Method for preparing dimethyl carbonate by catalyzing direct carbonylation of methanol by adopting molecular sieve membrane reactor
By using hydrophilic molecular sieve membrane in the molecular sieve membrane reactor in situ, the problem of limited reaction balance and by-product water when synthesising dimethyl carbonate is solved directly by using CO2 and methanol, and high efficiency, economical and environmental protection are achieved DMC production.
Patent Information
- Application Number
- CN202411458834.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-18
- Publication Date
- 2025-02-14
AI Technical Summary
The method of directly synthesizing dimethyl carbonate by CO2 and methanol is affected by the restriction of reaction equilibrium and by-product water, resulting in low DMC yield.
The molecular sieve membrane reactor is used to catalyze the direct carbonylation reaction of methanol and CO2, and remove water in situ through the hydrophilic molecular sieve membrane, breaking the limit of thermodynamic equilibrium and improving the methanol conversion rate.
It greatly improves the conversion rate of methanol, maintains the high selectivity of dimethyl carbonate, simplifies the process flow, and reduces operating costs and environmental pollution.
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Figure CN119431145A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of dimethyl carbonate preparation, and particularly relates to a method for preparing dimethyl carbonate by catalyzing direct carbonylation of methanol using a molecular sieve membrane reactor. Background Art
[0002] Dimethyl carbonate (DMC) is an important chemical raw material and organic solvent, widely used in medicine, pesticides, solvents, lubricants and polymer materials. Traditional DMC synthesis methods mainly include phosgene method and oxidative carbonylation method, but these methods have problems such as high raw material toxicity, complex process and environmental pollution. The technology of directly using CO2 and methanol to synthesize DMC has the following advantages: green and environmental protection: CO2 is a greenhouse gas. Its use can not only reduce emissions, but also convert it into valuable chemical products, which helps to achieve carbon cycle and reduce environmental pollution; raw materials are easy to obtain: methanol can be obtained from biomass, natural gas and other channels, with low cost and wide sources. CO2, as an industrial waste gas, can be captured in large quantities in many chemical processes; process simplification: the direct synthesis method avoids the use of highly toxic intermediates, the process is relatively simple and the operation is safe.
[0003] Although the direct use of CO2 and methanol to synthesize DMC is a green and environmentally friendly method, it is limited by the reaction equilibrium and the influence of by-product water, resulting in a low DMC yield. Therefore, we proposed to use molecular sieve membranes to remove water in situ, which effectively overcomes the problems of reaction equilibrium and by-product influence and promotes the generation of DMC. Compared with traditional separation methods, in situ water removal through molecular sieve membranes can greatly improve the conversion rate of methanol without introducing side reactions and will not reduce the selectivity of DMC. At the same time, it simplifies the process flow and reduces operating costs and environmental pollution. The development of this technology is expected to achieve a more green, economical and efficient DMC production and promote the sustainable development of the chemical industry. Summary of the invention
[0004] In order to solve the problem of low conversion rate of direct carbonylation of methanol and CO2 to prepare dimethyl carbonate, the present invention proposes a method for preparing dimethyl carbonate by direct carbonylation of methanol and CO2 using a molecular sieve membrane reactor. The byproduct water is selectively removed in situ through the hydrophilic molecular sieve membrane, breaking the thermodynamic equilibrium limitation and greatly improving the methanol conversion rate.
[0005] The present invention provides a method for preparing dimethyl carbonate by catalyzing direct carbonylation of methanol using a molecular sieve membrane reactor, wherein a molecular sieve membrane is coupled with a catalyst and fixed in a high-pressure reactor. A kettle-type catalytic membrane reactor is constructed. The catalyst reacts with methanol and carbon dioxide to generate dimethyl carbonate and water. The water is removed from the reaction side by the pressure difference between the inside and outside of the membrane, and CO2 and other substances are retained on the reaction side due to the selective permeability of the membrane. The reaction is promoted to proceed in the forward direction, the methanol conversion rate is improved, and the high selectivity of dimethyl carbonate is maintained.
