Metal salt-loaded molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention discloses a metal salt-loaded molecular sieve catalyst as well as a preparation method and application thereof. The catalyst comprises a molecular sieve and nitrogen heterocyclic crown ether alkali metal carbonate grafted on the surface of the molecular sieve. When the catalyst is used for catalyzing decarbonylation of dimethyl oxalate to prepare dimethyl carbonate, the activity is high, the service life of the catalyst is long, and side reactions can be effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a molecular sieve catalyst supported on a metal salt, its preparation method, and its application. Background Technology

[0002] Dimethyl carbonate (DMC) is an important organic synthesis intermediate widely used in pharmaceuticals, pesticides, synthetic materials, dyes, lubricant additives, food flavorings, and electronic chemicals. In recent years, with the rapid development of new energy vehicles, the market demand for DMC as a component of lithium battery electrolytes has been strong.

[0003] The main methods for synthesizing dimethyl carbonate include the phosgene method, transesterification, oxidative carbonylation, and low-pressure gas-phase CO synthesis. CN100335167C discloses a heterogeneous supported catalyst for transesterification to prepare dimethyl carbonate. This method features mild reaction conditions, easy catalyst separation, and excellent stability, but suffers from active component loss. Furthermore, the transesterification process uses petroleum-derived ethylene oxide, leading to significant cost fluctuations. CN115057777A employs a urea alcoholysis method, which is environmentally friendly but produces ammonia, resulting in uneconomical atom utilization. CN1323754C discloses a supported palladium catalyst for low-pressure gas-phase oxidative carbonylation to synthesize dimethyl carbonate. While this type of catalyst has demonstrated good catalytic efficiency, the soaring price of palladium in recent years has become a burden for users.

[0004] Currently, the capacity utilization rate of ethylene glycol production from syngas is low. Comprehensively utilizing surplus capacity to produce more economically valuable dimethyl carbonate is of great significance. In particular, leveraging existing ethylene glycol units for high-value-added utilization of dimethyl oxalate can significantly reduce costs, improve the green economy of coal chemical industry, and further optimize its development. CN113181894B discloses a supported alkali / alkaline earth metal inorganic acid salt catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate, but the product yield is low. Therefore, improving the dimethyl carbonate yield and leveraging the economic advantages of the decarbonylation method is of great importance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a molecular sieve catalyst supported on a metal salt, its preparation method, and its applications. The catalyst of this invention exhibits high activity, a long catalyst lifespan, and effectively reduces the generation of side reactions in the decarbonylation reaction of dimethyl oxalate to dimethyl carbonate.

[0006] The first aspect of the present invention provides a molecular sieve catalyst supported on a metal salt, the catalyst comprising a molecular sieve and a nitrogen-containing heterocyclic crown ether alkali metal carbonate grafted onto its surface.

[0007] Further, in the alkali metal carbonate of the azacyclic crown ether, the azacyclic crown ether is an azacyclic crown ether containing a tertiary amine, preferably selected from N-methylaza-12-crown-4-ether, 1-benzyl-1-aza-12-crown-4-ether, N-methoxyaza-15-crown-5-ether, N-phenylaza-15-crown-5-ether, benzylaza-15-crown-5-ether, 13-methyl-1,4,7,10-tetraoxa-13-azacyclopentadecane, N,N'-dibenzyl-4,13-di At least one of the following: aza-18-crown-6-ether, 5,6-benzo-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexadecane-5-ene, and 10,19-bis-(p-tolylsulphonyl)-1,4,7,13,16-pentaoxa-10,19-diazacyclohemicosane (CAS:120808-60-8).

[0008] Furthermore, the alkali metal is selected from at least one of lithium, sodium, potassium, rubidium, and cesium.

[0009] Furthermore, alkali metal carbonates of nitrogen-containing heterocyclic crown ethers are complex salts formed by the coordination of alkali metal cations with nitrogen-containing heterocyclic crown ether structures and then with carbonate ions.

