Method for preparing 1, 4-cyclohexanedicarboxylic acid by hydrogenation of terephthalic acid

Abstract

The invention relates to a method for preparing 1, 4-cyclohexanedicarboxylic acid by hydrogenation of terephthalic acid, which comprises the following steps: in the presence of a catalyst, contacting terephthalic acid with hydrogen for hydrogenation reaction, the catalyst comprises a modified molecular sieve, a noble metal element loaded on the modified molecular sieve and a coating layer coated on the surface of the modified molecular sieve, and the silica-alumina ratio of the modified molecular sieve is more than 50. According to the method disclosed by the invention, the conversion rate of terephthalic acid and the selectivity of 1, 4-cyclohexanedicarboxylic acid can be effectively improved, so that the conversion rate of terephthalic acid reaches 95-100%, and the selectivity of 1, 4-cyclohexanedicarboxylic acid can reach 100%.

Description

Technical Field

[0001] The present disclosure relates to the technical field of terephthalic acid hydrogenation, and in particular, to a method for preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid. Background Art

[0002] 1,4-cyclohexanedimethanol (CHDM) is an important organic chemical raw material and a common monomer for developing new polyester products. It is generally used to manufacture polyester fibers, polyester for films, polyester for bottles, polyester for sheets, unsaturated polyester resins, polyester glazes, and to produce lubricating oils and hydraulic fluids. At present, the main process for industrial production of CHDM is to use dimethyl terephthalate as raw material, first hydrogenate the benzene ring to produce dimethyl 1,4-cyclohexanedicarboxylate, and then further hydrogenate 1,4-cyclohexanedicarboxylate to prepare CHDM. In 1959, Eastman Chemical Company in the United States achieved industrial production using dimethyl terephthalate (DMT) as raw material. After 2000, Japan and South Korea also achieved industrial production. South Korea's SK Company used the technology of Japan's Shin Rika Co., Ltd. to build a 10,000-ton production unit. The first stage used Ru / Al2O3 catalyst, and the second stage used copper chromite catalyst for hydrogenation.

[0003] In comparison, the cost of terephthalic acid (PTA) is lower than that of dimethyl terephthalate raw materials, and the raw material source is more abundant, so it has become a new trend in research in recent years. The preparation of CHDM by hydrogenation of terephthalic acid (PTA) mostly adopts a two-step process. First, the PTA benzene skeleton is hydrogenated to produce CHDA under the action of a catalyst, and the generated CHDA is further hydrogenated to produce CHDM under the action of a catalyst. The reaction of hydrogenating PTA to produce CHDA generally uses Pd / C as a catalyst, and the CHDA yield is higher than 95%. The CHDA hydrogenation reaction to produce CHDM has higher requirements for catalysts.

[0004] In 1959, U.S. Patent No. 2888484 proposed the use of palladium-based catalysts to hydrogenate terephthalic acid to produce CHDA. In its example, 5 wt% Pd / C was used as a catalyst, the reaction temperature was 195°C, the reaction pressure was greater than 34 MPa, and after 2 hours of reaction, the conversion rate of terephthalic acid reached 100%, and the yield of 1,4-cyclohexanedicarboxylic acid also reached 98.5%, achieving good results. However, the reaction pressure was too high, making it difficult to implement.

[0005] US Patent No. 6291706 uses Pd / C catalyst to hydrogenate terephthalic acid (PTA) to produce CHDA. The catalyst is placed in a basket of an autoclave. A 5% aqueous solution of PTA is continuously stirred at 200°C and 4.5MPa for 45 minutes, and then the catalyst is contacted with the catalyst for reaction for 3 hours. The conversion rate reaches 66.5%, and the reaction liquid after removing the solvent water contains 98.5% of the product CHDA. Japanese Patent No. JP2002020346 uses PTA / H2O as raw material in an autoclave reactor, uses Pd-Ba / C catalyst, reacts at 170°C and 5.0MPa for 1 hour, and the CHDA yield reaches 96.4%. Other patents also propose to use relatively low-priced Ru as an active component, and Ru / C on an activated carbon carrier is used for the reaction. For example, US Patent Nos. 3027398 and 4654064 report the reaction; however, the activity and selectivity of the Ru / C catalyst used in the reaction are poor.

