Method for reducing content of harmful substances in propylene glycol n-methyl ether

Abstract

The invention relates to a method for reducing the content of harmful substances in propylene glycol n-methyl ether, which comprises the following steps: an etherification reaction liquid enters a methanol tower, a first gas-phase light component and a first liquid-phase heavy component are separated by heating, the first liquid-phase heavy component is gathered at the bottom of the methanol tower to form a kettle liquid, and a second gas-phase light component and a second liquid-phase heavy component are separated; the first gas-phase light component enters a compressor unit through the top of the methanol tower, enters a preheater through multi-stage compression and is cooled, a part of the first gas-phase light component is condensed to form condensate for reuse, the residual gas phase enters a flash tower and is heated to separate out a second liquid-phase heavy component and a second gas-phase light component, and the second gas-phase light component enters a condenser through the top of the flash tower; condensing to form a solution rich in acrolein; according to the method disclosed by the invention, methanol and acrolein are rapidly separated by utilizing the methanol tower, and then acrolein is rich in a small amount of materials to be separated by a compression flash evaporation method, so that the content of acrolein in the propylene glycol n-methyl ether product is kept at 0.0005% or below, and the product purity is effectively improved.

Description

A method for reducing the content of harmful substances in propylene glycol n-methyl ether Technical Field

[0001] This invention relates to the field of propylene glycol n-methyl ether preparation technology, and in particular to a method for reducing the content of harmful substances in propylene glycol n-methyl ether. Background Technology

[0002] Propylene glycol n-methyl ether is mainly used in the coatings and inks industry, the electronics industry, and also as an intermediate in the printing and dyeing industry and chemical synthesis. It is an intermediate for the herbicide metolachlor. As a solvent, dispersant, or diluent, it is used in the coatings, inks, printing and dyeing, pesticide, cellulose, and acrylate industries. It can also serve as an intermediate in organic synthesis, participating in various chemical reactions to prepare other more complex organic compounds. For example, it can undergo esterification and etherification reactions with other compounds to synthesize fine chemicals with special properties, finding applications in the synthesis processes of pharmaceuticals and pesticides.

[0003] The propylene glycol n-methyl ether (PME) is produced through an etherification reaction of excess methanol and propylene oxide (PO) under the action of a catalyst. During the production of propylene oxide, a small amount of acrolein is generated. Acrolein is a colorless or pale yellow liquid with a foul odor. Since acrolein does not react with methanol during the etherification process, a small amount of acrolein is present in the final product, propylene glycol n-methyl ether. This not only reduces the content and quality of the finished product but also makes it a hazardous substance in the use of propylene glycol n-methyl ether in chips and photoresists, significantly limiting its applicability. Since acrolein originates from the propylene oxide raw material, it is necessary to reduce its content through process improvements.

[0004] Therefore, this invention proposes a method for reducing the content of harmful substances in propylene glycol n-methyl ether to solve the above-mentioned problems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for reducing the content of harmful substances in propylene glycol n-methyl ether, thereby reducing the acrolein content in the propylene glycol n-methyl ether product and improving the product purity.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: a method for reducing the content of harmful substances in propylene glycol n-methyl ether, the innovation of which is that the method is completed by a purification system, which includes a methanol tower, a compressor unit, a preheater, a flash tower, and a condenser; the method includes the following steps: the etherification reaction liquid enters the methanol tower, is heated and separated to form a first gaseous light component and a first liquid heavy component, the first liquid heavy component accumulates at the bottom of the methanol tower to form a bottom liquid and is discharged from the bottom of the methanol tower, the first gaseous light component enters the compressor unit through the top of the methanol tower, enters the preheater through multi-stage compression, and after cooling, part of it condenses to form condensate for reuse, the remaining gaseous phase enters the flash tower, is heated and separated to form a second liquid heavy component and a second gaseous light component, the second liquid heavy component is discharged from the bottom of the flash tower for reuse, and the second gaseous light component enters the condenser through the top of the flash tower, and after condensation, forms a solution rich in acrolein.

