A catalyst for directly and continuously synthesizing dimethyl carbonate from carbon dioxide and methanol, and a preparation method and application thereof

Abstract

This invention provides a catalyst for the direct continuous synthesis of dimethyl carbonate from carbon dioxide and methanol, its preparation method, and its application, belonging to the field of catalyst preparation technology. The catalytically active components are firmly loaded onto the surface of a network support using a cyclic high- and low-pressure electrophoretic deposition method, forming a multi-level layered structure with alternating loose and dense layers. When used in a fixed-bed reactor or catalytic distillation reaction section, this catalyst achieves catalytic function while ensuring uniform mixing of reactants in the fixed bed, effectively improving the contact efficiency between reactants and active sites, reducing bed pressure drop, resulting in high dimethyl carbonate yield and selectivity, and also facilitating catalyst recovery and reuse.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and in particular to a catalyst for the direct and continuous synthesis of dimethyl carbonate from carbon dioxide and methanol, its preparation method, and its application. Background Technology

[0002] Dimethyl carbonate (DMC) is an important green chemical intermediate with low toxicity, good biodegradability, and excellent solubility, and is widely used in polycarbonate synthesis, lithium battery electrolytes, pharmaceutical intermediates, and environmentally friendly solvents. The direct synthesis of DMC from carbon dioxide (CO2) and methanol not only converts the greenhouse gas CO2 into a high-value-added chemical, aligning with the dual-carbon strategy, but also offers advantages such as high atom economy and a green synthetic route with water as the only byproduct, making it a current research hotspot in the field of catalysis.

[0003] However, this reaction faces two major technical bottlenecks: firstly, thermodynamic limitations result in a relatively small equilibrium constant; secondly, the water generated during the reaction inhibits the forward reaction. To address these issues, various improvement schemes have been disclosed in the existing technology, including using dehydrating agents (such as 2-cyanopyridine, acetal, trimethyl orthoformate, calcium chloride, magnesium oxide, 3A molecular sieve, 4A molecular sieve, 13X type molecular sieve, etc.) to remove byproduct water, developing highly active catalysts, and optimizing reaction process conditions.

[0004] Previous studies have used cordierite honeycomb ceramics as a support to load cerium-based composite oxide coatings via a coating method to form monolithic catalysts (CN201911306595.2). Other studies have encapsulated Cu-Ni alloy nanoparticles in porous organic polymers and then fixed them to honeycomb ceramics to form monolithic catalysts for the direct synthesis of dimethylcarbonate (DMC) from CO2 and methanol (Chen Y, Yang Y, Tian S, et al. Highly effective synthesis of dimethylcarbonate over CuNi alloy nanoparticles@ Porous organic polymers composite[J]. Applied Catalysis A: General, 2019, 587: 117275.). However, this approach still has the following drawbacks: ceramic supports have poor thermal conductivity, easily leading to localized overheating during the reaction, affecting catalyst lifetime and selectivity, and ultimately impacting DMC yield; the bonding strength between the catalyst and support in the coating method is limited, and the coating is prone to peeling off during long-term operation; although the pore structure of the honeycomb ceramics reduces the pressure drop, there is still room for improvement in the contact efficiency between the reactants and the catalytic active sites.

[0005] Regarding catalyst loading, the most common practice in fixed-bed reactors is to directly fill the reaction tube with powdered or shaped catalyst, or to mix it with inert packing materials (such as quartz sand or quartz wool) to improve fluid distribution and catalytic component dispersion. However, the existing method of mixing catalyst with inert materials still has the following drawbacks: the uniformity of the mixing of catalyst and quartz sand is difficult to control, and batch-to-batch yield fluctuations are easily caused by differences in loading operations; after mixing, the catalyst still exists in powder or granular form, which leads to catalyst loss and re-aggregation during use, especially in long-term operation of flow reaction systems, making catalyst recovery and reuse difficult; in continuous flow fixed-bed reactors, powdered catalysts are prone to problems such as bed settling, channeling, and increased pressure drop due to fluid impact, affecting the long-term stable operation of the unit.

[0006] Therefore, current catalysts used for the direct continuous synthesis of dimethyl carbonate from carbon dioxide and methanol still suffer from problems such as low contact efficiency between reactants and catalytically active sites, resulting in low yields and selectivity of dimethyl carbonate during their loading and application. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention utilizes a cyclic high- and low-pressure electrophoretic deposition method to load catalytically active components onto the surface of a porous metal or alloy mesh support, forming a catalyst with a special structure (a multi-level layered structure in which the active components form alternating loose and dense layers on the support surface). This catalyst is then used in a fixed-bed reactor or catalytic distillation reaction section. In this catalyst, the abundant micron-sized pores within the loose layers provide low-resistance mass transfer channels for the diffusion of reactants into the catalyst and products outward, allowing for full utilization of the active sites in the deep dense layers. This increases the contact efficiency between reactants and catalytically active sites, thereby improving the yield and selectivity of dimethyl carbonate. Furthermore, it facilitates catalyst recovery and reuse.

