A core-shell copper-based catalyst for ester hydrogenation, and its preparation and application methods.

Abstract

This invention discloses a core-shell copper-based catalyst for the hydrogenation of esters to ethylene glycol. The catalyst comprises 10-20 wt.% copper and 80-90 wt.% silica by weight. By changing the hydrothermal time of catalyst synthesis, the size of the chamber can be controlled, thereby regulating the enrichment of hydrogen and the diffusion path of reactants, solving the problem of excessively high hydrogen-ester ratio required in the hydrogenation of oxalate. Even at a relatively low H2 / DMO feed molar ratio (20), it exhibits excellent oxalate hydrogenation activity and ethylene glycol yield, with an oxalate conversion rate as high as 100% and an ethylene glycol yield of 98.5%. Simultaneously, due to the confinement effect of the structure, the catalyst possesses excellent thermal stability. Furthermore, the raw materials for this catalyst are widely available, which can significantly reduce the amount of hydrogen recycled during the reaction, saving power and equipment costs and improving the thermal stability of the catalyst, demonstrating high industrial prospects and application value.

Description

Technical Field

[0001] This invention belongs to the field of gas-phase ester hydrogenation catalyst technology, and relates to a core-shell copper-based catalyst with a cavity that has a hydrogen enrichment effect, especially a core-shell copper-based catalyst for the hydrogenation of ester to ethylene glycol, and its preparation and application methods. Background Technology

[0002] Ethylene glycol, as an important chemical raw material or solvent, is widely used in the production of polyester and its downstream products, antifreeze, lubricants, etc., and has a broad market prospect. In existing technologies, the process of producing dimethyl oxalate via carbon monoxide coupling from syngas, followed by hydrogenation of dimethyl oxalate to ethylene glycol, has the advantages of high atom economy, mild reaction conditions, high product selectivity, and environmental friendliness. It is one of the important non-petroleum routes for synthesizing ethylene glycol, and the hydrogenation of dimethyl oxalate to ethylene glycol is the core step of this process.

[0003] Copper-based catalysts have achieved good activity and selectivity in this reaction system, but the high required hydrogen-to-ester ratio (H2 / DMO molar ratio of hydrogen to oxalate) and poor catalyst stability remain unresolved. Currently, the hydrogenation reaction of dimethyl oxalate (DMO) requires a large excess of hydrogen (H2 / DMO molar feed ratio typically between 80 and 200) to achieve high activity and ethylene glycol yield. However, in industrial applications, an excessively high hydrogen-to-ester ratio leads to a larger hydrogen circulation volume, increasing the requirements for compressor and other equipment parameters, and significantly increasing the equipment and power costs required for this process. Simultaneously, copper particles are prone to agglomeration and sintering during the reaction, resulting in poor catalyst thermal stability. Therefore, designing novel, highly active copper-based catalysts that enable high ethylene glycol yields with excellent thermal stability even at low hydrogen-to-ester ratios in the oxalate hydrogenation reaction is crucial for optimizing the syngas-to-ethylene glycol process. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and address the problems of high hydrogen-to-ester ratio and poor high-temperature thermal stability in the hydrogenation of oxalate to ethylene glycol. This invention proposes a copper-based catalyst with a special core-shell structure and applies it to the oxalate hydrogenation system. Its special structure allows hydrogen to be enriched in the internal cavities of the catalyst during the reaction, thus solving the problem of the required high hydrogen-to-ester ratio in the hydrogenation reaction. Simultaneously, it alters the diffusion path of reactants within the catalyst channels, increasing the contact frequency between reactants and active sites, and improving catalytic performance. Furthermore, the confinement effect of the core-shell structure enhances the catalyst's thermal stability. The catalyst prepared by this method exhibits excellent oxalate hydrogenation activity and ethylene glycol yield even at a low H2 / DMO feed ratio, reducing hydrogen recycling volume and saving power and equipment costs. To verify the enrichment effect of the catalyst structure, ethylene carbonate and methyl acetate were selected as probe reactants to examine the catalytic performance changes with the hydrogen-to-ester ratio. Moreover, the prepared catalyst maintains excellent stability under high-temperature heat treatment, has a long service life, and low preparation cost, demonstrating high industrial prospects and application value.

[0005] This invention is achieved through the following technical solution:

[0006] The core-shell catalyst for oxalate hydrogenation in this invention has the following main chemical components: copper and silicon dioxide, wherein copper accounts for 2-30 wt.% of the catalyst mass and silicon dioxide accounts for 70-98 wt.% of the catalyst mass. A preferred embodiment is that copper accounts for 10-20 wt.% of the catalyst mass and silicon dioxide accounts for 80-90 wt.% of the catalyst mass.

