Preparation method of 1, 4-cyclohexanedimethanol

Abstract

The invention relates to the technical field of compound preparation, and discloses a 1, 4-cyclohexanedimethanol preparation method, which comprises: S1, carrying out mixing pretreatment on a hydrogenation catalyst, 1, 4-cyclohexanedicarboxylic acid, NH3.H2O and water at a temperature of 40-70 DEG C to obtain a mixed solution; and S2, contacting the mixed solution with hydrogen, and carrying out hydrogenation reaction to prepare the 1, 4-cyclohexanedimethanol. According to the method, before the CHDA is hydrogenated to prepare the CHDM, the NH3.H2O is adopted to carry out mixing pretreatment on the hydrogenation catalyst and the CHDA, so that the CHDA conversion rate and the CHDM selectivity can be ensured, the hydrogenation reaction temperature and pressure can be reduced, and the large-scale industrial production of the CHDA can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of compound preparation, and particularly relates to a preparation method of 1,4-cyclohexanedimethanol. BACKGROUND

[0002] 1,4-cyclohexanedimethanol (CHDM) is a commonly used raw material for synthesizing a series of novel polyesters, and has a wide application prospect in high-tech fields such as polyester fibers, polyester films, polyester bottles and polyester resins due to its excellent characteristics such as good transparency, impact resistance, wear resistance and corrosion resistance. In industry, CHDM is mainly prepared from dimethyl terephthalate (DMT), and the price of DMT is relatively high. In addition, a separate DMT device is needed, which leads to a high cost of CHDM and is not conducive to the large-scale use of CHDM. In comparison, terephthalic acid (PTA) is abundant and relatively low in price, and therefore, it is expected that the production of CHDM from PTA by hydrogenation will become a more economical production path.

[0003] Most of the preparation of 1,4-cyclohexanedimethanol by hydrogenation of terephthalic acid adopts a two-step hydrogenation method, that is, the benzene ring in terephthalic acid is first hydrogenated to generate 1,4-cyclohexanedicarboxylic acid (CHDA), and then the carboxyl group on 1,4-cyclohexanedicarboxylic acid is hydrogenated to obtain the target product 1,4-cyclohexanedimethanol. Due to the difficulty in reducing the carboxyl group to alcohol in the second reaction stage, it is difficult to achieve large-scale industrialization of the preparation of 1,4-cyclohexanedimethanol by two-step hydrogenation of terephthalic acid.

[0004] In the prior art, the conversion rate and selectivity of the preparation of 1,4-cyclohexanedimethanol by hydrogenation of 1,4-cyclohexanedicarboxylic acid are usually improved by improving the catalyst, but the effect is limited, and the reaction temperature and reaction pressure are still relatively high. For example, patent CN114308035A proposes a supported catalyst using Ru-Re-B-Mn as the active component, and under the conditions of 225 DEG C and a H2 pressure of 7.5 MPa, after 4 hours of reaction, the conversion rate of 1,4-cyclohexanedicarboxylic acid is 98.5%, and the yield of 1,4-cyclohexanedimethanol is 96.1%. SUMMARY

[0005] In order to solve the above technical problems, that is, in the existing method for preparing 1,4-cyclohexanedimethanol by hydrogenation of 1,4-cyclohexanedicarboxylic acid, a relatively high reaction temperature and reaction pressure are needed to achieve a high conversion rate, the present application provides a preparation method of 1,4-cyclohexanedimethanol. The preparation method of the present application can reduce the hydrogenation reaction temperature and pressure while ensuring the conversion rate of 1,4-cyclohexanedicarboxylic acid and the selectivity of 1,4-cyclohexanedimethanol.

[0006] The specific technical scheme of the present application is: A method for preparing 1,4-cyclohexanediethanol includes the following steps: S1: The hydrogenation catalyst, 1,4-cyclohexanedicarboxylic acid, NH3·H2O and water are mixed and pretreated at 40-70℃ to obtain a mixed solution; S2: The mixture is brought into contact with hydrogen to carry out a hydrogenation reaction to prepare 1,4-cyclohexanediethanol.

