A method for producing electronic grade dmc by low energy membrane process

Abstract

The application couples the pervaporation membrane process breaking the azeotropic system balance, the high-pressure rectification tower with high-efficiency separation and the reverse osmosis membrane process blocking the penetration of trace metal ions, so as to integrate a purification process for producing electronic-grade DMC. The method helps the membrane method to obtain practical industrial application in the electronic-grade DMC industry, and the NH2-PDMS composite membrane has organic solvent resistance, preferential selectivity for DMC organic matter, and blocking penetration effect on metal ions and micro-plastic particles with concentration of ppm or ppb.

Description

Technical Field

[0001] The present invention relates to a method for producing electronic-grade DMC by a low-energy membrane process. The preferred pervaporation membrane element and reverse osmosis membrane element are integrated with a high-pressure distillation tower and can be used in the field of purification and production of electronic-grade dimethyl carbonate (DMC), a high-value electronic chemical. Background Art

[0002] Electronic chemicals broadly refer to specialized chemicals and chemical materials used in the electronics industry, including various chemicals and materials used in the production and packaging of electronic components, printed circuit boards, and industrial and consumer devices. Wet electronic chemicals are diverse and have high technical barriers to entry, making them prone to technical bottlenecks. Dimethyl carbonate (DMC) is widely used in pesticides, pharmaceuticals, dyes, fine chemicals, and the electronics industry, earning it the nickname "green" chemical and a "new building block" for chemical synthesis.

[0003] Currently, the industrial production of electronic-grade DMC typically utilizes multi-stage continuous distillation and fractionation. For organic / organic or organic / water azeotropic systems, azeotropic or extractive distillation processes are often employed. Both require the addition of a third component as an entrainer to form a new azeotrope for separation and purification. This combined process is cumbersome, energy-intensive, and requires significant floor space.

[0004] Membrane technology is a new type of green and energy-saving technology with a wide range of applications. Pervaporation membranes can easily break the azeotropic equilibrium of the system without the introduction of a third component, reducing the intervention of foreign impurities. The pervaporation membranes and reverse osmosis membranes that are resistant to organic solvents and preferentially permeate organic matter are both dense membrane layers that can block the penetration of metal ions and microplastic particles, and at the same time can concentrate the target to a certain extent (such as the purification of DMC). The commercial NaA molecular sieve membranes that are more commonly used in the existing engineering applications of molecular sieve membrane separation processes have an effective pore size range of 0.3-0.5nm. The most classic industrial application is the dehydration of alcohols, including methanol and ethanol. Although the molecular kinetic diameter of methanol of 0.38nm is between this range, methanol usually exists in the form of methanol tetramers in the solution system, resulting in a large permeation resistance of methanol through the membrane layer. Usually, more than 95% of the methanol will be retained, resulting in a high content of methanol in the crude DMC product on the retentate side, resulting in a low separation factor and a low permeability coefficient (LiH, Qiu C, Ren S, et al. Na +-gated water-conducting nanochannels for boosting CO2conversion to liquid fuels[J].Science,2020,367(6478):667-671.). Moreover, the preparation process of molecular sieve membranes is complicated compared with organic membranes, so this technology is still far from practical application. Therefore, there is an urgent need to develop a new purification method for electronic-grade DMC. Summary of the Invention

[0005] To address these challenges, the present invention integrates a purification process for producing electronic-grade DMC by coupling a pervaporation membrane process to break the azeotropic equilibrium, a high-pressure distillation tower for efficient separation, and a reverse osmosis membrane process to block the permeation of trace metal ions. This method facilitates the practical industrial application of membrane processes in the electronic-grade DMC industry. Furthermore, the NH2-PDMS composite membrane exhibits resistance to organic solvents, preferential selectivity for DMC organics, and a permeation barrier effect against metal ions and microplastic particles at concentrations in the ppm or ppb range.