[0006] At present, when terephthalic acid is hydrogenated to generate 1,4-cyclohexanedicarboxylic acid in the prior art, the conversion rate of terephthalic acid and the selectivity of 1,4-cyclohexanedicarboxylic acid are still relatively low, resulting in a low yield of 1,4-cyclohexanedicarboxylic acid, and the loaded precious metals are prone to pulverization, shedding and loss. Summary of the invention

[0007] The purpose of the present disclosure is to provide a method for preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid. The catalyst used in the method includes a modified molecular sieve, a noble metal element loaded on the modified molecular sieve, and a coating layer coated on the surface of the modified molecular sieve. When the catalyst is used in the hydrogenation reaction of terephthalic acid, the conversion rate of terephthalic acid and the selectivity of 1,4-cyclohexanedicarboxylic acid can be improved.

[0008] In order to achieve the above-mentioned object, the present disclosure provides a method for preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid, the method comprising: contacting terephthalic acid with hydrogen in the presence of a catalyst to carry out a hydrogenation reaction; the catalyst comprises a modified molecular sieve, a noble metal element loaded on the modified molecular sieve and a coating layer coated on the surface of the modified molecular sieve, and the silicon-aluminum ratio of the modified molecular sieve is greater than 50.

[0009] Optionally, the temperature of the hydrogenation reaction is 150-250°C, preferably 160-210°C; the time is 1-10h, preferably 4-8h; the hydrogen pressure is 2-10MPa, preferably 3-6MPa; the weight ratio of the catalyst to terephthalic acid is 1:(2-30), preferably 1:(5-15); the hydrogenation reaction is carried out in a solvent, and the solvent includes water.

[0010] Optionally, the modified molecular sieve is one or more of modified mordenite molecular sieve, modified β-type molecular sieve, modified Y-type molecular sieve, modified MCM-22 molecular sieve and modified ZSM-5 molecular sieve, preferably modified ZSM-5 molecular sieve; more preferably, the silicon-aluminum ratio of the modified ZSM-5 molecular sieve is above 200.

[0011] Optionally, the coating layer has a thickness of 1.0 to 20 nm, preferably 2.0 to 12.0 nm; the coating layer is a mesh membrane layer with a porous structure, and the average pore size of the mesh membrane layer is 1.0 to 20 nm, preferably 1.0 to 10 nm; the coating layer includes a silicon dioxide membrane layer.

[0012] Optionally, the noble metal element is selected from one or more of Pd, Ru and Rh, preferably Pd.

[0013] Optionally, based on the total weight of the modified molecular sieve, the content of the precious metal element calculated as metal element is 0.5-5.0 weight %, preferably 2.5-5.0 weight %; the content of the coating layer calculated as SiO2 is 0.5-30 weight %, preferably 2.0-15 weight %.

[0014] Optionally, the method further comprises preparing the catalyst by the following steps:

[0015] (1) subjecting the molecular sieve to hydrothermal treatment to obtain a modified molecular sieve;

[0016] (2) contacting the modified molecular sieve with a first impregnation solution containing a noble metal source, performing a first impregnation treatment, and then drying to obtain a modified molecular sieve loaded with a noble metal element;

[0017] (3) contacting the modified molecular sieve loaded with precious metal elements with a silicon source solution, performing a second impregnation treatment, and then calcining and reducing to obtain the catalyst.

[0018] Optionally, in step (1), the temperature of the hydrothermal treatment is 200-650°C, preferably 300-600°C; the time is 1-10 hours, preferably 1.5-3 hours; the molecular sieve includes one or more of mordenite molecular sieve, β-type molecular sieve, Y-type molecular sieve, MCM-22 molecular sieve and ZSM-5 molecular sieve, preferably ZSM-5 molecular sieve.

