Preparation method of 2-methyl ethyl butyrate

Abstract

According to the preparation method of the ethyl 2-methylbutyrate, the use of strong acid in a traditional process is reduced through green processes such as immobilized bio-enzyme catalysis and three-stage microchannel reaction, the preparation process is efficient, and the reaction conditions are green and mild. And in the preparation process of the precursor 2-methylbutyric acid, 2-methylbutanol and hydrogen peroxide are adopted to realize high-purity and high-efficiency preparation of the precursor under the condition of an immobilized catalyst, so that a very good raw material is provided for preparing the 2-ethyl methylbutyrate, and the quality of the 2-ethyl methylbutyrate is better improved.

Description

Technical Field

[0001] This invention belongs to the field of fragrance synthesis technology, specifically relating to a method for preparing ethyl 2-methylbutyrate. Background Technology

[0002] Ethyl 2-methylbutyrate, a high-value-added food additive, possesses a strong fruity aroma reminiscent of apples and pineapples, and is widely used in flavoring beverages, dairy products, and baked goods. However, naturally occurring ethyl 2-methylbutyrate is present in extremely small amounts in nature, and its production primarily relies on chemical synthesis. Current industrial production employs a two-step process: first, the key precursor 2-methylbutyric acid is synthesized, followed by esterification to generate the target product. However, both steps suffer from the following drawbacks: First, the synthesis of the 2-methylbutyric acid precursor often involves oxidation under high-temperature, strong acid conditions. These conditions are demanding, resulting in numerous byproducts and complex subsequent processing. Second, the esterification process of ethyl 2-methylbutyrate similarly commonly uses concentrated sulfuric acid as a catalyst, triggering dehydration side reactions at high temperatures to generate olefinic ether impurities. Furthermore, the strong acid environment easily leads to contamination, making it difficult to completely remove residual sulfate ester compounds from the final product.

[0003] To overcome the pollution problem caused by concentrated sulfuric acid catalysis, lipase-catalyzed ester synthesis is considered an ideal alternative. Lipases can specifically catalyze the esterification reaction of carboxylic acids and primary alcohols under mild conditions, with water as the only byproduct, which conforms to the principles of green chemistry. However, the application of this technology suffers from insufficient enzyme activity stability, low reaction engineering efficiency, and the need for subsequent removal processes, making the process cumbersome. Immobilized enzymes can effectively improve enzyme catalytic efficiency, stability, and reusability; therefore, novel and efficient enzyme immobilization carriers are an important research direction of this application.

[0004] Microchannel reactors, by adjusting the structure and size of the microchannels, allow for precise control of reaction conditions, thus meeting the needs of different reaction systems. Furthermore, with the increasing global demand for green and sustainable production methods, microchannel reactors, as a highly efficient, energy-saving, and environmentally friendly reactor type, will receive wider attention and application. Therefore, how to apply microchannel reactors to the preparation of ethyl 2-methylbutyrate is the focus of this invention's research. Summary of the Invention

[0005] This invention discloses a method for preparing ethyl 2-methylbutyrate to solve any of the above-mentioned or potential problems in the prior art. To solve the above-mentioned technical problems, the specific process of this invention is as follows:

[0006] 80 parts of 2-methylbutyric acid and 80 parts of ethanol were subjected to a three-stage microchannel reaction. The mixture was premixed in a T-shaped microchannel with an inner diameter of 1 mm at a flow rate of 5 mL / min and a premixing temperature of 40-50 °C. The premixed solution was then pumped into a serpentine microchannel with an inner diameter of 2 mm and a length of 5 m, filled with 50-70 parts of immobilized lipase particles. The temperature was maintained at 55-60 °C for 5-7 h to obtain crude ethyl 2-methylbutyrate. A 5% sodium bicarbonate solution was added at a feed-to-solution ratio of 1:10 and stirred for 1 h. When the pH of the crude ethyl 2-methylbutyrate solution reached 7-8, it was allowed to stand. The separated aqueous solution was then placed in a wastewater treatment tank. Tap water was then added at an 8:1 ratio and stirred until it was allowed to stand. The separated wastewater was then placed in the wastewater treatment tank. The remaining crude ethyl 2-methylbutyrate was then fractionated under reduced pressure to obtain the final product.

[0007] The immobilized lipase was prepared as follows: 5 parts of lipase were dissolved in 1000 parts of pH 7.0 phosphate solution, with an enzyme activity ≥10000 U / g. SiO2 with a pore size of 50 nm was used to soak the lipase in dilute hydrochloric acid for 2 hours, washed with deionized water until neutral, dried at 110℃, and then immersed in a 2% dopamine solution. The mixture was shaken at 25℃ for 12 hours, filtered, and then immersed in an 8-20% magnesium diglycinate solution. The mixture was sonicated at 60℃ for 2 hours, centrifuged and dried, and then 100 parts of the immobilized lipase were added to the above lipase solution. The mixture was slowly shaken at 25℃ for 12 hours to adsorb the lipase. 100 parts of a 1% glutaraldehyde solution were added, and the mixture was cross-linked at 25℃ for 2 hours. After filtration, the mixture was washed three times with phosphate solution and freeze-dried for 24 hours to obtain solid immobilized lipase particles.

