A catalyst for preparing dialkyl carbonate, its preparation method and application

Abstract

This invention discloses a catalyst for the preparation of dialkyl carbonate, its preparation method, and its application. The catalyst comprises metal oxide nanoparticles and an ionic liquid coupling agent grafted onto their surface. By weight of the catalyst, the content of the metal oxide nanoparticles is 40 wt%–70 wt%, and the content of the ionic liquid coupling agent is 30 wt%–60 wt%. Using the catalyst of this invention to catalyze the preparation of dialkyl carbonate from dialkyl oxalate results in high yield of the target product, long catalyst life, and effectively reduces the generation of side reactions.

Description

Technical Field

[0001] This invention belongs to the field of catalysts, specifically relating to a catalyst for the preparation of dialkyl carbonates, its preparation method, and its application. Background Technology

[0002] Dimethyl carbonate is a low-toxicity, environmentally friendly, and widely used chemical raw material. It contains various functional groups such as CH3O-, CH3O-CO-, and -CO-, and is widely used as an intermediate in organic synthesis. Dimethyl carbonate can be used as a raw material to prepare a variety of high-value-added fine specialty chemicals, such as lithium battery electrolytes, pharmaceuticals, pesticides, synthetic materials, lubricant additives, and polycarbonate (PC) synthesis raw materials.

[0003] Numerous methods for synthesizing carbonates have been reported, primarily including the phosgene method, transesterification, oxidative carbonylation, and low-pressure CO gas-phase synthesis. The phosgene method for preparing dimethyl carbonate (DMC) involves harsh conditions, complex processes, severe equipment corrosion, and pollution from the highly toxic substance phosgene, making it a near-obsolete technology. CN105251496A discloses a supported catalyst for transesterification to prepare DMC, with mild reaction conditions and easy catalyst separation; however, it suffers from active component loss, and the raw material, ethylene oxide, is derived from petroleum, leading to significant cost fluctuations. CN114031500A employs an oxidative carbonylation method to directly synthesize DMC from CO2 and methanol. This method uses readily available raw materials and is safer and more environmentally friendly, but its conversion rates are consistently low, and it remains in the laboratory research stage with limited industrial applications. CN108144603A discloses a catalyst for the low-pressure CO gas-phase synthesis of DMC. This process exhibits high activity and good stability, but it suffers from low selectivity, introduces methyl nitrite, and faces equipment corrosion issues.

[0004] In summary, although the coal-to-ethylene glycol production capacity is large, the capacity utilization rate is low. If the existing coal-to-ethylene glycol plants are upgraded to produce dimethyl carbonate, which has a higher added value, it will have considerable economic benefits and high feasibility. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a catalyst for the preparation of dialkyl carbonates, its preparation method, and its applications. Using the catalyst of this invention to prepare dialkyl carbonates exhibits high selectivity for the target product, good catalyst stability, and effectively reduces the occurrence of side reactions.

[0006] The first aspect of the present invention provides a catalyst for preparing dialkyl carbonate, the catalyst comprising metal oxide nanoparticles and an ionic liquid coupling agent grafted onto their surface, wherein the content of the metal oxide nanoparticles is 40 wt% to 70 wt% and the content of the ionic liquid coupling agent is 30 wt% to 60 wt% by weight of the catalyst.

[0007] Furthermore, the metal oxide is selected from at least one of zirconium oxide, zinc oxide, titanium oxide, and cerium oxide, preferably at least one of zirconium oxide, zinc oxide, and titanium oxide.

[0008] Furthermore, the average diameter of the metal oxide nanoparticles is 3–5 nm.

[0009] Furthermore, the alkali content on the surface of the metal oxide is 200–500 μmol / g.

[0010] Furthermore, the ionic liquid coupling agent is a reaction product of a halosilane coupling agent and a nitrogen heterocyclic compound. The molar ratio of the nitrogen heterocyclic compound to the halosilane coupling agent is 1–1.5:1.

[0011] Further, the halosilane coupling agent is preferably selected from at least one of (3-chloropropyl)tris(1-methylethoxy)-silane, 3-chloropropyltrimethoxysilane, 3-bromopropyltrimethoxysilane, 4-bromobutyltrimethoxysilane, 5-bromopentyltrimethoxysilane, (4-bromobenzyloxy)trimethoxysilane, bromophenyltrimethoxysilane, m-(trimethylsiloxy)bromobenzene, 4-fluorobutyltrimethoxysilane, and 4-iodobutyltrimethoxysilane.