[0010] Further, preferably, at least one azacyclic crown ether selected from N-methylaza-12-crown-4-ether and 1-benzyl-1-aza-12-crown-4-ether is combined with Li + Coordination.

[0011] Further, preferably, at least one azacyclic crown ether selected from N-methoxyaza-15-crown-5-ether, N-phenylaza-15-crown-5-ether, benzylaza-15-crown-5-ether, and 13-methyl-1,4,7,10-tetraoxa-13-azacyclopentadecane is combined with Na + Coordination.

[0012] Further, preferably, at least one azacyclic crown ether selected from N,N'-dibenzyl-4,13-diaza-18-crown-6-ether and 5,6-benzo-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexadecane-5-ene is combined with K + and / or Rb + Coordination.

[0013] Further, preferably, 10,19-bis-(p-tolylsulphonyl)-1,4,7,13,16-pentaoxa-10,19-diazacyclohemicosane (CAS: 120808-60-8) and Cs +Coordination.

[0014] Furthermore, in the catalyst, the dispersion diameter of the alkali metal carbonate is 0.30–0.70 nm. The dispersion diameter of the alkali metal carbonate refers to the average diameter of the alkali metal carbonate particles.

[0015] Furthermore, the molecules are screened from at least one of MCM-41, MCM-48, and SBA-15.

[0016] Further, in the catalyst, based on the catalyst weight, the content of nitrogen-containing heterocyclic crown ether is 16% to 50%, the content of alkali metal carbonate is 5% to 24% based on alkali metal carbonate molecules, and the content of molecular sieve is 26% to 77%. Further, as a non-limiting example, the content of alkali metal carbonate is 5%, 5.5%, 6%, 6.5%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 24% based on alkali metal carbonate molecules, and any value within the range formed by any two of these values.

[0017] A second aspect of this invention provides a method for preparing a molecular sieve catalyst supported on a metal salt, comprising the following steps:

[0018] (1) Mix molecular sieve, metal chloride, epoxy haloalkane and solvent to react and obtain surface halogenated molecular sieve;

[0019] (2) Mix the aza-crown ether and the surface-halogenated molecular sieve obtained in step (1) to obtain the aza-crown ether-grafted molecular sieve;

[0020] (3) The molecular sieve grafted with nitrogen heterocyclic crown ether obtained in step (2) is reacted with an aqueous solution of alkali metal carbonate. After each reaction is completed and filtered, the alkali metal carbonate aqueous solution is added again to repeat the above steps. The number of repetitions is 3 to 5 times to obtain the catalyst.

[0021] Further, in step (1), the metal chloride is selected from at least one of ferric chloride, copper chloride, and zinc chloride. The molecule is screened from at least one of MCM-41, MCM-48, and SBA-15. The epoxy haloalkane is selected from at least one of epichlorohydrin, epichlorobutane, epibromopropane, and epibromobutane. The solvent is an organic solvent, preferably ethanol.

[0022] Further, in step (1), the mass ratio of molecular sieve to solvent is 1:20 to 50, the mass ratio of molecular sieve to metal chloride is 30 to 60:1, and the mass ratio of molecular sieve to epoxide haloalkane is 5 to 20:1.

[0023] Furthermore, in step (1), the reaction temperature is 70–90°C and the reaction time is 3–8 h.

[0024] Further, in step (1), after the reaction is completed, the surface-halogenated molecular sieve is obtained by filtration and washing. The washing order is alcohol (preferably ethanol) washing - water (preferably deionized water) washing - alcohol (preferably ethanol) washing.

[0025] Further, in step (2), the azacyclic crown ether is an azacyclic crown ether containing a tertiary amine, preferably selected from N-methylaza-12-crown-4-ether, 1-benzyl-1-aza-12-crown-4-ether, N-methoxyaza-15-crown-5-ether, N-phenylaza-15-crown-5-ether, benzylaza-15-crown-5-ether, 13-methyl-1,4,7,10-tetraoxa-13-azacyclopentadecane, N,N'-dibenzyl-4,13-diaza- At least one of 18-crown-6-ether, 5,6-benzo-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexadecane-5-ene, and 10,19-bis-(p-tolylsulphonyl)-1,4,7,13,16-pentaoxa-10,19-diazacyclohemicosane (CAS:120808-60-8).