[0019] Optionally, in step (2), the weight ratio of the modified molecular sieve to the precious metal source calculated as the metal element is 1:(0.005-0.05), preferably 1:(0.015-0.03); the temperature of the first impregnation treatment is 5-80°C, preferably 5-50°C; the time is 1-24h, preferably 3-8h; the drying temperature is 100-150°C, preferably 105-120°C; the time is 1-10h, preferably 3-6h; the precious metal source is selected from one or more of tetraammonium platinum dichloride, chloroplatinic acid, palladium chloride, tetraammonium platinum acetate, dinitrosodiammonium platinum, platinum nitrate, ruthenium nitrate and rhodium nitrate.

[0020] Optionally, in step (3), the weight ratio of the modified molecular sieve to the silicon source solution is 1: (0.05-1.0), preferably 1: (0.10-0.50); ​​the temperature of the second impregnation treatment is 5-80°C, preferably 5-50°C; the time is 1-10h, preferably 1-5h; the temperature of the calcination is 300-650°C, preferably 450-600°C; the time is 1-10h, preferably 2-6h; the reduction is carried out in the presence of a reducing gas, and the reducing gas is selected from hydrogen, hydrogen-containing nitrogen, carbon monoxide and one or more of hydrogen sulfide, preferably hydrogen; the reduction temperature is 100-300°C, preferably 150-230°C; the heating rate is 0.1-3.0°C / min, preferably 0.3-1.0°C / min; the time is 1-10h, preferably 3-6h; the pressure is 0.2-5.0MPa, preferably 0.5-1.5MPa; optionally, the silicon source solution is selected from one or more of silica sol, silica gel, silicon dioxide dispersion, water glass, sodium metasilicate solution and silicate solution, preferably silica sol.

[0021] Through the above technical scheme, the present disclosure provides a method for preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid, the catalyst used in the method includes a modified molecular sieve, a noble metal element loaded on the modified molecular sieve, and a coating layer coated on the surface of the modified molecular sieve, wherein the coating layer not only plays a role in fixing the noble metal element, avoiding the noble metal element from pulverizing, falling off and losing during the hydrogenation reaction, but also effectively improves the stability of the molecular sieve, making it difficult to collapse in a water-containing system, which is conducive to extending the service life of the catalyst. When the catalyst is used for the hydrogenation reaction of terephthalic acid, the conversion rate of terephthalic acid and the selectivity of 1,4-cyclohexanedicarboxylic acid can be improved, so that the conversion rate of terephthalic acid reaches 95% to 100%, and the selectivity of 1,4-cyclohexanedicarboxylic acid can reach 100%.

[0022] Other features and advantages of the present disclosure will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0023] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0024] The present disclosure provides a method for preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid, the method comprising: contacting terephthalic acid with hydrogen in the presence of a catalyst to carry out a hydrogenation reaction; the catalyst comprises a modified molecular sieve, a noble metal element loaded on the modified molecular sieve and a coating layer coated on the surface of the modified molecular sieve, and the silicon-aluminum ratio of the modified molecular sieve is greater than 50.

[0025] The present invention discloses a method for preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid. The catalyst used in the method includes a modified molecular sieve, a noble metal element loaded on the modified molecular sieve, and a coating layer coated on the surface of the modified molecular sieve, wherein the coating layer not only plays a role in fixing the noble metal element, avoiding the pulverization of the noble metal element during the hydrogenation reaction; but also effectively improves the stability of the molecular sieve, making it difficult to collapse in a water-containing system, which is conducive to extending the service life of the catalyst. When the catalyst is used for the hydrogenation reaction of terephthalic acid, the conversion rate of terephthalic acid and the selectivity of 1,4-cyclohexanedicarboxylic acid can be improved, so that the conversion rate of terephthalic acid reaches 95% to 100%, and the selectivity of 1,4-cyclohexanedicarboxylic acid can reach 100%.

[0026] In one embodiment of the present disclosure, the temperature of the hydrogenation reaction is 150-250°C, preferably 160-210°C; the time is 1-10h, preferably 4-8h; the hydrogen pressure is 2-10MPa, preferably 3-6MPa; the weight ratio of the catalyst to terephthalic acid is 1:(2-30), preferably 1:(5-15); the hydrogenation reaction is carried out in a solvent, and the solvent includes water.