[0012] Further, the nitrogen heterocyclic compound is preferably selected from at least one of N-methylpyrrolidone, 1-methylimidazolium, N-triphenylmethylimidazolium, N,N-diimidazolylmethane, pyridine, 4-dimethylaminopyridine, N-methylpyrrole, 4-methylpyridine, and N-methylindole.

[0013] A second aspect of the present invention provides a method for preparing a catalyst for preparing dialkyl carbonate, comprising:

[0014] (1) Mix the metal oxide precursor with benzyl alcohol and slowly add deionized water to carry out the reaction;

[0015] (2) The pre-reaction solution obtained in step (1) is subjected to a solvothermal reaction;

[0016] (3) After solid-liquid separation, the product obtained in step (2) is modified by adding halosilane coupling agent, water and organic solvent to the obtained solid to obtain a solid.

[0017] (4) The solid obtained in step (3) is dispersed in a dispersion medium, and a nitrogen heterocyclic compound is added to react and the catalyst is obtained.

[0018] Further, in step (1), the metal oxide precursor is selected from at least one of zirconium n-propoxide, zirconium isopropoxide, zirconium acetylacetonate, zinc isopropoxide, zinc acetylacetonate, tetraisopropyl titanate, tetrabutyl titanate, cerium n-propoxide, cerium isopropoxide, and cerium acetylacetonate. The concentration of the solution obtained after mixing the metal oxide precursor with benzyl alcohol is 0.1–0.5 mol / L.

[0019] Further, in step (1), the molar ratio of the added deionized water to the metal oxide precursor is x ~ 1.6x:1, where x represents the product MO obtained by hydrolysis of the metal oxide precursor. X The number of oxygen atoms in it.

[0020] Furthermore, in step (1), the reaction is carried out under stirring conditions, the reaction temperature is 45-70°C, and the reaction time is 10-40 min.

[0021] Furthermore, in step (2), the solvothermal reaction is carried out in a stainless steel reactor. The reaction temperature is 210–260°C, and the reaction time is 30–54 h.

[0022] Further, in step (3), the halosilane coupling agent is selected from at least one of (3-chloropropyl)tris(1-methylethoxy)-silane, 3-chloropropyltrimethoxysilane, 3-bromopropyltrimethoxysilane, 4-bromobutyltrimethoxysilane, 5-bromopentyltrimethoxysilane, (4-bromobenzyloxy)trimethoxysilane, bromophenyltrimethoxysilane, m-(trimethylsiloxy)bromobenzene, 4-fluorobutyltrimethoxysilane, and 4-iodobutyltrimethoxysilane.

[0023] Further, in step (3), the mass ratio of the amount of halosilane coupling agent added to the theoretical metal oxide (the metal oxide obtained by complete hydrolysis of the metal oxide precursor) is 1 to 2:1, the molar ratio of the amount of water added to the halosilane coupling agent is 1 to 4:1, and the mass ratio of the amount of organic solvent added to the theoretical metal oxide is 4 to 16:1.

[0024] Further, in step (3), the organic solvent is selected from at least one of cyclohexane, n-hexane, n-heptane, and isooctane, preferably cyclohexane.

[0025] Furthermore, in step (3), the modification temperature is 50-70℃ and the modification time is 1-3h.

[0026] Further, in step (3), after the modification is completed, the solvent is evaporated to dryness, and the solid is washed to obtain a solid. The washing is performed with ethanol, and the number of washing cycles is 3 to 5.

[0027] Further, in step (4), the dispersion medium is selected from at least one of toluene, ethylbenzene, p-xylene, and ethyl acetate, preferably ethyl acetate.

[0028] Further, in step (4), the nitrogen heterocyclic compound is selected from at least one of N-methylpyrrolidone, 1-methylimidazolium, N-triphenylmethylimidazolium, N,N-diimidazolylmethane, pyridine, 4-dimethylaminopyridine, N-methylpyrrole, 4-methylpyridine, and N-methylindole.

[0029] Further, in step (4), the molar ratio of the amount of nitrogen heterocyclic compound added to the halosilane coupling agent is 1 to 1.5:1, and the mass ratio of the dispersion medium to the nitrogen heterocyclic compound is 4 to 8:1.

[0030] Furthermore, in step (4), the reaction temperature is 50–70°C and the reaction time is 4–40 h.

[0031] Further, in step (4), after the reaction is complete, the lower layer product is taken, washed, and dried to obtain the catalyst. The washing uses at least one of toluene, ethylbenzene, p-xylene, and ethyl acetate, and the washing is performed 3 to 5 times. The drying is vacuum drying, with a vacuum drying temperature of 60 to 90°C and a vacuum drying time of 2 to 8 hours.

