A continuous process for the preparation of dimethyl 2-methylglutarate

Abstract

This invention provides a continuous preparation method for dimethyl 2-methylglutarate, carried out in a first microchannel reactor and a second microchannel reactor connected in series. The method includes: feeding 2-methylglutaronitrile and sulfuric acid solution into the first microchannel reactor for hydrolysis; and contacting them with methanol in the second microchannel reactor for esterification. The esterified material is then subjected to phase separation to obtain dimethyl 2-methylglutarate. The mass ratio of 2-methylglutaronitrile to sulfuric acid solution is 1:(5~20). The controlled temperature of the first microchannel reactor is 80~120℃; the controlled temperature of the second microchannel reactor is 65~105℃, and the controlled temperature of the second microchannel reactor is not higher than that of the first microchannel reactor; the mass ratio of 2-methylglutaronitrile to methanol is 1:(1~6). Through the synergistic operation of the microchannel reactor and multiple control parameters, the eutectic precipitation of intermediate products with ammonium sulfate can be avoided, clogging can be prevented, and efficient, high-yield continuous preparation can be achieved.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, and specifically to a method for preparing dimethyl 2-methylglutarate using a series of microchannel reactors. Background Technology

[0002] In the large-scale production of adiponitrile via butadiene cyanidation, a large amount of the byproduct 2-methylglutaronitrile is generated, which is usually incinerated. Converting this byproduct into dimethyl 2-methylglutarate allows for comprehensive resource utilization. Dimethyl 2-methylglutarate is an organic solvent with excellent environmental properties, possessing significant advantages such as transparency, colorlessness, mild odor, and biodegradability. It can be used as an environmentally friendly solvent in industrial coatings, electronic cleaning, or metal processing, replacing traditional solvents such as isophorone and cyclohexanone. It can also be used as an intermediate in the synthesis of plant-based surfactants, possessing broad market prospects and potential commercial value.

[0003] In the prior art, the continuous preparation methods of 2-methylglutarate mainly include: Patent CN109824514A discloses a method for synthesizing 2-methylglutarate, which uses a mixture of 2-methylglutaronitrile and sulfuric acid, and after separation, methanol is added for esterification. This method is a non-continuous operation with low production efficiency. Patent CN113788755A discloses a continuous preparation method of 2-methylglutarate, which involves adding concentrated sulfuric acid to a mixture of 2-methylglutaronitrile and methanol, allowing the concentrated sulfuric acid to react with the 2-methylglutaronitrile and methanol. Although this method achieves a one-step synthesis of 2-methylglutarate, it has low efficiency, produces many byproducts, and requires sophisticated equipment. Patent CN116199579A discloses a method for preparing 2-methylglutarate, which uses methyl acrylate to generate an intermediate under catalytic conditions, and then hydrogenates it to obtain the target product. This method is costly and the hydrogenation section is dangerous. Patent CN117886694A proposes a method for preparing methyl acrylate by reacting it with an organophosphorus reagent and then hydrogenating it. This process has high operating costs, the organophosphorus reagent is highly toxic, and the hydrogenation section is dangerous to operate.

[0004] Furthermore, when 2-methylglutaronitrile is used as a raw material for preparation via hydrolysis, the intermediate 2-methylglutaric acid has extremely high solubility in water at room temperature and easily forms eutectic with the by-product ammonium sulfate, resulting in reduced solubility of the solid product, precipitation and blockage of pipelines, making continuous production difficult. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention discloses a continuous preparation method for dimethyl 2-methylglutarate, which solves the problems of low efficiency and severe equipment corrosion caused by intermittent operation, or the technical problems of easy equipment blockage and high raw material costs in existing technologies.

[0006] To achieve the above technical objectives, this invention proposes a continuous preparation method for dimethyl 2-methylglutarate, wherein the preparation method is carried out in a first microchannel reactor and a second microchannel reactor connected in series, comprising: 2-Methylglutaronitrile and sulfuric acid solution are fed into the first microchannel reactor for hydrolysis. The hydrolyzed material is then fed into the second microchannel reactor and contacted with methanol for esterification. The esterified material is then separated to obtain dimethyl 2-methylglutarate. The mass ratio of 2-methylglutaronitrile to sulfuric acid solution is 1:(5~20); the control temperature of the first microchannel reactor is 80~120℃, the control temperature of the second microchannel reactor is 65~105℃, and the control temperature of the second microchannel reactor is not higher than the control temperature of the first microchannel reactor; the mass ratio of 2-methylglutaronitrile to methanol is 1:(1~6).

