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

Abstract

The invention provides a method for preparing 1, 4-cyclohexanedicarboxylic acid through continuous hydrogenation of terephthalic acid. The method comprises the following steps: mixing a reaction raw material terephthalic acid, a cosolvent 1, 4-cyclohexanedicarboxylic acid and a reaction solvent water at a preset temperature to obtain a mixed material; the mixed material is conveyed to a trickle bed reactor, terephthalic acid in the mixed material is subjected to a hydrogenation reaction in the presence of a catalyst and under preset hydrogenation reaction conditions, 1, 4-cyclohexanedicarboxylic acid is prepared, the catalyst comprises carrier modified activated carbon and an active component palladium loaded on the carrier, and the active component palladium is palladium loaded on the carrier. The activated carbon carrier is sequentially subjected to nitric acid treatment, thionyl chloride treatment and organic amine grafting to obtain the amino compound modified activated carbon carrier. According to the invention, the organic amine is grafted to the activated carbon through a chemical method to modify the activated carbon, so that the dispersity of palladium is improved, the interaction between a carrier and palladium is enhanced, and the activity and stability of the catalyst are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and specifically relates to a method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid and a catalyst. Background Art

[0002] 1,4-Cyclohexanedicarboxylic acid (CHDA) brings many unique properties to polyester resins and glass fiber reinforced plastics for high-performance coatings. Its products are used in automobiles, transportation, industrial maintenance, aerospace, buildings, equipment and instruments, and ordinary metals and gel coatings. In addition, in medicine, CHDA can also be used to synthesize peptic ulcer drugs.

[0003] CHDA is prepared by hydrogenation of terephthalic acid (PTA). U.S. Pat. No. 6,291,706 uses Pd / C catalyst, and the catalyst is placed in an autoclave basket. A 5% aqueous solution of PTA is continuously stirred at 200°C and 4.5 MPa 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 JP 2002020346 uses PTA / H2O as raw material in an autoclave reactor, uses Pd-Ba / C catalyst, and reacts at 170°C and 5.0 MPa for 1 hour. 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, U.S. Pat. Nos. 3,027,398 and 4,654,064 report the reaction; however, the activity and selectivity of the Ru / C catalyst used in the reaction are poor.

[0004] The surface of the activated carbon carrier is hydrophobic and lipophilic, which is not conducive to the adsorption of metal precursors such as palladium chloride. The metal Pd particles are easy to agglomerate during the drying and reduction steps. Therefore, the prepared Pd / C catalyst has low dispersion and poor catalyst activity. For industrial catalysts, catalyst life is crucial. Generally speaking, the deactivation of PTA hydrogenation to CHDA palladium carbon catalyst is mainly caused by the sintering of metal Pd particles and the coking deactivation of catalyst pores, and both deactivation situations exist. Summary of the invention

[0005] The purpose of the present invention is to modify the activated carbon of the palladium carbon catalyst, and to graft an organic amine onto the activated carbon by a chemical method to obtain a modified activated carbon carrier modified with an amino compound. The grafting of the amino compound can improve the dispersion of the active component palladium, slow down the agglomeration of metal Pd particles during the reaction, and inhibit the coking of the catalyst, thereby improving the activity and stability of the catalyst.

[0006] In order to achieve the above object, the present invention provides a method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid, the method comprising the following steps:

[0007] (1) Mixing the reaction raw material terephthalic acid, the co-solvent 1,4-cyclohexanedicarboxylic acid and the reaction solvent water at a preset temperature to obtain a mixed material, wherein the mass fraction of the terephthalic acid is 1 to 5.0 wt % based on the total weight of the mixed material being 100 wt %.

[0008] (2) transporting the mixed material to a trickle bed reactor, and subjecting the terephthalic acid in the mixed material to a hydrogenation reaction under a catalyst and preset hydrogenation reaction conditions to prepare a hydrogenated liquid including 1,4-cyclohexanedicarboxylic acid, wherein the preset hydrogenation reaction conditions include: a feed mass space velocity of terephthalic acid of 0.01 to 2.0 h / min; -1 , the molar ratio of hydrogen to terephthalic acid is 5.0 to 80.0, the reaction pressure is 5.0 MPa to 14.0 MPa, and the reaction temperature is 140 to 220° C.; wherein the catalyst includes a carrier-modified activated carbon and an active component palladium supported on the carrier, and the modified activated carbon is prepared by the following method.

[0009] The activated carbon is placed in a nitric acid solution for a first treatment to introduce oxygen-containing groups including carboxyl groups on the surface of the activated carbon.

[0010] The activated carbon treated with nitric acid is placed in a thionyl chloride solution for a second treatment to convert the carboxyl groups into acyl chlorides.

[0011] The activated carbon treated with thionyl chloride is placed in an organic amine solution for a third treatment to graft the amino compound onto the surface of the activated carbon.

[0012] The activated carbon treated with organic amine is dried to obtain modified activated carbon.

[0013] In a specific embodiment, the conditions of the first treatment include: a treatment temperature of 60 to 95° C. and a treatment time of 0.5 to 8 hours.