[0008] The process includes the preparation of 2-methylbutyric acid: 200 parts of 2-methylbutanol and 20-30 parts of immobilized catalyst are added sequentially, and 500 parts of 50% hydrogen peroxide are slowly added dropwise while maintaining the reaction temperature at 85-95℃. After the addition is completed, the reaction is continued for 3 hours. The reaction solution is cooled and transferred to a separatory funnel to separate the aqueous layer. The upper oil layer is adjusted to pH 9-10 with 10% sodium hydroxide aqueous solution and allowed to stand for separation. The organic phase is separated, and the aqueous phase is washed twice with 200 parts of methyl tert-butyl ether. Then, concentrated hydrochloric acid is added to adjust the pH to 2, and the solution is extracted twice with 200 parts of methyl tert-butyl ether. The organic layers are combined, and the solvent is removed by a rotary evaporator to obtain crude 2-methylbutyric acid. The crude product is then subjected to reduced pressure separation at -0.096 MPa to obtain the finished 2-methylbutyric acid product.

[0009] The preparation of the supported catalyst is as follows: 500 parts of toluene solution are added to 50 parts of SiO2, stirred and suspended, then 120 parts of 3-aminopropyltriethoxysilane are added, refluxed under N2 protection for 12 h, filtered, washed three times with anhydrous toluene, and dried under vacuum at 80 °C to obtain aminated SiO2. 10 parts of aminated SiO2 are added to 1200-1600 parts of ligand solution, 3-5 parts of manganese acetate tetrahydrate are added, 600 parts of water are added, stirred at 60 °C for 24 h, filtered, washed three times with ethanol, and dried under vacuum at 40 °C for 12 h to obtain the supported catalyst.

[0010] The ligand solution is prepared by mixing 2,2'-bipyridine-4,4'-dicarboxylic acid, DMF, and water in a ratio of 1:5:3.

[0011] The advantages and beneficial effects of this invention are as follows:

[0012] 1. This process achieves a green upgrade across the entire chain through the system integration of immobilized manganese catalyst, immobilized lipase technology, and a three-stage microchannel reactor. In the synthesis of 2-methylbutyric acid, the manganese-bipyridine carboxylic acid catalyst supported by aminated SiO2 precisely activates hydrogen peroxide through molecular-level active sites, avoiding the severe exothermic risks of traditional strong acid processes and the precious metal dependence of palladium-carbon systems, resulting in a significant improvement in product yield. For the synthesis of ethyl 2-methylbutyrate, an immobilized lipase carrier activated by non-toxic polydopamine and magnesium diglycinate maintains an enzyme activity of ≥10,000 U / g, replacing concentrated sulfuric acid catalysis. Combined with a three-stage microchannel reactor, continuous flow enzyme catalysis is achieved, improving mass transfer efficiency, shortening reaction time, and increasing yield. Furthermore, the immobilized enzyme can be recycled, providing a safe, efficient, and low-consumption new process for flavor production.

[0013] 2,2-Methylbutyrate ethyl ester was prepared using a biocatalytic process to create a non-toxic, highly stable immobilized lipase carrier. The carrier construction consisted of three steps: First, utilizing the self-polymerization properties of dopamine in a weakly alkaline environment, a uniform polydopamine biomimetic coating was formed on the surface of mesoporous SiO2. This coating significantly increased the specific surface area and enzyme loading site density through strong interactions between the phenolic hydroxyl / amino groups and the carrier and enzyme. Subsequently, a magnesium diglycinate solution was introduced for activation. Magnesium ions acted as a cofactor for the lipase, gently activating the catalytic active center. Simultaneously, the diglycinate ligand stabilized the metal ions through chelation, replacing traditional toxic metal ions and eliminating the potential for toxic residues in food additive production. The enzyme molecules in the lipase were first adsorbed onto the carrier via electrostatic interactions, and then moderately cross-linked with a low concentration of glutaraldehyde to form "flexibly bound" immobilized enzyme particles. This structure maximally preserves the enzyme's spatial conformation, maintaining enzyme activity at a high level.

[0014] 3. Traditional methods for preparing ethyl 2-methylbutyrate require the use of highly corrosive concentrated sulfuric acid, leading to equipment damage, side reactions, and large amounts of saline wastewater. In contrast, immobilized lipases specifically catalyze the esterification of acids and primary alcohols under mild conditions, producing no acidic wastewater. Furthermore, the enzyme's stereoselectivity to the substrate inhibits the formation of branched isomers, ensuring the product's optical purity meets food additive standards, further guaranteeing high purity and high yield of the final product.

