Catalytic preparation method of high-stability ethylene glycol monomethyl ether

Abstract

The invention relates to a catalytic preparation method of high-stability ethylene glycol monomethyl ether. Under the condition that the specific acid-base bifunctional ionic liquid serves as the catalyst, ethylene glycol and methanol serve as raw materials, ethylene glycol monomethyl ether is prepared, the conversion rate of ethyl alcohol and the selectivity of generated ethylene glycol monomethyl ether can be effectively improved, and after simple aftertreatment, the product is high in purity and stable in performance, and industrial production is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of organic synthesis, and in particular to a method for catalytically preparing ethylene glycol monomethyl ether with high stability. Background Art

[0002] Ethylene glycol monoether products are excellent green solvents. Ethylene glycol ether molecules contain both ether and alcohol structures, resulting in excellent solubility properties. They are not only miscible with water but also compatible with numerous organic compounds, polymers, and natural macromolecules, making them excellent solvents. Ethylene glycol monomethyl ether (HOCH2CH2OCH3) is a typical representative of ethylene glycol monoethers. A colorless, transparent liquid, it has been increasingly used in the pharmaceutical industry, jet fuel, anti-icing agents, brake fluid diluents, and other applications in recent years.

[0003] Currently, typical synthetic routes for glycol ethers include the Williamson synthesis, ethylene oxide ring-opening etherification, synthesis gas, ethylene addition, and ethylene glycol methods. The ethylene oxide and ethylene methods are the most predominant methods used industrially to produce glycol ethers. They primarily use petroleum as raw materials, and production costs are significantly affected by crude oil prices. The ethylene method uses expensive catalysts, resulting in high production costs. The Williamson synthesis uses alkyl halides as raw materials, which are expensive and have limited sources, making industrial production difficult. The synthesis gas method offers broad application prospects due to its abundant raw materials and low cost. However, the current process has low single-pass conversion rates, high reaction pressures, and complex products. The ethylene glycol method directly produces glycol ethers through the etherification reaction of ethylene glycol (EG) and alcohols. Traditionally, EG is produced through petrochemical production, resulting in abundant sources, stable chemical properties, and relatively mild process conditions. Currently reported methods for preparing EGME from EG and methanol include the following: Tomoharu Oku et al. (Journal of the American Chemical Society, 2004, 126(23): 7368-77) used a Cs / P / Si composite oxide as a catalyst to synthesize ethylene glycol monomethyl ether from ethylene glycol and methanol. At a reaction temperature of 300°C and a reaction pressure of 0.1-12 MPa, the ethylene glycol conversion was 46-23%, and the ethylene glycol ether selectivity was 10-76%. That is, at a low reaction pressure, the ethylene glycol conversion was 46%, but the ethylene glycol monomethyl ether selectivity was low, only 10%. At a high reaction pressure of 12 MPa, the ethylene glycol monomethyl ether selectivity reached 76%, but the ethylene glycol conversion was only 23%. Furthermore, a large number of by-products, including diethylene glycol, 1,4-dioxane, acetaldehyde, 3-hydroxybutyraldehyde, and 2-butenal, were produced, making separation difficult. The catalyst utilizes P and alkali metal Cs to adjust the acidity and alkalinity of the catalyst, so that it has multiple acidic and alkaline sites, thus having multifunctionality and adjustable pH.

[0004] US 20040044253 Al reported using the perfluorocarbon sulfonic acid polymer Nafion as a catalyst, with a molar ratio of monohydric alcohol to ethylene glycol of 3:1 to 5:1, a reaction temperature of 100-300°C, a pressure of 6.895 MPa, and a reaction time of 4-5 hours. The reaction achieved an ethylene glycol conversion of 75.7% and a combined selectivity of ethylene glycol monomethyl ether and ethylene glycol dimethyl ether of 94.3%. The polymer catalyst in this reaction swells during use, reducing its mechanical strength, specific surface area, and catalytic activity.

[0005] JP 2009179609 A reports that glycol ethers were synthesized from diols and lower alcohols using a quaternary ammonium salt as a catalyst, with a conversion rate of 40-76% and a selectivity of 91-98%. The catalyst used in this reaction is a quaternary ammonium salt, which has good solubility in the product, making it difficult to separate and unable to be reused. The catalyst has a dual function, having both an acidic cation moiety and a basic anion group with different ionic radii. The catalyst can preferably dissolve with the reaction system during the reaction. However, the catalyst separation is difficult and is only suitable for low-temperature reactions. When the temperature is high, degradation reactions may occur in the quaternary ammonium salt.

