Method for synthesizing high-efficiency catalyst of alkyl oxalate

Abstract

The application discloses a method for synthesizing an efficient catalyst for alkyl oxalate, and relates to a method for synthesizing a catalyst, which comprises the following steps: firstly, raw materials dimethyl oxalate and ethanol are subjected to an ester exchange reaction in a fixed bed or a slurry bed pre-reactor; liquid mixture generated in the pre-reactor is further subjected to reaction and separation in a reaction rectifying tower to separate by-product methanol; material in the reaction rectifying tower is subjected to pressure reduction in a catalyst recovery tower to separate excessive ethanol and triethylamine catalyst, and the catalyst is returned to the pre-reactor after dehydration; material in the catalyst recovery tower is subjected to pressure reduction in a product rectifying tower to separate product methyl ethyl oxalate and diethyl oxalate. The purity of the methyl ethyl oxalate and diethyl oxalate products produced by the process method is close to 99.99% or above, and the purity of the by-product methanol reaches 99.9% or above. The weak alkaline triethylamine catalyst has high catalytic efficiency, is easy to recover, has good stability, has a simple process route, has low requirements on the material selection of equipment and pipelines, has low energy consumption, and has good economic benefits.

Description

Technical Field

[0001] This invention relates to a method for synthesizing catalysts, and more particularly to a method for synthesizing alkyl oxalate esters using highly efficient catalysts. Background Technology

[0002] Ethylene glycol is an important basic chemical raw material with wide applications in various fields, mainly used in the production of polyester fibers, antifreeze, unsaturated polyester resins, lubricants, plasticizers, nonionic surfactants, and explosives. my country dominates ethylene glycol consumption in Asia and is also the world's largest ethylene glycol consumer market, with an apparent consumption of approximately 17 million tons in 2018. Currently, the petroleum-based ethylene process remains the mainstream technology for producing ethylene glycol. Due to my country's resource structure of "abundant coal, scarce oil, and lacking gas," coal chemical technologies, represented by coal-to-ethylene glycol and methanol-to-olefins, have developed significantly in my country. Coal-to-ethylene glycol technologies include coal gasification, methanol synthesis, carbon monoxide coupling carbonylation, and dimethyl oxalate hydrogenation; these technologies are favored by coal chemical enterprises due to their lower investment and relatively mature technology. According to the National Bureau of Statistics, as of October 2019, China's total ethylene glycol production capacity was approximately 10.805 million tons, of which coal-based ethylene glycol production capacity was 4.51 million tons, accounting for 41.8%. Xinjiang Tianye's ethylene glycol production capacity was 950,000 tons / year, accounting for approximately 9% of my country's ethylene glycol production capacity and 22% of the coal chemical route ethylene glycol production capacity.

[0003] Currently, the domestic coal-to-ethylene glycol (ETG) technology market is highly competitive due to homogeneity, resulting in a low overall operating rate. According to data from JLC Network Technology, the overall operating rate of ETG in 2019 was around 65%, a significant decrease compared to 2018, with a particularly low rate of only about 50% in September. More seriously, there are still ETG projects with a capacity of over 5 million tons per year under construction in my country. Furthermore, the prospect of persistently low international oil prices (below $30 per barrel) is causing a continued slump in ethylene glycol prices, which have currently fallen to 3,500 yuan per ton. With the continuous decline in oil prices, coal-to-ethylene glycol technology no longer holds a cost advantage over the petroleum-based method. Therefore, it is urgent to expand the downstream industries of ethylene glycol, develop a multi-tiered coal-to-ethylene glycol industrial chain, and seek opportunities for the development of downstream bulk or high-value-added products. Using dimethyl oxalate, an intermediate product of coal-to-ethylene glycol, as a transit point, to generate multifunctional alkyl oxalate fine chemicals or potential bulk chemical materials represents a major breakthrough in coal-to-ethylene glycol technology and a high-value supplement and extension to the industrial chain.

[0004] Methyl oxalate is an important organic chemical raw material, methyl / ethylating agent, and low-toxicity solvent. It can undergo various condensation reactions with fatty acid esters, amides, anilines, and many heterocyclic compounds. Diethyl oxalate is a low-toxicity, odorless solvent used in the pharmaceutical industry. It can be used to synthesize the hormone thymidine and is an intermediate in the manufacture of drugs such as phenobarbital, azathioprine, long-acting sulfonamides, sulfamethoxazole, carboxyphenyl penicillin, ampicillin, lactated chloroquine, thiabendazole, and ketone esters. Furthermore, methyl oxalate can also be used to manufacture plastic accelerators, cellulose and fragrance solvents, textile auxiliaries, dye intermediates and dye-sensitized battery additives, and high-pressure bearing lubricants. Methyl oxalate and diethyl oxalate can also react with corrosive carbonate matrices to form a unique oxalate surface layer, preventing further corrosion of the matrix. They can directly replace oxalic acid in the wood chip paper industry or in the extraction of hemicellulose from plant fibers. Methyl oxalate and diethyl oxalate can be used to prepare oxalic acid, methyl ethyl carbonate, and diethyl carbonate, which have important chemical applications, through simple hydrolysis and decarbonylation reactions. Summary of the Invention

