A process for the preparation of dimethyl carbonate from the reaction of co and methyl nitrite

Abstract

The application discloses a method for preparing dimethyl carbonate by reacting CO and methyl nitrite, belongs to the technical field of dimethyl carbonate preparation, and aims at solving the technical problems of high impurity conversion rate, high colority, and further improved conversion rate of methyl nitrite and service life of a catalyst in the process of preparing dimethyl carbonate by catalyzing the reaction of CO and methyl nitrite in the prior art, and specifically comprises the following steps: stirring isocyanic acid propyl triethoxysilane and N,N-dimethylformamide under an inert gas atmosphere, increasing the temperature of a reaction system to 50-60 DEG C, and adding 3-aminopropionic acid into the reaction system. The application is prepared by preparing a halogen-free palladium copper catalytic system, and then sequentially performing silicon aluminum coating, potassium modification and 18-crown-6-ether modification, so that the conversion rate of methyl nitrite and the service life of the catalyst are effectively improved while the impurity conversion rate and the colority value of the product are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of dimethyl carbonate preparation, and in particular to a method for preparing dimethyl carbonate by reacting CO and methyl nitrite. Background Art

[0002] As a green chemical, dimethyl carbonate is in great demand in the fields of lithium battery electrolyte, polycarbonate synthesis and pharmaceutical intermediates. In the preparation method of dimethyl carbonate, carbon monoxide and methyl nitrite are used as raw materials to directly synthesize dimethyl carbonate through a catalytic coupling method. During the reaction, the raw material methyl nitrite can be generated by the reaction of methanol and sodium nitrite. The reaction raw materials are easily available, the reaction conditions are mild, and the by-product NO can be recycled. It complies with the principles of green chemistry and has industrial potential.

[0003] In the prior art, the catalysts for the reaction of CO and methyl nitrite to produce dimethyl carbonate are mostly chlorides (such as palladium chloride), which are loaded onto carriers such as activated carbon by physical adsorption. The binding force between the catalytically active substance and the carrier is weak, and the catalytically active substance is easily lost during use, shortening the service life of the catalyst.

[0004] Moreover, during the catalytic reaction of CO and methyl nitrite to prepare dimethyl carbonate, halide ions easily undergo substitution reactions with reaction intermediates to generate halogenated impurities, and CO easily undergoes disproportionation or decomposition reactions with methylene nitrate to generate by-products such as dimethyl oxalate and methyl formate, resulting in the need to further improve the conversion rate of dimethyl carbonate. Summary of the Invention

[0005] The present invention aims to provide a method for preparing dimethyl carbonate by reacting CO and methyl nitrite, so as to solve the technical problems in the prior art of catalyzing the reaction of CO and methyl nitrite to prepare dimethyl carbonate, such as high impurity conversion rate, high chroma, and the need to further improve the conversion rate of methyl nitrite and the life of the catalyst.

[0006] The object of the present invention can be achieved by the following technical solution: A method for preparing dimethyl carbonate by reacting CO and methyl nitrite, comprising the following steps:

[0007] S1. Under an inert gas atmosphere, isocyanatepropyltriethoxysilane and N,N-dimethylformamide are mixed and stirred, the temperature of the reaction system is raised to 50-60°C, 3-aminopropionic acid is added to the reaction system, and the reaction is kept warm for 30-40 minutes. Pd-copper-loaded porous carbon and potassium hydroxide aqueous solution are added to the reaction system, and the reaction is kept warm for 60-80 minutes. Post-treatment is performed to obtain a catalyst precursor;

[0008] The synthesis reaction mechanism of the catalyst precursor is:

[0009] During the reaction, the isocyanate group on the isocyanatepropyltriethoxysilane molecule condenses with the amino group on the 3-aminopropionic acid molecule to form an amide bond. Then, potassium hydroxide provides an alkaline environment, promoting the hydrolysis of the siloxane bond while undergoing acid-base neutralization with the carboxyl group to form a potassium carboxylate. The silanol formed by the hydrolysis of the siloxane bond chemically bonds to the surface of the porous carbon particles loaded with palladium copper to form a modification, thereby preparing a catalyst precursor.

[0010] S2, modifying the catalyst precursor by using 4'-formylbenzo-18-crown-6-ether to prepare a coupling catalyst;

[0011] S3. CO and methyl nitrite are mixed and compressed to obtain a mixed compressed gas, which is then introduced into a coupling reactor filled with a catalyst to undergo a catalytic reaction to obtain a dimethyl carbonate mixed gas. The dimethyl carbonate mixed gas is washed and purified to obtain dimethyl carbonate.

[0012] Furthermore, in step S1, the amount ratio of the isocyanatepropyltriethoxysilane, N,N-dimethylformamide, palladium copper loaded porous carbon and potassium hydroxide aqueous solution is 1g:10mL:2.2-2.6g:3mL, the concentration of the potassium hydroxide aqueous solution is 3-5mol / L, and the amount ratio of the isocyanatepropyltriethoxysilane and 3-aminopropionic acid is 1mol:1mol. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water 3 times and then dried, and the filter cake is transferred to a drying oven at a temperature of 70-80°C and dried to constant weight to obtain a catalyst precursor.