[0006] The present invention provides a method for producing electronic-grade DMC by a low-energy membrane process. The method comprises the following steps: introducing a raw material containing DMC into a pervaporation membrane module, and continuously introducing a condensate on the permeation side into a high-pressure distillation tower to obtain an industrial-grade DMC solution in the tower bottom. The industrial-grade DMC solution is then pumped into a reverse osmosis membrane module via a feed pump to block the permeation of trace metal ions, thereby obtaining an electronic-grade DMC solution.

[0007] Preferably, the pervaporation membrane assembly uses a pervaporation membrane with a thickness of micrometers, and the pervaporation membrane preparation method comprises the following steps:

[0008] P1: dissolving aminopropyl-terminated polydimethylsiloxane in a first organic solvent to form a high-concentration pervaporation membrane casting solution, and evenly coating the solution on the surface of the PTFE base membrane by a doctor blade method to form a wet silicone rubber / PTFE composite membrane;

[0009] P2: Immerse the wet silicone rubber / PTFE composite membrane in a mixture of organic small molecules / alcohol containing formyl chloride for 1-8 hours, take it out and dry it in the shade for 1-4 days to allow it to slowly crosslink, and then dry it at a certain temperature for several hours. The concentration of formyl chloride in the mixture is 0.2-3wt%.

[0010] Preferably, the reverse osmosis membrane assembly adopts a nanometer-thick reverse osmosis membrane, and the reverse osmosis membrane uses layer-by-layer self-organization technology to control the thickness of the separation layer on the surface of the PTFE base membrane. The preparation method of the reverse osmosis membrane includes the following steps:

[0011] R1: dissolving aminopropyl-terminated polydimethylsiloxane in a second organic solvent to form a low-concentration reverse osmosis membrane casting solution, spraying it onto the surface of the PTFE base membrane and leaving it for several seconds; then spraying an organic small molecule / alcohol mixture containing formyl chloride onto the surface of the PTFE base membrane and leaving it for several seconds; repeating this step for 2-20 cycles, wherein the concentration of formyl chloride in the mixture is 0.1-1 wt%;

[0012] R2: Dry in the shade for several days to allow it to slowly crosslink, and then dry at a certain temperature for several hours.

[0013] Preferably, the raw material is selected from DMC / methanol azeotrope or waste liquid containing DMC; in the high-pressure distillation tower, depending on different conditions, if the top liquid is low-value waste liquid, it is directly treated; if the top liquid is DMC / methanol azeotrope, it is returned to the feed side of the pervaporation membrane process and recirculated to enrich DMC.

[0014] Preferably, the micron thickness is a separation layer thickness in the range of 1-5 microns, and the high concentration is in the range of 20-80 wt %; the drying at a certain temperature for several hours in step P2 is respectively 20-150° C.; 3-6 hours.

[0015] Preferably, the first organic solvent and the second organic solvent are each independently selected from one of alkanes, toluene, esters, and tetrahydrofuran; the organic small molecules containing formyl chloride are each independently selected from one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, phthaloyl chloride, pentafluorobenzoyl chloride, and benzoyl chloride.

[0016] Preferably, the nanometer thickness is a separation layer thickness in the range of 50-300 nanometers; and the low concentration is a mass concentration in the range of 0.1 wt%-5 wt%.

[0017] Preferably, the operating temperature of the pervaporation membrane module is in the range of 0-45°C.

[0018] Preferably, the operating conditions in the high-pressure distillation tower are: reflux ratio of 0.5-5, operating pressure of 0.2-1.0 MPa, and tower top temperature of 100-150°C.

[0019] Preferably, the pressure on the raw material side of the reverse osmosis membrane assembly is 1-30 MPa, and the operating temperature is 20-50°C.

[0020] The requirements for the source of the raw material of DMC in the present invention are relatively low. It can be a DMC / methanol azeotrope or a waste liquid containing DMC. The waste liquid can refer to a DMC solution mainly containing water, which also contains some small molecular organic matter, metal ions, electrolytes and solid particles; it can also refer to the colored and impure electrolyte waste liquid in the recycling process of waste lithium batteries, which contains metal ions, plastic impurities, graphite powder, etc.; it can also refer to the mixture of ultra-pure DMC after cleaning and other solvents and etched solid substances in the processing of semiconductor chips.