[0007] In the above technical solution, hydrolysis and esterification reactions are carried out sequentially by two microchannel reactors connected in series, thereby avoiding the following adverse effects in the prior art: 1) the simultaneous addition of 2-methylglutaronitrile, sulfuric acid aqueous solution and methanol to the reactor, which causes nitrile compounds and their initial hydrolysis products (amide compounds) to be attacked by methanol with stronger nucleophilicity to generate byproducts (such as cyclization products); 2) the stratification of the reaction system caused by the addition of methanol, which is not conducive to the mass and heat transfer of the reaction and reduces the reaction efficiency.

[0008] Furthermore, the research team of this invention discovered through experiments that in the preparation process of dimethyl 2-methylglutarate using 2-methylglutaronitrile and methanol as raw materials, the hydrolysis product 2-methylglutaric acid and ammonium sulfate are prone to eutectic phenomenon, and the two after precipitation are uniformly mixed and difficult to purify. In subsequent reactions, a large amount of ammonium sulfate solid will be generated, which will hinder the reaction and block the channel. In the above technical solution, on the one hand, the temperature of the first microchannel reactor is controlled at 80~120℃ to suppress the easy eutectic precipitation of 2-methylglutaric acid and ammonium sulfate with a relatively high reaction temperature; on the other hand, the mass ratio of 2-methylglutaronitrile to the sulfuric acid solution during the hydrolysis reaction is controlled at 1:(5~20), so that the amount of sulfuric acid solution used is significantly reduced compared with the prior art, thereby reducing the water content in the system during the esterification reaction; further combined with the relatively high amount of methanol used during the esterification reaction (the mass ratio of 2-methylglutaronitrile to the methanol is 1:(1~6)) and the control temperature not higher than that of the hydrolysis reaction, the methanol content in the system during the esterification reaction is high and the water content is relatively low, thereby further promoting the dissolution of intermediate products, and thus promoting the forward esterification reaction, avoiding precipitation and blockage.

[0009] The above technical solution achieves efficient and high-yield continuous preparation of dimethyl 2-methylglutarate through the synergistic combination of a microchannel reactor and multiple control parameters.

[0010] In a further example of the present invention, the mass ratio of the 2-methylglutaronitrile to the sulfuric acid solution is 1:(8~16). The present invention illustrates the preparation process of dimethyl 2-methylglutarate with different ratios of the 2-methylglutaronitrile and the sulfuric acid solution.

[0011] In a further example of the present invention, the mass ratio of 2-methylglutaronitrile to methanol is 1:(3~5), thereby improving both process cost and reaction efficiency by using an appropriate amount of methanol, and avoiding clogging conditions.

[0012] In a further example of the present invention, the feed rate of 2-methylglutaronitrile is 0.2~3 ml / min, thereby controlling the reaction process, matching the residence time of the reactants in the microchannel with the reaction rate, avoiding supersaturation precipitation caused by excessively high local concentrations of the intermediate product 2-methylglutaric acid, thus preventing microchannel blockage and achieving continuous and stable operation. In an optional example of the present invention, the feed rate of 2-methylglutaronitrile is 0.5~2.5 ml / min.

[0013] It should be noted that the present invention does not limit the specific operating equipment for injecting reaction raw materials, sulfuric acid solution or post-reaction materials into the microchannel reactor. Plunger pumps, peristaltic pumps, diaphragm pumps, etc. can be selected. Those skilled in the art can choose according to the actual working conditions, and this does not limit the scope of protection of the present invention.

[0014] In a further example of the present invention, the temperature of the first microchannel reactor is controlled at 100~110°C, so that the solubility of the intermediate products 2-methylglutaric acid and ammonium sulfate in the reaction system is maintained at a high level, avoiding pipe blockage caused by eutectic precipitation.

[0015] In a further example of the invention, the control temperature of the second microchannel reactor was explored and optimized.