[0013] Furthermore, in step S3, the volume ratio of CO and methyl nitrite is 9:1, the pressure of the mixed compressed gas is 0.2-0.3 MPa; the temperature of the coupling reactor is 80-100°C, the pressure is 0.2-0.3 MPa, and the contact time of the mixed compressed gas with the catalyst is 1.5-3s. The washing and purification operation includes: after the reaction is completed, the dimethyl carbonate mixed gas is washed by a methanol spray tower, and the methanol solution is transferred to a methanol separation tower to separate methanol and low-boiling impurities to obtain crude dimethyl carbonate, and the crude dimethyl carbonate is distilled to obtain dimethyl carbonate.

[0014] Furthermore, the preparation method of the porous carbon loaded with palladium copper is as follows: palladium copper loaded sawdust, a template and silica sol are mixed, stirred and dispersed at room temperature for 30-50 minutes, sodium aluminate solution is added to the reaction system, ultrasonically dispersed for 40-60 minutes, aged for 24 hours, and post-treated to obtain coated modified sawdust, and then the coated modified sawdust is calcined under an inert gas atmosphere to obtain porous carbon loaded with palladium copper.

[0015] The synthesis reaction mechanism of palladium-copper loaded porous carbon is:

[0016] During the reaction process, palladium-copper loaded sawdust is used as a carbon source and metal carrier, sodium aluminate provides an aluminum source, and polyvinyl alcohol is used as a template and binder. Its long-chain molecules can be wrapped around the surface of the sawdust to form a hydrophobic layer, and combine with Si-OH in the silica sol through hydrogen bonds to guide the formation of a pore structure. Aging at room temperature promotes further cross-linking of Al-O-Si bonds to form a stable three-dimensional skeleton, which wraps the sawdust and metal particles to prepare coated modified sawdust. Under an inert atmosphere, the cellulose / lignin of the sawdust in the coated modified sawdust is pyrolyzed to generate a porous carbon skeleton. The SiO2-Al2O3 coating layer forms a stable ceramic phase at high temperature to prevent the collapse of the carbon skeleton, thereby preparing porous carbon loaded with palladium-copper.

[0017] Furthermore, the amount ratio of the palladium-copper loaded sawdust, template, silica sol and sodium aluminate solution is 10-12g:5-6g:50-60mL:28-32mL, the template is polyvinyl alcohol, and the sodium aluminate solution is composed of sodium aluminate, sodium hydroxide and purified water in a ratio of 5-6g:1g:15mL. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is raised to 85-95°C, and low-boiling substances are evaporated under reduced pressure to obtain coated modified sawdust.

[0018] Furthermore, the roasting method is as follows: the coated modified sawdust is placed in a tubular furnace, and under argon protection, the temperature of the tubular furnace is increased to 500-550°C at a heating rate of 3-5°C / min, and the mixture is kept warm and roasted for 4-6 hours, and then naturally cooled to room temperature. The roasted material is washed three times with purified water and then transferred to a drying oven at a temperature of 70-80°C, and dried to constant weight to obtain porous carbon loaded with palladium copper.

[0019] Furthermore, the preparation method of palladium-copper loaded sawdust is as follows: sawdust and alkali solution are mixed, the temperature of the reaction system is raised to 80-90°C, heat-insulated for 60-80 minutes, and post-treated to obtain pretreated sawdust; palladium-copper solution and pretreated sawdust are mixed, ultrasonically dispersed for 50-70 minutes, sodium hydroxide solution is added to the reaction system, the pH of the system is adjusted to 8-9, and post-treated to obtain palladium-copper loaded sawdust.

[0020] The synthetic reaction mechanism of palladium copper loaded sawdust is:

[0021] During the reaction, the sodium hydroxide in the alkali solution destroys the ester bond between lignin and hemicellulose, causing it to dissolve in the alkali solution, thereby exposing the cellulose fiber structure and increasing the specific surface area and porosity; then nitric acid provides an acidic environment to make Pd 2+ and Cu 2+ It exists stably in the form of hydrated ions. After promoting ion dispersion by ultrasound, the pH of the system is adjusted to alkaline to promote Pd 2+ and Cu 2+Hydrolysis generates hydroxide precipitate, which is adsorbed on the surface of sawdust to prepare palladium-copper loaded sawdust.

[0022] Furthermore, in the preparation process of pretreated sawdust, the usage ratio of the sawdust and alkali solution is 1g:8-10mL, and the alkali solution is composed of 2-3mol / L sodium hydroxide aqueous solution and hexadecyltrimethylammonium bromide at a ratio of 100mL:1-2g. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water until it is neutral and then dried, and the filter cake is transferred to a drying oven at a temperature of 70-80°C and dried to constant weight to obtain pretreated sawdust.