[0026] Further, in step (2), the alkali metal in the alkali metal carbonate is selected from at least one of lithium, sodium, potassium, rubidium, and cesium. The solvent is an organic solvent, preferably ethanol.

[0027] Further, in step (2), the molar ratio of the azacyclic crown ether to the epoxy haloalkane in step (1) is 1 to 2, and the mass ratio of the azacyclic crown ether to the solvent is 1:30 to 150.

[0028] Furthermore, in step (2), the reaction temperature is 30–60°C and the reaction time is 1–3 h.

[0029] Furthermore, in step (2), after the reaction is complete, the residue obtained by filtration and washing is the molecular sieve grafted with nitrogen-containing heterocyclic crown ether. Washing is performed using alcohol (preferably ethanol).

[0030] Furthermore, in step (3), the mass concentration of the alkali metal carbonate aqueous solution is 5wt% to 20wt%, and the mass ratio of the molecular sieve to the alkali metal carbonate aqueous solution is 1:10 to 30.

[0031] Furthermore, in step (3), the reaction temperature is 40–80°C, and the reaction time is 0.5–2 h each time.

[0032] Further, in step (3), after the first reaction is completed, the mixture is filtered, and the filter residue is added to a fresh alkali metal carbonate aqueous solution to continue the reaction. This process is repeated 3 to 5 times, followed by filtration, washing, and drying to obtain the catalyst. The drying process includes a drying temperature of 80 to 120°C and a drying time of 2 to 6 hours.

[0033] Furthermore, the reaction of the present invention is preferably a stirred reaction, and there are no special restrictions on the stirring conditions.

[0034] Furthermore, in the obtained catalyst, the dispersion diameter of the alkali metal carbonate is 0.30–0.70 nm.

[0035] A third aspect of the present invention provides a method for preparing dimethyl carbonate, comprising: using dimethyl oxalate as a reactant, carrying out a decarbonylation reaction under the action of the above-mentioned catalyst to prepare dimethyl carbonate.

[0036] Furthermore, the decarbonylation reaction is carried out in a fixed bed, with the reaction raw materials fed from the top of the bed and reacting with the catalyst in a liquid-solid phase. The product generated by the reaction is collected from the bottom of the bed, separated, and dimethyl carbonate is obtained.

[0037] Furthermore, the reaction temperature is 150–200℃, preferably 170–190℃, the reaction pressure is 0.1–0.8 MPa, preferably 0.5–0.7 MPa (to ensure that dimethyl oxalate is in the liquid phase), and the weight hourly space velocity (WHSV) of the reactant dimethyl oxalate is 5–15 h⁻¹. -1 Preferably 7-12h -1 .

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] 1. The catalyst of this invention comprises a molecular sieve and nitrogen-containing heterocyclic crown ether alkali metal carbonates grafted onto its surface. It utilizes a coupling agent with a crown ether structure and alkali metal ions of suitable radius to achieve monomolecular dispersion of the alkali metal carbonate, resulting in a significantly higher activity level than directly supported catalysts, approaching homogeneous catalysis. Using the catalyst of this invention to catalyze the decarbonylation of dimethyl oxalate to prepare dimethyl carbonate exhibits high activity, a long catalyst lifespan, and effectively reduces the generation of side reactions.

