A method for the continuous production of diethyl maleate in a microchannel

Abstract

The application provides a method for continuously preparing maleic acid diethyl ester in a microchannel, comprising the following steps: mixing maleic anhydride and anhydrous ethanol, and then feeding the mixture into a micro-mixer A for pre-reaction to obtain a mixed solution containing mono-ester; feeding the mono-ester mixed solution into a micro-reactor B for esterification reaction with a mixed solution of sulfuric acid / anhydrous ethanol; collecting the solution flowing out of the reactor, and then purifying, drying and vacuum distilling the solution to obtain maleic acid diethyl ester product. The preparation process utilizes the high heat and mass transfer of the microchannel reactor, realizes continuous reaction, effectively improves the product selectivity and product yield, and does not need a water-carrying agent in the reaction, and the energy consumption of synthesis is low.

Description

Technical Field

[0001] This invention relates to a method for preparing diethyl maleate, and more specifically, to a method for the continuous microchannel preparation of diethyl maleate. Background Technology

[0002] Diethyl maleate, also known as diethyl maleate or dehydrated diethyl malate, is a dicarboxylic acid ester. It is a colorless, transparent liquid with a unique aromatic odor and is an important organic intermediate. Possessing double bonds and ester groups, it has wide applications in polymer materials, pharmaceuticals, pesticides, and fine chemicals. The first step of the diethyl maleate reaction is spontaneous, involving a ring-opening reaction at a specific temperature to produce monoethyl maleate, requiring no catalyst. The second step requires concentrated sulfuric acid as a catalyst to promote the reaction of monoethyl maleate with ethanol to produce diethyl maleate, and this reaction requires a relatively high temperature.

[0003] Currently, the main production processes for diethyl maleate include batch processes, continuous processes, and one-pot catalytic conversion of lignocellulose. The esterification reaction of maleic anhydride with anhydrous ethanol exists in chemical equilibrium, and the presence of reactive double bonds in maleic anhydride makes it highly susceptible to side reactions such as polymerization and oxidation during ester synthesis. Traditional batch processes typically involve adding dehydrating agents (benzene, toluene, and cyclohexane) to form a ternary azeotrope with anhydrous ethanol and water, thus removing water from the reaction system and directing the reaction towards ester formation. Traditional production processes use concentrated sulfuric acid as a catalyst, which offers high catalytic activity and low cost, but isomerization is common, leading to numerous side reactions, dark-colored products, and the corrosive nature of concentrated sulfuric acid on equipment, causing environmental pollution. Continuous production processes, which have been developed and applied, typically use cation exchange resins, solid superacids, and heteropolyacids as catalysts, but these catalysts are expensive and have limited catalytic performance. The one-pot catalytic conversion of lignocellulose, as an emerging synthetic process, is currently in the laboratory stage. Therefore, there is an urgent need to develop a process for the continuous production of diethyl maleate.

[0004] Continuous flow microreactors, also known as flow chemistry, are an advanced chemical production process that involves chemical reactions occurring in a continuous flow environment. Multi-stage processing replaces inter-step chemical operations. Microreactors in continuous flow microreactors can easily scale up laboratory-scale reactions to industrial scale by simply increasing the number or size of the reactors. These microreactors exhibit miniaturization and ease of assembly, integrating various functional reaction modules into a multifunctional, integrated reactor. This reduces equipment size and weight while extending continuous operating time. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for the continuous preparation of diethyl maleate in microchannels.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for the continuous microchannel preparation of diethyl maleate is characterized by being carried out in a plate microreactor, which consists of a micromixer A and a microreactor B connected by a connecting pipe. Maleic anhydride and anhydrous ethanol are pre-reacted in micromixer A to obtain a mixed solution containing monoesters. Then, an esterification reaction is carried out in microreactor B with a mixed solution of sulfuric acid and anhydrous ethanol. The solution flowing out of the reactor is collected, purified by separation, dried, and distilled under reduced pressure to obtain diethyl maleate.

[0007] Preferably, in the above-described method for continuous microchannel preparation of diethyl maleate, the micromixer A is composed of multiple droplet-shaped units connected in series, and the microreactor B is composed of multiple heart-shaped units connected in series.

[0008] Preferably, in the above-described method for the continuous microchannel preparation of diethyl maleate, the molar ratio of maleic anhydride to anhydrous ethanol is 1:3 to 1:8.