[0007] The catalyst is a core-shell type catalyst with cavities, and its specific surface area is 320-550 m². 2 / g, with an average pore volume of 0.15-0.5cm³. 3 / g, with an average pore size of 2-5nm; the preferred option is a catalyst with a specific surface area of ​​380-420m². 2 / g, with an average pore volume of 0.2-0.38cm³. 3 / g, with an average pore size of 2.3-3.5nm.

[0008] Another object of the present invention is to provide a method for preparing a cavity-type core-shell copper-based catalyst for oxalate hydrogenation, comprising the following steps:

[0009] (1) Using polyvinylpyrrolidone (PVP) as a surfactant, it is mixed with alcohol, maintaining a PVP to ethanol mass ratio of 0.5%-10%, and the temperature is maintained at 25-50℃. The mixture is stirred for 0.5-2 hours to obtain a clear solution. A copper precursor salt is added to the above clear solution, maintaining a PVP to copper precursor salt mass ratio of 1-10, and the mixture is stirred for 5-20 hours.

[0010] The alcohol is methanol or ethanol, and the copper precursor salt is any one of copper acetate, copper nitrate, copper chloride, or copper sulfate.

[0011] (2) Transfer the product from step (1) to an autoclave and perform hydrothermal treatment at 150-250℃, then let it stand for 1-30 hours. Under high temperature conditions, copper ions are reduced by alcohol solution to copper particles of different valence states and sizes. PVP acts as a surfactant to coat the surface of the copper particles, preventing them from agglomerating.

[0012] (3) Add the product from step (2) to a mixed solution of water and alcohol in a certain proportion, with a volume ratio of water to alcohol of 0.2-2. Stir for 0.5-2 hours, then add an alkaline agent solution dropwise, keeping the pH of the solution between 7 and 11, and stir for 5-30 minutes. Under the action of the alkaline agent, the copper particles are continuously etched into small particles and coated with PVP.

[0013] The alcohol is methanol or ethanol, and the alkaline agent is any one of ammonia, ammonium chloride, or sodium hydroxide.

[0014] (4) Using hexadecyltrimethylammonium bromide (CTAB) as a template agent, add it to the product of step (3), stir for 10-30 min, add silicon source dropwise, maintain the mass ratio of SiO2 to CTAB at 1-6, and maintain the temperature at 25-50℃, stir for 5-20 h. CTAB interacts with PVP, coats the outside of PVP, and acts as a template agent for the formation of mesoporous SiO2 by hydrolysis under the action of an alkaline agent.

[0015] The silicon source is any one of sodium silicate, silica sol, or tetraethyl orthosilicate.

[0016] (5) The product from step (4) is washed with deionized water and alcohol solution. The washed product is dried at 40-100℃ for 8-20h. Then it is calcined at 400-700℃ for 2-10h to remove surfactant and template agent and obtain core-shell catalyst with different cavity structure.

[0017] The washing method is either filtration washing or centrifugal washing, and the drying method is either ordinary drying method or vacuum drying method.

[0018] A more preferred embodiment of the above scheme is as follows: the alcohol is ethanol. The mass ratio of PVP to the alcohol solution is 1.5%-5%. The copper precursor salt solution is copper nitrate. The volume ratio of water to alcohol is 0.5-1.2. The alkaline agent is ammonia. The pH of the solution is 7.5-9. The silicon dioxide source is tetraethyl orthosilicate. The washing method is centrifugal washing. The drying method is vacuum drying. The mass ratio of PVP to the copper precursor salt is 3-6. The mass ratio of the silicon dioxide source to CTAB is 2.5-4.5.

[0019] In step 2, the valence state and size of copper particles are controlled by adjusting the hydrothermal treatment time, which is preferably 5-15 hours.

[0020] The catalyst needs to be reduced online before use. Specifically, the reduction temperature is 150-400℃, the reduction atmosphere is hydrogen, and the hydrogen flow rate required for the reduction of each gram of catalyst is 40-200 mL / min.