[0008] One of the objectives of this invention is to provide a method for preparing a catalyst for the direct and continuous synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0009] The second objective of this invention is to provide a catalyst prepared by the above method.

[0010] A third objective of this invention is to provide an application of the catalyst.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a method for preparing a catalyst for the direct and continuous synthesis of dimethyl carbonate from carbon dioxide and methanol, comprising the following steps: (1) Immerse the pretreated porous metal or alloy mesh support in a suspension containing catalytically active components; (2) The catalytic active components are loaded on the surface of a porous metal or alloy mesh support by electrophoretic deposition. The electrophoretic deposition method includes: at room temperature, using a porous metal or alloy mesh support as the cathode and a stainless steel plate as the anode, with an electrode spacing of 2-8 cm, electrophoretic deposition is carried out using a high- and low-voltage cyclic voltage mode, wherein the high voltage U1 is 50V-80V, the low voltage U2 is 3V-15V, and the ratio of U1 to U2 is 6-13. The high voltage duration is 2-10 min, the low voltage duration is 2-10 min, and the high and low voltage alternate once as one cycle. The alternation cycle is 2-10 cycles, and the alternation order is high voltage first and then low voltage or low voltage first and then high voltage. (3) After deposition, the catalyst is dried and calcined to obtain the catalyst.

[0012] The following is a detailed explanation: Step (1): In some embodiments, the pretreatment in step (1) includes: alkaline washing, acid washing and ultrasonic cleaning with deionized water on the porous metal or alloy mesh carrier. The alkali is one or more of KOH, NaOH, Na2CO3, Na3PO4, NH3•H2O, NaHCO3, and K2CO3; The acid is one or more of succinic acid, acetic acid, citric acid, oxalic acid, hydrochloric acid, nitric acid, and sulfuric acid.

[0013] In some embodiments, in step (1), the porous metal or alloy mesh carrier is selected from one or more of stainless steel wire mesh, copper foam, nickel foam, titanium foam, iron-chromium-aluminum wire mesh or metal felt; the mesh number of the porous metal or alloy mesh carrier is 20 mesh to 200 mesh, and the wire diameter is 0.02-0.4 mm.

[0014] In some embodiments, in step (1), the suspension containing the catalytically active component includes the catalytically active component, a binder, and a solvent; the concentration of the catalytically active component in the suspension is 1~20 g / L, and the mass of the binder is 0.1%~0.8% of the total mass of the suspension; Preferably, the catalytically active component is one or more of cerium, zirconium, iron, praseodymium, lanthanum, cobalt metals and oxides; Preferably, the adhesive is one or more of PVP (polyvinylpyrrolidone), PEI (polyethyleneimine), neutral silica sol, and alumina sol; Preferably, the solvent is anhydrous ethanol.

[0015] Preferably, the pH value of the suspension is 4.5 to 5.0.

[0016] Step (2): Electrophoretic deposition in high- and low-voltage cyclic modes can be performed in one of the following two ways: Method 1: Alternate between high pressure and low pressure in a cycle, with each high-pressure-low-pressure cycle constituting one round, repeating for a total of 2 to 10 rounds; Method 2: Alternate between low pressure and high pressure, low pressure and high pressure, etc. Each low pressure and high pressure cycle is one round, and repeat for a total of 2 to 10 rounds.

[0017] The catalytically active component layer formed by high-pressure deposition is a dense layer, meaning it has a relatively high density, while the layer formed by low-pressure deposition is a loose layer, meaning it has a relatively low density. The density of the dense layer is greater than that of the loose layer.

[0018] Step (3): In some embodiments, in step (3), the drying temperature is 80~120℃ and the drying time is 3~4 hours.

[0019] In some embodiments, in step (3), the calcination temperature is 400~700℃, the calcination time is 2~8 hours, and the calcination atmosphere is air.

[0020] Secondly, the present invention provides a catalyst for the direct and continuous synthesis of dimethyl carbonate from carbon dioxide and methanol, which is prepared by the above-described preparation method.

