Method and catalyst for hydrogenating and refining crude terephthalic acid while producing 1,4-cyclohexanedicarboxylic acid as a by-product

Abstract

The present invention provides a method and catalyst for hydrorefining crude terephthalic acid while producing 1,4-cyclohexanedicarboxylic acid as a by-product. The method comprises: (1) mixing crude terephthalic acid, a catalyst, and a solvent; (2) performing a hydrorefining reaction at a temperature of 250-285° C. and a pressure of 6-10 MPa to obtain purified terephthalic acid and 1,4-cyclohexanedicarboxylic acid; wherein the catalyst comprises a carrier and Pd and Rh supported on the carrier. The present invention achieves the by-production of 1,4-cyclohexanedicarboxylic acid (CHDA) during the preparation of purified terephthalic acid (PTA) by hydrorefining crude terephthalic acid (CTA). In particular, a specific catalyst is selected to match suitable reaction conditions, thereby not only eliminating the need for a new CHDA production plant but also maximizing the economic benefits of the plant.

Description

Technical Field

[0001] The present invention relates to a crude terephthalic acid hydrogenation refining technology, in particular to a method for hydrogenating and refining crude terephthalic acid while producing 1,4-cyclohexanedicarboxylic acid as a by-product and a catalyst thereof. Background Art

[0002] Purified terephthalic acid (PTA) is an important organic chemical raw material. It is typically produced by liquid-phase oxidation of paraxylene (PX) to produce crude terephthalic acid (CTA), which is then refined by hydrogenation. CTA typically contains a high content of para-carboxybenzaldehyde (4-CBA). The refining process primarily aims to remove 4-CBA, with the general industrial requirement for PTA to contain less than 25 ppm.

[0003] 1,4-Cyclohexanedicarboxylic acid (CHDA) is an aliphatic dibasic acid. Its main use is as a modifying monomer for the production of resins for powder coatings, high-solids melamine (tripolycyanamide) polyester baking enamels, resins for coil coatings, water-based polyester resins, unsaturated polyester resins for gel coats, unsaturated polyester resins for gel layers, and polyester polyols for polyurethane coatings.

[0004] In addition to being a modifying monomer, CHDA can also be used as an intermediate in the production of 1,4-cyclohexanedimethanol (CHDM), an industrially important raw material for polyester production, primarily used in polyester fiber production. Compared to polyester synthesized from ethylene glycol, polyester fibers produced from CHDM not only have lower density and a higher melting point, but also exhibit superior hydrolytic stability and electrical properties, making them particularly suitable for use in the manufacture of electrical equipment. Currently, the leading global company to achieve industrialized CHDA production is Eastman Chemical Company in the United States. Amoco in the United States and Towa Chemical Industries, Ltd. in Japan are also conducting research and development of CHDA-related technologies.

[0005] The most promising method for preparing CHDA using terephthalic acid as a raw material is currently US Pat. No. 2,888,484, published in 1959, proposed hydrogenating terephthalic acid to CHDA using a palladium-based catalyst. In an example, using 5 wt% Pd / C as the catalyst, at a reaction temperature of 195°C and a pressure greater than 34 MPa, the conversion of terephthalic acid reached 100% after 2 hours, and the yield of 1,4-cyclohexanedicarboxylic acid reached 98.5%. While this method achieved excellent results, the high reaction pressure made it difficult to implement. US Pat. No. 5,430,184 discloses a process for preparing 1,4-cyclohexanedicarboxylic acid, but using ethanol and water as solvents and increasing the feed concentration of the terephthalic acid solution. Similarly, a palladium-based catalyst with a palladium loading of 5% to 10% was used, and the carrier was an acid-resistant material such as aluminum, silicon, or carbon. Under hydrogenation conditions of 120-160°C, 0.19-0.95 MPa, and a reaction time of 30-120 minutes, after filtration of the catalyst, the CHDA product purity reached 98%, with the main byproducts being 4-methylcyclohexanecarboxylic acid and cyclohexanecarboxylic acid. Although the reaction temperature and pressure were lowered, the introduction of ethanol into the system resulted in a high concentration of byproducts, making their separation difficult.

