CN115947653A - Method and catalyst for simultaneously producing 1, 4-cyclohexanedicarboxylic acid as byproduct in hydrofining of crude terephthalic acid - Google Patents

Abstract

The invention provides a method and a catalyst for simultaneously producing 1, 4-cyclohexanedicarboxylic acid as a byproduct in the hydrofining of crude terephthalic acid. The method comprises the following steps: mixing crude terephthalic acid, a catalyst and a solvent; (2) Carrying out hydrofining reaction at the temperature of 250-285 ℃ and the pressure of 6-10MPa 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 invention realizes the byproduct 1, 4-cyclohexanedicarboxylic acid (CHDA) in the process of preparing Purified Terephthalic Acid (PTA) by hydrofining Crude Terephthalic Acid (CTA). In particular, the selection of a specific catalyst to match the appropriate reaction conditions not only eliminates the need for a new CHDA production facility, but also maximizes the economic efficiency of the facility.

Description

Method and catalyst for hydrotreating crude terephthalic acid while by-producing 1,4-cyclohexanedicarboxylic acid

technical field

The invention relates to a crude terephthalic acid hydrogenation refining technology, in particular to a method for the crude terephthalic acid hydrogenation refining while by-producing 1,4-cyclohexanedicarboxylic acid and a catalyst thereof.

Background technique

Purified terephthalic acid (PTA) is an important organic chemical raw material. Usually, crude terephthalic acid (CTA) is obtained by liquid-phase oxidation of p-xylene (PX), and then obtained by hydrogenation of CTA. Generally, CTA contains higher content of p-carboxybenzaldehyde (4-CBA). The refining process is mainly to remove 4-CBA. The general industry requires that the content of 4-CBA in PTA be lower than 25ppm.

1,4-cyclohexanedicarboxylic acid (CHDA) is an aliphatic dibasic acid, its main use is as a modified monomer for the production of resins for powder coatings, high solid content melamine (melamine) polyester baking Enamel paints, resins for coil coatings, water-based polyester resins, unsaturated polyester resins for gel coat coatings, unsaturated polyester resins for gel coats, and polyester polyols for polyurethane coatings.

In addition to being a modified monomer, CHDA can also be an intermediate in the production of 1,4-cyclohexanedimethanol (CHDM), and CHDM is an industrially important raw material for polyester production, mainly used in the production of polyester fibers. Compared with the polyester synthesized by ethylene glycol, the polyester fiber produced by CHDM not only has the characteristics of low density and high melting point, but also has better hydrolysis stability and electrical properties, and is especially suitable for making electrical equipment. At present, the world's enterprises that realize the industrialized production of CHDA are mainly represented by Eastman Chemical Company of the United States. In addition, Amoco Company of the United States and Towa Chemical Industry Co., Ltd. of Japan also have research and development of CHDA related technologies.

Using terephthalic acid as a raw material to prepare CHDA is currently the most promising method. As early as 1959, U.S. Patent No. 2,888,484 proposed the use of palladium catalysts to hydrogenate terephthalic acid to prepare CHDA. In its examples, 5 wt %Pd/C as the catalyst, at a reaction temperature of 195°C and a reaction pressure greater than 34MPa, the conversion rate of terephthalic acid reached 100% after 2 hours of reaction, and the yield of 1,4-cyclohexanedicarboxylic acid also reached 98.5 %, achieved good results, but its reaction pressure is too high, and it is difficult to implement. US5430184 discloses the preparation process of 1,4-cyclohexanedicarboxylic acid, but ethanol and water are used as solvents to increase the feed concentration of terephthalic acid solution, and palladium series catalysts are also used, and the palladium loading capacity is 5% to 10% %, the carrier is selected from acid-resistant substances such as aluminum, silicon or carbon. Under the condition of hydrogenation reaction temperature of 120-160℃, pressure of 0.19-0.95MPa, reaction time of 30-120min, the purity of CHDA product can reach 98% after filtering off the catalyst, and the by-products are mainly 4-methylcyclohexanecarboxylic acid and cyclohexane Alkanoic acid. Although the reaction temperature and reaction pressure are reduced, due to the introduction of ethanol in the system, there are many by-products and separation is difficult.

