A method for preparing dimethyl 1,4-cyclohexanedicarboxylate

Abstract

This invention pertains to the preparation method of chemical intermediates, specifically relating to a method for preparing dimethyl 1,4-cyclohexanedicarboxylate. Under the catalysis of a ruthenium monometallic catalyst supported on cerium dioxide, dimethyl terephthalate undergoes a hydrogenation reaction in a solvent in a hydrogen atmosphere to obtain the aforementioned dimethyl 1,4-cyclohexanedicarboxylate. The reaction formula is shown below. This invention discloses a method for preparing dimethyl 1,4-cyclohexanedicarboxylate by hydrogenation of dimethyl terephthalate, comprising the following steps: Under the catalysis of a ruthenium-containing catalyst supported on cerium dioxide, dimethyl terephthalate undergoes a hydrogenation reaction in a solvent in a hydrogen atmosphere. After the reaction is complete, only the catalyst needs to be filtered off, and the solvent concentrated to obtain high-purity dimethyl 1,4-cyclohexanedicarboxylate. The operation is simple.

Description

Technical Field

[0001] This invention pertains to methods for preparing chemical intermediates, specifically relating to a method for preparing dimethyl 1,4-cyclohexanedicarboxylate. Background Technology

[0002] Dimethyl 1,4-cyclohexanedicarboxylate (DMCD) has received widespread attention both domestically and internationally in the field of chemical raw materials and intermediates. It plays a crucial role not only in the production of polyester resins but can also be converted to 1,4-cyclohexanediethanol (CHDM) through hydrogenation, which is then widely used in the manufacture of high-performance polyesters and copolyesters, such as PETG, Spectar copolyesters, PCT, and PCTA. Global demand for DMCD and CHDM is steadily increasing. However, traditional DMCD production technologies rely on benzene produced from petroleum cracking and require a series of complex reaction steps. Therefore, producing DMCD by hydrogenating dimethyl terephthalate (DMT) obtained from the alcoholysis of waste polyester PET, and further hydrogenating the ester groups of DMCD to CHDM, not only reduces dependence on fossil fuels but also has significant implications for energy conservation, emission reduction, and environmental protection.

[0003] Currently, catalysts used in the hydrogenation reaction of DMT are mainly classified into four categories: palladium-based catalysts, ruthenium-based catalysts, palladium-ruthenium bimetallic composite catalysts, and nickel-based non-precious metal catalysts. Palladium-based catalysts are renowned for their excellent catalytic activity, but they require high reaction pressures and temperatures, and their large-scale application is expensive due to the high price of palladium. Compared to palladium-based catalysts, ruthenium-based catalysts are more economical in terms of cost and maintain high catalytic activity even at lower temperatures and pressures. However, in practical applications, the selectivity of ruthenium-based catalysts is generally lower than that of palladium-based catalysts. Bimetallic composite catalysts, due to the synergistic effect between the metals, can significantly enhance catalytic activity, showing unique advantages for the hydrogenation of DMT to DMCD and demonstrating potential for industrial application. However, these catalysts currently face challenges including high consumption of precious metals, complex preparation processes, and high costs, which limit their industrial application. Nickel-based catalysts, as a non-precious metal catalyst, are favored due to their low price and stable chemical properties. They not only maintain high catalytic activity and selectivity, but can also be carried out under milder reaction conditions, which is beneficial for the industrial production of DMCD by hydrogenation of DMT. However, the selectivity of nickel-based catalysts for DMCD still needs to be improved.

[0004] In summary, traditional DMT hydrogenation catalysts have drawbacks such as low selectivity, high cost, and harsh reaction conditions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing dimethyl 1,4-cyclohexanedicarboxylate. Under the catalysis of a ruthenium monometallic catalyst supported on cerium dioxide, dimethyl p-toluenedicarboxylate undergoes a hydrogenation reaction in a solvent to obtain the aforementioned dimethyl 1,4-cyclohexanedicarboxylate. The reaction formula is shown below:

[0006]

[0007] The operating steps are as follows: add a certain amount of dimethyl terephthalate and catalyst to the high-pressure reactor, add an appropriate amount of solvent, purge with hydrogen gas at a certain pressure, and react at a specific temperature for a certain time.