[0023] Furthermore, in the preparation process of palladium-copper loaded sawdust, the usage ratio of the palladium-copper solution and the pretreated sawdust is 60mL:20-25g, the palladium-copper solution is composed of palladium nitrate, copper nitrate and nitric acid in a usage ratio of 3g:1-1.5g:60mL, the concentration of the nitric acid is 0.6-0.8mol / L, and the concentration of the sodium hydroxide solution is 2-3mol / L. The post-treatment includes: after the reaction is completed, filtering, washing the filter cake with purified water until it is neutral and then drying it, transferring the filter cake to a drying oven at a temperature of 70-80°C, and drying it to constant weight to obtain palladium-copper loaded sawdust.

[0024] Furthermore, the coupling catalyst is prepared by mixing a catalyst precursor, toluene, 4'-formylbenzo-18-crown-6-ether and a catalyst, raising the temperature of the reaction system to reflux, keeping the reaction temperature for 5-6 hours, and post-treating to obtain the coupling catalyst.

[0025] The synthetic reaction mechanism of the coupling catalyst is:

[0026] During the reaction, p-toluenesulfonic acid is used as an acidic catalyst to promote the protonation of the carbonyl oxygen of the 4'-formylbenzo-18-crown-6-ether molecule, enhance the electrophilicity of the carbonyl carbon, and promote its nucleophilic addition-elimination reaction with the imino group (-NH-) on the surface of the catalyst precursor to form a Schiff base, thereby covalently modifying the crown ether structure to the catalyst precursor to prepare a coupled catalyst.

[0027] Furthermore, the amount ratio of the catalyst precursor, toluene, 4'-formylbenzo-18-crown-6-ether and catalyst is 3-5g:15mL:1-1.2g:0.1g, the catalyst is p-toluenesulfonic acid, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral and then dried, and the filter cake is transferred to a drying oven at a temperature of 70-80°C and dried to constant weight to obtain a coupling catalyst.

[0028] The present invention has the following beneficial effects:

[0029] 1. The present invention selects palladium nitrate and copper nitrate as raw materials for catalytically active components to form a halogen-free palladium-copper catalyst system, and utilizes silicon-aluminum coating to improve the stability of the catalytically active substance loading, thereby improving the conversion rate of dimethyl carbonate while increasing the catalytic life of the catalyst. Potassium and 18-crown-6-ether are modified on the coupling catalyst, the potassium in the coupling catalyst regulates the reaction path and the alkaline environment, the crown ether stabilizes the metal active sites and improves the selectivity, and combined with optimized reaction conditions, the product purity and conversion rate of dimethyl carbonate are improved.

[0030] 2. The present invention uses sawdust as raw material and uses alkali solution to treat it to provide a large number of loading sites for metal ion loading, so that palladium and copper can be evenly loaded on the sawdust. Sodium metaaluminate solution and silica sol form an aluminosilicate template, and polyvinyl alcohol acts as a template agent and cooperates with pine sawdust to form a porous structure of the coated modified sawdust after roasting, thereby increasing the specific surface area of ​​the catalyst, facilitating the adsorption and diffusion of reactants, and improving the catalytic efficiency.

[0031] 3. The present invention forms triethoxysilane modified with imine and carboxyl groups by condensing isocyanatepropyltriethoxysilane and 3-aminopropionic acid. Potassium hydroxide is used as a catalyst to catalyze the hydrolysis of triethoxysilane while acid-base neutralization occurs between potassium hydroxide and carboxyl groups to form potassium carboxylate. The imine is then used as a reaction active site to catalyze copper ammonia condensation by the catalyst to form 18-crown-6-ether modification. Potassium inhibits side reactions through a weakly alkaline environment while balancing the non-dissociation and dissociative activation of CO, thereby enhancing the catalyst's adsorption capacity for CO. The cavity structure of the crown ether selectively adsorbs CO and methyl nitrite, directionally arranges reactants, reduces by-products, promotes the transfer of reactants at the gas-solid interface, and improves the reaction rate. In addition, the oxygen atoms of the crown ether form coordination with palladium and copper to stabilize metal nanoparticles, prevent agglomeration during the reaction, and extend the life of the catalyst. DETAILED DESCRIPTION

[0032] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] In the present invention, the particle size of the pine sawdust is 1.5-3 mm;

[0034] In the present invention, polyvinyl alcohol is a commercially available product, model PVA2488, with an active ingredient content of 98% and CAS number 9002-89-5;

[0035] In the present invention, the CAS number of 3-aminopropionic acid is 107-95-9;

[0036] In the present application, the CAS number of 4'-formylbenzo-18-crown-6-ether is 60835-74-7;

[0037] In the present application, the silicon sol is a commercially available product, and the main component is sodium silicate, and the effective component content is 30%.