[0021] The above-mentioned catalyst is used in the hydrogenation reaction of oxalate esters at a reaction pressure of 1.5-3.5 MPa, a reaction temperature of 180-220℃, a hydrogen-to-ester ratio of 20-80, and a liquid hourly space velocity of 0.5-5 h⁻¹. -1 The liquid hourly space velocity (LHSV) refers to the LHSV of oxalate ester. For core-shell catalysts with small-sized cavities, a 98.5% ethylene glycol yield can still be obtained even with a hydrogen-to-ester ratio as low as 20 in the feed. Simultaneously, under high-temperature heat treatment, due to the confinement effect of the cavities on copper particles, the copper particles are blocked by the cavities and are difficult to aggregate, thus exhibiting excellent thermal stability.

[0022] The advantages and positive effects of this invention are:

[0023] 1. This invention exhibits excellent catalytic activity (ethylene glycol yield up to 98.5%) in the hydrogenation reaction of oxalate esters with a low hydrogen-to-ester ratio (H2 / DMO = 20). Industrially, it can significantly reduce the amount of hydrogen circulating, save power consumption of gas compressors, and improve the processing capacity of reactors per unit volume.

[0024] 2. The core-shell structure catalyst with a special cavity of the present invention can improve the enrichment effect of hydrogen, thereby reducing the hydrogen-ester ratio in the hydrogenation reaction of oxalate esters, and is also applicable to the hydrogenation reaction of other esters.

[0025] 3. In the hydrogenation catalyst of the present invention with a special structure, the active component is confined within the cavity, thus exhibiting excellent stability.

[0026] 4. In this invention, the core-shell form and size can be flexibly adjusted by changing the hydrothermal treatment time and the content of surfactant, thereby changing the diffusion path of reactants in the catalyst channels and the contact frequency with catalytic active sites. Attached Figure Description

[0027] Figure 1 Transmission electron microscopy (TEM) images of the core-shell catalyst, sheet-like catalyst, and nanotube catalyst synthesized under different hydrothermal treatment times in this invention.

[0028] In the figure, AC represents the core-shell catalyst (hydrothermal treatment time is A: 2h, B: 10h, C: 20h), D represents the layered catalyst, and E represents the nanotube catalyst.

[0029] Figure 2 The accompanying figure shows the N2 isothermal adsorption-desorption of the catalysts synthesized under different hydrothermal treatment times in this invention;

[0030] The hydrothermal treatment times are A: 2h, B: 10h, and C: 20h.

[0031] Figure 3 This is the X-ray diffraction (XRD) pattern of the catalyst after reduction according to the present invention.

[0032] Figure 4 Observation of catalyst lifetime for the hydrogenation of dimethyl oxalate to ethylene glycol;

[0033] Among them, A is a core-shell catalyst that has been hydrothermally heated for 10 hours, B is a layered catalyst, and C is a nanotube catalyst.

[0034] Figure 5 Transmission electron microscopy (TEM) images of samples after each step in the catalyst preparation process;

[0035] Wherein, A is the copper particles formed after hydrothermal treatment in step (2), B is the small particles formed after etching with an alkaline agent in step (3), and C is the core-shell structure catalyst with a cavity. Detailed Implementation

[0036] The present invention will be further described below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in the manual, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified.

[0037] Example 1

[0038] Catalyst preparation

[0039] 2.83 g of polyvinylpyrrolidone (PVP) was added to 150 ml of ethanol solution and stirred at 30 °C for 1 h to obtain a clear solution. 0.566 g of copper nitrate trihydrate was added to the clear solution and stirred at 30 °C for 12 h. The resulting mixture was transferred to an autoclave and allowed to stand at 190 °C for 10 h. Under high temperature conditions, copper ions were reduced by the ethanol solution to large metallic particles (see...). Figure 5 (A)). The hydrothermally heated product was added to a mixture of 100 ml water and 150 ml ethanol, and stirred for 1 hour. Then, 5 ml of ammonia was added dropwise, and the mixture was stirred for 10 minutes. Under the action of the ammonia, the copper particles were continuously etched into smaller particles (see...). Figure 5 (B) 0.75 g of hexadecyltrimethylammonium bromide (CTAB) was added to the above solution, and after stirring for 20 min, 3 ml of tetraethyl orthosilicate was added dropwise, and the mixture was stirred at 30 °C for 10 h. The obtained product was washed three times by centrifugation with deionized water and ethanol solution. The washed product was then vacuum dried at 60 °C for 12 h, and then calcined at 550 °C for 4 h to remove the surfactant and template agent, thus obtaining a core-shell catalyst with a cavity structure (see [link to product description]). Figure 5 (C)).