[0006] The technical solution provided by the present invention is as follows:
[0007] A method for preparing dimethyl carbonate by direct carbonylation of methanol catalyzed by a molecular sieve membrane reactor comprises the following steps:
[0008] 1) Construction of a kettle-type catalytic membrane reactor: The molecular sieve membrane tube includes a porous carrier tube and a hydrophilic molecular sieve membrane loaded on its surface, the molecular sieve membrane tube is fixed in a high-pressure reactor in a dead-end mode, the bottom end of the molecular sieve membrane tube is sealed and has a gap with the bottom inner wall of the high-pressure reactor, the upper end of the molecular sieve membrane tube passes through the outside of the high-pressure reactor, so that the permeate side is connected to the outside of the reactor, and the atmospheric pressure is maintained to construct a kettle-type catalytic membrane reactor; wherein, a stirrer is arranged at the bottom of the high-pressure reactor;
[0009] 2) adding methanol and a catalyst into a high-pressure reactor, and introducing carbon dioxide at a certain pressure, heating the high-pressure reactor, starting the stirring reaction, removing the by-product water through the pressure difference on both sides of the molecular sieve membrane tube during the reaction, cooling after the reaction is completed, and collecting the product;
[0010] The molecular sieve membrane is a ZSM-5 molecular sieve membrane or a NaA molecular sieve membrane.
[0011] Furthermore, a method for preparing dimethyl carbonate by catalyzing direct carbonylation of methanol using a molecular sieve membrane reactor is provided, wherein the porous carrier tube in step 1) is a porous ceramic tube or an alumina hollow fiber.
[0012] Furthermore, a method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor is provided, wherein the molecular sieve membrane tube is prepared by loading the molecular sieve membrane on the surface of a porous carrier tube, and the method comprises the following steps:
[0013] S1: The porous carrier tube is washed with ethanol and distilled water in sequence and then dried, and calcined in a muffle furnace to remove impurities;
[0014] S2: seal one end of the porous carrier tube treated in step S1, connect the other end to a vacuum pump, and then immerse the porous carrier tube in a ZSM-5 or NaA molecular sieve seed sol, perform vacuum suction at a vacuum pressure of 0.2-0.8 bar, and evacuate while immersing to load the seed sol on the carrier surface. After treating for 5-20 seconds, take out the porous carrier tube to obtain a seeded carrier;
[0015] S3: Immerse the seeded carrier in ZSM-5 or NaA crystallization solution, transfer them to a hydrothermal reactor and seal them, transfer the hydrothermal reactor to an oven for heating, and perform a hydrothermal crystallization reaction. After the reaction is completed, take them out for cleaning, and dry them to obtain the corresponding molecular sieve membrane tube.
[0016] Furthermore, a method for preparing dimethyl carbonate by catalyzing direct carbonylation of methanol using a molecular sieve membrane reactor is provided, wherein when the prepared molecular sieve membrane is a NaA molecular sieve membrane, the NaA molecular sieve seed sol in step S2 is prepared by mixing and dissolving a sodium source, an aluminum source, a silicon source, water, and tetramethylammonium hydroxide according to a molar ratio of Na2O:Al2O3:SiO2:H2O:(TMA)2O=0.6:1.0-3.0:10-12:700-750:10-15 until clarified, and then hydrothermally heating at 80-110°C for 2-8h;
[0017] The NaA crystallization solution in step S3 is prepared by mixing and dissolving a sodium source, an aluminum source, a silicon source and water in a molar ratio of Na2O:Al2O3:SiO2:H2O=40-60:1:4-6:500-1500, preferably 40-60:1:5:1000; the hydrothermal crystallization temperature in step S3 is 70-90°C, and the hydrothermal crystallization time is 3-6h.
[0018] Furthermore, a method for preparing dimethyl carbonate by catalyzing direct carbonylation of methanol using a molecular sieve membrane reactor is provided, wherein when the prepared molecular sieve membrane is a ZSM-5 molecular sieve membrane, the ZSM-5 molecular sieve seed sol in step S2 is prepared by mixing and dissolving a silicon source, tetrapropylammonium hydroxide and water in a molar ratio of SiO2:TPAOH:H2O=1.0-3.0:0.1-2:15-20 until clarified, and hydrothermally heating at 50-110°C for 72-120h;
[0019] The ZSM-5 crystallization solution in step S3 is prepared by mixing and dissolving silicon source, aluminum source, NaOH, NaF and water in a molar ratio of SiO2:Al2O3:NaOH:NaF:H2O=1-5:0.001-0.05:0.2-1:0.5-1.5:50-100; the hydrothermal crystallization temperature in step S3 is 150-200°C, and the hydrothermal crystallization time is 12-48h.
