CN111635313B - A kind of method for selenium-catalyzed oxidation of methyl acetate to prepare electrolyte solvent dimethyl carbonate - Google Patents

Abstract

The invention relates to a method for preparing electrolyte solvent dimethyl carbonate by oxidizing methyl acetate under the catalysis of selenium, which comprises the following steps: mixing a selenium catalyst, ferric trifluoride and methyl acetate according to a mass ratio of 0.001-0.005: 0.0002 to 0.0006:1, under the oxygen pressure of 0.5-1.0 MPa, 100-140 ^o Heating for 4-8 hours, and distilling to obtain dimethyl carbonate product. The method for synthesizing the dimethyl carbonate has the advantages of cheap and safe reaction raw materials and clean overall route, and is a brand new synthesis process for synthesizing the dimethyl carbonate.

Description

A kind of method for selenium-catalyzed oxidation of methyl acetate to prepare electrolyte solvent dimethyl carbonate

technical field

The invention relates to a method for preparing dimethyl carbonate as an electrolyte solvent by selenium-catalyzed oxidation of methyl acetate, and belongs to the technical field of chemical synthesis.

Background technique

Dimethyl carbonate (ie DMC) is an important chemical solvent with low toxicity, environmental protection and safety. It can be used as a solvent in battery electrolytes. With the rise of the lithium battery industry, the market demand for DMC is expanding, and it has a good development prospect. The traditional production route of DMC is the phosgene method, but this route is gradually being phased out due to the high toxicity and corrosiveness of phosgene and the environmental problems caused by the discharge of sodium chloride. At present, there are three commonly used synthetic routes: oxidative carbonylation reaction with copper chloride or nitric oxide as catalyst, transesterification reaction of propylene carbonate and methanol, and urea methanolysis reaction. However, the above three methods still have some problems, such as the use of nitrogen oxides that destroy the ozone layer, the high toxicity of the by-product allyl alcohol, and the production of odorous ammonia gas from the alcoholysis of urea. Overcoming the above problems and developing a green and clean new production route has good application value.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a kind of method of selenium-catalyzed methyl acetate oxidation to prepare electrolyte solvent dimethyl carbonate, using cheap and easily available methyl acetate as raw material, by nano-selenium-iron trifluoride catalyzed oxygen oxidation, to prepare carbonic acid The dimethyl ester has the advantages of simple method, easy-to-obtain raw materials, and high practical application value.

In order to solve the above-mentioned technical problems, the technical solution provided by the present invention is: a method for selenium-catalyzed oxidation of methyl acetate to prepare electrolyte solvent dimethyl carbonate, the steps of which are: selenium catalyst, iron trifluoride and methyl acetate are prepared according to the following steps: The mass ratio of 0.001-0.005:0.0002-0.0006:1 is mixed, and under 0.5-1.0MPa oxygen pressure, heated at 100-140°C for 4-8 hours, and the dimethyl carbonate product can be separated and obtained by distillation.

In the present invention, the preparation steps of the selenium catalyst are as follows: in a temperature environment of 0±1° C., stir and mix the ethanol solution of sodium borohydride and selenium powder, and then add sugar, brododecyl triethyl ammonium and bromine Substitute a mixture of diethyldiisopropylammonium mixture to obtain a mixed system; under stirring conditions, the temperature of the mixed system is raised to 20-60 ° C to carry out the reaction, after the reaction is completed, a precipitation is obtained, and after suction filtration, it is placed at a temperature of 450-550 °C. calcined at a temperature of ℃ to obtain nano-selenium material; when mixing, boron in an ethanol solution of selenium powder, sugar, bromododecyltriethylammonium, bromodiethyldiisopropylammonium and sodium borohydride The molar ratio of sodium hydride was 100:1000:8.20:2.60:100.

In the present invention, the mass ratio of selenium catalyst to methyl acetate is 0.001-0.005:1. Among them, 0.003:1 is preferred, and under this ratio, the selenium catalyst can be utilized to the greatest extent;

In the present invention, iron trifluoride is used as a co-catalyst. Its mass ratio to methyl acetate is 0.0002-0.0006:1, and 0.0004:1 is preferred. Under this condition, the conversion rate of raw materials can be improved, and the selectivity drop due to side reactions caused by the use of excess cocatalyst can be avoided.

In the present invention, the reaction is carried out in 0.5 to 1.0 MPa of oxygen, and 0.8 MPa is preferred among them. Oxygen at this pressure can promote the full conversion of the raw materials, and can avoid over-oxidation leading to a decrease in product selectivity

In the present invention, the reaction temperature is 100 to 140° C., and 120° C. is preferred. This temperature can make the raw materials fully converted and the product selectivity is high.

