A membrane coupled rectification dehydration method and system for recovering electronic grade ultra-high purity isopropanol

Abstract

This invention provides a membrane-coupled distillation dehydration method and system for the recovery of electronic-grade ultra-high purity isopropanol, belonging to the field of wastewater treatment and isopropanol recovery technology. The method includes: S1 raw material pretreatment, S2 distillation concentration, S3 membrane separation dehydration, and S4 product output and quality control, recovering the latent heat of vapor at the top of the distillation column and the residual heat on the membrane permeate side for preheating the raw material and heating the membrane feed. The distillation module concentrates the isopropanol to near its azeotropic composition, simultaneously removing the main water and high-boiling-point impurities; the NaA-type zeolite molecular sieve membrane utilizes the molecular sieving effect to overcome the azeotropic limitation, deeply dehydrating to a water content ≤100ppm; variable-temperature operation is used to restore membrane flux online; and unqualified products are automatically refluxed for recycling. This invention eliminates the need for external azeotropic agents or extractants, achieving zero-additive, continuous operation, low energy consumption, and high-purity electronic-grade isopropanol recovery.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and isopropanol recovery technology, specifically a membrane-coupled distillation dehydration method and system for the recovery of electronic-grade ultra-high purity isopropanol. Background Technology

[0002] Isopropyl alcohol (IPA) is widely used as a core cleaning agent and desiccant in semiconductor and display panel manufacturing processes due to its excellent wettability, rapid volatility, and good solubility for photoresist and organic residues. It is estimated that a 12-inch wafer fab can consume thousands of tons of high-purity IPA annually, while generating an equal or even greater amount of waste IPA. Water is the main impurity in these waste liquids, typically ranging from 5% to 30% by mass, and they also contain trace amounts (ppm to ppb levels) of photoresist monomers, etching byproducts, metal ions, particulate matter, and high-boiling-point polymers.

[0003] Currently, the mainstream industrial technologies for the recovery and purification of waste IPA can be summarized into the following three categories: Azeotropic distillation: Taking advantage of the property that IPA forms a minimum azeotrope with water, a third component (azeotropic agent, such as cyclohexane, diisopropyl ether, benzene, etc.) is added to change the azeotropic composition or relative volatility, thereby producing anhydrous IPA.

[0004] Adsorption dehydration method: This method utilizes the strong affinity of adsorbents such as molecular sieves or activated alumina for water to deeply dehydrate IPA that has been pre-concentrated to near its azeotropic composition. It typically employs an operation mode of alternating adsorption in two or more towers, followed by regeneration with hot nitrogen or steam purging.

[0005] Extractive distillation: A high-boiling-point extractant (such as ethylene glycol, dimethyl sulfoxide, ionic liquid, etc.) is added. The extractant does not form an azeotrope with IPA, but it can significantly change the relative volatility of IPA and water, breaking the azeotropic limitation. The extractant is discharged from the bottom of the column, regenerated, and recycled.

[0006] However, both azeotropic distillation and extractive distillation require the introduction of a third component (azeotropic agent / extractant). Even with a recovery tower, trace amounts still remain in the product. Semiconductor-grade IPA requires strict control over the types and amounts of organic impurities. Any azeotropic agent residue (such as cyclohexane or benzene) can cause fatal defects in subsequent photolithography processes (such as photoresist swelling and abnormal development). Moreover, both azeotropic distillation and extractive distillation are thermally driven separation processes, requiring repeated vaporization and condensation. Azeotropic agent recovery also requires additional towers, resulting in steam consumption typically reaching 1.5-3.0 tons of steam per ton of product.