[0007] Furthermore, the methanol tower is internally provided with a packing section and a plate section from bottom to top; the height of the packing section is two-thirds of the height of the methanol tower, and the packing section includes an upper packing section and a lower packing section, with the upper packing section located above the lower packing section; the plate section is provided with several first hot water jacket plates, which are arranged at equal intervals from top to bottom, and each first hot water jacket plate has several through holes; the methanol tower is provided with a methanol tower material inlet, a methanol tower gas phase outlet, and a methanol tower liquid phase outlet. The methanol tower material inlet is located at one-third of the height of the methanol tower and between the upper packing section and the lower packing section, the methanol tower gas phase outlet is located above the plate section, and the methanol tower liquid phase outlet is located below the lower packing section.

[0008] Furthermore, the compressor unit has a compressor unit gas phase inlet and a compressor unit gas phase outlet, and the methanol tower gas phase outlet is connected to the compressor unit gas phase inlet via a second pipeline; the preheater has a first heat exchange chamber and a second heat exchange chamber for heat exchange, the first heat exchange chamber has a preheater feed port at the top and a preheater material outlet at the bottom, the second heat exchange chamber has a preheater gas phase inlet and a preheater liquid phase outlet at the bottom and a preheater gas phase outlet at the top, the preheater material outlet is connected to the methanol tower material inlet via a first pipeline, and the compressor unit gas phase outlet is connected to the preheater gas phase inlet via a third pipeline; the flash tower has several second hot water jacket plates arranged sequentially from bottom to top, and the several second hot water jacket plates cooperate to form a serpentine channel, the flash tower has a flash tower gas phase inlet and a flash tower liquid phase outlet at the bottom and a flash tower gas phase outlet at the top, the preheater gas phase outlet is connected to the flash tower gas phase inlet via a fourth pipeline, and the flash tower gas phase outlet is connected to the condenser gas phase inlet via a fifth pipeline.

[0009] Furthermore, the etherification reaction solution includes the target product propylene glycol n-methyl ether, methanol, and light component impurities, wherein the mass content of propylene glycol n-methyl ether is 45-55%, the mass content of methanol is 40-50%, the mass content of light component impurities is 0.1-0.3%, the propylene glycol n-methyl ether includes heavy component derivatives, and the light component impurities include acrolein.

[0010] Furthermore, the etherification reaction liquid is preheated to 70-80°C by a preheater before entering the methanol tower.

[0011] Furthermore, the negative pressure inside the methanol tower is controlled to be ≤-0.08MPa, and the temperature inside the methanol tower is controlled to keep the temperature of the plate section within a range of 2~5℃ higher than the boiling point of methanol.

[0012] Furthermore, the first gaseous light component enters the compressor unit through the top of the methanol tower for 3 to 5 stages of compression, where the pressure changes from negative to positive (≤0.4MPa) and the temperature rises from 50 to 60°C to 95 to 105°C before entering the preheater.

[0013] Furthermore, the first gaseous light component enters a preheater and is cooled to 75~85°C, with the pressure reduced to 0.25~0.3MPa.

[0014] Furthermore, the flash tower is kept at atmospheric pressure and the temperature is controlled to be 2-5°C above the boiling point of acrolein.

[0015] Furthermore, the mass content of methanol and light component impurities in the reactor liquid is ≤0.005%, and the mass content of acrolein is ≤0.0005%; the mass content of methanol in the condensate is ≥99.5%; the mass content of methanol in the second liquid phase heavy component is ≥99.5%; and the mass content of light component impurities in the acrolein-rich solution is ≤5%.

[0016] The advantages of this invention are: the method of this invention utilizes a methanol tower to quickly separate methanol and acrolein, and then separates the acrolein-rich material in a small amount of material by compression flash evaporation, so that the acrolein content in the propylene glycol n-methyl ether product is kept at 0.0005% or less, which effectively improves the purity of the product.