[0014] In a specific embodiment, the mass ratio of the activated carbon to the nitric acid solution is 1:(2-10), and the mass percentage concentration of the nitric acid solution is 5-15%.

[0015] In a specific embodiment, the conditions of the second treatment include: a treatment temperature of 50 to 90° C., a treatment time of 0.5 to 4 hours; and a mass percentage concentration of the thionyl chloride solution of 1 to 40%.

[0016] In a specific embodiment, the conditions of the third treatment include: a treatment temperature of 50 to 95° C. and a treatment time of 0.5 to 4 hours.

[0017] In a specific embodiment, the organic amine is selected from at least one of ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, diethylenetriamine, and tetraethylenepentamine, and the mass percentage concentration of the organic amine solution is 1 to 20%. Preferably, the organic amine is 1,4-butylenediamine.

[0018] In a specific embodiment, based on the total weight of the catalyst being 100%, the theoretical loading amount of metal palladium in the catalyst is 0.1 to 10%, preferably, the theoretical loading amount of metal palladium in the catalyst is 0.65 to 1.0%,

[0019] In a specific embodiment, the preparation method of the catalyst comprises: first preparing a palladium / modified activated carbon catalyst precursor by an equal volume impregnation method, and then reducing the catalyst precursor with a reducing agent to obtain the catalyst, wherein the reducing agent is hydrogen, and the reduction treatment conditions include: a reduction temperature of 150 to 300°C, preferably 200 to 250°C; a hydrogen volume space velocity of 50 to 500 h -1 , preferably 100 to 200 hours -1 .

[0020] In a specific embodiment, the preset hydrogenation reaction conditions include: the feed mass space velocity of terephthalic acid is 1.1 to 1.3 h -1 , the molar ratio of hydrogen to terephthalic acid is 10-40, the reaction pressure is 8.5-10.5 MPa, and the reaction temperature is 195-205°C.

[0021] In a specific embodiment, in step (2), the yield of trans-1,4-cyclohexanedicarboxylic acid in the hydrogenated liquid can be increased by controlling the increase of any one of the reaction temperature, the molar ratio of hydrogen to terephthalic acid, and the reaction pressure.

[0022] The beneficial effects of the present invention include at least:

[0023] First, the present invention provides a technical problem that the existing Pd / C catalyst has low catalytic activity and is easy to deactivate, and solves the technical problem by modifying the carrier activated carbon. Specifically, the activated carbon carrier is sequentially treated with nitric acid, treated with thionyl chloride, grafted with organic amines, etc. to obtain an activated carbon carrier modified with amino compounds. First, the grafting of organic amines on the surface of the activated carbon carrier can improve the chelating ability of precursors such as palladium chloride, thereby preparing a highly dispersed Pd / C catalyst; second, the grafting of amino compounds provides alkalinity to the catalyst, which can significantly inhibit the coking of the catalyst; third, the grafting of amino compounds enhances the interaction between the carrier and the Pd particles, which can slow down the agglomeration of metal Pd particles during the reaction process; thus, the active component Pd of the catalyst prepared by the present invention has high dispersion, is not easy to agglomerate, and is not easy to coke on the surface of the catalyst after long-term reaction. The conversion rate of raw material PTA and the selectivity of the target product CHDA both reach more than 99.5%. At the same time, the catalyst has a long service life and can run for more than 3500 hours in a single pass without obvious deactivation.

[0024] 2. Trans-1,4-cyclohexanedicarboxylic acid has important applications in the synthesis of raw materials and as a polyester resin monomer. The present invention finds that, based on the catalyst provided by the present invention, the reaction temperature, the molar ratio of hydrogen to terephthalic acid and the reaction pressure are positively correlated with the proportion of trans-1,4-cyclohexanedicarboxylic acid in the hydrogenated liquid, and are negatively correlated with the mass space velocity of the terephthalic acid feed. That is to say, by controlling the increase of any one of the reaction temperature, the molar ratio of hydrogen to terephthalic acid and the reaction pressure or the decrease of the mass space velocity of the terephthalic acid feed, the yield of trans-1,4-cyclohexanedicarboxylic acid in the hydrogenated liquid can be increased; in this way, the proportion of trans-1,4-cyclohexanedicarboxylic acid in the reaction product can be controlled, and the application value of the reaction product of the present invention can be provided. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the embodiments.

[0026] In view of the technical problems of low dispersion, poor catalyst activity and easy deactivation of the Pd / C catalyst used for hydrogenation of terephthalic acid to prepare 1,4-cyclohexanedicarboxylic acid, the present invention uses nitric acid to treat the activated carbon carrier to introduce oxygen-containing groups on the carrier surface to increase the hydrophilicity of the carrier surface, and further grafts amino compounds such as ethylenediamine on the carrier surface to improve the chelating ability of precursors such as palladium chloride, thereby preparing a highly dispersed Pd / C catalyst. At the same time, due to the alkalinity provided by the grafting of amino compounds to the catalyst, the coking of the catalyst is significantly inhibited, and the grafting of amino compounds can also enhance the interaction between the carrier and the Pd particles, which can slow down the agglomeration of metal Pd particles during the reaction process, so that the prepared catalyst metal Pd has high dispersion, is not easy to agglomerate, and the catalyst surface is not easy to coke, so that the raw material PTA conversion rate and the selectivity of the target product CHDA are both above 99.5%, the catalyst has a long service life, and runs for more than 3500 hours in a single pass without obvious deactivation.