[0027] In one embodiment of the present disclosure, the modified molecular sieve is one or more of modified mordenite molecular sieve, modified β-type molecular sieve, modified Y-type molecular sieve, modified MCM-22 molecular sieve and modified ZSM-5 molecular sieve, preferably modified ZSM-5 molecular sieve; more preferably, the silicon-aluminum ratio of the modified ZSM-5 molecular sieve is above 200.

[0028] In one embodiment of the present disclosure, the coating layer has a thickness of 1.0 to 20 nm, preferably 2.0 to 12.0 nm; the coating layer is a mesh film layer with a porous structure, and the average pore size of the mesh film layer is 1.0 to 20 nm, preferably 1.0 to 10 nm; the coating layer includes a silicon dioxide film layer. In the above embodiment, the preferred silicon dioxide film layer is used, which is beneficial for the silicon hydroxyl groups of the coating layer to form Si-O-Si bonds with the silicon element of the modified molecular sieve, further preventing the migration, shedding and loss of precious metal elements, and preventing the molecular sieve from dealumination and collapse in an aqueous system. In addition, the coating layer is a mesh film layer with a porous structure, which facilitates the contact between terephthalic acid and precious metal elements through the mesh holes, thereby improving the catalytic effect of the catalyst.

[0029] In one embodiment of the present disclosure, the noble metal element is selected from one or more of Pd, Ru and Rh, preferably Pd.

[0030] In one embodiment of the present disclosure, based on the total weight of the modified molecular sieve, the content of the noble metal element calculated as metal element is 0.5-5.0 weight %, preferably 2.5-5.0 weight %; the content of the coating layer calculated as SiO2 is 0.5-30 weight %, preferably 2.0-15 weight %.

[0031] In one embodiment of the present disclosure, the method further comprises preparing the catalyst by the following steps:

[0032] (1) subjecting the molecular sieve to hydrothermal treatment to obtain a modified molecular sieve;

[0033] (2) contacting the modified molecular sieve with a first impregnation solution containing a noble metal source, performing a first impregnation treatment, and then drying to obtain a modified molecular sieve loaded with a noble metal element;

[0034] (3) contacting the modified molecular sieve loaded with precious metal elements with a silicon source solution, performing a second impregnation treatment, and then calcining and reducing to obtain the catalyst.

[0035] In one embodiment of the present disclosure, in step (1), the temperature of the hydrothermal treatment is 200-650°C, preferably 300-600°C; the time is 1-10 hours, preferably 1.5-3 hours; the molecular sieve includes one or more of mordenite molecular sieve, β-type molecular sieve, Y-type molecular sieve, MCM-22 molecular sieve and ZSM-5 molecular sieve, preferably ZSM-5 molecular sieve.

[0036] In one embodiment, the silicon-aluminum ratio of the molecular sieve is greater than 50, and based on the total pore volume of the molecular sieve, the micropore volume of the molecular sieve in the pore size range of 0.35 to 2.0 nm is 90% to 99.8%, and the mesopore volume in the pore size range of 2.0 to 10 nm is 0.2 to 10%. The modified molecular sieve obtained after hydrothermal treatment has a reduced content of micropores in the pore size range of 0.35 to 2.0 nm, for example, a reduction of 0.1 to 1%; and an increased content of mesopores in the pore size range of 2.0 to 10 nm, for example, an increase of 0.1 to 1%. In the above embodiment, by selecting the preferred hydrothermal treatment, the pore size of the molecular sieve can be adjusted, the micropore content can be appropriately reduced, the mesopore content can be appropriately increased, and the internal diffusion resistance inside the molecular sieve can be reduced, thereby improving the conversion rate of terephthalic acid and the selectivity of 1,4-cyclohexanedicarboxylic acid.

[0037] In one embodiment of the present disclosure, in step (2), the weight ratio of the modified molecular sieve to the precious metal source calculated as the metal element is 1:(0.005-0.05), preferably 1:(0.015-0.03); the temperature of the first impregnation treatment is 5-80°C, preferably 5-50°C; the time is 1-24h, preferably 3-8h; the temperature of the drying is 100-150°C, preferably 105-120°C; the time is 1-10h, preferably 3-6h; the precious metal source is selected from one or more of tetraammonium platinum dichloride, chloroplatinic acid, palladium chloride, tetraammonium platinum acetate, dinitrosodiammonium platinum, platinum nitrate, ruthenium nitrate and rhodium nitrate.

