Method for generating dimethyl carbonate by decarbonylation of dimethyl oxalate

Abstract

The invention relates to a method for generating dimethyl carbonate by decarbonylation of dimethyl oxalate, which comprises the following steps: dissolving dimethyl oxalate in a solvent to prepare a solution, adding a catalyst, and carrying out decarbonylation reaction to obtain dimethyl carbonate, the catalyst comprises a main catalyst and a cocatalyst, the main catalyst is alkoxide of alkali metal, and the cocatalyst is one or more of pyridine, acetone or triethylamine. According to the method, an alkoxide decarbonylation catalyst system of a single alkali metal is changed into a multi-element catalyst system by adding the auxiliary agent, so that the liquid-phase decarbonylation reaction can be carried out at low temperature and low pressure, the reaction condition is milder, the equipment cost and energy consumption of the reaction are reduced, and the catalyst can be recycled for multiple times and has good economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical synthesis, and particularly relates to a method for decarbonylating dimethyl oxalate to produce dimethyl carbonate. Background Art

[0002] Dimethyl carbonate (referred to as DMC), with the chemical formula C3H6O3, is insoluble in water, a colorless liquid with an aromatic odor. It is a low-toxic, environmentally friendly, and widely used chemical raw material, an important organic synthesis intermediate. Its molecular structure contains functional groups such as carbonyl, methyl, and methoxy, with various reaction properties, and has the characteristics of safe use, convenience, less pollution, and easy transportation in production.

[0003] Dimethyl carbonate can be divided into industrial grade and battery grade according to purity requirements, and the battery-grade dimethyl carbonate is used as a solvent for lithium battery electrolytes. With the development of new energy vehicles, the demand for lithium batteries has increased, which has also stimulated the demand for battery-grade dimethyl carbonate.

[0004] The initial production method of DMC was the phosgene method, which was developed successfully in 1918. However, the toxicity and corrosiveness of phosgene limited the application of this method. Especially with the increasing attention to environmental protection worldwide, the phosgene method has been phased out. The transesterification method is currently adopted by most enterprises in the industry. The total production capacity of DMC synthesis plants by the transesterification method accounts for more than 90% of the total DMC production capacity, becoming the mainstream process for DMC production in China.

[0005] The method for directly decarbonylating dimethyl oxalate (referred to as DMO) to produce dimethyl carbonate is currently still in the research stage. For example, US4544507 discloses that oxalic diester produces carbonic diester and carbon monoxide in a liquid medium containing catalysts such as alkali metal alcoholates at 50 - 150°C. However, in the examples, dimethyl oxalate was used as the raw material for the reaction, only the reaction temperature of 100°C was disclosed, the catalyst was sodium methoxide, and it was not indicated whether other solvents were added. There are no examples of other temperatures in the patent. CN113181894A discloses the decarbonylation reaction of dimethyl oxalate in a liquid phase medium, with a reaction temperature of 80 - 220°C. Only the reaction data at a reaction temperature above 100°C with ethylene glycol as the solvent are disclosed in the examples. CN112028771A discloses a method for liquid-phase decarbonylation of alkyl oxalate under the conditions of a temperature of 50 - 150°C and a pressure between 0.5 bar and 5 bar. When dimethyl oxalate is selected, the reaction temperature is 100°C and the pressure is 1.5 bar.

[0006] The technical solutions disclosed in the above patent documents require relatively high reaction temperatures and pressures, resulting in high equipment costs and energy consumption. Moreover, none of them involve research on catalyst deactivation and recycling. Based on the research on the technology of liquid-phase decarbonylation of dimethyl oxalate to dimethyl carbonate, the inventors of the present invention found that when using a single alkoxide of an alkali metal for the decarbonylation of dimethyl oxalate, the catalyst is prone to deactivation. Summary of the Invention

[0007] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a method for the decarbonylation of dimethyl oxalate to produce dimethyl carbonate. By adding a cocatalyst, the liquid-phase decarbonylation reaction of dimethyl oxalate can be carried out under low-temperature and low-pressure conditions, not only significantly reducing energy consumption, but also reducing the deactivation rate of the main catalyst, enabling it to be recycled multiple times and reducing the catalyst usage cost.

[0008] The present invention provides a method for the decarbonylation of dimethyl oxalate to produce dimethyl carbonate. The method is to dissolve dimethyl oxalate in a solvent to prepare a solution, add a catalyst, and carry out a decarbonylation reaction to obtain dimethyl carbonate. The catalyst includes a main catalyst and a cocatalyst. The main catalyst is an alkoxide of an alkali metal, and the cocatalyst is one or more of pyridine, acetone, or triethylamine.