[0006] US6291706 discloses a method for preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid. In the examples provided, a 0.5 wt% Pd / C catalyst is used, the mass fraction of phthalic acid in the aqueous solution is 5%, the temperature is within the range of 200-230°C, and the hydrogen pressure is 4.48 MPa. The purity of the hydrogenation reaction product, CHDA, reaches a maximum of 98%, but the conversion rate of terephthalic acid (TA) is only 66.5%.

[0007] Since the industrial demand for CHDA is relatively low, producing CHDA using a separate plant is not economical for industrial production. Reducing CHDA as a byproduct during the CTA purification process to produce PTA would be a more cost-effective method. However, there are significant inconsistencies between the CTA purification process to produce PTA and the CTA production process to produce CHDA. The reaction temperature for CTA hydrorefining is above 280°C. Hydrogenating TA to CHDA at this temperature results in severe decarboxylation and the production of large amounts of cyclohexanecarboxylic acid, which reduces CHDA yield. However, operating at 250°C significantly reduces the efficiency of the CTA hydrorefining process due to the low solubility of TA, resulting in inefficient utilization of the plant's production capacity. Summary of the Invention

[0008] The present invention aims to provide a method and catalyst for producing 1,4-cyclohexanedicarboxylic acid (CHDA) as a by-product during the hydrorefining of crude terephthalic acid (CTA) to produce purified terephthalic acid (PTA). This method can achieve the by-product CHDA during the CTA refining process to produce PTA.

[0009] The first aspect of the present invention is to provide a method for hydrogenating and refining crude terephthalic acid while producing 1,4-cyclohexanedicarboxylic acid as a by-product, comprising the following steps:

[0010] (1) mixing crude terephthalic acid, a catalyst and a solvent;

[0011] (2) performing a hydrogenation refining reaction at a temperature of 250-285° C. and a pressure of 6-10 MPa to obtain purified terephthalic acid and 1,4-cyclohexanedicarboxylic acid;

[0012] The catalyst comprises a carrier and Pd and Rh supported on the carrier.

[0013] Furthermore, based on the catalyst, the loading amount of Pd in ​​the catalyst is 0.5wt%-1wt%, and the loading amount of Rh is 0.1wt%-0.5wt%.

[0014] Furthermore, the carrier is activated carbon, preferably coconut shell activated carbon, more preferably the coconut shell activated carbon has a specific surface area of ​​800-1200m 2 / g, the sum of the contents of Na, K and Ca in activated carbon is not higher than 300ppm.

[0015] Furthermore, in step (1), the mass ratio of crude terephthalic acid to solvent is 1:99-30:70, and the mass ratio of crude terephthalic acid to catalyst is 100:(1-10).

[0016] Furthermore, the solvent in step (1) is preferably water.

[0017] Furthermore, the crude terephthalic acid in step (1) contains 0.1 wt% to 0.35 wt% of 4-formyl-benzoic acid.

[0018] Furthermore, the reaction time in step (2) is controlled within 15-90 min.

[0019] Furthermore, step (2) further includes a separation step, wherein the separation step includes filtering the reaction mixture at 80-160° C. to obtain purified terephthalic acid, and cooling the obtained filtrate to 5-20° C. and then filtering to obtain 1,4-cyclohexanedicarboxylic acid.

[0020] The second aspect of the present invention is to provide a catalyst for hydrogenating and refining crude terephthalic acid while producing 1,4-cyclohexanedicarboxylic acid as a by-product. The catalyst comprises a carrier and Pd and Rh supported on the carrier.

[0021] Furthermore, based on the catalyst, the loading amount of Pd in ​​the catalyst is 0.5wt%-1wt%, and the loading amount of Rh is 0.1wt%-0.5wt%.

[0022] Furthermore, the carrier is activated carbon, preferably coconut shell activated carbon, more preferably the coconut shell activated carbon has a specific surface area of ​​800-1200m 2 / g, the sum of the contents of Na, K and Ca in activated carbon is not higher than 300ppm.