[0038] In one embodiment of the present disclosure, in step (3), the weight ratio of the modified molecular sieve to the silicon source solution is 1: (0.05-1.0), preferably 1: (0.10-0.50); ​​the temperature of the second impregnation treatment is 5-80°C, preferably 5-50°C; the time is 1-10h, preferably 1-5h; the temperature of the calcination is 300-650°C, preferably 450-600°C; the time is 1-10h, preferably 2-6h; the The reduction is carried out in the presence of a reducing gas, wherein the reducing gas is selected from one or more of hydrogen, hydrogen-containing nitrogen, carbon monoxide and hydrogen sulfide, preferably hydrogen; the reduction temperature is 100-300°C, preferably 150-230°C; the heating rate is 0.1-3.0°C / min, preferably 0.3-1.0°C / min; the time is 1-10h, preferably 3-6h; the pressure is 0.2-5.0MPa, preferably 0.5-1.5MPa. The content of hydrogen in the hydrogen-containing nitrogen can be 10-99%.

[0039] In one embodiment, in step (3), the silicon source solution is selected from one or more of silica sol, silica gel, silicon dioxide dispersion, water glass, sodium metasilicate solution and silicate solution, preferably silica sol, and the mass fraction of the silica sol is 10-35%, preferably 20-30%.

[0040] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited thereby.

[0041] In the following examples, unless otherwise specified, the raw materials used are commercially available products.

[0042] In the following examples, the specific testing methods are as follows:

[0043] The chemical composition of the molecular sieve and the catalyst was determined using a 3013 X-ray fluorescence spectrometer from Rigaku Corporation, Japan, and the silicon-aluminum ratio of the molecular sieve was calculated. The target was a tungsten target, the excitation voltage was 40 kV, and the excitation current was 50 mA.

[0044] The total pore volume, micropore volume and mesopore volume of the molecular sieve were calculated using the BET method;

[0045] The thickness of the coating layer was tested by transmission electron microscopy, and the instrument model was FEI Tecnai G-20;

[0046] The test method for electrochemical cycle performance is the blue electric test system, and the instrument model is CT3001A.

[0047] Preparation Example 1

[0048] (1) The ZSM-5 molecular sieve is subjected to hydrothermal treatment at 400° C. for 3 h to obtain a modified ZSM-5 molecular sieve; wherein the silicon-aluminum ratio of the ZSM-5 molecular sieve is 200, and based on the total pore volume of the molecular sieve, the volume of micropores with a pore size range of 0.35 to 2.0 nm is 98.5%, and the volume of mesopores with a pore size range of 2.0 to 10 nm is 1.5%; the silicon-aluminum ratio of the obtained modified molecular sieve is 205, the volume of micropores with a pore size range of 0.35 to 2.0 nm is 98.48%, i.e., a decrease of 0.2%, and the volume of mesopores with a pore size range of 2.0 to 10 nm is 1.52%, i.e., an increase of 0.2%;

[0049] (2) 3.00 g of the modified molecular sieve, 15.0 g of a palladium chloride solution with a mass fraction of 0.5% in terms of Pd (a noble metal source, wherein the palladium content is 0.075 g), and 10 g of water were added to a small beaker, stirred and allowed to stand overnight at 25° C. (i.e., the temperature of the first impregnation treatment was 25° C., the time was 12 h, and the weight ratio of the modified molecular sieve to the noble metal source in terms of Pd was 1:0.025), and then dried at 120° C. for 6 h to obtain a modified molecular sieve loaded with 2.5% Pd;

[0050] (3) 2.00 g of the modified molecular sieve loaded with Pd was mixed with 0.80 g of silica sol (the mass fraction of SiO2 was 25%) (the weight ratio of the modified molecular sieve to the silica sol was 1:0.4) and subjected to a second impregnation treatment at a temperature of 40°C for 5 h. The mixture was then calcined at 600°C for 4.0 h and reduced in a hydrogen atmosphere for 6.0 h at a temperature of 200°C, a heating rate of 0.4°C / min, and a pressure of 1.0 MPa to obtain catalyst 1, denoted as C1, whose composition is shown in Table 1.

