Solid base catalyst for preparing methyl ethyl carbonate by transesterification method, preparation method and application

Abstract

The invention discloses a solid base catalyst for preparing methyl ethyl carbonate by a transesterification method, and a preparation method and application thereof, and relates to a production process of a chemical raw material. According to the invention, a carbon nanotube-doped chlorine ball is prepared, and a solid base catalyst is generated through a chemical modification method. The catalyst has the characteristics of easiness in separation, wear resistance, scouring resistance and high catalytic activity, and can be efficiently used for preparing methyl ethyl carbonate in a dimethyl carbonate and ethanol ester exchange reaction system. When the reaction temperature is 90 DEG C, the dosage of the catalyst accounts for 12wt% of dimethyl carbonate, the ratio of alcohol to ester is 4: 1, the reaction time is only 3 hours, the highest yield of methyl ethyl carbonate can reach 83%, the reaction time is continuously prolonged, and the conversion rate of dimethyl carbonate can reach 90%. The reacted catalyst can be reused after being simply filtered, and the catalytic activity of the catalyst can be maintained at 1.67 g.g <-1 >. H <-1 > under the conditions.

Description

Technical Field

[0001] The present invention belongs to the field of catalyst preparation, and particularly relates to a solid base catalyst doped with carbon nanotubes that can directly catalyze the reaction system of dimethyl carbonate and ethanol to prepare ethyl methyl carbonate. Background Art

[0002] Ethyl methyl carbonate (abbreviated as EMC), with the molecular formula C 4 H 8 O 3 , with a molecular weight of 104.1, is a colorless and transparent liquid with a slightly pungent odor. Its melting point is -14°C, boiling point is 107°C, it is insoluble in water but soluble in organic solvents such as alcohols and ethers, and it is an asymmetric carbonate. Since it contains both methyl and ethyl groups in the molecule, combining the characteristics of dimethyl carbonate and diethyl carbonate, EMC is also a solvent for special spices and intermediates. At the same time, it has strong solubility for lithium salts, safety and stability, etc., can significantly improve the energy density and discharge capacity of lithium-ion batteries, has a long cycle life, good safety performance, no memory effect, good low-temperature performance, etc., and is widely used in lithium-ion batteries in high-end electronic products such as mobile phones, portable audio-visual equipment, and laptop computers. With the rapid development of the lithium-ion battery industry, the domestic demand for ethyl methyl carbonate electrolyte is also increasing day by day. Developing a catalyst with high efficiency, no pollution and a long service life is an important method to meet the current demand.

[0003] Currently, there are mainly four synthesis methods for ethyl methyl carbonate: phosgene method, oxidative carbonylation method, urea alcoholysis method and transesterification method

[0004] (1) Phosgene method

[0005] The equation for synthesizing ethyl methyl carbonate by the phosgene method is as follows:

[0006]

[0007]

[0008] Phosgene methyl chloroformate is highly toxic and the intermediate product hydrogen chloride has strong corrosiveness, which will cause serious damage to production equipment. At the same time, the by-products generated by this reaction cause serious environmental pollution and do not meet the requirements of modern green chemistry and environmental protection. Therefore, this method has been phased out.

[0009] (2) Oxidative carbonylation method

[0010] The equation for synthesizing ethyl methyl carbonate by the oxidative carbonylation method is as follows:

[0011]

[0012] In this method, some of the catalysts are prone to deactivation during the reaction, which affects the continuity and economy of the reaction. Some side reactions may occur during the reaction, such as the combustion reaction of carbon monoxide, etc., reducing the selectivity of the reaction, increasing the difficulty of product separation and purification, and also causing waste of raw materials. Since the reaction needs to be carried out under certain pressure and temperature conditions, it poses relatively high requirements on the material and sealing performance of the reaction equipment, so it will also increase the equipment investment and maintenance costs.

[0013] (3) Urea alcoholysis method

[0014] The equation for synthesizing ethyl methyl carbonate by urea alcoholysis method is as follows:

[0015]

[0016]

[0017] Methanol and urea are cheap and easily available. There is no water generated in the alcoholysis reaction, and the by-product ammonia is recycled to urea production. Methyl carbamate continues to react with ethanol to produce ethyl methyl carbonate and ammonia. This reaction has mild operating conditions, is easy to separate, and has no pollution, but the catalyst cost is relatively high and the separation and recovery of the catalyst are difficult, which needs to be selected and improved.