In the present invention, the reaction time is 4 to 8 hours, preferably 6 hours. At this reaction time, sufficient conversion of the starting material can be ensured.

Compared with the prior art, the beneficial effects of the present invention are:

The invention provides a method for preparing dimethyl carbonate as an electrolyte solvent by selenium-catalyzed oxidation of methyl acetate. The reaction raw materials are cheap, the reaction process is environmentally friendly and mild, and no waste is generated. And because no toxic and harmful reactants and solvents are used, the synthesis process is safer and more reliable.

Detailed ways

In the present invention, using the selenium catalyst developed by the inventor before (see the invention patent "A method for synthesizing nano-selenium materials", patent number: ZL201610899676.8), supplemented by an appropriate amount of iron trifluoride co-catalyst, under certain conditions Under pressure, using cheap and readily available methyl acetate as a raw material, selenium-iron trifluoride catalyzes oxygen oxidation to prepare dimethyl carbonate, the method is simple, the raw materials are readily available, the reaction process is clean, and the selectivity is high. A new synthesis process for synthesizing dimethyl carbonate has good application prospects.

The following examples illustrate the present invention in more detail, but do not further limit the present invention.

Example 1

First, a selenium catalyst was prepared according to the method of Example 1 in the invention patent "A method for synthesizing nano-selenium materials" (patent number: ZL201610899676.8). Then, 100 g of methyl acetate, 0.3 g of the above-mentioned selenium catalyst, and 0.04 g (that is, 40 mg) of iron trifluoride were added to an autoclave, followed by oxygenation after stirring, and the reaction was carried out at 0.8 MPa and 120° C. for 6 hours. After cooling, dimethyl carbonate (boiling point at normal pressure 89.1°C-90.2°C) can be obtained by distillation, with a yield of 96%.

Example 2

Other conditions are with embodiment 1, check the effect of using different amounts of selenium catalysts, and the experimental results are shown in Table 1.

Table 1 Comparison of the effects of using different amounts of selenium catalysts

It can be seen from the above results that when the mass ratio of selenium catalyst and methyl acetate reaches 0.001:1, dimethyl carbonate can be obtained in high yield. When the mass ratio of selenium catalyst and methyl acetate reaches 0.003:1, the product yield reaches a peak, and subsequent increase in the catalyst dosage cannot further improve the product yield. Therefore, considering the efficiency, using the selenium catalyst and methyl acetate mass ratio of 0.003:1 has the best effect (Example 1). At the same time, it can be seen that the key to this reaction lies in the need to use a selenium catalyst, and without a selenium catalyst, the reaction will not occur.

Example 3

Other conditions are the same as in Example 1, and the effects of different cocatalysts are tested. The experimental results are shown in Table 2.

Table 2 Comparison of the effects of different co-catalysts

From the above results, it can be seen that the cocatalyst is very important in this reaction. Without the addition of a co-catalyst, the product yield is only 53% with only selenium catalyst catalysis, which cannot meet the requirements of industrial production. The oxidation of methyl acetate is essentially a Baeyer-Villiger oxidation. According to the previous experience of our research group in related selenium-catalyzed reactions, in this reaction, the attack of selenium peroxy species on the carbonyl carbon positive center will first occur (Adv. Synth. Catal. 2015, 357, 955-960). Therefore, the addition of a Lewis acid catalyst is beneficial to enhance the electropositivity of the carbon positive center, thereby facilitating the occurrence of this reaction. Iron trifluoride, as a metal salt with a strong electron withdrawing group, can achieve this effect. Based on past experience, we screened a series of Lewis acid catalysts, all of which are more or less effective. However, it is surprising that some common metal salts with strong Lewis acidity, such as ferric chloride, aluminum fluoride, yttrium fluoride, yttrium trifluoromethanesulfonate, etc., are far less effective than common and cheap, but not Frequently used iron trifluoride is strong. This experimental phenomenon shows that the effect of iron trifluoride is not limited to the expected Lewis acid, among which iron and fluorine play a key role in the activation of the catalyst. Metal-free fluoride salts, such as ammonium fluoride as co-catalysts, can also play a certain role in improving. This further confirms the role of fluoride ions. Through analysis, we believe that it may be that fluoride ions, as small ions, can easily penetrate into catalyst materials, thereby activating the catalyst. In addition, in the catalyst infiltrated by fluorine, the positive charge center of selenium can be strengthened, thereby enhancing its oxidizing ability, which is beneficial to the catalytic oxidation reaction (Appl. Organometal. Chem. 2014, 28, 652-656). On the other hand, similar to iron, copper salts with variable valences, such as copper fluoride, also work well as cocatalysts. This shows that in this reaction system, the oxygen-carrying properties of iron with variable valence also play a key role, which is consistent with the previous work of our research group (Adv. Synth. Catal. 2019, 361, 603-610). In conclusion, in this system, iron trifluoride enhances the selenium catalyst activity through three pathways: (1) Lewis acid; (2) fluoride ion permeation; (3) oxygen-carrying effect of variable valence iron.