[0032] A third aspect of the present invention provides an application of the catalyst, comprising: using dialkyl oxalate as a reactant, performing a decarbonylation reaction under the action of the catalyst to prepare dialkyl carbonate.

[0033] Furthermore, the dialkyl oxalate is preferably at least one of dimethyl oxalate, diethyl oxalate, methyl ethyl oxalate, etc.

[0034] Furthermore, the decarbonylation reaction is carried out in the bottom of a distillation column. The reactants and catalyst are fed into the bottom of the distillation column, mixed, and reacted. The light components generated by the reaction (including dialkyl carbonate and CO, etc.) are distilled and collected from the top of the column to obtain dialkyl carbonate.

[0035] Further, the reaction conditions include: a reaction temperature of 150–200°C, preferably 170–195°C; a reaction pressure of 0.1–0.6 MPa, preferably 0.15–0.4 MPa; a mass ratio of reactants to catalyst of 5–20:1, preferably 8–12:1; and a weight hourly space velocity (WHSV) of 1–10 h⁻¹ for the reactants. -1 Preferably 2-6 hours -1 The tower body temperature is 90–150℃, preferably 100–130℃.

[0036] Reaction mechanism: As shown in formula (1), taking dimethyl oxalate as an example, the carbonyl group is removed under catalysis to generate dimethyl carbonate. Dimethyl carbonate can be further decarbonated under catalysis to generate dimethyl ether as a byproduct.

[0037]

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

[0039] 1. The catalyst of this invention is based on metal oxide nanoparticles with a firmly grafted halosilane coupling agent. This coupling agent can subsequently add to nitrogen heterocyclic compounds to obtain an ionic liquid containing halo anions. The grafted ionic liquid has excellent compatibility with the reactants, which promotes the uniform dispersion of metal oxide nanoparticles in dialkyl oxalate, forming a pseudo-homogeneous reaction system and promoting the efficient catalysis of the decarbonylation reaction of dialkyl oxalate by active anions.

[0040] 2. The catalyst of this invention can firmly fix the ionic liquid onto the surface of the metal oxide, improving its stability compared to free ionic liquid catalysts, including catalyst separation stability and reaction thermal stability. This solves the problems of poor thermal stability and easy loss of halide ionic liquids, extending the catalyst's lifespan. Furthermore, the metal oxide can locally aggregate the anionic active centers of the ionic liquid, allowing oxalate molecules to rapidly undergo decarbonylation upon contact with the catalyst, reducing the possibility of condensation side reactions due to their long residence time.

[0041] 3. The catalyst of this invention has a suitable amount of basic centers on the surface of the metal oxide, which can synergistically catalyze the decarbonylation reaction with the grafted ionic liquid halide ions, thereby further improving the activity, selectivity and lifetime of the catalyst. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the process for producing dialkyl carbonate according to the present invention;

[0043] The product is 1-reactant (dialkyl oxalate); 2-catalyst; 3-light component of product (including dialkyl carbonate); 4-heavy component of product. Detailed Implementation

[0044] To more clearly illustrate the present invention, the following description, in conjunction with embodiments and accompanying drawings, further clarifies the invention. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0045] Combination Figure 1The process flow for producing dialkyl carbonate of the present invention is further explained using dimethyl oxalate as raw material: Dimethyl oxalate 1 and catalyst 2 are placed in the reaction vessel of a distillation column and reacted. The light component 3 of the product obtained by the reaction is collected from the top of the column by distillation and further separated to obtain dimethyl carbonate. The heavy component 4 of the product is discharged from the bottom of the distillation column.

[0046] In this invention, catalyst lifetime is defined as the time required for the dialkyl carbonate discharge rate to decrease to 90% of its initial value.

[0047] In this invention, the discharge rate represents the ability of a certain amount of catalyst to produce product per hour, and is directly measured by a flow meter. A higher discharge rate indicates higher catalyst activity.

[0048] Dialkyl carbonate selectivity (%) = (discharge mass flow rate of dialkyl carbonate / molecular weight of dialkyl carbonate) / (feed mass flow rate of dialkyl oxalate / molecular weight of dialkyl oxalate) × 100%.