[0040] 2. In the catalyst preparation process of this invention, the surface of the molecular sieve support is first halogenated with an epoxy haloalkane, then grafted with a crown ether molecule via a coupling reaction with a tertiary amine-containing nitrogen-containing crown ether. Finally, the alkali metal carbonate and crown ether are complexed to obtain a molecular sieve catalyst loaded with a single metal salt. Specifically, this invention utilizes the fact that the epoxy haloalkane can both form a quaternary ammonium salt ionic liquid with the tertiary amine-containing nitrogen-containing crown ether coupling agent and form stable ether bonds with the hydroxyl groups on the molecular sieve surface, firmly bridging the nitrogen-containing crown ether coupling agent to the molecular sieve. The ether bond is more stable than the conventional silicon-oxygen bond, increasing stability. Then, the molecular sieve grafted with the nitrogen-containing crown ether coupling agent reacts with the alkali metal carbonate, causing the alkali metal ion to complex with the crown ether, fixing the alkali metal ion, and simultaneously exchanging the halide ion for carbonate. In the catalyst of this invention, one alkali metal ion and one quaternary ammonium cation share one carbonate ion, enhancing the carbonate's resistance to leaching and aggregation, solving the problem of direct-loaded active centers migrating and leaching during the reaction, and further extending the catalyst's lifespan.

[0041] 3. The catalyst of the present invention is a liquid-phase active component immobilized catalyst. Compared with homogeneous catalysts, it retains its high activity, can reduce the reaction temperature, reduce the generation of side reactions, and eliminate the step of separating products and catalysts. Detailed Implementation

[0042] To more clearly illustrate the present invention, the following description, in conjunction with embodiments, provides further insight. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0043] In this invention:

[0044] Dimethyl oxalate conversion rate (%) = [1 - (mass flow rate of extracted dimethyl oxalate) / (mass flow rate of dimethyl oxalate feed)] × 100%;

[0045] Dimethyl carbonate selectivity (%) = (mass flow rate of dimethyl carbonate produced / 90) / (mass flow rate of dimethyl oxalate feed / 118) × 100%.

[0046] Catalyst lifetime is defined as the number of hours required for dimethyl oxalate conversion to be below 95%.

[0047] In this invention, the dispersion diameter of alkali metal carbonates is determined using high-resolution aberration-corrected transmission electron microscopy (HRTEM). The specific steps are as follows: the catalyst is ground and dispersed in ethanol, then dropped onto an ultrathin carbon film support. After drying, a high-resolution image of the sample is obtained using an HRTEM. The diameter of the alkali metal carbonate particles is measured using software. This process is repeated three times, and the average value is calculated.

[0048] Example 1

[0049] Catalyst preparation:

[0050] (1) Add 9g of MCM-41 molecular sieve, 0.2g of ZnCl2 and 0.9g of epichlorohydrin to 270g of ethanol and stir at 80℃ for 6h. Filter the reaction material and wash it with ethanol, deionized water and ethanol in sequence. The mass ratio of MCM-41 molecular sieve to ZnCl2 is 45:1, the mass ratio of MCM-41 molecular sieve to epichlorohydrin is 10:1 and the mass ratio of MCM-41 molecular sieve to ethanol is 1:30.

[0051] (2) The solid obtained in step (1) and 3g of N-methoxyaza-15-crown-5-ether were added to 120g of ethanol and reacted at 50℃ for 2h. The mixture was then filtered and washed with ethanol. The molar ratio of N-methoxyaza-15-crown-5-ether to epichlorohydrin was 1.17, and the mass ratio of N-methoxyaza-15-crown-5-ether to ethanol was 1:40.

[0052] (3) The filter residue obtained in step (2) is added to 180g of 15wt% sodium carbonate aqueous solution and reacted at 60℃ for 1h. After filtration, the filter residue is added to fresh sodium carbonate aqueous solution again. This process is repeated 3 times. After filtration and washing with water, the solution is dried at 110℃ for 4h to obtain the catalyst. The mass ratio of MCM-41 molecular sieve to sodium carbonate aqueous solution is 1:20.

[0053] Catalyst applications:

[0054] 8g of the catalyst obtained in Example 1 was loaded into a fixed bed, purged with nitrogen, and heated to 170°C. Dimethyl oxalate, the raw material, was then fed at a weight hourly space velocity (WHSV) of 8 h⁻¹. 1 Feed is introduced from the top, and after reacting with the above catalyst, dimethyl carbonate is produced and collected from the bottom. The pressure is maintained at 0.5 MPa until the device stabilizes, and the product is analyzed. The results are shown in Table 2.