[0038] Example 1

[0039] The present embodiment provides a method for preparing dimethyl carbonate by reacting CO and methyl nitrite, comprising the following steps:

[0040] Step one, preparation of sawdust loaded with palladium copper

[0041] Mix 2 mol / L aqueous sodium hydroxide solution and cetyltrimethylammonium bromide uniformly at 100 mL:1 g to obtain lye;

[0042] Mix pine sawdust and lye at 1 g:8 mL into a reaction bottle and stir, raise the temperature of the reaction bottle to 80℃, and keep the temperature for 60 min, then reduce the temperature of the reaction bottle to room temperature, and then extract and filter, wash the filter cake with purified water until it is neutral, and then extract and dry, transfer the filter cake to a drying box with a temperature of 70℃, and dry until the weight is constant to obtain pretreated sawdust;

[0043] Mix palladium nitrate, copper nitrate and 0.6 mol / L nitric acid uniformly at 3 g:1 g:60 mL to obtain a palladium copper solution;

[0044] Mix the palladium copper solution and pretreated sawdust at 60 mL:20 g into a reaction bottle and mix, ultrasonic dispersion for 50 min, add 2 mol / L sodium hydroxide solution to the reaction bottle to adjust the pH of the system to 8, extract and filter, wash the filter cake with purified water until it is neutral, and then extract and dry, transfer the filter cake to a drying box with a temperature of 70℃, and dry until the weight is constant to obtain sawdust loaded with palladium copper.

[0045] Step two, preparation of porous carbon loaded with palladium copper

[0046] Mix sodium aluminate, sodium hydroxide and purified water uniformly at 5 g:1 g:15 mL to obtain a sodium aluminate solution;

[0047] Weigh 100 g of sawdust loaded with palladium copper, 50 g of template agent polyvinyl alcohol and 500 mL of silicon sol into a reaction bottle and mix, stir and disperse at room temperature for 30 min, add 280 mL of sodium aluminate solution to the reaction bottle, ultrasonic dispersion for 40 min, and then age for 24 h, raise the temperature of the reaction bottle to 85℃, and evaporate low boiling point substances under reduced pressure to obtain coated modified sawdust;

[0048] The coated modified sawdust was placed in a tube furnace, and the temperature of the tube furnace was increased to 500℃ at a rate of 3℃ / min under argon protection, and then the coated modified sawdust was baked for 4h, and then naturally cooled to room temperature. After the baked coated modified sawdust was washed with purified water for 3 times, the coated modified sawdust was transferred to a drying box with a temperature of 70℃, and then dried until the weight was constant to obtain the porous carbon loaded with palladium and copper.

[0049] Step three, preparation of catalyst precursor

[0050] The isocyanate propyl triethoxysilane 24.7g, N,N-dimethylformamide 247mL, 3-aminopropionic acid 8.9g, porous carbon loaded with palladium and copper 54.3g, and 3mol / L potassium hydroxide aqueous solution 74.1mL were weighed and added into an argon-protected reaction bottle, and then stirred. The temperature of the reaction bottle was increased to 50℃, and then the 3-aminopropionic acid was reacted for 30min. Then, the temperature of the reaction bottle was decreased to room temperature, and then filtered. The filter cake was washed with purified water for 3 times, and then dried. The filter cake was transferred to a drying box with a temperature of 70℃, and then dried until the weight was constant to obtain the catalyst precursor.

[0051] Step four, preparation of coupling catalyst

[0052] The catalyst precursor 30g, toluene 150mL, 4'-formylbenzo-18-crown-6-ether 10g, and catalyst p-toluenesulfonic acid 1g were weighed and added into a reaction bottle, and then stirred. The temperature of the reaction bottle was increased to reflux, and then reacted for 5h. The temperature of the reaction bottle was decreased to room temperature, and then filtered. The filter cake was washed with purified water until neutral, and then dried. The filter cake was transferred to a drying box with a temperature of 70℃, and then dried until the weight was constant to obtain the coupling catalyst.

[0053] Step five, preparation of dimethyl carbonate

[0054] The CO and methyl nitrite were mixed at a volume ratio of 9:1, and then compressed to obtain a mixed compressed gas with a pressure of 0.2MPa.

[0055] The coupling catalyst was filled into a coupling reactor to form a coupling catalyst bed. The temperature of the coupling reactor was increased to 80℃, and the pressure was increased to 0.2MPa. The mixed compressed gas was introduced into the coupling reactor from the top of the coupling reactor. The mixed compressed gas contacted with the coupling catalyst bed from top to bottom. The flow rate of the mixed compressed gas was adjusted so that the contact time between the mixed compressed gas and the catalyst was 3s. After being catalyzed by the coupling catalyst bed, the dimethyl carbonate mixed gas was discharged from the bottom of the coupling reactor.

[0056] After the dimethyl carbonate mixed gas was washed by the methanol spraying tower, the methanol solution was transferred to a methanol separation tower to separate methanol and low-boiling impurities, and then a crude dimethyl carbonate was obtained. The crude dimethyl carbonate was subjected to rectification to obtain dimethyl carbonate.