[0049] In this invention, the total surface alkali of the metal oxide nanoparticles was measured using an AutoChem II 2920 chemisorption analyzer via CO2-TPD. The specific procedure was as follows: 0.1 g of sample was placed in a quartz sample tube and heated from room temperature to 500°C at a flow rate of 10 mL / min under a helium atmosphere of 25 mL / min, held for 1 hour, and then cooled to 110°C. CO2 was then passed through at a flow rate of 25 mL / min for 30 minutes, followed by purging the sample with helium at a flow rate of 50 mL / min for approximately 1 hour to remove physically adsorbed CO2. Afterward, the temperature was increased to 500°C at a flow rate of 10°C / min, and the amount of carbon dioxide desorbed was measured.

[0050] In this invention, the diameter of metal oxide particles is measured using a Hitachi HT7700 transmission electron microscope (TEM) to observe the size and dispersibility of the nanoparticles. When observing the nanoparticles, a sample of appropriate concentration is dropped onto a carbon film, allowed to air dry naturally, and then injected for observation. One hundred particles from a selected area are measured and their average diameter is calculated using ImageJ software.

[0051] Example 1

[0052] Catalyst preparation: 0.3 mol of zirconium propoxide was dissolved in 1 L of benzyl alcohol and stirred at room temperature. 12 g of deionized water was slowly added dropwise to the solution, and the mixture was heated to 60 °C and reacted for 20 min. The mixture was then transferred to a stainless steel reactor and reacted at 220 °C for 40 h. The product was centrifuged, and 40 g (0.16 mol) of 3-bromopropyltrimethoxysilane, 17 g of water, and 185 g of cyclohexane were added to the substrate. The mixture was modified at 60 °C for 2 h. The solvent was removed by rotary evaporation, and the mixture was washed three times with ethanol. The product was dispersed in 68 g of ethyl acetate, and 13.5 g (0.165 mol) of 1-methylimidazole was added. The mixture was reacted at 60 °C for 5 h. The lower layer was washed three times with ethyl acetate and dried under vacuum at 80 °C for 4 h to obtain the catalyst. The catalyst contained 46 wt% ZrO2 nanoparticles and 54 wt% coupling agent. The average diameter of the ZrO2 nanoparticles was 3.0 nm, and the surface alkali content was 486 μmol / g.

[0053] Catalyst application: Place 50g of catalyst at the bottom of a distillation column, add 350g of dimethyl oxalate, and premix at 95℃ for 1h to form a homogeneous and transparent dispersion. Purge the bottom of the column with nitrogen gas, controlling the pressure at 0.34MPa and the reaction temperature at 180℃. Stir the reaction, continuously feeding dimethyl oxalate into the bottom of the column. The weight hourly space velocity (WHSV) of dimethyl oxalate is 3h⁻¹. -1 The space velocity was adjusted slightly according to the liquid level to keep the liquid level constant. The tower temperature was 130℃. Dimethyl carbonate was collected from the top of the tower. After the device stabilized, the products were analyzed and are shown in Table 1.

[0054] Examples 2-4

[0055] Compared to Example 1, the only difference in the preparation of the catalysts in Examples 2-4 is the use of different types of metal oxide precursors (see Table 1 for details).

[0056] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 1.

[0057] Table 1 Evaluation results for each case

[0058]

[0059] Examples 5-7

[0060] Compared to Example 1, Examples 5-7 differ in the reaction temperature at which the catalyst is applied.

[0061] The catalyst was prepared using the same method as in Example 1, and the results are shown in Table 2.

[0062] Table 2 Evaluation Results for Each Case

[0063]

[0064] Examples 8-10

[0065] Compared with Example 1, Examples 8-10 differ in that different solvothermal reaction temperatures were used during catalyst preparation.

[0066] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 3.

[0067] Table 3 Evaluation Results for Each Case

[0068]

[0069] Example 11

[0070] Catalyst preparation: 0.35 mol tetrabutyl titanate was dissolved in 1 L benzyl alcohol and stirred at room temperature. 10 g of deionized water was slowly added dropwise to the solution, and the mixture was heated to 55 °C and reacted for 25 min. The mixture was then transferred to a stainless steel reactor and reacted at 230 °C for 32 h. The product was centrifuged, and 36 g (0.18 mol) of 3-chloropropyltrimethoxysilane, 20 g of water, and 200 g of cyclohexane were added to the substrate. The mixture was modified at 70 °C for 1 h. The solvent was removed by rotary evaporation, and the mixture was washed three times with ethanol. The product was dispersed in 85 g of ethyl acetate, and 19 g (0.19 mol) of N-methylpyrrolidone was added. The mixture was reacted at 70 °C for 30 h. The lower layer was washed three times with ethyl acetate and dried under vacuum at 75 °C for 6 h to obtain the catalyst. The catalyst contained 58 wt% TiO2 nanoparticles and 42 wt% coupling agent. The average diameter of the TiO2 nanoparticles was 3.8 nm, and the surface alkali content was 411 μmol / g.