[0020] Further, a method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor is characterized in that the catalyst in step 2) is In x Ga y Ce z O m The nanocomposite metal oxide catalyst is prepared by a citric acid-assisted sol-gel method, comprising the following steps: dissolving an indium salt, a gallium salt and a cerium salt in deionized water, stirring to make them dissolved and dispersed uniformly, then weighing a certain mass of citric acid and adding it to the above solution to form a catalyst precursor solution, dripping nitric acid to adjust the pH of the precursor solution to 1-2, heating the precursor solution in an oil bath at 50-150° C., preferably 60-90° C., after the water evaporates to form a sol, placing it in a 50-150° C. oven to dry overnight, preferably 70-120° C., and then placing it in a muffle furnace for calcination to obtain In x Ga y Ce z O m Nanocomposite metal catalysts.
[0021] Furthermore, in the preparation of the catalyst, the metal salts of indium, gallium and cerium are independently selected from the chloride, nitrate, sulfate or acetylacetonate of each metal; based on 1 mol of citric acid, the amounts of the metal salts of indium, gallium and cerium are 0.1-0.2 mol, 0.05-0.1 mol and 0.8-0.9 mol respectively; the ratio of the total molar amount of the indium metal salt and the gallium metal salt to the molar amount of citric acid is 0.2-0.25:1.
[0022] Furthermore, in the preparation of the catalyst, calcination is carried out in two stages in a muffle furnace. In the first stage, the temperature is 200-500°C, preferably 300-350°C, and the calcination is carried out for 1-3 hours. In the second stage, the temperature is increased to 600-900°C, preferably 700-750°C, and the calcination is carried out for 4-8 hours.
[0023] Furthermore, a method for preparing dimethyl carbonate by direct carbonylation of methanol catalyzed by a molecular sieve membrane reactor is provided, wherein the initial pressure of the carbon dioxide introduced in step 2) is 0.1-10 MPa, preferably 3-8 MPa.
[0024] Furthermore, a method for preparing dimethyl carbonate by direct carbonylation of methanol catalyzed by a molecular sieve membrane reactor is provided, wherein the reaction temperature in step 2) is 50-200° C., preferably 80-160° C., and the reaction time is 1-48 h, preferably 6-24 h.
[0025] The present invention couples the catalyst and the molecular sieve membrane in the same system, so that it has both catalytic and separation functions. Methanol is directly carbonylated with CO2 under the action of the catalyst, and the generated byproduct water is selectively removed in situ through the molecular sieve membrane, thereby breaking the thermodynamic equilibrium limitation and achieving an increase in the reaction conversion rate. Compared with the conventional dimethyl carbonate production method, the present invention achieves a significant increase in the reaction conversion rate, a greener production process, and a significant reduction in the product separation cost.
[0026] Compared with the prior art, the technical solution of the present invention has the following advantages:
[0027] 1. The catalytic membrane reactor can achieve in-situ water removal, break the equilibrium limitation, promote the reaction towards the formation of dimethyl carbonate, improve the reaction conversion rate, and maintain high product selectivity.
[0028] 2. Using CO2 as raw material not only reduces greenhouse gas emissions, but also avoids the use of highly toxic intermediates in traditional methods, reduces environmental pollution, and complies with the principles of green chemistry.
[0029] 3. Catalytic reaction and membrane separation are integrated into one device, which reduces process steps and equipment investment and simplifies the operation process.
[0030] 4. Through catalytic membrane reactor technology, continuous and large-scale production of dimethyl carbonate can be achieved, which has good prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Figure 1 This is a scanning electron microscope spectrum of the hydrophilic NaA molecular sieve membrane prepared in Example 2.
[0032] Figure 2 This is a scanning electron microscope spectrum of the hydrophilic ZSM-5 molecular sieve membrane prepared in Example 3.
[0033] Figure 3 In prepared in Example 1 0.1 Ga 0.1 Ce 0.8 O x Transmission electron microscopy spectrum of the catalyst.
[0034] Figure 4 It is a schematic diagram of the structure of the kettle type catalytic membrane reactor constructed in the present invention. DETAILED DESCRIPTION
[0035] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.