[0023] The present invention achieves the by-production of 1,4-cyclohexanedicarboxylic acid (CHDA) during the hydrorefining of crude terephthalic acid (CTA) to produce purified terephthalic acid (PTA). The by-product CHDA herein refers to a CHDA content of at least 5 wt% in the product. In particular, by selecting a specific catalyst and matching appropriate reaction conditions, this not only eliminates the need for new CHDA production equipment but also maximizes the economic benefits of the equipment. DETAILED DESCRIPTION

[0024] The present invention is exemplarily described below in conjunction with specific embodiments, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0025] The analysis of the metal content in the present invention is carried out by ICP-AES.

[0026] The analysis of the reaction products was mainly carried out by liquid chromatography using the external standard method.

[0027] [Example 1]

[0028] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1108m 2 / g, Na content 138ppm, K content 53ppm, Ca content 73ppm) as a carrier, 50g of a mixed solution of chloropalladic acid and chlororhodic acid, containing 0.375g of palladium and 0.075g of rhodium, as an impregnation solution, 100g of activated carbon was impregnated therein and stirred continuously. After the mixed solution of chloropalladic acid and chlororhodic acid was completely absorbed by the activated carbon, it was aged at a temperature of 80°C for 4h. After the aging was completed, a reducing agent, hydrazine hydrate, was added for reduction. After the reduction was completed, the catalyst was washed with deionized water until no chloride ions were detected. Finally, the catalyst was dried at 80°C for 2h. ICP-AES analysis showed that the Pd content of the catalyst was 0.75wt% and the Rh content was 0.15wt%.

[0029] The hydrogenation of crude terephthalic acid was performed by placing 10g of the above-mentioned catalyst in a hanging basket in a reactor. 300g of crude terephthalic acid (containing 0.9g of 4-CBA) and 700g of water were added to the reactor. The mixture was then stirred and heated to 280°C. The reactor pressure was controlled at 8MPa. After temperature and pressure reached the required values, the catalyst hanging basket was placed in the reaction solution and hydrogen was introduced simultaneously to react. The reaction time was 25min. After the reaction was completed, the reactor temperature was cooled to room temperature. The reaction product was taken out and sampled after adopting ammoniacal liquor to fully dissolve the product for liquid chromatographic analysis of 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For comparison purposes, the analytical results are listed in Table 1.

[0030] [Example 2]

[0031] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1108m 2 / g, Na content 138ppm, K content 53ppm, Ca content 73ppm) as a carrier, 50g of a mixed solution of chloropalladic acid and chlororhodic acid, containing 0.25g of palladium and 0.175g of rhodium, as an impregnation solution, 100g of activated carbon was impregnated therein and continuously stirred, after the mixed solution of chloropalladic acid and chlororhodic acid was completely absorbed by the activated carbon, it was aged at a temperature of 80°C for 4h, and after the aging was completed, a reducing agent, hydrazine hydrate, was added for reduction, and after the reduction was completed, the catalyst was washed with deionized water until no chloride ions were detected, and finally the catalyst was dried at 80°C for 2h. ICP-AES analysis showed that the Pd content of the catalyst was 0.5wt% and the Rh content was 0.35wt%.

[0032] The hydrogenation of crude terephthalic acid was performed by placing 10g of the above-mentioned catalyst in a hanging basket in a reactor. 300g of crude terephthalic acid (containing 0.9g of 4-CBA) and 700g of water were added to the reactor. The mixture was then stirred and heated to 280°C. The reactor pressure was controlled at 8MPa. After temperature and pressure reached the required values, the catalyst hanging basket was placed in the reaction solution and hydrogen was introduced simultaneously to react. The reaction time was 25min. After the reaction was completed, the reactor temperature was cooled to room temperature. The reaction product was taken out and sampled after adopting ammoniacal liquor to fully dissolve the product for liquid chromatographic analysis of 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For comparison purposes, the analytical results are listed in Table 1.

