A copper-based catalyst for the hydrogenation of dimethyl oxalate and its preparation method

Abstract

This invention relates to the field of catalyst preparation technology, specifically to a copper-based catalyst for the hydrogenation of dimethyl oxalate and its preparation method. The catalyst is a Cu / SiO2 catalyst with a copper content of 5-25 wt% as the active component. It is prepared from raw materials such as a silicon source, a copper source, a hydroxyl protectant, and a hydrothermal promoter via a low-pressure ammonia stripping method. During the preparation process, by protecting the silanol hydroxyl groups and optimizing the ammonia stripping and complexation conditions, copper is highly dispersed and stable on the silicon support surface, effectively avoiding copper particle sintering and desilication problems. This catalyst exhibits excellent performance in the hydrogenation of dimethyl oxalate to ethylene glycol. Under reaction conditions of 170℃ and 2.8 MPa, the dimethyl oxalate conversion rate is ≥99%, the ethylene glycol selectivity is ≥97%, and the continuous operating time is ≥3000 h. It can significantly inhibit the formation of byproducts and carbon deposition, extend service life, and simultaneously reduce separation and purification energy consumption and catalyst replacement frequency. The raw materials used are conventional and controllable, and the preparation process is suitable for industrial production, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, specifically to a copper-based catalyst for the hydrogenation of dimethyl oxalate and its preparation method. Background Technology

[0002] Ethylene glycol (EG) is a core raw material for chemical products such as polyester fibers, plastics, and antifreeze, with a global annual demand exceeding 40 million tons. Traditional industrial production of EG primarily involves the gas-phase oxidation of petroleum ethylene to ethylene oxide, followed by liquid-phase catalytic hydration to produce EG. In recent years, the coal-based EG industry has experienced rapid development, with production proceeding in two steps: first, CO gas-phase catalytic synthesis of oxalate, followed by hydrogenation of the oxalate to obtain EG; this method is now widely used. The key step is the hydrogenation of dimethyl oxalate (DMO) to EG. This reaction requires a highly efficient catalyst, and copper-silicon catalysts (Cu / SiO2) have become the mainstream industrial choice due to their low cost and high selective hydrogenation activity towards the C=O bond.

[0003] Currently, the catalysts used in the hydrogenation of dimethyl oxalate to ethylene glycol are mostly Cu / SiO2 catalysts, such as those in patents CN101411990A and CN101648134A. However, copper-silicon catalysts in the hydrogenation process of dimethyl oxalate suffer from problems such as particle sintering and valence state imbalance, leading to phenomena like carbon deposition, coking, active component aggregation, and desilication, making it difficult to maintain stable catalyst activity over a long period. Carbon deposition is one of the core reasons for catalyst deactivation. The intermediate product methyl glycolate accumulates on the catalyst and forms polymers with the reactants or products, or the product ethylene glycol polymerizes to form polymers such as polyethylene glycol and diethylene glycol. These carbon deposits cover the active centers of the catalyst, blocking the pores, reducing catalyst activity, and even causing coking. Coking necessitates catalyst replacement, increasing production costs and operational complexity. In the hydrogenation catalysis process, catalyst deactivation mainly occurs in the upper layer, with the parts in contact with the materials deactivating and coking first. Furthermore, the hot spot temperature gradually decreases, and the middle and lower layers of the catalyst also deactivate, requiring complete catalyst replacement.

[0004] Therefore, developing a highly active, highly selective, and long-life dimethyl oxalate hydrogenation catalyst is of great significance for promoting the sustainable development of the coal-to-ethylene glycol industry. Summary of the Invention

[0005] The purpose of this invention is to provide a copper-based catalyst for the hydrogenation of dimethyl oxalate and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a copper-based catalyst for the hydrogenation of dimethyl oxalate, wherein the catalyst is a Cu / SiO2 catalyst, the content of the active component copper is 5-25 wt%, and the catalyst is prepared from raw materials including a silicon source, a copper source, a hydroxyl protectant, a hydrothermal promoter, ammonia water and deionized water by a low-pressure ammonia stripping method; the silanol groups on the surface of the silicon source are protected by the hydroxyl protectant, and the hydrothermal promoter is used to optimize the reaction environment so that the active component copper is highly dispersed and stable on the surface of the silicon support.