[0016] Optionally, the temperature difference between the first microchannel reactor and the second microchannel reactor is controlled to be 0~50℃. By coordinating the temperature control of the two microchannel reactors, the precipitation of intermediate products is further avoided, side reactions are reduced, and the forward esterification reaction is promoted. Simultaneously, while maintaining a homogeneous flow state in the reaction system, reaction energy consumption is reduced to decrease side reactions and improve economic efficiency. In an optional example of the present invention, the temperature difference between the first microchannel reactor and the second microchannel reactor is controlled to be 5~40℃.

[0017] In a further example of the present invention, the pressures of the first microchannel reactor and the second microchannel reactor are 0.1~2.0 MPa (gauge pressure), respectively. It should be noted that the pressures of the first microchannel reactor and the second microchannel reactor can be self-generated pressure, or back pressure can be applied using a back pressure valve, etc. The present invention does not limit the specific structure and specifications of the back pressure valve. In an optional example of the present invention, the pressures of the first microchannel reactor and the second microchannel reactor are 0.5~1.5 MPa (gauge pressure), respectively.

[0018] In a further example of the present invention, the concentration of the sulfuric acid solution is 35wt%~65wt%. The sulfuric acid solution acts as a catalyst for the hydrolysis reaction. Optimization of the sulfuric acid solution is beneficial to the reaction process and improves the operability of the process. In an optional example of the present invention, the concentration of the sulfuric acid solution is 40wt%~60wt%.

[0019] In a further example of the invention, the structure of the microchannel reaction was optimized.

[0020] Optionally, the first microchannel reactor and the second microchannel reactor are made of glass, ceramic, or ceramic with a corrosion-resistant coating, respectively. In this invention, a microchannel reactor made of a material resistant to dilute acids and possessing a certain pressure-bearing capacity is preferred. Further optionally, the ceramic is alumina ceramic, silicon nitride ceramic, or silicon carbide ceramic. Further optionally, the ceramic with a corrosion-resistant coating is alumina ceramic with an enamel coating or alumina ceramic with a polytetrafluoroethylene coating.

[0021] It should be noted that the present invention does not limit the specific structure and specifications of the microchannel reactor. The reaction tube of the microchannel reactor can be selected to have a volume of 10~100mL and a pressure resistance of 1~2MPa, etc., but is not limited to the listed range. Those skilled in the art can select a reactor with a suitable structure and specifications for the reaction of 2-methylglutarate dimethyl ester based on the technical solution of the present invention through non-creative labor. All technical solutions formed therefrom are within the protection scope of the present invention.

[0022] In a further example of the present invention, the phase separation operation includes: separating the material after esterification reaction into layers, collecting the upper organic phase as the product; the lower aqueous phase contains inorganic substances such as water, sulfuric acid, and ammonium sulfate, and can be treated as wastewater.

[0023] Optionally, the preparation method of the present invention further includes purifying the dimethyl 2-methylglutarate obtained by phase separation by distillation with deionized water extractant to further obtain a high-purity dimethyl 2-methylglutarate product.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention carries out the hydrolysis reaction and esterification reaction of 2-methylglutaronitrile sequentially in two microchannel reactors connected in series, which can reduce the occurrence of side reactions and enhance mass transfer, thereby improving the reaction efficiency; by optimizing the control temperature, sulfuric acid solution feed rate and methanol feed rate of the first microchannel reactor, the precipitation of eutectic of hydrolysis products and ammonium sulfate can be effectively reduced, promoting the forward esterification reaction and avoiding precipitation and blockage conditions, thus realizing the efficient and high-yield continuous preparation of dimethyl 2-methylglutarate. Attached Figure Description

[0025] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A process flow diagram of the continuous preparation method of dimethyl 2-methylglutarate of the present invention is shown.

[0026] Figure 2 The gas chromatographic detection results of 2-methylglutarate dimethyl ester prepared in Example 1 are shown; the peak with the largest area is the product 2-methylglutarate dimethyl ester.

[0027] Figure 3 The gas chromatogram of Comparative Example 2 is shown; no product was detected, and the highest peak was the 2-methylglutaronitrile raw material peak. Detailed Implementation

[0028] To facilitate understanding of the present invention, a more comprehensive description will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the invention in any way, i.e., not intended to limit the scope of protection of the invention.