[0051] Preparation Example 2

[0052] The same as Preparation Example 1, the only difference is that in step (2), the palladium chloride solution with a mass fraction of 0.5% in terms of Pd is adjusted from 15.0 g to 30.0 g (precious metal source, wherein the palladium content is 0.15 g), the weight ratio of the modified molecular sieve to the precious metal source in terms of Pd is 1:0.05 (i.e., 5.0% Pd loading), and finally catalyst 2 is obtained, denoted as C2, and its composition is shown in Table 1.

[0053] Preparation Example 3

[0054] The same as Preparation Example 1, the only difference is that: in step (2), 15.0 g of ruthenium chloride solution with a mass fraction of 0.5% calculated as Ru (precious metal source, wherein the ruthenium content is 0.075 g) is further added to the small beaker, and the weight ratio of the modified molecular sieve to the precious metal source calculated as Pd and Ru is 1:0.05 (i.e., loading 2.5% Pd + 2.5% Ru), and finally catalyst 3 is obtained, denoted as C3, and its composition is shown in Table 1.

[0055] Preparation Example 4

[0056] The same as Preparation Example 1, the only difference is that in step (3), the silica sol is replaced by an equal weight of cyclohexane containing tetraethyl orthosilicate (the mass fraction of SiO2 is 20%), the weight ratio of the modified molecular sieve to tetraethyl orthosilicate is 1:0.5, the calcination temperature is 500°C, and finally catalyst 4 is obtained, denoted as C4, whose composition is shown in Table 1.

[0057] Preparation Example 5

[0058] The same as Preparation Example 1, the only difference is that in step (1), the ZSM-5 molecular sieve with a silicon-aluminum ratio of 200 is replaced by the same amount of ZSM-5 molecular sieve with a silicon-aluminum ratio of 100, and the silicon-aluminum ratio of the obtained modified ZSM-5 molecular sieve is 102.3. Finally, catalyst 5 is obtained, denoted as C5, and its composition is shown in Table 1.

[0059] Preparation Example 6

[0060] The same as Preparation Example 1, the only difference is that in step (1), the ZSM-5 molecular sieve with a silicon-aluminum ratio of 200 is replaced by the same amount of mordenite molecular sieve with a silicon-aluminum ratio of 50, and the silicon-aluminum ratio of the obtained modified mordenite molecular sieve is 51.0. Finally, catalyst 6 is obtained, denoted as C6, and its composition is shown in Table 1.

[0061] Preparation Comparative Example 1

[0062] The same as Preparation Example 1, the only difference is that in step (3), the modified molecular sieve loaded with Pd is not subjected to the second impregnation treatment, but is directly calcined and reduced, and finally a comparative catalyst 1 is obtained, denoted as D1, and its composition is shown in Table 1.

[0063] Preparation Comparative Example 2

[0064] The same as Preparation Example 1, the only difference is that in step (1), the ZSM-5 molecular sieve with a silicon-aluminum ratio of 200 is replaced by the same amount of mordenite molecular sieve with a silicon-aluminum ratio of 25 (the pore structure is basically the same as that of the ZSM-5 molecular sieve), and the silicon-aluminum ratio of the obtained modified mordenite molecular sieve is 25.3. Finally, comparative catalyst 2 is obtained, denoted as D2, and its composition is shown in Table 1.