[0021] The structure of the catalyst is as follows Figure 1 , Figure 2 As shown, it includes a porous metal or alloy mesh support and a catalytically active component supported on the surface of the support; The catalytically active component forms a multi-level layered structure with alternating loose and dense layers on the surface of a porous metal or alloy mesh support. In the multi-level layered structure, the thickness of the loose layer is 5~30μm, the thickness of the dense layer is 5~30μm, and the total number of loose and dense layers is 4~20 layers.

[0022] Thirdly, the present invention provides an application of the above-mentioned catalyst in the direct and continuous synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0023] The applications include: loading the catalyst into a fixed-bed reactor or a catalytic distillation reaction section, and conducting reactions at a temperature of 80-200°C, a pressure of 0.5-5 MPa, and a space velocity of 100-2000 h⁻¹. -¹ The catalytic reaction is carried out under the condition that the molar ratio of raw material CO2 to methanol is 1:10 to 10:1; a dehydrating agent (selected from at least one of 2-cyanopyridine, acetal, trimethyl orthoformate, calcium chloride, magnesium oxide, 3A molecular sieve, 4A molecular sieve, and 13X type molecular sieve) is added to the reaction system, and the mass ratio of the dehydrating agent to methanol is 1:10 to 1:1.

[0024] The filling method can be to roll the calcined catalyst into a shape that matches the inner diameter of the fixed bed reactor. Specifically, it can be made into a shape with a multi-layer coaxial or spiral roll structure, with 2 to 20 layers, and the size matches the inner diameter of the reaction tube of the fixed bed reactor.

[0025] Beneficial effects: This invention utilizes a cyclic high- and low-pressure electrophoretic deposition method to load catalytically active components onto a porous mesh support. This results in a multi-level layered structure on the support surface, with alternating loose and dense layers. This avoids the agglomeration that occurs when directly loading powdered catalysts and ensures the uniformity of each batch of monolithic catalyst. Simultaneously, the abundant micron-sized pores within the loose layer provide low-resistance mass transfer channels for reactant diffusion into the catalyst and product diffusion outwards, fully utilizing the active sites in the deep dense layer. This increases the contact probability between reactants and catalytically active components, ensuring improved and stable DMC yields across batches. Furthermore, the use of electrophoretic deposition followed by high-temperature calcination forms chemical bonds between the catalytically active components and the metal support. Compared to existing physical retention or coating methods, this significantly improves the bonding strength, making it less prone to detachment and loss during long-term operation and enhancing reusability.

[0026] The introduction of this catalyst with a special structure resulted in a selectivity of 99.1% and a yield of 44.2% for DMC in the direct continuous catalytic synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0027] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the catalyst of the present invention; Figure 2 This is a radial cross-sectional view of a single fiber of the catalyst of the present invention. Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0030] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0031] The calculation methods for the yield and selectivity of dimethyl carbonate in the following examples can be found in the relevant methods in the paper (Xu Demei, Zhang Wenchao, Bai Ziwei, et al. Performance of CeSnxO2 catalyst in the direct continuous synthesis of dimethyl carbonate from CO2 and methanol [J]. Acta Petrolei Sinica (Petroleum Processing), 2026, 42(2):382-396).

[0032] Example 1 Copper foam (40 mesh, 0.15 mm wire diameter) was cut into rectangular sheets of 5 cm × 10 cm. These sheets were then sequentially immersed in 10 wt% NaOH aqueous solution and 10 wt% oxalic acid solution, and ultrasonically cleaned for 15 min each time to remove surface oil and oxide layers. Next, the sheets were ultrasonically vibrated in deionized water for 10 min and dried in an oven at 80℃ for 2 h to obtain the pretreated copper foam carrier.

[0033] 1.5 g of CeO2 nanoparticles (particle size of about 50 nm) were dispersed in 100 mL of anhydrous ethanol. 0.5 g of polyvinylpyrrolidone (PVP) was added as a dispersant and binder. The pH was adjusted to 4.5-5.0 with dilute nitric acid and ultrasonically dispersed for 60 min to obtain a uniform suspension with a CeO2 concentration of 15 g / L.

[0034] The suspension was placed in a self-made I-shaped electrophoresis tank (volume 110 cm³). 3 In this embodiment, the pretreated copper wire mesh carrier is used as the cathode, and a stainless steel plate is used as the anode, with a 4cm distance between the two electrodes to ensure that the electrode plate is completely immersed in the suspension. Electrophoretic deposition is performed in the electrophoresis tank at room temperature. The electrophoretic deposition adopts a high-voltage-low-voltage-high-voltage-low-voltage cyclic voltage mode; first, a voltage of 60V (high voltage) is applied for deposition for 3 minutes, then a voltage of 5V (low voltage) is applied for deposition for 3 minutes. This alternation of high and low voltage constitutes one cycle, and a total of 5 cycles are repeated, with a total deposition time of 30 minutes. After deposition, the plate is removed, rinsed with anhydrous ethanol, and vacuum dried at 80°C for 3 hours.