[0007] Before the hydrogenation of CHDA to CHDM, this invention pretreats the hydrogenation catalyst and CHDA by mixing them with NH3·H2O. This neutralizes the acidic sites on the surface of the hydrogenation catalyst support or forms surface ammonium salts, thereby reducing side reactions (such as decarboxylation and deamination) during the subsequent hydrogenation reaction. At the same time, it enhances the adsorption capacity of carboxylic acid groups and promotes their hydrogenation. This invention enables the efficient conversion of CHDA at lower reaction temperatures and pressures, and achieves high CHDM selectivity, which is beneficial for the large-scale industrial production of CHDA.

[0008] Preferably, in step S1, the mass ratio of 1,4-cyclohexanedicarboxylic acid to NH3·H2O is 1:1 to 1.5.

[0009] This invention controls the mass ratio of CHDA to NH3·H2O within the aforementioned range, enabling higher conversion rates in subsequent hydrogenation reactions at lower temperatures and pressures. When the amount of NH3·H2O is too low, it cannot effectively perform its function. When the amount of NH3·H2O is too high, excess NH3 molecules will completely cover the active sites on the catalyst surface through strong coordination, hindering the adsorption of CHDA and H2, thus reducing the conversion rate of CHDA in the hydrogenation reaction.

[0010] Preferably, in step S1, the mixing pretreatment time is 1 to 4 hours.

[0011] Preferably, in step S1, the mass ratio of 1,4-cyclohexanedicarboxylic acid to the catalyst is 15 to 25:1.

[0012] Preferably, in step S1, the mass ratio of 1,4-cyclohexanedicarboxylic acid to water is 1:20-25.

[0013] Preferably, in step S2, the conditions for the hydrogenation reaction are: temperature of 210–215°C, hydrogen pressure of 6.8–7.2 MPa, and time of 3–3.5 h.

[0014] Preferably, in step S1, the preparation step of the hydrogenation catalyst includes: mixing alumina with a molybdenum salt solution, drying and calcining, and then reducing it with hydrogen at 250-350°C to obtain an Al2O3-MoO3 composite support; and loading metal Ru, metal Pt and Y2O3 onto the Al2O3-MoO3 composite support to obtain the hydrogenation catalyst.

[0015] In this invention, through the special design of the hydrogenation catalyst components and preparation method, higher conversion rates, reaction selectivity, and catalyst stability can be achieved when used in the hydrogenation of CHDA to CHDM. Specifically: (1) An Al2O3-MoO3 composite support is used, and metals Ru, Pt, and Y2O3 are loaded onto it. The components work together to improve the overall catalytic activity, selectivity, and stability of the catalyst. In the Al2O3-MoO3 composite support, the presence of MoO3 helps suppress the decarboxylation side reaction during hydrogenation and increases the binding strength of active sites on the support, thereby improving the stability and selectivity of the hydrogenation catalyst. Metallic Ru constitutes the catalytic active sites in the catalyst, catalyzing the hydrogenation of CHDA to CHDM. During the catalytic reaction, the d-orbital electronic structure of Pt can form a strong interaction with the oxygen vacancies in MoO3, promoting the reaction of Mo… 6+ →Mo 5+ The reduction increases surface reactive oxygen species (such as O2). - This enhances the adsorption capacity of CHDA. Y2O3 can optimize the surface electronic structure of the Al2O3 support through charge compensation effect, reducing the d-band center of Ru and weakening the strong adsorption of H2, thereby avoiding methanation side reactions and enhancing H2 adsorption. + The activation efficiency of Pt is improved, thus enhancing catalytic efficiency. Furthermore, the rare earth properties of Y can regulate the crystal phase of MoO3 through lattice strain effects (inhibiting the MoO3→MoO2 phase transition), maintaining the long-term stability of the catalyst. The acid resistance of Pt combined with the electronic regulation of Y can form unique "bifunctional sites," where Pt promotes the stability of Mo sites, and Y optimizes H2 dissociation and intermediate adsorption, thereby achieving higher CHDM selectivity and catalyst stability.