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

Since the industrial demand for CHDA is not too high, it is not economical to prepare CHDA with a separate device in industrial production. It will be a more economical and effective means if CHDA can be produced by-product in the process of refining CTA to prepare PTA. However, due to the obvious contradiction between the process of refining CTA to prepare PTA and the process of preparing CHDA from CTA, the reaction temperature of CTA hydrogenation refining is above 280 ° C, and if TA is hydrogenated to generate CHDA at this temperature, serious problems will occur. The decarboxylation reaction will generate a large amount of cyclohexanecarboxylic acid, which affects the CHDA yield. However, if the reaction is performed at 250°C, the efficiency of CTA hydrofining will be greatly reduced due to the low solubility of TA, so that the production capacity of the device will not be effectively utilized.

Contents of the invention

The object of the present invention is to provide a kind of method and catalyst that can by-produce 1,4-cyclohexanedicarboxylic acid (CHDA) in the process of preparing purified terephthalic acid (PTA) by hydrogenation of crude terephthalic acid (CTA) . To realize by-product CHDA in the process of refining CTA to prepare PTA.

The first aspect of the present invention is to provide a method for crude terephthalic acid hydrogenation refining while by-producing 1,4-cyclohexanedicarboxylic acid, comprising the following steps:

(1) crude terephthalic acid, catalyst and solvent are mixed;

(2) Under the conditions of a temperature of 250-285°C and a pressure of 6-10MPa, hydrogenation refining reaction is carried out to obtain purified terephthalic acid and 1,4-cyclohexanedicarboxylic acid;

Wherein the catalyst comprises a carrier and Pd and Rh loaded on the carrier.

Further, 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%.

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

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

Further, the solvent described in step (1) is preferably water.

Further, the crude terephthalic acid in step (1) contains 0.1wt%-0.35wt% 4-formyl-benzoic acid.

Further, the reaction time in step (2) is controlled at 15-90min.

Further, after step (2), a separation step is also included, the separation step includes filtering the reaction mixture at 80-160°C to obtain purified terephthalic acid, cooling the obtained filtrate to 5-20°C and then filtering to obtain 1, 4-Cyclohexanedicarboxylic acid.

The second aspect of the present invention is to provide a catalyst for hydrofinishing crude terephthalic acid while by-producing 1,4-cyclohexanedicarboxylic acid. The catalyst includes a carrier and Pd and Rh loaded on the carrier.

Further, 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%.

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

The invention realizes the by-production of 1,4-cyclohexanedicarboxylic acid (CHDA) in the process of preparing purified terephthalic acid (PTA) through hydrogenation refining of crude terephthalic acid (CTA). The by-product CHDA mentioned in the present invention means that the content of CHDA in the product reaches at least 5wt%. In particular, the selection of a specific catalyst to match the appropriate reaction conditions will not only eliminate the need to build a new CHDA production unit, but also maximize the economic benefits of the unit.

Detailed ways

The present invention will be illustrated 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.

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

The analysis of the reaction products is mainly carried out by liquid chromatography with external standard method.

【Example 1】

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1108m ² /g, Na content 138ppm, K content is 53ppm, Ca content 73ppm) as carrier, chloropalladic acid and chlororhodium acid mixed solution 50g, containing 0.375g of palladium and 0.075g of rhodium as the impregnating solution, impregnating 100g of activated carbon in it and stirring continuously, after the mixed solution of chloropalladic acid and chlororhodium acid is completely absorbed by the activated carbon, aging for 4 hours at a temperature of 80°C, aging After completion, add reducing agent hydrazine hydrate for reduction. After reduction, clean the catalyst with deionized water until no chloride ion is detected. Finally, the catalyst can be dried at 80°C for 2 hours. The Pd content of the catalyst is analyzed by ICP-AES to be 0.75wt%. The Rh content is 0.15 wt%.