[0057] Example 2

[0058] This embodiment provides a method for preparing dimethyl carbonate by reacting CO and methyl nitrite, comprising the following steps:

[0059] Step 1: Preparation of palladium-copper loaded sawdust

[0060] Mix 2.5 mol / L sodium hydroxide aqueous solution and cetyltrimethylammonium bromide at a ratio of 100 mL:1.5 g to obtain an alkali solution;

[0061] Pine sawdust and alkali solution were added to a reaction flask at a ratio of 1 g:9 mL and stirred. The temperature of the reaction flask was raised to 85°C and kept warm for 70 minutes. The temperature of the reaction flask was lowered to room temperature and filtered. The filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at a temperature of 75°C and dried to constant weight to obtain pretreated sawdust.

[0062] Palladium nitrate, copper nitrate, and 0.7 mol / L nitric acid were mixed in a ratio of 3 g:1.3 g:60 mL to obtain a palladium-copper solution;

[0063] The palladium-copper solution and pretreated sawdust were added to a reaction flask at a ratio of 60 mL:23 g, mixed, and ultrasonically dispersed for 60 min. A 2.5 mol / L sodium hydroxide solution was added to the reaction flask to adjust the pH of the system to 8.5. The mixture was filtered, and the filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 75°C and dried to constant weight to obtain palladium-copper loaded sawdust.

[0064] Step 2: Preparation of porous carbon loaded with palladium and copper

[0065] Sodium metaaluminate, sodium hydroxide, and purified water were mixed uniformly at a ratio of 5.5 g:1 g:15 mL to obtain a sodium metaaluminate solution;

[0066] Weigh: 110 g of palladium-copper loaded sawdust, 55 g of template agent polyvinyl alcohol, and 550 mL of silica sol are added to a reaction flask, mixed, and stirred and dispersed at room temperature for 40 min. 300 mL of sodium metaaluminate solution is added to the reaction flask, ultrasonically dispersed for 50 min, aged for 24 h, and the temperature of the reaction flask is raised to 90° C. Low-boiling substances are evaporated under reduced pressure to obtain coated modified sawdust;

[0067] The coated modified sawdust was placed in a tube furnace. Under argon protection, the temperature of the tube furnace was increased to 525°C at a heating rate of 4°C / min, and the mixture was kept warm and calcined for 5 hours. The mixture was naturally cooled to room temperature. The calcined material was washed three times with purified water and then transferred to a drying oven at a temperature of 75°C and dried to constant weight to obtain porous carbon loaded with palladium and copper.

[0068] Step 3: Preparation of catalyst precursor

[0069] Weigh: 24.7 g of isocyanatepropyltriethoxysilane and 247 mL of N,N-dimethylformamide were added to a reaction flask protected by argon and stirred. The temperature of the reaction flask was raised to 55°C. 8.9 g of 3-aminopropionic acid was added to the reaction flask and the reaction was kept warm for 35 minutes. 59.3 g of palladium-copper loaded porous carbon and 74.1 mL of 4 mol / L potassium hydroxide aqueous solution were added to the reaction flask and the reaction was kept warm for 70 minutes. The temperature of the reaction flask was lowered to room temperature, filtered, and the filter cake was washed three times with purified water and then dried. The filter cake was transferred to a drying oven at 75°C and dried to constant weight to obtain a catalyst precursor.

[0070] Step 4: Preparation of coupling catalyst

[0071] Weigh: 40 g of catalyst precursor, 150 mL of toluene, 11 g of 4'-formylbenzo-18-crown-6-ether and 1 g of catalyst p-toluenesulfonic acid, add them into the reaction flask and stir, raise the temperature of the reaction flask to reflux, keep warm and react for 5.5 hours, lower the temperature of the reaction flask to room temperature, filter, wash the filter cake with purified water until neutral and then dry, transfer the filter cake to a drying oven at a temperature of 75°C, and dry to constant weight to obtain a coupling catalyst.

[0072] Step 5: Preparation of dimethyl carbonate

[0073] CO and methyl nitrite were mixed in a volume ratio of 9:1 and compressed to obtain a mixed compressed gas with a pressure of 0.25 MPa;

[0074] A coupling catalyst is placed in a coupling reactor to form a coupling catalytic bed. The temperature and pressure of the coupling reactor are raised to 90° C. and 0.25 MPa, and a mixed compressed gas is introduced into the coupling reactor from the top. The mixed compressed gas contacts the coupling catalytic bed from top to bottom. The flow rate of the compressed mixed gas is adjusted so that the contact time between the mixed compressed gas and the catalyst is 2 seconds. After catalysis by the coupling catalytic bed, the dimethyl carbonate mixed gas is discharged from the bottom of the coupling reactor.

[0075] After the dimethyl carbonate mixed gas is washed by a methanol spray tower, the methanol solution is transferred to a methanol separation tower to separate methanol and low-boiling impurities to obtain crude dimethyl carbonate. The crude dimethyl carbonate is distilled to obtain dimethyl carbonate.

