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

Abstract

The present invention provides a method and catalyst for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid. The catalyst is Pd / carbon nanospheres, wherein Pd is an active component and carbon nanospheres are a carrier. The catalyst Pd / carbon nanospheres are prepared by the following method: PdCl 2 Dissolved in ammonia to form [Pd(NH 3 ) 4 ]Cl 2 Solution, add ethanol and water, stir for a first preset time at a first preset temperature to obtain a mixed solution; under stirring and at a first preset temperature, first add resorcinol to the mixed solution, then drop the formaldehyde solution, react for a second preset time, and obtain a first reaction liquid; place the first reaction liquid in a hydrothermal reactor for hydrothermal treatment to obtain a second reaction liquid; filter and calcine the second reaction liquid under an inert atmosphere to obtain a Pd / carbon nanosphere catalyst. The Pd / carbon nanosphere catalyst provided by the present invention has the advantages of acid resistance and anti-agglomeration, and is applied to the continuous hydrogenation of terephthalic acid to prepare 1,4-cyclohexanedicarboxylic acid, and has good stability.

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 produced by hydrogenation of terephthalic acid (PTA). US Patent US6291706 uses Pd / C catalyst, and the catalyst is placed in the basket of an autoclave. First, a 5% aqueous solution of PTA is stirred continuously at 200°C and 4.5 MPa for 45 minutes, and then the solution is contacted with the catalyst 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 / H in an autoclave reactor. 2 O as raw material, using Pd-Ba / C catalyst, reacting at 170℃, 5.0 MPa for 1 hour, CHDA yield reached 96.4%. Other patents also proposed using relatively low-priced Ru as active component, and using Ru / C on activated carbon carrier for this reaction, such as US Pat. No. 3027398 and US Pat. No. 4654064 reported this reaction; however, the activity and selectivity of Ru / C catalyst for this reaction were poor.

[0004] Since both the raw material PTA and the product CHDA are acidic, especially at high temperatures, the corrosion of PTA and CHDA to metals is more serious, which will cause the loss of metal Pd in ​​the Pd / C catalyst and the agglomeration of metal Pd, which is an important reason for the deactivation of the catalyst for preparing CHDA by hydrogenation of PTA. The loss of metal Pd not only shortens the service life of the catalyst, but also the residual metal ions will contaminate the final product. Summary of the invention

[0005] The present invention aims to provide an acid-resistant and anti-agglomeration palladium carbon catalyst Pd / carbon nanospheres prepared by hydrothermal reaction, which is applied to the preparation of 1,4-cyclohexanedicarboxylic acid by hydrogenation of terephthalic acid, and has the advantages of high catalytic activity and good stability.

[0006] In order to achieve the above object, the present invention provides a catalyst for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid, wherein the catalyst is Pd / carbon nanospheres, wherein Pd is an active component and carbon nanospheres are a carrier, and the catalyst Pd / carbon nanospheres are prepared by the following method:

[0007] PdCl 2 Dissolved in ammonia to form [Pd(NH 3 ) 4 ]Cl 2 solution, then adding ethanol and water, stirring at a first preset temperature for a first preset time to obtain a mixed solution, wherein PdCl 2 The mass ratio with ethanol is 1:(50~300);

[0008] Under stirring and at the first preset temperature, resorcinol is first added to the mixed solution, and then the formaldehyde solution is dropped into the mixed solution. After reacting for a second preset time, a first reaction liquid is obtained, wherein PdCl 2 The mass ratio of resorcinol is 1:(62.5~625), and the molar ratio of resorcinol to formaldehyde is 1:(0.95~1.1);

[0009] placing the first reaction liquid in a hydrothermal reactor for hydrothermal treatment to obtain a second reaction liquid;

[0010] The second reaction liquid is filtered and calcined under an inert atmosphere to obtain the Pd / carbon nanospheres.

[0011] In a specific embodiment, based on the total weight of the Pd / carbon nanospheres being 100 wt %, the Pd content in the Pd / carbon nanospheres is 0.1-1.0 wt %.

