Synthesis method for improving conversion rate of propylene glycol n-methyl ether

Abstract

The invention relates to a synthesis method for improving the conversion rate of propylene glycol n-methyl ether, which comprises the following steps of: firstly, mixing raw materials, namely methanol and epoxypropane, sequentially introducing the mixed raw materials into three stages of horizontal reactors, and carrying out etherification reaction on the mixed raw materials and solid acid catalysts in the horizontal reactors at multiple stages of temperatures to obtain the propylene glycol n-methyl ether. And after the reaction is finished, dealcoholizing, rectifying and separating to obtain high-purity propylene glycol n-methyl ether. According to the synthesis method disclosed by the invention, a multi-section temperature control technology is adopted for etherification reaction, so that the reaction temperature is increased by 5-10 DEG C section by section, high-temperature reaction is avoided, side reaction is effectively inhibited, 10-15% of by-product propylene glycol isomethyl ether is effectively reduced, and the conversion rate of propylene glycol n-methyl ether is increased to 97% or above.

Description

Technical Field

[0001] This invention relates to the field of propylene glycol n-methyl ether production, and particularly to a synthesis method for improving the conversion rate of propylene glycol n-methyl ether. Background Technology

[0002] Propylene glycol n-methyl ether (PM), as an important environmentally friendly solvent, is widely used in coatings, inks, electronic cleaning, and pesticides. With environmental and health concerns leading to restrictions on ethylene glycol ether products, the demand for propylene glycol ethers and their esters is increasing. Currently, industrial production of propylene glycol methyl ether mostly uses liquid acid catalysts, which suffers from severe equipment corrosion, numerous side reactions, poor product selectivity, and complex post-processing. In particular, the reaction process easily generates the byproduct propylene glycol isomethyl ether, affecting product purity and market competitiveness.

[0003] In existing technologies, problems such as imprecise reaction temperature control and difficulty in catalyst recovery hinder the development of propylene glycol methyl ether production efficiency and environmental friendliness. Therefore, there is an urgent need to develop a high-efficiency, low-consumption, and green propylene glycol methyl ether synthesis process. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a synthesis method for improving the conversion rate of propylene glycol n-methyl ether, which can reduce the generation of by-products and waste in production, and improve etherification efficiency and product content.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: a synthesis method for improving the conversion rate of propylene glycol n-methyl ether, the innovation of which is: including the following steps: first, mixing raw material methanol with propylene oxide, then passing the mixed raw material sequentially into a three-stage horizontal reactor, and carrying out an etherification reaction with the solid acid catalyst in each stage of the horizontal reactor at multiple temperatures, and after the reaction is completed, obtaining high-purity propylene glycol n-methyl ether by de-alcoholization and distillation separation.

[0006] Furthermore, the specific steps are as follows: S1: Etherification raw material preparation: Add methanol and propylene oxide to the preparation container in sequence and mix them. Heat the mixed raw materials to 100±10℃. At the same time, add solid acid catalyst to the first-stage horizontal reactor, the second-stage horizontal reactor and the third-stage horizontal reactor respectively. S2: Etherification reaction: The heated mixed raw materials first enter a primary horizontal reactor for etherification reaction at a temperature of 125±2℃ and a reaction pressure of 1-1.2MPa for 2 hours. Then, the mixed raw materials enter a secondary horizontal reactor for reaction at a temperature of 130±2℃ and a reaction pressure of 1-1.2MPa for 1 hour. Finally, the mixed raw materials enter a tertiary horizontal reactor for further reaction at a temperature of 135±2℃ and a reaction pressure of 1-1.2MPa for 1 hour. The etherification reaction is then completed, yielding the reactants, which include a solid acid catalyst and liquid products. The liquid products include, but are not limited to, propylene glycol methyl ether, byproducts, and unreacted raw materials. S3: Catalyst recovery: Separate the solid acid catalyst from the liquid product in the reactants, retain the solid acid catalyst particles, and allow the liquid product to pass through smoothly. The recovered solid acid catalyst particles are then recycled in the horizontal reactors of each stage. S4: De-alcoholization: The liquid product is then treated by methanol removal in the bottom of the de-alcoholization tower to remove excess methanol and unreacted propylene oxide. The temperature of the bottom of the de-alcoholization tower is 115℃±5℃ and the temperature of the top of the tower is 105℃±5℃. After de-alcoholization, crude propylene glycol n-methyl ether is obtained. S5: Distillation: The crude propylene glycol methyl ether after de-alcoholization is fed into a distillation column for distillation. The bottom temperature of the distillation column is about 145℃±5℃, and the top temperature is 125℃±5℃. 99.9% propylene glycol methyl ether is obtained at the top of the column, and heavy tar is obtained as a by-product at the bottom of the distillation column.

[0007] Furthermore, in step S1, the solid acid catalyst is a sulfuric acid-modified silica-supported heteropolyacid composite material, preferably a sulfuric acid-modified SiO2-supported phosphotungstic acid.

[0008] Furthermore, in step S1, the mass ratio of methanol to propylene oxide is 20:7.

[0009] Furthermore, the amount of the solid acid catalyst used is 1% to 2% of the total mass of the mixed raw materials.