[0007] Adsorption dehydration is essentially an intermittent or semi-continuous operation, requiring frequent switching of adsorption towers, resulting in complex operation, unstable product output, and unfavorable conditions for downstream continuous production processes. While traditional distillation can be continuous, it requires frequent adjustments to the reflux ratio and steam flow rate to cope with fluctuations in the moisture content of the raw materials (e.g., from 10% to 25%), leading to significant control lag and potentially causing product defects. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a membrane-coupled distillation dehydration method and system for the recovery of electronic-grade ultra-high purity isopropanol. A fully continuous, thermally integrated, and deeply coupled IPA dehydration and purification system is constructed, fundamentally resolving the core contradiction between ensuring the purity of electronic-grade products and high energy consumption, as detailed below: A membrane-coupled distillation dehydration method for the recovery of electronic-grade ultra-high purity isopropanol, characterized by comprising the following steps: S1. Raw material pretreatment: Waste isopropanol raw material is sent to the raw material receiving and pretreatment module for storage and filtration pretreatment; S2. Distillation Concentration: The pretreated material is fed into the distillation concentration module, and isopropanol is concentrated to near but not above its azeotropic composition through distillation separation to obtain an azeotropic isopropanol-water mixture; at the same time, the main water and high-boiling-point impurities are separated and discharged. S3. The azeotropic isopropanol-water mixture is fed into the membrane separation and dehydration module in liquid form for pervaporation separation; the membrane separation and dehydration module is equipped with a NaA type zeolite molecular sieve membrane for selectively removing water, thereby breaking through the azeotropic limitation of isopropanol-water and deeply dehydrating isopropanol. S4. Product Output and Quality Control: The deeply dehydrated isopropanol is sent to the product output and quality control module for online water content detection. If the water content is ≤100ppm, it is output as electronic-grade ultra-high purity isopropanol. If the water content is >100ppm, it is returned to the raw material receiving pretreatment module or the distillation and concentration module for recirculation. The latent heat of vapor from the distillation and concentration module and the waste heat of high-temperature material on the permeate side of the membrane separation and dehydration module are recovered and used to preheat the waste isopropanol raw material in step S1 and / or to heat the azeotropic isopropanol-water mixture in step S3.

[0009] Preferably, in step S2, the waste isopropanol raw material is waste isopropanol raw material generated in the electronics industry, with a water content of 5wt%-30wt%, and the isopropanol mass fraction in the azeotropic isopropanol-water mixture is 87.5wt%-87.9wt%, which is close to but not higher than its azeotropic composition; the high-boiling-point impurities are photoresist monomers, etching by-products, metal ions, particulate matter and high-boiling-point polymers.

[0010] Preferably, the NaA-type zeolite molecular sieve membrane has a pore size of 0.40-0.45 nm, a separation factor of 5000-10000, a flux of 0.5-2.0 kg / (m²·h), an operating temperature of 95-110 °C, and an absolute pressure on the membrane permeation side of 1-5 kPa.

[0011] Preferably, in step S3, a variable temperature operation is adopted: the permeate flux of the membrane separation and dehydration module is monitored in real time, and the feed temperature of the membrane module is dynamically adjusted according to the change of permeate flux; when the permeate flux drops to below 85% of the initial value, the feed temperature is increased by 5-10℃ to restore the flux, and the temperature is adjusted back after the flux is restored, with the maximum feed temperature not exceeding 120℃.

[0012] In a second aspect, the present invention provides a membrane coupled distillation and dehydration system, comprising: a raw material receiving and pretreatment module, a distillation and concentration module, a membrane separation and dehydration module, and a product output and quality control module connected in sequence, and a heat integration and heat exchange module respectively coupled to the raw material receiving and pretreatment module, the distillation and concentration module, and the membrane separation and dehydration module; The raw material receiving and pretreatment module is used to receive waste isopropanol raw material and perform storage and filtration pretreatment. The inlet of the distillation and concentration module is connected to the outlet of the raw material receiving and pretreatment module, and is used to concentrate isopropanol to a level close to but not higher than its azeotropic composition through distillation separation, while separating and discharging the main water and high-boiling-point impurities. The feed inlet of the membrane separation and dehydration module is connected to the outlet of the distillation and concentration module to receive the isopropanol-water mixture with a near-azeotropic composition. By utilizing the preferential water permeability of the NaA-type zeolite molecular sieve membrane, the limitation of the isopropanol-water azeotropic composition is overcome, and the isopropanol is deeply dehydrated. The inlet of the product output and quality control module is connected to the outlet of the membrane separation and dehydration module. It is used to perform online water content detection on the deep dehydrated isopropanol, and output qualified products to the product tank according to the detection results, and return unqualified products to the raw material receiving and pretreatment module or the distillation and concentration module. The heat integration and heat exchange module is connected to the top steam outlet of the distillation and concentration module, the discharge port on the permeate side of the membrane separation and dehydration module, the raw material inlet of the raw material receiving and pretreatment module, and the feed inlet of the membrane separation and dehydration module, respectively. It is used to recover the latent heat of the top steam of the distillation and concentration module and the waste heat of the high-temperature material on the permeate side of the pervaporation membrane module, and to preheat the raw material and / or heat the feed of the membrane separation and dehydration module.