[0016] (2) After loading MoO3 onto Al2O3 through calcination, a reduction is first carried out at 250–350 °C, followed by loading of metallic Ru, metallic Pt, and Y2O3, which can improve the catalytic activity and selectivity of the catalyst: The conventional procedure in catalyst preparation involves a single reduction after all elements are loaded onto the support or before the catalyst is used. Unlike this conventional procedure, this invention performs a reduction before the support is prepared, controlling the reduction temperature to 250–350°C. This induces the formation of a Mott-Schottky heterojunction (MoO3) between MoO3 and Al2O3. 6+ With Al 3+ (charge transfer), this heterojunction can stabilize the dispersion of Ru nanoparticles through electronic interactions when Ru is subsequently loaded, avoiding Ru particle agglomeration caused by high-temperature calcination, thereby improving the catalytic activity of the catalyst.

[0017] Furthermore, excessively high or low temperatures during the support reduction treatment can adversely affect catalytic activity and selectivity. When the temperature is too high, it triggers a crystal transformation in the Al2O3-MoO3 composite support (e.g., γ-Al2O3 → θ-Al2O3), leading to pore structure collapse, a decrease in specific surface area, and hindering the diffusion of CHDA molecules to the active sites. Simultaneously, excessive reduction of MoO3 to Mo... 3+ The strong reducing properties of the cluster may directly reduce CHDA to cyclohexane (instead of the target product CHDM); when the temperature of the support reduction treatment is too low, the strong metal-support interaction (SMSI) between Ru and the Al2O3-MoO3 composite support cannot be fully formed, resulting in excessively high H2 adsorption energy and insufficient H2 dissociation efficiency, and the reaction tends to decarboxylate rather than hydrogenate.

[0018] Furthermore, in the hydrogenation catalyst, the molar ratio of Al to Mo is 1:0.5-0.6, and the contents of Ru, Pt, and Y are 2-4 wt%, 1-2 wt%, and 5-8 wt%, respectively.

[0019] This invention controls the molar ratio of Al to Mo within the range of 1:0.5 to 0.6, enabling the catalyst to achieve higher CHDM selectivity in the hydrogenation of CHDA to CHDM. When the Al / Mo molar ratio is too high (Al excess), the excess Al... 3+ It can change the electronic structure of MoO3 through charge transfer, Al 3+ The strong Lewis acidity will enhance Mo 6+ The polarization ability of the Mo-O bond leads to increased covalentity of the Mo-O bond, weakening its interaction with H. + The interaction between them will inhibit H + The activation of Al (a key step in the hydrogenation reaction) causes the reaction to tend towards side pathways such as decarboxylation or isomerization, leading to a decrease in reaction selectivity; furthermore, when Al is in excess, Al... 3+The disruption of the Mott-Schottky heterojunction structure between Al and MoO3 leads to a decrease in H2 dissociation efficiency, which in turn reduces reaction selectivity. When the Al / Mo molar ratio is too small (Mo in excess), the proportion of L acid sites in the support is too high, resulting in excessive protonation of the carboxylic acid groups to form -COO. - Its relationship with H + The rapid reaction triggers decarboxylation rather than hydrogenation; moreover, when MoO3 is in excess, it forms a three-dimensional network structure, which blocks the mesopores of the support, hinders the mass transfer of reactants / products, causes the retention of macromolecular intermediates and side reactions, and also affects the catalytic efficiency.

[0020] Furthermore, the calcination temperature is 500–550°C, and the time is 3–4 hours; the reduction treatment time is 2–2.5 hours.

[0021] Furthermore, the specific steps for loading metal Ru, metal Pt and Y2O3 onto the Al2O3-MoO3 composite support include: mixing the Al2O3-MoO3 composite support, ruthenium salt, platinum salt, yttrium salt and solvent, drying, calcining at 500-550℃ for 2-3 hours, and reducing with hydrogen at 400-450℃ for 2-3 hours.