[0065] Table 1

[0066]

[0067] Example 1

[0068] 0.20g of the catalyst C1 obtained in Example 1 was placed in two 80mL reactors, 1.0g of terephthalic acid (PTA, the weight ratio of catalyst C1 to terephthalic acid was 1:5) and 20g of water were added to the two reactors, stirring was started and the temperature was raised to 180°C. The initial hydrogen pressure of the reactor was controlled at 4.0MPa. When the temperature and pressure reached the requirements, hydrogenation reaction was carried out. After 6.0h of reaction, the first reactor was taken out, the temperature of the first reactor was lowered to room temperature, and the reaction product was taken out; after 24h of reaction, the second reactor was taken out, the temperature of the second reactor was lowered to room temperature, and the reaction product was taken out; the two reaction products were placed in an oven at 105°C to dry the water, and the solid reaction product was obtained and dissolved in dimethyl sulfoxide (DMSO). The 1,4-cyclohexanedicarboxylic acid (CHDA) content in the supernatant was analyzed by gas chromatography. The reaction results are shown in Table 2. The PTA conversion rate and CHDA selectivity were calculated according to the following formulas (1) to (2):

[0069]

[0070]

[0071] Embodiments 2 to 6

[0072] The hydrogenation reaction was carried out using the method and reaction conditions of Example 1, except that the catalysts C2 to C6 prepared in Preparation Examples 2 to 6 were used to catalyze the hydrogenation reaction. The reaction results are shown in Table 2.

[0073] Comparative Examples 1-2

[0074] The hydrogenation reaction was carried out according to the method and reaction conditions of Example 1, except that the comparative catalysts D1-D2 prepared in Comparative Preparation Examples 1-2 were used to catalyze the hydrogenation reaction. The reaction results are shown in Table 2.

[0075] Table 2

[0076]

[0077]

[0078] It can be seen from the results of the above examples and comparative examples that the use of the method disclosed in Examples 1 to 6 can effectively improve the conversion rate of terephthalic acid and the selectivity of 1,4-cyclohexanedicarboxylic acid.

[0079] Comparison of the data of Example 1 with Examples 5 to 6 shows that when the modified ZSM-5 molecular sieve is preferably used in Example 1 and the silicon-aluminum ratio of the modified ZSM-5 molecular sieve is limited to 200 or more, when the obtained catalyst is used for the hydrogenation reaction of terephthalic acid, the conversion rate of terephthalic acid and the selectivity of 1,4-cyclohexanedicarboxylic acid are both as high as 100%;

[0080] Comparison of the data of Example 1 and Comparative Example 1 shows that when the surface of the modified molecular sieve of Example 1 has a coating layer, the conversion rate of terephthalic acid and the selectivity of 1,4-cyclohexanedicarboxylic acid of the prepared catalyst after 24 hours of hydrogenation reaction do not decrease significantly; while the surface of the modified molecular sieve of Comparative Example 1 does not contain a coating layer, and the selectivity of 1,4-cyclohexanedicarboxylic acid of the prepared catalyst after 24 hours of hydrogenation reaction decreases significantly. This is because the precious metal elements on the surface of the modified molecular sieve are pulverized, shed and lost during the reaction, and the molecular sieve collapses after a long period of reaction, resulting in a decrease in the catalytic performance of the catalyst and a shortened service life;

[0081] Comparison of the data of Example 1 and Comparative Example 2 shows that when Example 1 uses a modified molecular sieve with a silicon-aluminum ratio greater than 50 as a carrier, the prepared catalyst has excellent catalytic performance, and the catalytic performance of the catalyst does not decrease significantly after a long period of hydrogenation reaction in an aqueous system. However, when Comparative Example 2 uses a modified molecular sieve with a silicon-aluminum ratio less than 50 as a carrier, the conversion rate of terephthalic acid of the prepared catalyst is low, and the catalyst is unstable and has a short service life.

[0082] The preferred embodiments of the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0083] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0084] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid, characterized in that: The method comprises: contacting terephthalic acid with hydrogen in the presence of a catalyst to perform a hydrogenation reaction; The catalyst comprises a modified molecular sieve, a noble metal element loaded on the modified molecular sieve and a coating layer coated on the surface of the modified molecular sieve, and the silicon-aluminum ratio of the modified molecular sieve is greater than 50.

2. The method according to claim 1, characterized in that The temperature of the hydrogenation reaction is 150-250°C, preferably 160-210°C; the time is 1-10h, preferably 4-8h; the hydrogen pressure is 2-10MPa, preferably 3-6MPa; the weight ratio of the catalyst to terephthalic acid is 1:(2-30), preferably 1:(5-15); The hydrogenation reaction is carried out in a solvent, and the solvent includes water.

