A method for directly preparing dimethyl carbonate from carbon dioxide and methanol

Abstract

The invention discloses a method for synthesizing dimethyl carbonate from carbon dioxide and methanol, wherein olefin, carbon dioxide, methanol and a catalyst are added into a reactor, reacted at a certain temperature and pressure, and the olefin hydration reaction is coupled with the carbon dioxide methanol reaction to simultaneously prepare the olefin hydration product (alcohol) and dimethyl carbonate, and the route is clean and environmentally friendly. Water in the reaction system is quickly removed, the reaction efficiency is improved, and dimethyl carbonate is efficiently prepared from carbon dioxide and methanol.

Description

Technical Field

[0001] The invention relates to a method for synthesizing dimethyl carbonate from carbon dioxide and methanol, and belongs to the field of chemistry and chemical engineering. Background Art

[0002] Dimethyl carbonate (DMC) is an important organic chemical intermediate that can be used to produce a variety of chemical products such as polycarbonate, isocyanate, polyurethane, polycarbonate diol, etc. Because DMC is non-toxic, it is also an environmentally friendly solvent, gasoline additive, methylation agent or carbonylation agent. It can also be used to prepare lithium battery electrolytes and plays an important role in the development of new energy vehicles. In addition, DMC can also be used as an additive for detergents, surfactants and softeners. Due to its wide range of uses, DMC is known as the "new cornerstone" of today's organic synthesis.

[0003] At present, the DMC production process mainly includes: phosgene methanol method, ester exchange method (CN201410300187.7, CN201410677148.9), urea alcoholysis method (CN201410585479.X), methanol oxidation carbonylation method (CN201510257233.4), carbon dioxide and methanol reaction method (CN201310103111.0). Due to the mild reaction conditions of the ester exchange production process, the production process does not corrode the equipment, and the product purity is high, the ester exchange process has been developed on a large scale. The current production capacity accounts for more than 90% of the total, and it is also the mainstream process for DMC production in my country. Despite this, the ester exchange method still has the following disadvantages: the required raw material propylene oxide is not suitable for long-distance transportation, and the by-product 1,2-propylene glycol is difficult to sell due to purity issues.

[0004] The technology of synthesizing dimethyl carbonate by carboxylation reaction of alcohols using CO2 and methanol as raw materials through non-reductive conversion is a new green synthesis route that has attracted much attention in recent years (CN 201911150805.3). The advantages of this technology are wide raw material sources, low cost, high atomic utilization rate of the reaction, and only water by-products. It has important theoretical and practical significance both from the perspective of environmental protection and from the perspective of resource recycling. Since the reaction is subject to severe thermodynamic limitations, in order to improve the reaction conversion rate, the existing method must introduce additional chemical dehydrating agents into the reaction system, such as dicyclohexylcarbodiimide, dimethoxypropane, trimethyl orthoformate, phenylacetonitrile, etc. However, the separation and regeneration cost of the dehydrating agent is very high. The development of a low-cost and high-efficiency dehydration method is the key to the industrialization of the route of directly preparing dimethyl carbonate from carbon dioxide and methanol. Summary of the invention

[0005] According to one aspect of the present application, a method for preparing dimethyl carbonate from carbon dioxide and methanol is provided, wherein a raw material containing olefin, carbon dioxide and methanol is contacted with a catalyst and reacted in a closed container to obtain a product containing dimethyl carbonate;

[0006] The olefin is selected from at least one of ethylene, propylene, isobutylene or cyclohexene.

[0007] The reaction temperature is 80-200°C;

[0008] The reaction pressure is 1-10 MPa.

[0009] The catalyst is selected from hydrotalcite-like catalysts;

[0010] The catalyst includes divalent metal cations and trivalent metal cations;

[0011] The divalent metal cation is selected from Ni 2+ Mg 2+ 、Co 2+ 、Zn 2+ Cu 2+ At least one of;

[0012] The trivalent metal cation is selected from Ce 3+ ;

[0013] The molar ratio of the divalent metal cation to the trivalent metal cation is 1.0 to 4.0:1.