[0027] The present invention provides a method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid, the method comprising the following steps:

[0028] (1) Mixing the reaction raw material terephthalic acid, the co-solvent 1,4-cyclohexanedicarboxylic acid and the reaction solvent water at a preset temperature to obtain a mixed material, wherein the mass fraction of the terephthalic acid is 1 to 5.0 wt % based on the total weight of the mixed material being 100 wt %.

[0029] Preferably, the preset temperature is 150-200°C.

[0030] Preferably, the mass fraction of 1,4-cyclohexanedicarboxylic acid (CHDA) in the raw material liquid is 10-40%, the mass fraction of terephthalic acid (PTA) is 1-5.0wt%, and the more preferred mass fraction of PTA is 1-3wt%.

[0031] (2) transporting the mixed material to a trickle bed reactor, and subjecting the terephthalic acid in the mixed material to a hydrogenation reaction under a catalyst and preset hydrogenation reaction conditions to prepare a hydrogenated liquid including 1,4-cyclohexanedicarboxylic acid, wherein the preset hydrogenation reaction conditions include: a feed mass space velocity of terephthalic acid of 0.01 to 2.0 h / min; -1 , the molar ratio of hydrogen to terephthalic acid is 5.0 to 80.0, the reaction pressure is 5.0 MPa to 14.0 MPa, and the reaction temperature is 140 to 220° C.; wherein the catalyst includes a carrier-modified activated carbon and an active component palladium supported on the carrier.

[0032] Preferably, the preset hydrogenation reaction conditions include: the feed mass space velocity of terephthalic acid is 1.1 to 1.3 h -1, the molar ratio of hydrogen to terephthalic acid is 10-40, the reaction pressure is 8.5-10.5 MPa, and the reaction temperature is 195-205°C.

[0033] More preferably, the preset hydrogenation reaction conditions include: the feed mass space velocity of terephthalic acid is 1.3h -1 , the molar ratio of hydrogen to terephthalic acid is 10, the reaction pressure is 9 MPa, and the reaction temperature is 195°C.

[0034] Preferably, based on the total weight of the catalyst being 100%, the theoretical loading amount of the metal palladium in the catalyst is 0.1 to 10%, preferably, the theoretical loading amount of the metal palladium in the catalyst is 0.65 to 1.0%.

[0035] Preferably, the yield of trans-1,4-cyclohexanedicarboxylic acid in the hydrogenated liquid can be increased by controlling the increase of any one of the reaction temperature, the molar ratio of hydrogen to terephthalic acid, and the reaction pressure.

[0036] Preferably, the yield of trans-1,4-cyclohexanedicarboxylic acid in the hydrogenated liquid can be increased by reducing the feed mass space velocity of terephthalic acid.

[0037] In the present invention, the yield of trans-1,4-cyclohexanedicarboxylic acid can be controlled by adjusting the hydrogenation reaction conditions, thereby increasing the application value of the reaction product 1,4-cyclohexanedicarboxylic acid.

[0038] The catalyst is prepared by the following method:

[0039] (a) The palladium / modified activated carbon catalyst precursor was prepared by the equal volume impregnation method.

[0040] The equal volume impregnation method is specifically as follows: a precursor of metallic palladium is prepared into a palladium solution, adsorbed on a modified activated carbon carrier, left to stand for 24 hours to 36 hours, and then dried to obtain a catalyst precursor.

[0041] Preferably, the precursor of metallic palladium is selected from palladium chloride, palladium acetate and palladium nitrate.

[0042] Preferably, the mass concentration of the palladium solution is 0.001-0.05 g / ml.

[0043] Preferably, the drying conditions include: drying temperature of 60 to 120° C. and drying time of 2 to 8 hours.

[0044] (b) treating the catalyst precursor with a reducing agent to obtain the catalyst, wherein the reducing agent is hydrogen, and the conditions of the reduction treatment include: a reduction temperature of 150 to 300° C., a hydrogen volume space velocity of 50 to 500 h / min -1 .

[0045] Preferably, the reduction treatment conditions include: a reduction temperature of 200-250°C, a hydrogen volume space velocity of 100-200h -1 .

[0046] In the present invention, the modified activated carbon is prepared by the following method:

[0047] Step (a), placing the activated carbon in a nitric acid solution for a first treatment to introduce oxygen-containing groups including carboxyl groups on the surface of the activated carbon.

[0048] Preferably, the activated carbon is flake activated carbon or columnar activated carbon.

[0049] Preferably, the conditions of the first treatment include: treatment temperature of 60-95° C., and treatment time of 0.5-8 h.

[0050] Preferably, the mass ratio of the activated carbon to the nitric acid solution is 1:(2-10), and the mass percentage concentration of the nitric acid solution is 5-15%, more preferably, the mass percentage concentration of the nitric acid solution is 5-10%.