[0006] Zhang Dong et al. (Henan Chemical Industry, 2014, 31(3), 40-44) synthesized ethylene glycol monomethyl ether using coal-based ethylene glycol as raw material and methanol as direct method. Using AlCl3 / (NH4)2HPO4 as composite catalyst, reaction temperature was 260℃, reaction time was 4 h, and reaction pressure was 7 MPa. At this time, the ethylene glycol conversion rate was 39%, the ethylene glycol monomethyl ether selectivity was 84%, and the ethylene glycol monomethyl ether yield was 32%.

[0007] Numerous methods for preparing ethylene glycol monomethyl ether have been disclosed in the prior art. However, these methods still suffer from low raw material conversion, low product purity, expensive reaction reagents, and complex process flows, making them unsuitable for industrialization. In particular, when a large number of by-products are produced during the reaction, this is detrimental to the subsequent use and storage of the product, potentially leading to unstable performance of the ethylene glycol monomethyl ether. Therefore, developing a highly stable method for preparing ethylene glycol monomethyl ether suitable for industrialization has significant economic and market value. Summary of the Invention

[0008] To address the above technical problems in the prior art, the present invention provides a highly stable catalytic preparation method for ethylene glycol monomethyl ether. The method of the present invention has mild reaction conditions, a cheap and readily available catalyst, high yield and purity, few by-products, and a highly stable product, making it more suitable for industrial production.

[0009] The present invention provides a catalytic preparation method of ethylene glycol monomethyl ether with high stability, which is characterized by comprising the following steps: (1) In the presence of an acid-base bifunctional ionic liquid, ethylene glycol and methanol are reacted to prepare a reaction solution containing ethylene glycol monomethyl ether; (2) post-treating the reaction solution obtained in step (1) to obtain a finished product of ethylene glycol monomethyl ether; Wherein: the acid-base dual-functionalized ionic liquid is selected from: .

[0010] Preferably, the acid-base dual-functionalized ionic liquid in step 1) is selected from: .

[0011] Preferably, step 1) is performed under pressure, and the pressure is 2-6 MPa, more preferably 4-5 MPa, and most preferably 4.5 MPa.

[0012] Preferably, the reaction temperature of step 1) is 200°C to 400°C, more preferably 250°C to 300°C.

[0013] Preferably, the reaction time of step 1) is 3 to 6 hours, more preferably 4 to 5 hours.

[0014] Preferably, in step 1), the molar ratio of ethylene glycol to methanol is 1:2.0-5.0, more preferably 1:2.5-3.5, and most preferably 1:3.0.

[0015] Preferably, in step 1), the molar mass ratio of ethylene glycol to the acid-base dual-functionalized ionic liquid is 1:5-50, expressed in mol / g, more preferably 1:10-15.

[0016] Preferably, step 2) comprises the following steps: subjecting the reaction solution of step (1) to atmospheric distillation, and collecting the fraction between 120° C. and 130° C., which is the target product, ethylene glycol monomethyl ether.

[0017] Because both ethylene glycol and methanol have active hydroxyl groups and similar chemical reactivity, dehydration occurs between ethylene glycol molecules during the production of ethylene glycol ethers. The resulting oligomers, such as diethylene glycol and triethylene glycol, have high boiling points and are difficult to separate, affecting the quality of the ethylene glycol ethers. Therefore, it is of great significance to design and prepare an efficient catalyst and optimize the synthesis process to achieve high ethylene glycol conversion while avoiding the formation of high-boiling-point byproducts such as diethylene glycol.