[0018] (4) Transesterification method

[0019] The equation for synthesizing ethyl methyl carbonate by transesterification method is as follows:

[0020]

[0021] Using dimethyl carbonate and ethanol as raw materials, ethyl methyl carbonate is synthesized by transesterification method. The raw materials used in this route are all non-toxic, the reaction conditions are mild, and there is no pollution to the environment. Therefore, there are many reports on synthesizing ethyl methyl carbonate through this route.

[0022] Qian Jun et al. used dendrite fibrous silica prepared by hydrothermal synthesis method as the carrier and potassium acetate as the precursor to impregnate solid base catalysts with different K loadings. At 80 °C and reaction for 5 h, the conversion rate of DMC can reach 91.0%, but the catalyst performance begins to decline significantly after multiple uses.

[0023] CN1900047A discloses a catalyst method using alumina, activated carbon, and molecular sieve as carriers and loading one of alkali metal oxides, alkaline earth metal oxides, and rare earth metal oxides. It is carried out in a reactive distillation device, and the yield of ethyl methyl carbonate can reach up to more than 90%. Although there is no problem with catalyst separation, the catalyst stability is insufficient and the active components are easy to lose.

[0024] In CN103483200A, a modified molecular sieve is used as a catalyst, and the modifying elements are one or more of alkali metals, alkaline earth metals, Fe, Zn, Ni, and Cu. Although the catalyst preparation process is simple, the selectivity of ethyl methyl carbonate can reach over 90%, and the yield can reach over 55%, but the reaction temperature required is high, and the yield needs to be improved.

[0025] CN117563663A points out that a strong base anion resin can be used to catalyze the reaction of dimethyl carbonate and ethanol. Reacting at 95 °C for 2 h can achieve an EMC yield of over 86.0%, but the preparation of this strong base anion resin is complex and the cost is relatively high.

[0026] In summary, the above-mentioned catalysts all have problems such as low product yield, difficult catalyst recovery, large catalyst dosage, difficulty in maintaining activity, and high reaction energy consumption during the transesterification reaction of dimethyl carbonate and ethanol to prepare ethyl methyl carbonate. Summary of the Invention

[0027] The purpose of the present invention is to provide a catalyst for the method of preparing ethyl methyl carbonate by the transesterification of dimethyl carbonate and ethanol. The present invention uses a carbon nanotube-doped chlorinated bead as a carrier, and by regulating the content of carbon nanotubes and the content of cross-linking agent to ensure the performance of the chlorinated bead such as uniform size, high strength, firmness, heat resistance and wear resistance, and then loading different organic bases to provide catalytic activity for efficiently catalyzing the reaction of dimethyl carbonate and ethanol to prepare ethyl methyl carbonate. After the reaction, the catalyst can be reused again after simple filtration treatment. The reaction duration exceeds 100 h, and the catalyst can still maintain a 40% yield of ethyl methyl carbonate.

[0028] The purpose of the present invention is achieved by the following technical solutions:

[0029] A preparation method of a solid base catalyst for preparing ethyl methyl carbonate by transesterification, the steps are as follows:

[0030] 1) Uniformly disperse carbon nanotubes in a dispersant to obtain a dispersion;

[0031] 2) Prepare carbon nanotube-doped chlorinated beads: Mix a pore-forming agent, an initiator, a monomer, and a cross-linking agent in proportion, drop the mixed solution into the dispersion in step 1), and produce carbon nanotube-doped chlorinated beads by suspension polymerization, filter, wash, and dry for later use.

[0032] 3) The dried chlorinated beads are first swollen and then reacted with an organic base to prepare a chlorinated bead containing a quaternary ammonium salt. After washing the surface solution, the Cl in the chlorinated bead is replaced by ion exchange -1 with OH -1 , and the quaternary ammonium salt is converted into a quaternary ammonium base.

[0033] 4) The product obtained in step 3) is washed repeatedly with deionized water and dried under vacuum to obtain a solid base catalyst doped with carbon nanotubes.

[0034] Further, in step 1), the carbon nanotubes need to be purified and washed before dispersion. The purification refers to calcining the carbon nanotubes in a muffle furnace at 500 - 600 °C for 1 - 3 h. The washing is to wash the calcined carbon nanotubes with deionized water.

[0035] Further, in step 1), the dosage of the carbon nanotubes is 0.05% - 0.5% of the monomer mass, preferably 0.15% - 0.25%.

[0036] Further, in step 1), the dispersant is one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, cetyltrimethylammonium bromide, polyvinyl alcohol, and carboxymethyl cellulose, and the dosage is 1% - 5% of the monomer mass.

[0037] Further, in step 2), the dosage of the pore-forming agent is 10% - 30% of the monomer mass; the dosage of the initiator is 1% - 5% of the monomer mass; the dosage of the crosslinking agent is 0% - 15% of the monomer mass.

