthalate reaction catalyst.

[0053] Comparative Example 6 (too much molecular sieve added): A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 30 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 60 was uniformly mixed with 100 g of 0.1 mol / L citric acid solution, stirred at 60° C. for 60 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 90° C. for 12 h, and calcined at 500° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) The modified H-ZSM-5 molecular sieve obtained in step (1) was mixed with 5 g of anatase titanium dioxide (particle size of 100 nm) to obtain a mixed powder; the mixed powder was added to 150 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 60° C. for 5 h, filtered, and the obtained solid was dried at 110° C. for 12 h to obtain a composite carrier; (3) Dissolve polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the composite support to make the content of polyferric sulfate in the catalyst 3 wt %. After impregnation at room temperature for 12 h, the obtained catalyst preparation sample is dried at 120° C. for 12 h to obtain the crude methyl terephthalate reaction catalyst.

[0054] Comparative Example 7 (too much titanium dioxide added): A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 60 was uniformly mixed with 100 g of 0.1 mol / L citric acid solution, stirred at 60° C. for 60 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 90° C. for 12 h, and calcined at 500° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) The modified H-ZSM-5 molecular sieve obtained in step (1) was mixed with 20 g of anatase titanium dioxide (particle size of 100 nm) to obtain a mixed powder; the mixed powder was added to 150 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 60° C. for 5 h, filtered, and the obtained solid was dried at 110° C. for 12 h to obtain a composite carrier; (3) Dissolve polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the composite support to make the content of polyferric sulfate in the catalyst 3 wt %. After impregnation at room temperature for 12 h, the obtained catalyst preparation sample is dried at 120° C. for 12 h to obtain the crude methyl terephthalate reaction catalyst.

[0055] Comparative Example 8 (too much polyferric sulfate added): A method for preparing a crude terephthalic acid methyl esterification catalyst, comprising the following steps: (1) 10 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 60 was uniformly mixed with 100 g of 0.1 mol / L citric acid solution, stirred at 60° C. for 60 min, filtered, and the obtained solid A was washed with deionized water until neutral, dried at 90° C. for 12 h, and calcined at 500° C. for 4 h to obtain a modified H-ZSM-5 molecular sieve; (2) The modified H-ZSM-5 molecular sieve obtained in step (1) was mixed with 5 g of anatase titanium dioxide (particle size of 100 nm) to obtain a mixed powder; the mixed powder was added to 150 g of deionized water, stirred evenly, and then loaded into a polytetrafluoroethylene reactor, heated at 60° C. for 5 h, filtered, and the obtained solid was dried at 110° C. for 12 h to obtain a composite carrier; (3) Dissolve polyferric sulfate in ethanol to prepare a 0.1 mol / L impregnation solution, and evenly drip the impregnation solution onto the composite carrier to make the content of polyferric sulfate in the catalyst be 10 wt %. After impregnation at room temperature for 12 h, the obtained catalyst preparation sample is dried at 120° C. for 12 h to obtain the crude methyl terephthalate reaction catalyst.

[0056] Application Example 1: 160 g of crude terephthalic acid, 350 g of methanol and 5 g of the crude terephthalic acid methyl esterification catalyst prepared in Example 1 were added into a high-temperature and high-pressure reactor, and reacted for 2 h at a reaction temperature of 240° C. and a reaction pressure of 3 MPa.

[0057] Application Example 2: 160 g of crude terephthalic acid, 380 g of methanol and 5 g of the crude terephthalic acid methyl esterification catalyst prepared in Example 2 were added into a high temperature and high pressure reactor, and reacted for 2 h at a reaction temperature of 240° C. and a reaction pressure of 3 MPa.

[0058] Application Example 3: 160 g of crude terephthalic acid, 370 g of methanol and 5 g of the crude terephthalic acid methyl esterification catalyst prepared in Example 3 were added into a high-temperature and high-pressure reactor, and the reaction was carried out for 3 hours at a reaction temperature of 240° C. and a reaction pressure of 3 MPa.

