Process for the preparation of dimethyl carbonate by decarboxylation of dimethyl oxalate

Abstract

The application provides a method for preparing dimethyl carbonate by decarboxylation of dimethyl oxalate, and relates to the technical field of dimethyl carbonate preparation, and specifically comprises the following steps: adding dimethyl oxalate into a reactor, heating to melt the dimethyl oxalate, adding a catalyst into the system, and obtaining dimethyl carbonate by catalytic decarboxylation; the catalyst is an alkali metal alcoholate. The catalyst selected by the preparation method is low in price and easy to prepare; under the catalytic condition of the catalyst, the conversion rate of raw materials is high, the selectivity of the product, i.e. dimethyl carbonate, is high, and the by-products are few. The preparation method is simple in process flow and mild in process condition, can reduce industrial cost and improve industrial production efficiency in many aspects, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the technical field of dimethyl carbonate preparation, and more specifically to a method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate. Background Technology

[0002] Dimethyl carbonate is a low-toxicity, environmentally friendly, and widely used chemical raw material. It is also an important organic synthesis intermediate. Its molecular structure contains functional groups such as carbonyl, methyl, and methoxy groups, so it can be widely used in organic synthesis reactions such as carbonylation, methylation, methoxylation, and carbonyl methylation. It has a very wide range of applications, mainly as a carbonylation and methylation reagent, gasoline additive, and raw material for the synthesis of polycarbonate. In production, it is safe, convenient, low-polluting, and easy to transport.

[0003] Dimethyl carbonate (DMC) can be classified into industrial grade, medical grade, and battery grade according to purity. Industrial grade DMC accounts for more than half of the market share. Currently, the main methods for synthesizing DMC include the phosgene method, urea method, transesterification method, direct methanol oxidation carbonylation method, indirect methyl nitrite oxidation carbonylation method, and dimethyl oxalate decarbonylation method. The phosgene method was the earliest industrial method for producing DMC, but it has been phased out due to the toxicity of phosgene and the corrosive effects of its byproducts on equipment and the environment. The urea method has poor product selectivity and low yield. The transesterification method relies on petroleum resources and is easily affected by fluctuations in the petrochemical raw material market. Oxidative carbonylation methods include direct liquid-phase methanol oxidation carbonylation and indirect methyl nitrite oxidation carbonylation. The direct liquid-phase methanol oxidation carbonylation method suffers from the instability of the monovalent copper catalyst, while the indirect methyl nitrite oxidation carbonylation method overcomes the inherent safety issues of explosion associated with the direct oxidation carbonylation method and avoids the influence of petrochemical raw materials, making it of great research significance and application potential. Meanwhile, the indirect oxidative carbonylation method can produce dimethyl oxalate, which is a downstream product of coal chemical industry, cheap and readily available. Therefore, research on the decarbonylation of dimethyl oxalate to prepare dimethyl carbonate is of great significance for the development of the dimethyl carbonate industry and for the blending of dimethyl oxalate and dimethyl carbonate according to market demand.

[0004] In the route for preparing dimethyl carbonate from dimethyl oxalate via decarbonylation, the catalyst is a key factor. Patent CN105478150B discloses a multilayered alkaline catalyst, its preparation method, and its applications. The active components potassium, rubidium, and cesium are supported on titanium dioxide to prepare an alkaline catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate. Patent CN113385207B discloses a catalyst for the synthesis of dimethyl carbonate, its preparation method, and its applications. Activated carbon is used as a support, Na2SiO3 is used as an auxiliary agent, and K2CO3, Rb2CO3, and Cs2CO3 are supported to prepare a catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate. The above-mentioned prior art decarbonylation catalysts for dimethyl oxalate are complex to prepare, expensive, produce many byproducts, and involve high reaction temperatures and harsh process conditions.

[0005] Therefore, the current research and development needs are to select a more suitable catalyst that makes the process reaction conditions milder, reduces process complexity and production costs, while ensuring that the reaction has high conversion rate and high selectivity. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate, which solves the technical problems of harsh process conditions, high process complexity, difficulty in catalyst preparation, low raw material conversion rate, and low product selectivity in existing technologies.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate, the specific method being as follows:

[0011] Dimethyl oxalate was added to a reactor and heated to melt it. A catalyst was then added to the system to catalyze the decarbonylation to obtain dimethyl carbonate. The catalyst was an alkali metal alkoxide.