[0055] Examples 2-4

[0056] Compared to Example 1, the only difference in the preparation of the catalysts in Examples 2-4 is the use of different nitrogen-containing heterocyclic crown ether coupling agents (see Table 1 for details).

[0057] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 2.

[0058] Table 1 Properties of each catalyst example

[0059]

[0060] Table 2 Evaluation results of each catalyst example

[0061]

[0062] Examples 5-6

[0063] Compared with Example 1, Examples 5-6 differ in that the reaction temperature during the application of the catalyst is different.

[0064] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 3.

[0065] Table 3 Evaluation results at different reaction temperatures

[0066]

[0067]

[0068] Examples 7-8

[0069] Compared with Example 1, Examples 7-8 differ in the reaction pressure when the catalyst is applied.

[0070] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 4.

[0071] Table 4 Evaluation results under different reaction pressures

[0072]

[0073] Example 9

[0074] Catalyst preparation:

[0075] (1) Add 9g of MCM-48 molecular sieve, 0.25g of CuCl2 and 1.2g of epoxy propane to 250g of ethanol, stir at 70℃ for 8h, and filter the reaction material and wash it with ethanol, deionized water and ethanol in sequence; wherein the mass ratio of MCM-48 molecular sieve to CuCl2 is 36:1, the mass ratio of MCM-48 molecular sieve to epoxy propane is 7.5:1, and the mass ratio of MCM-48 molecular sieve to ethanol is 1:27.8;

[0076] (2) The solid obtained in step (1) and 5g of N,N′-dibenzyl-4,13-diaza-18-crown-6-ether were added to 220g of ethanol and reacted at 60℃ for 1.5h. The mixture was then filtered and washed with ethanol. The molar ratio of N,N′-dibenzyl-4,13-diaza-18-crown-6-ether to epichlorohydrin was 1.29, and the mass ratio of N,N′-dibenzyl-4,13-diaza-18-crown-6-ether to ethanol was 1:44.

[0077] (3) The filter residue obtained in step (2) is added to 200g of 10wt% potassium carbonate aqueous solution and reacted at 70℃ for 0.8h. After filtration, the filter residue is added to fresh potassium carbonate solution again. This process is repeated 3 times. After filtration and washing with water, the solution is dried at 120℃ for 3.5h to obtain the catalyst. The mass ratio of MCM-48 molecular sieve to potassium carbonate aqueous solution is 1:22.2.

[0078] In the catalyst obtained in Example 9, the potassium carbonate dispersion diameter was 0.54 nm. The content of N,N′-dibenzyl-4,13-diaza-18-crown-6-ether was 26.35%, the content of potassium carbonate was 5.90%, and the content of MCM-48 molecular sieve was 64.36%.

[0079] Catalyst applications:

[0080] 8g of the catalyst obtained in Example 9 was loaded into a fixed bed, purged with nitrogen, and heated to 180°C. Dimethyl oxalate was fed at a weight hourly space velocity (WHSV) of 10 h⁻¹. -1 Feed is introduced from the top, and the product is reacted with a catalyst to produce dimethyl carbonate, which is then extracted from the bottom. The pressure is maintained at 0.6 MPa until the device stabilizes. The product is then analyzed, and the results are shown in Table 5.

[0081] Example 10

[0082] Catalyst preparation:

[0083] (1) Add 9g of SBA-15 molecular sieve, 0.15g of FeCl3 and 0.8g of epoxy propane to 260g of ethanol, stir at 85℃ for 4h, filter the reaction material and wash it with ethanol, deionized water and ethanol in sequence; wherein the mass ratio of SBA-15 molecular sieve to FeCl3 is 60:1, the mass ratio of SBA-15 molecular sieve to epoxy propane is 11.25:1, and the mass ratio of SBA-15 molecular sieve to ethanol is 1:28.9;

[0084] (2) The solid obtained in step (1) and 5 g of 10,19-bis-(p-tolylsulphonyl)-1,4,7,13,16-pentaoxa-10,19-diazacyclohemicosane were added to 275 g of ethanol and reacted at 50 °C for 2.5 h. The mixture was then filtered and washed with ethanol. The molar ratio of 10,19-bis-(p-tolylsulphonyl)-1,4,7,13,16-pentaoxa-10,19-diazacyclohemicosane to epoxypropane was 1.39, and the mass ratio of 10,19-bis-(p-tolylsulphonyl)-1,4,7,13,16-pentaoxa-10,19-diazacyclohemicosane to ethanol was 1:55.