[0015] 4. To achieve efficient utilization of the immobilized enzyme, this process employs a three-stage microchannel reactor system: the first stage is a T-shaped mixing channel, where premixing ensures molecular-level homogenization of 2-methylbutyric acid and ethanol; the second stage is a serpentine reaction channel filled with the immobilized enzyme, where enzyme particles form a stable packed bed within the microchannels. The advantages of the microreactor are: firstly, high mass and heat transfer efficiency; the high specific surface area within the channel enhances substrate-enzyme contact efficiency, resulting in a higher reaction rate compared to batch-type processes; secondly, precise process control; a constant temperature environment prevents enzyme inactivation due to localized overheating; and the continuous flow mode eliminates batch variations, ensuring a stable esterification yield of over 95%; thirdly, enhanced catalyst recyclability; and fourthly, the enzyme particles, rigidly confined within the reaction channel, can be reused, significantly reducing production costs.

[0016] 5. This process first achieves efficient synthesis of 2-methylbutyric acid through a highly active heterogeneous catalyst. Its core lies in the unique structure of a manganese-bipyridine carboxylic acid complex supported on amino-functionalized silica. The SiO2 surface is covalently modified with 3-aminopropyltriethoxysilane to form an amino-rich support framework; subsequently, manganese active centers are constructed in situ on the support surface using the coordination interaction between 2,2'-bipyridine-4,4'-dicarboxylic acid and manganese acetate. First, the amino functional group acts as a strong coordination site to immobilize manganese ions, firmly anchoring the metal ions through nitrogen-manganese bonds and significantly reducing the risk of manganese dissolution during the reaction. Second, the rigid conjugated structure of the bipyridine carboxylic acid ligand optimizes the electron cloud distribution of the manganese center, enhancing its activation ability for hydrogen peroxide and enabling the oxidation reaction to proceed efficiently under mild conditions. Third, compared with traditional strong acid oxidation processes, it avoids the risk of severe exothermic reactions under strong acid environments. More importantly, compared with conventional solid acid catalysts, this catalyst system achieves high selectivity for primary alcohol oxidation through molecular-level active site design, significantly reducing excessive oxidation side reactions and providing high-quality raw materials for subsequent esterification steps. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the embodiments. The lipase used below is Candida antarctica B, with a molecular weight of 33kDa, purchased from Guangzhou Weber Technology Co., Ltd. The SiO2 used below has a pore size of 50nm and a specific surface area of ​​300m² / g.

[0018] Example 1

[0019] Preparation of the immobilized catalyst: 500 parts of toluene solution were added to 50 parts of SiO2 and stirred to suspend the mixture. Then 120 parts of 3-aminopropyltriethoxysilane were added, and the mixture was refluxed under N2 protection for 12 h. After filtration, the mixture was washed three times with anhydrous toluene and dried under vacuum at 80 °C to obtain aminated SiO2. 10 parts of the aminated SiO2 were added to 1400 parts of ligand solution, which was obtained by mixing 2,2'-bipyridine-4,4'-dicarboxylic acid, DMF, and water in a ratio of 1:5:3. 4 parts of manganese acetate tetrahydrate were added, followed by 600 parts of water. The mixture was stirred at 60 °C for 24 h, filtered, washed three times with ethanol, and dried under vacuum at 40 °C for 12 h to obtain the immobilized catalyst.

[0020] Preparation process of 2-methylbutyric acid: 200 parts of 2-methylbutanol and 25 parts of immobilized catalyst were added sequentially, and 500 parts of 50% hydrogen peroxide were slowly added dropwise. The reaction temperature was maintained at 90℃. After the addition was completed, the reaction was continued at this temperature for 3 hours. The reaction solution was cooled and transferred to a separatory funnel to separate the aqueous layer. The upper oil layer was adjusted to pH 9.5 with 10% sodium hydroxide aqueous solution. The mixture was allowed to stand and separate into layers. The organic phase was separated. The aqueous phase was washed twice with 200 parts of methyl tert-butyl ether. The pH was then adjusted to 2 with concentrated hydrochloric acid. The mixture was extracted twice with 200 parts of methyl tert-butyl ether. The organic layers were combined, and the solvent was removed by a rotary evaporator to obtain crude 2-methylbutyric acid. The crude product was then subjected to reduced pressure separation at -0.096 MPa to obtain the final 2-methylbutyric acid product.

[0021] Example 2

[0022] Preparation of the immobilized catalyst: 500 parts of toluene solution were added to 50 parts of SiO2 and stirred to suspend the mixture. Then, 120 parts of 3-aminopropyltriethoxysilane were added, and the mixture was refluxed for 12 h under N2 protection. After filtration, the mixture was washed three times with anhydrous toluene and dried under vacuum at 80 °C to obtain aminated SiO2. 10 parts of the aminated SiO2 were added to 1200 parts of a ligand solution, which was obtained by mixing 2,2'-bipyridine-4,4'-dicarboxylic acid, DMF, and water in a ratio of 1:5:3. 5 parts of manganese acetate tetrahydrate were added, followed by 600 parts of water. The mixture was stirred at 60 °C for 24 h, filtered, washed three times with ethanol, and dried under vacuum at 40 °C for 12 h to obtain the immobilized catalyst.