[0051] In the present invention, the mass percentage concentration of nitric acid is associated with the introduction of carboxyl oxygen-containing groups. When the mass percentage concentration of nitric acid is low, a small number of carboxyl oxygen-containing groups will be introduced, thereby affecting the subsequent grafting of organic amines.

[0052] In the present invention, the treatment temperature of nitric acid will affect the pore structure of the carrier. When the treatment temperature of nitric acid is greater than 95°C, the pore structure of the carrier will be destroyed, thereby affecting the catalyst performance. At the same time, the treatment temperature of nitric acid will also affect the number of carboxyl oxygen-containing groups introduced. More preferably, the treatment temperature in the first treatment condition is 90-95°C.

[0053] Step (b), placing the activated carbon treated with nitric acid in a thionyl chloride solution for a second treatment to convert the carboxyl group into an acyl chloride.

[0054] Preferably, the conditions of the second treatment include: treatment temperature of 50-90° C. and treatment time of 0.5-4 h.

[0055] Preferably, the mass percentage concentration of the thionyl chloride solution is 1 to 40%.

[0056] In the present invention, the solvent of the thionyl chloride solution is xylene.

[0057] In the present invention, thionyl chloride is used to react with carboxyl to generate acyl chloride, which is convenient for subsequent grafting of organic amines.

[0058] Step (c), placing the activated carbon treated with thionyl chloride in an organic amine solution for a third treatment to graft the amino compound onto the surface of the activated carbon.

[0059] Preferably, the conditions of the third treatment include: treatment temperature of 50-95° C., and treatment time of 0.5-4 h.

[0060] Preferably, the organic amine is selected from at least one of ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, diethylenetriamine, and tetraethylenepentamine. More preferably, the organic amine is 1,4-butylenediamine.

[0061] Preferably, the mass percentage concentration of the organic amine solution is 1-20%.

[0062] In the present invention, the solvent of the organic amine solution is xylene.

[0063] In the present invention, acyl chloride and organic amine undergo nucleophilic substitution reaction to form amide, and the organic amine is grafted onto the surface of activated carbon by a chemical method to complete the modification of activated carbon.

[0064] In step (d), the activated carbon treated with the organic amine is dried to obtain modified activated carbon.

[0065] Preferably, the drying conditions include: drying temperature of 60 to 120° C. and drying time of 2 to 8 hours.

[0066] In the present invention, the method further comprises a post-treatment step, wherein the hydrogenated liquid is subjected to gas-liquid separation and cooling crystallization to obtain 1,4-cyclohexanedicarboxylic acid solid.

[0067] Catalyst preparation

[0068] The catalyst of Example A1 uses untreated activated carbon, the carrier in the catalysts of Examples A2 to A7 is activated carbon pretreated only with nitric acid, the carrier-modified activated carbon in the catalysts of Examples A8 to A16 is treated three times with nitric acid, thionyl chloride and organic amine in sequence, and the carrier in the catalyst of Example A17 is treated only with organic amine. For details, please see the description of each example and Table 1.

[0069] Example A1

[0070] Support: Untreated flake activated carbon (AC-0) was used as the support.

[0071] Preparation of catalyst:

[0072] The catalyst was prepared by an equal volume impregnation method. A palladium chloride solution was prepared according to a theoretical palladium loading of 0.50 wt%, and then impregnated on the untreated sheet activated carbon support for 24 h. After drying at 110 ° C for 6 h and reducing with hydrogen, a palladium catalyst was obtained, which was recorded as Cat.-1. The conditions for hydrogen reduction were: hydrogen volume space velocity 200 h -1 , reduction temperature 250℃.

[0073] Example A2

[0074] Preparation of the carrier: The sheet activated carbon carrier (denoted as AC-0) was pretreated with a nitric acid solution, the mass percentage concentration of the nitric acid solution was 5.0wt%, the mass ratio of the activated carbon carrier to the nitric acid solution was 1:4, the nitric acid treatment temperature was 90°C, and the nitric acid treatment time was 3h; after the nitric acid pretreatment, the activated carbon carrier was washed with purified water until the filtrate was neutral, and dried at 110°C for 6h. The modified activated carbon sample obtained was denoted as AC-1.

[0075] Preparation of catalyst:

[0076] The catalyst was prepared by an equal volume impregnation method. A palladium chloride solution was prepared according to the theoretical palladium loading of 0.50 wt%, and then impregnated on the modified activated carbon AC-1 for 24 h. After drying at 110 ° C for 6 h and hydrogen reduction, a palladium catalyst was obtained, which was recorded as Cat.-2. The conditions for hydrogen reduction were: hydrogen volume space velocity 200 h -1 , reduction temperature 250℃.

[0077] Example A3

[0078] Example A3 is the same as Example A2, the only difference being that the concentration of the nitric acid solution when preparing the carrier is 2.5wt%, and the modified activated carbon sample obtained is recorded as AC-2; the carrier used in the catalyst preparation step is AC-2, and the palladium catalyst obtained is recorded as Cat.-3.

[0079] Example A4

[0080] Example A4 is the same as Example A2, the only difference being that the concentration of the nitric acid solution when preparing the carrier is 10wt%, and the modified activated carbon sample obtained is recorded as AC-3; the carrier used in the catalyst preparation step is AC-3, and the palladium catalyst obtained is recorded as Cat.-4.