[0033] [Example 3]

[0034] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1108m 2 / g, Na content 138ppm, K content 53ppm, Ca content 73ppm) as a carrier, 50g of a mixed solution of chloropalladic acid and chlororhodic acid, containing 0.5g of palladium and 0.05g of rhodium, as an impregnation solution, 100g of activated carbon was impregnated therein and continuously stirred, after the mixed solution of chloropalladic acid and chlororhodic acid was completely absorbed by the activated carbon, it was aged at a temperature of 80°C for 4h, and after the aging was completed, a reducing agent, hydrazine hydrate, was added for reduction, and after the reduction was completed, the catalyst was washed with deionized water until no chloride ions were detected, and finally the catalyst was dried at 80°C for 2h. ICP-AES analysis showed that the Pd content of the catalyst was 1.0wt% and the Rh content was 0.1wt%.

[0035] The hydrogenation of crude terephthalic acid was performed by placing 10g of the above-mentioned catalyst in a hanging basket in a reactor. 300g of crude terephthalic acid (containing 0.9g of 4-CBA) and 700g of water were added to the reactor. The mixture was then stirred and heated to 280°C. The reactor pressure was controlled at 8MPa. After temperature and pressure reached the required values, the catalyst hanging basket was placed in the reaction solution and hydrogen was introduced simultaneously to react. The reaction time was 25min. After the reaction was completed, the reactor temperature was cooled to room temperature. The reaction product was taken out and sampled after adopting ammoniacal liquor to fully dissolve the product for liquid chromatographic analysis of 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For comparison purposes, the analytical results are listed in Table 1.

[0036] [Example 4]

[0037] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1108m 2 / g, Na content 138ppm, K content 53ppm, Ca content 73ppm) as a carrier, 50g of a mixed solution of chloropalladic acid and chlororhodic acid, containing 0.35g of palladium and 0.25g of rhodium, as an impregnation solution, 100g of activated carbon was impregnated therein and continuously stirred, after the mixed solution of chloropalladic acid and chlororhodic acid was completely absorbed by the activated carbon, it was aged at a temperature of 80°C for 4h, and after the aging was completed, a reducing agent, hydrazine hydrate, was added for reduction, and after the reduction was completed, the catalyst was washed with deionized water until no chloride ions were detected, and finally the catalyst was dried at 80°C for 2h. ICP-AES analysis showed that the Pd content of the catalyst was 0.7wt% and the Rh content was 0.5wt%.

[0038] The hydrogenation of crude terephthalic acid was performed by placing 10g of the above-mentioned catalyst in a hanging basket in a reactor. 300g of crude terephthalic acid (containing 0.9g of 4-CBA) and 700g of water were added to the reactor. The mixture was then stirred and heated to 280°C. The reactor pressure was controlled at 8MPa. After temperature and pressure reached the required values, the catalyst hanging basket was placed in the reaction solution and hydrogen was introduced simultaneously to react. The reaction time was 25min. After the reaction was completed, the reactor temperature was cooled to room temperature. The reaction product was taken out and sampled after adopting ammoniacal liquor to fully dissolve the product for liquid chromatographic analysis of 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For comparison purposes, the analytical results are listed in Table 1.

[0039] [Example 5]

[0040] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1108m 2 / g, Na content 138ppm, K content 53ppm, Ca content 73ppm) as a carrier, 50g of a mixed solution of chloropalladic acid and chlororhodic acid, containing 0.375g of palladium and 0.075g of rhodium, as an impregnation solution, 100g of activated carbon was impregnated therein and stirred continuously. After the mixed solution of chloropalladic acid and chlororhodic acid was completely absorbed by the activated carbon, it was aged at a temperature of 80°C for 4h. After the aging was completed, a reducing agent, hydrazine hydrate, was added for reduction. After the reduction was completed, the catalyst was washed with deionized water until no chloride ions were detected. Finally, the catalyst was dried at 80°C for 2h. ICP-AES analysis showed that the Pd content of the catalyst was 0.75wt% and the Rh content was 0.15wt%.