[0085] (3) The filter residue obtained in step (2) was added to 200g of 16wt% cesium carbonate aqueous solution and reacted at 70℃ for 0.8h. After filtration, the filter residue was added to fresh cesium carbonate solution again and repeated 3 times. After filtration and washing with water, it was dried at 120℃ for 4h to obtain the catalyst. The mass ratio of SBA-15 molecular sieve to cesium carbonate aqueous solution was 1:22.2.

[0086] In the catalyst obtained in Example 10, the cesium carbonate dispersion diameter was 0.61 nm. The content of 10,19-bis-(p-tolylsulphonyl)-1,4,7,13,16-pentaoxa-10,19-diazacyclohemicosane was 24.73%, the content of cesium carbonate was 7.76%, and the content of SBA-15 molecular sieve was 65.21%.

[0087] Catalyst applications:

[0088] 8g of the catalyst obtained in Example 10 was loaded into a fixed bed, purged with nitrogen, and heated to 170°C. Dimethyl oxalate, the raw material, was fed at a weight hourly space velocity (WHSV) of 9 h⁻¹. 1 Feed is introduced from the top, and the product is reacted with a catalyst to produce dimethyl carbonate, which is then extracted from the bottom. The pressure is maintained at 0.5 MPa until the device stabilizes. The product is then analyzed, and the results are shown in Table 5.

[0089] Example 11

[0090] Catalyst preparation:

[0091] (1) Add 9g of MCM-48 molecular sieve, 0.3g of CuCl2 and 1g of epoxy propane to 280g of ethanol, stir at 90℃ for 3h, filter the reaction material and wash with ethanol, deionized water and ethanol respectively; wherein the mass ratio of MCM-48 molecular sieve to CuCl2 is 30:1, the mass ratio of MCM-48 molecular sieve to epoxy propane is 9:1, and the mass ratio of MCM-48 molecular sieve to ethanol is 1:31.1;

[0092] (2) The solid obtained in step (1) and 4.5 g of 5,6-benzo-4,7,13,16,21,24-hexoxa-1,10-diazabicyclo[8.8.8]hexadec-5-ene were added to 300 g of ethanol and reacted at 40 °C for 3 h. The mixture was then filtered and washed with ethanol. The molar ratio of 5,6-benzo-4,7,13,16,21,24-hexoxa-1,10-diazabicyclo[8.8.8]hexadec-5-ene to epoxybromopropane was 1.45, and the mass ratio of 5,6-benzo-4,7,13,16,21,24-hexoxa-1,10-diazabicyclo[8.8.8]hexadec-5-ene to ethanol was 1:66.7.

[0093] (3) The filter residue obtained in step (2) was added to 200g of 14wt% rubidium carbonate aqueous solution and reacted at 70℃ for 0.8h. After filtration, the filter residue was added to fresh rubidium carbonate solution again and repeated three times. After filtration and washing with water, it was dried at 100℃ for 5h to obtain the catalyst. The mass ratio of MCM-48 molecular sieve to rubidium carbonate aqueous solution was 1:22.2.

[0094] In the catalyst obtained in Example 11, the rubidium carbonate dispersion diameter was 0.57 nm. The content of 5,6-benzo-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexadec-5-ene was 22.07%, the content of rubidium carbonate was 7.56%, and the content of MCM-48 molecular sieve was 67.41%.