[0076] Example 3

[0077] This embodiment provides a method for preparing dimethyl carbonate by reacting CO and methyl nitrite, comprising the following steps:

[0078] Step 1: Preparation of palladium-copper loaded sawdust

[0079] Mix 3 mol / L sodium hydroxide aqueous solution and cetyltrimethylammonium bromide at a ratio of 100 mL:2 g to obtain an alkali solution;

[0080] Pine sawdust and alkali solution were added to a reaction flask at a ratio of 1 g:10 mL and stirred. The temperature of the reaction flask was raised to 90°C and kept warm for 80 minutes. The temperature of the reaction flask was lowered to room temperature and filtered. The filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 80°C and dried to constant weight to obtain pretreated sawdust.

[0081] Palladium nitrate, copper nitrate, and 0.8 mol / L nitric acid were mixed in a ratio of 3 g:1.5 g:60 mL to obtain a palladium-copper solution;

[0082] The palladium-copper solution and pretreated sawdust were added to a reaction flask at a ratio of 60 mL:25 g, mixed, and ultrasonically dispersed for 70 min. A 3 mol / L sodium hydroxide solution was added to the reaction flask to adjust the pH of the system to 9. The mixture was filtered, and the filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 80°C and dried to constant weight to obtain palladium-copper loaded sawdust.

[0083] Step 2: Preparation of porous carbon loaded with palladium and copper

[0084] Sodium metaaluminate, sodium hydroxide, and purified water were mixed uniformly at a ratio of 6 g:1 g:15 mL to obtain a sodium metaaluminate solution;

[0085] Weigh: 120 g of palladium-copper loaded sawdust, 60 g of template agent polyvinyl alcohol, and 600 mL of silica sol are added to a reaction flask, mixed, and stirred and dispersed at room temperature for 50 min. 320 mL of sodium metaaluminate solution is added to the reaction flask, ultrasonically dispersed for 60 min, aged for 24 h, and the temperature of the reaction flask is raised to 95°C. Low-boiling substances are evaporated under reduced pressure to obtain coated modified sawdust;

[0086] The coated modified sawdust was placed in a tube furnace. Under argon protection, the temperature of the tube furnace was increased to 550°C at a heating rate of 5°C / min, and the mixture was kept warm and calcined for 6 hours. The mixture was naturally cooled to room temperature. The calcined material was washed three times with purified water and then transferred to a drying oven at 80°C and dried to constant weight to obtain porous carbon loaded with palladium and copper.

[0087] Step 3: Preparation of catalyst precursor

[0088] Weigh: 24.7 g of isocyanatepropyltriethoxysilane and 247 mL of N,N-dimethylformamide were added to a reaction flask protected by argon and stirred. The temperature of the reaction flask was raised to 60°C. 8.9 g of 3-aminopropionic acid was added to the reaction flask and the reaction was kept warm for 40 minutes. 64.2 g of palladium-copper loaded porous carbon and 74.1 mL of 5 mol / L potassium hydroxide aqueous solution were added to the reaction flask and the reaction was kept warm for 80 minutes. The temperature of the reaction flask was lowered to room temperature and filtered. The filter cake was washed three times with purified water and then dried. The filter cake was transferred to a drying oven at 80°C and dried to constant weight to obtain a catalyst precursor.

[0089] Step 4: Preparation of coupling catalyst

[0090] Weigh: 50 g of catalyst precursor, 150 mL of toluene, 12 g of 4'-formylbenzo-18-crown-6-ether and 1 g of catalyst p-toluenesulfonic acid, add them into the reaction flask and stir, raise the temperature of the reaction flask to reflux, keep warm and react for 6 hours, lower the temperature of the reaction flask to room temperature, filter, wash the filter cake with purified water until neutral and then dry, transfer the filter cake to a drying oven at 80°C, and dry to constant weight to obtain a coupling catalyst.

[0091] Step 5: Preparation of dimethyl carbonate

[0092] CO and methyl nitrite were mixed in a volume ratio of 9:1 and compressed to obtain a mixed compressed gas with a pressure of 0.3 MPa;

[0093] A coupling catalyst is placed in a coupling reactor to form a coupling catalytic bed. The temperature of the coupling reactor is increased to 100° C., and the pressure is increased to 0.3 MPa. A mixed compressed gas is introduced into the coupling reactor from the top of the coupling reactor. The mixed compressed gas contacts the coupling catalytic bed from top to bottom. The flow rate of the compressed mixed gas is adjusted so that the contact time between the mixed compressed gas and the catalyst is 1.5 s. After catalysis by the coupling catalytic bed, the dimethyl carbonate mixed gas is discharged from the bottom of the coupling reactor.