[0081] Example A5

[0082] Example A5 is the same as Example A2, the only difference being that the nitric acid treatment temperature is 80°C when preparing the carrier, and the modified activated carbon sample obtained is denoted as AC-4; the carrier used in the catalyst preparation step is AC-4, and the palladium catalyst obtained is denoted as Cat.-5.

[0083] Example A6

[0084] Example A6 is the same as Example A2, the only difference being that the nitric acid treatment temperature is 98°C when preparing the carrier, and the modified activated carbon sample obtained is denoted as AC-5; the carrier used in the catalyst preparation step is AC-5, and the palladium catalyst obtained is denoted as Cat.-6.

[0085] Example A7

[0086] Example A7 is the same as Example A2, the only difference being that the activated carbon used in preparing the carrier is columnar activated carbon, and the modified activated carbon sample obtained is recorded as AC-6; the carrier used in the catalyst preparation step is AC-6, and the palladium catalyst obtained is recorded as Cat.-7.

[0087] Example A8

[0088] Preparation of vector:

[0089] The modified activated carbon AC-1 prepared in Example A2 was placed in a 5wt% thionyl chloride solution (solvent: xylene), treated at 65°C for 3h, then placed in a 5wt% ethylenediamine solution (solvent: xylene), treated at 70°C for 3h, and then dried at 110°C for 6h. The obtained modified activated carbon sample was recorded as AC-7.

[0090] The preparation steps of the catalyst are the same as those in Example A2, the carrier used is AC-7, and the obtained palladium catalyst is denoted as Cat.-8.

[0091] Embodiment A9

[0092] Example A9 is the same as Example A8, the only difference being that 1,3-propylenediamine is used instead of ethylenediamine when preparing the carrier, and the modified activated carbon sample obtained is recorded as AC-8; the carrier used in the catalyst preparation step is AC-8, and the palladium catalyst obtained is recorded as Cat.-9.

[0093] Embodiment A10

[0094] Example A10 is the same as Example A8, the only difference being that 1,4-butanediamine is used instead of ethylenediamine when preparing the carrier, and the modified activated carbon sample obtained is recorded as AC-9; the carrier used in the catalyst preparation step is AC-9, and the palladium catalyst obtained is recorded as Cat.-10.

[0095] Embodiment A11

[0096] Example A11 is the same as Example A10, except that the carrier used is AC-9. The only difference is that when preparing the catalyst, the mass of the palladium solution added is different. The theoretical loading amount of palladium is 0.35wt%. The obtained palladium catalyst is recorded as Cat.-11.

[0097] Example A12

[0098] Example A12 is the same as Example A10, except that the carrier used is AC-9. The only difference is that when preparing the catalyst, the mass of the palladium solution added is different. The theoretical loading amount of palladium is 0.65wt%. The obtained palladium catalyst is recorded as Cat.-12.

[0099] Embodiment A13

[0100] The modified activated carbon AC-3 prepared in Example A4 was placed in a 5wt% thionyl chloride solution (solvent: xylene), treated at 65°C for 3h, then placed in a 5wt% 1,4-butanediamine solution (solvent: xylene), treated at 70°C for 3h, and then dried at 110°C for 6h. The obtained modified activated carbon sample was recorded as AC-10.

[0101] The preparation steps of the catalyst are the same as those in Example A2, the carrier used is AC-10, and the obtained palladium catalyst is denoted as Cat.-13.

[0102] Embodiment A14

[0103] The modified activated carbon AC-2 prepared in Example A3 was placed in a 5wt% thionyl chloride solution (solvent: xylene), treated at 65°C for 3h, then placed in a 5wt% 1,4-butanediamine solution (solvent: xylene), treated at 70°C for 3h, and then dried at 110°C for 6h. The obtained modified activated carbon sample was recorded as AC-11.

[0104] The carrier used in the catalyst preparation step is AC-11, and the obtained palladium catalyst is recorded as Cat.-14.

[0105] Embodiment A15

[0106] The modified activated carbon AC-4 prepared in Example A5 was placed in a 5wt% thionyl chloride solution (solvent: xylene), treated at 65°C for 3h, then placed in a 5wt% 1,4-butanediamine solution (solvent: xylene), treated at 70°C for 3h, and then dried at 110°C for 6h. The obtained modified activated carbon sample was recorded as AC-12.

[0107] The carrier used in the catalyst preparation step is AC-12, and the obtained palladium catalyst is recorded as Cat.-15.

[0108] Embodiment A16

[0109] The modified activated carbon AC-5 prepared in Example A6 was placed in a 5wt% thionyl chloride solution (solvent: xylene), treated at 65°C for 3h, then placed in a 5wt% 1,4-butanediamine solution (solvent: xylene), treated at 70°C for 3h, and then dried at 110°C for 6h. The obtained modified activated carbon sample was recorded as AC-13.

[0110] The carrier used in the catalyst preparation step is AC-13, and the obtained palladium catalyst is recorded as Cat.-16.