[0012] In a specific implementation, the first preset temperature is 30-80° C., and the first preset time is 1 h-4 h.

[0013] In a specific implementation, the second preset time is 20h~30h.

[0014] In a specific embodiment, the conditions of the hydrothermal treatment include: the hydrothermal treatment temperature is 100-180° C., and the hydrothermal treatment time is 6 h to 24 h.

[0015] In a specific embodiment, the inert atmosphere is a nitrogen atmosphere, and the calcination treatment conditions include: a calcination temperature of 300-700° C., and a calcination time of 1 h to 8 h.

[0016] The present invention also provides a method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid, the method comprising the following steps:

[0017] (1) mixing terephthalic acid, a reaction raw material, 1,4-cyclohexanedicarboxylic acid, a co-solvent, and water, a reaction solvent, at a second preset temperature to obtain a mixed material, wherein the mass fraction of the terephthalic acid is 1 to 10.0% based on the total weight of the mixed material being 100 wt%;

[0018] (2) The mixed material is transported to a fixed bed reactor, and the terephthalic acid in the mixed material is subjected to a hydrogenation reaction under a catalyst and preset hydrogenation reaction conditions to prepare 1,4-cyclohexanedicarboxylic acid, wherein the catalyst is the catalyst according to any one of claims 1 to 6, and the preset hydrogenation reaction conditions include: a hydrogen pressure of 4.0 MPa to 12.0 MPa, and a reaction temperature of 130 to 250°C.

[0019] In a specific embodiment, in step (2), the feed mass space velocity of terephthalic acid in the mixed material is 0.1h -1 ~1.0 h -1 , and the molar ratio of hydrogen to terephthalic acid is (10~60):1.

[0020] In a specific embodiment, in step (1), the second preset temperature is 150-200°C.

[0021] In a specific embodiment, in step (1), based on the total weight of the mixed material being 100 wt%, the mass fraction of the 1,4-cyclohexanedicarboxylic acid is 20 wt%, and the mass fraction of the terephthalic acid is 1-2 wt%.

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

[0023] 1. The catalyst Pd / carbon nanospheres provided by the present invention are composed of an active component Pd and a carrier carbon nanosphere. They are prepared by hydrothermal reaction and have the advantages of acid resistance and anti-agglomeration. When they are applied to the hydrogenation of terephthalic acid to prepare 1,4-cyclohexanedicarboxylic acid, they have the advantages of high catalytic activity (high conversion rate, high selectivity) and good stability (no deactivation for 2000 hours).

[0024] 2. When the catalyst Pd / carbon nanospheres provided by the present invention are used for hydrogenation of terephthalic acid to prepare 1,4-cyclohexanedicarboxylic acid, a fixed bed reactor can be used as the reaction site to achieve continuous hydrogenation reaction. Compared with the prior art of hydrogenation reaction in a reactor, the continuous hydrogenation process has greatly improved production capacity and correspondingly greatly reduced production costs, and has broader application prospects. DETAILED DESCRIPTION

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

[0026] Aiming at the technical problems that the catalyst used for preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid is not resistant to corrosion and is easy to agglomerate, resulting in easy deactivation of the catalyst, the present invention provides a catalyst Pd / carbon nanospheres prepared by hydrothermal reaction. The catalyst consists of an active component Pd and a carrier carbon nanosphere. When the catalyst is used for preparing 1,4-cyclohexanedicarboxylic acid by hydrogenating terephthalic acid, a fixed bed reactor can be used as a reaction site to achieve continuous hydrogenation reaction. The catalyst also has the advantages of acid resistance and anti-agglomeration, and is not deactivated after 2000 hours of reaction.

[0027] The catalyst Pd / carbon nanospheres provided by the present invention, wherein Pd is an active component and carbon nanospheres are a carrier, is prepared by the following method:

[0028] Step 1: PdCl 2 Dissolved in ammonia to form [Pd(NH 3 ) 4 ]Cl 2 solution, adding ethanol and water, and stirring at a first preset temperature for a first preset time to obtain a mixed solution.

[0029] Preferably, PdCl 2 The mass ratio of sodium iodide to ethanol is 1:(50~300).