[0021] Beneficial effects

[0022] Compared with the prior art, the present invention has the following advantages: 1) the present invention has relatively low requirements for the source of raw materials containing DMC, and can be a DMC / methanol azeotrope or a waste liquid containing DMC; 2) the micron-thick and nanometer-thick aminopropyl-terminated polydimethylsiloxane / PTFE composite membranes designed and prepared by the present invention have organic solvent resistance, high separation performance, and high stability. In addition, the pervaporation membrane and the reverse osmosis membrane both use the same membrane material and a similar synthesis process, which can simplify the overall membrane production process and reduce membrane production costs; 3) the NH2-PDMS composite membrane has preferential selectivity for DMC organic matter, resulting in a lower methanol content in the crude DMC product on the permeate side, reducing the energy consumption of subsequent high-pressure distillation. In addition, the high-pressure distillation tower combined with the pervaporation membrane and the reverse osmosis membrane has 20-30% lower energy consumption than the current electronic-grade DMC production process, and has universal applicability and industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of the membrane integrated process for producing electronic-grade DMC according to the present invention, wherein 1 is a pervaporation membrane assembly; 2 is a high-pressure distillation tower; 3 is a screw pump; 4 is a valve; 5 is a reverse osmosis membrane assembly; 6 is a pressure gauge; 7 is a high-pressure air compressor; and 8 is a Teflon storage tank.

[0024] Figure 2 Cross-sectional SEM images of (a) the micron-thick organic solvent-resistant silicone rubber / PTFE pervaporation laminated membrane and (b) the nanometer-thick organic solvent-resistant silicone rubber / PTFE reverse osmosis roll membrane designed and prepared in Example 3 of the present invention, and actual images of their membrane assemblies. DETAILED DESCRIPTION

[0025] like Figure 1As shown, a waste liquid containing 10-50 wt% DMC or a 30 wt% DMC / methanol azeotrope is used as the feedstock, heated to 20-50°C, and passed through a pervaporation composite membrane 1 to concentrate the DMC, resulting in a DMC concentration of 35-80 wt% on the permeate side. The condensed DMC solution on the permeate side is directly fed into a quartz high-pressure distillation tower 2, operating at a reflux ratio of 0.5-5, an operating pressure of 0.2-1.0 MPa, and a tower top temperature of 100-150°C. Industrial-grade DMC with a concentration of ≥99.5 wt% is obtained in the bottom of the tower, while a waste liquid with a lower DMC concentration or a 30 wt% DMC-methanol azeotrope is obtained at the top of the tower. This is returned to the feed liquid of the initial pervaporation membrane module 1 and re-permeated through the pervaporation membrane to enrich the DMC. A batch of material is regularly pumped into the reverse osmosis membrane assembly 5 by the screw pump 3 (a valve 4 is provided between the reverse osmosis membrane assembly 5 and the screw pump 3), and the pressure on the upstream side of the membrane is maintained by the high-pressure air compressor 7 (detected by a pressure gauge 6), thereby further concentrating the industrial-grade DMC and trapping trace metal ions, thereby obtaining an electronic-grade DMC reagent.

[0026] Example 1 (comparative case)

[0027] A commercial tubular PDMS / ceramic composite membrane was selected as the pervaporation membrane element; a commercial polyamide membrane was selected as the reverse osmosis membrane element.

[0028] Using 30 wt% DMC / methanol azeotrope as raw material, DMC was concentrated by pervaporation using a commercial tubular PDMS / ceramic composite membrane at room temperature, and the DMC concentration on the permeate side was 39.6 wt%.

[0029] The condensed DMC solution from the permeate side is fed directly into a quartz high-pressure distillation column with a reflux ratio of 4.9, an operating pressure of 1.4 MPa, and a tower top temperature of 140°C. The bottom of the column produces industrial-grade DMC with a concentration of 99.5 wt%. A waste liquid containing 30 wt% DMC is obtained at the top of the column and returned to the feed solution of the initial pervaporation membrane for re-concentration through the pervaporation membrane.