[0041] The hydrogenation of crude terephthalic acid was performed by placing 10g of the above-mentioned catalyst in a hanging basket in a reactor. 125g of crude terephthalic acid (the amount containing 4-CBA was 0.375g) and 2375g of water were added to the reactor. The mixture was then opened and stirred and warmed to 265°C. The reactor pressure was controlled at 10MPa. After temperature and pressure reached the requirements, the catalyst hanging basket was placed in the reaction solution and hydrogen was introduced simultaneously to react. The reaction time was 60min. After the reaction finished, the reactor temperature was cooled to room temperature. The reaction product was taken out and sampled after adopting ammoniacal liquor to fully dissolve the reaction product for liquid chromatographic analysis of 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For convenience of comparison, the analytical results are listed in Table 1.

[0042] [Example 6]

[0043] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1108m 2 / g, Na content 138ppm, K content 53ppm, Ca content 73ppm) as a carrier, 50g of a mixed solution of chloropalladic acid and chlororhodic acid, containing 0.375g of palladium and 0.075g of rhodium, as an impregnation solution, 100g of activated carbon was impregnated therein and stirred continuously. After the mixed solution of chloropalladic acid and chlororhodic acid was completely absorbed by the activated carbon, it was aged at a temperature of 80°C for 4h. After the aging was completed, a reducing agent, hydrazine hydrate, was added for reduction. After the reduction was completed, the catalyst was washed with deionized water until no chloride ions were detected. Finally, the catalyst was dried at 80°C for 2h. ICP-AES analysis showed that the Pd content of the catalyst was 0.75wt% and the Rh content was 0.15wt%.

[0044] The hydrogenation of crude terephthalic acid was performed by placing 10g of the above-mentioned catalyst in a hanging basket in a reactor. 100g of crude terephthalic acid (containing 0.3g of 4-CBA) and 900g of water were added to the reactor. The mixture was then stirred and heated to 280°C. The reactor pressure was controlled at 8MPa. After the temperature and pressure reached the required levels, the catalyst hanging basket was placed in the reaction solution and hydrogen was introduced to react for 25min. After the reaction was completed, the reactor temperature was cooled to room temperature. The reaction product was taken out and sampled after full dissolution with ammoniacal liquor to determine the 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For comparison purposes, the analytical results are listed in Table 1.

[0045] [Example 7]

[0046] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1108m 2 / g, Na content 138ppm, K content 53ppm, Ca content 73ppm) as a carrier, 50g of a mixed solution of chloropalladic acid and chlororhodic acid, containing 0.375g of palladium and 0.075g of rhodium, as an impregnation solution, 100g of activated carbon was impregnated therein and stirred continuously. After the mixed solution of chloropalladic acid and chlororhodic acid was completely absorbed by the activated carbon, it was aged at a temperature of 80°C for 4h. After the aging was completed, a reducing agent, hydrazine hydrate, was added for reduction. After the reduction was completed, the catalyst was washed with deionized water until no chloride ions were detected. Finally, the catalyst was dried at 80°C for 2h. ICP-AES analysis showed that the Pd content of the catalyst was 0.75wt% and the Rh content was 0.15wt%.

[0047] The hydrogenation of crude terephthalic acid was performed by placing 10g of the above-mentioned catalyst in a hanging basket in a reactor. 200g of crude terephthalic acid (containing 0.6g of 4-CBA) and 800g of water were added to the reactor. The mixture was then stirred and heated to 280°C. The reactor pressure was controlled at 8MPa. After temperature and pressure reached the required values, the catalyst hanging basket was placed in the reaction solution and hydrogen was introduced simultaneously to react. The reaction time was 25min. After the reaction was completed, the reactor temperature was cooled to room temperature. The reaction product was taken out and sampled after full dissolution with ammoniacal liquor to analyze the 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content by liquid chromatography. For comparison purposes, the analytical results are listed in Table 1.