[0040] Catalyst evaluation:

[0041] In this invention, the gas-phase hydrogenation reaction of oxalate is carried out in a fixed-bed reactor. The calcined catalyst is pressed into tablets and sieved to a size of 40-60 mesh. 0.5 g of catalyst is loaded and reduced at 300°C in a 2.5 MPa H₂ atmosphere at a gas flow rate of 100 mL / min. The temperature is increased from room temperature to 300°C at a rate of 2°C / min and maintained for 4 h. The temperature is then lowered to the reaction temperature of 200°C, and the oxalate is vaporized and mixed with hydrogen before entering the reaction tube. The hydrogen-to-ester ratio is 20, and the oxalate mass hourly space velocity (WHSV) is 1.0 h⁻¹. -1 The reaction was carried out at 2.5 MPa. Gas chromatography was used to analyze the products and obtain the components of dimethyl oxalate (DMO), ethylene glycol (EG), methyl glycolate (MG), and ethanol (EtOH). Catalyst evaluation results are shown in Table 1. Figure 3 The X-ray diffraction (XRD) pattern of the catalyst of this invention shows a broad diffraction peak at 2θ = 22°, which is attributed to the characteristic diffraction peak of amorphous SiO2. The characteristic diffraction peak at 2θ = 37.0° is the diffraction peak of Cu2O(111) (JCPDS 34-1354), while the characteristic diffraction peaks at 2θ = 43.3° and 74.1° are the diffraction peaks of metallic copper (Cu) (JCPDS 65-9743). These peaks are all weak and broad, indicating that Cu and Cu2O are highly dispersed in the reduced catalyst, resulting in good catalyst activity.

[0042] Example 2

[0043] The catalyst preparation method and evaluation conditions are the same as in Example 1. Changing the hydrothermal treatment time to 2 hours yields a core-shell catalyst with a larger cavity. The cavity size can be characterized by N2 isothermal adsorption-desorption and TEM. (See [link to example 1]). Figure 1 (A) and Figure 2 The (A) curve is shown. Catalyst results evaluation is shown in Table 1.

[0044] Example 3

[0045] The catalyst preparation method and evaluation conditions are the same as in Example 1, except that the hydrothermal treatment time is changed to 20 h, which yields a cavity-free core-shell catalyst. The cavity size can be characterized by N2 isothermal adsorption-desorption and TEM, see [link to relevant documentation]. Figure 1 (C) and Figure 2 The (C) curve is shown. Catalyst results evaluation is shown in Table 1.

[0046] Comparative Example 1

[0047] Catalyst preparation

[0048] 2.78 g of copper nitrate trihydrate was dissolved in 100 ml of deionized water by stirring. Then, an appropriate amount of 28% ammonia solution was slowly added to prepare a copper ammonia solution. Next, 14 g of 30% silica sol solution was added to the copper ammonia solution, and the mixture was stirred and aged for 4 hours. The temperature was raised to 80℃ to remove ammonia from the solution until the pH reached 6-7. The solid was filtered to separate the solid material, dried at 80℃ for 10 hours, and calcined at 450℃ for 4 hours to obtain the product described in previous literature (Gong J, et al. Synthesis of Ethanol via Syngas on Cu / SiO2 Catalysts with Balanced Cu). 0 -Cu + Sites. Journal of the American Chemical Society 134, 13922-13925 (2012); Chen L, et al. Cu / SiO2 Catalysts Prepared by the Ammonia-Evaporation Method: Texture, Structure, and Catalytic Performance in Hydrogenation of Dimethyl Oxalate to Ethylene Glycol. Journal of Catalysis 257, 172-180 (2008)) and the layered copper-based catalysts reported in the patent, whose structures can be characterized by TEM, see Figure 1 (D)

[0049] Catalyst evaluation:

[0050] The catalyst evaluation conditions were the same as in Example 1, and the catalyst results are shown in Table 1.

[0051] Comparative Example 2

[0052] 4.5 g of copper nitrate trihydrate and 7.0 g of ammonium chloride were dissolved in 140 ml of deionized water by stirring. Then, an appropriate amount of 28% ammonia solution was slowly added. Next, 7 g of 30% silica sol solution was added to the copper ammonia solution, and the mixture was stirred and aged for 4 h. The resulting mixture was transferred to an autoclave and hydrothermally heated at 180 °C for 36 h. The solid material was filtered off and dried at 110 °C for 10 h, then calcined at 450 °C for 4 h to obtain the tubular copper-based catalyst reported in previous literature (Yuan Y, et al. Copper nanoparticles socketed insitu into copper phyllosilicate nanotubes with enhanced performance for chemoselective hydrogenation of esters. Chemical Communication 53, 6933-6936 (2017)) and patents. Its structure can be characterized by TEM, see [link to TEM]. Figure 1 (E)

[0053] Catalyst evaluation: The evaluation conditions for the catalyst were the same as in Example 1, and the catalyst evaluation results are shown in Table 1.