[0018] The dehydration reaction between ethylene glycol and methanol molecules is a typical etherification reaction. In theory, both acid and base can be used as catalysts. The pKa value of methanol (15.54) is larger than that of ethylene glycol (14.77), making methanol molecules less likely to ionize to release H than ethylene glycol molecules. + , the acidity is relatively weak, so the acid catalyst primarily activates methanol molecules, forming carbocations. These carbocations attack the hydroxyl oxygen atoms of ethylene glycol to produce ethylene glycol monomethyl ether. When more methanol carbocations are formed, they further react with the hydroxyl groups on ethylene glycol monomethyl ether to produce ethylene glycol dimethyl ether. Because the pKa values of ethylene glycol and methanol are not much different, some ethylene glycol is activated by the acid catalyst to form carbocations. Consequently, dehydration reactions between ethylene glycol molecules also occur to produce diethylene glycol. The base-catalyzed process, in contrast to the acid-catalyzed process, preferentially activates the more acidic ethylene glycol molecules, forming alkoxy anions. These alkoxy anions attack the hydrogen atoms on the hydroxyl groups of methanol to form transition products, which dehydrate to produce ethylene glycol monomethyl ether.

[0019] JP 2009179609 A discloses the preparation of glycol ethers using a bifunctional quaternary ammonium salt catalyst comprising both an acidic cation and a basic anion group with different ionic radii. Zhang Dong et al. reported the catalytic preparation of glycol ethers using a Lewis acid, AlCl, and a basic (NH)HPO composite catalyst. This indicates that the use of bifunctional acid-base catalysts in the catalytic preparation of glycol ethers has attracted considerable attention.

[0020] Ionic liquids have been one of the hot research areas in recent years because of their unique physicochemical properties and catalytic characteristics. The structure of ionic liquids is flexible and changeable, and two or more functional groups can be introduced into the same ionic liquid, so that the ionic liquid has different functions. Acid-base bifunctional ionic liquids refer to ionic liquids that have both acidic and alkaline functions. This type of ionic liquid has a wide range of applications in the field of organic catalysis. It can provide acidic and alkaline active sites, achieve acid-base synergistic catalysis, and improve the selectivity and yield of the reaction. After a large number of experiments, the inventors have screened out specific acid-base bifunctional ionic liquids, which can effectively improve the conversion rate of ethanol and the selectivity of generating ethylene glycol monomethyl ether. After simple post-treatment, the product has high purity and stable performance, which is conducive to industrial production. DETAILED DESCRIPTION

[0021] The present invention is described in detail below by way of examples. In the present invention, the following examples are provided to better illustrate the present invention and are not intended to limit the scope of the present invention. The materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0022] Therefore, before describing the present invention in detail, it should be understood that the present invention is not limited to the system or process parameters of the specific examples that can be varied. It should also be understood that the terms used herein are only for the purpose of describing specific embodiments of the present invention and are not intended to limit the scope of the present invention in any way. The examples used anywhere in this specification (including the examples of any terms discussed herein) are merely illustrative and in no way limit the scope and meaning of the present invention or any of the terms illustrated. Similarly, the present invention is not limited to the various embodiments given in this specification. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those of ordinary skill in the art to which the present invention belongs. In the event of a conflict, this document (including definitions) shall prevail.

[0023] The ionic liquid used in the present invention is prepared with reference to patent document CN 107673957 A, and its structural formula is as follows: .

[0024] Example 1 Effect of catalyst type on reaction Step (1): Weigh 62.1 g of ethylene glycol (1 mol), 96.0 g of methanol (3 mol), and 10 g of an acid-base bifunctional ionic liquid catalyst, add them to a high-pressure reactor, seal it, and replace the gas in the high-pressure reactor with nitrogen three times to make the reactor oxygen-free. Fill the autoclave with nitrogen to pressurize it, heat the contents to 250°C, and control the pressure in the reactor to be approximately 4.5 MPa. Monitor the temperature and pressure changes during the reaction. After 5 hours of reaction, stop heating, cool the contents to below 30°C in a water bath or ice-water bath, open the autoclave, take samples, and perform gas phase analysis.

[0025] Step (2): The reaction solution from step (1) is distilled under normal pressure, and the fraction between 120°C and 130°C is collected, which is the target product, ethylene glycol monomethyl ether. The purity of the product is determined by gas chromatography.

[0026] The types of ionic liquids and their catalytic activities are shown below: Example 2 Effect of reaction temperature on reaction Step (1): Weigh 62.1 g of ethylene glycol (1 mol), 96.0 g of methanol (3 mol), and 10 g of an acid-base bifunctional ionic liquid catalyst, add them to a high-pressure reactor, seal it, and replace the gas in the high-pressure reactor with nitrogen three times to make the reactor oxygen-free. Fill the autoclave with nitrogen to pressurize it, heat the contents to a certain temperature, and control the pressure in the reactor to be approximately 4.5 MPa. Monitor the temperature and pressure changes during the reaction. After 5 hours of reaction, stop heating, cool the contents in the reactor to below 30°C in a water bath or ice-water bath, open the reactor, take samples, and perform gas phase analysis.