[0111] Embodiment A17

[0112] An untreated activated carbon sample (AC-0) was placed in a 5wt% thionyl chloride solution (solvent: xylene) and treated at 65°C for 3h, then placed in a 5wt% 1,4-butanediamine solution (solvent: xylene) and treated at 70°C for 3h, and then dried at 110°C for 6h. The obtained modified activated carbon sample was recorded as AC-14.

[0113] The carrier used in the catalyst preparation step is AC-14, and the obtained palladium catalyst is recorded as Cat.-17.

[0114] Table 1 Catalyst serial number and composition

[0115]

[0116]

[0117] Catalyst evaluation

[0118] In the present invention, the reaction of preparing CHDA by hydrogenation of PTA is carried out according to the following steps: raw material PTA, product CHDA (solubilization effect) and purified water are put into an autoclave, and PTA is dissolved at high temperature; then the material is transported to a fixed bed reactor by a high temperature pump, and the material undergoes a hydrogenation reaction on a catalyst; after the hydrogenated liquid is separated from the gas and liquid, it enters a crystallization kettle, and is cooled and crystallized to obtain a CHDA solid. The reaction liquid is sampled through a side line. Since PTA and CHDA have very poor solubility in water at room temperature, the reaction liquid is analyzed after being dissolved in a NaOH solution to form a salt, and a liquid chromatography is used for quantitative analysis to calculate the PTA conversion rate and the CHDA yield.

[0119] Specifically: the evaluation was conducted on a fixed bed reactor (gas-liquid-solid three-phase trickle bed reactor) with an inner diameter of 20 mm, with a catalyst loading of 20.0 g. The reaction evaluation conditions were: pressure 9.0 MPa, reaction temperature 195°C, molar ratio of hydrogen to PTA 10.0, and feed mass space velocity of raw PTA 1.3 h -1 (Raw material composition: 3wt% PTA, 30wt% CHDA, the rest is water), the evaluation results are shown in Table 2.

[0120] Table 2 Performance evaluation of different catalysts used in PTA hydrogenation to CHDA

[0121]

[0122]

[0123] Note: trans = trans isomer / (cis isomer + trans isomer)*100%

[0124] Comparing the data of Example B1 and Example B2 to B4, it can be seen that the activated carbon carrier can significantly improve the activity of the palladium carbon catalyst after being treated with nitric acid. The reason is that after the nitric acid treatment, oxygen-containing groups are introduced on the surface of the activated carbon carrier, and the oxygen-containing groups provide "anchoring positions" for the metal palladium particles, and the dispersion of the palladium carbon catalyst is improved. Comparing the data of Example B2 to B4, it can be seen that with the increase of the nitric acid treatment concentration, the PTA conversion rate increases, and when the nitric acid treatment concentration is 5%, the PTA conversion rate tends to be stable.

[0125] From the data of comparative examples B2, B5, and B6, it can be seen that as the nitric acid treatment temperature increases, the PTA conversion first increases and then decreases, and the most suitable treatment temperature is 90° C. The reason may be that when the nitric acid treatment temperature is 80° C., the number of oxygen-containing groups introduced on the surface of the activated carbon carrier is small, and when the nitric acid treatment temperature reaches 98° C., it may have a certain destructive effect on the pores of the activated carbon carrier.

[0126] By comparing the data of Examples B2 and B7, it can be seen that for the sheet-like activated carbon carrier and the columnar activated carbon carrier, the performance of the catalysts prepared after the carriers are treated with nitric acid is equivalent, indicating that this method has a certain universality.

[0127] Comparing the catalytic activity data of comparative examples B2 to B7 with those of examples B8 to B16, it can be seen that after the activated carbon carrier is treated with nitric acid and grafted with organic amine, the catalytic activity is further improved, and the selectivity of the product CHDA is also improved; the reason may be that the organic amine ligand has a stronger coordination ability with the metal palladium precursor. On the other hand, the improvement of CHDA selectivity may be due to the fact that the grafted surface organic amine groups provide alkaline sites for the catalyst, inhibiting the polymerization of hydrogenation intermediate olefins. Comparative examples B8 to B10 data show that the catalyst grafted with 1,4-butanediamine has the best effect, followed by 1,3-propylenediamine, and ethylenediamine has the worst effect, but they are all better than the catalyst without grafted organic amine.

[0128] From the data of comparative examples B10 to B12, it can be seen that when the metal palladium loading is 0.35wt%, the PTA conversion rate is relatively low, at 88.5%. When the metal palladium loading is 0.65wt%, PTA is nearly completely converted and the selectivity is still maintained at 99.7%.

[0129] From the data of Example B10 and Examples B13 and B14, it can be seen that the concentration of nitric acid treatment has a certain influence on the subsequent grafting of organic amines. When the concentration of nitric acid treatment is 2.5wt%, due to the small number of oxygen-containing groups such as carboxyl introduced, the subsequent grafted 1,4-butanediamine is correspondingly small, resulting in a lower dispersion and poorer performance of the prepared catalyst (Example B14). When the concentration of nitric acid treatment is higher, reaching 10%, the CHDA selectivity decreases slightly (Example B13).