[0023] Preparation process of 2-methylbutyric acid: 200 parts of 2-methylbutanol and 20 parts of immobilized catalyst were added sequentially, and 500 parts of 50% hydrogen peroxide were slowly added dropwise. The reaction temperature was maintained at 95℃. After the addition was completed, the reaction was continued at this temperature for 3 hours. The reaction solution was cooled and transferred to a separatory funnel to separate the aqueous layer. The upper oil layer was adjusted to pH 9 with 10% sodium hydroxide aqueous solution and allowed to stand for separation. The organic phase was separated. The aqueous phase was washed twice with 200 parts of methyl tert-butyl ether, and then concentrated hydrochloric acid was added to adjust the pH to 2. The solution was extracted twice with 200 parts of methyl tert-butyl ether. The organic layers were combined, and the solvent was removed by a rotary evaporator to obtain crude 2-methylbutyric acid. The crude product was then subjected to reduced pressure separation at -0.096 MPa to obtain the finished 2-methylbutyric acid product.

[0024] Example 3

[0025] Preparation of the immobilized catalyst: 500 parts of toluene solution were added to 50 parts of SiO2 and stirred to suspend the catalyst. Then 120 parts of 3-aminopropyltriethoxysilane were added, and the mixture was refluxed under N2 protection for 12 h. The mixture was filtered, washed three times with anhydrous toluene, and dried under vacuum at 80 °C to obtain aminated SiO2. 10 parts of the aminated SiO2 were added to 1600 parts of ligand solution, which was obtained by mixing 2,2'-bipyridine-4,4'-dicarboxylic acid, DMF, and water in a ratio of 1:5:3. 3 parts of manganese acetate tetrahydrate and 600 parts of water were added. The mixture was stirred at 60 °C for 24 h, filtered, washed three times with ethanol, and dried under vacuum at 40 °C for 12 h to obtain the immobilized catalyst.

[0026] Preparation process of 2-methylbutyric acid: 200 parts of 2-methylbutanol and 30 parts of immobilized catalyst were added sequentially, and 500 parts of 50% hydrogen peroxide were slowly added dropwise. The reaction temperature was maintained at 85℃. After the addition was completed, the reaction was continued at this temperature for 3 hours. The reaction solution was cooled and transferred to a separatory funnel to separate the aqueous layer. The upper oil layer was adjusted to pH 10 with 10% sodium hydroxide aqueous solution and allowed to stand for separation. The organic phase was separated. The aqueous phase was washed twice with 200 parts of methyl tert-butyl ether, and then concentrated hydrochloric acid was added to adjust the pH to 2. The solution was extracted twice with 200 parts of methyl tert-butyl ether. The organic layers were combined, and the solvent was removed by a rotary evaporator to obtain crude 2-methylbutyric acid. The crude product was then subjected to reduced pressure separation at -0.096 MPa to obtain the finished 2-methylbutyric acid product.

[0027] Comparative Example 1

[0028] The difference between this comparative example and Example 1 is that the supported catalyst in this comparative example is replaced with trioctylmethylammonium bromide; otherwise, it is the same as in Example 1.

[0029] Comparative Example 2

[0030] The difference between this comparative example and Example 1 is that no ligand solution will be added in this comparative example. The specific preparation method is as follows:

[0031] Preparation of the immobilized catalyst: 500 parts of toluene solution were added to 50 parts of SiO2 and stirred to suspend the solution. Then 120 parts of 3-aminopropyltriethoxysilane were added and the mixture was refluxed under N2 protection for 12 h. The mixture was filtered, washed three times with anhydrous toluene, and dried under vacuum at 80 °C to obtain aminated SiO2. 4 parts of manganese acetate tetrahydrate were added, followed by 600 parts of water. The mixture was stirred at 60 °C for 24 h, filtered, washed three times with ethanol, and dried under vacuum at 40 °C for 12 h to obtain the immobilized catalyst.

[0032] Preparation process of 2-methylbutyric acid: 200 parts of 2-methylbutanol and 25 parts of immobilized catalyst were added sequentially, and 500 parts of 50% hydrogen peroxide were slowly added dropwise. The reaction temperature was maintained at 90℃. After the addition was completed, the reaction was continued at this temperature for 3 hours. The reaction solution was cooled and transferred to a separatory funnel to separate the aqueous layer. The upper oil layer was adjusted to pH 9.5 with 10% sodium hydroxide aqueous solution. The mixture was allowed to stand and separate into layers. The organic phase was separated. The aqueous phase was washed twice with 200 parts of methyl tert-butyl ether. The pH was then adjusted to 2 with concentrated hydrochloric acid. The mixture was extracted twice with 200 parts of methyl tert-butyl ether. The organic layers were combined, and the solvent was removed by a rotary evaporator to obtain crude 2-methylbutyric acid. The crude product was then subjected to reduced pressure separation at -0.096 MPa to obtain the final 2-methylbutyric acid product.

