A process for the preparation of a catalyst for the carbonate-based synthesis of oxygenate fuel components additives

Abstract

Carbonate compounds are excellent additives of oxygen-containing fuel, and play an important role in improving the oxygen content of fuel. The present application mainly relates to a preparation method of a catalyst for synthesizing carbonate additives. The catalyst is used for catalyzing the preparation of a mixture of methyl ethyl carbonate and diethyl carbonate by means of an ester exchange reaction with dimethyl carbonate and ethanol as raw materials. The mixture obtained after the reaction is used as an oxygen-containing fuel additive. The catalyst is characterized in that the catalyst is a high-efficiency ester exchange catalyst with a multistage-pore ZSM-5 molecular sieve as a carrier, a double-molecule as a connecting agent and an alcohol salt as an active component. In the preparation process of the catalyst, the connecting agent is added. The connecting agent has the advantages of increasing the stability of the sodium alcoholate active component and increasing the loading capacity by using a molecular connecting agent with multiple active groups. The performance of the catalyst is evaluated by using a tank reactor, and the stability of the prepared catalyst in the ester exchange reaction is investigated. The performance evaluation shows that the catalyst prepared by using the connecting agent has higher product yield and more excellent product yield. This has important significance for improving the combustion performance of the oxygen-containing fuel and reducing the fuel cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalyst preparation for fine chemical process, since carbonate compounds are excellent additives for oxygen-containing fuels, and play an important role in increasing the oxygen content of fuels, the present application relates to a preparation method of a catalyst for synthesizing carbonate additives. BACKGROUND

[0002] Oxygen-containing fuels are clean alternative fuels for diesel engines, and have a wide range of raw materials and excellent emission performance. The application of oxygen-containing fuels as additives or substitutes for diesel in diesel engines can reduce exhaust emissions and improve combustion efficiency, so the research on oxygen-containing fuels has attracted much attention.

[0003] The application of oxygen-containing fuels in internal combustion engines has a long history, but in the past, the focus of research was on energy substitution, and little attention was paid to combustion emission characteristics. Since the 1990s, global energy consumption has increased dramatically, and limited oil resources cannot meet people's demand for energy; and the number of cars on the road has increased, causing harmful substances emitted by vehicles into the atmosphere to increase. Therefore, from the perspective of energy security and environmental protection, countries have begun to look for clean alternative energy. Oxygen-containing fuels can reduce harmful emissions from diesel engines, especially particulate emissions, and oxygen-containing fuels made from biomass are renewable energy sources that do not increase the net release of CO2 in the atmosphere during the natural energy cycle of biofuels, making oxygen-containing fuels a clean energy source with great development potential.

[0004] There are many types of oxygen-containing fuels for diesel engines, including plant oils and their esterified fuels, biomass pyrolysis fuels, alcohol fuels, and dimethyl ether, etc.

[0005] Oxygen-containing fuels refer to fuels that can provide additional oxygen for diesel engines to make fuel combustion more complete. Oxygen-containing fuels can reduce harmful emissions such as unburned HC, CO, PM, and soot from diesel engines, and the use of low-emission oxygen-containing fuels is one of the effective technologies for controlling diesel emissions. Among the alternative fuels studied, oxygen-containing fuels have a better future.

[0006] Methyl ethyl carbonate and diethyl carbonate are excellent oxygen-containing fuel additive components, which can significantly increase the oxygen content of fuel and improve combustion, and are excellent fuel additives. They are also green and environmentally friendly asymmetric carbonates. Because of the methyl, ethyl, carbonyl, methoxy, and ethoxy groups in their structures, they have active chemical properties. Methyl ethyl carbonate has many excellent properties, such as high dielectric constant and high lithium salt solubility, and is widely used as electrolyte for lithium ion batteries and fuel additive. Therefore, methyl ethyl carbonate and diethyl carbonate have good market prospects. There are many studies on the synthesis of methyl ethyl carbonate catalyst, but most of them have certain limitations, such as difficult preparation of catalyst, low activity of catalyst, and catalyst cannot be reused multiple times. Therefore, it is of great significance to develop high-activity and high-selectivity catalysts for the preparation of methyl ethyl carbonate.