[0054] Hydrothermal treatment time (h) DMO conversion rate (%) EG yield (%) Example 1 10 100 98.5 Example 2 2 100 82.3 Example 3 20 63.9 18.4 Comparative Example 1 82.7 27.9 Comparative Example 2 93.2 49.3

[0055] Table 1: Performance evaluation of catalysts prepared by different hydrothermal treatment times and preparation methods

[0056] Table 1 shows that when the hydrothermal treatment time is 2 h and 10 h, the shell-shell catalyst with a cavity exhibits the highest conversion rate (100%) of dimethyl oxalate (DMO) at a hydrogen-to-ester ratio as low as 20. However, for the catalyst with a hydrothermal treatment time of 10 h, the core-shell structure with a smaller cavity exhibits the best catalytic activity, achieving a ethylene glycol (EG) yield of 98.5%. This indicates that the cavity size affects the hydrogen enrichment effect, with a smaller cavity size being more conducive to hydrogen enrichment. Figure 2 As can be seen from the data, the sample (Example 2) subjected to hydrothermal treatment for 2 hours exhibited almost no hysteresis loops when P / P0 was less than 0.9, indicating that the shell was formed by CTAB with uniformly sized mesopores. When P / P0 was greater than 0.9, the N2 adsorption capacity increased rapidly, indicating that the catalyst had a large internal cavity size. Figure 1(A) The structures are consistent; the average pore diameter of this sample is 3.2 nm, and the pore volume is 0.35 cm³. 3 / g. The sample (Example 3) subjected to hydrothermal treatment for 20 hours showed almost overlapping adsorption and desorption curves, indicating that the catalyst has uniformly sized mesopores and no cavity structure. Figure 1 (C) The structure is consistent; the average pore diameter of this sample is 2.4 nm, and the pore volume is 0.2 cm³. 3 / g. For the sample hydrothermally heated for 10 hours (Example 1), P / P0 was between 0.5 and 0.6, and the desorption curve rapidly decreased and closed, indicating that the catalyst has a slightly larger cavity structure connected to mesopores. Figure 1 (B) The structure is consistent; the average pore diameter of this sample is 2.7 nm, and the pore volume is 0.24 cm³. 3 / g. Furthermore, the different internal cavity structures and sizes of the catalyst also lead to different diffusion paths of the reactants within the pores. For samples with larger cavities (Example 2), the reactants can diffuse rapidly out of the cavities, reducing the contact frequency with the catalyst metal core sites. Meanwhile, for samples without internal cavities (Example 3), the lack of an internal cavity diffusion path results in the lowest contact frequency between the reactants and the catalyst metal core sites. Samples with smaller cavities (Example 1), due to the confinement effect of their internal cavities on the reactants, can increase the contact frequency between the reactants and the catalyst metal core sites, thus exhibiting optimal catalytic performance.

[0057] Examples 4-8

[0058] The catalyst preparation method was the same as in Example 1. The catalyst performance evaluation method was also the same as in Example 1, with the hydrogen-to-ester ratio set at 80 and the oxalate mass hourly space velocity (H₂S₀) at 0.5 h₀. -1 1.0h -1 2.0h -1 3.0h -1 4.0h -1 Everything else remains unchanged. The performance evaluation results of the catalyst are shown in Table 2.

[0059]

[0060]

[0061] Table 2: Catalyst performance evaluation at different oxalate mass space velocities

[0062] As can be seen from Table 2, the conversion rate of oxalate ester (DMO) gradually decreases with increasing space velocity, and the yield of ethylene glycol (EG) gradually decreases, with the highest ethylene glycol yield reaching 98.5%.

[0063] Examples 9-12

[0064] The catalyst preparation method was the same as in Example 1. The catalyst performance evaluation method was also the same as in Example 1, with the hydrogen-to-ester ratio set to 60, 50, 40, and 30, while other parameters remained unchanged. The performance evaluation results of the catalyst are shown in Table 3.

[0065] Comparative Examples 3-6

[0066] The catalyst preparation method was the same as in Comparative Example 1. The catalyst performance evaluation method was the same as in Example 1, with the hydrogen-to-ester ratio set to 60, 50, 40, and 30, and other parameters remaining unchanged. The performance evaluation results of the catalyst are shown in Table 3.