[0038] Further, in step 2), the pore-forming agent is one or more of toluene, xylene, cyclohexane, n-heptane, polyethylene glycol, and sodium bicarbonate; the initiator is one or more of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, dicumyl peroxide, and potassium persulfate; the monomer is 4-chloromethylstyrene; the crosslinking agent is divinylbenzene.

[0039] Further, in step 2), the temperature of the suspension polymerization process is 70 - 90 °C; the time is 4 - 6 h.

[0040] Further, in step 3), the swelling is to soak the chlorinated beads with the solvent N,N-dimethylformamide, and the swelling time is 12 - 24 h;

[0041] Further, in step 3), the organic base is one or more of trimethylamine, triethylamine, tri-n-butylamine, N-methylimidazole, dicyclohexylmethylamine, isopropylamine, N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, N,N-bis(2-hydroxyethyl)-p-toluidine, and N-methyl-N-(2-hydroxyethyl)-p-toluidine. The dosage of the organic base is 1 - 3 times the molar equivalent of the chlorine content in the monomer.

[0042] Further, in step 3), the solution used for ion exchange is sodium hydroxide or potassium hydroxide; the concentration is 0.5 - 5 mol / L.

[0043] Further, in the step 3), the temperature for the reaction of the chlorinated resin beads after swelling with the organic base is 60 - 80°C; the time is 10 - 12 h.

[0044] The general structural formula of a solid base catalyst for preparing ethyl methyl carbonate by transesterification prepared by the above method is as follows:

[0045] Wherein, n is a positive integer, and R is methyl, ethyl or n-butyl.

[0046] The application of a solid base catalyst for preparing ethyl methyl carbonate by transesterification is specifically as follows: Using dimethyl carbonate and ethanol as raw materials, transesterification reaction is carried out in the presence of a self-made solid base catalyst doped with carbon nanotubes to prepare ethyl methyl carbonate.

[0047] Further, the molar ratio of ethanol to dimethyl carbonate is 2:1 - 10:1. The dosage of the solid base catalyst is 1 - 24 wt% of the raw material dimethyl carbonate.

[0048] Further, the reaction temperature is 78 - 92°C, and the reaction duration is 1 - 18 h. Preferably, it is an oil bath.

[0049] The advantages and effects of the present invention are as follows: The present invention prepares a chlorinated resin bead doped with carbon nanotubes, and generates a solid base catalyst through a chemical modification method. By regulating the content of the introduced carbon nanotubes, while maintaining the good morphology of the chlorinated resin beads, it ensures a certain strength, overcoming the disadvantages of deformation and fragility of conventional chlorinated resin beads after use. This catalyst has the characteristics of being separable during use, high catalytic activity, and long durability, and can be efficiently applied to the transesterification reaction system of dimethyl carbonate and ethanol to prepare ethyl methyl carbonate. The preparation process of this catalyst is simple, the process is short, and it can be reused again after simple filtration treatment after use, and the active sites are easily restored by means of ion exchange. Description of the Drawings

[0050] Figure 1 It is the yield curve graph of ethyl methyl carbonate when the solid base catalyst #1 prepared in Example 1 is continuously reused 40 times, 3 h each time, and the cumulative time exceeds 100 h. After calculation, the final reaction activity of this catalyst can still maintain a catalytic activity of 1.67 g·g -1 ·h -1 under this condition. Detailed Description of the Invention

[0051] The present invention will be described in detail below with reference to the embodiments.

[0052] Example 1

[0053] Weigh 0.2 g of the dispersant sodium dodecyl sulfate and add it to a beaker. Add approximately 50 ml of deionized water and stir evenly. Then weigh 20 mg of carbon nanotubes (calcined in a muffle furnace at 550 °C for 1 h and washed with deionized water) and pour them into the beaker. Use an ultrasonic cleaner to ultrasonically disperse for about 3 hours at an ultrasonic frequency of 20 - 25 kHz until the carbon nanotubes can be relatively evenly dispersed in the aqueous phase.