[0036] Example 1: In 0.1 Ga 0.1 Ce 0.8 Ox The preparation of the nanocomposite metal catalyst comprises the following steps:
[0037] Preparation of In using citric acid-assisted sol-gel method 0.1 Ga 0.1 Ce 0.8 O x Catalyst, weigh a certain mass of indium nitrate, gallium nitrate, cerium nitrate, dissolve in 40g deionized water, stir and heat to mix and dissolve thoroughly, stir for 30min, add 2.1014g citric acid (AC) to the solution to form a catalyst precursor solution, so that the molar ratio of the precursor solution is AC: In(NO3)3: Ga(NO3)3: Ce(NO3)3 = 1: 0.1: 0.1: 0.8, where the concentration of citric acid AC in the solution is 0.274mmol / mL. Nitric acid is added dropwise to adjust the pH of the precursor solution to 1-2. Heat and stir the precursor solution in an 80℃ oil bath, take it out after the water evaporates to form a sol mixture, put it in a 110℃ oven and dry it overnight, put the dried sample in a muffle furnace with an air atmosphere at 350℃ and calcine it for 1h, then the temperature is raised to 700℃ and calcined for 5h to obtain In0.1Ga0.1Ce0.8Ox catalyst.
[0038] In prepared in Example 1 0.1 Ga 0.1 Ce 0.8 O x The transmission electron microscopy spectrum of the catalyst is shown in Figure 3 As shown, from Figure 3 It can be seen that 0.1 Ga 0.1 Ce 0.8 O x The catalyst is a nanoparticle with a large specific surface area, which can expose more active sites and greatly promote the improvement of catalytic performance.
[0039] Example 2: Preparation of NaA molecular sieve membrane, comprising the following steps:
[0040] 1) Alumina hollow fiber (outer diameter 3.5 mm, length 4 mm, 4 axial hollow channels evenly distributed inside, each hollow channel with a pore size of about 1 mm) was used as a carrier, washed and dried in ethanol and distilled water, respectively, and then calcined in a muffle furnace at 500° C. for 2 h.
[0041] 2) The preparation of NaA molecular sieve seed crystals is as follows: according to the molar ratio of Na2O:Al2O3:SiO2:H2O:(TMA)2O=0.6:1.5:11.25:725:13.14, a sodium source, an aluminum source, a silicon source, water, and tetramethylammonium hydroxide are mixed and dissolved until clear, wherein the sodium source is sodium hydroxide, the aluminum source is aluminum isopropoxide, and the silicon source is silica sol, and the mixture is hydrothermal treated at 100°C for 6 hours, and then the solid obtained by the reaction is collected by centrifugation, washed with water, and dried to obtain NaA molecular sieve seed crystal powder. Subsequently, the NaA molecular sieve seed crystal powder is dispersed in water at a mass fraction of 0.3% to obtain NaA molecular sieve seed crystal sol.
[0042] 3) Seal one end of the alumina hollow fiber carrier treated in step 1), connect the other end to a vacuum pump, and then immerse the alumina hollow fiber in the NaA molecular sieve seed sol obtained in step 2), perform vacuum suction at a vacuum pressure of 0.5 bar, and evacuate while immersing to load the seed sol on the carrier surface. After treating for 15 seconds, take out the carrier to obtain a seeded carrier.
[0043] 4) Prepare a crystallization solution for seed growth according to the molar ratio of 50Na2O:1Al2O3:5SiO2:1000H2O. The sodium source is sodium hydroxide, the aluminum source is sodium aluminate, and the silicon source is silica sol. Fix the seeded carrier tube vertically in an autoclave containing a PTFE liner, transfer the crystallization solution into the autoclave, immerse the seeded carrier in the crystallization solution, seal it, and place it in a pre-set temperature forced drying oven for crystallization. The crystallization conditions are 80°C and 5h. After the crystallization is completed, cool the autoclave to room temperature with water, take out the NaA molecular sieve membrane, wash it repeatedly with deionized water until it is neutral, and then place it in an oven at 80°C to dry overnight to obtain the NaA molecular sieve membrane.
[0044] The SEM spectrum of the hydrophilic NaA molecular sieve membrane prepared in Example 2 is as follows: Figure 1 shown.