[0017] The method of this invention utilizes the boiling point difference of different components in the etherification reaction liquid, and uses high specific heat hot water to enhance the separation of gases in the methanol tower. Negative pressure distillation and temperature control are used to achieve rapid separation of the first gas phase light component (methanol and acrolein). At the same time, the lower section of the methanol tower is designed with packing, which has high separation efficiency and can efficiently separate propylene glycol n-methyl ether and the first gas phase light component. The upper section of the methanol tower has a tray structure, and the separated first gas phase light component can rise rapidly into the compressor unit.

[0018] The first gaseous light component separated by the methanol tower of the present invention is continuously compressed by the compressor unit, changing from negative pressure to positive pressure and from low temperature gas to high temperature gas. While providing a heat source for preheating the etherification reaction liquid in the preheater, the methanol in the high temperature gas is initially separated for reuse, effectively reducing the energy consumption of the methanol tower by 5-8%.

[0019] The remaining gas after the first gaseous light component of the present invention is cooled by a preheater and then enters a flash tower, where it is rapidly reduced from high pressure to atmospheric pressure. The flash tower is heated by a jacket, and the first gaseous light component rich in acrolein enters the flash tower condenser for condensation and collection. Methanol with a lower acrolein content is reused as a heavy component, which effectively reduces the cost of raw materials.

[0020] The method of this invention overcomes the high energy consumption and high investment measures such as deep distillation and high reflux ratio adopted in traditional distillation separation processes to eliminate small amounts of impurities. It separates impurities rich in a small amount of material, while recovering part of the heat source, improving separation efficiency and reducing energy consumption. This keeps the harmful substances in the product at an extremely low level, providing sufficient guarantee for the wide application of the product in new fields. Attached Figure Description

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0022] Figure 1 is a schematic diagram of the connection of the impurity removal system of the present invention. Detailed Implementation

[0023] 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.

[0024] This embodiment provides a method for reducing the content of harmful substances in propylene glycol n-methyl ether, which is accomplished using a purification system.

[0025] As shown in Figure 1, the impurity removal system includes a methanol tower 1, a compressor unit 2, a preheater 3, a flash tower 4, and a condenser 5.

[0026] The methanol tower 1 has a packing section and a plate section 13 arranged sequentially from bottom to top. The height of the packing section is two-thirds of the height of the methanol tower 1. The packing section includes an upper packing section 12 and a lower packing section 11. The upper packing section 12 is located above the lower packing section 1. The plate section 13 is provided with a number of first hot water jacket plates 131. The number of first hot water jacket plates 131 are arranged at equal intervals from top to bottom. Each first hot water jacket plate 131 has a number of through holes and has a first hot water flow channel inside. The methanol tower body is provided with a first jacket to control the internal temperature of the methanol tower and to supply hot water to the first hot water flow channel. The methanol tower 1 is equipped with a methanol tower material inlet 1a, a methanol tower gas phase outlet 1b, and a methanol tower liquid phase outlet 1c. The methanol tower material inlet 1a is located at one-third of the height of the methanol tower 1, between the upper packing section 12 and the lower packing section 11. The methanol tower gas phase outlet 1b is located above the plate section and is opened at the top of the methanol tower 1. The methanol tower liquid phase outlet 1c is located below the lower packing section and is opened at the bottom of the methanol tower 1.

[0027] Compressor unit 2 has a compressor unit gas phase inlet 2a and a compressor unit gas phase outlet 2b. The methanol tower gas phase outlet 1b is connected to the compressor unit gas phase inlet 2a through the second pipeline L2.

[0028] The preheater 3 has a first heat exchange chamber and a second heat exchange chamber for heat exchange. The top of the first heat exchange chamber is provided with a preheater feed port 3c and the bottom of the first heat exchange chamber is provided with a preheater material outlet 3d. The bottom of the second heat exchange chamber is provided with a preheater gas phase inlet 3a and a preheater liquid phase outlet, and the top of the second heat exchange chamber is provided with a preheater gas phase outlet 3b. The preheater material outlet 3d is connected to the methanol tower material inlet 1a through a first pipeline L1, and the compressor unit gas phase outlet 2b is connected to the preheater gas phase inlet 3a through a third pipeline L3.