[0071] Catalyst application: 45g of catalyst was placed at the bottom of a distillation column, and 350g of diethyl oxalate was added and premixed at 95℃ for 1h to form a homogeneous and transparent dispersion. Nitrogen gas was introduced to purge the bottom of the column, and the pressure was controlled at 0.15MPa. The reaction temperature was 195℃, and the reaction was stirred. Diethyl oxalate was continuously fed into the bottom of the column, with a weight hourly space velocity (WHSV) of 3.1h. -1 The space velocity was finely adjusted according to the liquid level to keep the liquid level constant. The tower temperature was 120℃. Diethyl carbonate was collected from the top of the tower. After the device stabilized, the products were analyzed and shown in Table 4.

[0072] Example 12

[0073] Catalyst preparation: 0.2 mol of zirconium acetylacetonate was dissolved in 1 L of benzyl alcohol and stirred at room temperature. 7.5 g of deionized water was slowly added dropwise to the solution, and the mixture was heated to 55 °C for 25 min. The mixture was then transferred to a stainless steel reactor and reacted at 230 °C for 32 h. The product was centrifuged, and 25 g (0.1 mol) of 4-bromobutyltrimethoxysilane, 12 g of water, and 52 g of cyclohexane were added to the substrate. The mixture was modified at 70 °C for 1 h. The solvent was removed by rotary evaporation, and the mixture was washed three times with ethanol. The product was dispersed in 70 g of ethyl acetate, and 10.5 g (0.13 mol) of N-methylpyrrole was added. The mixture was reacted at 70 °C for 30 h. The lower layer was washed three times with ethyl acetate and dried under vacuum at 65 °C for 7 h to obtain the catalyst. The catalyst contained 55 wt% ZrO2 nanoparticles and 45 wt% coupling agent. The average diameter of the titanium dioxide nanoparticles was 3.4 nm, and the surface alkali content was 435 μmol / g.

[0074] Catalyst application: 45g of catalyst was placed at the bottom of a distillation column, and 350g of diethyl oxalate was added and premixed at 95℃ for 1h to form a homogeneous and transparent dispersion. Nitrogen gas was introduced to purge the bottom of the column, and the pressure was controlled at 0.15MPa. The reaction temperature was 195℃, and the reaction was stirred. Diethyl oxalate was continuously fed into the bottom of the column, with a weight hourly space velocity (WHSV) of 3.2h. -1 The space velocity was finely adjusted according to the liquid level to keep the liquid level constant. The tower temperature was 120℃. Diethyl carbonate was collected from the top of the tower. After the device stabilized, the products were analyzed and shown in Table 4.

[0075] Example 13

[0076] Catalyst preparation: 0.22 mol of cerium n-propoxide was dissolved in 1 L of benzyl alcohol and stirred at room temperature. 7.5 g of deionized water was slowly added dropwise to the solution, and the mixture was heated to 55 °C for 25 min. The mixture was then transferred to a stainless steel reactor and reacted at 230 °C for 32 h. The product was centrifuged, and 39 g (0.143 mol) of 5-bromopentyltrimethoxysilane, 13 g of water, and 100 g of cyclohexane were added to the substrate. Modification was carried out at 70 °C for 1 h. The solvent was removed by rotary evaporation, and the mixture was washed three times with ethanol. The product was dispersed in 142 g of ethyl acetate, and 23.2 g (0.19 mol) of 4-dimethylaminopyridine was added. The reaction was carried out at 70 °C for 30 h. The lower layer was washed three times with ethyl acetate and dried under vacuum at 90 °C for 3 h to obtain the catalyst. The catalyst contained 61 wt% CeO2 nanoparticles and 39 wt% coupling agent. The average diameter of the CeO2 nanoparticles was 4.2 nm, and the surface alkali content was 345 μmol / g.

[0077] Catalyst application: 45g of catalyst was placed at the bottom of a distillation column, and 350g of dimethyl oxalate was added and premixed at 95℃ for 1h to form a homogeneous and transparent dispersion. Nitrogen gas was introduced to purge the bottom of the column, and the pressure was controlled at 0.35MPa. The reaction temperature was 182℃, and the reaction was stirred. Dimethyl oxalate was continuously fed into the bottom of the column, with a weight hourly space velocity (WHSV) of 2.9h. -1 The space velocity was finely adjusted according to the liquid level to keep the liquid level constant. The tower temperature was 120℃. Dimethyl carbonate was collected from the top of the tower. After the device stabilized, the products were analyzed and shown in Table 4.