[0030] In the present invention, [Pd(NH 3 ) 4 ]Cl 2 PdCl in solution 2 The mass fraction is 13~15wt%.

[0031] Preferably, the first preset temperature is 30-80° C., and the first preset time is 1 h-4 h.

[0032] More preferably, the first preset temperature is 30-40°C.

[0033] That is, step one is: PdCl 2 Dissolved in ammonia to form [Pd(NH 3 ) 4 ]Cl 2 solution, add ethanol and water, stir at 30~80℃ for 1h~4h to obtain a mixed solution, in which PdCl 2 The mass ratio of [Pd(NH 3 ) 4 ]Cl 2 PdCl in solution 2 The mass fraction is 13~15wt%.

[0034] Step 2: under stirring and at the first preset temperature, first add resorcinol to the mixed solution, then drop the formaldehyde solution into it, and react for a second preset time to obtain a first reaction liquid.

[0035] Preferably, PdCl 2 The mass ratio of resorcinol to formaldehyde is 1:(62.5~625), and the molar ratio of resorcinol to formaldehyde is 1:(0.95~1.1).

[0036] In the present invention, the mass fraction of the formaldehyde solution is 38%.

[0037] Preferably, the second preset time is 20h~30h, more preferably, the second preset time is 24h~26h.

[0038] That is, step 2 is: under stirring at 30-80°C, resorcinol is first added to the mixed solution, and then formaldehyde solution is added dropwise, and after reacting for 20h-30h, a first reaction liquid is obtained, wherein PdCl 2 The mass ratio of resorcinol to formaldehyde is 1:(62.5~625), and the molar ratio of resorcinol to formaldehyde is 1:(0.95~1.1).

[0039] Step three: placing the first reaction liquid in a hydrothermal reactor for hydrothermal treatment to obtain a second reaction liquid.

[0040] Preferably, the conditions of the hydrothermal treatment include: a hydrothermal treatment temperature of 100-180° C., and a hydrothermal treatment time of 6 h to 24 h.

[0041] More preferably, the conditions of the hydrothermal treatment include: the hydrothermal treatment temperature is 120-140° C., and the hydrothermal treatment time is 10 h to 12 h.

[0042] Step 4: filtering the second reaction liquid and calcining it under an inert atmosphere to obtain the Pd / carbon nanosphere catalyst.

[0043] Preferably, the inert atmosphere is a nitrogen atmosphere, and the calcination treatment conditions include: a calcination temperature of 300-700° C., and a calcination time of 1-8 h.

[0044] More preferably, the calcination treatment conditions include: a calcination temperature of 400-500° C. and a calcination time of 5-8 hours.

[0045] Preferably, based on the total weight of the Pd / carbon nanospheres as 100wt%, the mass content of Pd in ​​the Pd / carbon nanospheres is 0.1-1.0wt%, and more preferably, the mass content of Pd in ​​the Pd / carbon nanospheres is 0.15-0.25wt%.

[0046] The present invention also provides a method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid, the method comprising the following steps:

[0047] (1) The reaction raw material terephthalic acid, the co-solvent 1,4-cyclohexanedicarboxylic acid and the reaction solvent water are mixed at a second preset temperature to obtain a mixed material.

[0048] Preferably, based on the total weight of the mixed material as 100wt%, the mass fraction of the 1,4-cyclohexanedicarboxylic acid is 20wt%, and the mass fraction of the terephthalic acid is 1-10.0wt%. More preferably, the mass fraction of the 1,4-cyclohexanedicarboxylic acid is 20wt%, and the mass fraction of the terephthalic acid is 1-2wt%.

[0049] Preferably, the second preset temperature is 150°C to 200°C.

[0050] (2) The mixed material is transported to a fixed bed reactor, and the terephthalic acid in the mixed material is hydrogenated to prepare 1,4-cyclohexanedicarboxylic acid under a catalyst and preset hydrogenation reaction conditions, wherein the catalyst is the Pd / carbon nanosphere catalyst described above, and the preset hydrogenation reaction conditions include: a hydrogen pressure of 4.0 MPa to 12.0 MPa, and a reaction temperature of 130 to 250°C.