[0033] Comparative Example 3

[0034] The difference between this comparative example and Example 1 is that 2,2'-bipyridine-4,4'-dicarboxylic acid is replaced with ethylenediaminetetraacetic acid in this comparative example; the rest is the same as in Example 1.

[0035] Experiment 1: Determination of 2-methylbutyric acid

[0036] The final synthesis rate of 2-methylbutyric acid was determined according to GB / T 11538-2006, and the purity of the obtained 2-methylbutyric acid was measured using a flame ionization detector (FID) in section 10.4. The refractive index was measured according to GB / T 14454.4. The results are shown in Table 1 below.

[0037] Table 1

[0038] Group Synthesis rate (%) Purity content (%) Refractive index relative density Example 1 96.25 99.6 1.4062 0.9356 Example 2 95.84 99.5 1.4058 0.9355 Example 3 95.27 99.3 1.4060 0.9351 Comparative Example 1 87.52 95.4 1.4041 0.9310 Comparative Example 2 90.46 96.2 1.4047 0.9315 Comparative Example 3 91.51 98.0 1.4051 0.9323

[0039] The 2-methylbutyric acid used in the following embodiments is derived from Example 1.

[0040] Example 4

[0041] Preparation of immobilized lipase: 5 parts of lipase were dissolved in 1000 parts of pH 7.0 phosphate solution, with an enzyme activity ≥10000 U / g. SiO2 with a pore size of 50 nm was used to soak the lipase in dilute hydrochloric acid for 2 h, washed with deionized water until neutral, dried at 110℃, and then immersed in a 2% dopamine solution. The mixture was shaken at 25℃ for 12 h, filtered, and then immersed in a 14% magnesium diglycinate solution. The mixture was sonicated at 60℃ for 2 h, centrifuged and dried, and then 100 parts of the immobilized lipase were added to the above lipase solution. The mixture was slowly shaken at 25℃ for 12 h to adsorb the lipase. 100 parts of a 1% glutaraldehyde solution were added, and the mixture was crosslinked at 25℃ for 2 h. After filtration, the mixture was washed three times with phosphate solution and freeze-dried for 24 h to obtain solid immobilized lipase particles.

[0042] Preparation of ethyl 2-methylbutyrate: 80 parts of 2-methylbutyric acid and 80 parts of ethanol were subjected to a three-stage microchannel reaction. The mixture was premixed in a T-shaped microchannel with an inner diameter of 1 mm at a flow rate of 5 mL / min and a premixing temperature of 45 °C. The premixed solution was then pumped into a serpentine microchannel with an inner diameter of 2 mm and a length of 5 m, filled with 60 parts of immobilized lipase particles. The temperature was maintained at 58 °C for 6 h to obtain crude ethyl 2-methylbutyrate. A 5% sodium bicarbonate solution was added at a feed-to-solution ratio of 1:10 and stirred for 1 h. When the pH of the crude ethyl 2-methylbutyrate solution reached 7.5, it was allowed to stand. The separated aqueous solution was then placed in a wastewater treatment tank. Tap water was then added at an 8:1 ratio and stirred until set. The separated wastewater was then placed in the wastewater treatment tank. The remaining crude ethyl 2-methylbutyrate was obtained by vacuum fractionation.

[0043] Example 5

[0044] Preparation of immobilized lipase: 5 parts of lipase were dissolved in 1000 parts of pH 7.0 phosphate solution, with an enzyme activity ≥10000 U / g. SiO2 with a pore size of 50 nm was used to soak the lipase in dilute hydrochloric acid for 2 h, washed with deionized water until neutral, dried at 110℃, and then immersed in a 2% dopamine solution. The mixture was shaken at 25℃ for 12 h, filtered, and then immersed in a 20% magnesium diglycinate solution. The mixture was sonicated at 60℃ for 2 h, centrifuged and dried, and then 100 parts of the immobilized lipase were added to the above lipase solution. The mixture was slowly shaken at 25℃ for 12 h to adsorb the lipase. 100 parts of a 1% glutaraldehyde solution were added, and the mixture was cross-linked at 25℃ for 2 h. After filtration, the mixture was washed three times with phosphate solution and freeze-dried for 24 h to obtain solid immobilized lipase particles.