[0022] Compared with the prior art, the present invention has the following advantages: (1) By using NH3·H2O to pretreat the hydrogenation catalyst and CHDA before preparing CHDM by hydrogenation of CHDA, and controlling the amount of NH3·H2O, the present invention can reduce the hydrogenation reaction temperature and pressure while ensuring the conversion rate of CHDA and the selectivity of CHDM, which is conducive to the large-scale industrial production of CHDA.

[0023] (2) The present invention improves the CHDA conversion rate, CHDM selectivity and catalyst stability in the hydrogenation catalyst by employing ① the Al2O3-MoO3 composite support and the metal Ru, metal Pt and Y2O3 loaded on it in combination with ② after loading MoO3 onto Al2O3 by calcination, first reducing it at 250-350℃, and then loading metal Ru, metal Pt and Y2O3. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments.

[0025] A method for preparing 1,4-cyclohexanediethanol includes the following steps: S1: The hydrogenation catalyst, 1,4-cyclohexanedicarboxylic acid, NH3·H2O and water are mixed and pretreated at 40-70℃ to obtain a mixed solution; S2: The mixture is brought into contact with hydrogen to carry out a hydrogenation reaction to prepare 1,4-cyclohexanediethanol.

[0026] In one specific implementation, in step S1, the mass ratio of 1,4-cyclohexanedicarboxylic acid to NH3·H2O is 1:1 to 1.5.

[0027] In one specific implementation, the mixing pretreatment time in step S1 is 1 to 4 hours.

[0028] In one specific embodiment, in step S1, the mass ratio of 1,4-cyclohexanedicarboxylic acid to the catalyst is 15 to 25:1.

[0029] In one specific implementation, in step S1, the mass ratio of 1,4-cyclohexanedicarboxylic acid to water is 1:20-25.

[0030] In one specific implementation, the conditions for the hydrogenation reaction in step S2 are: temperature of 210-215°C, hydrogen pressure of 6.8-7.2 MPa, and time of 3-3.5 h.

[0031] In one specific embodiment, step S1, the preparation step of the hydrogenation catalyst includes: mixing alumina with a molybdenum salt solution, drying and calcining, and then reducing it with hydrogen at 250–350°C to obtain an Al2O3-MoO3 composite support; loading metallic Ru, metallic Pt, and Y2O3 onto the Al2O3-MoO3 composite support to obtain the hydrogenation catalyst. In this specific embodiment: Optionally or preferably, in the hydrogenation catalyst, the molar ratio of Al to Mo is 1:0.5-0.6, and the contents of Ru, Pt and Y are 2-4 wt%, 1-2 wt% and 5-8 wt%, respectively. Optionally or preferably, the calcination temperature is 500–550°C and the time is 3–4 hours; Optionally or preferably, the reduction process takes 2 to 2.5 hours. Optionally or preferably, the specific steps for loading metal Ru, metal Pt and Y2O3 onto the Al2O3-MoO3 composite support include: mixing the Al2O3-MoO3 composite support, ruthenium salt, platinum salt, yttrium salt and solvent, drying, calcining at 500-550°C for 2-3 hours, and reducing with hydrogen at 400-450°C for 2-3 hours.

[0032] The present invention will now be described through specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0033] Examples 1-2 and Comparative Examples 1-2: Effect of NH3·H2O Pretreatment and NH3·H2O Dosage on Hydrogenation Reaction. Following the steps below, 1,4-cyclohexanedicarboxylic acid was used as a raw material to prepare 1,4-cyclohexanediethanol via hydrogenation reaction: S1: Preparation of hydrogenation catalyst 10.2 g of Al2O3 was weighed and impregnated in a 25 mM MoCl5 ethanol solution. After stirring for 5 hours, it was first vacuum dried at 80 °C for 2 hours, then calcined at 500 °C for 3 hours, and finally reduced with hydrogen at 300 °C for 2 hours to obtain an Al2O3-MoO3 composite support with a molar ratio of Al to Mo of 1:0.25.