[0008] The solvent used is a C1-C4 alkyl alcohol or ester catalyst. Isopropanol or ethyl acetate are preferred.

[0009] Based on the mass ratio of dimethyl terephthalate, the catalyst dosage is 2wt%–20wt%, and the solvent dosage is 5–20w / w. Preferably, based on the mass ratio of dimethyl terephthalate, the catalyst dosage is 5wt%–10wt%, and the solvent dosage is 8–12w / w.

[0010] The reaction temperature is 100–180℃, the hydrogen pressure is 2 MPa–8 MPa, and the reaction time is 0.5 h–6 h. Preferably, the reaction temperature is 140–160℃, the hydrogen pressure is 4 MPa–6 MPa, and the reaction time is 2 h–4 h.

[0011] In the ruthenium monometallic catalyst supported on cerium dioxide, the ruthenium loading is 0.1% to 5 wt%, and the cerium dioxide support contains three different nanostructures: nanoparticles, nanorods, and nanocubes.

[0012] The present invention also provides a cerium dioxide-supported ruthenium monometallic catalyst and its preparation method. The catalyst was first applied to the hydrogenation reaction of dimethyl terephthalate (DMT) to prepare dimethyl 1,4-cyclohexanedicarboxylate (DMCD), and showed excellent catalytic performance. Moreover, the catalytic performance did not change significantly after multiple cycles.

[0013] A ruthenium monometallic catalyst supported on cerium dioxide, wherein the ruthenium loading in the cerium dioxide supported ruthenium monometallic catalyst is 0.1% to 5 wt%, and the cerium dioxide support comprises three different nanostructures: nanoparticles, nanorods, and nanocubes.

[0014] The preparation method of the cerium dioxide-supported ruthenium monometallic catalyst of the present invention is as follows: (I) A certain amount of cerium nitrate hexahydrate is dissolved in deionized water to obtain solution a, and a certain amount of sodium hydroxide is dissolved in deionized water to obtain solution b. Solution a is added dropwise to solution b at room temperature and stirred for 2 hours. The solution is then transferred to a reaction vessel and hydrothermally reacted at 120°C for 24 hours. The product is washed with deionized water and filtered until the pH is 7. It is then dried at 100°C overnight and placed in a muffle furnace. The temperature is increased to 500°C at a heating rate of 2.5°C / min and held for 5 hours to obtain cerium dioxide supports with three different nanostructures: nanoparticles, nanorods, and nanocubes. (II) A certain amount of ruthenium trichloride is dissolved in deionized water and impregnated into the three different nanostructures of cerium dioxide supports using an equal-volume impregnation method. The mixture is stirred for 4 hours, sonicated for 30 minutes, dried at 100°C overnight, and placed in a muffle furnace. The temperature is increased to 550°C at a heating rate of 5°C / min and held for 5 hours to obtain the target catalyst.

[0015] The cerium dioxide carrier in the above method comprises three different nanostructures: nanoparticles, nanorods, and nanocubes.

[0016] The ruthenium loading (relative to the support) in the cerium dioxide-supported ruthenium monometallic catalyst prepared by the above method is 0.1 wt% to 5 wt%.

[0017] The cerium dioxide-supported ruthenium monometallic catalyst prepared by the above method was applied to the hydrogenation of dimethyl terephthalate (DMT) to prepare dimethyl 1,4-cyclohexanedicarboxylate (DMCD). The specific reaction conditions were as follows: a certain amount of dimethyl terephthalate and catalyst were added to a high-pressure reactor, along with an appropriate amount of isopropanol or ethyl acetate as a solvent. Hydrogen gas was introduced at a certain pressure, and the reaction was carried out at a specific temperature for a certain time. After the reaction was completed, the catalyst was separated by centrifugation, and the reaction solution was quantitatively analyzed by gas chromatography and area normalization.