[0059] Application example 4: 160 g of crude terephthalic acid, 360 g of methanol and 5 g of the crude terephthalic acid methyl esterification catalyst prepared in Example 4 were added into a high-temperature and high-pressure reactor, and reacted for 2 h at a reaction temperature of 220° C. and a reaction pressure of 3 MPa.

[0060] Application Example 5: 160 g of crude terephthalic acid, 360 g of methanol and 5 g of the crude terephthalic acid methyl esterification catalyst prepared in Example 5 were added to a high-temperature and high-pressure reactor, and the reaction was carried out for 2 hours at a reaction temperature of 210° C. and a reaction pressure of 2.5 MPa.

[0061] Comparative application examples 1 to 8: 160 g of crude terephthalic acid and 350 g of methanol were added into a high-temperature and high-pressure reactor together with 5 g of the crude terephthalic acid methyl esterification catalyst prepared in Comparative Examples 1 to 8, and reacted for 2 h at a reaction temperature of 240° C. and a reaction pressure of 3 MPa.

[0062] The reaction products obtained in the above application examples and comparative application examples were analyzed, and the terephthalic acid conversion rate and dimethyl terephthalate selectivity were calculated. The results are shown in Table 1.

[0063] Table 1: Reaction results.

[0064] It can be seen from the above test results that the catalysts of the present invention used in Application Examples 1 to 5 show excellent catalytic performance in the reaction of methyl esterification of crude terephthalic acid to dimethyl terephthalate, and the crude terephthalic acid conversion rate and dimethyl terephthalate selectivity both reach more than 98%.

[0065] In the catalyst of comparative application example 1, the H-ZSM-5 molecular sieve is not modified with organic acid. Due to the decrease in the protonic acid concentration and pore volume in the catalyst, the terephthalic acid conversion rate and dimethyl terephthalate selectivity are significantly reduced compared with the examples. In the catalyst of comparative application example 2, the modified H-ZSM-5 molecular sieve is directly blended with titanium dioxide as a composite carrier, and the two are not hydrothermally composited. The H-ZSM-5 molecular sieve and titanium dioxide are mixed unevenly, and the terephthalic acid conversion rate and dimethyl terephthalate selectivity are also reduced. In the catalyst of comparative application example 3, only titanium dioxide is used as a carrier, and titanium dioxide is not composited with H-ZSM-5 molecular sieve. The protonic acid concentration in the catalyst is too low, resulting in a significant decrease in the terephthalic acid conversion rate and dimethyl terephthalate selectivity. In the catalyst of comparative application example 4, only modified H-ZSM-5 molecular sieve is used as a carrier, and titanium dioxide is not composited. The Lewis acid concentration in the catalyst is too low, which will also lead to a decrease in the conversion rate of terephthalic acid and the selectivity of dimethyl terephthalate. In comparative application example 5, polyferric sulfate is not loaded on the composite carrier. Because the activation energy of the esterification reaction cannot be effectively reduced, and the adsorption rate of the reactant molecules is reduced, the conversion rate of terephthalic acid and the selectivity of dimethyl terephthalate are greatly reduced. In the catalyst of comparative application example 6, the amount of H-ZSM-5 molecular sieve is too much, which exceeds the scope of the present invention, and the proton acid concentration is too high, resulting in a decrease in the selectivity of dimethyl terephthalate. In the catalyst of comparative application example 7, the amount of titanium dioxide added is too much, and when the Lewis acid concentration is too high, the selectivity of dimethyl terephthalate is also reduced. In the catalyst of Comparative Application Example 8, the amount of polyferric sulfate used is too much. Since the excessive polyferric sulfate is hydrolyzed to generate a large amount of iron complexes with more hydroxyl groups, the selectivity of dimethyl terephthalate is also reduced.

[0066] The above content is a further detailed description of the technical solution of the present invention in combination with a specific preferred implementation method, and should not be understood as a limitation on the applicable scope of the present invention. For ordinary technicians in the field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the present invention, which should be deemed to fall within the scope of patent protection determined by the claims submitted for the present invention.