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 (containing 4-CBA is 0.9g) and 700g of water are added in the reactor, and then Start stirring and raise the temperature to 280°C. The pressure of the reactor is controlled at 8MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time feed hydrogen to react. The reaction time is 25min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and a sample was taken after fully dissolving with ammonia water for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For the convenience of comparison, the analysis results are listed in Table 1.

[Example 2]

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1108m ² /g, Na content 138ppm, K content is 53ppm, Ca content 73ppm) as carrier, chloropalladic acid and chlororhodium acid mixed solution 50g, containing 0.25g of palladium and 0.175g of rhodium as the impregnating solution, impregnating 100g of activated carbon in it and stirring continuously, after the mixed solution of chloropalladic acid and chlororhodium acid is completely absorbed by the activated carbon, aging at 80°C for 4h, aging After completion, add reducing agent hydrazine hydrate for reduction. After reduction, clean the catalyst with deionized water until no chloride ion is detected. Finally, the catalyst can be dried at 80°C for 2 hours. The Pd content of the catalyst is analyzed by ICP-AES to be 0.5wt%. The Rh content is 0.35 wt%.

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 (containing 4-CBA is 0.9g) and 700g of water are added in the reactor, and then Start stirring and raise the temperature to 280°C. The pressure of the reactor is controlled at 8MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time feed hydrogen to react. The reaction time is 25min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and a sample was taken after fully dissolving with ammonia water for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For the convenience of comparison, the analysis results are listed in Table 1.

[Example 3]

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1108m ² /g, Na content 138ppm, K content is 53ppm, Ca content 73ppm) as carrier, chloropalladic acid and chlororhodium acid mixed solution 50g, containing 0.5g of palladium and 0.05g of rhodium as the impregnating solution, impregnating 100g of activated carbon in it and stirring continuously, after the mixed solution of chloropalladic acid and chlororhodium acid is completely absorbed by the activated carbon, aging for 4 hours at a temperature of 80°C, aging After completion, add reducing agent hydrazine hydrate for reduction. After reduction, clean the catalyst with deionized water until no chloride ion is detected. Finally, the catalyst can be dried at 80° C. for 2 hours. The Pd content of the catalyst is analyzed by ICP-AES to be 1.0 wt%. The Rh content is 0.1 wt%.

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 (containing 4-CBA is 0.9g) and 700g of water are added in the reactor, and then Start stirring and raise the temperature to 280°C. The pressure of the reactor is controlled at 8MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time feed hydrogen to react. The reaction time is 25min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and a sample was taken after fully dissolving with ammonia water for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For the convenience of comparison, the analysis results are listed in Table 1.

【Example 4】

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1108m ² /g, Na content 138ppm, K content is 53ppm, Ca content 73ppm) as carrier, chloropalladic acid and chlororhodium acid mixed solution 50g, containing 0.35g of palladium and 0.25g of rhodium as the impregnating solution, impregnating 100g of activated carbon in it and stirring continuously, after the mixed solution of chloropalladic acid and chlororhodium acid is completely absorbed by the activated carbon, it is aged at 80°C for 4h, aged After the completion, the reducing agent hydrazine hydrate was added for reduction. After the reduction, the catalyst was washed with deionized water until no chloride ions were detected. Finally, the catalyst was dried at 80°C for 2 hours. The Pd content of the catalyst was analyzed by ICP-AES to be 0.7wt%. The Rh content is 0.5 wt%.