[0009] In some embodiments of the present invention, the alkoxide of the alkali metal is selected from one or more of sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, and potassium tert-butoxide.

[0010] In some embodiments of the present invention, the dosage of the main catalyst is 5% - 10% of the mass of dimethyl oxalate.

[0011] In some embodiments of the present invention, the molar ratio of the main catalyst to the cocatalyst is 1:1 - 3.

[0012] In some embodiments of the present invention, the solvent is dimethyl carbonate.

[0013] In some embodiments of the present invention, the temperature of the reaction is 50 - 70 °C.

[0014] In some embodiments of the present invention, the pressure of the reaction is 0.1 - 0.5 MPa (absolute pressure).

[0015] In some embodiments of the present invention, the time of the reaction is 0.5 - 1.5 h.

[0016] In some embodiments of the present invention, the mass fraction of dimethyl oxalate in the solution is 15% - 25%.

[0017] In some embodiments of the present invention, the reaction is carried out under anhydrous and anaerobic conditions.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate provided by the present invention changes the single alkali metal alkoxide decarbonylation catalyst system into a multi-component catalyst system by adding an auxiliary agent, enabling the liquid-phase decarbonylation reaction to be carried out at low temperature and low pressure. The reaction conditions are milder, reducing the equipment cost and energy consumption of the reaction. Moreover, the catalyst can be recycled multiple times, having good economic benefits. Specific Embodiments

[0020] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate according to the present invention will be described in detail below. It should be noted that the expressions "comprising" or similar expressions "including", "containing" and "having" synonymous therewith in the present invention are open-ended and do not exclude additional unlisted elements, steps or components. The expression "consisting of" excludes any unstated element, step or component. The expression "consisting essentially of" means that the scope is limited to the specified elements, steps or components, plus optionally existing elements, steps or components that do not substantially affect the basic and novel features of the claimed subject matter. It should be understood that the expression "comprising" encompasses the expressions "consisting essentially of" and "consisting of". The term "one or more" or "at least one" may mean one, two, three, four, five, six, seven, eight, nine or more. The ranges recited herein (such as numerical ranges) may cover each value within the range and each sub-range formed by the individual values. Unless otherwise stated in the text, the singular forms "a", "an" and "the" include plural references.

[0021] The present invention provides a method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate. The method is to dissolve dimethyl oxalate in a solvent to prepare a solution, add a catalyst, and carry out a decarbonylation reaction to obtain dimethyl carbonate; the catalyst includes a main catalyst and a co-catalyst, the main catalyst is an alkali metal alkoxide, and the co-catalyst is one or more of pyridine, acetone or triethylamine.

[0022] The method for the decarbonylation of dimethyl oxalate to produce dimethyl carbonate provided by the present invention is carried out in a liquid phase system. By dissolving dimethyl oxalate in a solvent to prepare a solution and adding a catalyst to the solution, a liquid phase system is obtained. The cocatalyst of the present invention can specifically be pyridine, acetone, triethylamine, a combination of pyridine and acetone, a combination of pyridine and triethylamine, a combination of acetone and triethylamine, or a combination of pyridine, acetone, and triethylamine. During the research process of the present invention, it was found that when using a single alkoxide of an alkali metal for the decarbonylation of dimethyl oxalate, the catalyst is prone to deactivation. However, when using one or several of pyridine, acetone, or triethylamine in combination with the alkoxide of an alkali metal as a multi-component catalyst, the deactivation time of the alkoxide of an alkali metal is significantly extended, and it can be recycled more than 12 times. Moreover, it was unexpectedly found that the liquid phase decarbonylation of dimethyl oxalate can be achieved under relatively low temperature and pressure conditions.

[0023] In some embodiments of the present invention, the alkoxide of an alkali metal is selected from one or several of sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, and potassium tert-butoxide. Specifically, it can be sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, potassium tert-butoxide, a combination of sodium methoxide and potassium methoxide, a combination of sodium methoxide and sodium ethoxide, a combination of potassium ethoxide and sodium tert-butoxide, or a combination of sodium methoxide, potassium ethoxide, and sodium tert-butoxide, etc.

[0024] In some embodiments of the present invention, the dosage of the main catalyst is 5% - 10% of the mass of dimethyl oxalate, and it can be 5% - 6%, 6% - 7%, 7% - 8%, 8% - 9%, or 9% - 10%; in some more specific embodiments, it can be 5%, 8%, 9%, or 10%.