[0030] A batch of material was regularly pumped into a commercial polyamide membrane assembly using a screw pump. At 40°C, a high-pressure air compressor was used to maintain the pressure on the upstream side of the membrane at 12 MPa. While further concentrating 99.5 wt% of industrial-grade DMC, metal ions with a concentration of 850 ppb were retained. However, electronic-grade DMC reagent could not be obtained.

[0031] Example 2

[0032] Aminopropyl-terminated polydimethylsiloxane was dissolved in n-heptane to form a coating solution with a concentration of 40 wt %. The coating solution was then applied to the surface of the PTFE base membrane using a 40-μm scraper at a speed of 1 m / min. The membrane was then immersed in a 0.5 wt % trimesoyl chloride / methanol mixture for 2 hours. After removal, the membrane was dried in the shade for two days and then baked at 100°C for 3 hours to obtain a 2-μm-thick NH2-PDMS / PTFE pervaporation composite membrane.

[0033] Aminopropyl-terminated polydimethylsiloxane was dissolved in n-heptane to form a coating solution with a concentration of 0.8 wt %. The solution was sprayed on the surface of the PTFE base membrane using spray gun A at a speed of 0.5 m / min. Spray gun B containing a 0.3 wt % trimesoyl chloride / methanol mixture was replaced and sprayed on the surface of the PTFE base membrane at a speed of 0.5 m / min. Spray guns A and B were alternated repeatedly until 10 cycles (A+B) were completed. The membrane was then dried in the shade for two days and then dried at 100°C for 3 hours to obtain a 100 nm thick NH2-PDMS / PTFE reverse osmosis composite membrane.

[0034] Using 30 wt % DMC / methanol azeotrope as raw material, DMC was concentrated through a 2 μm thick NH2-PDMS / PTFE pervaporation composite membrane at room temperature, and the DMC concentration on the permeate side was 61.5 wt %.

[0035] The condensed DMC solution from the permeate side is fed directly into a quartz high-pressure distillation column with a reflux ratio of 4.7, an operating pressure of 0.9 MPa, and a tower top temperature of 135°C. A 99.9 wt% industrial-grade DMC solution is obtained in the bottom of the column, and a 30 wt% DMC / methanol azeotrope is obtained at the top of the column. This solution is returned to the feed solution of the initial pervaporation membrane and re-concentrated through the pervaporation membrane.

[0036] A batch of material is regularly pumped into a 100-nanometer-thick NH2-PDMS / PTFE reverse osmosis composite membrane assembly using a screw pump. At room temperature, a high-pressure air compressor is used to maintain the pressure on the upstream side of the membrane at 20 MPa. This further concentrates 99.9wt% of industrial-grade DMC while retaining metal ions at a concentration of 100ppb, resulting in a 99.99wt% electronic-grade DMC reagent.

[0037] Example 3

[0038] Aminopropyl-terminated polydimethylsiloxane was dissolved in toluene to form a coating solution with a concentration of 60 wt %. The coating solution was then applied to the surface of the PTFE base membrane using a 10-μm scraper at a speed of 1.5 m / min. The membrane was then immersed in a 1.2 wt % trimesoyl chloride / methanol mixture for 4 hours. After removal, the membrane was dried in the shade for three days and then baked at 120°C for 5 hours to obtain a 1.2-μm-thick NH2-PDMS / PTFE pervaporation composite membrane.

[0039] Aminopropyl-terminated polydimethylsiloxane was dissolved in toluene to form a coating solution with a concentration of 0.5 wt %. The solution was sprayed on the surface of the PTFE base membrane through spray gun A at a speed of 0.7 m / min. Spray gun B containing a 0.15 wt % trimesoyl chloride / methanol mixture was replaced and sprayed on the surface of the PTFE base membrane at a speed of 0.7 m / min. Spray guns A and B were repeatedly alternated until 30 cycles (A+B) were completed. The solution was dried in the shade for two days and then dried at 120°C for 5 hours to obtain a 260 nm thick NH2-PDMS / PTFE reverse osmosis composite membrane.