[0035] The dried wire mesh was placed in a tube furnace and heated to 500°C at a rate of 2°C / min in air atmosphere. It was then baked at a constant temperature for 3 hours and cooled in the furnace.

[0036] The calcined catalyst was rolled into a cylindrical shape with four layers and an outer diameter of approximately 9.8 mm. It was then bound and fixed with fine copper wire to obtain the desired shaped catalyst. Based on weighing calculations, the CeO2 loading of the catalyst obtained in this example was 6.33 wt% of the mass of the copper foam.

[0037] The shaped catalyst was loaded into the isothermal zone of a fixed-bed reactor (10 mm inner diameter), with a bed height of approximately 5 cm, and fixed at both ends with quartz wool. Before the reaction, it was pretreated at 150 °C for 1 hour under a N2 atmosphere by heating at 5 °C / min.

[0038] Reaction conditions: reaction temperature 150℃, reaction pressure 2.0MPa, CO2 to methanol molar ratio 3:1, methanol feed rate 0.437mL / min, CO2 flow rate 40mL / min, space velocity 1156h⁻¹ - ¹. Add 2-cyanopyridine as a dehydrating agent (molar ratio with methanol 1:2), run for 6 hours.

[0039] Gas chromatography analysis of the product showed that the yield of dimethyl carbonate was 44.2% and the selectivity was 99.1%.

[0040] Example 2 Except for changing the number of high and low pressure alternation cycles from 5 to 3, the other conditions are the same as in Example 1.

[0041] The yield of dimethyl carbonate was 36.0%, and the selectivity was 99.0%.

[0042] Example 3 Except for changing the CeO2 suspension concentration to 10 g / L during high and low pressure cyclic electrophoretic deposition of CeO2, the other conditions were the same as in Example 1.

[0043] The yield of dimethyl carbonate was 37.6%, and the selectivity was 99.1%.

[0044] Example 4 Except for the high-pressure and low-pressure cyclic electrophoretic deposition of CeO2, the high-pressure deposition time was changed to 5 minutes and the low-pressure deposition time was changed to 5 minutes, and the other conditions were the same as in Example 1.

[0045] The yield of dimethyl carbonate was 40.2%, and the selectivity was 98.9%. Example 5 Except that the electrophoretic deposition of CeO2 was changed to electrophoretic deposition of ZrO2, the other conditions were the same as in Example 1.

[0046] The yield of dimethyl carbonate was 35.3%, with a selectivity of 99.1%.

[0047] Example 6 Except that the electrophoretic deposition of CeO2 was replaced with electrophoretic deposition of metallic cobalt, the other conditions were the same as in Example 1.

[0048] The yield of dimethyl carbonate was 26.3%, and the selectivity was 97.1%.

[0049] Example 7 Except for the reaction temperature being changed to 130°C, the other conditions were the same as in Example 1.

[0050] The yield of dimethyl carbonate was 26.6%, with a selectivity of 99.5%.

[0051] Example 8 Except for the high-low pressure cyclic electrophoretic deposition, in which low pressure deposition is performed first and then high pressure deposition is performed, the other conditions are the same as in Example 1.

[0052] The yield of dimethyl carbonate was 40.6%, and the selectivity was 99.4%.

[0053] Comparative Example 1 A CeO2 catalyst supported on copper foam was prepared by impregnation. 1.5 g of CeO2 nanoparticles (approximately 50 nm in diameter) were added to 100 mL of anhydrous ethanol and ultrasonically dispersed for 30 min to form a CeO2 suspension. A piece of copper foam support pretreated in Example 1 was weighed and recorded as m0, and immersed in the above suspension, allowing it to stand at room temperature for 6 hours. After removal, excess suspension was gently rinsed off with anhydrous ethanol, and the surface was vacuum dried at 80 °C for 3 hours, with the weight recorded as m1. The above "impregnation-drying" steps were repeated 4 times. Finally, the dried support was placed in a tube furnace and calcined at 500 °C at a rate of 2 °C / min in air atmosphere for 3 hours, followed by furnace cooling. Based on weighing calculations, the CeO2 loading of the catalyst obtained in this comparative example was approximately 6.41 wt% of the copper foam mass, which is basically consistent with Example 1.

[0054] Under the same conditions, the yield of dimethyl carbonate was 22.4%, with a selectivity of 96.3%.