[0007] Methyl ethyl carbonate synthesis catalysts mainly include the following categories:

[0008] (1) Homogeneous catalyst

[0009] The homogeneous catalyst yttrium triflate was used to catalyze the ester exchange reaction of DMC and ethanol. Although the conversion rate of DMC was high, the selectivity of EMC was very low, so it was not suitable for the catalytic synthesis of EMC. In addition, NaOH, KOH, CH3ONa, CH3OK and other inorganic and organic strong bases have high activity in the ester exchange reaction of dimethyl carbonate and ethanol. When n(DMC) / n(EtOH) = 4, the reaction was carried out at 351 K and normal pressure for 4 h, the yield of EMC was 54.7%, and the selectivity of EMC was 100%. However, the catalyst is not easy to dissolve, easy to precipitate and scale, and block the distillation.

[0010] To solve the above problems, the complex formed by sodium methoxide and alcohol amine compounds was used as catalyst. Because sodium methoxide has good solubility in alcohol amine compounds, and the complex of the two has good solubility in the reaction solution, the catalytic activity is significantly improved. The product and excess DMC can be distilled from the reaction mixture to recover the catalyst. The operation process does not scale and precipitate, and the addition of reaction raw materials can directly proceed to the next round of reaction. At the same time, alcohol amine compounds themselves are organic bases, which help catalysis.

[0011] (2) Heterogeneous catalyst

[0012] Based on the acid-base synergistic catalysis, KF / Al2O3 catalyst with KF supported on modified Al2O3 can effectively catalyze the transesterification of DMC and EtOH. The research shows that with the increase of KF loading, the number of weak and strong basic sites of the catalyst gradually increases, the specific surface area gradually decreases, the conversion of DMC increases, but the selectivity of EMC gradually decreases. This is because the surface active substances Al-[OH…F]- and K+ formed by KF and Al2O3 during the reaction can improve the basicity of KF / Al2O3, enhance the nucleophilic attack of EtO-, form EMC and methoxy ions, and then combine with protons to form MeOH. Therefore, the stronger the basicity of the catalyst, the higher the conversion of DMC, and the selectivity of EMC decreases. With 10% KF / Al2O3 as the catalyst, under the conditions of n(DMC) / n(EtOH) = 1 / 4, catalyst dosage of 2wt%, 353K temperature and reaction time of 4h, the conversion of DMC is 63.9%, and the selectivity of EMC can reach 804%, but the catalyst needs to be treated by vacuum distillation after use to restore its activity. In addition, the acid-base bifunctional catalyst prepared by loading basic oxides on zeolite molecular sieve carriers exhibits good catalytic activity and selectivity in this reaction, but the reusability of the catalyst is not discussed.

[0013] Therefore, it is of great significance to develop supported high-catalytic-activity catalysts for the synthesis of methyl ethyl carbonate and diethyl carbonate. SUMMARY

[0014] Carbonate compounds are excellent additives for oxygen-containing fuels and play an important role in increasing the oxygen content of fuels. The present application mainly relates to a preparation method of a catalyst for synthesizing carbonate additives, which is used to catalyze the preparation of a mixture of methyl ethyl carbonate and diethyl carbonate by transesterification reaction with dimethyl carbonate and ethanol as raw materials. The mixture obtained after the reaction is used as an oxygen-containing fuel additive. The catalyst is characterized by using a multi-level pore ZSM-5 molecular sieve as a carrier, using a double-molecule as a connecting agent, and using an alkoxide as an active component of a high-efficiency transesterification catalyst.

[0015] The specific preparation method is as follows:

[0016] First step: preparation of precursor solution

[0017] 5.5g of sodium hydroxide is weighed and added to 250g of deionized water, followed by 25g of tetrapropylammonium bromide, an anionic polyacrylamide (APAM) is added as a soft template, the addition amount is n(APAM):n(SiO2)=0.1:1-10:1, after dissolution, 2.7g of aluminum sulfate is added, and the solution is stirred vigorously at room temperature until the aluminum sulfate is completely dissolved, and then 157g of SiO2-sol (30wt.%) is added dropwise.

[0018] Second step: crystallization process

[0019] The prepared precursor solution was stirred at 30℃ for 2h, and then aged overnight. The white sol changed into a gel. Then it was transferred into a 100mL Teflon-lined stainless steel crystallization kettle. Then it was transferred into a temperature programmed drying oven. The heating rate was 2℃ / min, and maintained at 160℃ for 48h. Then the temperature was programmed to decrease to 25℃ at a rate of 0.5℃ / min.