[0054] Pour approximately 50 ml of deionized water into a 500 - ml three - necked glass bottle. Pour the above - ultrasonically - dispersed carbon nanotube suspension into the bottle, fix the position with a mechanical stirring device, heat the oil bath to 80 °C, turn on the mechanical stirrer to maintain 500 r / min, and pre - heat and disperse for 0.5 h. Then take a beaker, weigh 10 g of the monomer 4 - chloromethylstyrene, 0.1 g of the initiator azobisisobutyronitrile (AIBN), 2 g of the porogen toluene, and 1 g of the cross - linker divinylbenzene, pour them into the beaker and mix evenly. Use a constant - flow pump to control the dropping rate of about 1 drop per second into the three - necked flask, and react while passing N 2 After maintaining the temperature for about 5 h and no more solid particles are formed in the system, the reaction ends. Pour the product onto a 40 - mesh stainless - steel sieve, rinse the surface impurities with deionized water and sieve out the smaller reaction particles. Put the washed product into a vacuum drying oven and dry at 80 °C for 12 h to obtain a homogeneous chlorinated sphere doped with carbon nanotubes.

[0055] Weigh 10 g of the chlorinated sphere doped with carbon nanotubes into a beaker, pour in DMF to submerge the particles, and soak and swell for 12 h. Pour the swollen chlorinated sphere into a 500 - ml single - necked bottle, add three - fold equivalent of the organic base triethylamine according to the chlorine content, and then add about 100 ml of DMF as the solvent. Heat the oil bath to 60 °C, adjust the rotation speed to 500 r / min, and carry out condensation circulation, N 2 Protect the reaction for 10 h. After the reaction ends, pour out the product and wash it repeatedly with ethanol first and then with deionized water. After washing the surface solvent clean, pour all the product into a column, add 2 mol / L NaOH solution to start eluting, and replace the Cl -1 in the chlorinated sphere with OH -1 , after 12 h of elution, wash the solid base repeatedly with deionized water. When the pH of the eluate = 7, it indicates that the NaOH on the surface of the solid base has been washed clean. Put the washed product into a vacuum drying oven and dry at 80 °C for 12 h to obtain a carbon nanotube - doped solid base catalyst #1 with a doping amount of 0.2%.

[0056] Example 2

[0057] Under the condition that other conditions of Example 1 remain unchanged, the content of carbon nanotubes was replaced with 0%, 0.15%, and 0.25% respectively, and solid base catalysts doped with different contents of carbon nanotubes can be prepared: chlorinated resin catalyst #0, carbon nanotube solid base catalyst #2, and carbon nanotube solid base catalyst #3.

[0058] Example 3

[0059] Under the condition that other conditions of Example 1 remain unchanged, the content of divinylbenzene as the crosslinking agent was replaced with 5% and 15% respectively, and solid base catalysts with different proportions of crosslinking agents can be prepared: carbon nanotube solid base catalyst #4 and carbon nanotube solid base catalyst #5.

[0060] Example 4

[0061] Under the condition that other conditions of Example 1 remain unchanged, the organic base was replaced with trimethylamine, tri-n-butylamine, and N-methylimidazole respectively, and solid base catalysts with different organic bases can be prepared: carbon nanotube solid base catalyst #6, carbon nanotube solid base catalyst #7, and carbon nanotube solid base catalyst #8.

[0062] Example 5

[0063] In a three-necked flask, 3.6 g of dimethyl carbonate and 7.36 g of ethanol were loaded, and their molar ratio was 1:4. Different numbered solid base catalysts in Examples 1-4 (chlorinated resin catalyst #0 as a control group) were added, and the dosage was 12% of dimethyl carbonate. The reaction temperature was 90 °C, and the reaction was carried out under heating reflux for 1 h. The product was sampled for chromatographic analysis and calculation.

[0064] The experimental steps in the examples in Table 1 were the same as those in Example 5, except for the experimental conditions of catalyst type and reaction time. Specifically as follows:

[0065] Table 1 Influence of different catalysts on the yield of ethyl methyl carbonate

[0066]

[0067] Example 6

[0068] In a three-necked flask, 3.6 g of dimethyl carbonate and 7.36 g of ethanol were loaded, and their molar ratio was 1:4. The self-made solid base catalyst #1 in Example 1 was added. The ester-alcohol ratio, the dosage of the solid base catalyst, the reaction temperature, and the reaction time are shown in Table 2. The above catalyst was a solid base catalyst doped with 0.2% carbon nanotubes, 10% crosslinking agent, and triethylamine as the organic base. The three-necked flask was placed in an oil bath and heated under reflux at 90 °C for 1 h. The product was sampled for chromatographic analysis and calculation. The experimental results are specifically as follows:

[0069] Table 2 Influence of different reaction conditions on the yield of ethyl methyl carbonate

[0070]

[0071]

[0072] As described above, these are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the relevant art, without departing from the scope of the technical solution of the present application, making some changes or modifications using the technical content disclosed above is equivalent to equivalent embodiments and all fall within the scope of the technical solution.