[0009] Preferably, in the above-described microchannel continuous preparation method for diethyl maleate, the molar ratio of maleic anhydride to sulfuric acid is 1:0.02 to 1:0.25.

[0010] Preferably, in the above-described method for the continuous microchannel preparation of diethyl maleate, the temperature inside the micromixer A is 30~90°C.

[0011] Preferably, in the above-described method for continuous microchannel preparation of diethyl maleate, the temperature of the microreactor B is 60~120℃.

[0012] Compared with existing technologies, the present invention has the following advantages: The microchannel continuous preparation method for diethyl maleate provided by the present invention is simple and can be continuously produced; the droplet-shaped unit of the micro-mixed gas A achieves efficient molecular diffusion through "segmentation-recombination", realizing perfect premixing and effectively avoiding side reactions or product decomposition caused by local overheating; the baffles and curved channels in the microreactor B induce the deformation and controllable breakage of bubbles or liquids, producing smaller droplets and larger phase interfaces, resulting in a larger contact area of ​​raw materials during the reaction process, higher mass and heat transfer efficiency, effectively reducing by-products in the product, and increasing the selectivity and yield of diethyl maleate; the two-stage reaction process makes the maleic anhydride reaction more complete and promotes a more thorough esterification reaction; the modular design of the microreactor makes the reaction easy to scale up for production. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the microchannel reaction process of the present invention. A represents the micromixer and its internal unit structure; B represents the microreactor and its internal unit structure; 1 and 3 represent the reaction liquid inlets; 2 represents the connecting pipe between micromixer A and microreactor B; and 4 represents the product collection port. Detailed Implementation

[0014] The present invention is illustrated by the following embodiments, but is not limited to these embodiments. Variations are included within the scope of the present invention without departing from the spirit of the preceding description. Example 1

[0015] like Figure 1 As shown, the reaction apparatus consists of a micromixer A and a microreactor B connected in series via a connecting pipe 2. Micromixer A is composed of 16 teardrop-shaped units connected in series, and microreactor B is composed of 8 heart-shaped units connected in series. 1 is the reaction liquid inlet of micromixer A, 3 is the reaction liquid inlet of microreactor B, and 4 is the product collection port.

[0016] 10g of maleic anhydride and 23.3mL of ethanol were dissolved by heating and stirring to obtain a mixed solution. This mixed solution was then pumped into micromixer A, which was set to a temperature of 65°C. o C. The product from micromixer A is directly fed into microreactor B via a connecting pipe. 0.5 mL of sulfuric acid and 23.3 mL of anhydrous ethanol are mixed and then subjected to an esterification reaction in microreactor B via inlet 3 continuous reaction. The temperature of the microreactor is 85°C. o C. The product after the reaction was collected at collection port 4, purified by separation, dried and distilled under reduced pressure to obtain diethyl maleate. The esterification rate of diethyl maleate was determined to be 97.8%.

[0017] Example 2: The reaction apparatus is the same as in Example 1.

[0018] 10g of maleic anhydride and 23.3mL of ethanol were dissolved by heating and stirring to obtain a mixed solution. This mixed solution was then pumped into micromixer A, which was set to a temperature of 50°C. o C. The product from micromixer A is directly fed into microreactor B via a connecting pipe. 0.5 mL of sulfuric acid and 18 mL of anhydrous ethanol are mixed and then subjected to an esterification reaction in continuous microreactor B via an inlet. The temperature of the microreactor is 90°C. o C. The product after the reaction was collected at collection port 4, purified by separation, dried and distilled under reduced pressure to obtain diethyl maleate. The esterification rate of diethyl maleate was determined to be 98.8%.

[0019] Example 3: The reaction apparatus is the same as in Example 1.

[0020] 10g of maleic anhydride and 18mL of ethanol were dissolved by heating and stirring to obtain a mixed solution. This mixed solution was then pumped into micromixer A, which was set to a temperature of 70°C. o C. The product from micromixer A is directly fed into microreactor B via a connecting pipe. 0.5 mL of sulfuric acid and 18 mL of anhydrous ethanol are mixed and then subjected to esterification in continuous reaction microreactor B via an inlet. The temperature of the microreactor is 85°C. o C. The product after the reaction was collected at collection port 4, purified by separation, dried and distilled under reduced pressure to obtain diethyl maleate. The esterification rate of diethyl maleate was determined to be 97.4%.

[0021] Example 4: The reaction apparatus is the same as in Example 1.