[0018] The above reaction temperature is 120–180℃, the reaction pressure is 2–8 MPa, and the reaction time is [missing information].

[0019] 0.5 to 5 hours.

[0020] The catalyst used in the above method is 2wt% to 20wt%, preferably 5wt% to 10wt%.

[0021] The solvent used in the above method is 5-20 w / w, preferably 8-12 w / w.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (a) The catalyst support of the present invention is cerium dioxide. Cerium dioxide is an excellent support for ruthenium, mainly because it has the redox ability of Ce3+ / Ce4+, oxygen storage capacity and abundant oxygen vacancies, which can increase the electron density of the surface active component ruthenium, which is beneficial to improve the dispersibility of the active component ruthenium, promote the adsorption and activation of hydrogen, and have a synergistic promoting effect on ruthenium catalytic hydrogenation, thereby improving the reaction selectivity.

[0024] (b) The catalyst of the present invention has a simple preparation process, a short cycle, good catalytic performance, and is easy to prepare in large quantities. Under optimal reaction conditions, the DMT conversion rate can reach more than 99%, and the DMCD selectivity can reach about 99%.

[0025] (c) This catalyst is used to prepare DMCD by hydrogenation of DMT. The reaction conditions are mild. After the reaction is completed, the catalyst can be simply filtered off and the solvent can be concentrated to obtain a high-purity product. The operation is simple.

[0026] This invention discloses a method for preparing dimethyl 1,4-cyclohexanedicarboxylate by hydrogenation of dimethyl terephthalate, comprising the following steps: under the catalysis of a ruthenium-containing catalyst supported on cerium dioxide, dimethyl terephthalate undergoes a hydrogenation reaction in a solvent in a hydrogen atmosphere. After the reaction is complete, only the catalyst needs to be filtered off, and the solvent is concentrated to obtain high-purity dimethyl 1,4-cyclohexanedicarboxylate. The operation is simple.

[0027] This invention prepared cerium dioxide with three different nanostructures—nanoparticles, nanorods, and nanocubes—as supports, and used an equal-volume impregnation method to prepare single-metal ruthenium catalysts with loadings ranging from 0.1 wt% to 5 wt%. Due to the redox capacity, oxygen storage capacity, and abundant oxygen vacancies of Ce3+ / Ce4+, the electron density of the surface-active component ruthenium can be increased, which is beneficial for improving the dispersibility of the active component ruthenium, promoting hydrogen adsorption and activation, and exhibiting a synergistic effect with metallic ruthenium in catalytic hydrogenation, demonstrating excellent catalytic performance. This invention is the first to apply this catalyst to the hydrogenation of dimethyl terephthalate to dimethyl 1,4-cyclohexanedicarboxylate. Under optimal conditions, the conversion rate and selectivity both reached over 99%, and the post-treatment is simple. The catalyst can be recycled, has a long service life, and shows no significant deactivation after multiple reuses, indicating good prospects for industrial production. Detailed Implementation

[0028] The present invention will be further explained and illustrated below with reference to the following embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention, which is not limited thereto.

[0029] It is worth noting that after centrifugation, the filtrate of the prepared solid catalyst was diluted with isopropanol and analyzed by gas chromatography. The conversion rate and selectivity were quantified using the normalization method. The chromatographic analysis conditions were as follows: FuLi gas chromatograph (model FuLi9790Ⅱ), capillary column (model RB-5, 30m×0.25mm×0.25μm), flame ionization detector (FID); nitrogen was used as the carrier gas, the injection port temperature was 280℃, the detector temperature was 280℃, and the column temperature was programmed. The conversion rate of dimethyl terephthalate and the selectivity of dimethyl 1,4-cyclohexanedicarboxylate were calculated using the following formulas:

[0030]