[0010] Furthermore, in step S3, the solid acid catalyst and the liquid product are separated by a plate and frame filter press.

[0011] The advantages of this invention are as follows: The synthesis method of this invention uses multi-stage temperature control technology to gradually increase the reaction temperature by 5~10℃ in stages, avoiding high-temperature reactions, effectively suppressing side reactions, effectively reducing the formation of byproduct propylene glycol isomethyl ether by 10~15%, and increasing the conversion rate of propylene glycol n-methyl ether to over 97%.

[0012] This invention replaces the traditional catalyst with a solid acid catalyst, thus avoiding the corrosion of equipment by liquid acid, and the catalyst is easy to recycle and reuse.

[0013] The synthesis method of this invention uses a recyclable solid catalyst, and the overall process is green and environmentally friendly, meeting the requirements of modern clean chemical production and possessing good prospects for industrialization. Attached Figure Description

[0014] Figure 1 This is a production flow diagram of the synthesis method for improving the conversion rate of propylene glycol n-methyl ether according to the present invention. Detailed Implementation

[0015] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0016] The following is in conjunction with the appendix Figure 1 The method for synthesizing propylene glycol n-methyl ether to improve the conversion rate of the present invention will be further described below: Example 1 Methanol and propylene oxide were mixed at a mass ratio of 20:7. 2% sulfuric acid-modified SiO2-supported phosphotungstic acid was added in equal proportions to three horizontal reactors: a primary horizontal reactor, a secondary horizontal reactor, and a tertiary horizontal reactor. The heated mixture first entered the primary horizontal reactor for etherification at 125°C and 1.2 MPa for 2 hours. Then, the mixture entered the secondary horizontal reactor for further reaction at 130°C and 1.2 MPa for 1 hour. Finally, the mixture entered the tertiary horizontal reactor for continued reaction at 135°C and 1.2 MPa for 1 hour, completing the etherification reaction and yielding the reactants. These reactants included a solid acid catalyst and liquid products, including, but not limited to, propylene glycol methyl ether, byproducts, and unreacted reactants.

[0017] The solid acid catalyst in the reactants is separated from the liquid product. The solid acid catalyst particles are retained while the liquid product is allowed to pass through smoothly. The recovered solid acid catalyst particles are recycled in the horizontal reactors of each stage. The liquid product is then treated to remove methanol from the bottom of a dealcoholization tower to remove excess methanol and unreacted propylene oxide. The temperature of the bottom of the dealcoholization tower is 115℃±5℃, and the temperature of the top of the tower is 105℃±5℃. After dealcoholization, crude propylene glycol n-methyl ether is obtained.

[0018] The crude propylene glycol n-methyl ether, after being de-alcoholized, is fed into a distillation column for distillation. The bottom temperature of the distillation column is approximately 145℃±5℃, and the top temperature is 125℃±5℃. 97.6% propylene glycol n-methyl ether is obtained at the top of the column, with 0.05% propylene glycol isomethyl ether as a byproduct. Heavy tar is obtained at the bottom of the distillation column as a byproduct.

[0019] Example 2 Methanol and propylene oxide were mixed at a mass ratio of 20:7. 2% sulfuric acid-modified SiO2-supported phosphotungstic acid was added to a single-stage reactor, and the reaction was carried out directly in the single-stage reactor at a reaction temperature of 135°C and a pressure of 1.2 MPa for a total reaction time of 4 hours. After the reaction, the treatment was the same as in Example 1. Propylene glycol n-methyl ether was obtained by separation and distillation with a conversion rate of 97.3% and a content of 0.06% for the byproduct propylene glycol isomethyl ether.

[0020] Example 3 Methanol and propylene oxide are mixed at a mass ratio of 20:7, and a liquid catalyst sodium methoxide methanol solution of 5% of the total mass of the raw materials is added in equal proportions to the first-stage horizontal reactor, the second-stage horizontal reactor, and the third-stage horizontal reactor.

[0021] The heated mixed raw materials first enter a primary horizontal reactor for etherification at a temperature of 125°C and a pressure of 1.2 MPa for 2 hours. Then, the mixed raw materials enter a secondary horizontal reactor for further reaction at a temperature of 130°C and a pressure of 1.2 MPa for 1 hour. Finally, the mixed raw materials enter a tertiary horizontal reactor for continued reaction at a temperature of 135°C and a pressure of 1.2 MPa for 1 hour, at which point the etherification reaction is complete, yielding the reactants. These reactants include a solid acid catalyst and liquid products, including, but not limited to, propylene glycol methyl ether, byproducts, and unreacted raw materials.

[0022] The solid acid catalyst in the reactants is separated from the liquid product. The solid acid catalyst particles are retained while the liquid product is allowed to pass through smoothly. The recovered solid acid catalyst particles are recycled in the horizontal reactors of each stage. The liquid product is then treated to remove methanol from the bottom of a dealcoholization tower to remove excess methanol and unreacted propylene oxide. The temperature of the bottom of the dealcoholization tower is 115℃±5℃, and the temperature of the top of the tower is 105℃±5℃. After dealcoholization, crude propylene glycol n-methyl ether is obtained.