[0078] Example 14

[0079] Catalyst preparation: 0.25 mol of cerium isopropoxide was dissolved in 1 L of benzyl alcohol and stirred at room temperature. 10 g of deionized water was slowly added dropwise to the solution, and the mixture was heated to 55 °C for 25 min. The mixture was then transferred to a stainless steel reactor and reacted at 230 °C for 32 h. The product was centrifuged, and 40 g (0.20 mol) of 4-fluorobutyltrimethoxysilane, 18 g of water, and 300 g of cyclohexane were added to the substrate. The mixture was modified at 70 °C for 1 h. The solvent was removed by rotary evaporation, and the mixture was washed three times with ethanol. The product was dispersed in 142 g of ethyl acetate, and 22.8 g (0.25 mol) of 4-methylpyridine was added. The mixture was reacted at 70 °C for 30 h. The lower layer was washed three times with ethyl acetate and dried under vacuum at 85 °C for 3 h to obtain the catalyst. The catalyst contained 64 wt% CeO2 nanoparticles and 36 wt% coupling agent. The average diameter of the CeO2 nanoparticles was 4.7 nm, and the surface alkali content was 287 μmol / g.

[0080] Catalyst application: 45g of catalyst was placed at the bottom of a distillation column, and 350g of methyl ethyl oxalate was added and premixed at 95℃ for 1h to form a homogeneous and transparent dispersion. Nitrogen gas was introduced to purge the bottom of the column, and the pressure was controlled at 0.2MPa. The reaction temperature was 185℃, and the reaction was stirred. methyl ethyl oxalate was continuously fed into the bottom of the column, with a weight hourly space velocity (WHSV) of 2.8h. -1 The space velocity was adjusted according to the liquid level to keep the liquid level constant. The tower temperature was 120℃. Ethyl methyl carbonate was collected from the top of the tower. After the device stabilized, the products were analyzed and shown in Table 4.

[0081] Table 4 Evaluation Results for Each Case

[0082]

[0083] Comparative Example 1

[0084] Compared with Example 1, the catalyst of Comparative Example 1 is an ionic liquid coupling agent grafted onto the catalyst of Example 1 (the coupling agent content is the same as that of Example 1).

[0085] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 5.

[0086] Comparative Example 2

[0087] Compared to Example 1, Comparative Example 2 used zirconium dioxide with an average diameter of 8.2 nm.

[0088] Catalyst preparation: 0.3 mol of zirconium propoxide was dissolved in 1 L of benzyl alcohol and stirred at room temperature. 12 g of deionized water was slowly added dropwise to the solution, and the mixture was heated to 60 °C and reacted for 20 min. The mixture was then transferred to a stainless steel reactor and reacted at 265 °C for 60 h. The product was centrifuged, and 40 g (0.16 mol) of 3-bromopropyltrimethoxysilane, 17 g of water, and 185 g of cyclohexane were added to the substrate. The mixture was modified at 60 °C for 2 h. The solvent was removed by rotary evaporation, and the mixture was washed three times with ethanol. The product was dispersed in 68 g of ethyl acetate, and 13.5 g (0.165 mol) of 1-methylimidazole was added. The mixture was reacted at 60 °C for 5 h. The lower layer was washed three times with ethyl acetate and dried under vacuum at 80 °C for 4 h to obtain the catalyst. The catalyst contained 46 wt% ZrO2 nanoparticles and 54 wt% coupling agent. The average diameter of the ZrO2 nanoparticles was 8.2 nm, and the surface alkali content was 171 μmol / g.

[0089] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 5.

[0090] Comparative Example 3

[0091] Compared with Example 1, Comparative Example 3 used KBr as a catalyst (the amount of Br- was the same as in Example 1).

[0092] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 5.

[0093] Comparative Example 4

[0094] Compared with Example 1, Comparative Example 4 uses copper oxide nanoparticles grafted with ionic liquid coupling agents.