[0051] Preferably, the feed mass space velocity of terephthalic acid in the mixed material is 0.1-1.0 h -1 , and the molar ratio of hydrogen to terephthalic acid is (10~60):1.

[0052] Preferably, the preset hydrogenation reaction conditions include: hydrogen pressure of 6.0 MPa to 8.0 MPa, and reaction temperature of 160 to 180°C.

[0053] Example 1 to Example 8 Preparation of Catalyst Pd / Carbon Nanospheres

[0054] Example 1

[0055] Step 1: 0.084 g PdCl 2 Dissolve in 0.5 g of ammonia water to form [Pd(NH 3 ) 4 ]Cl 2 The solution was added with 30 g of water and 24.0 g of ethanol and stirred at 30 °C for 1 h to obtain a mixed solution.

[0056] Step 2: Under stirring at a temperature of 30° C., first add 17.86 g of resorcinol to the mixed solution, then drop 12.79 g of formaldehyde solution (formaldehyde mass percentage 38 wt %, formaldehyde 4.86 g), and stir for 24 h to obtain a first reaction liquid.

[0057] Step 3: Transfer all the first reaction liquid to a hydrothermal reactor, and heat-treat it at 120° C. (hydrothermal reaction temperature) for 12 h (hydrothermal reaction time) to obtain a second reaction liquid.

[0058] Step 4: Filter the second reaction liquid, and calcine the obtained solid at 400°C for 6 h in a tubular furnace under a nitrogen atmosphere to obtain Pd / carbon nanospheres, wherein the mass content of Pd in ​​the Pd / carbon nanospheres is 0.25wt%, recorded as 0.25 wt%Pd / carbon nanospheres-120°C@400°C.

[0059] It should be noted that, in 0.25 wt% Pd / carbon nanospheres-120°C@400°C, 0.25 wt% represents the mass content of Pd, 120°C represents the hydrothermal reaction temperature, and 400°C represents the calcination temperature.

[0060] Example 2

[0061] Example 2 is the same as Example 1, except that PdCl is added in step 1. 2 The added mass was 0.05 g, and the Pd mass content in the obtained catalyst Pd / carbon nanospheres was 0.15 wt%, recorded as 0.15 wt% Pd / carbon nanospheres-120°C@400°C.

[0062] Example 3

[0063] Example 3 is the same as Example 1, except that PdCl is added in step 1. 2 The added mass was 0.118 g, and the Pd mass content in the obtained catalyst Pd / SC was 0.35 wt%, recorded as 0.35 wt% Pd / carbon nanospheres-120°C@400°C.

[0064] Example 4

[0065] Example 4 is the same as Example 1, except that the insulation temperature (hydrothermal reaction temperature) in step 3 is different. In Example 1, the insulation is carried out at 120°C, and in Example 4, the insulation is carried out at 100°C. The obtained Pd / carbon nanosphere catalyst is recorded as 0.25%wtPd / carbon nanosphere-100°C@400°C.

[0066] Example 5

[0067] Example 5 is the same as Example 1, except that the insulation temperature (hydrothermal reaction temperature) in step 3 is different. In Example 1, the insulation is carried out at 120°C, and in Example 5, the insulation is carried out at 140°C. The obtained Pd / carbon nanosphere catalyst is recorded as 0.25%wtPd / carbon nanosphere-140°C@400°C.

[0068] Example 6

[0069] Example 6 is the same as Example 1, except that the calcination temperature in step 4 is different. In Example 1, the calcination is carried out at 400°C, and in Example 6, the calcination is carried out at 300°C. The obtained Pd / carbon nanosphere catalyst is recorded as 0.25 wt% Pd / carbon nanosphere-120°C@300°C.

[0070] Example 7

[0071] Example 7 is the same as Example 1, except that the calcination temperature in step 4 is different. In Example 1, the calcination is carried out at 400°C, and in Example 7, the calcination is carried out at 500°C. The obtained Pd / carbon nanosphere catalyst is recorded as 0.25 wt% Pd / carbon nanosphere-120°C@500°C.