[0031] Example 1:

[0032] 6.9674 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 19.2081 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The mixture was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanorods. 0.1063 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 0.5000 g of cerium dioxide nanorods using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0033] The target catalyst prepared according to Example 1 above was applied to the reaction of hydrogenating dimethyl terephthalate (DMT) to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0029 g of dimethyl terephthalate, 0.1005 g of catalyst, and 4.0000 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged three times with 1.0 MPa hydrogen gas, followed by 5.0 MPa hydrogen gas, and reacted at 160 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 99.86%, and the selectivity for dimethyl 1,4-cyclohexanedicarboxylate was 99.44%.

[0034] Example 2:

[0035] 6.9674 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 19.2081 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The mixture was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanorods. 0.1063 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 0.5000 g of cerium dioxide nanorods using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0036] The target catalyst prepared according to Example 2 above was applied to the reaction of hydrogenating dimethyl terephthalate (DMT) to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0069 g of dimethyl terephthalate, 0.1018 g of catalyst, and 4.0000 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged three times with 1.0 MPa hydrogen gas, followed by 5.0 MPa hydrogen gas, and reacted at 150 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 100%, and the selectivity for dimethyl 1,4-cyclohexanedicarboxylate was 99.96%.

[0037] Example 3:

[0038] 6.9674 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 19.2081 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The mixture was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanorods. 0.0409 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 0.6014 g of cerium dioxide nanorods using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0039] The target catalyst prepared according to Example 3 above was applied to the reaction of hydrogenating dimethyl terephthalate (DMT) to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0038 g of dimethyl terephthalate, 0.1007 g of catalyst, and 4.0051 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged three times with 1.0 MPa hydrogen gas, followed by 5.0 MPa hydrogen gas, and reacted at 160 °C for 1 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 95.41%, and the selectivity for dimethyl 1,4-cyclohexanedicarboxylate was 99.24%.

[0040] Example 4:

[0041] 6.9674 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 19.2081 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The mixture was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanorods. 0.0409 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 0.6014 g of cerium dioxide nanorods using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0042] The target catalyst prepared according to Example 4 above was applied to the reaction of hydrogenating dimethyl terephthalate (DMT) to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0033 g of dimethyl terephthalate, 0.1014 g of catalyst, and 4.0015 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged three times with 1.0 MPa hydrogen gas, followed by 6.0 MPa hydrogen gas, and reacted at 160 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 99.59%, and the selectivity for dimethyl 1,4-cyclohexanedicarboxylate was 99.10%.

[0043] Example 5:

[0044] 6.9624 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 1.6143 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The mixture was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanoparticles. 0.1080 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 0.5083 g of cerium dioxide nanoparticles using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0045] The target catalyst prepared according to Example 5 above was applied to the reaction of hydrogenating dimethyl terephthalate (DMT) to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0011 g of dimethyl terephthalate, 0.1003 g of catalyst, and 4.0008 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged with hydrogen at 1.0 MPa three times, followed by purging with hydrogen at 4.0 MPa, and reacted at 160 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 99.68%, and the selectivity for dimethyl 1,4-cyclohexanedicarboxylate was 99.07%.

[0046] Example 6:

[0047] 6.9624 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 1.6143 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The mixture was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanoparticles. 0.1080 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 0.5083 g of cerium dioxide nanoparticles using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0048] The target catalyst prepared according to Example 6 above was applied to the reaction of dimethyl terephthalate (DMT) hydrogenation to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0017 g of dimethyl terephthalate, 0.1003 g of catalyst, and 4.0010 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged with hydrogen at 1.0 MPa three times, followed by purging with hydrogen at 4.0 MPa, and reacted at 140 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 98.83%, and the selectivity of dimethyl 1,4-cyclohexanedicarboxylate was 98.26%.