[0048] [Example 8]

[0049] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1108m 2 / g, Na content 138ppm, K content 53ppm, Ca content 73ppm) as a carrier, 50g of a mixed solution of chloropalladic acid and chlororhodic acid, containing 0.375g of palladium and 0.075g of rhodium, as an impregnation solution, 100g of activated carbon was impregnated therein and stirred continuously. After the mixed solution of chloropalladic acid and chlororhodic acid was completely absorbed by the activated carbon, it was aged at a temperature of 80°C for 4h. After the aging was completed, a reducing agent, hydrazine hydrate, was added for reduction. After the reduction was completed, the catalyst was washed with deionized water until no chloride ions were detected. Finally, the catalyst was dried at 80°C for 2h. ICP-AES analysis showed that the Pd content of the catalyst was 0.75wt% and the Rh content was 0.15wt%.

[0050] The hydrogenation of crude terephthalic acid was performed by placing 10g of the above-mentioned catalyst in a hanging basket in a reactor. 300g of crude terephthalic acid (containing 0.9g of 4-CBA) and 700g of water were added to the reactor. The mixture was then stirred and heated to 250°C. The reactor pressure was controlled at 6MPa. After the temperature and pressure reached the requirements, the catalyst hanging basket was placed in the reaction solution and hydrogen was introduced to react for 90min. After the reaction was completed, the reactor temperature was cooled to room temperature. The reaction product was taken out and sampled after fully dissolving with ammoniacal liquor to analyze the 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content in liquid chromatography. For comparison purposes, the analytical results are listed in Table 1.

[0051] [Example 9]

[0052] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1135m 2 / g, Na content 207ppm, K content 132ppm, Ca content 18ppm) as a carrier, 50g of a mixed solution of chloropalladic acid and chlororhodic acid, containing 0.375g of palladium and 0.075g of rhodium, as an impregnation solution, 100g of activated carbon was impregnated therein and continuously stirred, after the mixed solution of chloropalladic acid and chlororhodic acid was completely absorbed by the activated carbon, it was aged at a temperature of 80°C for 4h, and after the aging was completed, a reducing agent, hydrazine hydrate, was added for reduction, and after the reduction was completed, the catalyst was washed with deionized water until no chloride ions were detected, and finally the catalyst was dried at 80°C for 2h. ICP-AES analysis showed that the Pd content of the catalyst was 0.75wt% and the Rh content was 0.15wt%.

[0053] The hydrogenation of crude terephthalic acid was performed by placing 10g of the above-mentioned catalyst in a hanging basket in a reactor. 300g of crude terephthalic acid (containing 0.9g of 4-CBA) and 700g of water were added to the reactor. The mixture was then stirred and heated to 280°C. The reactor pressure was controlled at 8MPa. After temperature and pressure reached the required values, the catalyst hanging basket was placed in the reaction solution and hydrogen was introduced simultaneously to react. The reaction time was 25min. After the reaction was completed, the reactor temperature was cooled to room temperature. The reaction product was taken out and sampled after adopting ammoniacal liquor to fully dissolve the product for liquid chromatographic analysis of 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For comparison purposes, the analytical results are listed in Table 1.

[0054] [Comparative Example 1]

[0055] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1108m 2 / g, Na content 138ppm, K content 53ppm, Ca content 73ppm) as a carrier, 50g of chloropalladic acid solution, containing 0.45g of palladium as an impregnation liquid, 100g of activated carbon is impregnated therein and continuously stirred. After the chloropalladic acid solution is completely absorbed by the activated carbon, it is aged at a temperature of 80°C for 4h. After the aging is completed, a reducing agent hydrazine hydrate is added for reduction. After the reduction is completed, the catalyst is washed with deionized water until no chloride ions are detected. Finally, the catalyst is dried at 80°C for 2h. The Pd content of the catalyst is analyzed by ICP-AES and is 0.9wt%.