[0014] The trivalent metal cations also include Al 3+ or Fe 3+ At least one of;

[0015] The Ce 3+ The molar amount of the trivalent metal cation accounts for 10% to 80% of the total molar amount of the trivalent metal cation.

[0016] The preparation method of the catalyst comprises at least the following steps:

[0017] Mixing a metal cation precursor with water to obtain a mixed solution I;

[0018] mixing the precipitant with water to obtain a mixed solution II;

[0019] The mixed solution I is mixed with the mixed solution II to undergo a coprecipitation reaction, and then aged and calcined to obtain the catalyst.

[0020] The metal cation precursor is selected from at least one of nitrate, sulfate, acetate or chloride of the corresponding metal cation;

[0021] The precipitant is selected from at least one of Na2CO3 and NaOH in ammonia water;

[0022] The temperature of the coprecipitation reaction is 60-70°C;

[0023] The pH of the coprecipitation reaction is 8 to 12;

[0024] The aging temperature is 40 to 120° C.

[0025] The aging time is 6 to 96 hours;

[0026] The calcination temperature is 400-600°C;

[0027] The calcination time is 3 to 5 hours.

[0028] According to another aspect of the present application, there is provided a use of a hydrotalcite-like catalyst containing a rare earth metal in preparing dimethyl carbonate from carbon dioxide and methanol.

[0029] The specific steps are: mixing raw materials containing olefins, carbon dioxide, methanol and catalyst in a reactor, causing olefin hydration reaction and carbon dioxide and methanol reaction, and the two reactions are coupled to obtain alcohol and dimethyl carbonate. The methanol conversion rate and the yield of dimethyl carbonate can be effectively improved.

[0030] The steps of preparing the catalyst are as follows: firstly, dissolving the metal cation salt and the precipitant in water to prepare mixed solutions I and II respectively, co-precipitating the mixed solution I containing the metal cation and the mixed solution II containing the precipitant, aging to obtain a hydrotalcite catalyst, and calcining to obtain a hydrotalcite-like catalyst.

[0031] The beneficial effects of this application include:

[0032] 1) The olefin hydration reaction is coupled with the carbon dioxide methanol reaction to quickly remove water from the reaction system, improve the reaction efficiency, and realize the efficient preparation of dimethyl carbonate from carbon dioxide and methanol.

[0033] 2) The catalyst preparation method provided by the present invention is simple, easy to operate, low in cost, reusable, and has potential economic benefits. DETAILED DESCRIPTION

[0034] The present invention is described in detail below in conjunction with embodiments, but the present invention is not limited to these embodiments.

[0035] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0036] The analysis method, conversion rate and selectivity in the embodiment are calculated as follows:

[0037] The qualitative and quantitative analysis of the products was performed offline using an Agilent 7890A gas chromatograph, with Agilent HP-PLOT Q and CP-WAX capillary columns used for separation and a hydrogen flame ionization detector (FID) for detection and analysis.

[0038] Methanol conversion rate = (total methanol mass - residual methanol mass) / total methanol mass * 100%

[0039] DMC selectivity = (DMC moles*2) / converted methanol moles*100;

[0040] Olefin conversion rate = (total olefin amount - residual olefin amount) / total olefin amount * 100%;

[0041] Alcohol selectivity = mole number of alcohol / mole number of converted olefin*100%.

[0042] The ratios of ions in the examples are all molar ratios unless otherwise specified.

[0043] Example 1 Preparation of 1.0Ni 1.0Mg 1.0Al 1.0Ce Hydrotalcite-like Catalyst

[0044] 36.35gNi(NO3)2·6H2O, 46.89gAl(NO3)3·9H2O, 32.05gMg(NO3)2·6H2O and 54.28gCe(NO3)3·6H2O were completely dissolved in 500ml water to obtain a mixed solution I; 26.5gNa2CO3 and 70gNaOH were weighed and completely dissolved in 1L water to obtain a mixed solution II; the two mixed solutions were slowly added dropwise to 200mL water at the same time, stirred vigorously at a speed of 600r / min, and the pH was maintained at 10. After the addition was completed, the obtained colloidal suspension was transferred to an oven and aged at 65°C for 72h. After cooling, it was washed with distilled water until neutral and dried. The precursor was further calcined at 500°C for 4h to obtain the catalyst.