[0094] After the dimethyl carbonate mixed gas is washed by a methanol spray tower, the methanol solution is transferred to a methanol separation tower to separate methanol and low-boiling impurities to obtain crude dimethyl carbonate. The crude dimethyl carbonate is distilled to obtain dimethyl carbonate.

[0095] Comparative Example 1

[0096] The difference between this comparative example and Example 3 is that in step 1, the preparation method of palladium-copper loaded sawdust is as follows: 2.31 g of palladium chloride, 0.72 g of copper chloride and 60 mL of anhydrous ethanol are mixed to form a palladium-copper solution, the palladium-copper solution and pretreated sawdust are added to a reaction flask at a ratio of 60 mL:25 g, mixed, ultrasonically dispersed for 70 min, and the solvent is evaporated under reduced pressure to obtain palladium-copper loaded sawdust.

[0097] Comparative Example 2

[0098] The difference between this comparative example and Example 3 is that in step 2, palladium-copper loaded sawdust is used instead of coated modified sawdust to participate in the preparation of palladium-copper loaded porous carbon.

[0099] Comparative Example 3

[0100] The difference between this comparative example and Example 3 is that in step 3, 5 mol / L sodium hydroxide is used instead of potassium hydroxide solution.

[0101] Comparative Example 4

[0102] The difference between the present comparative example and Example 3 is that step four is cancelled, and the coupling catalyst in step five is replaced by the catalyst precursor in step three.

[0103] Performance test:

[0104] The mass fraction of the crude dimethyl carbonate sample prepared in Examples 1-3 and Comparative Examples 1-4 was determined according to the standard GB / T 33107-2016 "Dimethyl Carbonate for Industrial Use".

[0105] The colority of the crude dimethyl carbonate sample prepared in Examples 1-3 and Comparative Examples 1-4 was determined according to the standard GB / T 3143-1982 "Determination of Color of Liquid Chemical Products (Hazen Units-Palladium-Cobalt Color Number)".

[0106] After the coupling catalyst in the preparation of dimethyl carbonate in Examples 1-3 and Comparative Examples 1-4 catalyzed the reaction of CO and methyl nitrite stably for 100 h, the conversion rate of methyl nitrite in the reaction catalyzed by the coupling catalyst in the time period of 0-1 h and 99-100 h was determined.

[0107] The conversion rate was determined according to the formula , wherein n DMC is the molar amount of the generated dimethyl carbonate, and n MN is the molar amount of the consumed methyl nitrite. The specific test data are shown in Table 1 below.

[0108] Table 1-Performance test data table of the sample

[0109]

[0110] Data analysis:

[0111] Comparative analysis of the data in Table 1 above shows that the mass fraction of the crude dimethyl carbonate prepared by the present application reaches 99.85%, the colority (Pt-Co) is ≤5, the conversion rate of methyl nitrite in the time period of 0-1 h reaches 86.8%, and the conversion rate of methyl nitrite in the time period of 99-100 h reaches 85.0%. The performance test data are all better than those of the comparative examples, indicating that the present application prepares a halogen-free palladium-copper catalytic system by selecting raw materials, and utilizes silicon-aluminum coating and modification by potassium and 18-crown-6-ether to effectively reduce the colority value of dimethyl carbonate with impurities and improve the conversion rate of methyl nitrite. Moreover, the coupling catalyst prepared by the present application still has good catalytic conversion activity after 100 h of catalytic circulation, effectively prolonging the catalytic life of the catalyst.

[0112] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing dimethyl carbonate by reacting CO and methyl nitrite, characterized in that: The following steps are involved: S1. Under an inert gas atmosphere, isocyanatepropyltriethoxysilane and N,N-dimethylformamide are mixed and stirred, the temperature of the reaction system is raised to 50-60°C, 3-aminopropionic acid is added to the reaction system, and the reaction is kept warm for 30-40 minutes. Pd-copper-loaded porous carbon and potassium hydroxide aqueous solution are added to the reaction system, and the reaction is kept warm for 60-80 minutes. Post-treatment is performed to obtain a catalyst precursor; S2, modifying the catalyst precursor by using 4'-formylbenzo-18-crown-6-ether to prepare a coupling catalyst; S3, CO and methyl nitrite are mixed and compressed to obtain a mixed compressed gas, and the mixed compressed gas is then passed into a coupling reactor filled with a catalyst to obtain a dimethyl carbonate mixed gas through a catalytic reaction, and the dimethyl carbonate mixed gas is washed and purified to obtain dimethyl carbonate; The preparation method of palladium-copper loaded porous carbon comprises: mixing palladium-copper loaded sawdust, a template agent and silica sol, stirring and dispersing at room temperature for 30-50 minutes, adding sodium aluminate solution to the reaction system, ultrasonically dispersing for 40-60 minutes, aging for 24 hours, and post-processing to obtain coated modified sawdust, and then calcining the coated modified sawdust under an inert gas atmosphere to obtain palladium-copper loaded porous carbon, wherein the template agent is polyvinyl alcohol; The preparation method of palladium-copper loaded sawdust comprises the following steps: mixing sawdust and alkali solution, raising the temperature of the reaction system to 80-90°C, maintaining the temperature for 60-80 minutes, and performing post-treatment to obtain pre-treated sawdust; mixing the palladium-copper solution and the pre-treated sawdust, performing ultrasonic dispersion for 50-70 minutes, adding sodium hydroxide solution to the reaction system, adjusting the pH of the system to 8-9, and performing post-treatment to obtain palladium-copper loaded sawdust; The preparation method of the coupling catalyst comprises: mixing a catalyst precursor, toluene, 4'-formylbenzo-18-crown-6-ether and a catalyst, raising the temperature of the reaction system to reflux, keeping the temperature to react for 5-6 hours, and post-treating to obtain the coupling catalyst.