[0013] Preferably, the raw material receiving and pretreatment module includes a raw material storage tank, a dual precision filter, and a raw material preheater; The raw material storage tank is used to store waste isopropanol raw materials with a water content of 5wt%-30wt% generated in the electronics industry, and the discharge end is connected to the feed end of the dual precision filter. The discharge end of the dual precision filter is connected to the feed end of the raw material preheater, and is used to filter, preheat and pretreat the raw material.

[0014] Specifically, the raw material storage tank is made of 304 or 316L stainless steel, and its volume is determined according to the processing scale (e.g., 20-100 m³). A nitrogen sealing device is installed at the top to maintain a slight positive pressure (0.5-2 kPa) to isolate air and prevent IPA oxidation and secondary moisture absorption. The tank is equipped with a level gauge and thermometer, and is fitted with a stirrer or circulating pump to prevent material stratification.

[0015] Dual precision filters: Two filters are installed in parallel, one in use and one on standby, and can be switched and cleaned online. The filtration accuracy is 0.45μm or 1μm, and the filter element material is polytetrafluoroethylene (PTFE) or polypropylene (PP). It is used to remove mechanical particles, photoresist fragments, microorganisms, etc. from the raw materials, protecting the subsequent tower internals and membrane modules from clogging.

[0016] Feed preheater: Plate heat exchanger or spiral plate heat exchanger. Its hot-side medium is the overhead vapor from a high-efficiency distillation column. By adjusting the bypass flow rate of the overhead vapor, the feed temperature is precisely preheated to 5-10°C below the bubble point temperature (usually 65-75°C) to reduce the flash evaporation effect of the feed entering the column and stabilize the gas-liquid distribution inside the column.

[0017] Preferably, the distillation and concentration module includes a high-efficiency distillation column, a reboiler, a top condenser, a reflux tank, and a reflux pump; The discharge end of the raw material preheater is connected to the feed inlet of the high-efficiency distillation column; The reboiler is located outside the bottom of the high-efficiency distillation column and is used to provide rising steam for the high-efficiency distillation column. The top vapor outlet of the high-efficiency distillation column is connected to the heat integration and heat exchange module and the top condenser, respectively. The discharge end of the top condenser is connected to the reflux tank; The bottom discharge end of the reflux tank is connected to a reflux pump. The outlet of the reflux pump is divided into two branches. One branch is a reflux branch connected to the top of the high-efficiency distillation column for distillation reflux. The other branch is a collection branch connected to the membrane separation and dehydration module for conveying the azeotropic isopropanol-water mixture to the membrane separation unit.

[0018] Specifically, high-efficiency distillation columns: Tower body: Made of 316L stainless steel, with the inner wall electrochemically polished to a surface roughness Ra≤0.4μm, to prevent metal ion leaching and microbial adhesion.

[0019] Internal components: High-efficiency structured packing is used, such as CY700 or BX500 type metal wire mesh corrugated packing, with a theoretical plate count of 45-55. The packing section is equipped with a liquid distributor (trough or tubular type) and a liquid redistributor to ensure uniform gas-liquid distribution. The high-efficiency distillation column is used to increase the IPA concentration from 5%-30% of the feed to 87.5wt%~87.9wt% (slightly lower than the azeotropic composition), while simultaneously enriching impurities with boiling points higher than IPA (such as photoresist resin, plasticizers, and high-boiling-point organic compounds) in the bottom of the column, which are periodically discharged.

[0020] Operating parameters: The operating pressure at the top of the column is atmospheric pressure (101.3 kPa), the temperature at the top of the column is 80-82℃, and the temperature at the bottom of the column is 85-95℃. The reflux ratio is controlled between 1.0 and 2.5.

[0021] Reboiler in the column bottom: A forced circulation or thermosiphon reboiler is used, with saturated steam at 0.3-0.6 MPa as the heating medium. A steam regulating valve is installed to automatically adjust the steam flow rate according to the column bottom temperature or pressure difference.