[0007] This invention also provides a method for preparing a copper-based catalyst for the hydrogenation of dimethyl oxalate, comprising the following steps: S1: Preparation of silica sol: Mix the silicon source with deionized water or dilute ammonia water and stir. Add hydroxyl protectant as needed and continue stirring to obtain silica sol. S2: Preparation of copper-ammonia complex solution: Dissolve the copper source in 20wt% ammonia water, control the molar ratio of ammonia to copper to be 15 and the pH value to be 10, and stir to form a stable copper-ammonia complex solution. S3: Mixed Complexation: Mix the silica sol of S1 with the copper-ammonia complex solution of S2, add hydrothermal accelerator as needed, and stir to allow Cu... 2+ Fully react with silanol groups; S4: Low-pressure ammonia stripping: The mixture is subjected to low-pressure ammonia stripping until pH < 7, forming a viscous material; S5: Washing: Wash the viscous material with deionized water until the washing solution is neutral; S6: Drying, shaping and calcination: The washed material is dried, pressed into tablets and then calcined to obtain Cu / SiO2 catalyst.

[0008] Preferably, the silicon source is at least one of silicate ester, fumed silica, or silica sol; and the copper source is one of copper oxalate, copper acetate, copper chloride, or copper nitrate.

[0009] Preferably, the hydroxyl protectant is one of aminosilane, hydrophobic alkylsilane, or sodium citrate; and the hydrothermal accelerator is one or more of ammonium dihydrogen phosphate, biuret, or urea.

[0010] Preferably, the ammonia water has a mass fraction of 1 wt% or 20 wt%, with 1 wt% ammonia water used for silica sol preparation and 20 wt% ammonia water used for preparing copper ammonia complex solution; the conductivity of the deionized water is ≤10 μS / cm.

[0011] Preferably, in S1, when the silicon source is mixed with 1wt% dilute ammonia, the mixing temperature is 60℃, the stirring speed is 250rpm, and the stirring time is 2 hours; the amount of hydroxyl protectant added is 3.5g (based on 60g of silicon source), and stirring continues for 30min after addition.

[0012] Preferably, in S3, the mixing speed is 250-350 rpm and the mixing time is 120 min; the amount of hydrothermal accelerator added is 3.6 g (based on 60 g of silicon source).

[0013] Preferably, in S4, the low-pressure ammonia stripping temperature is 50-94℃, the stirring speed is 100-250rpm, and the ammonia stripping time is 2-5h; when a hydrothermal accelerator is added, the ammonia stripping temperature is 60℃, the stirring speed is 100rpm, and the ammonia stripping time is 2h.

[0014] Preferably, in S6, the drying temperature is 120℃ and the drying time is 12 hours; the calcination temperature is 500℃ and the calcination time is 6 hours.

[0015] Preferably, the catalyst is used in a reaction at a temperature of 170°C, a reaction pressure of 2.8 MPa, and a space velocity of 0.3 h⁻¹. -1 Under the condition of a hydrogen-to-ester ratio of 100, the conversion rate of dimethyl oxalate is ≥99%, the selectivity of ethylene glycol is ≥97%, and the continuous operating time is ≥3000h.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes a low-pressure ammonia stripping process to effectively enhance and protect the silanol groups (Si-OH) on the surface of the silica gel carrier. These silanol groups can firmly anchor Cu through multiple mechanisms, including electrostatic attraction, ion exchange, and surface complexation. 2+ This method enables the active component, copper, to be highly dispersed and stable on the support surface over a long period, avoiding the problems of copper particle sintering, active component aggregation, and desilication common in traditional copper-silicon catalysts. Performance testing showed that this catalyst maintained a stable DMO conversion rate of over 99% and an ethylene glycol yield of over 96% in the hydrogenation reaction of dimethyl oxalate. After thousands of hours of continuous operation, its activity showed no significant decline, significantly outperforming traditional catalysts. This invention precisely controls the structure and distribution of catalytic active sites by optimizing catalyst preparation process parameters, selecting highly efficient silanol protectants such as sodium citrate, and hydrothermal promoters such as urea. This enhances the selective hydrogenation capability of C=O bonds and effectively inhibits the formation of byproducts such as methyl glycolate (MG). Experimental data show that the MG selectivity of this catalyst can be as low as 0.39%-0.55%, significantly reducing the risk of byproduct polymerization forming coking precursors. This not only improves the purity and yield of the target product ethylene glycol but also reduces the energy consumption and cost of subsequent separation and purification. Because the active components are uniformly dispersed and byproduct formation is suppressed, the rate of carbonaceous deposit formation (coking) on ​​the catalyst surface is significantly reduced, avoiding the problems of active centers being covered and support pores being blocked. Compared to the 9-12 month industrial service life of traditional copper-silicon catalysts, the stable operating cycle of the catalyst of this invention is greatly extended, reducing production interruptions caused by catalyst deactivation from the source, and lowering the frequency of catalyst replacement and operation and maintenance costs. The raw materials used in this invention (silicon source, copper source, protective agent, accelerator, etc.) are all common and cost-controllable conventional materials in the chemical industry. The preparation process does not require extreme reaction conditions. The steps such as low-pressure ammonia stripping, stirring and mixing, drying and calcination are all in line with the existing industrial production process. The process has good repeatability and is easy to operate. It can be directly adapted to the catalyst preparation needs of existing coal chemical ethylene glycol production equipment without large-scale equipment modification and has significant industrial promotion value. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention provides a copper-based catalyst for the hydrogenation of dimethyl oxalate. The raw materials used include a silicon source, a copper source, a hydroxyl protectant, a hydrothermal accelerator, ammonia, and deionized water. The silicon source includes silicates, fumed silica, and silica sol; the copper source includes copper oxalate, copper acetate, copper chloride, and copper nitrate; the hydroxyl protectant includes aminosilanes, hydrophobic alkylsilanes, and sodium citrate; the hydrothermal accelerator includes ammonium dihydrogen phosphate, biuret, and urea; the ammonia is 1 wt% or 20 wt% industrial-grade ammonia; and the deionized water is high-purity water with a conductivity ≤10 μS / cm.