2. The method for preparing dimethyl carbonate by reacting CO and methyl nitrite according to claim 1, wherein: In step S1, the amount ratio of the isocyanatepropyl triethoxysilane, N,N-dimethylformamide, palladium copper loaded porous carbon and potassium hydroxide aqueous solution is 1g:10mL:2.2-2.6g:3mL, the concentration of the potassium hydroxide aqueous solution is 3-5mol / L, the amount ratio of the isocyanatepropyl triethoxysilane and 3-aminopropionic acid is 1mol:1mol, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water 3 times and then dried, and the filter cake is transferred to a drying oven at a temperature of 70-80°C and dried to constant weight. , obtaining a catalyst precursor; in step S3, the volume ratio of CO and methyl nitrite is 9:1, the pressure of the mixed compressed gas is 0.2-0.3 MPa; the temperature of the coupling reactor is 80-100°C, the pressure is 0.2-0.3 MPa, and the contact time of the mixed compressed gas with the catalyst is 1.5-3s. The washing and purification operation includes: after the reaction is completed, the dimethyl carbonate mixed gas is washed by a methanol spray tower, and the methanol solution is transferred to a methanol separation tower to separate methanol and low-boiling impurities to obtain crude dimethyl carbonate, and the crude dimethyl carbonate is distilled to obtain dimethyl carbonate.

3. The method for preparing dimethyl carbonate by reacting CO and methyl nitrite according to claim 1, wherein: The palladium-copper loaded sawdust, template, silica sol and sodium aluminate solution are used in a ratio of 10-12 g: 5-6 g: 50-60 mL: 28-32 mL, and the sodium aluminate solution is composed of sodium aluminate, sodium hydroxide and purified water in a ratio of 5-6 g: 1 g: 15 mL. The post-treatment comprises: after the reaction is completed, raising the temperature of the reaction system to 85-95° C., and removing low-boiling substances by distillation under reduced pressure to obtain coated modified sawdust.

4. The method for preparing dimethyl carbonate by reacting CO and methyl nitrite according to claim 1, wherein: The calcination method is as follows: the coated modified sawdust is placed in a tubular furnace, and under argon protection, the temperature of the tubular furnace is increased to 500-550°C at a heating rate of 3-5°C / min, and the mixture is kept warm and calcined for 4-6 hours, and then naturally cooled to room temperature. The calcined material is washed three times with purified water and then transferred to a drying oven at a temperature of 70-80°C, and dried to constant weight to obtain porous carbon loaded with palladium copper.

5. The method for preparing dimethyl carbonate by reacting CO and methyl nitrite according to claim 1, wherein: In the process of preparing pretreated sawdust, the ratio of sawdust and alkali solution is 1g:8-10mL, and the alkali solution is 2-3mol / L sodium hydroxide aqueous solution and hexadecyltrimethylammonium bromide according to 100mL:1-2g. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral and then dried, and the filter cake is transferred to a drying oven at a temperature of 70-80°C and dried to constant weight to obtain pretreated sawdust; in the process of preparing palladium copper loaded sawdust, the palladium copper The amount ratio of the solution and the pretreated sawdust is 60 mL:20-25 g; the palladium-copper solution is composed of palladium nitrate, copper nitrate and nitric acid in the amount ratio of 3 g:1-1.5 g:60 mL; the concentration of the nitric acid is 0.6-0.8 mol / L; the concentration of the sodium hydroxide solution is 2-3 mol / L; and the post-processing comprises: after the reaction is completed, suction filtration, washing the filter cake with purified water until it is neutral and then drying it, transferring the filter cake to a drying oven at a temperature of 70-80 DEG C, and drying it to constant weight to obtain palladium-copper loaded sawdust.

6. The method for preparing dimethyl carbonate by reacting CO and methyl nitrite according to claim 1, wherein: The catalyst precursor, toluene, 4'-formylbenzo-18-crown-6-ether and catalyst are used in a ratio of 3-5 g:15 mL:1-1.2 g:0.1 g, and the catalyst is p-toluenesulfonic acid. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral and then dried, and the filter cake is transferred to a drying oven at a temperature of 70-80° C. and dried to constant weight to obtain a coupling catalyst.

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