[0020] Step 3: Preparation of hierarchical pore ZSM-5 zeolite

[0021] After the crystallization was completed, the white crystalline product was obtained by suction filtration, and repeatedly washed with deionized water until the pH value of the filtrate was close to neutral. Then the filter cake was vacuum dried at 80℃ for 10h. Finally, the obtained sample was calcined at 550℃ in an air atmosphere for 5h to obtain the hierarchical pore ZSM-5 zeolite.

[0022] Step 4: Loading process of active component

[0023] The prepared hierarchical pore ZSM-5 zeolite, the linking agent and the active component solution were ultrasonically impregnated in equal volumes according to a certain proportion, and each impregnation was 8h, and the ultrasonic assistance was 30min, and the total impregnation time was 24h. After the impregnation was completed, the solid was placed in a vacuum drying oven at 110℃ for 2h, and then calcined in a muffle furnace at 550℃ in an air atmosphere for 4h to obtain the responsible catalyst.

[0024] The active component is one or more of sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide and sodium tert-butoxide, and the addition amount of the active component is 0.1%-5%(mass ratio) of the carrier.

[0025] The linking agent used in the catalyst preparation process is a molecule with multiple active groups, and the linking agent is one of sucrose, lactose, starch, polyvinyl alcohol, polyethylene glycol, citric acid and cyclodextrin, and the addition amount is determined according to the mass ratio of the linking agent to the active component of 1:1-10:1.

[0026] Advantages of the present application

[0027] In the catalyst preparation process of the present application, a linking agent is added. The molecule with multiple active groups has the advantages of increasing the stability of the sodium alcoholate active component and increasing the loading amount. The performance of the catalyst is evaluated by using a kettle reactor, and the stability of the prepared catalyst in the ester exchange reaction is investigated.

[0028] The technical content and effects of the present application will be further illustrated by the following examples, but the scope of the present application is not limited thereto.

[0029] Example 1:

[0030] Step 1: Preparation of precursor solution

[0031] Take 5.5 g of sodium hydroxide into 250 g of deionized water, then add 25 g of tetrapropylammonium bromide, add anionic polyacrylamide (APAM) as a soft template, the addition amount is n (APAM) : n (SiO2) = 0.1:1, after dissolving, add 2.7 g of aluminum sulfate, stir vigorously at room temperature until the aluminum sulfate is completely dissolved, and then add 157 g of SiO2-sol (30 wt. %) dropwise.

[0032] Second step: crystallization process

[0033] The prepared precursor solution is stirred at 30℃ for 2h, and then aged overnight. The white sol state changes to gel. Then transfer to a 100mL polytetrafluoroethylene lined stainless steel crystallization kettle. Then transfer to a programmed temperature drying oven. The heating rate is 2℃·min-1, and maintained at 160℃ for 48h; then programmed cooling to 25℃ at a rate of 0.5℃·min-1.

[0034] Third step: preparation of hierarchical pore ZSM-5 molecular sieve

[0035] After the crystallization is completed, white crystalline product is obtained by suction filtration, and repeatedly washed with deionized water until the pH value of the filtrate approaches neutral. Then the filter cake is vacuum dried at 80℃ for 10h. Finally, the obtained sample is calcined at 550℃ in air atmosphere for 5h to obtain hierarchical pore ZSM-5 molecular sieve.

[0036] Fourth step: loading process of active component

[0037] The prepared hierarchical pore ZSM-5 molecular sieve is ultrasonically immersed in equal volume of a solution of a linking agent and an active component at a certain ratio, ultrasonic assisted for 30min every 8h, for a total of 24h. After the immersion is completed, the solid is placed in a vacuum oven at 110℃ for 2h, and then calcined in a muffle furnace at 550℃ in air atmosphere for 4h to obtain a responsible catalyst.

[0038] Among them: the active component is sodium methoxide and sodium ethoxide, the mass ratio of the two is 1:1, and the addition amount of the active component is 0.5% (mass ratio) of the carrier;

[0039] The linking agent used in the preparation of the catalyst is a molecule with multiple active groups, and the additive is cyclodextrin, and the addition amount is determined according to the mass ratio of the linking agent to the active component 5:1.