[0056] The hydrogenation of crude terephthalic acid was performed by placing 10g of the above-mentioned catalyst in a hanging basket in a reactor. 300g of crude terephthalic acid (the amount containing 4-CBA was 0.9g) and 700g of water were added to the reactor. The mixture was then stirred and warmed to 280°C. The reactor pressure was controlled at 8MPa. After temperature and pressure reached the requirements, the catalyst hanging basket was placed in the reaction solution and hydrogen was introduced simultaneously to react. The reaction time was 25min. After the reaction finished, the reactor temperature was cooled to room temperature. The reaction product was taken out and sampled after adopting ammoniacal liquor to fully dissolve to perform liquid chromatographic analysis of 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For convenience of comparison, the analytical results are listed in Table 1.

[0057] [Comparative Example 2]

[0058] Preparation of catalyst: 100g coconut shell activated carbon (supplied by Nanjing Mulinsen Activated Carbon Co., Ltd., with a specific surface area of ​​1108m 2 / g, Na content 138ppm, K content 53ppm, Ca content 73ppm) as a carrier, 50g of a mixed solution of chloropalladic acid and chlororuthenic acid, containing 0.375g of palladium and 0.075g of ruthenium, as an impregnation solution, 100g of activated carbon was impregnated therein and stirred continuously. After the mixed solution of chloropalladic acid and chlororuthenic acid was completely absorbed by the activated carbon, it was aged at 80°C for 4h. After the aging was completed, the reducing agent hydrazine hydrate was added for reduction. After the reduction was completed, the catalyst was washed with deionized water until no chloride ions were detected. Finally, the catalyst was dried at 80°C for 2h. ICP-AES analysis showed that the Pd content of the catalyst was 0.75wt% and the Ru content was 0.15wt%.

[0059] The hydrogenation of crude terephthalic acid: 10g of the above-mentioned catalyst is placed in the hanging basket in the reactor. 300g of crude terephthalic acid (the amount containing 4-CBA is 0.9g) and 700g of water are added to the reactor. Then, stirring is opened and the mixture is warming up to 280°C. The reactor pressure is controlled at 8MPa. After temperature and pressure all reach the requirements, the catalyst hanging basket is put into the reaction solution. The hydrogen is fed simultaneously and reacted. The reaction time is 25min. After the reaction finishes, the reactor temperature is cooled to room temperature. The reaction product is taken out and the fully dissolved back ammoniacal liquor is sampled to carry out liquid chromatographic analysis of 4-CBA content, CHDA content, and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For convenience, the analytical results are listed in Table 1.

[0060] Table 1

[0061]

[0062] The above describes in detail the specific embodiments of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as the contents disclosed by the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for hydrogenating and refining crude terephthalic acid while producing 1,4-cyclohexanedicarboxylic acid as a by-product, characterized in that: The steps include: (1) Mixing crude terephthalic acid, a catalyst and a solvent; (2) performing a hydrogenation refining reaction at a temperature of 250-285°C and a pressure of 6-10 MPa to obtain purified terephthalic acid and 1,4-cyclohexanedicarboxylic acid; The catalyst comprises a carrier and Pd and Rh supported on the carrier; Based on the catalyst, the Pd loading amount in the catalyst is 0.5wt%-1wt%, and the Rh loading amount is 0.1wt%-0.5wt%; The carrier is coconut shell activated carbon, and the specific surface area of ​​the coconut shell activated carbon is 800-1200m 2 / g, the sum of the contents of Na, K and Ca in activated carbon is not higher than 300ppm.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of crude terephthalic acid to solvent is 1:99-30:70, and the mass ratio of crude terephthalic acid to catalyst is 100:(1-10).

3. The method according to claim 1, characterized in that The crude terephthalic acid in step (1) contains 0.1 wt% to 0.35 wt% of 4-formyl-benzoic acid.

4. The method according to claim 1, wherein The reaction time in step (2) is controlled within 15-90 min.

5. The method according to claim 1, wherein After step (2), a separation step is also included, wherein the separation step includes filtering the reaction mixture at 80-160° C. to obtain purified terephthalic acid, and cooling the obtained filtrate to 5-20° C. and then filtering to obtain 1,4-cyclohexanedicarboxylic acid.

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