[0005] The purpose of this invention is to provide a highly efficient catalyst method for the synthesis of alkyl oxalate. This method uses dimethyl oxalate and ethanol as raw materials, and involves reactive distillation, separation of the catalyst and unreacted ethanol from the product, vacuum distillation of methyl ethyl oxalate and diethyl oxalate, and methanol as a byproduct. The generated product does not contain azeotropes, and the process route is short and energy consumption is low.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for synthesizing alkyl oxalate using a highly efficient catalyst, the method comprising the following process steps:

[0008] (1) The raw materials, dimethyl oxalate and ethanol, first undergo transesterification in a fixed-bed or slurry-bed pre-reactor;

[0009] (2) The liquid mixture generated in the pre-reactor enters the reactive distillation column for further reaction and separation of the by-product methanol;

[0010] (3) The bottom material of the reactive distillation column enters the catalyst recovery column to separate excess ethanol and triethylamine catalyst under reduced pressure, and then returns it to the pre-reactor after dehydration;

[0011] (4) The bottom material of the catalyst recovery tower enters the product distillation tower and is separated into methyl ethyl oxalate and diethyl oxalate under reduced pressure.

[0012] The method for synthesizing alkyl oxalate using a highly efficient catalyst involves heterogeneous catalytic transesterification to synthesize methyl ethyl oxalate. The feed molar ratio of dimethyl oxalate (purity greater than 98%) and ethanol (purity greater than 99.5%) is 1:0.5 to 1:6.

[0013] The method for synthesizing alkyl oxalate using a highly efficient catalyst, wherein the catalyst is triethylamine.

[0014] The method for synthesizing alkyl oxalate using a highly efficient catalyst, wherein the reaction temperature of the pre-reactor is 40~110℃.

[0015] The method for synthesizing alkyl oxalate using a highly efficient catalyst involves a reactive distillation column that simultaneously performs the reaction and distillation. The product generated by the reaction is a non-azeotropic compound, and the byproduct methanol is separated in a single column to obtain methanol with a purity of 99.9%.

[0016] The method for synthesizing alkyl oxalate catalysts describes a catalyst recovery tower operated under reduced pressure (50-80 kPa). The distilled ethanol and triethylamine catalyst are dehydrated and returned to the pre-reactor for recycling.

[0017] The method for synthesizing alkyl oxalate using a highly efficient catalyst involves a distillation column with multiple side streams, operating under reduced pressure (1-5 kPa), which yields methyl ethyl oxalate and diethyl oxalate with a purity close to 99.99%.

[0018] The advantages and effects of this invention are:

[0019] 1. This invention utilizes dimethyl oxalate and ethanol as raw materials to produce methyl ethyl oxalate and diethyl oxalate. The products produced do not contain azeotropes. The reaction and distillation are carried out simultaneously in one column. The by-product methanol can be separated in a single column. The process route is short and the energy consumption is low.

[0020] 2. The maximum temperature of the process in this invention is 160°C, and the operating pressure is normal pressure or low vacuum. The overall requirements for equipment and pipeline materials are not strict, and the energy consumption is not high.

[0021] 3. Although the triethylamine catalyst of the present invention is weakly basic, it has excellent catalytic oxalate exchange efficiency.

[0022] 4. In the process flow of this invention, the boiling point of triethylamine is much lower than that of the product, making it very easy to separate and circulate with unreacted ethanol raw materials.

[0023] 5. The methyl ethyl oxalate and diethyl oxalate products generated by this invention have a purity of nearly 99.99%, and the by-product methanol has a purity of 99.9%. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of an embodiment of the process flow of the present invention. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings.

[0026] This invention uses dimethyl oxalate and ethanol as raw materials, with a weakly basic triethylamine catalyst, and proceeds through reactive distillation, separation of the catalyst and unreacted ethanol from the products, and vacuum distillation of methyl oxalate and diethyl oxalate to produce methanol as a byproduct.

[0027] The specific process of this invention is as follows:

[0028] The raw materials, dimethyl oxalate and ethanol, first react in a fixed-bed or slurry-bed pre-reactor under the action of triethylamine at a reaction temperature of 70–110 °C. The liquid mixture after the pre-reaction is pumped to a reactive distillation column, where the generated byproduct methanol is distilled off from the top. The top temperature of the distillation column is 63.6 °C, the bottom temperature is 80–110 °C, and the operating pressure is atmospheric pressure. The separated byproduct methanol has a purity of 99.9%. The bottom material of the reactive distillation column is pumped to an ethanol and catalyst recovery column. Under reduced pressure, excess ethanol and triethylamine catalyst in the raw materials are distilled off. The distilled ethanol and triethylamine are then passed through a 4A molecular sieve to remove any carried water before being returned to the pre-reactor for recycling. The bottom material of the catalyst recovery column is then pumped to a product distillation column for reduced-pressure distillation. The product distillation column has multiple side-streams and a maximum operating temperature of 160 °C, yielding products of methyl ethyl oxalate and diethyl oxalate with purities higher than 99.9%.