[0029] The flash tower 4 has several second hot water jacket plates 41 arranged sequentially from bottom to top. These second hot water jacket plates 41 cooperate to form a serpentine channel. Each second hot water jacket plate 41 has a second hot water flow channel. The tower body of the flash tower 4 is equipped with a second jacket, which is used to control the internal temperature of the flash tower 4 and supply hot water to the second hot water flow channel. The bottom of the flash tower 4 is equipped with a flash tower gas phase inlet 4a and a flash tower liquid phase outlet 4b. The top of the flash tower 4 is equipped with a flash tower gas phase outlet 4c. The preheater gas phase outlet 3b is connected to the flash tower gas phase inlet 4a through a fourth pipeline L4, and the flash tower gas phase outlet 4c is connected to the condenser 5 gas phase inlet through a fifth pipeline L5.

[0030] The above-mentioned impurity removal system is used to reduce the content of harmful substances in propylene glycol n-methyl ether. The etherification reaction solution includes the target product propylene glycol n-methyl ether, methanol, and light component impurities. The mass content of propylene glycol n-methyl ether is 53.3%, the mass content of methanol is 46.5%, and the mass content of light component impurities is 0.2%. Propylene glycol n-methyl ether includes heavy component derivatives, and light component impurities include acrolein.

[0031] The method for reducing the content of harmful substances in propylene glycol n-methyl ether includes the following steps: S1, the etherification reaction liquid enters the first heat exchange chamber of the preheater 3 through the feed port 3c of the preheater and is preheated to 75°C. Then it leaves the preheater through the material outlet 3d of the preheater and enters the methanol tower 1 through the material inlet 1a of the methanol tower. The negative pressure in the methanol tower 1 is controlled at -0.08MPa. The etherification reaction liquid is heated and separated into a first gas phase light component and a first liquid phase heavy component. The first liquid phase heavy component accumulates at the bottom of the methanol tower to form a bottom liquid and is discharged from the methanol tower liquid outlet 1c at the bottom of the methanol tower 1.

[0032] After the etherification reaction liquid enters methanol tower 1, the lower packing section 11 separates a small amount of methanol containing light component impurities from the first liquid phase heavy component, reducing the amount of methanol entering the reactor liquid. This ensures that the mass content of methanol and light component impurities in the reactor liquid is ≤0.005%, and the mass content of acrolein is ≤0.0005%. The upper packing section 12 separates the propylene glycol n-methyl ether heavy component, increasing the content of the first gas phase light component before the plate section 13. The plate section 13, under the action of the first hot water jacket plate 131, simultaneously heats methanol and cools propylene glycol n-methyl ether, controlling the temperature of the plate section 13 within 5°C above the boiling point of methanol. This rapidly removes the first gas phase light component from methanol tower 1, while reducing methanol reflux and lowering the separation difficulty of the first liquid phase light component.

[0033] S2. The first gaseous light component leaves methanol tower 1 from the gaseous outlet 1b of the methanol tower, enters compressor unit 2 through the gaseous inlet 2a of the compressor unit, and undergoes five-stage compression. The pressure changes from negative pressure -0.08MPa to positive pressure 0.4MPa, and the temperature rises from 53℃ to 100℃. After leaving compressor unit 2 through the gaseous outlet 2b of the compressor unit, it enters the second heat exchange chamber of preheater 3 through the gaseous inlet 3a of the preheater.

[0034] S3, the first gaseous light component in the second heat exchange chamber of preheater 3 serves as a heat source to heat the etherification reaction liquid in the first heat exchange chamber of preheater 3. It cools down to 80°C and the pressure drops to 0.25MPa. A portion of it condenses to form condensate for reuse. The methanol content in the condensate is ≥99.5%.