[0027] Step (2): The reaction solution from step (1) is distilled under normal pressure, and the fraction between 120°C and 130°C is collected, which is the target product, ethylene glycol monomethyl ether. The purity of the product is determined by gas chromatography.

[0028] The acid-base bifunctional ionic liquid catalyst used is .

[0029] Example 3 Effect of reaction pressure on reaction Step (1): Weigh 62.1 g of ethylene glycol (1 mol), 96.0 g of methanol (3 mol), and 10 g of an acid-base bifunctional ionic liquid catalyst, add them to a high-pressure reactor, seal it, and replace the gas in the high-pressure reactor with nitrogen three times to make the reactor oxygen-free. Fill the autoclave with nitrogen to pressurize it, heat the contents to 250°C, and control the pressure in the reactor. Monitor the temperature and pressure changes during the reaction. After 5 hours of reaction, stop heating, cool the contents to below 30°C in a water bath or ice-water bath, open the autoclave, take samples, and perform gas phase analysis.

[0030] Step (2): The reaction solution from step (1) is distilled under normal pressure, and the fraction between 120°C and 130°C is collected, which is the target product, ethylene glycol monomethyl ether. The purity of the product is determined by gas chromatography.

[0031] The acid-base bifunctional ionic liquid catalyst used is .

[0032] Example 4 Effect of the Ratio of Methanol to Ethylene Glycol on the Reaction Step (1): Weigh a certain amount of ethylene glycol and methanol and 10g of an acid-base bifunctional ionic liquid catalyst, add them to a high-pressure reactor, seal it, and replace the gas in the high-pressure reactor with nitrogen three times to make the reactor oxygen-free. Fill the autoclave with nitrogen to pressurize it, heat the contents to 250°C, and control the pressure in the reactor to be approximately 4.5 MPa. Monitor the temperature and pressure changes during the reaction. After 5 hours of reaction, stop heating, cool the contents to below 30°C in a water bath or ice-water bath, open the autoclave, take samples, and perform gas phase analysis.

[0033] Step (2): The reaction solution from step (1) is distilled under normal pressure, and the fraction between 120°C and 130°C is collected, which is the target product, ethylene glycol monomethyl ether. The purity of the product is determined by gas chromatography.

[0034] The acid-base bifunctional ionic liquid catalyst used is .

[0035]

Claims

1. A catalytic preparation method of ethylene glycol monomethyl ether with high stability, characterized in that The steps include: (1) In the presence of an acid-base bifunctional ionic liquid, ethylene glycol and methanol are reacted to prepare a reaction solution containing ethylene glycol monomethyl ether; (2) post-treating the reaction solution obtained in step (1) to obtain a finished product of ethylene glycol monomethyl ether; Wherein: the acid-base dual-functionalized ionic liquid is selected from: 。 2. The preparation method according to claim 1, wherein: Step 1) The acid-base dual functionalized ionic liquid is selected from .

3. The preparation method according to claim 1 or 2, characterized in that: Step 1) is carried out under pressure, wherein the pressure is 4-5 MPa.

4. The preparation method according to claim 1 or 2, characterized in that: The reaction temperature of step 1) is 250°C to 300°C.

5. The preparation method according to claim 1 or 2, characterized in that: The reaction time of step 1) is 3 to 6 hours.

6. The preparation method according to claim 1 or 2, characterized in that: In step 1), the molar ratio of ethylene glycol to methanol is 1:2.5-3.

5.

7. The preparation method according to claim 6, characterized in that: The molar ratio of ethylene glycol to methanol is 1:3.

0.

8. The preparation method according to claim 1 or 2, characterized in that: In step 1), the molar mass ratio of ethylene glycol to the acid-base bifunctionalized ionic liquid is 1:5-50, expressed in mol / g.

9. The preparation method according to claim 1 or 2, characterized in that: Step 2) comprises the following steps: subjecting the reaction solution of step (1) to atmospheric distillation, and collecting the fraction between 120° C. and 130° C., which is the target product, ethylene glycol monomethyl ether.

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