[0034] 4.3 g RuCl3, 2.4 g H2PtCl6, 15.0 g Y(NO3)3·6H2O and 50.0 g Al2O3-MoO3 composite support were weighed and added to ultrapure water. The mixture was sonicated at 50 °C for 30 minutes, then transferred to a flask and heated and stirred at 90 °C until the solvent evaporated. The collected solid was dried overnight in an oven at 60 °C, then placed in a muffle furnace and heated to 500 °C at a rate of 3 °C / min. After calcination at 500 °C for 2 hours, the solid was cooled to room temperature and then heated to 400 °C at a rate of 3 °C / min. The solid was then reduced at 400 °C in a mixed atmosphere of H2 / N2 (H2 volume fraction of 5%) for 2 hours. The hydrogenation catalyst was obtained after the reduction was completed.

[0035] S2: Pretreatment and hydrogenation reaction 100g of 1,4-cyclohexanedicarboxylic acid and 1000mL of ultrapure water were added to a single-necked flask, followed by 5g of the hydrogenation catalyst prepared according to step S1, and then a certain amount of NH3·H2O (the amount of NH3·H2O used in Examples 1-2 and Comparative Examples 1-2 is shown in Table 1). The flask was stoppered, and the temperature was raised to 50°C. The mixture was stirred at this temperature for 1 hour. The mixture in the flask was transferred to an autoclave, heated, and hydrogen gas was introduced. The reaction temperature was controlled at 210°C, and the hydrogen pressure was 7MPa. After reacting for 3 hours, heating was stopped, and the autoclave was allowed to cool to room temperature. The catalyst in the autoclave was then recovered. The solution after the reaction was analyzed by liquid chromatography, and the CHDA conversion and CHDM selectivity were calculated using the external standard method. The CHDM yield was then calculated based on these results, which are shown in Table 1.

[0036] Table 1. Effects of NH3·H2O pretreatment and NH3·H2O dosage on hydrogenation reaction

[0037] Data Analysis: (1) Compared with Comparative Example 1, Examples 1 and 2 pretreated the hydrogenation catalyst and CHDA with NH3·H2O before the hydrogenation reaction, which enabled the hydrogenation reaction to achieve a higher CHDA conversion rate under lower temperature (210°C) and lower pressure (7MPa) conditions. The reason for this is that NH3·H2O neutralizes the acidic sites on the surface of the hydrogenation catalyst support or forms surface ammonium salts, thereby reducing the occurrence of side reactions (such as decarboxylation and deamination) in the subsequent hydrogenation reaction, while enhancing the adsorption capacity of carboxylic acid groups and promoting their hydrogenation.

[0038] (2) In Examples 1, 2 and Comparative Example 2, the CHDA conversion rate decreased with the increase of NH3·H2O dosage. The reason is that when the amount of NH3·H2O is too high, the excess NH3 molecules will completely cover the active sites on the catalyst surface through strong coordination, hindering the adsorption of CHDA and H2, thus causing a decrease in the CHDA conversion rate in the hydrogenation reaction.

[0039] Examples 3-4: Hydrogenation reaction under different pretreatment temperatures and times Examples 3 and 4 differed from Example 1 by altering the temperature and time during the pretreatment process. Specifically, Examples 3 and 4 followed these steps to prepare 1,4-cyclohexanedicarboxylic acid via a hydrogenation reaction: S1: Preparation of hydrogenation catalyst 10.2 g of Al2O3 was weighed and impregnated in a 25 mM MoCl5 ethanol solution. After stirring for 5 hours, it was first vacuum dried at 80 °C for 2 hours, then calcined at 500 °C for 3 hours, and finally reduced with hydrogen at 300 °C for 2 hours to obtain an Al2O3-MoO3 composite support with a molar ratio of Al to Mo of 1:0.25.