[0045] Embodiments 2 to 9

[0046] According to the conditions of Example 1, only the type and mass of nitrate were changed to prepare a hydrotalcite-like catalyst. The catalyst preparation conditions are shown in Table 1.

[0047] Table 1 Catalyst preparation conditions

[0048]

[0049]

[0050] Evaluation of the reaction performance of the catalysts of Examples 10 to 25

[0051] A 100mL reactor was used for evaluation. 200mg of catalyst and 15g of methanol were accurately weighed in a PTFE liner, and a stirring magnet was placed. The autoclave lid was covered and tightened symmetrically. The air in the autoclave was replaced and purged with CO2, and the air intake was about 0.5MPa each time, and repeated 5 times. After the air in the autoclave was replaced and exhausted, a certain amount of olefins and high-pressure CO2 gas were filled in, the reactor was sealed, and the heater control switch was turned on. When the temperature in the autoclave reached the reaction temperature, the start reaction time was recorded. After a certain reaction time, heating and stirring were stopped, the reactor was taken out and rapidly cooled in an ice water bath. After the autoclave was completely cooled, gas was collected and analyzed using an air bag. The pressure was released and the reactor was opened. 1mL of n-hexanol was accurately measured with a pipette and added to the mixed liquid in the autoclave as an internal standard for quantitative analysis. The liquid was slowly stirred for 30s to mix evenly. The mixed liquid was aspirated with a disposable syringe and filtered through a membrane and transferred to a chromatographic analysis bottle for subsequent analysis. Table 2 shows the results of the reaction of carbon dioxide and methanol on the catalyst; Table 3 shows the reaction performance when different types of olefins were added.

[0052] Table 2 Results of the reaction of carbon dioxide and methanol on the catalyst

[0053]

[0054]

[0055] Table 3 Reaction performance when adding different types of olefins

[0056]

[0057] As can be seen from Tables 2 and 3, the catalysts provided in the embodiments of the present invention have excellent reaction performance in the direct preparation of dimethyl carbonate from carbon dioxide and methanol. The activity and selectivity of the catalyst can be effectively adjusted by adjusting the composition of the hydrotalcite-like catalyst. On the 1.0Ni1.0Mg1.0Al1.0Ce catalyst, the propylene hydration reaction and the carbon dioxide and methanol reaction are coupled, and the methanol conversion rate reaches 71.5%, the DMC selectivity reaches 99.1%, and the catalyst performance is excellent. The use of olefins such as ethylene, propylene, isobutylene, and cyclohexene to improve the reaction performance of carbon dioxide and methanol through hydration reaction has a significant effect.

[0058] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing dimethyl carbonate from carbon dioxide and methanol, characterized in that: The raw material containing olefin, carbon dioxide and methanol is contacted with a catalyst and reacted in a closed container to obtain a product containing dimethyl carbonate; The olefin is selected from at least one of ethylene, propylene, isobutylene or cyclohexene; The catalyst is selected from hydrotalcite-like catalysts; The catalyst includes a metal cation; The metal cations include divalent metal cations and trivalent metal cations; The divalent metal cation is selected from Ni 2+ Mg 2+ 、Zn 2+ Cu 2+ Two of them; The trivalent metal cation is selected from Ce 3+ ; The trivalent metal cations also include Al 3+ or Fe 3+ One of; The reaction temperature is 80-200°C; The reaction pressure is 1-10 MPa; The molar ratio of the divalent metal cation to the trivalent metal cation is 1.0 to 4.0:1; The Ce 3+ The molar amount accounts for 10% to 80% of the total molar amount of the trivalent metal cation.

2. The method according to claim 1, characterized in that The preparation method of the catalyst comprises at least the following steps: Mixing a metal cation precursor with water to obtain a mixed solution I; mixing the precipitant with water to obtain a mixed solution II; The mixed solution I is mixed with the mixed solution II to undergo a coprecipitation reaction, and then aged and calcined to obtain the catalyst.

3. The method according to claim 2, characterized in that The metal cation precursor is selected from at least one of nitrate, sulfate, acetate or chloride of the corresponding metal cation; The precipitant is selected from at least one of Na2CO3 and NaOH.

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