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 (containing 4-CBA is 0.9g) and 700g of water are added in the reactor, and then Start stirring and raise the temperature to 280°C. The pressure of the reactor is controlled at 8MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time feed hydrogen to react. The reaction time is 25min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and a sample was taken after fully dissolving with ammonia water for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For the convenience of comparison, the analysis results are listed in Table 1.

【Example 5】

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1108m ² /g, Na content 138ppm, K content is 53ppm, Ca content 73ppm) as carrier, chloropalladic acid and chlororhodium acid mixed solution 50g, containing 0.375g of palladium and 0.075g of rhodium as the impregnating solution, impregnating 100g of activated carbon in it and stirring continuously, after the mixed solution of chloropalladic acid and chlororhodium acid is completely absorbed by the activated carbon, aging for 4 hours at a temperature of 80°C, aging After completion, add reducing agent hydrazine hydrate for reduction. After reduction, clean the catalyst with deionized water until no chloride ion is detected. Finally, the catalyst can be dried at 80°C for 2 hours. The Pd content of the catalyst is analyzed by ICP-AES to be 0.75wt%. The Rh content is 0.15 wt%.

The hydrogenation of crude terephthalic acid: 10g of the above-mentioned catalysts are placed in the hanging basket in the reactor, 125g of crude terephthalic acid (the amount containing 4-CBA is 0.375g) and 2375g of water are added in the reactor, and then Start stirring and raise the temperature to 265°C. The pressure of the reactor is controlled at 10MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time pass in hydrogen to react. The reaction time is 60min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and a sample was taken after fully dissolving with ammonia water for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For the convenience of comparison, the analysis results are listed in Table 1.

[Example 6]

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1108m ² /g, Na content 138ppm, K content is 53ppm, Ca content 73ppm) as carrier, chloropalladic acid and chlororhodium acid mixed solution 50g, containing 0.375g of palladium and 0.075g of rhodium as the impregnating solution, impregnating 100g of activated carbon in it and stirring continuously, after the mixed solution of chloropalladic acid and chlororhodium acid is completely absorbed by the activated carbon, aging for 4 hours at a temperature of 80°C, aging After completion, add reducing agent hydrazine hydrate for reduction. After reduction, clean the catalyst with deionized water until no chloride ion is detected. Finally, the catalyst can be dried at 80°C for 2 hours. The Pd content of the catalyst is analyzed by ICP-AES to be 0.75wt%. The Rh content is 0.15 wt%.

The hydrogenation of crude terephthalic acid: 10g of the above-mentioned catalyst is placed in the hanging basket in the reactor, 100g of crude terephthalic acid (the amount containing 4-CBA is 0.3g) and 900g of water are added in the reactor, and then Start stirring and raise the temperature to 280°C. The pressure of the reactor is controlled at 8MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time feed hydrogen to react. The reaction time is 25min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and a sample was taken after fully dissolving with ammonia water for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For the convenience of comparison, the analysis results are listed in Table 1.

[Example 7]

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1108m ² /g, Na content 138ppm, K content is 53ppm, Ca content 73ppm) as carrier, chloropalladic acid and chlororhodium acid mixed solution 50g, containing 0.375g of palladium and 0.075g of rhodium as the impregnating solution, impregnating 100g of activated carbon in it and stirring continuously, after the mixed solution of chloropalladic acid and chlororhodium acid is completely absorbed by the activated carbon, aging at 80°C for 4h, aging After completion, add reducing agent hydrazine hydrate for reduction. After reduction, clean the catalyst with deionized water until no chloride ion is detected. Finally, the catalyst can be dried at 80°C for 2 hours. The Pd content of the catalyst is analyzed by ICP-AES to be 0.75wt%. The Rh content is 0.15 wt%.

The hydrogenation of crude terephthalic acid: 10g of the above-mentioned catalyst is placed in the hanging basket in the reactor, 200g of crude terephthalic acid (the amount containing 4-CBA is 0.6g) and 800g of water are added in the reactor, and then Start stirring and raise the temperature to 280°C. The pressure of the reactor is controlled at 8MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time feed hydrogen to react. The reaction time is 25min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and a sample was taken after fully dissolving with ammonia water for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For the convenience of comparison, the analysis results are listed in Table 1.