[0035] S4. The remaining gaseous phase of the first gaseous light component leaves the preheater 3 through the gaseous outlet 3b of the preheater, and then enters the flash tower 4 through the gaseous inlet 4a of the flash tower for rapid flash evaporation. The flash tower is under atmospheric pressure control. Under the action of the second hot water jacket plate 41 in the flash tower 4, the temperature is controlled to be 3°C higher than the boiling point of acrolein. At the same time, acrolein is heated and methanol is cooled. The second liquid phase heavy component and the second gaseous light component are separated by heating. The second liquid phase heavy component is discharged from the flash tower liquid outlet 4b at the bottom of the flash tower 4 for reuse. The mass content of methanol in the second liquid phase heavy component is ≥99.5%. S5. The second gaseous light component leaves the flash tower 4 through the flash tower gaseous outlet 4c at the top of the flash tower 4, and enters the condenser 5 through the gaseous inlet of the condenser 5. The condenser 5 cools the second gaseous light component, and after condensation, a solution rich in acrolein is formed. The mass content of light component impurities in the solution rich in acrolein is ≤5%.

[0036] The above-mentioned method for reducing the content of harmful substances in propylene glycol n-methyl ether utilizes the boiling point difference of different components in the etherification reaction liquid. High-specific-heat hot water is used to enhance the separation of gases in the methanol tower, and negative-pressure distillation with temperature control achieves rapid separation of the first gaseous light components (methanol and acrolein). Simultaneously, the lower section of the methanol tower is designed with packing, resulting in high separation efficiency, effectively separating propylene glycol n-methyl ether and the first gaseous light components. The upper section of the methanol tower has a tray structure, allowing the separated first gaseous light components to rise rapidly into the compressor unit. Through continuous compression by the compressor unit, the pressure changes from negative to positive, and from low-temperature gas to high-temperature gas. This provides a heat source for preheating the etherification reaction liquid in the preheater while simultaneously pre-separating methanol from the high-temperature gas for reuse, effectively reducing the methanol tower's energy consumption by 5-8%. The remaining gas phase after condensation of the first gaseous light components is cooled by the preheater and enters the flash tower, where it is rapidly reduced from high pressure to atmospheric pressure. The flash tower is heated by a jacket, and the first gaseous light components rich in acrolein enter the flash tower condenser for collection. Methanol with lower acrolein content is reused as a heavy component, effectively reducing raw material costs.

[0037] The method for reducing the content of harmful substances in propylene glycol n-methyl ether of the present invention overcomes the high energy consumption and high investment measures such as deep distillation and high reflux ratio adopted in the traditional distillation separation process to eliminate a small amount of impurities. The method separates the impurities into a small amount of material, while recovering part of the heat source, thereby improving the separation efficiency and reducing energy consumption. This keeps the harmful substances in the product at an extremely low level, providing sufficient guarantee for the wide application of the product in new fields.

[0038] 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 reducing the content of harmful substances in propylene glycol n-methyl ether, characterized in that: The method employs a purification system comprising a methanol tower, a compressor unit, a preheater, a flash tower, and a condenser. The method includes the following steps: the etherification reaction liquid enters the methanol tower, where it is heated to separate a first gaseous light component and a first liquid heavy component. The first liquid heavy component accumulates at the bottom of the methanol tower to form a bottom liquid, which is discharged from the bottom of the methanol tower. The first gaseous light component enters the compressor unit through the top of the methanol tower, undergoes multi-stage compression, and enters the preheater. After cooling, a portion condenses to form condensate for reuse. The remaining gaseous phase enters the flash tower, where it is heated to separate a second liquid heavy component and a second gaseous light component. The second liquid heavy component is discharged from the bottom of the flash tower for reuse. The second gaseous light component enters the condenser through the top of the flash tower, where it condenses to form a solution rich in acrolein.