[0022] Tower reboiler: A forced circulation or thermosiphon reboiler is adopted, and the heating medium is saturated steam at 0.3-0.6MPa. The steam feed pipeline is equipped with a PID automatic regulating valve. The system dynamically adjusts the steam feed rate in small amplitudes based on the tower bottom temperature and the IPA concentration signal collected from the top of the tower. Under all operating conditions, the steam regulation range is constrained to a narrow range by thermal integration coupling, eliminating the need for large-scale start-stop / large-range load change operations due to fluctuations in the moisture content of the raw materials.

[0023] Tower top condenser: Shell-and-tube or plate heat exchanger, with circulating cooling water (32℃ / 38℃) as the cooling medium. It condenses the tower top vapor into liquid.

[0024] Reflux tank and reflux pump: The reflux tank has a volume sufficient to hold reflux liquid for 5-10 minutes. The tank is nitrogen-sealed. The reflux pump is a variable frequency centrifugal pump that sends a portion of the condensate back to the top of the column as reflux, controlling the reflux ratio; the other portion is pumped from the top of the column to the membrane separation module.

[0025] Preferably, the membrane separation and dehydration module includes a membrane feed heater, a pervaporation membrane assembly, a vacuum unit, and a permeate-side condensation and collection unit; The feed end of the membrane feed heater is connected to the outlet branch of the reflux pump. This outlet branch is a pipeline connecting the distillation concentration module to the membrane separation and dehydration module, used to transport the material from the reflux pump to the membrane separation and dehydration module. The discharge end of the membrane feed heater is connected to the feed end of the pervaporation membrane module; The permeate side of the pervaporation membrane assembly is connected to the product output and quality control module, and the permeate side of the pervaporation membrane assembly is sequentially connected to the vacuum unit and the permeate side condensation collection unit.

[0026] Specifically, the membrane feed heater is a plate heat exchanger. The heat source preferentially utilizes the latent heat of the overhead steam from the high-efficiency distillation column (through series or parallel connection with the overhead steam system), or low-pressure steam / hot water. The material from the top of the high-efficiency distillation column (IPA content 87.5wt%–87.9wt%) is heated to the optimal operating temperature of the pervaporation membrane, i.e., 95-110℃. Precise temperature control is crucial; too low a temperature will reduce membrane flux, while too high a temperature may damage the membrane structure or exacerbate membrane fouling. During production, the pervaporation membrane module's permeate flux data is collected online in real time. When the membrane flux decays to below 85% of the initial flux, the feed temperature is slightly increased by 5–10℃ via the membrane feed heater. Once the flux recovers, the temperature is adjusted back down, with the feed temperature controlled to not exceed 120℃ throughout the process. Impurities adsorbed on the membrane surface are stripped and membrane flux is restored through small temperature variations online, eliminating the need for shutdown and membrane element cleaning.

[0027] Pervaporation membrane module: Membrane material: NaA-type zeolite molecular sieve membrane. This inorganic membrane has uniform sub-nanometer pores (approximately 0.42 nm), allowing water molecules (kinetic diameter 0.29 nm) to pass through rapidly, while IPA molecules (kinetic diameter 0.47 nm) are effectively retained. Its separation factor (α) can reach 5000-10000, and its flux can reach 0.5-2.0 kg / (m²·h).

[0028] Pervaporation membrane module structure: Utilizing a multi-channel tubular membrane module, each membrane tube contains 19 or 37 channels, resulting in a large effective membrane area. The membrane tubes are made of a porous α-Al₂O₃ support, with the NaA-type zeolite molecular sieve membrane located on either the inner or outer surface of the support. The module housing is made of 316L stainless steel and sealed using O-rings or graphite gaskets. The module is designed to withstand temperatures up to 150℃ and pressures up to 1.0 MPa.

[0029] Operating procedure: The material flows inside (or outside) the membrane tube, and a high vacuum (absolute pressure 1-5 kPa) is maintained on the downstream side (permeate side) by a vacuum pump system. Driven by both concentration and pressure differences, water molecules selectively permeate through the membrane and vaporize on the permeate side; the water content of the concentrated IPA (permeate side) is reduced to below 100 ppm.

[0030] Vacuum unit: A two-stage unit consisting of a Roots vacuum pump and a liquid ring vacuum pump, or a dry screw vacuum pump, is used to ensure a stable low vacuum downstream of the membrane over a long period. A condenser is installed before the vacuum system to condense permeated water vapor and prevent it from entering the vacuum pump and damaging the equipment.