[0040] Example two:

[0041] First step: preparation of precursor solution

[0042] Weigh 5.5 g of sodium hydroxide into 250 g of deionized water, then add 25 g of tetrapropylammonium bromide, add anionic polyacrylamide (APAM) as a soft template, the addition amount is n (APAM) : n (SiO2) = 0.2:1, after dissolution, add 2.7 g of aluminum sulfate, stir vigorously at room temperature until the aluminum sulfate is completely dissolved, and then add 157 g of SiO2-sol (30 wt.%).

[0043] Second step: crystallization process

[0044] The prepared precursor solution is stirred at 30℃ for 2h, and then aged overnight. The white sol state changes to gel. Then transfer to a 100mL polytetrafluoroethylene lined stainless steel crystallization kettle. Then transfer to a programmed temperature drying oven. The heating rate is 2℃·min-1, and maintained at 160℃ for 48h; then programmed cooling to 25℃ at a rate of 0.5℃·min-1.

[0045] Third step: preparation of hierarchical pore ZSM-5 molecular sieve

[0046] After the crystallization is completed, white crystalline product is obtained by suction filtration, and repeatedly washed with deionized water until the pH value of the filtrate approaches neutral. Then the filter cake is vacuum dried at 80℃ for 10h. Finally, the obtained sample is calcined at 550℃ in air atmosphere for 5h to obtain hierarchical pore ZSM-5 molecular sieve.

[0047] Fourth step: loading process of active component

[0048] The prepared hierarchical pore ZSM-5 molecular sieve is ultrasonically immersed in equal volume of a solution of a linking agent and an active component at a certain ratio, ultrasonic assisted for 30min every 8h of immersion, for a total of 24h of immersion. After the immersion is completed, the solid is placed in a vacuum oven at 110℃ for 2h, and then calcined in a muffle furnace at 550℃ in air atmosphere for 4h to obtain a responsible catalyst.

[0049] The active component is sodium ethoxide, and the addition amount of the active component is 0.6% (mass ratio) of the carrier.

[0050] The linking agent used in the catalyst preparation process is a molecule with multiple active groups, and the linking agent is polyvinyl alcohol, and the addition amount is determined according to the mass ratio of linking agent to active component of 2:1.

[0051] Example three:

[0052] First step: preparation of precursor solution

[0053] Take 5.5 g of sodium hydroxide into 250 g of deionized water, then add 25 g of tetrapropylammonium bromide, add anionic polyacrylamide (APAM) as a soft template, the addition amount is n (APAM) : n (SiO2) = 0.3:1, after dissolving, add 2.7 g of aluminum sulfate, stir vigorously at room temperature until the aluminum sulfate is completely dissolved, and then add 157 g of SiO2-sol (30 wt.%).

[0054] Second step: crystallization process

[0055] The prepared precursor solution is stirred at 30℃ for 2h, and then aged overnight. The white sol state changes to gel. Then transfer to a 100 mL polytetrafluoroethylene lined stainless steel crystallization kettle. Then transfer to a programmed temperature drying oven. The heating rate is 2℃·min-1, and maintained at 160℃ for 48h; then programmed cooling to 25℃ at a rate of 0.5℃·min-1.

[0056] Third step: preparation of hierarchical pore ZSM-5 molecular sieve

[0057] After the crystallization is completed, white crystalline product is obtained by suction filtration, and repeatedly washed with deionized water until the pH value of the filtrate approaches neutral. Then the filter cake is vacuum dried at 80℃ for 10h. Finally, the obtained sample is calcined at 550℃ in air atmosphere for 5h to obtain hierarchical pore ZSM-5 molecular sieve.

[0058] Fourth step: loading process of active component

[0059] The prepared hierarchical pore ZSM-5 molecular sieve is ultrasonically immersed in equal volume of a solution of a linking agent and an active component at a certain ratio, ultrasonically assisted for 30 min every 8h of immersion, for a total of 24h of immersion. After the immersion is completed, the solid is placed in a vacuum oven at 110℃ for 2h, and then calcined in a muffle furnace at 550℃ in air atmosphere for 4h to obtain a responsible catalyst.