2. The method for reducing the content of harmful substances in propylene glycol n-methyl ether according to claim 1, characterized in that: The methanol tower is internally equipped with a packing section and a plate section from bottom to top. The height of the packing section is two-thirds of the height of the methanol tower. The packing section includes an upper packing section and a lower packing section, with the upper packing section located above the lower packing section. The plate section is equipped with several first hot water jacket plates, which are arranged at equal intervals from top to bottom. Each first hot water jacket plate has several through holes. The methanol tower is equipped with a methanol tower material inlet, a methanol tower gas phase outlet, and a methanol tower liquid phase outlet. The methanol tower material inlet is located at one-third of the height of the methanol tower, between the upper and lower packing sections. The methanol tower gas phase outlet is located above the plate section, and the methanol tower liquid phase outlet is located below the lower packing section.

3. The method for reducing the content of harmful substances in propylene glycol n-methyl ether according to claim 2, characterized in that: The compressor unit has a compressor unit gas phase inlet and a compressor unit gas phase outlet. The methanol tower gas phase outlet is connected to the compressor unit gas phase inlet via a second pipeline. The preheater has a first heat exchange chamber and a second heat exchange chamber for heat exchange. The first heat exchange chamber has a preheater feed port at the top and a preheater material outlet at the bottom. The second heat exchange chamber has a preheater gas phase inlet and a preheater liquid phase outlet at the bottom and a preheater gas phase outlet at the top. The preheater material outlet is connected to the methanol tower material inlet via a first pipeline. The compressor unit gas phase outlet is connected to the preheater gas phase inlet via a third pipeline. The flash tower has several second hot water jacket plates arranged sequentially from bottom to top. The several second hot water jacket plates cooperate to form a serpentine channel. The flash tower has a flash tower gas phase inlet and a flash tower liquid phase outlet at the bottom and a flash tower gas phase outlet at the top. The preheater gas phase outlet is connected to the flash tower gas phase inlet via a fourth pipeline and the flash tower gas phase outlet is connected to the condenser gas phase inlet via a fifth pipeline.

4. The method for reducing the content of harmful substances in propylene glycol n-methyl ether according to claim 1, characterized in that: The etherification reaction solution includes the target product propylene glycol n-methyl ether, methanol, and light component impurities, wherein the mass content of propylene glycol n-methyl ether is 45-55%, the mass content of methanol is 40-50%, the mass content of light component impurities is 0.1-0.3%, the propylene glycol n-methyl ether includes heavy component derivatives, and the light component impurities include acrolein.

5. The method for reducing the content of harmful substances in propylene glycol n-methyl ether according to claim 1, characterized in that: Before entering the methanol tower, the etherification reaction liquid is preheated to 70~80℃ by a preheater.

6. The method for reducing the content of harmful substances in propylene glycol n-methyl ether according to claim 1, characterized in that: The negative pressure inside the methanol tower is controlled to be ≤-0.08MPa, and the temperature inside the methanol tower is controlled to keep the temperature of the plate section within a range of 2~5℃ higher than the boiling point of methanol.

7. The method for reducing the content of harmful substances in propylene glycol n-methyl ether according to claim 1, characterized in that: The first gaseous light component enters the compressor unit through the top of the methanol tower for 3 to 5 stages of compression, where the pressure changes from negative to positive (≤0.4MPa) and the temperature rises from 50 to 60°C to 95 to 105°C before entering the preheater.

8. The method for reducing the content of harmful substances in propylene glycol n-methyl ether according to claim 1, characterized in that: The first gaseous light component enters the preheater and is cooled to 75~85°C, and the pressure drops to 0.25~0.3MPa.

9. The method for reducing the content of harmful substances in propylene glycol n-methyl ether according to claim 1, characterized in that: The flash tower is kept under normal pressure, and the temperature is controlled to be 2-5°C above the boiling point of acrolein.

10. The method for reducing the content of harmful substances in propylene glycol n-methyl ether according to claim 1, characterized in that: The mass content of methanol and light component impurities in the reactor liquid is ≤0.005%, and the mass content of acrolein is ≤0.0005%; the mass content of methanol in the condensate is ≥99.5%; the mass content of methanol in the second liquid phase heavy component is ≥99.5%; and the mass content of light component impurities in the acrolein-rich solution is ≤5%.

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