[0072] Example 8

[0073] Example 6 is the same as Example 1, except that the calcination temperature in step 4 is different. In Example 1, the calcination is carried out at 400°C, and in Example 6, the calcination is carried out at 600°C. The obtained Pd / carbon nanosphere catalyst is recorded as 0.25wt%Pd / carbon nanosphere-120°C@600°C.

[0074] Catalyst evaluation

[0075] Continuous hydrogenation of terephthalic acid to produce 1,4-cyclohexanedicarboxylic acid

[0076] The catalysts prepared in Examples 1 to 8 were evaluated in a fixed bed reactor with an inner diameter of 13 mm, and the catalyst loading amount was 10.0 g.

[0077] The parameters of the fixed bed reactor are as follows: the reaction tube is a quartz tube with an inner diameter of 13 mm and a length of 60 cm.

[0078] The reaction evaluation conditions include: hydrogen pressure 6.0 MPa, reaction temperature 170°C, hydrogen to PTA molar ratio 15.0, raw material PTA feed mass space velocity 0.8h -1 (Mixed raw material composition: 2wt% PTA, 20wt% CHDA, and the rest is water).

[0079] The process of preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid is as follows: first, raw material terephthalic acid PTA, auxiliary solvent 1,4-cyclohexanedicarboxylic acid CHDA and reaction solvent purified water are added into an autoclave, and then PTA is stirred and dissolved at 180°C to obtain a mixed material; then the mixed material in the autoclave is transported to a fixed bed reactor by a high-temperature pump, and the PTA in the mixed material undergoes a hydrogenation reaction on the catalyst; after the hydrogenated liquid is separated from the gas and liquid, it enters a crystallization kettle, and is cooled and crystallized to obtain CHDA solid.

[0080] Since PTA and CHDA have very poor solubility in water at room temperature, the reaction solution was sampled through the side line and analyzed after being dissolved in NaOH solution to form salts. Liquid chromatography was used for quantitative analysis to calculate the PTA conversion rate and CHDA yield. The results of terephthalic acid hydrogenation catalyzed by different catalysts are shown in Table 1.

[0081] Table 1 Results of terephthalic acid hydrogenation catalyzed by the catalysts prepared in Examples 1 to 8 and commercially purchased catalysts

[0082]

[0083] It should be noted that when evaluating the catalyst, the loading amount of the catalyst in Example 2 was 16.67 g, and the loading amount of the catalyst in Example 3 was 7.14 g, to ensure that the total amount of metal Pd was the same.

[0084] It is understandable that, in order to ensure the same total amount of metal Pd when evaluating the catalyst, except for Example 2 and Example 3, the loading amounts of the other examples are all 10 g.

[0085] It should be noted that the commercial catalyst was purchased from Kangna New Materials (Hangzhou) Co., Ltd.

[0086] Comparing the experimental results of Examples 1 to 3, it can be seen that the mass content of the active component Pd is in the range of 0.15% to 0.35%, and the PTA conversion rate and CHDA selectivity are not much different. When the mass content of Pd is 0.25%, the PTA conversion rate is the highest and the CHDA selectivity is the highest. Comparing the experimental results of Examples 1, 4 and 5, it can be seen that the hydrothermal treatment temperature has a certain effect on the catalyst performance. When the hydrothermal treatment temperature is 120°C, the catalyst performance is the best, the raw material PTA conversion rate reaches 99.8%, and the CHDA selectivity is 99.6%. Comparing the experimental results of Examples 1, 6 and 8, it can be seen that the calcination temperature has a great influence on the catalyst performance. When the calcination temperature is low (300°C), the PTA conversion rate is only 88.5%. The possible reason is that there are more chloride ions remaining on the catalyst, and the catalyst calcination temperature is too high, and the catalyst activity shows a downward trend. The possible reason is that the metal Pd particles are partially agglomerated at high temperature. The optimal calcination temperature is 400°C. Comparing the experimental results of Example 1 and Comparative Example 1, it can be seen that the activity and selectivity of the catalyst Pd / carbon nanospheres are better than those of the commercial catalyst Pd / C.