Claims

1. A method for preparing a solid base catalyst for preparing ethyl methyl carbonate by an ester exchange process, characterized in that: Here are the steps: 1) uniformly dispersing carbon nanotubes in a dispersant to obtain a dispersion; 2) preparing chlorine balls doped with carbon nanotubes: mixing a porogen, an initiator, a monomer and a crosslinking agent in proportion, dropping the mixture into the dispersion of step 1), producing chlorine balls doped with carbon nanotubes by suspension polymerization, filtering, washing and drying them for later use; 3) The dried chlorine ball first swells and then reacts with an organic base to prepare a chlorine ball containing a quaternary ammonium salt. After washing the surface solution, the Cl in the chlorine ball is removed by ion exchange. -1 Replace with OH -1 , the quaternary ammonium salt is converted into a quaternary ammonium base; 4) The product obtained in step 3) is repeatedly washed with deionized water and vacuum dried to obtain a solid base catalyst doped with carbon nanotubes.

2. The method for preparing a solid base catalyst for preparing ethyl methyl carbonate by ester exchange according to claim 1, characterized in that: In the step 1), the carbon nanotubes need to be purified and washed before dispersion; the purification refers to calcining the carbon nanotubes at 500-600° C. in a muffle furnace for 1-3 hours; The washing step is to wash the calcined carbon nanotubes with deionized water.

3. The method for preparing a solid base catalyst for preparing ethyl methyl carbonate by ester exchange according to claim 1, characterized in that: In the step 1), the amount of the carbon nanotubes is 0.05%-0.5% of the monomer mass, and the dispersant is one or a mixture of two or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide, polyvinyl alcohol, and carboxymethyl cellulose, and the amount is 1%-5% of the monomer mass.

4. The method for preparing a solid base catalyst for preparing ethyl methyl carbonate by ester exchange according to claim 1, characterized in that: In the step 2), the amount of the porogen is 10%-30% of the monomer mass; the amount of the initiator is 1%-5% of the monomer mass; the amount of the crosslinker is 0%-15% of the monomer mass; the porogen is one or a mixture of two or more of toluene, xylene, cyclohexane, n-heptane, polyethylene glycol, and sodium bicarbonate; the initiator is one or a mixture of two or more of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, diisopropylbenzene peroxide, and potassium persulfate; the monomer is 4-chloromethylstyrene; and the crosslinker is divinylbenzene.

5. The method for preparing a solid base catalyst for preparing ethyl methyl carbonate by ester exchange according to claim 1, characterized in that: In the step 2), the temperature of the suspension polymerization process is 70-90° C. and the time is 4-6 hours. The swelling is performed by soaking the chlorine balls in solvent N,N-dimethylformamide, and the swelling time is 12-24 hours.

6. The method for preparing a solid base catalyst for preparing ethyl methyl carbonate by ester exchange according to claim 1, characterized in that: In the step 3), the organic base is one or a mixture of two or more of trimethylamine, triethylamine, tri-n-butylamine, N-methylimidazole, dicyclohexylmethylamine, isopropylamine, N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, N,N-dihydroxyethyl-p-toluidine, and N-methyl-N-hydroxyethyl-p-toluidine; and the amount of the organic base is 1-3 times the molar equivalent of the chlorine content in the monomer.

7. The method for preparing a solid base catalyst for preparing ethyl methyl carbonate by ester exchange according to claim 1, characterized in that: In the step 3), the solution used for ion exchange is sodium hydroxide or potassium hydroxide; the concentration is 0.5-5 mol / L; the temperature of the chlorine ball after swelling and reacting with the organic base is 60-80°C; and the time is 10-12h.

8. A solid base catalyst for preparing ethyl methyl carbonate by transesterification method obtained by the preparation method of a solid base catalyst for preparing ethyl methyl carbonate by transesterification method according to any one of claims 1 to 7, characterized in that: The general structure is as follows: Wherein, n is a positive integer, and R is a methyl group, an ethyl group or a n-butyl group.

9. Use of a solid base catalyst for preparing ethyl methyl carbonate by transesterification method prepared by the method for preparing a solid base catalyst for preparing ethyl methyl carbonate by transesterification method according to any one of claims 1 to 7, characterized in that: Ethyl methyl carbonate was prepared by transesterification reaction of dimethyl carbonate and ethanol in the presence of a self-made solid base catalyst doped with carbon nanotubes.

10. The use according to claim 9, characterized in that: The molar ratio of ethanol to dimethyl carbonate is 2:1-10:1; the amount of solid base catalyst used is 1-24wt% of the raw material dimethyl carbonate; the reaction temperature is 78-92°C, and the reaction time is 1-18h.

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