[0029] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0030] Furthermore, it should be noted that although the steps of the continuous preparation method of the present invention are described in a specific order in the description of the present invention, these orders are not restrictive. Without departing from the basic principles of the present invention, those skilled in the art can perform the steps in different orders.

[0031] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "multiple" or "at least one" means two or more.

[0032] All numerical designations, such as temperature, pressure, flow rate, and range, are approximate values. It should be understood that, while not always explicitly stated, all numerical designations are preceded by the term "approximately." It should also be understood that, while not always explicitly stated, the reagents described herein are merely examples, and their equivalents are known in the art.

[0033] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0034] Example 1

[0035] A continuous preparation method for dimethyl 2-methylglutarate. Figure 1 The process flow is shown, specifically: 2-Methylglutaronitrile and 50% sulfuric acid were added to the first microchannel reactor at a mass ratio of 1:12 for hydrolysis. The 2-methylglutaronitrile flow rate was 2 mL / min, and the temperature of the first microchannel reactor was set to 105℃. After hydrolysis, methanol was injected into the second microchannel reactor at a mass ratio of 1:4 to 2-methylglutaronitrile for esterification. The temperature of the second microchannel reactor was 70℃, and the pressure was 0.6 MPa. The liquid after esterification was collected and separated into layers, with the upper organic phase being the product. Further, this organic phase was distilled using deionized water extractant to obtain dimethyl 2-methylglutarate. The distillation was carried out in a conventional glass distillation column, which could have an inner diameter of 10 cm, a length of 1.2 m, a top temperature of 70-80℃, a bottom temperature of 150-170℃, and a pressure of 5-10 kPa. The product was collected using a reflux ratio controller of 1:(4-5). The conversion rate was determined to be 99% by gas chromatography (see Appendix). Figure 2 The selectivity rate was 93%.

[0036] Example 2

[0037] A continuous preparation method for dimethyl 2-methylglutarate, specifically: 2-Methylglutaronitrile and 40% sulfuric acid were introduced into the first microchannel reactor at a mass ratio of 1:16. The 2-methylglutaronitrile flow rate was 0.5 mL / min, and the temperature of the first microchannel reactor was set to 100 °C. After hydrolysis in the first microchannel reactor, methanol was injected into the second microchannel reactor at a mass ratio of 1:3 (2-methylglutaronitrile to methanol). The temperature of the second microchannel reactor was set to 95 °C, and the pressure to 0.3 MPa. The liquid after the esterification reaction was collected and separated into layers, with the upper organic phase being the product. This organic phase was then distilled using deionized water extractant to obtain dimethyl 2-methylglutarate. Gas chromatography showed a conversion rate of 99% and a selectivity of 93%.

[0038] Example 3

[0039] A continuous preparation method for dimethyl 2-methylglutarate, specifically: 2-Methylglutaronitrile and 37% sulfuric acid were introduced into the first microchannel reactor at a mass ratio of 1:18. The 1,2-methylglutaronitrile flow rate was 2.8 mL / min, and the temperature of the first microchannel reactor was set to 115 °C. After hydrolysis in the first microchannel reactor, methanol was injected into the second microchannel reactor at a mass ratio of 1:2 (2-methylglutaronitrile to methanol). The temperature of the second microchannel reactor was set to 66 °C, and the pressure to 0.3 MPa. The liquid after the esterification reaction was collected and separated into layers, with the upper organic phase being the product. This organic phase was then purified by distillation using deionized water extractant to obtain dimethyl 2-methylglutarate. Gas chromatography showed a conversion rate of 90% and a selectivity of 83%.

[0040] Example 4

[0041] A continuous preparation method for dimethyl 2-methylglutarate, specifically: 2-Methylglutaronitrile and 38% sulfuric acid were added to the first microchannel reactor at a mass ratio of 1:12 for hydrolysis. The 2-methylglutaronitrile flow rate was 2 mL / min, and the temperature of the first microchannel reactor was set to 105 °C. After hydrolysis, methanol was injected into the second microchannel reactor at a mass ratio of 1:4 (2-methylglutaronitrile and methanol) for esterification. The temperature of the second microchannel reactor was set to 70 °C, and the pressure to 0.6 MPa. The liquid after esterification was collected and separated into layers, with the upper organic phase being the product. This organic phase was then distilled using deionized water extractant to obtain dimethyl 2-methylglutarate. Gas chromatography showed a conversion rate of 93% and a selectivity of 90%.