[0031] Permeate-side condensation and collection unit: This unit consists of a condenser and collection tank on the membrane permeate side, which condenses water vapor into liquid water, which is periodically discharged into the wastewater treatment system. The collection tank is equipped with a level gauge and interlocked with the vacuum unit to prevent the liquid level from becoming too high.

[0032] Preferably, the product output and quality control module includes a product cooler, an online trace water analyzer, an automatic three-way switching valve, and a finished product storage tank; The feed end of the product cooler is connected to the permeate side of the pervaporation membrane module, and the discharge end is connected in series with the online trace water analyzer and the automatic three-way switching valve. The automatic three-way switching valve has a first outlet and a second outlet. The first outlet is connected to the finished product storage tank; the second outlet is connected to the raw material storage tank and / or the high-efficiency distillation column, forming a closed loop for the reflux of unqualified products.

[0033] If the online trace water analyzer detects that the water content of the deeply dehydrated isopropanol is ≤100ppm, it will be output as electronic-grade ultra-high purity isopropanol product to the finished product storage tank through the first outlet of the automatic three-way switching valve; if the water content is >100ppm, it will be returned to the raw material storage tank or high-efficiency distillation column for recirculation through the second outlet of the automatic three-way switching valve. Specifically, the product cooler is a plate heat exchanger with circulating cooling water as the cooling medium, which cools the dehydrated high-purity IPA (95-110℃) to room temperature (≤40℃) for easy storage.

[0034] Online trace water analyzer: Installed after the product cooler, it uses tunable diode laser absorption spectroscopy (TDLAS) or Fourier transform infrared spectroscopy (FTIR) technology to monitor the water content in the product in real time, with a measurement accuracy of ±10ppm.

[0035] Automatic three-way switching valve: a pneumatic or electric three-way ball valve interlocked with an online trace water analyzer. When the water content is ≤100ppm (and other online indicators such as conductivity are normal), the valve switches to the product tank direction; when the water content is >100ppm or fails to meet the standard for any reason, the valve automatically switches to the non-conforming product return pipeline, returning the product to the raw material storage tank or the feed inlet of the high-efficiency distillation column for reprocessing.

[0036] Preferably, the heat integration and heat exchange module constructs a multi-stream cascade heat exchange network to collect the waste heat of the top steam of the high-efficiency distillation column and the waste heat of the high-temperature material on the permeate side of the membrane module, respectively, to provide a heat source for the raw material preheater and the membrane feed heater, thereby realizing the heat recovery and utilization of the entire system.

[0037] Specifically, a multi-stream cascade heat exchange network: Heat source 1: Top steam of the high-efficiency distillation column. Its temperature is approximately 80-82℃, and its latent heat is approximately 400kJ / kg. This heat source first enters the feed preheater to heat the feed; if there is still excess heat, it can be connected in series to the membrane feed heater for supplementary heating.

[0038] Heat source 2: Product exiting the membrane module on the permeate side. Its temperature is approximately 95-110℃ (depending on the feed temperature and the temperature drop inside the membrane). This heat source can be used for preheating demineralized water, plant heating, or other low-grade hotspots, achieving cascaded utilization of heat.

[0039] Control logic: Temperature sensors are installed at the outlets of the raw material preheater and the membrane feed heater. By adjusting the bypass valve of the steam / heat source, precise PID control of the temperature is achieved to ensure stable thermal balance.

[0040] Workflow: 1. Raw material preparation and pretreatment stage: The collected waste IPA (5%-30% moisture content) is pumped into the feed storage tank, where it is nitrogen-sealed and allowed to settle. Then, it is pumped to a dual precision filter to remove particles ≥0.45μm. The filtered liquid then enters the feed preheater, where it exchanges heat with the overhead vapor from the high-efficiency distillation column, raising its temperature to 65-75℃. It then enters the middle section of the high-efficiency distillation column.

[0041] 2. Distillation Concentration and Heavy Removal Stage: In a high-efficiency distillation column, rising vapor and falling liquid undergo multi-stage gas-liquid mass transfer.