[0025] In some embodiments of the present invention, the molar ratio of the main catalyst to the cocatalyst is 1:1 - 3, and it can be 1:1 - 1.5, 1:1.5 - 2, 1:2 - 2.5, or 1:2.5 - 3; in some more specific embodiments, it can be 1:1, 1:1.5, 1:2, 1:2.5, or 1:3.

[0026] In some embodiments of the present invention, the solvent is dimethyl carbonate. Dimethyl carbonate itself is a reaction product. Using dimethyl carbonate as the solvent simplifies the subsequent separation operation and reduces the equipment cost and energy consumption of separation.

[0027] In some embodiments of the present invention, the reaction temperature is 50 - 70 °C, and it can be 50 - 55 °C, 55 - 60 °C, 60 - 65 °C, or 65 - 70 °C; in some more specific embodiments, it can be 50 °C, 60 °C, or 70 °C. The reaction temperature of the existing liquid phase decarbonylation of dimethyl oxalate is above 80 °C. By adding a cocatalyst and forming a multi-component catalyst system with the alkoxide of an alkali metal, the present invention enables the conversion rate of DMO to be greater than 99% and the selectivity of DMC to be greater than 96% at a reaction temperature of 50 - 70 °C.

[0028] In some embodiments of the present invention, the pressure of the reaction is 0.1 to 0.5 MPa (absolute pressure); in some more specific embodiments, it can be 0.1 MPa (absolute pressure), 0.3 MPa (absolute pressure), or 0.5 MPa (absolute pressure). CN112028771A discloses a method for liquid-phase decarbonylation of alkyl oxalate under the condition that the pressure is between 0.5 bar and 5 bar. When dimethyl oxalate is selected, the pressure is 1.5 bar. By adopting a co-catalyst and forming a multi-component catalyst system with an alcoholate of an alkali metal, the present invention reduces the reaction pressure to below 0.5 MPa, reducing the equipment and operation costs.

[0029] In some embodiments of the present invention, the reaction time is 0.5 to 1.5 h; in some more specific embodiments, it can be 0.5 h, 0.75 h, 1 h, or 1.5 h. The reaction time of the existing liquid-phase decarbonylation of dimethyl oxalate is greater than 3 h. By adopting a co-catalyst and forming a multi-component catalyst system with an alcoholate of an alkali metal, the present invention greatly shortens the reaction time and improves the reaction efficiency.

[0030] In some embodiments of the present invention, the mass fraction of dimethyl oxalate in the solution is 15% to 25%, and can be 15% to 20% or 20% to 25%; in some more specific embodiments, it can be 15%, 20%, or 25%.

[0031] In some embodiments of the present invention, the reaction is carried out under anhydrous and anaerobic conditions. The anhydrous and anaerobic conditions in the present invention refer to operating the reagents under anhydrous and anaerobic conditions during the reaction process to avoid the situation of impure reaction caused by moisture or air oxygen, thereby improving the reaction accuracy and precision. Specifically, it can be achieved by replacing the air in the reaction vessel with an inert gas such as nitrogen to prevent moisture and oxygen in the atmosphere from entering the reaction system.

[0032] The technical solutions of the present invention are illustrated below through specific specific examples. It should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combined steps or the insertion of other method steps between these clearly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Moreover, unless otherwise specified, the numbers of the method steps are only convenient tools for identifying the method steps, rather than limiting the arrangement order of the method steps or the scope of the present invention that can be implemented. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope that the present invention can implement.

[0033] Example 1

[0034] The method for decarbonylating dimethyl oxalate to produce dimethyl carbonate provided in this embodiment is specifically operated as follows:

[0035] Add 15 g of dimethyl oxalate substrate, 85 g of dimethyl carbonate solvent, 0.75 g of sodium methoxide main catalyst, 1.10 g of pyridine, and 0.7 g of triethylamine co-catalyst into a high-pressure reaction kettle in sequence. After purging with nitrogen, fill with nitrogen to 0.5 MPa. Start stirring and heating, and maintain at 60 °C for 1.5 h. After the reaction kettle is cooled, discharge the gas in the reaction kettle, and after purging with nitrogen, take out the liquid, weigh and analyze it.