[0040] 4.3 g RuCl3, 2.4 g H2PtCl6, 15.0 g Y(NO3)3·6H2O and 50.0 g Al2O3-MoO3 composite support were weighed and added to ultrapure water. The mixture was sonicated at 50 °C for 30 minutes, then transferred to a flask and heated and stirred at 90 °C until the solvent evaporated. The collected solid was dried overnight in an oven at 60 °C, then placed in a muffle furnace and heated to 500 °C at a rate of 3 °C / min. After calcination at 500 °C for 2 hours, the solid was cooled to room temperature and then heated to 400 °C at a rate of 3 °C / min. The solid was then reduced at 400 °C in a mixed atmosphere of H2 / N2 (H2 volume fraction of 5%) for 2 hours. The hydrogenation catalyst was obtained after the reduction was completed.

[0041] S2: Pretreatment and hydrogenation reaction 100g of 1,4-cyclohexanedicarboxylic acid and 1000mL of ultrapure water were added to a single-necked flask, followed by 5g of the hydrogenation catalyst prepared according to step S1, and then 100g of NH3·H2O. The flask was then stoppered and heated to a certain temperature (the temperatures in Examples 1 and 3-4 are shown in Table 2). The mixture was stirred at this temperature for a certain time (the times in Examples 1 and 3-4 are shown in Table 2). The mixture in the flask was transferred to an autoclave, heated, and hydrogen gas was introduced. The reaction temperature was controlled at 210℃ and the hydrogen pressure at 7MPa. After reacting for 3 hours, heating was stopped, and the autoclave was allowed to cool to room temperature. The catalyst was then recovered from the autoclave. The solution after the reaction was analyzed by liquid chromatography, and the CHDA conversion and CHDM selectivity were calculated using the external standard method. The CHDM yield was then calculated based on these results, which are shown in Table 2.

[0042] Table 2 Hydrogenation reaction under different pretreatment temperatures and times

[0043] Comparative Example 3: Effect of Catalyst Components on Hydrogenation Reaction Comparative Example 3, based on Example 1, replaced the Pt and Y elements in the hydrogenation catalyst with V and B elements, respectively. Specifically, this comparative example followed the steps below to prepare 1,4-cyclohexanedicarboxylic acid as a raw material via hydrogenation reaction: S1: Preparation of hydrogenation catalyst 10.2 g of Al2O3 was weighed and impregnated in a 25 mM MoCl5 ethanol solution. After stirring for 5 hours, it was first vacuum dried at 80 °C for 2 hours, then calcined at 500 °C for 3 hours, and finally reduced with hydrogen at 300 °C for 2 hours to obtain an Al2O3-MoO3 composite support with a molar ratio of Al to Mo of 1:0.25.

[0044] 4.3 g RuCl3, 0.7 g NH4VO3, 2.1 g KBH4, and 50.0 g Al2O3-MoO3 composite support were weighed and added to ultrapure water. The mixture was sonicated at 50 °C for 30 minutes, then transferred to a flask and heated and stirred at 90 °C until the solvent evaporated. The collected solid was dried overnight in a 60 °C oven, then placed in a muffle furnace and heated to 500 °C at a rate of 3 °C / min. After calcination at 500 °C for 2 hours, the solid was cooled to room temperature and then heated to 400 °C at a rate of 3 °C / min. The solid was then reduced at 400 °C in a H2 / N2 mixed atmosphere (H2 volume fraction of 5%) for 2 hours to obtain the hydrogenation catalyst.

[0045] S2: Pretreatment and hydrogenation reaction 100 g of 1,4-cyclohexanedicarboxylic acid and 1000 mL of ultrapure water were added to a single-necked flask, followed by 5 g of the hydrogenation catalyst prepared according to step S1, and then 100 g of NH3·H2O. The flask was then sealed, and the temperature was raised to 50 °C. The mixture was stirred at this temperature for 1 hour. The mixture in the flask was transferred to an autoclave, heated, and hydrogen gas was introduced. The reaction temperature was controlled at 210 °C, and the hydrogen pressure at 7 MPa. After reacting for 3 hours, heating was stopped, and the autoclave was allowed to cool to room temperature. The catalyst was then recovered from the autoclave. The solution after the reaction was analyzed by liquid chromatography, and the CHDA conversion and CHDM selectivity were calculated using the external standard method. The CHDM yield was then calculated based on these results, which are shown in Table 3.