[0087] Catalyst life evaluation

[0088] The catalyst 0.25% Pd / carbon nanospheres-120℃@400℃ prepared in Example 1 and the commercially purchased catalyst 0.25wt% Pd / C were evaluated for long-term life, wherein the catalyst loading was 10.0 g. The reaction evaluation conditions included: pressure 6.0 MPa, reaction temperature 170℃, molar ratio of hydrogen to PTA 15.0, raw material PTA feed mass space velocity 0.8h -1 (Raw material composition: 2 wt% PTA, 20 wt% CHDA, the remainder is water.) The catalyst life evaluation results are shown in Tables 2 and 3.

[0089] Table 2 Stability test results of the catalyst prepared in Example 1

[0090]

[0091] Table 3 Stability test results of commercially purchased 0.25% Pd / C catalyst

[0092]

[0093] Comparing the data in Table 2 and Table 3, it can be seen that the 0.25wt% Pd / carbon nanosphere-120℃@400℃ catalyst prepared in Example 1 has basically stable catalyst activity and selectivity within the 2000h life evaluation period without obvious fluctuations; while for the commercially purchased 0.25wt% Pd / C catalyst, the catalyst is obviously deactivated after 500h. This shows that the catalyst Pd / carbon nanosphere provided by the present invention has good stability and solves the technical problem of easy deactivation of the catalyst in the prior art.

[0094] 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 the reaction raw material terephthalic acid, the co-solvent 1,4-cyclohexanedicarboxylic acid and the reaction solvent water at 150-200° C. to obtain a mixed material, wherein the mass fraction of the terephthalic acid is 1-10.0wt% based on the total weight of the mixed material being 100wt%; 2) transporting the mixed material to a fixed 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 1,4-cyclohexanedicarboxylic acid, wherein the catalyst is acid-resistant and anti-agglomeration Pd / carbon nanospheres, and the mass content of Pd in ​​the Pd / carbon nanospheres is 0.15-0.25wt% based on the total weight of the Pd / carbon nanospheres as 100wt%, and the feed mass space velocity of the terephthalic acid in the mixed material is 0.1-1.0h -1 , and the molar ratio of hydrogen to terephthalic acid is 10-60:1, the preset hydrogenation reaction conditions include: hydrogen pressure of 4.0-12.0 MPa, reaction temperature of 130-250°C, wherein the Pd / carbon nanospheres, Pd is the active component, carbon nanospheres are the carrier, and are prepared by the following method: PdCl2 is dissolved in ammonia water to form a [Pd(NH3)4]Cl2 solution, and then ethanol and water are added, and stirred at 30-80°C for 1-4 hours to obtain a mixed solution, wherein the mass ratio of PdCl2 to ethanol is 1:50-300; under stirring at 30-80°C, resorcinol is first added to the mixed solution, and then formaldehyde solution is dropped into it, and after reacting for 20-30 hours, a first reaction liquid is obtained, wherein the mass ratio of PdCl2 to resorcinol is 1:62.5-625 , the molar ratio of resorcinol to formaldehyde is 1:0.95~1.1; placing the first reaction liquid in a hydrothermal reactor for hydrothermal treatment to obtain a second reaction liquid; the hydrothermal treatment temperature is 100~140°C, and the hydrothermal treatment time is 6~24h; filtering the second reaction liquid and calcining it under an inert atmosphere to obtain the Pd / carbon nanospheres, wherein the inert atmosphere is a nitrogen atmosphere, and the calcination treatment conditions include: a calcination temperature of 400~500°C, and a calcination time of 1~8 h.

2. The method for preparing 1,4-cyclohexanedicarboxylic acid by continuous hydrogenation of terephthalic acid according to claim 1, characterized in that: In step 1), based on the total weight of the mixed material being 100 wt%, the mass fraction of the 1,4-cyclohexanedicarboxylic acid is 20 wt%, and the mass fraction of the terephthalic acid is 1-2 wt%.

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