[0036] Example 2

[0037] The method for decarbonylating dimethyl oxalate to produce dimethyl carbonate provided in this embodiment is specifically operated as follows:

[0038] Add 20 g of dimethyl oxalate, 80 g of dimethyl carbonate, 2 g of sodium methoxide, 1.46 g of pyridine, and 1.87 g of triethylamine into a high-pressure reaction kettle in sequence. After purging with nitrogen, fill with nitrogen to 0.1 MPa. Start stirring and heating, and maintain at 60 °C for 0.5 h. After the reaction kettle is cooled, discharge the gas in the reaction kettle, and after purging with nitrogen, take out the liquid, weigh and analyze it.

[0039] Example 3

[0040] The method for decarbonylating dimethyl oxalate to produce dimethyl carbonate provided in this embodiment is specifically operated as follows:

[0041] Add 25 g of dimethyl oxalate, 75 g of dimethyl carbonate, 2 g of sodium methoxide, 4.39 g of pyridine, and 1.87 g of triethylamine into a high-pressure reaction kettle in sequence. After purging with nitrogen, fill with nitrogen to 0.3 MPa. Start stirring and heating, and maintain at 70 °C for 0.75 h. After the reaction kettle is cooled, discharge the gas in the reaction kettle, and after purging with nitrogen, take out the liquid, weigh and analyze it.

[0042] Example 4

[0043] The method for decarbonylating dimethyl oxalate to produce dimethyl carbonate provided in this embodiment is specifically operated as follows:

[0044] Add 15 g of dimethyl oxalate, 85 g of dimethyl carbonate, 0.75 g of sodium methoxide, 2.19 g of pyridine, and 1.40 g of triethylamine into a high-pressure reaction kettle in sequence. After purging with nitrogen, fill with nitrogen to 0.5 MPa. Start stirring and heating, and maintain at 70 °C for 0.75 h. After the reaction kettle is cooled, discharge the gas in the reaction kettle, and after purging with nitrogen, take out the liquid, weigh and analyze it.

[0045] Example 5

[0046] The method for decarbonylating dimethyl oxalate to produce dimethyl carbonate provided in this embodiment is specifically operated as follows:

[0047] 20 g of dimethyl oxalate, 80 g of dimethyl carbonate, 2 g of sodium methoxide, 3.22 g of acetone and 1.87 g of triethylamine were successively added into a high-pressure reactor. After purging with nitrogen, nitrogen was filled to 0.5 MPa. Stirring and heating were started. After the reaction kettle was cooled at 50 °C for 1 h, the gas in the reaction kettle was discharged. After purging with nitrogen, the liquid was taken out, weighed and analyzed.

[0048] Example 6

[0049] The method for decarbonylation of dimethyl oxalate to produce dimethyl carbonate provided in this example is specifically operated as follows:

[0050] 25 g of dimethyl oxalate, 75 g of dimethyl carbonate, 2.5 g of potassium methoxide, 2.07 g of acetone and 3.61 g of triethylamine were successively added into a high-pressure reactor. After purging with nitrogen, nitrogen was filled to 0.1 MPa. Stirring and heating were started. The temperature was maintained at 60 °C for 0.5 h. After the reaction kettle was cooled, the gas in the reaction kettle was discharged. After purging with nitrogen, the liquid was taken out, weighed and analyzed.

[0051] Example 7

[0052] The method for decarbonylation of dimethyl oxalate to produce dimethyl carbonate provided in this example is specifically operated as follows:

[0053] 15 g of dimethyl oxalate, 85 g of dimethyl carbonate, 0.75 g of potassium methoxide, 1.02 g of pyridine and 1.30 g of triethylamine were successively added into a high-pressure reactor. After purging with nitrogen, nitrogen was filled to 0.5 MPa. Stirring and heating were started. The temperature was maintained at 50 °C for 1.5 h. After the reaction kettle was cooled, the gas in the reaction kettle was discharged. After purging with nitrogen, the liquid was taken out, weighed and analyzed.

[0054] Example 8

[0055] The method for decarbonylation of dimethyl oxalate to produce dimethyl carbonate provided in this example is specifically operated as follows:

[0056] 20 g of dimethyl oxalate, 80 g of dimethyl carbonate, 1.4 g of potassium methoxide and 4.74 g of pyridine were successively added into a high-pressure reactor. After purging with nitrogen, nitrogen was filled to 0.3 MPa. Stirring and heating were started. The temperature was maintained at 60 °C for 0.75 h. After the reaction kettle was cooled, the gas in the reaction kettle was discharged. After purging with nitrogen, the liquid was taken out, weighed and analyzed.