[0012] Preferably, the catalyst is an alkali metal alkoxide containing sodium or potassium.

[0013] Preferably, the catalyst is any one or more of potassium methoxide, sodium methoxide, potassium ethoxide, sodium ethoxide, potassium tert-butoxide, and sodium tert-butoxide.

[0014] Preferably, the mass ratio of the catalyst to the dimethyl oxalate is (2.5-5):100.

[0015] Preferably, the reaction temperature is 80℃~150℃.

[0016] Preferably, the reaction pressure is (0-0.05MPa).

[0017] Preferably, the reaction time is 3 to 6 hours.

[0018] (III) Beneficial Effects

[0019] This invention provides a method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate. Compared with the prior art, it has the following advantages:

[0020] 1. The catalyst selected in the preparation method of the present invention is inexpensive and easy to prepare. Under the catalytic conditions of the catalyst, the conversion rate of the raw materials is high, the selectivity of the product, namely dimethyl carbonate, is high, and the by-products are minimal.

[0021] 2. The preparation method of the present invention has a simple process flow and mild process conditions, which can reduce industrial costs and improve industrial production efficiency in many ways, and is suitable for industrial production. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This application provides a method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate, which solves the technical problems of harsh process conditions, high process complexity, difficulty in catalyst preparation, low raw material conversion rate, and low product selectivity in the prior art. The preparation process is simple, the reaction conditions are mild, the catalyst is inexpensive and readily available, and the raw material conversion rate and product selectivity are high.

[0024] The technical solution in this application is to solve the above-mentioned technical problems, and the general idea is as follows:

[0025] Existing catalysts for the preparation of dimethyl carbonate involve cumbersome processes and expensive raw materials, increasing production costs for enterprises. Therefore, the inventors reviewed numerous existing technologies and conducted small-scale trials using alkali metal alkoxides based on existing alkali metal / alkaline earth metal catalysts. The results showed that using this catalyst resulted in milder process conditions, a simpler process flow, and, most importantly, improved conversion rates of dimethyl oxalate and selectivity of dimethyl carbonate. The inventors aim to protect this intellectual property.

[0026] To better understand the above technical solutions, the following will provide a detailed explanation of the specific implementation methods described in the specification.

[0027] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0028] Dimethyl oxalate was added to a reactor, and the system was heated to 80℃~150℃ to melt the dimethyl oxalate. A catalyst was added to the system to carry out a catalytic reaction. The mass ratio of the catalyst to dimethyl oxalate was (2.5~5):100. Under a slight positive pressure of (0-0.05MPa), the catalytic decarbonylation reaction was carried out for 3~6 hours to obtain dimethyl carbonate. The catalyst was an alkali metal alkoxide.

[0029] The catalyst is any one or more of potassium methoxide, sodium methoxide, potassium ethoxide, sodium ethoxide, potassium tert-butoxide, and sodium tert-butoxide.

[0030] Example 1:

[0031] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0032] 120g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 114℃ to melt the dimethyl oxalate. 5.4g of sodium methoxide was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 4 hours to obtain dimethyl carbonate.

[0033] The conversion rate of dimethyl oxalate and the selectivity of dimethyl carbonate were calculated using the following formulas:

[0034]

[0035]

[0036] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 99.41%, and the selectivity of dimethyl carbonate is 98.87%.

[0037] Example 2:

[0038] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0039] 120g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 115℃ to melt the dimethyl oxalate. 4.32g of sodium methoxide was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 4 hours to obtain dimethyl carbonate.

[0040] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 98.3%, and the selectivity of dimethyl carbonate is 98.85%.

[0041] Example 3:

[0042] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0043] 268g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 135℃ to melt the dimethyl oxalate. 11g of sodium methoxide was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 4 hours to obtain dimethyl carbonate.

[0044] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 99.51%, and the selectivity of dimethyl carbonate is 96.85%.

[0045] Example 4:

[0046] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0047] 150g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 90℃ to melt the dimethyl oxalate. 6.75g of sodium methoxide was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 3 hours to obtain dimethyl carbonate.

[0048] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 90.48%, and the selectivity of dimethyl carbonate is 100%.