[0042] At the top of the column: an azeotropic mixture of isopropanol and water is obtained. The vapor at the top of the column first enters the feed preheater to release some heat, and then enters the top condenser to condense into liquid, which is collected in the reflux tank. Part of the reflux liquid is pumped back to the top of the column as reflux (to control the composition at the top of the column), and the other part is used as feed for the membrane unit.

[0043] Reboiler: High-boiling-point impurities such as photoresist monomers, etching byproducts, metal ions, particulate matter, and high-boiling-point polymers accumulate in the reboiler and are periodically discharged through the reboiler drain outlet for hazardous waste disposal. The reboiler continuously provides the power for the rising steam.

[0044] 3. Membrane separation deep dehydration stage: The azeotropic feed collected from the top of the high-efficiency distillation column is pressurized by a pump and then enters the membrane feed heater, where it is heated to 95-110°C (preferably utilizing the residual heat of the steam at the top of the column). It then enters the feed side of the pervaporation membrane module. Under the suction of the vacuum pump system, the pressure on the permeate side of the membrane is maintained at 1-5 kPa. Water molecules preferentially permeate through the NaA molecular sieve membrane, vaporize on the permeate side, and condense into water in the permeate side condenser, which is collected in the permeate collection tank and then discharged. The IPA retained by the membrane flows out on the effluent side, with its water content reduced to below 100 ppm, becoming electronic-grade high-purity IPA. The entire membrane unit utilizes the above-mentioned variable temperature control method to activate the membrane surface online, allowing the device to operate continuously without interruption.

[0045] 4. Product cooling and quality control stage: High-purity IPA (95-110℃) flowing out from the permeate side of the membrane module enters the product cooler, where it exchanges heat with circulating cooling water and is cooled to ≤40℃. An online trace water analyzer reads the product water content in real time.

[0046] Qualified path: If the water content is ≤100ppm, the automatic three-way switching valve is turned on to the product tank, and the high-purity IPA enters the product tank for storage.

[0047] Non-conforming path: If the water content is >100ppm (e.g., membrane performance degradation, excessive raw material fluctuations, etc.), the automatic three-way switching valve instantly switches to the non-conforming product return pipeline, sending the material back to the raw material storage tank or the inlet of the high-efficiency distillation column for reprocessing, ensuring that the product in the product tank is 100% qualified.

[0048] 5. Thermal integration cycle: In this system, the overhead vapor from the high-efficiency distillation column is preferentially used to heat the feed in the feed preheater before entering the overhead condenser, achieving the initial recovery and utilization of the latent heat at the top of the column. Simultaneously, the membrane feed heater also preferentially uses the waste heat from the overhead vapor as a heat source. Thus, after completing its mass transfer mission, the latent heat of the overhead vapor is fully utilized, significantly reducing the cooling load on the overhead condenser and the heating load on the reboiler.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Addressing the complex composition of electronic industry waste isopropanol, which contains a large amount of water (5wt%-30wt%), trace amounts of photoresist monomers, etching byproducts, metal ions, and high-boiling-point polymers, this invention provides a membrane-coupled distillation dehydration method for recovering electronic-grade ultra-high purity isopropanol. It constructs a dual-module synergistic purification method combining distillation for rough impurity removal and membrane separation for azeotropic dehydration. The distillation module concentrates the isopropanol to near its azeotropic composition (87.5wt%-87.9wt%) while simultaneously separating and discharging the main water and high-boiling-point impurities from the bottom of the distillation column. This avoids the high energy consumption of excessive distillation and provides a clean and stable optimal feed window for the membrane separation module. Subsequently, NaA-type zeolite molecules... With its uniform pore size of 0.40-0.45nm, the membrane sieve selectively allows water molecules to pass through while retaining isopropanol molecules using the molecular sieving effect. This successfully overcomes the azeotropic limitation of isopropanol-water, achieving deep dehydration to a water content of ≤100ppm through pervaporation. Simultaneously, the latent heat of vapor at the top of the distillation column is recovered for preheating the feed, and the waste heat from the high-temperature product on the membrane permeate side is recovered for heating the membrane feed, forming a tiered thermal integration network that significantly reduces the total energy consumption of the system. The distillation column is responsible for removing high-boiling-point impurities to protect the membrane module, while the membrane separation is dedicated to dehydration. The two have clear divisions of labor and protect each other. Online water content detection and automatic reflux circulation send unqualified products back to the distillation or pretreatment stage, forming a closed-loop quality control system to ensure that the final product is 100% qualified.