[0067] Comparative Examples 7-10

[0068] The catalyst preparation method was the same as in Comparative Example 2. The catalyst performance evaluation method was the same as in Example 1, with the hydrogen-to-ester ratio set to 60, 50, 40, and 30, and other parameters remaining unchanged. The performance evaluation results of the catalyst are shown in Table 3.

[0069] <![CDATA[H2 / DMO]]> DMO conversion rate (%) EG yield (%) Example 1 20 100 98.5 Example 9 60 100 95.6 Example 10 50 100 95.9 Example 11 40 100 96.2 Example 12 30 100 96.5 Comparative Example 3 60 99.5 88.5 Comparative Example 4 50 99.5 85.2 Comparative Example 5 40 98 74.4 Comparative Example 6 30 93 52.3 Comparative Example 7 60 100 93.7 Comparative Example 8 50 99.9 89.5 Comparative Example 9 40 99.2 81.8 Comparative Example 10 30 97.6 70.1

[0070] Table 3: Catalyst performance evaluation at different hydrogen-ester ratios

[0071] As shown in Table 3, with the decrease of hydrogen-ester ratio, the core-shell catalyst with smaller cavity size exhibits the best activity. The conversion rate of oxalate and the yield of ethylene glycol remain basically unchanged. The catalytic activity of catalysts with sheet-like and tubular structures decreases with the hydrogen-ester ratio, with the sheet-like catalyst showing the fastest decrease in catalytic activity.

[0072] Examples 13-14

[0073] The catalyst preparation method was the same as in Example 1, except that the mass of PVP was changed to 0 and 5.66 g, while other parameters remained unchanged. The catalyst performance evaluation method was the same as in Example 1, and the performance evaluation results are shown in Table 4.

[0074] PVP mass (g) DMO conversion rate (%) EG yield (%) Example 1 2.83 100 98.5 Example 13 0 80.3 11.7 Example 14 5.66 88.1 40.5

[0075] Table 4: Performance Evaluation of Catalysts Prepared with Different PVP Masses. As shown in Table 4, the catalyst without added PVP exhibits the worst catalytic activity, and excessive PVP addition also leads to a decrease in catalytic activity. The cavity size can be altered by changing the mass of PVP added during synthesis. The catalyst without added PVP (Example 13) is essentially cavity-free, with an average pore diameter of 2.2 nm and a pore volume of 0.18 cm³. 3 / g, adding excess PVP (Example 14) resulted in a larger cavity size; the average pore diameter of this sample was 3.3 nm, and the pore volume was 0.35 cm³. 3 / g, which again demonstrates that catalysts with appropriate cavity size have optimal hydrogen enrichment capacity and reactant diffusion pathways.

[0076] Examples 15-18

[0077] To verify the hydrogen enrichment effect of the core-shell structure of the present invention, the performance changes of the hydrogenation of ethylene carbonate to methanol and ethylene glycol were further investigated under different hydrogen-to-ester ratios.

[0078] The catalyst preparation method is the same as in Example 1.

[0079] Catalyst evaluation:

[0080] The gas-phase hydrogenation reaction of ethylene carbonate used in this invention is carried out in a fixed-bed reactor. The calcined catalyst is pressed into tablets and sieved to a size of 40-60 mesh. 0.5 g of catalyst is loaded and reduced at 300 °C in a 3.0 MPa H2 atmosphere at a gas flow rate of 100 mL / min. The temperature is increased from room temperature to 300 °C at a rate of 2 °C / min and maintained for 4 h. The temperature is then lowered to the reaction temperature of 180 °C, and the ethylene carbonate is vaporized and mixed with hydrogen before entering the reaction tube. The reaction is carried out at 3.0 MPa, with a mass hourly space velocity (WHSV) of ethylene carbonate of 0.5 h⁻¹. -1 The hydrogen-to-ester ratios were set to 140, 100, 60, and 20, respectively. Gas chromatography was used to analyze the products and obtain the components of ethylene carbonate (EC), ethylene glycol (EG), and methanol (MeOH). The catalyst evaluation results are shown in Table 5.

[0081] Comparative Examples 11-14

[0082] The catalyst preparation method was the same as in Comparative Example 1. The catalyst performance evaluation method was the same as in Examples 15-18, and the performance evaluation results are shown in Table 5.

[0083] Comparative Examples 15-18

[0084] The catalyst preparation method was the same as in Comparative Example 2. The catalyst performance evaluation method was the same as in Examples 15-18, and the performance evaluation results are shown in Table 5.