[0130] By comparing the data of Example B10 with Examples B15 and B16, it can be seen that the nitric acid treatment temperature has a certain influence on the subsequent organic amine grafting. When the nitric acid treatment temperature is 80°C, the number of carboxyl oxygen-containing groups introduced is small, so the subsequent grafted 1,4-butanediamine is correspondingly small, resulting in a low dispersion and poor performance of the prepared catalyst (Example B15); when the nitric acid treatment temperature is 98°C, it may have a certain destructive effect on the catalyst pore structure, and the catalyst performance deteriorates (Example B16).

[0131] By comparing the data of Examples B10 to B16 and Example B17, it can be seen that for the activated carbon samples that have not been treated with nitric acid, the catalyst effect prepared by directly adsorbing 1,4-butanediamine is poor. The main reason is that the untreated activated carbon and 1,4-butanediamine only have an adsorption effect, and the effect is weak.

[0132] In summary, nitric acid treatment is a necessary step for grafting organic amines onto activated carbon, and the nitric acid treatment conditions have a direct impact on the grafting of organic amines. Under appropriate nitric acid treatment conditions, the pore structure of activated carbon is not destroyed and the amount of organic amine grafted is large, which can ensure that the prepared catalyst has high dispersion and good catalytic activity.

[0133] Optimization of reaction conditions

[0134] Examples C1-C9 used the catalyst Cat.-10 prepared in Example A10 to carry out catalytic reactions. The reaction conditions and catalytic activity of hydrogenating terephthalic acid to prepare 1,4-cyclohexanedicarboxylic acid are detailed in Table 3.

[0135] Table 3 Effect of reaction conditions on the performance of terephthalic acid hydrogenation to 1,4-cyclohexanedicarboxylic acid

[0136]

[0137]

[0138] It should be noted that: 1. Composition of the raw material liquid: 3wt% PTA, 30wt% CHDA, and the rest is water; 2. trans = trans isomer / (cis isomer+trans isomer)*100%.

[0139] From the data in Table 3, it can be seen that the PTA feed space velocity is 1.30h -1 When PTA was nearly completely converted, the CHDA selectivity reached 99.8%, the trans isomer ratio was 69.7%, and the PTA space velocity increased to 1.50h -1 , the PTA conversion rate dropped to 98.5%. The H2 / PTA molar ratio has a great influence on the reaction. When the H2 / PTA molar ratio is 5, the PTA conversion rate is low, only 97.6%. When the H2 / PTA molar ratio is greater than 10.0, the effect on the PTA conversion rate is not significant. Excessive H2 / PTA molar ratio will increase the consumption of hydrogen. Therefore, the H2 / PTA molar ratio of 10.0 is selected. When the reaction temperature is low (185°C), the PTA conversion rate is only 94.7%. When the reaction temperature is high (205°C), although the PTA conversion rate can be further improved, the product CHDA selectivity decreases significantly. Therefore, the reaction temperature of 195°C is selected. When the reaction pressure is low, the PTA conversion rate is low. When the reaction pressure is greater than 9.0MPa, it has little effect on the reaction. The preferred reaction pressure is 9.0MPa.

[0140] Comparison of the experimental data of Examples C1, C6 and C7 shows that, under the same conditions of PTA feed space velocity, H2 / PTA molar ratio and reaction pressure, the trans isomer ratio in the hydrogenated liquid increases with increasing reaction temperature; Comparison of the experimental data of Examples C1, C2 and C3 shows that, under the same conditions of H2 / PTA molar ratio, reaction pressure and reaction temperature, the trans isomer ratio decreases with increasing PTA feed space velocity; Comparison of the experimental data of Examples C1, C8 and C9 shows that, under the same conditions of PTA feed space velocity, H2 / PTA molar ratio and reaction temperature, the trans isomer ratio increases with increasing reaction pressure; Comparison of the experimental data of Examples C1, C4 and C5 shows that, under the same conditions of PTA feed space velocity, reaction temperature and reaction pressure, the trans isomer ratio increases with increasing H2 / PTA molar ratio.

[0141] That is, in the present invention, trans-1,4-cyclohexanedicarboxylic acid in the hydrogenated liquid is positively correlated with the reaction temperature, H2 / PTA molar ratio and reaction pressure, and is negatively correlated with the PTA feed space velocity. In the reaction of preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid under the catalyst provided by the present invention, the yield of trans-1,4-cyclohexanedicarboxylic acid can be adjusted by controlling the preset hydrogenation reaction conditions.

[0142] Catalyst life evaluation

[0143] The long-term life evaluation of the catalyst Cat.-10 prepared in Example A10 was conducted under the following reaction conditions: the evaluation was conducted on a fixed bed reactor (gas-liquid-solid three-phase trickle bed reactor) with an inner diameter of 20 mm, and the catalyst loading was 20.0 g. The reaction evaluation conditions were: pressure 9.0 MPa, reaction temperature 195°C, molar ratio of hydrogen to PTA 10.0, and feed mass space velocity of raw material PTA 1.30 h -1 (Raw material composition: 3wt% PTA, 30wt% CHDA, the rest is water), the evaluation results are shown in Table 4.