[0045] from Figure 1 It can be seen that the NaA seeds grow in an interlaced manner, and the surface of the formed NaA molecular sieve membrane is smooth and dense without obvious defects, and there are no needle-shaped defects and non-zeolite voids. The highly hydrophilic and dense NaA molecular sieve membrane is the core component for preparing a catalytic membrane reactor.
[0046] Example 3: Preparation of ZSN-5 molecular sieve membrane, comprising the following steps:
[0047] 1) Alumina hollow fiber (outer diameter 3.5 mm, length 4 mm, 4 axial hollow channels evenly distributed inside, each hollow channel with a pore size of about 1 mm) was used as a carrier, washed and dried in ethanol and distilled water, respectively, and then calcined in a muffle furnace at 500° C. for 2 h.
[0048] 2) The preparation of ZSN-5 molecular sieve membrane seed crystals is to mix and dissolve the silicon source, tetrapropylammonium hydroxide and water according to the molar ratio SiO2:TPAOH:H2O=1:0.36:19.6 until it is clear. The silicon source is tetraethyl orthosilicate. It is hydrothermal at 90°C for 96 hours, and then the solid obtained by the reaction is collected by centrifugation, washed with water, and dried to obtain ZSN-5 molecular sieve membrane seed crystal powder. Subsequently, the ZSN-5 molecular sieve membrane seed crystal powder is dispersed in water at a mass fraction of 0.25% to obtain a ZSN-5 molecular sieve membrane seed crystal sol.
[0049] 3) Seal one end of the alumina hollow fiber carrier treated in step 1), connect the other end to a vacuum pump, and then immerse the alumina hollow fiber in the ZSN-5 molecular sieve membrane seed sol obtained in step 2), perform vacuum suction at a vacuum pressure of 0.5 bar, and evacuate while immersing to load the seed sol on the carrier surface. After treating for 15 seconds, take out the carrier to obtain a seeded carrier.
[0050] 4) Prepare a crystallization solution for seed growth according to the molar ratio of SiO2:Al2O3:NaOH:NaF:H2O=1:0.05:0.2:0.99:50, the silicon source is tetraethyl orthosilicate, and the aluminum source is sodium aluminate. Fix the seeded carrier tube vertically in an autoclave containing a PTFE liner, transfer the crystallization solution into the autoclave, immerse the seeded carrier in the crystallization solution, seal it and place it in a pre-set temperature blast drying oven for crystallization, the crystallization conditions are 180°C, 48h. After the crystallization is completed, cool the autoclave to room temperature with water, take out the ZSM-5 molecular sieve membrane, wash it repeatedly with deionized water until it is neutral, and then place it in an oven at 80°C to dry overnight. The ZSM-5 molecular sieve membrane can be obtained.
[0051] The SEM spectrum of the hydrophilic ZSM-5 molecular sieve membrane prepared in Example 3 is as follows: Figure 2 shown.
[0052] from Figure 2 It can be seen that the surface of the ZSM-5 molecular sieve membrane is smooth and dense without obvious defects, and there are no needle-shaped defects and non-zeolite voids. The dense ZSM-5 molecular sieve membrane is the core component for preparing a catalytic membrane reactor.
[0053] Example 4: In 0.1 Ga 0.1 Ce 0.8 O x @NaA catalytic membrane reactor construction and catalytic direct carbonylation of methanol and CO2 to produce dimethyl carbonate, including the following steps:
[0054] 1) Using the In prepared in Example 1 0.1 Ga 0.1 Ce 0.8 Ox Catalysts for catalytic experiments;
[0055] 2) The NaA molecular sieve membrane synthesized in Example 2 was fixed in a high-pressure reactor in a dead-end mode, the hollow channel opening at the lower end was sealed, and the upper end was sealed and passed out to the top of the high-pressure reactor, so that the permeation side of the NaA molecular sieve membrane (i.e., the hollow channel of the NaA molecular sieve membrane) was connected to the outside of the reactor, and the atmospheric pressure was maintained to construct a kettle-type catalytic membrane reactor (the structural schematic diagram of the kettle-type catalytic membrane reactor constructed by the present invention is shown in Figure 4 ).