[0045] Preparation of ethyl 2-methylbutyrate: 80 parts of 2-methylbutyric acid and 80 parts of ethanol were subjected to a three-stage microchannel reaction. The mixture was premixed in a T-shaped microchannel with an inner diameter of 1 mm at a flow rate of 5 mL / min and a premixing temperature of 50 °C. The premixed solution was then pumped into a serpentine microchannel with an inner diameter of 2 mm and a length of 5 m, filled with 50 parts of immobilized lipase particles. The temperature was maintained at 60 °C for 7 h to obtain crude ethyl 2-methylbutyrate. A 5% sodium bicarbonate solution was added at a feed-to-solution ratio of 1:10 and stirred for 1 h. When the pH of the crude ethyl 2-methylbutyrate solution reached 8, it was allowed to stand. The separated aqueous solution was then placed in a wastewater treatment tank. Tap water was then added at an 8:1 ratio and stirred until it was allowed to stand. The separated wastewater was then placed in the wastewater treatment tank. The remaining crude ethyl 2-methylbutyrate was obtained by vacuum fractionation.

[0046] Example 6

[0047] Preparation of immobilized lipase: 5 parts of lipase were dissolved in 1000 parts of pH 7.0 phosphate solution, with an enzyme activity ≥10000 U / g. SiO2 with a pore size of 50 nm was used to soak the lipase in dilute hydrochloric acid for 2 h, washed with deionized water until neutral, dried at 110℃, and then immersed in a 2% dopamine solution. The mixture was shaken at 25℃ for 12 h, filtered, and then immersed in an 8% magnesium diglycinate solution. The mixture was sonicated at 60℃ for 2 h, centrifuged and dried, and then 100 parts of the immobilized lipase were added to the above lipase solution. The mixture was slowly shaken at 25℃ for 12 h to adsorb the lipase. 100 parts of a 1% glutaraldehyde solution were added, and the mixture was cross-linked at 25℃ for 2 h. After filtration, the mixture was washed three times with phosphate solution and freeze-dried for 24 h to obtain solid immobilized lipase particles.

[0048] Preparation of ethyl 2-methylbutyrate: 80 parts of 2-methylbutyric acid and 80 parts of ethanol were subjected to a three-stage microchannel reaction. The mixture was premixed in a T-shaped microchannel with an inner diameter of 1 mm at a flow rate of 5 mL / min and a premixing temperature of 40 °C. The premixed solution was then pumped into a serpentine microchannel with an inner diameter of 2 mm and a length of 5 m, filled with 70 parts of immobilized lipase particles. The temperature was maintained at 55 °C for 5 h to obtain crude ethyl 2-methylbutyrate. A 5% sodium bicarbonate solution was added at a feed-to-solution ratio of 1:10 and stirred for 1 h. When the pH of the crude ethyl 2-methylbutyrate solution reached 7, it was allowed to stand. The separated aqueous solution was then placed in a wastewater treatment tank. Tap water was then added at an 8:1 ratio and stirred until it was allowed to stand. The separated wastewater was then placed in the wastewater treatment tank. The remaining crude ethyl 2-methylbutyrate was obtained by vacuum fractionation.

[0049] Comparative Example 4

[0050] 80 parts of 2-methylbutyric acid, 80 parts of ethanol, and 10 parts of zirconium oxide sulfate were reacted at 120°C for 10 hours. After cooling and washing, crude ethyl 2-methylbutyrate was obtained. A 5% sodium bicarbonate solution was added at a ratio of 1:10 and stirred for 1 hour. When the pH of the crude ethyl 2-methylbutyrate solution reached 7, it was allowed to stand. The aqueous solution after settling and separation was placed in a wastewater treatment tank. Then, tap water was added at a ratio of 8:1 and stirred until settling. The wastewater after settling and separation was placed in the wastewater treatment tank. The remaining crude ethyl 2-methylbutyrate was obtained by vacuum fractionation.

[0051] Comparative Example 5

[0052] The difference between this comparative example and Example 1 is that in this comparative example, ethyl 2-methylbutyrate was prepared as follows: 80 parts of 2-methylbutyric acid and 80 parts of ethanol were added to a reaction vessel and heated to 40-50°C. Then, 50-70 parts of immobilized lipase were added and heated to 55-60°C for 5-7 hours to obtain crude ethyl 2-methylbutyrate. A 5% sodium bicarbonate solution was added at a ratio of 1:10 and stirred for 1 hour. When the pH of the crude ethyl 2-methylbutyrate solution was 7-8, it was allowed to stand. The aqueous solution after standing and separating was placed in a wastewater treatment tank. Then, tap water was added at a ratio of 8:1 and stirred and allowed to stand. The wastewater after standing and separating was placed in a wastewater treatment tank. The remaining crude ethyl 2-methylbutyrate was obtained by vacuum fractionation. The rest was the same as in Example 1.