[0095] Catalyst preparation: 0.3 mol of copper acetylacetonate was dissolved in 1 L of benzyl alcohol and stirred at room temperature. 7 g of deionized water was slowly added dropwise to the solution, and the mixture was heated to 60 °C for 20 min. The mixture was then transferred to a stainless steel reactor and reacted at 220 °C for 40 h. The product was centrifuged, and 40 g (0.16 mol) of 3-bromopropyltrimethoxysilane, 17 g of water, and 185 g of cyclohexane were added to the substrate. The mixture was modified at 60 °C for 2 h. The solvent was removed by rotary evaporation, and the mixture was washed three times with ethanol. The product was dispersed in 68 g of ethyl acetate, and 13.5 g (0.165 mol) of 1-methylimidazole was added. The mixture was reacted at 60 °C for 5 h. The lower layer was washed three times with ethyl acetate and dried under vacuum at 80 °C for 4 h to obtain the catalyst. The catalyst contained 46 wt% CuO nanoparticles and 54 wt% coupling agent. The average diameter of the CuO nanoparticles was 3.5 nm, and the surface alkali content was 54 μmol / g.

[0096] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 5.

[0097] Comparative Example 5

[0098] Compared with Example 1, the preparation process of the catalyst in Comparative Example 5 is as follows: the ionic liquid coupling agent and zirconium dioxide of Example 1 are prepared separately, and then the ionic liquid coupling agent and nanoparticles are directly mixed for the reaction.

[0099] The catalyst evaluation method was the same as in Example 1, and the results are shown in Table 5.

[0100] Comparative Example 6

[0101] Catalyst preparation: 40 g (0.16 mol) of 3-bromopropyltrimethoxysilane was added to 68 g of ethyl acetate and 13.5 g (0.165 mol) of 1-methylimidazole, and the mixture was reacted at 60 °C for 5 h. The lower layer was washed three times with ethyl acetate and dried under vacuum at 80 °C for 4 h to obtain the ionic liquid coupling agent.

[0102] 0.3 mol of zirconium propoxide was dissolved in 1 L of benzyl alcohol and stirred at room temperature. 12 g of deionized water was slowly added dropwise to the solution, and the mixture was heated to 60 °C for 20 min. The mixture was then transferred to a stainless steel reactor and reacted at 220 °C for 40 h. The product was centrifuged, and the substrate was modified with the aforementioned ionic liquid coupling agent, 17 g of water, and 185 g of cyclohexane at 60 °C for 2 h. The solvent was removed by rotary evaporation, and the product was washed three times with ethanol to obtain the catalyst. The catalyst contained 85 wt% ZrO2 nanoparticles and 15 wt% coupling agent by weight. The average diameter of the ZrO2 nanoparticles was 3.0 nm, and the surface alkali content was 486 μmol / g.

[0103] Catalyst application: Place 50g of catalyst at the bottom of a distillation column, add 350g of dimethyl oxalate, and premix at 95℃ for 1h to form a homogeneous and transparent dispersion. Purge the bottom of the column with nitrogen gas, controlling the pressure at 0.34MPa and the reaction temperature at 180℃. Stir the reaction, continuously feeding dimethyl oxalate into the bottom of the column. The weight hourly space velocity (WHSV) of dimethyl oxalate is 3h⁻¹. -1 The space velocity was adjusted slightly according to the liquid level to keep the liquid level constant. The tower temperature was 130℃. Dimethyl carbonate was collected from the top of the tower. After the device stabilized, the products were analyzed and shown in Table 5.

[0104] Table 5 Evaluation results of the catalysts in Example 1 and Comparative Examples 1-6

[0105]

[0106] Comparative Example 7

[0107] Compared with Example 1, Comparative Example 7 differs in that the catalyst and dimethyl oxalate are reacted in a closed high-pressure stirred tank to prepare dimethyl carbonate. 5g of catalyst and 35g of dimethyl oxalate are added to the high-pressure tank, stirred and mixed, nitrogen is introduced for purging, the heating jacket is heated to 180°C, the reaction is stirred, and after 1 hour of reaction, the product is analyzed after cooling. The results are shown in Table 6.

[0108] Table 6 shows the evaluation results of the catalysts in Comparative Example 7 and Example 1.

[0109] Example number reactor Dimethyl carbonate selectivity (%) Example 1 Distillation tower 97.5 Comparative Example 7 autoclave 75.2

[0110] 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 catalyst for preparing dialkyl carbonate, characterized in that, The catalyst comprises metal oxide nanoparticles and an ionic liquid coupling agent grafted onto their surface. By weight of the catalyst, the content of the metal oxide nanoparticles is 40wt%~70wt%, and the content of the ionic liquid coupling agent is 30wt%~60wt%. The metal oxide is selected from at least one of zirconium oxide, zinc oxide, titanium oxide, and cerium oxide. The average diameter of the metal oxide nanoparticles is 3~5nm, and the alkali content on the surface of the metal oxide is 200~500μmol / g. The ionic liquid coupling agent is a reaction product of a halosilane coupling agent and a nitrogen heterocyclic compound, wherein the molar ratio of the nitrogen heterocyclic compound to the halosilane coupling agent is 1~1.5:

1. The halosilane coupling agent is selected from at least one of (3-chloropropyl)tris(1-methylethoxy)silane, 3-chloropropyltrimethoxysilane, 3-bromopropyltrimethoxysilane, 4-bromobutyltrimethoxysilane, 5-bromopentyltrimethoxysilane, (4-bromobenzyloxy)trimethoxysilane, bromophenyltrimethoxysilane, m-(trimethylsiloxy)bromobenzene, 4-fluorobutyltrimethoxysilane, and 4-iodobutyltrimethoxysilane. The nitrogen heterocyclic compound is selected from at least one of N-methylpyrrolidone, 1-methylimidazolium, N-triphenylmethylimidazolium, N,N-diimidazolylmethane, pyridine, 4-dimethylaminopyridine, N-methylpyrrole, 4-methylpyridine, and N-methylindole.

2. The method for preparing the catalyst for preparing dialkyl carbonate according to claim 1, comprising: (1) Mix the metal oxide precursor with benzyl alcohol, and slowly add deionized water to carry out the reaction; (2) The pre-reaction solution obtained in step (1) undergoes a solvothermal reaction; (3) After solid-liquid separation, the product obtained in step (2) is modified by adding halosilane coupling agent, water and organic solvent to the obtained solid to obtain a solid. (4) The solid obtained in step (3) is dispersed in a dispersion medium, and a nitrogen heterocyclic compound is added to react and the catalyst is obtained.

3. The preparation method according to claim 2, characterized in that, In step (1), the metal oxide precursor is selected from at least one of zirconium n-propoxide, zirconium isopropoxide, zirconium acetylacetonate, zinc isopropoxide, zinc acetylacetonate, tetraisopropyl titanate, tetrabutyl titanate, cerium n-propoxide, cerium isopropoxide, and cerium acetylacetonate. And / or, in step (3), the organic solvent is selected from at least one of cyclohexane, n-hexane, n-heptane, and isooctane; And / or, in step (4), the dispersion medium is selected from at least one of toluene, ethylbenzene, p-xylene, and ethyl acetate.

4. The preparation method according to claim 3, characterized in that, In step (3), the organic solvent is cyclohexane; And / or, in step (4), the dispersion medium is ethyl acetate.

5. The preparation method according to claim 2, characterized in that, In step (1), after the metal oxide precursor is mixed with benzyl alcohol, the concentration of the resulting solution is 0.1~0.5 mol / L; And / or, in step (1), the molar ratio of deionized water to the metal oxide precursor is x ~ 1.6x:1, where x represents the product MO obtained by hydrolysis of the metal oxide precursor. X The number of oxygen atoms in it; And / or, in step (3), the mass ratio of the amount of halosilane coupling agent added to the theoretical metal oxide is 1~2:1, the molar ratio of the amount of water added to the halosilane coupling agent is 1~4:1, and the mass ratio of the amount of organic solvent added to the theoretical metal oxide is 4~16:

1. And / or, in step (4), the molar ratio of the amount of nitrogen heterocyclic compound added to the halosilane coupling agent is 1~1.5:1, and the mass ratio of the dispersion medium to the nitrogen heterocyclic compound is 4~8:

1.

6. The preparation method according to claim 2, characterized in that, In step (1), the reaction temperature is 45~70℃ and the reaction time is 10~40min; And / or, in step (2), the reaction temperature is 210~260℃ and the reaction time is 30~54h; And / or, in step (3), the modification temperature is 50~70℃ and the modification time is 1~3h; And / or, in step (4), the reaction temperature is 50~70℃ and the reaction time is 4~40h.

7. The application of the catalyst according to claim 1, characterized in that, The application is as follows: using dialkyl oxalate as a reactant, a decarbonylation reaction is carried out under the action of the catalyst to prepare dialkyl carbonate.

8. The application according to claim 7, characterized in that, The dialkyl oxalate is at least one of dimethyl oxalate, diethyl oxalate, and methyl ethyl oxalate.

9. The application according to claim 7, characterized in that, The decarbonylation reaction is carried out in a distillation column. The reaction raw materials and catalyst are fed from the bottom of the distillation column, mixed, and reacted. The light components generated by the reaction are distilled and collected from the top of the column to obtain dialkyl carbonate.

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