[0055] Comparative Example 2 Except for using a constant 75V voltage for continuous deposition for 30 minutes, the other conditions were the same as in Example 1.

[0056] The yield of dimethyl carbonate was 23.5%, and the selectivity was 95.7%.

[0057] Comparative Example 3 Except for using a constant 4V voltage for continuous deposition for 30 minutes, the other conditions were the same as in Example 1.

[0058] The yield of dimethyl carbonate was 22.8%, and the selectivity was 90.1%.

[0059] Comparative Example 4 Except for changing the deposition low voltage to 12V, the other conditions were the same as in Example 1.

[0060] The yield of dimethyl carbonate was 24.3%, and the selectivity was 94.9%.

[0061] Comparative Example 5 Except for changing the number of electrophoretic deposition cycles to 12, the other conditions were the same as in Example 1.

[0062] The yield of dimethyl carbonate was 22.4%, and the selectivity was 95.8%.

[0063] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a catalyst for the direct and continuous synthesis of dimethyl carbonate from carbon dioxide and methanol, characterized in that, Includes the following steps: (1) Immerse the pretreated porous metal or alloy mesh support in a suspension containing catalytically active components; (2) The catalytic active components are loaded on the surface of a porous metal or alloy mesh support by electrophoretic deposition. The electrophoretic deposition method includes: at room temperature, using a porous metal or alloy mesh support as the cathode and a stainless steel plate as the anode, with an electrode spacing of 2-8 cm, electrophoretic deposition is carried out using a high- and low-voltage cyclic voltage mode, wherein the high voltage U1 is 50V-80V, the low voltage U2 is 3V-15V, and the ratio of U1 to U2 is 6-13. The high voltage duration is 2-10 min, the low voltage duration is 2-10 min, and the high and low voltage alternate once as one cycle. The alternation cycle is 2-10 cycles, and the alternation order is high voltage first and then low voltage or low voltage first and then high voltage. (3) After deposition, the catalyst is dried and calcined to obtain the catalyst.

2. The preparation method according to claim 1, characterized in that, The pretreatment in step (1) includes: alkaline washing, acid washing and ultrasonic cleaning with deionized water on the porous metal or alloy mesh carrier; The alkali is one or more of KOH, NaOH, Na2CO3, Na3PO4, NH3•H2O, NaHCO3, and K2CO3; The acid is one or more of succinic acid, acetic acid, citric acid, oxalic acid, hydrochloric acid, nitric acid, and sulfuric acid.

3. The preparation method according to claim 1, characterized in that, In step (1), the porous metal or alloy mesh carrier is selected from one or more of stainless steel wire mesh, copper foam, nickel foam, titanium foam, iron-chromium-aluminum wire mesh or metal felt.

4. The preparation method according to claim 1, characterized in that, In step (1), the suspension containing the catalytically active component includes the catalytically active component, a binder, and a solvent; the concentration of the catalytically active component in the suspension is 1~20 g / L, and the mass of the binder is 0.1%~0.8% of the total mass of the suspension.

5. The preparation method according to claim 4, characterized in that, The catalytically active component is one or more of cerium, zirconium, iron, praseodymium, lanthanum, cobalt metals and oxides.

6. The preparation method according to claim 4, characterized in that, The adhesive is one or more of polyvinylpyrrolidone, polyethyleneimine, neutral silica sol, and alumina sol. The solvent is anhydrous ethanol.

7. The preparation method according to claim 1, characterized in that, In step (3), the roasting temperature is 400~700℃, the roasting time is 2~8 hours, and the roasting atmosphere is air.

8. A catalyst for the direct and continuous synthesis of dimethyl carbonate from carbon dioxide and methanol, characterized in that, Prepared by the preparation method according to any one of claims 1-7; The catalyst comprises a porous metal or alloy mesh support and a catalytically active component loaded on the surface of the support; the catalytically active component forms a multi-level layered structure on the surface of the porous metal or alloy mesh support, with alternating loose and dense layers.

9. The application of the catalyst according to claim 8 in the direct continuous synthesis of dimethyl carbonate from carbon dioxide and methanol.

10. The application according to claim 9, characterized in that, The process includes the following steps: loading the catalyst into a fixed-bed reactor or a catalytic distillation reaction section, and reacting at a temperature of 80-200°C, a pressure of 0.5-5 MPa, and a space velocity of 100-2000 h⁻¹. - ¹ The catalytic reaction is carried out under the condition that the molar ratio of CO2 to methanol is 1:10 to 10:1; a dehydrating agent is added to the reaction system, and the mass ratio of the dehydrating agent to methanol is 1:10 to 1:1.

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