[0095] Catalyst applications:

[0096] 8g of the catalyst obtained in Example 11 was loaded into a fixed bed, purged with nitrogen, and heated to 173°C. Dimethyl oxalate was fed at a weight hourly space velocity (WHSV) of 12 h⁻¹. -1 Feed is introduced from the top, and the product is reacted with a catalyst to produce dimethyl carbonate, which is then extracted from the bottom. The pressure is maintained at 0.55 MPa until the device stabilizes. The product is then analyzed, and the results are shown in Table 5.

[0097] Table 5 Evaluation results of each catalyst example

[0098]

[0099] Comparative Example 1

[0100] Compared with Example 1, Comparative Example 1 differs in that a gas-phase fixed-bed reaction is used, and the reaction pressure is atmospheric pressure (0.1 MPa).

[0101] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 6.

[0102] Table 6 Evaluation results of the catalyst in Comparative Example 1

[0103]

[0104] Comparative Example 2

[0105] Compared with Example 1, Comparative Example 2 differs in that: during the catalyst preparation process, the coupling agent N-methoxyaza-15-crown-5-ether is first complexed with sodium carbonate, and then impregnated and loaded onto MCM-41 molecular sieve by an equal volume method.

[0106] In the catalyst obtained in Comparative Example 2, the sodium carbonate dispersion diameter was 0.48 nm. The content of N-methoxyaza-15-crown-5-ether was 19.12%, the content of sodium carbonate was 6.03%, and the content of MCM-41 molecular sieve was 70.71%.

[0107] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 7.

[0108] Table 7 Evaluation results of the catalyst in Comparative Example 2

[0109]

[0110] Comparative Example 3

[0111] Compared to Example 1, Comparative Example 3 differs in that sodium carbonate was directly loaded onto the MCM-41 molecular sieve using an equal-volume impregnation method during catalyst preparation. The sodium carbonate content was the same as in Example 1.

[0112] In the catalyst obtained in Comparative Example 3, the sodium carbonate dispersion diameter was 5.2 nm.

[0113] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 8.

[0114] Table 8 Evaluation results of catalyst in Comparative Example 3

[0115]

[0116] Comparative Example 4

[0117] Compared with Example 1, Comparative Example 4 differs in that the coupling agent N-methoxyaza-15-crown-5-ether used in step (2) of the catalyst preparation process is replaced with an equal amount of 1-methylimidazole, and the rest is the same as in Example 1.

[0118] In the catalyst obtained in Comparative Example 4, the sodium carbonate dispersion diameter was 5.60 nm. The content of 1-methylimidazole was 7.14%, the content of sodium carbonate was 0.19%, and the content of MCM-41 molecular sieve was 84.63%.

[0119] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 9.

[0120] Table 9 Evaluation results of catalyst in Comparative Example 4

[0121]

[0122] Comparative Example 5

[0123] Compared with Example 1, Comparative Example 5 differs in that the reaction temperature when the catalyst is applied is 210°C, while the rest is the same as in Example 1.

[0124] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 10.

[0125] Table 10 Evaluation results of catalyst in Comparative Example 5

[0126]

[0127] The specific embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A molecular sieve catalyst supported on a metal salt, characterized in that, The catalyst comprises a molecular sieve and nitrogen-containing heterocyclic crown ether alkali metal carbonates grafted onto its surface.

2. The catalyst according to claim 1, characterized in that, In the alkali metal carbonate of the azacyclic crown ether, the azacyclic crown ether is an azacyclic crown ether containing a tertiary amine, preferably selected from N-methylaza-12-crown-4-ether, 1-benzyl-1-aza-12-crown-4-ether, N-methoxyaza-15-crown-5-ether, N-phenylaza-15-crown-5-ether, benzylaza-15-crown-5-ether, 13-methyl-1,4,7,10-tetraoxa-13-azacyclopentadecane, N,N'-dibenzyl-4,13-diaza At least one of the following: -18-crown-6-ether, 5,6-benzo-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexadecane-5-ene, and 10,19-bis-(p-tolylsulphonyl)-1,4,7,13,16-pentaoxa-10,19-diazacyclohemicosane (CAS:120808-60-8); And / or, the alkali metal is selected from at least one of lithium, sodium, potassium, rubidium, and cesium.