[0060] The active component is sodium methoxide and sodium ethoxide, and the mass ratio of the two is 2:1, and the addition amount of the active component is 0.3% (mass ratio) of the carrier;

[0061] The linking agent used in the preparation of the catalyst is a molecule with multiple active groups, and the linking agent is cyclodextrin, and the addition amount is determined according to the mass ratio of the linking agent to the active component, which is 5:1.

[0062] Example four:

[0063] First step: preparation of precursor solution

[0064] Take 5.5 g of sodium hydroxide into 250 g of deionized water, then add 25 g of tetrapropylammonium bromide, add anionic polyacrylamide (APAM) as a soft template, the addition amount is n (APAM) : n (SiO2) = 0.2:1, after dissolving, add 2.7 g of aluminum sulfate, stir vigorously at room temperature until the aluminum sulfate is completely dissolved, and then add 157 g of SiO2-sol (30 wt.%).

[0065] Second step: crystallization process

[0066] The prepared precursor solution is stirred at 30℃ for 2h, and then aged overnight. The white sol state changes to gel. Then transfer to a 100 mL polytetrafluoroethylene lined stainless steel crystallization kettle. Then transfer to a programmed temperature drying oven. The heating rate is 2℃·min-1, and the temperature is maintained at 160℃ for 48h; then the temperature is programmed to decrease to 25℃ at a rate of 0.5℃·min-1.

[0067] Third step: preparation of hierarchical pore ZSM-5 molecular sieve

[0068] After the crystallization is completed, white crystalline product is obtained by suction filtration, and repeatedly washed with deionized water until the pH value of the filtrate approaches neutral. Then the filter cake is vacuum dried at 80℃ for 10h. Finally, the obtained sample is calcined at 550℃ in air atmosphere for 5h to obtain hierarchical pore ZSM-5 molecular sieve.

[0069] Fourth step: loading process of active component

[0070] The prepared hierarchical pore ZSM-5 molecular sieve is ultrasonically immersed in equal volume of a solution of a linking agent and an active component at a certain ratio, and the immersion is repeated for 24h, with ultrasonic assistance for 30min each time. After the immersion is completed, the solid is placed in a vacuum oven at 110℃ for 2h, and then calcined in a muffle furnace at 550℃ in air atmosphere for 4h to obtain a responsible catalyst.

[0071] Among them: the active component is potassium methoxide and sodium tert-butoxide, and the mass ratio of the two is 1:1, and the addition amount of the active component is 0.7% (mass ratio) of the carrier;

[0072] The linking agent used in the preparation of the catalyst is a molecule with multiple active groups, and the linking agent is citric acid, and the addition amount is determined according to the mass ratio of the linking agent to the active component, which is 2:1.

[0073] Comparative example one:

[0074] First step: preparation of precursor solution

[0075] Take 5.5 g of sodium hydroxide into 250 g of deionized water, then add 25 g of tetrapropyl ammonium bromide, add anionic polyacrylamide (APAM) as a soft template, the addition amount is n (APAM) : n (SiO2) = 0.2:1, after dissolving, add 2.7 g of aluminum sulfate, stir vigorously at room temperature until the aluminum sulfate is completely dissolved, and then add 157 g of SiO2-sol (30 wt.%) dropwise.

[0076] Second step: crystallization process

[0077] The prepared precursor solution is stirred at 30℃ for 2h, and then aged overnight. The white sol state changes to gel. Then transfer to a 100 mL polytetrafluoroethylene lined stainless steel crystallization kettle. Then transfer to a programmed temperature drying oven. The heating rate is 2℃·min-1, and the temperature is maintained at 160℃ for 48h; then the temperature is programmed to decrease to 25℃ at a rate of 0.5℃·min-1.

[0078] Third step: preparation of hierarchical pore ZSM-5 molecular sieve

[0079] After the crystallization is completed, white crystalline product is obtained by suction filtration, and repeatedly washed with deionized water until the pH value of the filtrate approaches neutral. Then the filter cake is vacuum dried at 80℃ for 10h. Finally, the obtained sample is calcined at 550℃ in air atmosphere for 5h to obtain hierarchical pore ZSM-5 molecular sieve.

[0080] Fourth step: loading process of active component

[0081] The prepared hierarchical pore ZSM-5 molecular sieve and the active component solution are ultrasonically immersed in equal volume according to a certain proportion, each immersion is 8h, and the ultrasonic assistance is 30min, and the total immersion time is 24h. After the immersion is completed, the solid is placed in a vacuum drying oven at 110℃ for 2h, and then calcined in a muffle furnace at 550℃ in air atmosphere for 4h to obtain a responsible catalyst.