[0049] Example 5:

[0050] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0051] 212g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 126℃ to melt the dimethyl oxalate. 9.5g of sodium methoxide was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 4 hours to obtain dimethyl carbonate.

[0052] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 99.56%, and the selectivity of dimethyl carbonate is 97.92%.

[0053] Example 6:

[0054] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0055] 120g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 125℃ to melt the dimethyl oxalate. 4.6g of potassium ethoxide was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 4 hours to obtain dimethyl carbonate.

[0056] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 98.4%, and the selectivity of dimethyl carbonate is 96.3%.

[0057] Example 7:

[0058] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0059] 120g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 124℃ to melt the dimethyl oxalate. 4.3g of sodium tert-butoxide was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 4 hours to obtain dimethyl carbonate.

[0060] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 97.2%, and the selectivity of dimethyl carbonate is 96.4%.

[0061] Comparative Example 1:

[0062] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0063] 120g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 114℃ to melt the dimethyl oxalate. 2.6g of sodium methoxide was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 4 hours to obtain dimethyl carbonate.

[0064] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 68.6%, and the selectivity of dimethyl carbonate is 99.3%.

[0065] Comparative Example 2:

[0066] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0067] 120g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 100℃ to melt the dimethyl oxalate. 4.1g of sodium methoxide was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 2 hours to obtain dimethyl carbonate.

[0068] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 43.8%, and the selectivity of dimethyl carbonate is 99.2%.

[0069] Comparative Example 3

[0070] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0071] 120g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 114℃ to melt the dimethyl oxalate. 5.4g of potassium carbonate was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 4 hours to obtain dimethyl carbonate.

[0072] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 56.3%, and the selectivity of dimethyl carbonate is 97.8%.

[0073] Comparative Example 4

[0074] The method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate is as follows:

[0075] 120g of dimethyl oxalate was weighed and added to the reactor. The system was heated to 114℃ to melt the dimethyl oxalate. 5.4g of sodium silicate was added to the system to carry out the reaction. Under slightly positive pressure, the decarbonylation reaction was catalyzed for 4 hours to obtain dimethyl carbonate.

[0076] Experimental calculations show that the conversion rate of dimethyl oxalate in this embodiment is 63.8%, and the selectivity of dimethyl carbonate is 98.3%.

[0077] Experimental data analysis

[0078] 1. As can be seen from the seven sets of examples and the two sets of comparative examples, the reaction parameters of the system have a significant impact on the conversion rate of dimethyl oxalate and the selectivity of dimethyl carbonate. Therefore, only a reasonable combination of reaction parameters can achieve the ideal reaction effect.

[0079] 2. Comparison of Comparative Examples 3 and 4 with Example 2 shows that, under the same reaction conditions, the present invention uses sodium methoxide, an alkali metal alkoxide, as a catalyst. Compared with the alkali metals or alkali metal salts commonly used in the market, the product conversion rate and product selectivity are significantly improved.

[0080] In summary, compared with existing technologies, it has the following beneficial effects:

[0081] 1. The catalyst selected in the preparation method of the present invention is inexpensive and easy to prepare. Under the catalytic conditions of the catalyst, the conversion rate of the raw materials is high, the selectivity of the product, namely dimethyl carbonate, is high, and the by-products are minimal.

[0082] 2. The preparation method of the present invention has a simple process flow and mild process conditions, which can reduce industrial costs and improve industrial production efficiency in many ways, and is suitable for industrial production.

[0083] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate, characterized in that, The specific method is as follows: 1) Add dimethyl oxalate to the reactor and heat it to melt; 2) Add a catalyst to the system to catalyze the decarbonylation reaction. The reaction pressure is slightly positive to obtain dimethyl carbonate. The amounts of dimethyl oxalate, catalyst, catalyst, heating temperature, and decarbonylation reaction time are as follows: 120g, 5.4g, sodium methoxide, 114℃, 4h, or 120g, 4.32g, sodium methoxide, 115℃, 4h, or 268g, 11g, sodium methoxide, 135℃, 4h, or 212g, 9.5g, sodium methoxide, 126℃, 4h, or 120g, 4.6g, potassium ethoxide, 125℃, 4h, or 120g, 4.3g, sodium tert-butoxide, 124℃, 4h.

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