[0049] Example 7:

[0050] 6.9624 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 1.6143 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The mixture was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanoparticles. 0.0450 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 0.6010 g of cerium dioxide nanoparticles using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0051] The target catalyst prepared according to Example 7 above was applied to the reaction of dimethyl terephthalate (DMT) hydrogenation to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0045 g of dimethyl terephthalate, 0.1054 g of catalyst, and 4.0020 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged three times with 1.0 MPa hydrogen gas, followed by 6.0 MPa hydrogen gas, and reacted at 160 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 99.79%, and the selectivity for dimethyl 1,4-cyclohexanedicarboxylate was 97.22%.

[0052] Example 8:

[0053] 6.9624 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 1.6143 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The mixture was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanoparticles. 0.0450 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 0.6010 g of cerium dioxide nanoparticles using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0054] The target catalyst prepared according to Example 8 above was applied to the reaction of hydrogenating dimethyl terephthalate (DMT) to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0029 g of dimethyl terephthalate, 0.1021 g of catalyst, and 4.0015 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged three times with 1.0 MPa hydrogen gas, followed by 6.0 MPa hydrogen gas, and reacted at 160 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 99.27%, and the selectivity for dimethyl 1,4-cyclohexanedicarboxylate was 98.24%.

[0055] Example 9:

[0056] 6.9673 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 38.4024 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The mixture was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanocubes. 0.2149 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 1.0003 g of cerium dioxide nanocubes using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0057] The target catalyst prepared according to Example 9 above was applied to the reaction of dimethyl terephthalate (DMT) hydrogenation to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0006 g of dimethyl terephthalate, 0.1004 g of catalyst, and 4.0099 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged with hydrogen at 1.0 MPa three times, followed by purging with hydrogen at 4.0 MPa, and reacted at 160 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 99.53%, and the selectivity of dimethyl 1,4-cyclohexanedicarboxylate was 99.83%.

[0058] Example 10:

[0059] 6.9673 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 38.4024 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The mixture was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanocubes. 0.2149 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 1.0003 g of cerium dioxide nanocubes using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0060] The target catalyst prepared according to Example 10 above was applied to the reaction of dimethyl terephthalate (DMT) hydrogenation to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0079 g of dimethyl terephthalate, 0.1048 g of catalyst, and 4.0018 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged with hydrogen at 1.0 MPa three times, followed by purging with hydrogen at 4.0 MPa, and reacted at 140 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 99.96%, and the selectivity for dimethyl 1,4-cyclohexanedicarboxylate was 98.31%.

[0061] Example 11:

[0062] 6.9673 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 38.4024 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The solution was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanocubes. 0.0439 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 0.6018 g of cerium dioxide nanocubes using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 500 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0063] The target catalyst prepared according to Example 11 above was applied to the reaction of hydrogenating dimethyl terephthalate (DMT) to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0012 g of dimethyl terephthalate, 0.1011 g of catalyst, and 4.0010 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged with hydrogen at 1.0 MPa three times, followed by purging with hydrogen at 4.0 MPa, and reacted at 160 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 99.44%, and the selectivity for dimethyl 1,4-cyclohexanedicarboxylate was 98.38%.

[0064] Example 12:

[0065] 6.9673 g of cerium nitrate hexahydrate was dissolved in 5 mL of deionized water to obtain solution a, and 38.4024 g of sodium hydroxide was dissolved in 35 mL of deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 h. The solution was then transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. The product was washed with deionized water and filtered until the pH reached 7. The sample was dried overnight in a 100 °C oven and then heated to 500 °C at a heating rate of 2.5 °C / min in a muffle furnace and held for 5 h to obtain cerium dioxide nanocubes. 0.0439 g of ruthenium trichloride was dissolved in 20 mL of deionized water and impregnated into 0.6018 g of cerium dioxide nanocubes using an equal-volume impregnation method. The mixture was stirred for 4 h, sonicated for 30 min, dried overnight at 100 °C, and then heated to 550 °C at a heating rate of 5 °C / min in a muffle furnace and held for 5 h to obtain the target catalyst.