Claims

1. A catalyst for the methylation reaction of crude terephthalic acid, characterized in that: It includes a composite carrier and polyferric sulfate loaded on the composite carrier; the composite carrier is formed by a modified H-ZSM-5 molecular sieve and titanium dioxide through a hydrothermal reaction; the modified H-ZSM-5 molecular sieve is formed by calcining the H-ZSM-5 molecular sieve after being treated with an organic acid solution; In the composite carrier, the mass ratio of the modified H-ZSM-5 molecular sieve and titanium dioxide is 1:1-5:1; the mass ratio of the composite carrier and polyferric sulfate is 95:5-99:

1.

2. The crude terephthalic acid methyl esterification catalyst according to claim 1, characterized in that: The silicon-aluminum ratio in H-ZSM-5 molecular sieve is 30~120.

3. The crude terephthalic acid methyl esterification catalyst according to claim 1, characterized in that: The organic acid solution is one or a combination of two or more of citric acid solution, oxalic acid solution, tartaric acid solution, acetic acid solution, malic acid solution, and succinic acid solution; the concentration of the organic acid solution is 0.001-0.5 mol / L, and the mass ratio of the H-ZSM-5 molecular sieve to the organic acid solution is 1:5-1:

100.

4. The crude terephthalic acid methyl esterification catalyst according to claim 1 or 3, characterized in that: The calcination temperature after organic acid treatment is 400~600℃, and the calcination time is 2~8h.

5. A method for preparing a crude terephthalic acid methyl esterification catalyst as claimed in any one of claims 1 to 4, characterized in that: The steps include: (1) mixing H-ZSM-5 molecular sieve with an organic acid solution, stirring the reaction, filtering, washing, drying, and then calcining the product to obtain a modified H-ZSM-5 molecular sieve; (2) Mixing the modified H-ZSM-5 molecular sieve and titanium dioxide to obtain a mixed powder; mixing the mixed powder with deionized water, stirring evenly, and then performing a hydrothermal reaction; filtering and drying the product to obtain a composite carrier; (3) dissolving polyferric sulfate in an organic solvent to form an impregnation solution; impregnating the composite carrier in the impregnation solution and then drying the impregnation solution to obtain the crude terephthalic acid methyl esterification reaction catalyst.

6. The method for preparing a crude terephthalic acid methyl esterification catalyst according to claim 5, characterized in that: In step (1), the temperature during the stirring reaction is 25-90° C., and the stirring time is 10-120 min; the drying temperature is 80-120° C., and the drying time is 2-15 h.

7. The method for preparing a crude terephthalic acid methyl esterification catalyst according to claim 5, characterized in that: In step (2), the mass ratio of the mixed powder to deionized water is 1:2-1:50; the hydrothermal reaction temperature is 50-90° C., and the hydrothermal reaction time is 2-10 h; the drying temperature of the product is 80-120° C., and the drying time is 2-15 h.

8. The method for preparing a crude terephthalic acid methyl esterification catalyst according to claim 5, characterized in that: The concentration of the impregnation solution in step (3) is 0.05-0.5 mol / L; the composite carrier is immersed in the impregnation solution for 5-24 hours; the drying temperature is 80-150° C., and the drying time is 2-15 hours.

9. Use of the crude terephthalic acid methyl esterification catalyst as claimed in any one of claims 1 to 5 in the esterification of crude terephthalic acid with methanol to produce dimethyl terephthalate, characterized in that: The mass fraction of terephthalic acid in the crude terephthalic acid is above 90%.

10. Use of the crude terephthalic acid methyl esterification catalyst according to claim 9 in the esterification reaction of crude terephthalic acid and methanol to produce dimethyl terephthalate, characterized in that: During the reaction, the feed mass ratio of methanol to crude terephthalic acid is 2:1-6:1; the mass of the crude terephthalic acid methyl esterification reaction catalyst is 2-6% of the mass of the crude terephthalic acid.

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