[Embodiment 8]

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1108m ² /g, Na content 138ppm, K content is 53ppm, Ca content 73ppm) as carrier, chloropalladic acid and chlororhodium acid mixed solution 50g, containing 0.375g of palladium and 0.075g of rhodium as the impregnating solution, impregnating 100g of activated carbon in it and stirring continuously, after the mixed solution of chloropalladic acid and chlororhodium acid is completely absorbed by the activated carbon, aging for 4 hours at a temperature of 80°C, aging After completion, add reducing agent hydrazine hydrate for reduction. After reduction, clean the catalyst with deionized water until no chloride ion is detected. Finally, the catalyst can be dried at 80°C for 2 hours. The Pd content of the catalyst is analyzed by ICP-AES to be 0.75wt%. The Rh content is 0.15 wt%.

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 (containing 4-CBA is 0.9g) and 700g of water are added in the reactor, and then Start stirring and raise the temperature to 250°C. The pressure of the reactor is controlled at 6MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time pass in hydrogen to react. The reaction time is 90min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and a sample was taken after fully dissolving with ammonia water for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For the convenience of comparison, the analysis results are listed in Table 1.

[Example 9]

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1135m ² /g, Na content 207ppm, K content is 132ppm, Ca content 18ppm) as carrier, chloropalladic acid and chlororhodium acid mixed solution 50g, containing 0.375g of palladium and 0.075g of rhodium as the impregnating solution, impregnating 100g of activated carbon in it and stirring continuously, after the mixed solution of chloropalladic acid and chlororhodium acid is completely absorbed by the activated carbon, aging for 4 hours at a temperature of 80°C, aging After completion, add reducing agent hydrazine hydrate for reduction. After reduction, clean the catalyst with deionized water until no chloride ion is detected. Finally, the catalyst can be dried at 80°C for 2 hours. The Pd content of the catalyst is analyzed by ICP-AES to be 0.75wt%. The Rh content is 0.15 wt%.

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 (containing 4-CBA is 0.9g) and 700g of water are added in the reactor, and then Start stirring and raise the temperature to 280°C. The pressure of the reactor is controlled at 8MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time feed hydrogen to react. The reaction time is 25min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and a sample was taken after fully dissolving with ammonia water for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For the convenience of comparison, the analysis results are listed in Table 1.

[Comparative Example 1]

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1108m ² /g, Na content 138ppm, K content is 53ppm, Ca content 73ppm) as carrier, chloropalladium acid solution 50g, wherein contains palladium 0.45g was used as the impregnating solution, impregnated 100g activated carbon in it and kept stirring, after the chloropalladium acid solution was completely absorbed by the activated carbon, aged for 4 hours at a temperature of 80°C, after the aging was completed, the reducing agent hydrazine hydrate was added for reduction, after the reduction was completed, use The catalyst was washed with ionized water until no chlorine ions were detected, and finally the catalyst was dried at 80° C. for 2 hours. The Pd content of the catalyst was analyzed by ICP-AES to be 0.9 wt%.

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 (containing 4-CBA is 0.9g) and 700g of water are added in the reactor, and then Start stirring and raise the temperature to 280°C. The pressure of the reactor is controlled at 8MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time feed hydrogen to react. The reaction time is 25min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and after being fully dissolved with ammonia water, a sample was taken for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content therein. For the convenience of comparison, the analysis results are listed in Table 1.