[0040] NH2-PDMS / PTFE pervaporation composite membrane and NH2-PDMS / PTFE reverse osmosis membrane membrane cross-section photos and membrane elements such as Figure 2 shown.

[0041] The raw material is 15wt% DMC waste liquid with color and solid impurities. The waste liquid comes from the electrolyte wastewater in the recycling process of waste lithium batteries. The main components are water (accounting for 30-40wt%), dimethyl carbonate, metal ions (Fe 3+ 、 Li+ etc.), tetrahydrofuran, electrolyte lithium salt (lithium hexafluoroarsenate, lithium hexafluorophosphate, etc.), etc., at 40°C, DMC was concentrated through a 2.4 μm thick NH2-PDMS / PTFE pervaporation composite membrane, the DMC concentration on the permeate side was 59.4wt%, and the solution was clear and transparent.

[0042] The condensed DMC solution from the permeate side is fed directly into a quartz high-pressure distillation column with a reflux ratio of 4.1, an operating pressure of 0.88 MPa, and a tower top temperature of 120°C. A 99.6wt% industrial-grade DMC solution is obtained in the bottom of the column, while a 20wt% DMC waste liquid is obtained at the top of the column. This waste liquid is returned to the initial pervaporation membrane feed solution and re-concentrated through the pervaporation membrane.

[0043] A batch of material is regularly pumped into a 210-nanometer-thick NH2-PDMS / PTFE reverse osmosis composite membrane assembly using a screw pump. At 30°C, a high-pressure air compressor is used to maintain the pressure on the upstream side of the membrane at 12 MPa. This further concentrates 99.6wt% of industrial-grade DMC while retaining metal ions at a concentration of 600ppb, resulting in a 99.99wt% electronic-grade DMC reagent.

[0044] Example 4

[0045] Aminopropyl-terminated polydimethylsiloxane was dissolved in toluene to form a coating solution with a concentration of 60 wt %. The solution was then coated on the surface of the PTFE base membrane using a 10-μm scraper at a speed of 1.5 m / min. The membrane was then immersed in a 1.2 wt % trimesoyl chloride / methanol mixture for 4 hours. After removal, the membrane was dried in the shade for three days and then baked at 120°C for 5 hours to obtain a 1.2-μm-thick NH2-PDMS / PTFE pervaporation composite membrane.

[0046] For comparison with Example 3, the reverse osmosis membrane was modified as follows: Aminopropyl-terminated polydimethylsiloxane was dissolved in n-heptane to form a coating solution A with a concentration of 0.5 wt%. A 0.15 wt% trimesoyl chloride / methanol mixed solution B was sprayed onto a commercial polyamide PA hollow fiber as the base membrane. The fiber was dip-coated with solution A at a speed of 0.9 m / min. The surface solvent was allowed to dry slightly. The fiber was then immersed in solution B at the same speed until the surface solvent dried slightly. This cycle was repeated for 30 cycles (A + B). The membrane was then air-dried in the shade for two days and then oven-dried at 80°C for 10 hours to obtain a 160 nm thick NH2-PDMS / PA reverse osmosis composite membrane.

[0047] Using waste liquid containing 15wt% DMC with color and solid impurities as raw material, DMC was concentrated through a 2.4 μm thick NH2-PDMS / PTFE pervaporation composite membrane at 40°C. The DMC concentration on the permeate side was 59.4wt%, and the solution was clear and transparent.

[0048] The condensed DMC solution from the permeate side is fed directly into a quartz high-pressure distillation column with a reflux ratio of 4.1, an operating pressure of 0.88 MPa, and a tower top temperature of 120°C. A 99.6wt% industrial-grade DMC solution is obtained in the bottom of the column, while a 20wt% DMC waste liquid is obtained at the top of the column. This waste liquid is returned to the initial pervaporation membrane feed solution and re-concentrated through the pervaporation membrane.

[0049] A batch of material is regularly pumped into a 120-nanometer-thick NH2-PDMS / PA reverse osmosis composite membrane assembly using a screw pump. At 40°C, a high-pressure air compressor is used to maintain the pressure on the upstream side of the membrane at 12 MPa. This further concentrates 99.6wt% of industrial-grade DMC while retaining metal ions at a concentration of 600ppb, resulting in 99.99wt% electronic-grade DMC reagent.