[0042] Example 5

[0043] A continuous preparation method for dimethyl 2-methylglutarate, specifically: 2-Methylglutaronitrile and 50% sulfuric acid were added to the first microchannel reactor at a mass ratio of 1:6 for hydrolysis. The 2-methylglutaronitrile flow rate was 2 mL / min, and the temperature of the first microchannel reactor was set to 105 °C. After hydrolysis, methanol was injected into the second microchannel reactor at a mass ratio of 1:4 (2-methylglutaronitrile and methanol) for esterification. The temperature of the second microchannel reactor was set to 70 °C, and the pressure to 0.6 MPa. The liquid after esterification was collected and separated into layers, with the upper organic phase being the product. This organic phase was then distilled using deionized water extractant to obtain dimethyl 2-methylglutarate. Gas chromatography showed a conversion rate of 94% and a selectivity of 88%.

[0044] Example 6

[0045] A continuous preparation method for dimethyl 2-methylglutarate, specifically: 2-Methylglutaronitrile and 50% sulfuric acid were added to the first microchannel reactor at a mass ratio of 1:12 for hydrolysis. The 2-methylglutaronitrile flow rate was 2 mL / min, and the temperature of the first microchannel reactor was set to 105 °C. After hydrolysis, methanol was injected into the second microchannel reactor at a mass ratio of 1:2 (2-methylglutaronitrile and methanol) for esterification. The temperature of the second microchannel reactor was set to 70 °C, and the pressure to 0.6 MPa. The liquid after esterification was collected and separated into layers, with the upper organic phase being the product. This organic phase was then distilled using deionized water extractant to obtain dimethyl 2-methylglutarate. Gas chromatography showed a conversion rate of 91% and a selectivity of 89%.

[0046] Example 7

[0047] A continuous preparation method for dimethyl 2-methylglutarate, specifically: 2-Methylglutaronitrile and 50% sulfuric acid were added to the first microchannel reactor at a mass ratio of 1:12 for hydrolysis. The 2-methylglutaronitrile flow rate was 0.3 mL / min, and the temperature of the first microchannel reactor was set to 105 °C. After hydrolysis, methanol was injected into the second microchannel reactor at a mass ratio of 1:4 (2-methylglutaronitrile and methanol) for esterification. The temperature of the second microchannel reactor was set to 70 °C, and the pressure to 0.6 MPa. The liquid after esterification was collected and separated into layers, with the upper organic phase being the product. This organic phase was then distilled using deionized water extractant to obtain dimethyl 2-methylglutarate. Gas chromatography showed a conversion rate of 92% and a selectivity of 93%.

[0048] Example 8

[0049] A continuous preparation method for dimethyl 2-methylglutarate, specifically: 2-Methylglutaronitrile and 50% sulfuric acid were added to the first microchannel reactor at a mass ratio of 1:12 for hydrolysis. The 2-methylglutaronitrile flow rate was 2 mL / min, and the temperature of the first microchannel reactor was set to 90 °C. After hydrolysis, methanol was injected into the second microchannel reactor at a mass ratio of 1:4 (2-methylglutaronitrile and methanol) for esterification. The temperature of the second microchannel reactor was set to 70 °C, and the pressure to 0.6 MPa. The liquid after esterification was collected and separated into layers, with the upper organic phase being the product. This organic phase was then distilled using deionized water extractant to obtain dimethyl 2-methylglutarate. Gas chromatography showed a conversion rate of 92% and a selectivity of 90%.

[0050] Example 9

[0051] A continuous preparation method for dimethyl 2-methylglutarate, specifically: 2-Methylglutaronitrile and 50% sulfuric acid were added to the first microchannel reactor at a mass ratio of 1:12 for hydrolysis. The 2-methylglutaronitrile flow rate was 2 mL / min, and the temperature of the first microchannel reactor was set to 105 °C. After hydrolysis, methanol was injected into the second microchannel reactor at a mass ratio of 1:4 (2-methylglutaronitrile and methanol) for esterification. The temperature of the second microchannel reactor was set to 102 °C, and the pressure to 0.6 MPa. The liquid after esterification was collected and separated into layers, with the upper organic phase being the product. This organic phase was then distilled using deionized water extractant to obtain dimethyl 2-methylglutarate. Gas chromatography showed a conversion rate of 95% and a selectivity of 90%.