【Comparative example 2】

The preparation of catalyst: get 100g coconut shell activated carbon (Nanjing Mulinsen Activated Carbon Co., Ltd. provides, specific surface area is 1108m ² /g, Na content 138ppm, K content is 53ppm, Ca content 73ppm) as carrier, chloropalladic acid and chlororuthenic acid mixed solution 50g, containing 0.375g of palladium and 0.075g of ruthenium as the impregnating solution, impregnated 100g of activated carbon in it and kept stirring, after the mixed solution of chloropalladic acid and chlororuthenic acid was completely absorbed by the activated carbon, aged at 80°C for 4h, aged After completion, add reducing agent hydrazine hydrate for reduction. After reduction, clean the catalyst with deionized water until no chloride ion is detected. Finally, the catalyst can be dried at 80°C for 2 hours. The Pd content of the catalyst is analyzed by ICP-AES to be 0.75wt%. The Ru content is 0.15 wt%.

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 (containing 4-CBA is 0.9g) and 700g of water are added in the reactor, and then Start stirring and raise the temperature to 280°C. The pressure of the reactor is controlled at 8MPa. When the temperature and pressure meet the requirements, put the catalyst hanging basket into the reaction solution, and at the same time feed hydrogen to react. The reaction time is 25min. After the reaction, The temperature of the reaction kettle was lowered to room temperature, and the reaction product was taken out, and a sample was taken after fully dissolving with ammonia water for liquid chromatography analysis of 4-CBA content, CHDA content and decarboxylation product (benzoic acid+cyclohexanecarboxylic acid) content. For convenience, the analysis results are listed in Table 1.

Table 1

The specific embodiments of the present invention have been described in detail above, however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the disclosed content of the present invention. All belong to the protection scope of the present invention.

Claims (10)

1. A method for simultaneously producing 1, 4-cyclohexanedicarboxylic acid as a byproduct in the hydrofining of crude terephthalic acid is characterized by comprising the following steps:

(1) Mixing crude terephthalic acid, a catalyst and a solvent;

(2) Carrying out hydrofining reaction at the temperature of 250-285 ℃ and the pressure of 6-10MPa to obtain purified terephthalic acid and 1, 4-cyclohexanedicarboxylic acid;

wherein the catalyst comprises a carrier and Pd and Rh supported on the carrier.

2. The process of claim 1, wherein the catalyst has a Pd loading of 0.5 wt.% to 1 wt.% and Rh loading of 0.1 wt.% to 0.5 wt.%, based on the catalyst.

3. The process according to claim 1 or 2, characterized in that the support is activated carbon, preferably coconut shell activated carbon, more preferably the coconut shell activated carbon has a specific surface area of 800-1200m ² Per g, the sum of the contents of Na, K and Ca in the active carbon is not highAt 300ppm.

4. The process according to claim 1, wherein the mass ratio of the crude terephthalic acid to the solvent in step (1) is 1:99-30:70, the mass ratio of the crude terephthalic acid to the catalyst is 100: (1-10).

5. The process according to claim 1, wherein the crude terephthalic acid in step (1) contains 0.1 to 0.35 wt.% of 4-aldehyde-benzoic acid.

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

7. The process according to claim 1, wherein the step (2) is followed by a separation step comprising filtering the reaction mixture at 80-160 ℃ to obtain purified terephthalic acid, cooling the obtained filtrate to 5-20 ℃ and filtering to obtain 1, 4-cyclohexanedicarboxylic acid.

8. A catalyst for simultaneously producing 1, 4-cyclohexanedicarboxylic acid by hydrogenation and purification of crude terephthalic acid is characterized by comprising a carrier and Pd and Rh which are loaded on the carrier.

9. The catalyst of claim 8 wherein the catalyst has a Pd loading of 0.5 wt.% to 1 wt.% and Rh loading of 0.1 wt.% to 0.5 wt.%, based on the catalyst.

10. Catalyst according to claim 8 or 9, characterized in that the support is activated carbon, preferably coconut shell activated carbon, more preferably the coconut shell activated carbon has a specific surface area of 800-1200m ² The sum of the contents of Na, K and Ca in the activated carbon is not higher than 300ppm.