[0056] 3) Add 10ml methanol, 0.5g catalyst, and magnetic stirring bar into the autoclave, fill with 3MPa carbon dioxide, check the air tightness of the autoclave and NaA molecular sieve membrane, and place the autoclave on a magnetic stirrer. When ensuring good air tightness, increase the temperature to 150℃ at a rate of 5℃ / min, stir continuously at a speed of 400r / min, react for 6h, and collect the product for analysis after cooling. 0.1 Ga 0.1 Ce 0.8 O x @NaA catalytic membrane reactor catalyzes the direct carbonylation of methanol and CO2 to produce dimethyl carbonate. The experimental results are: methanol conversion rate is 5.6%, and dimethyl carbonate selectivity is nearly 100%.
[0057] Example 5: In 0.1 Ga 0.1 Ce 0.8 O x @Construction of ZSM-5 catalytic membrane reactor and catalytic direct carbonylation of methanol and CO2 to prepare dimethyl carbonate. The experimental steps are repeated in Example 4, with the only difference being that "the NaA molecular sieve membrane synthesized in Example 2 is replaced by the ZSM-5 molecular sieve membrane synthesized in Example 3". The other conditions remain unchanged. The reaction is carried out for 6 hours. After cooling, the product is collected for analysis. The experimental results are: methanol conversion rate is 4.7%, and dimethyl carbonate selectivity is nearly 100%.
[0058] Comparative Example 1:
[0059] In 0.1 Ga 0.1 Ce 0.8 O x The method of catalyzing direct carbonylation of methanol and CO2 to prepare dimethyl carbonate comprises the following steps:
[0060] Using the In prepared in Example 1 0.1 Ga 0.1 Ce 0.8 O xCatalyst. Add 10ml methanol, 0.5g catalyst, and magnetic stirring bar into the autoclave, fill with 3MPa carbon dioxide, check the airtightness of the autoclave, and place the autoclave on a magnetic stirrer. While ensuring good airtightness, increase the temperature to 150℃ at a rate of 5℃ / min, stir continuously at a speed of 400r / min, react for 6h, and collect the product for analysis after cooling. 0.1 Ga 0.1 Ce 0.8 O x The catalytic performance of direct carbonylation of methanol and CO2 to prepare dimethyl carbonate is as follows: methanol conversion rate is 1.8% and dimethyl carbonate selectivity is nearly 100%.
[0061] Comparative Example 2: Ga 0.2 Ce 0.8 O x The method of preparing dimethyl carbonate by direct carbonylation of alcohol and CO2 comprises the following steps:
[0062] 1)Ga 0.2 Ce 0.8 O x Catalyst preparation: Preparation of Ga using citric acid-assisted sol-gel method 0.2 Ce 0.8 O x Catalyst, weigh a certain mass of gallium nitrate and cerium nitrate, dissolve in 40mL deionized water, stir and heat to mix and dissolve thoroughly, stir for 30 minutes, add 2.1g citric acid (AC) to the solution to form a catalyst precursor solution, and make the molar ratio of the precursor solution AC: Ga(NO3)3: Ce(NO3)3 = 1: 0.2: 0.8. Add nitric acid to adjust the pH of the precursor solution to 1-2, where the concentration of citric acid AC in the solution is 0.274mmol / mL. Heat and stir the precursor solution in an 80℃ oil bath, take it out after the water evaporates to form a sol mixture, put it in a 110℃ oven and dry it overnight, and the dried sample is placed in a muffle furnace with an air atmosphere at 350℃ and calcined for 1h, then the temperature is raised to 700℃ and calcined for 5h to obtain Ga 0.2 Ce 0.8 O x catalyst.
[0063] 2) Using the prepared Ga 0.2 Ce 0.8 O xCatalytic experiment: Use the catalyst to add 10ml methanol, 0.5g catalyst, and magnetic stirring to the autoclave, fill with 3MPa carbon dioxide, check the air tightness of the autoclave, and place the autoclave on a magnetic stirrer. When the air tightness is good, heat the temperature to 150℃ at a rate of 5℃ / min, stir continuously at 400r / min, react for 6h, and collect the product for analysis after cooling. 0.2 Ce 0.8 O x The catalytic performance of direct carbonylation of methanol and CO2 to prepare dimethyl carbonate is as follows: methanol conversion rate is 1.1% and dimethyl carbonate selectivity is nearly 100%.