[0082] Among them: the active components are sodium methoxide and sodium ethoxide, which are added in a mass ratio of 1:1, and the addition amount of the active component is 0.5% (mass ratio) of the carrier;

[0083] Comparative example two:

[0084] First step: preparation of precursor solution

[0085] Take 5.5 g of sodium hydroxide into 250 g of deionized water, then add 25 g of tetrapropyl ammonium bromide, dissolve, then add 2.7 g of aluminum sulfate, stir vigorously at room temperature until the aluminum sulfate is completely dissolved, and then add 157 g of SiO2-sol (30 wt.%) dropwise.

[0086] Second step: crystallization process

[0087] The prepared precursor solution was stirred at 30℃ for 2h, and then aged overnight. The white sol changed into a gel. The gel was then transferred into a 100mL Teflon-lined stainless steel autoclave. The autoclave was then transferred into a temperature-programmed drying oven. The temperature was increased at a rate of 2℃ / min, and maintained at 160℃ for 48h. The temperature was then decreased to 25℃ at a rate of 0.5℃ / min.

[0088] Third step: preparation of ZSM-5 molecular sieve

[0089] After the crystallization was completed, the white crystalline product was obtained by suction filtration, and repeatedly washed with deionized water until the pH value of the filtrate was close to neutral. The filter cake was then vacuum dried at 80℃ for 10h. Finally, the obtained sample was calcined at 550℃ in an air atmosphere for 5h to obtain the hierarchical pore ZSM-5 molecular sieve.

[0090] Fourth step: loading process of active component

[0091] The prepared hierarchical pore ZSM-5 molecular sieve, the linker and the active component solution were ultrasonically impregnated in equal volumes according to a certain proportion, and each impregnation was performed for 8h, with ultrasonic assistance for 30min, and the total impregnation time was 24h. After the impregnation was completed, the solid was placed in a vacuum drying oven at 110℃ for 2h, and then calcined at 550℃ in a muffle furnace in an air atmosphere for 4h to obtain the responsible catalyst.

[0092] The active component was sodium ethoxide, and the addition amount of the active component was 0.5% (mass ratio) of the carrier.

[0093] The linker used in the catalyst preparation process was a molecule with multiple active groups, and the linker was citric acid, and the addition amount was determined according to the mass ratio of the linker to the active component being 1:1.

[0094] Comparative Example Three:

[0095] First step: preparation of precursor solution

[0096] 5.5g of sodium hydroxide was weighed into 250g of deionized water, followed by 25g of tetrapropylammonium bromide. Anionic polyacrylamide (APAM) was added as a soft template, and the addition amount was n(APAM):n(SiO2) = 0.2:1. After dissolution, 2.7g of aluminum sulfate was added, and the mixture was stirred vigorously at room temperature until the aluminum sulfate was completely dissolved. Then, 157g of SiO2-sol (30wt.%) was added dropwise.

[0097] Second step: crystallization process

[0098] The prepared precursor solution was stirred at 30℃ for 2h, and then aged overnight. The white sol changed into a gel. The gel was then transferred into a 100mL Teflon-lined stainless steel autoclave. The autoclave was then transferred into a temperature-programmed drying oven. The temperature was raised at a rate of 2℃ / min, and maintained at 160℃ for 48h. The temperature was then decreased to 25℃ at a rate of 0.5℃ / min.

[0099] Step 3: Preparation of hierarchical ZSM-5 zeolite

[0100] After the crystallization was completed, the white crystalline product was obtained by suction filtration, and repeatedly washed with deionized water until the pH value of the filtrate was close to neutral. The filter cake was then vacuum dried at 80℃ for 10h. Finally, the obtained sample was calcined at 550℃ in an air atmosphere for 5h to obtain the hierarchical ZSM-5 zeolite.

[0101] Step 4: Loading process of active component

[0102] The prepared hierarchical ZSM-5 zeolite and the active component solution were ultrasonically impregnated in equal volumes at a certain ratio, for 8h each time, with ultrasonic assistance for 30min, for a total of 24h. After the impregnation was completed, the solid was placed in a vacuum drying oven at 110℃ for 2h, and then calcined in a muffle furnace at 550℃ in an air atmosphere for 4h to obtain the responsible catalyst.