[0019] The copper-based catalyst for dimethyl oxalate hydrogenation of the present invention is prepared by low-pressure ammonia stripping. The core process includes: preparation of silica sol (including hydroxyl protection treatment), preparation of copper ammonia complex solution, mixing and complexation, low-pressure ammonia stripping, washing, drying, molding, and calcination, finally obtaining Cu / SiO2 catalyst. Example 1

[0020] Preparation steps: S1: Preparation of silica sol: At room temperature (25℃) and stirring speed of 250rpm, 60g of fumed silica was added to 300mL of deionized water and stirred continuously for 30min to obtain a uniformly dispersed silica sol. S2: Preparation of copper-ammonia complex solution: At room temperature, dissolve 27.04g of copper nitrate (Cu(NO3)2·3H2O) in 330mL of 20wt% ammonia water, control the molar ratio of ammonia to copper in the solution to be 15, adjust the pH value to 10, and stir at 250rpm for 30min to form a stable copper-ammonia complex solution. S3: Mixing and Complexing: Maintaining room temperature, mix the silica sol prepared in step 1 with the copper ammonia complex solution prepared in step 2, increase the stirring speed to 350 rpm, and continue stirring for 120 min to allow the Cu... 2+ Fully react with silanol groups; S4: Low-pressure ammonia stripping: Transfer the mixture to the ammonia stripping device, control the temperature at 94℃ and the stirring speed at 250rpm, and continue to strip ammonia for 5 hours until the solution pH < 7 and a viscous material is formed. S5: Washing: Wash the viscous material multiple times with deionized water until the washing solution is neutral (pH=6.5-7.5). S6: Drying and calcination: The washed material is dried at 120°C for 12 hours, crushed and pressed into tablets, and then placed in a muffle furnace and calcined at 500°C for 6 hours. After cooling, Cu / SiO2 catalyst is obtained, denoted as catalyst a, with a finished product weight of 80g and a Cu content of about 20%. Example 2

[0021] Preparation steps: Preparation of silica sol: Same as step 1 in Example 1, that is, 60g of fumed silica is mixed with 300mL of deionized water and stirred at 250rpm for 30min to obtain silica sol; Preparation of copper-ammonia complex solution: At room temperature, 61.56 g of copper nitrate was dissolved in 330 mL of 20 wt% ammonia water, and the molar ratio of ammonia to copper was controlled at 15 and pH=10. The mixture was stirred at 250 rpm for 30 min to obtain the copper-ammonia complex solution. Mixing and complexing: Same as step 3 in Example 1, stirring at 350 rpm for 120 min; Low-pressure ammonia stripping: Same as step 4 in Example 1, strip ammonia at 94°C for 5 hours until pH < 7, forming a viscous material; Washing, drying and molding calcination: Same as steps 5-6 in Example 1, finally obtaining Cu / SiO2 catalyst, denoted as catalyst b, with a finished product mass of 70g and a Cu content of approximately 10%. Example 3