[0064] It can be concluded that the catalytic performance of the catalytic membrane reactor is significantly better than that of the traditional kettle reactor. The difference in performance between the two reactors is mainly attributed to the addition of the molecular sieve membrane. The NaA molecular sieve membrane is a three-dimensional skeleton structure composed of silicon-oxygen tetrahedrons and aluminum-oxygen tetrahedrons, with a specific pore size and strong hydrophilicity. This pore size is very close to the pore size of water molecules. Water molecules enter through the pores of the molecular sieve and occupy the pores of the molecular sieve. The pores of the molecular sieve are relatively small for dimethyl carbonate molecules, so dimethyl carbonate is blocked, thereby selectively removing water molecules. ZSM-5 molecular sieve membrane is a zeolite molecular sieve with a ten-membered ring pore structure. Its main component is silicon oxide, which contains a large amount of silicon and has a relatively strong silicon-oxygen bond. Therefore, its hydrophilicity is relatively poorer than that of NaA molecular sieve membrane, so In 0.1 Ga 0.1 Ce 0.8 O x @The catalytic performance of ZSM-5 catalytic membrane reactor is relatively weaker than that of In 0.1 Ga 0.1 Ce 0.8 O x @NaA catalytic membrane reactor. By selectively removing byproduct water, the thermodynamic equilibrium limit of the reaction is broken, the reaction is driven forward, and the methanol conversion rate is greatly improved. In-situ dehydration of the molecular sieve membrane does not introduce other side reactions, so the high selectivity of the target product dimethyl carbonate can be maintained.
[0065] In summary, the performance of catalytic membrane reactors is obviously better than that of traditional kettle reactors. By-product water is removed from the reaction system in situ, and separation is achieved while reacting, so as to achieve the coupling of reaction and separation, break the thermodynamic equilibrium limitation, improve the reaction conversion rate, and keep the reaction in a highly stable operation. Therefore, catalytic membrane reactors are feasible and promising for some chemical reactions restricted by by-product water. Obviously, the above embodiments are only examples for clear explanation, and are not limitations on the implementation methods. For ordinary technicians in the field, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the scope of protection of the invention.
[0066] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be regarded as being limited to the specific forms described in the embodiments.
Claims
1. A method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor, characterized in that The following steps are involved: 1) Construction of kettle-type catalytic membrane reactor: The molecular sieve membrane tube includes a porous carrier tube and a hydrophilic molecular sieve membrane loaded on its surface. The molecular sieve membrane tube is fixed in a high-pressure reactor in a dead-end mode. The bottom end of the molecular sieve membrane tube is sealed and has a gap with the bottom inner wall of the high-pressure reactor. The upper end of the molecular sieve membrane tube passes through the outside of the high-pressure reactor so that the permeate side is connected to the outside of the reactor and the atmospheric pressure is maintained to construct a kettle-type catalytic membrane reactor; wherein, a stirrer is arranged at the bottom of the high-pressure reactor; 2) Methanol and a catalyst are added to the autoclave, and a certain pressure of carbon dioxide is introduced. The autoclave is heated and stirred to react. During the reaction, the byproduct water is removed by the pressure difference on both sides of the molecular sieve membrane tube. After the reaction is completed, the temperature is lowered and the product is collected; The molecular sieve membrane is a ZSM-5 molecular sieve membrane or a NaA molecular sieve membrane.
2. A method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor as claimed in claim 1, characterized in that The porous carrier tube in step 1) is a porous ceramic tube or an alumina hollow fiber.
3. A method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor as claimed in claim 1, characterized in that The preparation of the molecular sieve membrane tube is to load the molecular sieve membrane on the surface of the porous carrier tube, including the following steps: S1: The porous carrier tube is washed with ethanol and distilled water in sequence and then dried, and calcined in a muffle furnace to remove impurities; S2: seal one end of the porous carrier tube treated in step S1, connect the other end to a vacuum pump, and then immerse the porous carrier tube in a ZSM-5 or NaA molecular sieve seed sol, perform vacuum suction at a vacuum pressure of 0.2-0.8 bar, and evacuate while immersing to load the seed sol on the carrier surface. After treating for 5-20 seconds, take out the porous carrier tube to obtain a seeded carrier; S3: Immerse the seeded carrier in ZSM-5 or NaA crystallization solution, transfer them to a hydrothermal reactor and seal them, transfer the hydrothermal reactor to an oven for heating, and perform a hydrothermal crystallization reaction. After the reaction is completed, take them out for cleaning, and dry them to obtain the corresponding molecular sieve membrane tube.