[0023] The crude propylene glycol n-methyl ether, after being de-alcoholized, is fed into a distillation column for distillation. The bottom temperature of the distillation column is approximately 145℃±5℃, and the top temperature is 125℃±5℃. 96.4% propylene glycol n-methyl ether is obtained at the top of the column, with 0.12% propylene glycol isomethyl ether as a byproduct. Heavy tar is obtained at the bottom of the distillation column as a byproduct.

[0024] Example 4 Methanol and propylene oxide were mixed at a mass ratio of 20:7, and then 5% of the total mass of the raw materials was added as a liquid catalyst sodium methoxide methanol solution. The reaction was carried out in a single-stage reactor at a reaction temperature of 135°C and a pressure of 1.2 MPa for a total reaction time of 4 hours. After the reaction, the treatment was the same as in Example 3. Propylene glycol n-methyl ether was obtained by separation and distillation with a conversion rate of 95% and a content of 0.14% of the byproduct propylene glycol isomethyl ether.

[0025] Example 5 Methanol and propylene oxide were mixed at a mass ratio of 20:7. 2% of the total mass of the raw materials was added to the reactor along with phosphotungstic acid modified with sulfuric acid at a yield of 2%. The reaction was the same as in Example 1. Propylene glycol n-methyl ether was obtained by separation and distillation with a conversion rate of 97.4%. The content of the byproduct propylene glycol isomethyl ether was 0.06%.

[0026] The results of the above case studies show that by using solid catalysts or recycled solid catalysts and employing multi-stage temperature control, the conversion rate of propylene glycol n-methyl ether can be increased from 95% to 97.6%, and the content of the byproduct propylene glycol isomethyl ether can be reduced from 0.14% to 0.05%.

[0027] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for synthesizing propylene glycol n-methyl ether with improved conversion rate, characterized in that: The process includes the following steps: First, methanol and propylene oxide are mixed. Then, the mixed raw materials are sequentially fed into a three-stage horizontal reactor and undergo etherification with solid acid catalysts in each stage of the horizontal reactor at multiple temperatures. After the reaction is completed, high-purity propylene glycol n-methyl ether is obtained by de-alcoholization and distillation.

2. The method for improving the conversion rate of propylene glycol n-methyl ether according to claim 1, characterized in that: The specific steps are as follows: S1: Etherification raw material preparation: Add methanol and propylene oxide to the preparation container in sequence and mix them. Heat the mixed raw materials to 100±10℃. At the same time, add solid acid catalyst to the first-stage horizontal reactor, the second-stage horizontal reactor and the third-stage horizontal reactor respectively. S2: Etherification reaction: The heated mixed raw materials first enter a primary horizontal reactor for etherification reaction at a temperature of 125±2℃ and a reaction pressure of 1-1.2MPa for 2 hours. Then, the mixed raw materials enter a secondary horizontal reactor for reaction at a temperature of 130±2℃ and a reaction pressure of 1-1.2MPa for 1 hour. Finally, the mixed raw materials enter a tertiary horizontal reactor for further reaction at a temperature of 135±2℃ and a reaction pressure of 1-1.2MPa for 1 hour. The etherification reaction is then completed, yielding the reactants, which include a solid acid catalyst and liquid products. The liquid products include, but are not limited to, propylene glycol methyl ether, byproducts, and unreacted raw materials. S3: Catalyst recovery: Separate the solid acid catalyst from the liquid product in the reactants, retain the solid acid catalyst particles, and allow the liquid product to pass through smoothly. The recovered solid acid catalyst particles are then recycled in the horizontal reactors of each stage. S4: De-alcoholization: The liquid product is then treated by methanol removal in the bottom of the de-alcoholization tower to remove excess methanol and unreacted propylene oxide. The temperature of the bottom of the de-alcoholization tower is 115℃±5℃ and the temperature of the top of the tower is 105℃±5℃. After de-alcoholization, crude propylene glycol n-methyl ether is obtained. S5: Distillation: The crude propylene glycol methyl ether after de-alcoholization is fed into a distillation column for distillation. The bottom temperature of the distillation column is about 145℃±5℃, and the top temperature is 125℃±5℃. 99.9% propylene glycol methyl ether is obtained at the top of the column, and heavy tar is obtained as a by-product at the bottom of the distillation column.

3. The method for improving the conversion rate of propylene glycol n-methyl ether according to claim 2, characterized in that: In step S1, the solid acid catalyst is a sulfuric acid-modified silica-supported heteropolyacid composite material, preferably sulfuric acid-modified SiO2-supported phosphotungstic acid.

4. The method for improving the conversion rate of propylene glycol n-methyl ether according to claim 2, characterized in that: In step S1, the mass ratio of methanol to propylene oxide is 20:

7.

5. The method for synthesizing propylene glycol n-methyl ether according to claim 2, characterized in that: The amount of the solid acid catalyst used is 1% to 2% of the total mass of the mixed raw materials.

6. The method for synthesizing propylene glycol n-methyl ether according to claim 2, characterized in that: In step S3, the solid acid catalyst and the liquid product are separated by a plate and frame filter press.

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