Claims

1. A method for producing electronic grade DMC by a low energy consumption membrane process, characterized in that: The raw material containing DMC is passed through a pervaporation membrane module, and the condensate on the permeation side is further passed through a high-pressure distillation column to obtain an industrial-grade DMC solution in the bottom of the column. The solution is then pumped into a reverse osmosis membrane module via a feed pump to block the permeation of trace metal ions, thereby obtaining an electronic-grade DMC solution. The pervaporation membrane assembly adopts a micron-thick pervaporation membrane; the reverse osmosis membrane assembly adopts a nanometer-thick reverse osmosis membrane; the pervaporation membrane and the reverse osmosis membrane both adopt the same membrane material; the membrane material is an aminopropyl-terminated polydimethylsiloxane / PTFE composite membrane.

2. The method according to claim 1, characterized in that The pervaporation membrane preparation method comprises the following steps: P1: dissolving aminopropyl-terminated polydimethylsiloxane in a first organic solvent to form a high-concentration pervaporation membrane casting solution, and evenly coating the solution on the surface of the PTFE base membrane by a doctor blade method to form a wet silicone rubber / PTFE composite membrane; P2: Immerse the wet silicone rubber / PTFE composite membrane in a mixture of organic small molecules / alcohol containing formyl chloride for 1-8 hours, take it out and dry it in the shade for 1-4 days to allow it to slowly crosslink, and then dry it at a certain temperature for several hours. The concentration of formyl chloride in the mixture is 0.2-3wt%.

3. The method according to claim 1, characterized in that The reverse osmosis membrane utilizes layer-by-layer self-organization technology to control the thickness of the separation layer on the surface of the PTFE base membrane. The preparation method of the reverse osmosis membrane includes the following steps: R1: The aminopropyl-terminated polydimethylsiloxane is dissolved in a second organic solvent to form a low concentration reverse osmosis membrane casting solution, by spraying on the PTFE base membrane surface, stay for a few seconds; the organic small molecule / alcohol mixture containing formyl chloride continues to be sprayed on the PTFE base membrane surface, stay for a few seconds; repeat this step 2-20 cycles, the concentration of formyl chloride in the mixture is 0.1-1wt%; R2: Dry in the shade for several days to allow it to slowly crosslink, and then dry at a certain temperature for several hours.

4. The method according to claim 1, wherein The raw material is selected from DMC / methanol azeotrope or waste liquid containing DMC; in the high-pressure distillation tower, depending on different conditions, if the top liquid is low-value waste liquid, it is directly treated; if the top liquid is DMC / methanol azeotrope, it is returned to the feed side of the pervaporation membrane process and recirculated to enrich DMC.

5. The method according to claim 2, wherein The micron thickness is a separation layer thickness in the range of 1-5 microns, and the high concentration is in the range of 20-80 wt%; the drying at a certain temperature for several hours in step P2 is 20-150°C; 3-6 hours.

6. The method according to claim 2 or 3, characterized in that The first organic solvent and the second organic solvent are independently selected from one of alkanes, toluene, esters, and tetrahydrofuran; the organic small molecules containing formyl chloride are independently selected from one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, phthaloyl chloride, pentafluorobenzoyl chloride, and benzoyl chloride.

7. The method according to claim 3, wherein The nanometer thickness refers to the separation layer thickness in the range of 50-300 nanometers; the low concentration refers to the mass concentration in the range of 0.1 wt%-5 wt%.

8. The method according to claim 1, characterized in that The operating temperature of the pervaporation membrane module is in the range of 0-45°C.

9. The method according to claim 1, wherein The operating conditions in the high-pressure distillation tower are: reflux ratio of 0.5-5, operating pressure of 0.2-1.0 MPa, and tower top temperature of 100-150°C.

10. The method according to claim 1, wherein The pressure on the raw material side of the reverse osmosis membrane assembly is 1-30 MPa, and the operating temperature is 20-50 ℃.

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