[0053] Comparative Example 6

[0054] The preparation of ethyl 2-methylbutyrate is as follows: 80 parts of 2-methylbutyric acid and 80 parts of ethanol are reacted in a three-stage microchannel reaction. The mixture is premixed in a T-type microchannel with an inner diameter of 1 mm at a flow rate of 5 mL / min and a premixing temperature of 45 °C. The premixed solution is then pumped into a microchannel with an inner diameter of 2 mm and a length of 5 m. 5 parts of lipase are dissolved in 1000 parts of pH 7.0 phosphate solution, with an enzyme activity ≥10000 U / g. 60 parts of the lipase solution are added to the three-stage microchannel at a temperature of 58 °C for 5-7 h to obtain crude ethyl 2-methylbutyrate. A 5% sodium bicarbonate solution is added at a feed-to-solution ratio of 1:10 and stirred for 1 h. When the pH of the crude ethyl 2-methylbutyrate solution reaches 7.5, it is allowed to stand. The separated aqueous solution is then placed in a wastewater treatment tank. Tap water is then added at an 8:1 ratio and stirred until it stands. The separated wastewater is then placed in the wastewater treatment tank. The remaining crude ethyl 2-methylbutyrate is obtained by vacuum fractionation.

[0055] Comparative Example 7

[0056] The difference between this comparative example and Example 1 is that the preparation of immobilized lipase in this comparative example is as follows: 5 parts of lipase were dissolved in 1000 parts of pH 7.0 phosphate solution, with an enzyme activity ≥10000 U / g. SiO2 with a pore size of 50 nm was used and soaked in dilute hydrochloric acid for 2 hours, washed with deionized water until neutral, dried at 110°C, and then immersed in a 2% dopamine solution. After shaking at 25°C for 12 hours, centrifuged and dried, 100 parts were added to the above lipase solution and slowly shaken at 25°C for 12 hours for adsorption. Then, 100 parts of a 1% glutaraldehyde solution were added and crosslinked at 25°C for 2 hours. After filtration, the particles were washed three times with phosphate solution and freeze-dried for 24 hours to obtain solid immobilized lipase particles; the rest is the same as in Example 1.

[0057] Comparative Example 8

[0058] The difference between this comparative example and Example 1 is that the magnesium diglycine solution in this comparative example is replaced with magnesium chloride solution; otherwise, it is the same as in Example 1.

[0059] Comparative Example 9

[0060] The difference between this comparative example and Example 1 is as follows: In this comparative example, the immobilized lipase was prepared as follows: 5 parts of lipase were dissolved in 1000 parts of pH 7.0 phosphate solution, with an enzyme activity ≥10000 U / g. SiO2 with a pore size of 50 nm was used, and the mixture was soaked in dilute hydrochloric acid for 2 hours, washed with deionized water until neutral, dried at 110°C, and then immersed in a 2% (w / w) dopamine solution. The mixture was shaken at 25°C for 12 hours, filtered, and then further immersed in a 30% (w / w) magnesium diglycinate solution. The mixture was sonicated at 60°C for 2 hours, centrifuged, dried, and then 100 parts were added to the above lipase solution. The mixture was slowly shaken at 25°C for 12 hours to adsorb the lipase. Then, 100 parts (w / w) of a 1% (w / w) glutaraldehyde solution were added, and the mixture was cross-linked at 25°C for 2 hours. After filtration, the mixture was washed three times with phosphate solution and freeze-dried for 24 hours to obtain solid immobilized lipase particles. The rest of the process was the same as in Example 1.

[0061] Comparative Example 10

[0062] The difference between this comparative example and Example 1 is as follows: In this comparative example, the immobilized lipase was prepared as follows: 5 parts of lipase were dissolved in 1000 parts of pH 7.0 phosphate solution, with an enzyme activity ≥10000 U / g. SiO2 with a pore size of 50 nm was used, and the mixture was soaked in dilute hydrochloric acid for 2 hours, washed with deionized water until neutral, dried at 110°C, and then immersed in a 2% (w / w) dopamine solution. The mixture was shaken at 25°C for 12 hours, filtered, and then further immersed in a 5% (w / w) magnesium diglycinate solution. The mixture was sonicated at 60°C for 2 hours, centrifuged, dried, and then 100 parts were added to the above lipase solution. The mixture was slowly shaken at 25°C for 12 hours to adsorb the lipase. Then, 100 parts (w / w) of a 1% (w / w) glutaraldehyde solution were added, and the mixture was cross-linked at 25°C for 2 hours. After filtration, the mixture was washed three times with phosphate solution and freeze-dried for 24 hours to obtain solid immobilized lipase particles. The rest of the process was the same as in Example 1.

[0063] Experiment 2: Determination of ethyl 2-methylbutyrate

[0064] The synthesis rate of ethyl 2-methylbutyrate was determined, the purity was measured according to QB / T 1776-2014, the relative density was measured according to GB / T 11540, and the refractive index was measured according to GB / T 14454.4. The results are shown in Table 2.