[0057] Comparative Example 1

[0058] The method for decarbonylation of dimethyl oxalate to produce dimethyl carbonate provided in this comparative example is specifically operated as follows:

[0059] Add 15 g of dimethyl oxalate, 85 g of dimethyl carbonate, and 0.75 g of sodium methoxide into a high-pressure reactor in sequence. After purging with nitrogen, fill nitrogen to 0.5 MPa. Start stirring and heating, and maintain at 60 °C for 1.5 h. After the reactor cools down, discharge the gas in the reactor, and after purging with nitrogen, take out the liquid, weigh it, and analyze it.

[0060] (I) Recyclability of the catalyst

[0061] After recovering the catalyst after the reaction in Example 1, continue to use it according to the reaction conditions in Example 1. After recovering the catalyst after the reaction in Comparative Example 1, continue to use it according to the reaction conditions in Comparative Example 1.

[0062] The conversion rate calculation formula of dimethyl oxalate (DMO) is as follows:

[0063]

[0064] The selectivity calculation formula of dimethyl carbonate (DMC) is as follows:

[0065]

[0066] The above results are compared as shown in Table 1 below:

[0067] Table 1 Comparison of the recyclability of the catalysts in Example 1 and Comparative Example 1

[0068]

[0069] As can be seen from Table 1, the reaction conditions of the example and the comparative example are the same. A co-catalyst is added in the example. Compared with the alcohol salt of a single alkali metal, the activity is slightly improved, but the deactivation rate is slowed down.

[0070] After recycling the catalyst in Example 1 once and then recovering it, continue to reuse it until the conversion rate of dimethyl oxalate (DMO) drops below 97% after 12 cycles of use.

[0071] (II) Scale-up experiment

[0072] Scale up the feed amount in Example 5 by 10 times, and keep the other conditions unchanged. After the reaction, recover the catalyst and reuse it until the conversion rate of dimethyl oxalate drops below 97%, and then stop using it. The experimental results are shown in Table 2 below:

[0073] Table 2 Results of the scale-up experiment

[0074]

[0075] The above experimental results show that the addition of an auxiliary agent in the present invention changes the single alkali metal alkoxide decarbonylation catalyst system into a multi-component catalyst system, enabling the liquid-phase decarbonylation reaction of dimethyl oxalate to proceed at low temperature and low pressure, reducing the reaction cost, increasing the reaction rate, and prolonging the inactivation time of the alkali metal alkoxide.

[0076] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for the decarbonylation of dimethyl oxalate to produce dimethyl carbonate, characterized in that, The method is to dissolve dimethyl oxalate in a solvent to prepare a solution, add a catalyst, and perform a decarbonylation reaction to obtain dimethyl carbonate; the catalyst includes a main catalyst and a co-catalyst, the main catalyst is an alcoholate of an alkali metal, and the co-catalyst is one or more of pyridine, acetone or triethylamine.

2. The method for producing dimethyl carbonate by decarbonylation of dimethyl oxalate according to claim 1, wherein The alcoholate of the alkali metal is selected from one or more of sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, and potassium tert-butoxide.

3. The method for producing dimethyl carbonate by decarbonylation of dimethyl oxalate according to claim 1, characterized in that, The dosage of the main catalyst is 5% to 10% of the mass of dimethyl oxalate.

4. The method for producing dimethyl carbonate by decarbonylation of dimethyl oxalate according to claim 1, characterized in that, The molar ratio of the main catalyst to the co-catalyst is 1:1 to 3.

5. The method for producing dimethyl carbonate by decarbonylation of dimethyl oxalate according to claim 1, wherein The solvent is dimethyl carbonate.

6. The method for producing dimethyl carbonate by decarbonylation of dimethyl oxalate according to claim 1, characterized in that, The temperature of the reaction is 50 to 70 °C.

7. The method for producing dimethyl carbonate by decarbonylation of dimethyl oxalate according to claim 1, characterized in that, The pressure of the reaction is 0.1 to 0.5 MPa (absolute pressure).

8. The method for producing dimethyl carbonate by decarbonylation of dimethyl oxalate according to claim 1, wherein The time of the reaction is 0.5 to 1.5 h.

9. The method for producing dimethyl carbonate by decarbonylation of dimethyl oxalate according to claim 1, characterized in that, The mass fraction of dimethyl oxalate in the solution is 15% to 25%.

10. The method for producing dimethyl carbonate by decarbonylation of dimethyl oxalate according to claim 1, wherein The reaction is carried out under anhydrous and anaerobic conditions.

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