[0046] Table 3. Effect of catalyst composition on hydrogenation reaction

[0047] Data Analysis: Compared to Comparative Example 3, using the hydrogenation catalyst component in Example 1 achieves higher CHDA conversion and CHDM selectivity. The reason for this is that during the catalytic reaction, the d-orbital electronic structure of Pt can form a strong interaction with the oxygen vacancies in MoO3, promoting the reaction of Mo… 6+ →Mo 5+ The reduction increases surface reactive oxygen species (such as O2). - This enhances the adsorption capacity of CHDA. Y2O3 can optimize the surface electronic structure of the Al2O3 support through charge compensation effect, reducing the d-band center of Ru and weakening the strong adsorption of H2, thereby avoiding methanation side reactions and enhancing H2 adsorption. + This improves activation efficiency and enhances catalytic efficiency.

[0048] Examples 5-6 and Comparative Examples 4-6: Effects of support reduction treatment and temperature on hydrogenation reaction in catalysts Examples 5-6 and Comparative Examples 4-6, based on Example 1, modified the hydrogen reduction step in the preparation process of the Al2O3-MoO3 composite support. Specifically, Examples 5-6 and Comparative Examples 4-6 prepared 1,4-cyclohexanedicarboxylic acid as a raw material through a hydrogenation reaction according to the following steps: S1: Preparation of hydrogenation catalyst 10.2 g of Al2O3 was weighed and impregnated in a 25 mM MoCl5 ethanol solution. After stirring for 5 hours, it was first vacuum dried at 80 °C for 2 hours, then calcined at 500 °C for 3 hours, and finally reduced with hydrogen at a certain temperature for 2 hours (hydrogen reduction was not performed in Comparative Example 4; the hydrogen reduction temperatures in Examples 1, 5-6 and Comparative Examples 5-6 are shown in Table 4) to obtain an Al2O3-MoO3 composite support, wherein the molar ratio of Al to Mo was 1:0.25.

[0049] 4.3 g RuCl3, 2.4 g H2PtCl6, 15.0 g Y(NO3)3·6H2O and 50.0 g Al2O3-MoO3 composite support were weighed and added to ultrapure water. The mixture was sonicated at 50 °C for 30 minutes, then transferred to a flask and heated and stirred at 90 °C until the solvent evaporated. The collected solid was dried overnight in an oven at 60 °C, then placed in a muffle furnace and heated to 500 °C at a rate of 3 °C / min. After calcination at 500 °C for 2 hours, the solid was cooled to room temperature and then heated to 400 °C at a rate of 3 °C / min. The solid was then reduced at 400 °C in a mixed atmosphere of H2 / N2 (H2 volume fraction of 5%) for 2 hours. The hydrogenation catalyst was obtained after the reduction was completed.

[0050] S2: Pretreatment and hydrogenation reaction 100 g of 1,4-cyclohexanedicarboxylic acid and 1000 mL of ultrapure water were added to a single-necked flask, followed by 5 g of the hydrogenation catalyst prepared according to step S1, and then 100 g of NH3·H2O. The flask was then sealed, and the temperature was raised to 50 °C. The mixture was stirred at this temperature for 1 hour. The mixture in the flask was transferred to an autoclave, heated, and hydrogen gas was introduced. The reaction temperature was controlled at 210 °C, and the hydrogen pressure at 7 MPa. After reacting for 3 hours, heating was stopped, and the autoclave was allowed to cool to room temperature. The catalyst was then recovered from the autoclave. The solution after the reaction was analyzed by liquid chromatography, and the CHDA conversion and CHDM selectivity were calculated using the external standard method. The CHDM yield was then calculated based on these results, which are shown in Table 4.