[0065] Table 2

[0066] Group Synthesis rate (%) Purity content (%) Refractive index relative density Example 4 96.2 99.8 1.3962 0.8654 Example 5 95.8 99.6 1.3956 0.8651 Example 6 95.6 99.7 1.3960 0.8649 Comparative Example 4 84.7 98.0 1.3930 0.8620 Comparative Example 5 88.3 98.8 1.3947 0.8632 Comparative Example 6 86.5 98.4 1.3951 0.8637 Comparative Example 7 87.1 98.7 1.3952 0.8642 Comparative Example 8 88.2 98.9 1.3954 0.8646 Comparative Example 9 94.8 99.5 1.3963 0.8654 Comparative Example 10 91.3 99.2 1.3960 0.8649

Claims

1. A method for preparing ethyl 2-methylbutyrate, characterized in that, The process is as follows: 80 parts of 2-methylbutyric acid and 80 parts of ethanol were subjected to a three-stage microchannel reaction. The mixture was premixed in a T-shaped microchannel with an inner diameter of 1 mm at a flow rate of 5 mL / min and a premixing temperature of 40-50 °C. The premixed solution was then pumped into a serpentine microchannel with an inner diameter of 2 mm and a length of 5 m, filled with 50-70 parts of immobilized lipase particles. The temperature was maintained at 55-60 °C for 5-7 h to obtain crude ethyl 2-methylbutyrate. A 5% sodium bicarbonate solution was added at a feed-to-solution ratio of 1:10 and stirred for 1 h. When the pH of the crude ethyl 2-methylbutyrate solution reached 7-8, it was allowed to stand. The separated aqueous solution was then placed in a wastewater treatment tank. Tap water was then added at an 8:1 ratio and stirred until it was allowed to stand. The separated wastewater was then placed in the wastewater treatment tank. The remaining crude ethyl 2-methylbutyrate was then fractionated under reduced pressure to obtain the final product.

2. The preparation method according to claim 1, characterized in that, The immobilized lipase was prepared as follows: 5 parts of lipase were dissolved in 1000 parts of pH 7.0 phosphate solution, with an enzyme activity ≥ 10000 U / g. SiO2 with a pore size of 50 nm was used to soak the lipase in dilute hydrochloric acid for 2 hours, washed with deionized water until neutral, dried at 110℃, and then immersed in a 2% (w / w) dopamine solution. The mixture was shaken at 25℃ for 12 hours, filtered, and then further immersed in an 8-20% (w / w) magnesium diglycinate solution. The mixture was sonicated at 60℃ for 2 hours, centrifuged, dried, and then 100 parts were added to the above lipase solution. The mixture was slowly shaken at 25℃ for 12 hours to adsorb the lipase. 100 parts (w / w) of 1% (w / w) glutaraldehyde solution were added, and the mixture was cross-linked at 25℃ for 2 hours. After filtration, the mixture was washed three times with phosphate solution and freeze-dried for 24 hours to obtain solid immobilized lipase particles.

3. The preparation method according to claim 1, characterized in that, The process also includes the preparation of 2-methylbutyric acid: 200 parts of 2-methylbutanol and 20-30 parts of immobilized catalyst are added sequentially, and 500 parts of 50% hydrogen peroxide are slowly added dropwise. The reaction temperature is maintained at 85-95℃. After the addition is completed, the reaction is continued for 3 hours. The reaction solution is cooled and transferred to a separatory funnel to separate the aqueous layer. The upper oil layer is adjusted to pH 9-10 with 10% sodium hydroxide aqueous solution and allowed to stand for separation. The organic phase is separated. The aqueous phase is washed twice with 200 parts of methyl tert-butyl ether, and then concentrated hydrochloric acid is added to adjust the pH to 2. The solution is extracted twice with 200 parts of methyl tert-butyl ether. The organic layers are combined, and the solvent is removed by a rotary evaporator to obtain crude 2-methylbutyric acid. The crude product is then subjected to reduced pressure separation at -0.096 MPa to obtain the finished 2-methylbutyric acid product.

4. The preparation method according to claim 3, characterized in that, The preparation of the supported catalyst is as follows: 500 parts of toluene solution are added to 50 parts of SiO2, stirred and suspended, then 120 parts of 3-aminopropyltriethoxysilane are added, refluxed under N2 protection for 12 h, filtered, washed 3 times with anhydrous toluene, and dried under vacuum at 80 °C to obtain aminated SiO2. 10 parts of aminated SiO2 are added to 1200-1600 parts of ligand solution, 3-5 parts of manganese acetate tetrahydrate are added, 600 parts of water are added, stirred at 60 °C for 24 h, filtered, washed 3 times with ethanol, and dried under vacuum at 40 °C for 12 h to obtain the supported catalyst.

5. The preparation method according to claim 4, characterized in that, The ligand solution was prepared by mixing 2,2'-bipyridine-4,4'-dicarboxylic acid, DMF, and water in a ratio of 1:5:3.