[0022] 10g of maleic anhydride and 23.3mL of ethanol were dissolved by heating and stirring to obtain a mixed solution. This mixed solution was then pumped into micromixer A, which was set to a temperature of 65°C. o C. The product from micromixer A is directly fed into microreactor B via a connecting pipe. 0.5 mL of sulfuric acid and 23.3 mL of anhydrous ethanol are mixed and then subjected to an esterification reaction in microreactor B via inlet 3 continuous reaction. The temperature of the microreactor is 85°C. o C. The product after the reaction was collected at collection port 4, purified by separation, dried and distilled under reduced pressure to obtain diethyl maleate. The esterification rate of diethyl maleate was determined to be 97.3%.

[0023] Example 5: The reaction apparatus is the same as in Example 1, except that the number of micromixers A is changed to 8 sets in series, and the number of microreactors B is changed to 5 sets in series.

[0024] 100g of maleic anhydride and 200mL of ethanol were dissolved by heating and stirring to obtain a mixed solution. This mixed solution was then pumped into micromixer A, whose temperature was 65°C. o C. The product from micromixer A is directly fed into microreactor B via a connecting pipe. 4 mL of sulfuric acid and 200 mL of anhydrous ethanol are mixed and then subjected to an esterification reaction in continuous reaction microreactor B via an inlet. The temperature of the microreactor is 85°C. o C. The product after the reaction was collected at collection port 4, purified by separation, dried and distilled under reduced pressure to obtain diethyl maleate. The esterification rate of diethyl maleate was determined to be 98.7%.

[0025] Example 6: The reaction apparatus is the same as in Example 1, except that the number of micromixers A is changed to 6 sets in series, and the number of microreactors B is changed to 5 sets in series.

[0026] 100g of maleic anhydride and 200mL of ethanol were dissolved by heating and stirring to obtain a mixed solution. This mixed solution was then pumped into micromixer A, whose temperature was 65°C. o C. The product from micromixer A is directly fed into microreactor B via a connecting pipe. 4 mL of sulfuric acid and 200 mL of anhydrous ethanol are mixed and then subjected to an esterification reaction in continuous reaction microreactor B via an inlet. The temperature of the microreactor is 85°C. o C. The product after the reaction was collected at collection port 4, purified by separation, dried and distilled under reduced pressure to obtain diethyl maleate. The esterification rate of diethyl maleate was determined to be 99.1%.

[0027] Comparative Example 1: The traditional batch synthesis method was used. 10 g of maleic anhydride, 23.3 mL of ethanol, 0.5 mL of concentrated sulfuric acid, and 16 mL of cyclohexane were added to a round-bottom flask and heated to 80 °C. o The mixture was stirred and refluxed at C for 4 hours, after which the reaction was stopped. After cooling, the product was neutralized, purified by separation, dried, and distilled under reduced pressure to obtain diethyl maleate with a conversion rate of 75.1%.

Claims

1. A method for the continuous microchannel preparation of diethyl maleate, characterized in that: The reaction is carried out in a plate microreactor, which consists of a micromixer (A) and a microreactor (B). The micromixer (A) and the microreactor (B) are connected by a connecting pipe. Maleic anhydride and anhydrous ethanol are pre-reacted in the micromixer (A) to obtain a mixed solution containing monoester. Then, the solution undergoes an esterification reaction with a mixed solution of sulfuric acid and anhydrous ethanol in the microreactor (B). The solution flowing out of the reactor is collected, purified by separation, dried and distilled under reduced pressure to obtain diethyl maleate.

2. The method for continuous microchannel preparation of diethyl maleate according to claim 1, characterized in that, The micromixer (A) is composed of multiple teardrop-shaped units connected in series, and the microreactor (B) is composed of multiple heart-shaped units connected in series.

3. The method for continuous microchannel preparation of diethyl maleate according to claim 1, characterized in that, The molar ratio of maleic anhydride to anhydrous ethanol is 1:3 to 1:

8.

4. The method for continuous microchannel preparation of diethyl maleate according to claim 1, characterized in that, The molar ratio of maleic anhydride to sulfuric acid is 1:0.02 to 1:0.

25.

5. The method for continuous microchannel preparation of diethyl maleate according to claim 1, characterized in that, The temperature inside the micro mixer (A) is 30~90℃.

6. The method for continuous microchannel preparation of diethyl maleate according to claim 1, characterized in that, The temperature of the microreactor (B) is 60~120℃.

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