[0052] Example 10

[0053] A continuous preparation method for dimethyl 2-methylglutarate, specifically: 2-Methylglutaronitrile and 50% sulfuric acid were added to the first microchannel reactor at a mass ratio of 1:12 for hydrolysis. The 2-methylglutaronitrile flow rate was 2 mL / min, and the temperature of the first microchannel reactor was set to 105 °C. After hydrolysis, methanol was injected into the second microchannel reactor at a mass ratio of 1:4 (2-methylglutaronitrile and methanol) for esterification. The temperature of the second microchannel reactor was set to 70 °C, and the pressure to 1.8 MPa. The liquid after esterification was collected and separated into layers, with the upper organic phase being the product. This organic phase was then distilled using deionized water extractant to obtain dimethyl 2-methylglutarate. Gas chromatography showed a conversion rate of 96% and a selectivity of 88%.

[0054] Comparative Example 1 A method for preparing dimethyl 2-methylglutarate is disclosed. The process and raw material parameters of this comparative example are the same as those in Example 1, except that the mass ratio of 2-methylglutaronitrile to sulfuric acid solution is 1:4. The process results are shown in Table 1.

[0055] Comparative Example 2 A method for preparing dimethyl 2-methylglutarate is disclosed. The process and raw material parameters of this comparative example are the same as in Example 1, except that the mass ratio of 2-methylglutaronitrile to methanol is 1:0.5. During the process, it was found that due to insufficient methanol, a pale yellow solid was observed to form in the second microchannel reactor, causing short-term blockage of the microchannel and a gradual increase in pressure. This was mainly because the methanol content decreased sharply after the reaction with 2-methylglutaric acid, making it impossible to dissolve the product. Gas chromatography detection (optional, see [link]). Figure 3 The results showed that no product was detected, and the highest peak was the 2-methylglutaronitrile feedstock peak; the specific process results are shown in Table 1.

[0056] Comparative Example 3 A method for preparing dimethyl 2-methylglutarate is disclosed. The process and raw material parameters of this comparative example are the same as those in Example 1, except that the temperature of the first microchannel reactor is 70°C. The process results are shown in Table 1.

[0057] Comparative Example 4 A method for preparing dimethyl 2-methylglutarate via microchannels is described. The process and raw material parameters of this comparative example are the same as those in Example 1, except that the temperature of the second microchannel reactor is 125°C. The process results are shown in Table 1.

[0058] Comparative Example 5 A method for preparing dimethyl 2-methylglutarate via microchannels is described. The process and raw material parameters of this comparative example are the same as those in Example 1, except that 2-methylglutaronitrile, sulfuric acid solution and methanol are simultaneously introduced into the first microchannel reactor, and the first microchannel reactor and the second microchannel reactor are connected in series. The process results are shown in Table 1.

[0059] Table 1

[0060] Table 1 confirms that the technical solution of this invention has significant technical advantages: Examples 1 and 2 achieved a 99% conversion rate of 2-methylglutaronitrile and a 93% selectivity of dimethyl 2-methylglutarate, respectively, indicating that the tandem dual-microchannel reactor structure, combined with specific temperature and material ratio conditions, can achieve near-quantitative conversion effects and excellent selectivity for the target product. Examples 3 to 10 also maintained a conversion rate of over 90% and a selectivity of over 83%, verifying that the technical solution of this invention has good reproducibility and stability within the scope defined by the claims.

[0061] Compared with Example 1: Comparative Example 1 showed that reducing the amount of sulfuric acid to a mass ratio of 1:4 resulted in a conversion rate of 51%, confirming that the amount of sulfuric acid needed to be controlled within a suitable and sufficient range to promote complete hydrolysis.