[0022] This embodiment, based on Example 2, adds a step to protect the silanol groups on the support. The preparation steps are as follows: Preparation of silica sol and hydroxyl protection: 60g of fumed silica was mixed with 300g of 1wt% dilute ammonia water and placed in an environment of 60℃. The mixture was stirred at 250rpm for 2 hours. Then, 3.5g of sodium citrate was added as a hydroxyl protectant and the mixture was stirred for another 30 minutes. The carboxyl groups of sodium citrate were combined with the silanol groups through hydrogen bonds to obtain silica sol containing the protectant. Preparation of copper-ammonia complex solution: Same as step 2 in Example 2, i.e., 61.56g of copper nitrate is dissolved in 330mL of 20wt% ammonia water, with an ammonia-copper molar ratio of 15 and pH=10, and stirred at 250rpm for 30min; Mixing and complexing: Same as step 3 in Example 1, stirring at 350 rpm for 120 min; Low-pressure ammonia stripping: Same as step 4 in Example 1, strip ammonia at 94°C for 5 hours until pH < 7, forming a viscous material; Washing, drying and molding calcination: Same as steps 5-6 in Example 1, finally obtaining Cu / SiO2 catalyst, denoted as catalyst c, with a finished product mass of 70g and a Cu content of approximately 10%. Example 4

[0023] Based on Example 3, this embodiment further introduces a hydrothermal accelerator and adopts a low-pressure ammonia stripping process. The preparation steps are as follows: Preparation of silica sol and hydroxyl protection: Same as step 1 in Example 3, 60g of fumed silica and 300g of 1wt% dilute ammonia water are mixed and stirred at 60℃ and 250rpm for 2 hours, then 3.5g of sodium citrate is added and stirred for 30min. Preparation of copper-ammonia complex solution: Same as step 2 in Example 2, 61.56g of copper nitrate was dissolved in 330mL of 20wt% ammonia water, with an ammonia-copper molar ratio of 15 and pH=10, and stirred at 250rpm for 30min; Mixing and adding accelerator: Keep at room temperature, mix the silica sol from step 1 with the copper ammonia complex solution from step 2, add 3.6g of urea as a hydrothermal accelerator, adjust the stirring speed to 250rpm, and continue stirring for 120min; Low-pressure ammonia stripping: The mixture is transferred to a negative-pressure ammonia stripping device, and the temperature is controlled at 60℃ and the stirring speed at 100rpm. Ammonia is stripped for 2 hours under negative-pressure filtration to form a viscous material. Washing, drying and molding calcination: Same as steps 5-6 in Example 1, finally obtaining Cu / SiO2 catalyst, denoted as catalyst d, with a finished product mass of 70g and a Cu content of approximately 10%.

[0024] The above embodiments were subjected to performance testing.

[0025] Test apparatus: Miniature fixed-bed reactor, 10mm inner diameter, with built-in thermocouple sheath; Catalyst pretreatment: The catalysts of each embodiment were crushed and screened to 40-60 mesh, and 2g were loaded into the reactor and activated by reduction for 3 hours at 300℃ and atmospheric pressure under pure hydrogen atmosphere; Reaction parameters: reaction temperature 170℃, reaction pressure 2.8MPa, space velocity 0.3h. -1 The hydrogen-to-ester ratio (molar ratio of H2 to dimethyl oxalate) is 100. Test parameters: dimethyl oxalate (DMO) conversion, ethylene glycol (EG) selectivity, byproduct methyl glycolate (MG) selectivity, and catalyst continuous operation stability.

[0026] The test results are shown in Table 1:

[0027] The test data shows that: The catalysts prepared in Examples 1-4 all exhibited excellent hydrogenation activity, with DMO conversion rates consistently above 99% and EG selectivity above 97%. In Example 3, sodium citrate was added as a hydroxyl protectant. Compared with Examples 1 and 2 without the protectant, the continuous operating time was significantly extended (from about 3000h to 5300h), and the MG selectivity was further reduced, indicating that silanol protection can effectively improve catalyst stability and suppress by-products. Example 4, which simultaneously added sodium citrate and urea, had the longest continuous operating time (6200 h) and the highest EG selectivity (98.11%), indicating that the hydrothermal promoter can synergistically optimize the structure of catalytic active sites with the protectant, further enhancing the stability and selectivity of the catalyst.