[0051] Table 4. Effects of catalyst support reduction treatment and temperature on hydrogenation reaction

[0052] Data Analysis: (1) Compared to Comparative Example 4, Examples 1 and 5-6, by first performing a reduction process during the preparation of the Al2O3-MoO3 composite support, and then loading Ru, Pt, and Y2O3, achieved higher CHDA conversion and CHDM selectivity. The reason for this is that after loading MoO3 onto Al2O3, the reduction treatment induces the formation of a Mott-Schottky heterojunction (MoO3-Al2O3-MoO3 heterojunction). 6+ With Al 3+ (charge transfer), this heterojunction can stabilize the dispersion of Ru nanoparticles through electronic interactions when Ru is subsequently loaded, avoiding Ru particle agglomeration caused by high-temperature calcination, thereby improving the catalytic activity of the catalyst and reducing the occurrence of decarboxylation side reactions.

[0053] (2) In Examples 1, 5-6, and Comparative Examples 5-6, the CHDA conversion rate and CHDM selectivity showed a trend of first increasing and then decreasing with the increase of the carrier reduction treatment temperature. The reason for this is that when the carrier reduction treatment temperature is too high, it will trigger the crystal transformation of the Al2O3-MoO3 composite carrier (such as γ-Al2O3→θ-Al2O3), which leads to the collapse of the pore structure, a decrease in specific surface area, and hinders the diffusion of CHDA molecules to the active sites. At the same time, MoO3 is excessively reduced to generate Mo. 3+ The strong reducing properties of the cluster may directly reduce CHDA to cyclohexane (instead of the target product CHDM); when the temperature of the support reduction treatment is too low, the strong metal-support interaction (SMSI) between Ru and the Al2O3-MoO3 composite support cannot be fully formed, resulting in excessively high H2 adsorption energy and insufficient H2 dissociation efficiency, and the reaction tends to decarboxylate rather than hydrogenate.

[0054] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used in this invention are conventional in the art and can be obtained through conventional commercial means; unless otherwise specified, the methods used in this invention are conventional methods in the art.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing 1,4-cyclohexanediethanol, characterized in that, Includes the following steps: S1: The hydrogenation catalyst, 1,4-cyclohexanedicarboxylic acid, NH3·H2O and water are mixed and pretreated at 40-70℃ to obtain a mixed solution; S2: The mixture is brought into contact with hydrogen to carry out a hydrogenation reaction to prepare 1,4-cyclohexanediethanol.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of 1,4-cyclohexanedicarboxylic acid to NH3·H2O is 1:1 to 1.

5.

3. The preparation method according to claim 1, characterized in that, In step S1, the mixing pretreatment time is 1 to 4 hours.

4. The preparation method according to claim 1 or 2, characterized in that, In step S1, the mass ratio of 1,4-cyclohexanedicarboxylic acid to the catalyst is 15 to 25:

1.

5. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of 1,4-cyclohexanedicarboxylic acid to water is 1:20-25.

6. The preparation method according to claim 1, characterized in that, In step S2, the conditions for the hydrogenation reaction are: temperature of 210-215℃, hydrogen pressure of 6.8-7.2MPa, and time of 3-3.5h.

7. The preparation method according to claim 1, characterized in that, In step S1, the preparation steps of the hydrogenation catalyst include: mixing alumina with a molybdenum salt solution, drying and calcining, and then reducing it with hydrogen at 250-350°C to obtain an Al2O3-MoO3 composite support; and loading metal Ru, metal Pt and Y2O3 onto the Al2O3-MoO3 composite support to obtain the hydrogenation catalyst.

8. The preparation method according to claim 7, characterized in that, In the hydrogenation catalyst, the molar ratio of Al to Mo is 1:0.5-0.6, and the contents of Ru, Pt and Y are 2-4 wt%, 1-2 wt% and 5-8 wt%, respectively.

9. The preparation method according to claim 7, characterized in that, The calcination temperature is 500–550°C, and the time is 3–4 hours; the reduction treatment time is 2–2.5 hours.

10. The preparation method according to claim 7, characterized in that, The specific steps for loading metal Ru, metal Pt and Y2O3 onto the Al2O3-MoO3 composite support include: mixing the Al2O3-MoO3 composite support, ruthenium salt, platinum salt, yttrium salt and solvent, drying, calcining at 500-550℃ for 2-3 hours, and reducing with hydrogen at 400-450℃ for 2-3 hours.

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