[0066] The target catalyst prepared according to Example 12 above was applied to the reaction of dimethyl terephthalate (DMT) hydrogenation to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) under mild conditions. 1.0039 g of dimethyl terephthalate, 0.1005 g of catalyst, and 4.0079 g of isopropanol were added to a 25 mL high-pressure reactor. The reactor was purged with hydrogen at 1.0 MPa three times, followed by purging with hydrogen at 6.0 MPa, and reacted at 160 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and gas chromatography analysis showed that the conversion rate of dimethyl terephthalate was 99.86%, and the selectivity for dimethyl 1,4-cyclohexanedicarboxylate was 99.01%.

Claims

1. A method for preparing dimethyl 1,4-cyclohexanedicarboxylate, characterized in that, Catalyzed by a ruthenium monometallic catalyst supported on cerium dioxide, dimethyl p-toluenedicarboxylate undergoes a hydrogenation reaction in a solvent under a hydrogen atmosphere to yield dimethyl 1,4-cyclohexanedicarboxylate, as shown in the following reaction formula: The ruthenium loading in the cerium dioxide-supported ruthenium monometallic catalyst is 0.1% to 5 wt%, and the cerium dioxide support comprises three different nanostructures: nanoparticles, nanorods, and nanocubes. The method for preparing the cerium dioxide-supported ruthenium monometallic catalyst includes the following steps: (I) Preparation of cerium dioxide support: A certain amount of cerium nitrate hexahydrate was dissolved in deionized water to obtain solution a, and a certain amount of sodium hydroxide was dissolved in deionized water to obtain solution b. Solution a was added dropwise to solution b at room temperature and stirred for 2 hours. The solution was then transferred to a reaction vessel and hydrothermally reacted at 120°C for 24 hours. The product was washed with deionized water and filtered until the pH reached 7. The product was dried at 100°C overnight and placed in a muffle furnace. The temperature was increased to 500°C at a rate of 2.5°C / min and held for 5 hours to obtain three different nanostructures of cerium dioxide support: nanoparticles, nanorods, and nanocubes. (II) Preparation of supported catalyst: A certain amount of ruthenium trichloride was dissolved in deionized water and impregnated into three different nanostructures of cerium dioxide using an equal volume impregnation method. The mixture was stirred for 4 hours, sonicated for 30 minutes, dried at 100°C overnight, and then placed in a muffle furnace and heated to 550°C at a heating rate of 5°C / min and held for 5 hours to obtain the target catalyst.

2. The method for preparing dimethyl 1,4-cyclohexanedicarboxylate according to claim 1, characterized in that, The operating steps are as follows: add a certain amount of dimethyl terephthalate and catalyst to the high-pressure reactor, add an appropriate amount of solvent, purge with hydrogen gas at a certain pressure, and react at a specific temperature for a certain time.

3. The method for preparing dimethyl 1,4-cyclohexanedicarboxylate according to claim 1, characterized in that, The selected solvents are C1-C4 alkyl alcohols or esters.

4. The method for preparing dimethyl 1,4-cyclohexanedicarboxylate according to claim 3, characterized in that, The solvent used is isopropanol or ethyl acetate.

5. The method for preparing dimethyl 1,4-cyclohexanedicarboxylate according to claim 1, characterized in that, Based on the mass ratio of dimethyl terephthalate, the catalyst dosage is 2wt% to 20wt%, and the solvent dosage is 5 to 20w / w.

6. The method for preparing dimethyl 1,4-cyclohexanedicarboxylate according to claim 5, characterized in that, Based on the mass ratio of dimethyl terephthalate, the catalyst dosage is 5wt%–10wt%, and the solvent dosage is 8–12w / w.

7. The method for preparing dimethyl 1,4-cyclohexanedicarboxylate according to claim 1, characterized in that, The reaction temperature is 100–180℃, the hydrogen pressure is 2 MPa–8 MPa, and the reaction time is 0.5 h–6 h.

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