3. The method according to claim 1, characterized in that The modified molecular sieve is one or more of modified mordenite molecular sieve, modified β-type molecular sieve, modified Y-type molecular sieve, modified MCM-22 molecular sieve and modified ZSM-5 molecular sieve, preferably modified ZSM-5 molecular sieve; more preferably, the silicon-aluminum ratio of the modified ZSM-5 molecular sieve is above 200.

4. The method according to claim 1, characterized in that: The coating layer has a thickness of 1.0 to 20 nm, preferably 2.0 to 12.0 nm; the coating layer is a mesh membrane layer with a porous structure, and the average pore size of the mesh membrane layer is 1.0 to 20 nm, preferably 1.0 to 10 nm; the coating layer includes a silicon dioxide membrane layer.

5. The method according to claim 1, characterized in that The noble metal element is selected from one or more of Pd, Ru and Rh, preferably Pd.

6. The method according to claim 1, characterized in that Based on the total weight of the modified molecular sieve, the content of the noble metal element in terms of metal element is 0.5-5.0 wt%, preferably 2.5-5.0 wt%; the content of the coating layer in terms of SiO2 is 0.5-30 wt%, preferably 2.0-15 wt%.

7. The method according to claim 1, characterized in that The method further comprises preparing the catalyst by the following steps: (1) subjecting the molecular sieve to hydrothermal treatment to obtain a modified molecular sieve; (2) contacting the modified molecular sieve with a first impregnation solution containing a noble metal source, performing a first impregnation treatment, and then drying to obtain a modified molecular sieve loaded with a noble metal element; (3) contacting the modified molecular sieve loaded with precious metal elements with a silicon source solution, performing a second impregnation treatment, and then calcining and reducing to obtain the catalyst.

8. The method according to claim 7, characterized in that In step (1), the temperature of the hydrothermal treatment is 200 to 650° C., preferably 300 to 600° C.; the time is 1 to 10 hours, preferably 1.5 to 3 hours; The molecular sieve includes one or more of mordenite molecular sieve, β-type molecular sieve, Y-type molecular sieve, MCM-22 molecular sieve and ZSM-5 molecular sieve, preferably ZSM-5 molecular sieve.

9. The method according to claim 7, characterized in that: In step (2), the weight ratio of the modified molecular sieve to the precious metal source calculated as the metal element is 1: (0.005-0.05), preferably 1: (0.015-0.03); the temperature of the first impregnation treatment is 5-80° C., preferably 5-50° C.; the time is 1-24 h, preferably 3-8 h; the temperature of the drying is 100-150° C., preferably 105-120° C.; the time is 1-10 h, preferably 3-6 h; The noble metal source is selected from one or more of tetraammonium platinum dichloride, chloroplatinic acid, palladium chloride, tetraammonium platinum acetate, dinitrosodiammonium platinum, platinum nitrate, ruthenium nitrate and rhodium nitrate.

10. The method according to claim 7, characterized in that In step (3), the weight ratio of the modified molecular sieve to the silicon source solution is 1:(0.05-1.0), preferably 1:(0.10-0.50); The temperature of the second immersion treatment is 5 to 80° C., preferably 5 to 50° C.; the time is 1 to 10 hours, preferably 1 to 5 hours; The calcination temperature is 300-650°C, preferably 450-600°C; the calcination time is 1-10h, preferably 2-6h; The reduction is carried out in the presence of a reducing gas, wherein the reducing gas is selected from one or more of hydrogen, hydrogen-containing nitrogen, carbon monoxide and hydrogen sulfide, preferably hydrogen; the reduction temperature is 100-300°C, preferably 150-230°C; the heating rate is 0.1-3.0°C / min, preferably 0.3-1.0°C / min; the time is 1-10h, preferably 3-6h; the pressure is 0.2-5.0MPa, preferably 0.5-1.5MPa; Optionally, the silicon source solution is selected from one or more of silica sol, silica gel, silicon dioxide dispersion, water glass, sodium metasilicate solution and silicate solution, preferably silica sol.

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