[0029] Example 1

[0030] 150 g of dimethyl oxalate (DMO) was mixed with 350 g of ethanol (the molar ratio of DMO to ethanol was approximately 1 / 6), and about 3.8 g of triethylamine catalyst (the catalyst content was approximately 3% of the molar amount of DMO) was added. The reaction temperature was 80 °C. The DMO conversion, selectivity of methyl ethyl oxalate (EMO) and diethyl oxalate (DEO), and yield are shown in Table 1.

[0031] Table 1. Effects of triethylamine on the conversion of DMO to EMO and DEO at 80℃

[0032]

[0033] The data in Table 1 show that the homogeneous triethylamine catalyst exhibits excellent performance in converting DMO to alkyl oxalate. After only 1 minute of reaction at 80℃, the DMO conversion rate reached 83.64%, with an EMO selectivity of 71.88% and a DEO selectivity of 28.12%, indicating that triethylamine possesses excellent catalytic ability for DMO conversion.

[0034] Example 2

[0035] like Figure 1The process shown, along with a pilot-scale experiment for the synthesis of 200 tons / year of oxalate, uses dimethyl oxalate and ethanol in a molar ratio of 1 / 4 to 1 / 6, with triethylamine as the catalyst (3% of the DMO mass). The transesterification reaction occurs in a pre-reactor at a temperature of 40-110℃. The resulting mixture is pumped to a reactive distillation column (10m high, 200mm inner diameter, packed with φ6 θ-ring packing). The reaction continues within the column, and byproduct separation is achieved. The generated methanol byproduct is separated from the reaction system at the top of the column. The top temperature is controlled at 63-64℃, with a reflux ratio between 1 / 1 and 3 / 1, achieving a methanol purity of over 99.9% at the top. After 5-8 hours of reaction, the DMO conversion rate in the bottom of the column approaches 99%, with a DEO selectivity approaching 95%. The bottom product of the reactive distillation column is pumped to the catalyst recovery column, with a controlled pressure of 50-80 kPa and a bottom temperature below 130℃. Triethylamine and unreacted ethanol recovered from the top are then recycled back to the pre-reactor after being dehydrated using a 4A molecular sieve. The bottom product of the catalyst recovery column is then pumped to the product distillation column for vacuum separation, with multiple side streams. Since DMO, EMO, and DEO are completely non-azeotropic, they are very easy to separate. The theoretical number of plates in the product distillation column is approximately 40, with a packing height of 4m, φ8θ ring packing, and a controlled pressure of 1-5 kPa, yielding EMO and DEO with a purity close to 99.99%.

Claims

1. A method for synthesizing alkyl oxalate using a highly efficient catalyst, characterized in that, The method includes the following process steps: (1) The raw materials, dimethyl oxalate and ethanol, first undergo transesterification in a fixed-bed or slurry-bed pre-reactor; (2) The liquid mixture generated in the pre-reactor enters the reactive distillation column for further reaction and separation of the by-product methanol; (3) The bottom material of the reactive distillation column enters the catalyst recovery column to separate the excess ethanol and triethylamine catalyst under reduced pressure, and then returns it to the pre-reactor after dehydration. (4) The bottom material of the catalyst recovery tower enters the product distillation tower and is separated into methyl ethyl oxalate and diethyl oxalate under reduced pressure. The specific process of step (1) is as follows: The raw materials, dimethyl oxalate and ethanol, first react in a fixed-bed or slurry-bed pre-reactor under the action of triethylamine catalyst at a reaction temperature of 70–110 °C.

2. The method for synthesizing alkyl oxalate using a highly efficient catalyst according to claim 1, characterized in that, This method involves homogeneous catalytic transesterification to synthesize methyl ethyl oxalate. The feed molar ratio of dimethyl oxalate (purity greater than 98%) and ethanol (purity greater than 99.5%) is 1:0.5 to 1:

6.

3. The method for synthesizing alkyl oxalate using a highly efficient catalyst according to claim 1, characterized in that, The reaction temperature of the pre-reactor is 40–110°C.

4. The method for synthesizing alkyl oxalate using a highly efficient catalyst according to claim 1, characterized in that, The reactive distillation column simultaneously performs the reaction and distillation. The product generated by the reaction is a non-azeotropic substance. The byproduct methanol is separated in a single column to obtain methanol with a purity of 99.9%.

5. The method for synthesizing alkyl oxalate using a highly efficient catalyst according to claim 1, characterized in that, The catalyst recovery tower operates under reduced pressure, with a pressure range of 50–80 kPa. The distilled ethanol and triethylamine catalyst are dehydrated and returned to the pre-reactor for recycling.

6. The method for synthesizing alkyl oxalate using a highly efficient catalyst according to claim 1, characterized in that, The distillation column has multiple side-stream outputs and operates under reduced pressure, ranging from 1 to 5 kPa, to obtain methyl ethyl oxalate and diethyl oxalate with a purity close to 99.99%.

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