Example 4

Other conditions are the same as in Example 1, and the effects of different iron trifluoride promoters and methyl acetate mass ratios are checked. The experimental results are shown in Table 3.

Table 3 Effect comparison of different iron trifluoride cocatalyst and methyl acetate mass ratio

It can be seen from the above results that the mass ratio of iron trifluoride cocatalyst to methyl acetate is 0.0004:1, and the effect is the best (Example 1). The co-catalyst needs to reach this amount in order to achieve the best effect, but further increase of the amount of the co-catalyst is not beneficial to the improvement of the catalyst effect, but will slightly decrease the yield.

Example 5

Other conditions are the same as in Example 1, and the effects of different reaction oxygen pressures are tested. The experimental results are shown in Table 4.

Table 4 Comparison of the effects of different oxygen pressures

As can be seen from the above results, this reaction hardly occurs under normal pressure. Gradually increasing the pressure to 0.5 MPa gave a leap in yield, with the best results at 0.8 MPa pressure (Example 1). Further increasing the pressure did not significantly improve the response effect.

Example 6

Other conditions are the same as in Example 1, and the effects of different reaction temperatures are examined, and the experimental results are shown in Table 5.

Table 5 Comparison of the effects of different reaction temperatures

It can be seen from the above results that the reaction is the best at 120°C. Too low or too high temperature will result in decreased product yield.

Example 7

Other conditions are the same as in Example 1, and the effects of different reaction times are tested, and the experimental results are shown in Table 6.

Table 6 Comparison of the effects of different reaction times

As can be seen from the above results, the reaction reached the end point in 6 hours (Example 1). Further prolongation of the time did not improve the product yield.

The above are only preferred embodiments of the present invention, and do not limit the present invention in any form. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, according to the technical essence of the present invention, Any simple modifications, equivalent replacements and improvements made in the above embodiments still fall within the protection scope of the technical solutions of the present invention.

Claims (10)

1. A method for preparing electrolyte solvent dimethyl carbonate by catalyzing methyl acetate oxidation by selenium is characterized by comprising the following steps: methyl acetate is taken as a raw material, a selenium catalyst and ferric trifluoride are taken as a catalytic system, and the reaction is carried out for a period of time in an oxygen atmosphere to obtain a dimethyl carbonate product;

wherein, the preparation steps of the selenium catalyst are as follows: stirring and mixing an ethanol solution of sodium borohydride and selenium powder at the temperature of 0 +/-1 ℃, and then adding a mixture consisting of sugar, dodecyl ammonium bromide, triethyl ammonium bromide and diethyl ammonium bromide, diisopropyl ammonium bromide to obtain a mixed system; heating the mixed system to 20-60 ℃ under the stirring condition for reaction, obtaining precipitate after the reaction is finished, and calcining at the temperature of 450-550 ℃ after suction filtration to obtain the nano selenium material; the molar ratio of selenium powder, sugar, dodecyl triethyl ammonium bromide, diethyl diisopropyl ammonium bromide and sodium borohydride in the ethanol solution of sodium borohydride is 100: 1000: 8.20: 2.60: 100.

2. The method of claim 1, wherein: the mass ratio of the selenium catalyst to the methyl acetate is 0.001-0.005: 1.

3. the method of claim 1, wherein: the mass ratio of the selenium catalyst to the methyl acetate is 0.003: 1.

4. The method of claim 1, wherein: the mass ratio of ferric trifluoride to methyl acetate is 0.0002-0.0006: 1.

5. the method of claim 1, wherein: the mass ratio of ferric trifluoride to methyl acetate is 0.0004:1.

6. The method of claim 1, wherein: reacting under the oxygen pressure of 0.5-1.0 MPa.

7. The method of claim 1, wherein: the reaction was carried out under an oxygen pressure of 0.8MPa.

8. The method of claim 1, wherein: heating and reacting for 4-8 hours at 100-140 ℃.

9. The method of claim 1, wherein: the reaction was heated at 120 ℃ for 6 hours.

10. The method of claim 1, wherein: after the reaction is finished, the dimethyl carbonate product is obtained by distillation separation.