[0085] <![CDATA[H2 / DMO]]> EC conversion rate (%) EG selectivity (%) MeOH selectivity (%) Example 15 140 100 97.6 90.0 Example 16 100 100 98.0 91.3 Example 17 60 100 98.4 92.5 Example 18 20 98.5 98.2 90.5 Comparative Example 11 140 100 97.5 80.3 Comparative Example 12 100 98 98.1 81.5 Comparative Example 13 60 94 97.8 76.2 Comparative Example 14 20 85 97.3 69.5 Comparative Example 15 140 100 97.9 83.5 Comparative Example 16 100 100 98.0 85.3 Comparative Example 17 60 97 97.5 80.6 Comparative Example 18 20 90 97.7 73.5

[0086] Table 5: Catalyst performance evaluation of ethylene carbonate at different hydrogen-to-ester ratios

[0087] Examples 19-22

[0088] To verify the hydrogen enrichment effect of the core-shell structure of the present invention, the performance changes of the hydrogenation of methyl acetate to ethanol were further investigated under different hydrogen-ester ratios.

[0089] The catalyst preparation method is the same as in Example 1.

[0090] Catalyst evaluation:

[0091] The gas-phase hydrogenation reaction of methyl acetate used in this invention is carried out in a fixed-bed reactor. The calcined catalyst is pressed into tablets and sieved to a size of 40-60 mesh. 0.5 g of catalyst is loaded and reduced at 300 °C in a 2.5 MPa H2 atmosphere at a gas flow rate of 100 mL / min. The temperature is increased from room temperature to 300 °C at a rate of 2 °C / min and maintained for 4 h. The temperature is then lowered to the reaction temperature of 220 °C, and methyl acetate is vaporized and mixed with hydrogen before entering the reaction tube. The reaction is carried out at 2.5 MPa, with a mass hourly space velocity (WHSV) of methyl acetate of 0.3 h⁻¹. -1 The hydrogen-to-ester ratios were set to 40, 20, 10, and 5, respectively. Gas chromatography was used to analyze the products and obtain the components of methyl acetate (MA) and ethanol (EtOH). The catalyst evaluation results are shown in Table 6.

[0092] Comparative Examples 19-22

[0093] The catalyst preparation method was the same as in Comparative Example 1. The catalyst performance evaluation method was the same as in Examples 19-22, and the performance evaluation results are shown in Table 6.

[0094] Comparative Examples 23-26

[0095] The catalyst preparation method was the same as in Comparative Example 2. The catalyst performance evaluation method was the same as in Examples 19-22, and the performance evaluation results are shown in Table 6.

[0096] <![CDATA[H2 / DMO]]> MA conversion rate (%) EtOH selectivity (%) Example 19 40 93.8 90.0 Example 20 20 93.8 90.3 Example 21 10 92.5 88.5 Example 22 5 91.0 87.8 Comparative Example 19 40 88.5 84.2 Comparative Example 20 20 82.6 77.6 Comparative Example 21 10 75.8 67.5 Comparative Example 22 5 62.3 55.3 Comparative Example 23 40 90.2 85.2 Comparative Example 24 20 88.5 81.5 Comparative Example 25 10 82.4 77.7 Comparative Example 26 5 72.6 69.3

[0097] Table 6: Catalytic performance evaluation of methyl acetate at different hydrogen-to-ester ratios

[0098] As shown in Tables 5 and 6, the hydrogenation reactions of ethylene carbonate and methyl acetate exhibit similar performance trends to those of oxalate hydrogenation on three different catalyst structures. The core-shell catalyst demonstrates the best effect in reducing the hydrogen-to-ester ratio. For both lamellar and tubular catalysts, the catalytic activity decreases with increasing hydrogen-to-ester ratio, with the rate of decrease accelerating as the ratio decreases. The lamellar catalyst shows the fastest decrease in catalytic activity. This indicates that the core-shell catalyst of this invention also possesses a certain hydrogen enrichment effect in other ester hydrogenation reactions.

[0099] Example 23

[0100] To verify the thermal stability of the core-shell catalyst in this invention, it was subjected to high-temperature thermal shock treatment, and the changes in catalyst performance before and after the treatment were examined.

[0101] The catalyst preparation method is the same as in Example 1.