3. The catalyst according to claim 1, characterized in that, The molecules are screened from at least one of MCM-41, MCM-48, and SBA-15.

4. The catalyst according to claim 1, characterized in that, The catalyst, based on its weight, contains 16%–50% nitrogen-containing heterocyclic crown ethers, 5%–24% alkali metal carbonates (calculated as alkali metal carbonate molecules), and 26%–77% molecular sieves.

5. A method for preparing a molecular sieve catalyst supported on a metal salt, comprising: (1) Mix molecular sieve, metal chloride, epoxy haloalkane and solvent to react and obtain surface halogenated molecular sieve; (2) Mix the aza-crown ether and the surface-halogenated molecular sieve obtained in step (1) to obtain the aza-crown ether-grafted molecular sieve; (3) The molecular sieve grafted with nitrogen heterocyclic crown ether obtained in step (2) is reacted with an aqueous solution of alkali metal carbonate. After each reaction is completed and filtered, the alkali metal carbonate aqueous solution is added again to repeat the above steps. The number of repetitions is 3 to 5 times to obtain the catalyst.

6. The preparation method according to claim 5, characterized in that, The metal chloride is selected from at least one of ferric chloride, copper chloride, and zinc chloride; And / or, the molecules are screened from at least one of MCM-41, MCM-48, and SBA-15; And / or, the epoxy haloalkane is selected from at least one of epichlorohydrin, epichlorobutane, epibromopropane, and epibromobutane; And / or, the solvent is an organic solvent, preferably ethanol; And / or, the azacyclic crown ether is an azacyclic crown ether containing a tertiary amine, preferably selected from N-methylaza-12-crown-4-ether, 1-benzyl-1-aza-12-crown-4-ether, N-methoxyaza-15-crown-5-ether, N-phenylaza-15-crown-5-ether, benzylaza-15-crown-5-ether, 13-methyl-1,4,7,10-tetraoxa-13-azacyclopentadecane, N,N'-dibenzyl-4,13-diaza-18-crown- At least one of the following: 6-ether, 5,6-benzo-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexadecane-5-ene, and 10,19-bis-(p-tolylsulphonyl)-1,4,7,13,16-pentaoxa-10,19-diazacyclohemicosane (CAS:120808-60-8); And / or, the alkali metal in the alkali metal carbonate is selected from at least one of lithium, sodium, potassium, rubidium, and cesium.

7. The preparation method according to claim 5, characterized in that, In step (1), the mass ratio of molecular sieve to solvent is 1:20 to 50; and / or, the mass ratio of molecular sieve to metal chloride is 30 to 60:1; and / or, the mass ratio of molecular sieve to epoxy haloalkane is 5 to 20:

1. And / or, in step (2), the molar ratio of the azacyclic crown ether to the epoxy haloalkane in step (1) is 1 to 2; And / or, in step (3), the mass concentration of the alkali metal carbonate aqueous solution is 5 wt% to 20 wt%; And / or, in step (3), the mass ratio of molecular sieve to alkali metal carbonate aqueous solution is 1:10 to 30.

8. The preparation method according to claim 5, characterized in that, In step (1), the reaction temperature is 70-90℃ and the reaction time is 3-8h; And / or, in step (2), the reaction temperature is 30–60°C and the reaction time is 1–3 h; And / or, in step (3), the reaction temperature is 40-80℃ and the reaction time is 0.5-2h each time.

9. A method for preparing dimethyl carbonate, comprising: Dimethyl carbonate is prepared by decarbonylation reaction using dimethyl oxalate as a reactant and under the action of the catalyst described in any one of claims 1-4 or the catalyst prepared according to the preparation method described in any one of claims 5-8.

10. The method according to claim 9, characterized in that, The operating conditions for the reaction are as follows: reaction temperature is 150–200℃, preferably 170–190℃; reaction pressure is 0.1–0.8 MPa; and the weight hourly space velocity (WHSV) of dimethyl oxalate is 5–15 h⁻¹. -1 Preferably 7-12h -1 .

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