[0144] Table 4 Stability test results of Cat.-10 catalyst

[0145] Reaction time / h PTA conversion rate / % CHDA selectivity / % Trans / % 10 99.7 99.8 69.7 100 99.8 99.8 69.8 200 99.6 99.7 69.6 500 99.6 99.5 69.5 1000 99.7 99.6 69.4 1500 99.8 99.6 69.5 2000 99.7 99.8 69.3 2500 99.6 99.8 69.4 3000 99.5 99.6 69.5 3500 99.6 99.7 69.4

[0146] Note: trans = trans isomer / (cis isomer + trans isomer)*100%

[0147] It can be seen from the data in Table 4 that within the 3500h life evaluation period, the PTA conversion rate and CHDA selectivity of the catalyst are basically stable without obvious fluctuations, indicating that the catalyst has good stability. The present invention solves the technical problem of easy deactivation of the existing Pd / C catalyst by modifying the carrier. In the present invention, the good stability of the catalyst is attributed on the one hand to the strong complexing effect of the organic amine grafted on the surface of the activated carbon carrier on the metal Pd particles, and on the other hand to the basic sites introduced by the organic amine on the catalyst surface, which inhibits the coking of the catalyst surface.

[0148] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid, characterized in that: The method comprises the following steps: (1) mixing a reaction raw material of terephthalic acid, a co-solvent of 1,4-cyclohexanedicarboxylic acid, and a reaction solvent of water at a preset temperature to obtain a mixed material, wherein the mass fraction of the terephthalic acid is 1 to 5.0 wt % based on the total weight of the mixed material being 100 wt %; (2) transporting the mixed material to a trickle bed reactor, and subjecting the terephthalic acid in the mixed material to a hydrogenation reaction under a catalyst and preset hydrogenation reaction conditions to prepare a hydrogenated liquid including 1,4-cyclohexanedicarboxylic acid, wherein the preset hydrogenation reaction conditions include: a feed mass space velocity of terephthalic acid of 0.01 to 2.0 h / min; -1 , the molar ratio of hydrogen to terephthalic acid is 5.0 to 80.0, the reaction pressure is 5.0 MPa to 14.0 MPa, and the reaction temperature is 140 to 220° C.; wherein the catalyst comprises a carrier-modified activated carbon and an active component palladium supported on the carrier, and the modified activated carbon is prepared by the following method: The activated carbon is placed in a nitric acid solution for a first treatment to introduce oxygen-containing groups including carboxyl groups on the surface of the activated carbon; The activated carbon treated with nitric acid is placed in a thionyl chloride solution for a second treatment to convert the carboxyl groups into acyl chlorides; placing the activated carbon treated with thionyl chloride in an organic amine solution for a third treatment to graft the amino compound onto the surface of the activated carbon; The activated carbon treated with organic amine is dried to obtain modified activated carbon.

2. The method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid according to claim 1, characterized in that: The conditions of the first treatment include: a treatment temperature of 60 to 95° C. and a treatment time of 0.5 to 8 hours.

3. The method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid according to claim 2, characterized in that: The mass ratio of the activated carbon to the nitric acid solution is 1:(2-10), and the mass percentage concentration of the nitric acid solution is 5-15%.

4. The method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid according to claim 3, characterized in that: The conditions of the second treatment include: a treatment temperature of 50 to 90° C., a treatment time of 0.5 to 4 hours; and a mass percentage concentration of the thionyl chloride solution of 1 to 40%.

5. The method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid according to claim 4, characterized in that: The conditions of the third treatment include: treatment temperature of 50 to 95° C. and treatment time of 0.5 to 4 hours.

6. The method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid according to claim 5, characterized in that: The organic amine is selected from at least one of ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, diethylenetriamine, and tetraethylenepentamine, and the mass percentage concentration of the organic amine solution is 1-20%. Preferably, the organic amine is 1,4-butylenediamine.

7. The method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid according to any one of claims 1 to 6, characterized in that: Based on the total weight of the catalyst being 100%, the theoretical loading amount of the metal palladium in the catalyst is 0.1 to 10%, preferably, the theoretical loading amount of the metal palladium in the catalyst is 0.65 to 1.0%.

8. The method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid according to claim 7, characterized in that: The preparation method of the catalyst comprises: firstly preparing a palladium / modified activated carbon catalyst precursor by an equal volume impregnation method, and then reducing the catalyst precursor with a reducing agent to obtain the catalyst, wherein the reducing agent is hydrogen, and the reduction treatment conditions include: a reduction temperature of 150 to 300° C., preferably 200 to 250° C.; a hydrogen volume space velocity of 50 to 500 h -1 , preferably 100 to 200 hours -1 .

9. The method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid according to claim 1, characterized in that: The preset hydrogenation reaction conditions include: the feed mass space velocity of terephthalic acid is 1.1 to 1.3 h -1 , the molar ratio of hydrogen to terephthalic acid is 10-40, the reaction pressure is 8.5-10.5 MPa, and the reaction temperature is 195-205°C.

10. The method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid according to claim 1 or 9, characterized in that: In step (2), the yield of trans-1,4-cyclohexanedicarboxylic acid in the hydrogenated liquid can be increased by controlling the increase of any one of the reaction temperature, the molar ratio of hydrogen to terephthalic acid and the reaction pressure.

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