[0103] The active component was sodium ethoxide, and the addition amount of the active component was 0.6% (mass ratio) of the carrier.

[0104] Comparative Example 4:

[0105] The commercial ZSM-5 zeolite and sodium ethoxide were directly mixed, and the addition amount of sodium ethoxide was 0.2% (mass ratio) of the carrier.

[0106] The performance of the catalyst was evaluated in a high-pressure reaction kettle. Dimethyl carbonate and ethanol were added to the high-pressure kettle in a molar ratio of 1:20, and the catalyst was added in an amount of 1% of the mass of the raw materials. The high-pressure kettle was then closed, the temperature was set to 85℃, and the reaction was carried out for 3h. After the reaction, the temperature was decreased, and the composition of the mixture after the reaction was analyzed by gas chromatography. The conversion rate was calculated based on dimethyl carbonate. After the reaction, the mixture was aspirated, and dimethyl carbonate and ethanol were added again for repeated performance evaluation of the catalyst. The reaction and evaluation were carried out in the same way. The experimental results are shown in Table 1.

[0107] Table 1 Comparison of catalyst performance between application examples and comparative examples

[0108]

[0109]

[0110] The catalyst of the present application is prepared by adding a connecting agent, which can utilize the advantages of the molecular connecting agent with multiple active groups to increase the stability of the sodium alcoholate active component and increase the loading capacity. The performance of the catalyst is evaluated by using a tank reactor, and the stability of the prepared catalyst in the ester exchange reaction is investigated. The performance evaluation shows that the catalyst prepared by using the connecting agent has higher product yield and more excellent product yield. This is of great significance for improving the combustion performance of oxygen-containing fuels and reducing fuel costs.

Claims

1. A method for preparing a carbonate-based synthesis catalyst for oxygenated fuel additives, wherein the catalyst is used to catalyze the preparation of a mixture of ethyl methyl carbonate and diethyl carbonate from dimethyl carbonate and ethanol via transesterification; the resulting mixture is used as an oxygenated fuel additive; the specific preparation method is as follows: Step 1: Preparation of precursor solution Weigh 5.5g of sodium hydroxide and add it to 250g of deionized water, then add 25g of tetrapropylammonium bromide, add anionic polyacrylamide (APAM) as a soft template agent, dissolve it, then add 2.7g of aluminum sulfate, stir vigorously at room temperature until the aluminum sulfate is completely dissolved, and add 157g of SiO2-sol with a mass fraction of 30wt.% dropwise, where n(APAM):n(SiO2) = 0.1:1 to 10:1; Step 2: Crystallization Process The prepared precursor solution was stirred at 30°C for 2 hours, then allowed to stand overnight for aging. The white sol turned into a gel, which was then transferred to a 100 mL stainless steel crystallization vessel lined with polytetrafluoroethylene, and then transferred to a programmed temperature drying oven with a heating rate of 2°C / min. -1 The temperature was maintained at 160℃ for 48 hours, and then programmed to decrease to 25℃ at a rate of 0.5℃·min. -1 ; Step 3: Preparation of hierarchical porous ZSM-5 molecular sieve After crystallization, the white crystalline product was obtained by filtration and repeatedly washed with deionized water until the pH of the filtrate was close to neutral. The filter cake was then vacuum dried at 80°C for 10 hours. Finally, the sample was calcined at 550°C in air for 5 hours to obtain hierarchical ZSM-5 molecular sieve. Step 4: Loading process of active components The prepared hierarchical porous ZSM-5 molecular sieve was ultrasonically impregnated with a binder and active component solution in a certain proportion. For every 8 hours of impregnation, ultrasonic assistance was performed for 30 minutes, for a total of 24 hours. After impregnation, the resulting solid was vacuum dried at 110℃ for 2 hours, and then calcined at 550℃ for 4 hours in an air atmosphere in a muffle furnace to obtain the supported catalyst. The active component is one or more of sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, and sodium tert-butoxide, and the amount added is 0.1% to 5% of the carrier mass. The binder includes one of sucrose, lactose, starch, polyvinyl alcohol, polyethylene glycol, citric acid, and cyclodextrin, and the amount added is determined according to the mass ratio of binder to active component of 1:1 to 10:1.

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