[0062] Comparative Example 2 reduced the methanol content to a mass ratio of 1:0.5, and the selectivity dropped from 93% to 11%, with channel blockage occurring, demonstrating the indispensability of high methanol content in promoting the dissolution of intermediate products and driving the esterification reaction forward.

[0063] Comparative Example 3 set the temperature of the first microchannel reactor to 70℃, with a conversion rate of only 11% and a selectivity of only 31%, making the reaction almost impossible. This confirmed the necessity of the temperature range of 80~120℃. This temperature not only ensures the hydrolysis reaction kinetics, but more importantly, it inhibits the eutectic precipitation of 2-methylglutaric acid and ammonium sulfate.

[0064] Although the conversion rate of Comparative Example 4 remained at 96%, the selectivity was only 23%, indicating that excessively high temperatures in the second microchannel reactor could lead to serious side reactions. This also indirectly confirms the technical advantage of coordinated temperature control between the first and second microchannel reactors.

[0065] In Comparative Example 5, 2-methylglutaronitrile, sulfuric acid solution and methanol were simultaneously added to the first microchannel reactor. Although the conversion rate still reached 90%, the selectivity dropped sharply to 8%, and the target product could hardly be obtained. This comparative condition fully demonstrates the key role of the tandem dual microchannel reactor in stepwise hydrolysis and esterification in avoiding premature contact of methanol with reactants and inhibiting the generation of cyclization side reactions.

[0066] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple improvements can be made without departing from the concept of the present invention, and all such improvements should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for the continuous preparation of dimethyl 2-methylglutarate, characterized in that, The preparation method is carried out in a first microchannel reactor and a second microchannel reactor connected in series, including: 2-Methylglutaronitrile and sulfuric acid solution are fed into the first microchannel reactor for hydrolysis. The hydrolyzed material is then fed into the second microchannel reactor and contacted with methanol for esterification. The esterified material is then separated to obtain dimethyl 2-methylglutarate. The mass ratio of 2-methylglutaronitrile to sulfuric acid solution is 1:(5~20); the control temperature of the first microchannel reactor is 80~120℃, the control temperature of the second microchannel reactor is 65~105℃, and the control temperature of the second microchannel reactor is not higher than the control temperature of the first microchannel reactor; the mass ratio of 2-methylglutaronitrile to methanol is 1:(1~6).

2. The process for the continuous preparation of dimethyl 2-methylglutarate according to claim 1, characterized in that, The mass ratio of the 2-methylglutaronitrile to the sulfuric acid solution is 1:(8~16).

3. The continuous process for the preparation of dimethyl 2-methylglutarate according to claim 1, characterized in that, The mass ratio of 2-methylglutaronitrile to methanol is 1:(3~5).

4. The continuous process for the preparation of dimethyl 2-methylglutarate according to claim 1, characterized in that, The feed rate of the 2-methylglutaronitrile is 0.2–3 ml / min, preferably 0.5–2.5 ml / min.

5. The continuous preparation method of dimethyl 2-methylglutarate according to claim 1, characterized in that, The controlled temperature of the first microchannel reactor is 100~110℃.

6. The continuous preparation method of dimethyl 2-methylglutarate according to claim 1, characterized in that, The temperature difference between the first microchannel reactor and the second microchannel reactor is controlled to be 0~50℃, preferably 5~40℃.

7. The continuous preparation method of dimethyl 2-methylglutarate according to claim 1, characterized in that, The pressures of the first microchannel reactor and the second microchannel reactor are 0.1~2.0MPa, preferably controlled between 0.5~1.5MPa.

8. The continuous preparation method of dimethyl 2-methylglutarate according to claim 1, characterized in that, The concentration of the sulfuric acid solution is 35wt%~65wt%, preferably 40wt%~60wt%.

9. The continuous preparation method of dimethyl 2-methylglutarate according to claim 1, characterized in that, The first microchannel reactor and the second microchannel reactor are made of glass, ceramic or ceramic with an anti-corrosion coating, respectively.

10. The continuous preparation method of dimethyl 2-methylglutarate according to claim 9, characterized in that, The ceramic is alumina ceramic, silicon nitride ceramic or silicon carbide ceramic; Preferably, the ceramic with the anti-corrosion coating is an alumina ceramic with an enamel coating or an alumina ceramic with a polytetrafluoroethylene coating.

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