4. A method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor as claimed in claim 1, characterized in that When the prepared molecular sieve membrane is a NaA molecular sieve membrane, the NaA molecular sieve seed sol in step S2 is prepared by mixing and dissolving a sodium source, an aluminum source, a silicon source, water, and tetramethylammonium hydroxide according to a molar ratio of Na2O: Al2O3: SiO2: H2O: (TMA)2O = 0.6: 1.0-3.0: 10-12: 700-750: 10-15 until the mixture is clarified, and then hydrothermally heated at 80-110 ° C for 2-8 h. In step S3, the NaA crystallization solution is prepared by mixing and dissolving a sodium source, an aluminum source, a silicon source and water in a molar ratio of Na2O: Al2O3: SiO2: H2O=40-60:1:4-6:500-1500, preferably 40-60:1:5:1000; the hydrothermal crystallization temperature of step S3 is 70-90°C, and the hydrothermal crystallization time is 3-6 h.
5. The method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor as claimed in claim 1, characterized in that When the prepared molecular sieve membrane is a ZSM-5 molecular sieve membrane, the ZSM-5 molecular sieve seed sol in step S2 is prepared by mixing and dissolving a silicon source, tetrapropylammonium hydroxide, and water in a molar ratio of SiO2:TPAOH:H2O = 1.0-3.0:0.1-2:15-20 until clarified, and hydrothermally heating at 50-110°C for 72-120 h; The ZSM-5 crystallization solution in step S3 is prepared by mixing and dissolving a silicon source, an aluminum source, NaOH, NaF and water in a molar ratio of SiO2:Al2O3:NaOH:NaF:H2O = 1-5:0.001-0.05:0.2-1:0.5-1.5:50-100; the hydrothermal crystallization temperature in step S3 is 150-200°C, and the hydrothermal crystallization time is 12-48h.
6. A method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor as claimed in claim 1, characterized in that In step 2), the catalyst is In x Ga y Ce z O m The nanocomposite metal oxide catalyst is prepared by a citric acid-assisted sol-gel method, comprising the following steps: indium salt, gallium salt and cerium salt are dissolved in deionized water, stirred to make them dissolved and dispersed uniformly, then citric acid is added to the above solution to form a catalyst precursor solution, nitric acid is added dropwise to adjust the pH of the precursor solution to 1-2, the precursor solution is heated in an oil bath at 50-150°C, preferably 60-90°C, after the water evaporates to form a sol, the precursor solution is placed in a 50-150°C oven and dried overnight, preferably 70-120°C, and then placed in a muffle furnace for calcination to obtain In x Ga y Ce z O m Nanocomposite metal catalysts.
7. A method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor as claimed in claim 6, characterized in that In the preparation of the catalyst, the metal salts of indium, gallium and cerium are independently selected from chlorides, nitrates, sulfates or acetylacetonates of the respective metals; based on 1 mol of citric acid, the amounts of the metal salts of indium, gallium and cerium are 0.1-0.2 mol, 0.05-0.1 mol and 0.8-0.9 mol respectively; and the ratio of the total molar amount of the indium metal salt and the gallium metal salt to the molar amount of citric acid is 0.2-0.25:
1.
8. A method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor as claimed in claim 6, characterized in that In the preparation of the catalyst, calcination is carried out in two stages in a muffle furnace. In the first stage, the temperature is 200-500°C, preferably 300-350°C, and the calcination is carried out for 1-3 h. In the second stage, the temperature is increased to 600-900°C, preferably 700-750°C, and the calcination is carried out for 4-8 h.
9. A method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor as claimed in claim 1, characterized in that The initial pressure of the carbon dioxide introduced in step 2) is 0.1-10 MPa, preferably 3-8 MPa.
10. The method for preparing dimethyl carbonate by direct carbonylation of methanol using a molecular sieve membrane reactor as claimed in claim 1, characterized in that In step 2), the reaction temperature is 50-200°C, preferably 80-160°C, and the reaction time is 1-48h, preferably 6-24h.