[0028] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the invention.

[0029] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A copper-based catalyst for the hydrogenation of dimethyl oxalate, characterized in that, The catalyst is a Cu / SiO2 catalyst with a copper content of 5-25 wt%. The catalyst is prepared from raw materials including a silicon source, a copper source, a hydroxyl protectant, a hydrothermal promoter, ammonia, and deionized water by a low-pressure ammonia stripping method. The silanol groups on the surface of the silicon source are protected by the hydroxyl protectant, and the hydrothermal promoter is used to optimize the reaction environment so that the active copper component is highly dispersed and stable on the surface of the silicon carrier.

2. A method for preparing a copper-based catalyst for the hydrogenation of dimethyl oxalate, characterized in that, Includes the following steps: S1: Preparation of silica sol: Mix the silicon source with deionized water or dilute ammonia water and stir. Add hydroxyl protectant as needed and continue stirring to obtain silica sol. S2: Preparation of copper-ammonia complex solution: Dissolve the copper source in 20wt% ammonia water, control the molar ratio of ammonia to copper to be 15 and the pH value to be 10, and stir to form a stable copper-ammonia complex solution. S3: Mixed Complexation: Mix the silica sol of S1 with the copper-ammonia complex solution of S2, add hydrothermal accelerator as needed, and stir to allow Cu... 2+ Fully react with silanol groups; S4: Low-pressure ammonia stripping: The mixture is subjected to low-pressure ammonia stripping until pH < 7, forming a viscous material; S5: Washing: Wash the viscous material with deionized water until the washing solution is neutral; S6: Drying, shaping and calcination: The washed material is dried, pressed into tablets and then calcined to obtain Cu / SiO2 catalyst.

3. The copper-based catalyst for the hydrogenation of dimethyl oxalate according to claim 1, characterized in that, The silicon source is at least one of silicate ester, fumed silica, or silica sol; the copper source is one of copper oxalate, copper acetate, copper chloride, or copper nitrate.

4. The copper-based catalyst for the hydrogenation of dimethyl oxalate according to claim 1, characterized in that, The hydroxyl protectant is one of aminosilane, hydrophobic alkylsilane, or sodium citrate; the hydrothermal accelerator is one or more of ammonium dihydrogen phosphate, biuret, or urea.

5. The copper-based catalyst for the hydrogenation of dimethyl oxalate according to claim 1, characterized in that, The ammonia solution has a mass fraction of 1 wt% or 20 wt%, with 1 wt% ammonia solution used for silica sol preparation and 20 wt% ammonia solution used for preparing copper ammonia complex solution; the conductivity of the deionized water is ≤10 μS / cm.

6. The preparation method according to claim 2, characterized in that, In S1, when the silicon source is mixed with 1wt% dilute ammonia, the mixing temperature is 60℃, the stirring speed is 250rpm, and the stirring time is 2 hours; the amount of hydroxyl protectant added is 3.5g (based on 60g of silicon source), and stirring continues for 30min after addition.

7. The preparation method according to claim 2, characterized in that, In S3, the mixing speed is 250-350 rpm and the mixing time is 120 min; the amount of hydrothermal accelerator added is 3.6 g (based on 60 g silicon source).

8. The preparation method according to claim 2, characterized in that, In S4, the low-pressure ammonia stripping temperature is 50-94℃, the stirring speed is 100-250rpm, and the ammonia stripping time is 2-5h; when a hydrothermal accelerator is added, the ammonia stripping temperature is 60℃, the stirring speed is 100rpm, and the ammonia stripping time is 2h.

9. The preparation method according to claim 2, characterized in that, In S6, the drying temperature is 120℃ and the drying time is 12 hours; the calcination temperature is 500℃ and the calcination time is 6 hours.

10. The copper-based catalyst for the hydrogenation of dimethyl oxalate according to claim 1, characterized in that, The catalyst was used in a reaction at a temperature of 170°C, a pressure of 2.8 MPa, and a space velocity of 0.3 h⁻¹. -1 Under the condition of a hydrogen-to-ester ratio of 100, the conversion rate of dimethyl oxalate is ≥99%, the selectivity of ethylene glycol is ≥97%, and the continuous operating time is ≥3000h.

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