[0102] Catalyst evaluation

[0103] In this invention, the gas-phase hydrogenation reaction of oxalate is carried out in a fixed-bed reactor. The calcined catalyst is pressed into tablets and sieved to a size of 40-60 mesh. 0.5 g of catalyst is loaded and reduced at 300°C in a 2.5 MPa H2 atmosphere at a gas flow rate of 100 mL / min. The temperature is increased from room temperature to 300°C at a rate of 2°C / min and maintained for 4 hours. The temperature is then lowered to the reaction temperature of 200°C, and the oxalate is vaporized and mixed with hydrogen before entering the reaction tube. The hydrogen-to-ester ratio is 80. After reacting at 2.5 MPa for 100 hours, the liquid feed is stopped, and the inlet gas is switched from hydrogen to nitrogen. The temperature is raised to 450°C and maintained for 10 hours for high-temperature heat treatment, followed by cooling to the reaction temperature of 200°C. After switching the inlet gas from nitrogen to hydrogen, the liquid feed is introduced to continue the reaction. The catalytic performance evaluation results over time are shown in [the table below]. Figure 4 The (A) curve.

[0104] Comparative Example 27

[0105] The catalyst preparation method was the same as in Comparative Example 1. The catalyst performance evaluation method was the same as in Example 23, and the performance evaluation results are shown below. Figure 4 The (B) curve.

[0106] Comparative Example 28

[0107] The catalyst preparation method was the same as in Comparative Example 2. The catalyst performance evaluation method was the same as in Example 23, and the performance evaluation results are shown below. Figure 4 The (C) curve.

[0108] from Figure 4 It can be seen that before heat treatment, the three types of catalysts have similar ethylene glycol (EG) yields. After high-temperature heat treatment, the core-shell catalyst (… Figure 4 The catalytic performance of the (A) curve decreased slightly, but the ethylene glycol yield remained relatively stable over time. (Laminated) Figure 4 (B) curve) and tubular catalyst ( Figure 4 The (C) curve shows a significant decrease in catalytic performance after heat treatment, and the ethylene glycol yield continues to decrease with increasing time. These results indicate that the core-shell catalyst of this invention, due to the confinement effect of its shell, can suppress the aggregation and growth of copper particles in the adjacent core, thus maintaining excellent catalytic activity even after high-temperature treatment. In contrast, layered and nanotube catalysts exhibit significant reduction in catalytic activity after high-temperature heat treatment due to the aggregation and growth of copper particles. Therefore, this demonstrates that the core-shell catalyst of this invention possesses excellent thermal stability.

Claims

1. A core-shell copper-based catalyst for ester hydrogenation, characterized in that: The catalyst comprises copper and silica support, wherein the copper accounts for 10-20 wt.% of the catalyst mass and the support accounts for 80-90 wt.% of the catalyst mass; The catalyst is a core-shell type catalyst with cavities, and the specific surface area of ​​the catalyst is 380-420 m². 2 / g, with an average pore volume of 0.2-0.38 cm³. 3 / g, with an average pore size of 2.3-3.5nm; The preparation method of the core-shell copper-based catalyst for ester hydrogenation includes the following steps: Polyvinylpyrrolidone and copper precursor salt were added to alcohol and stirred to form a mixed solution; The mixed solution was hydrothermally treated for a period of time; The product after hydrothermal treatment was added to a mixed solution of water and alcohol, stirred, and then an alkaline agent solution was added and stirred. Add hexadecyltrimethylammonium bromide and a silicon dioxide source to the obtained product and stir. The obtained product was washed, dried, and calcined to obtain a core-shell copper-based catalyst with a cavity structure. The alcohol is either methanol or ethanol; The copper precursor salt is any one of copper acetate, copper nitrate, copper chloride, or copper sulfate. The alkaline agent is any one of ammonia, ammonium chloride, or sodium hydroxide; The silicon source is any one of sodium silicate, silica sol, or tetraethyl orthosilicate. The mass ratio of polyvinylpyrrolidone to copper precursor salt is 3-6; The mass ratio of the silicon dioxide source to hexadecyltrimethylammonium bromide is 2.5-4.5; The selected hydrothermal treatment time is 5-15 hours; The method of using the core-shell copper-based catalyst is as follows: In the hydrogenation of oxalate to ethylene glycol, the reaction pressure is 1.5-3.5 MPa, the reaction temperature is 180-220℃, the hydrogen-to-ester ratio is 20-80, and the liquid hourly space velocity is 0.5-5.0 h⁻¹. -1 The liquid hourly space velocity (LISH) refers to the LISH of oxalate ester. The catalyst described above can achieve a 98.5% yield of ethylene glycol when the H2 / DMO ratio is 20.

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