[0050] 2. This invention provides a membrane-coupled distillation dehydration method for the recovery of electronic-grade ultra-high purity isopropanol. It eliminates the need for any azeotropic agents or extractants, thus avoiding the risk of organic impurity contamination of electronic-grade products by a third component. At the same time, it achieves the separate removal of moisture and high-boiling-point impurities, and is specifically designed to meet the stringent purity requirements of semiconductor manufacturing for ultra-high purity isopropanol, fundamentally satisfying the stringent requirements of semiconductor-grade isopropanol for trace organic impurities.

[0051] 3. To address the problems of dispersed sources and large fluctuations in water content (5wt%-30wt%) of waste isopropanol in the electronics industry, which necessitate frequent adjustments to the reflux ratio and steam volume and result in severe control lag in traditional distillation, this invention provides a membrane-coupled distillation dehydration method for the recovery of electronic-grade ultra-high purity isopropanol. The distillation module only needs to concentrate the isopropanol to near the azeotropic composition rather than the strict azeotropic point, making it insensitive to fluctuations in the water content of the feedstock. Simultaneously, the membrane separation module adopts variable temperature operation. When the permeate flux drops below 85% of the initial value, the membrane flux can be restored online by increasing the feed temperature by 5-10℃, without the need for shutdown and membrane element cleaning. This achieves adaptability to feedstock fluctuations and continuous operation, overcoming the shortcomings of adsorption methods that require frequent switching of adsorption towers and complex operation.

[0052] 4. Addressing the challenge of removing numerous impurities (photoresist monomers, etching byproducts, metal ions, particulate matter, and high-boiling-point polymers) from waste isopropanol in the electronics industry, which is difficult to remove simultaneously using a single technology, this invention establishes a three-stage impurity classification and removal path: filtration, distillation, and membrane separation. A front-end dual-stage precision filter removes particulate matter; a high-efficiency distillation column utilizes boiling point differences to enrich high-boiling-point organic impurities and metal ions in the column bottom and periodically discharges them; the membrane separation is dedicated to dehydration and does not bear the pressure of impurity removal, effectively avoiding high-boiling-point impurities contaminating the membrane module and causing flux decline, extending the service life of the NaA molecular sieve membrane, and ensuring that the final product meets electronic-grade requirements in terms of moisture, particulate matter, metal ions, and organic matter. Experimental data shows that the lowest overall energy consumption of this invention is 393.9 kWh / ton of product, saving significant energy. During 30 days of continuous operation using the variable-temperature operation of this invention, the product water content remained consistently within the excellent range of 32.3-51.9 ppm, truly achieving long-term continuous and stable production of electronic-grade isopropanol recovery technology, which is of great significance for ensuring continuous supply to downstream semiconductor manufacturing. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the electronic-grade ultra-high purity isopropanol recovery membrane coupled distillation and dehydration system and process flow of the present invention. Detailed Implementation

[0054] Example 1: As Figure 1As shown, a membrane-coupled distillation and dehydration system includes: a raw material receiving and pretreatment module, a distillation and concentration module, a membrane separation and dehydration module, and a product output and quality control module connected in sequence; and a heat integration and heat exchange module coupled to the raw material receiving and pretreatment module, the distillation and concentration module, and the membrane separation and dehydration module respectively. The raw material receiving and pretreatment module is used to receive waste isopropanol raw material and perform storage and filtration pretreatment. The inlet of the distillation and concentration module is connected to the outlet of the raw material receiving and pretreatment module, and is used to concentrate isopropanol to a level close to but not higher than its azeotropic composition through distillation separation, while separating and discharging the main water and high-boiling-point impurities. The feed inlet of the membrane separation and dehydration module is connected to the outlet of the distillation and concentration module to receive the isopropanol-water mixture with a near-azeotropic composition. By utilizing the preferential water permeability of the NaA-type zeolite molecular sieve membrane, the limitation of the isopropanol-water azeotropic composition is overcome, and the isopropanol is deeply dehydrated. The inlet of the product output and quality control module is connected to the outlet of the membrane separation and dehydration module. It is used to perform online water content detection on the deep dehydrated isopropanol, and output qualified products to the product tank according to the detection results, and return unqualified products to the raw material receiving and pretreatment module or the distillation and concentration module. The heat integration and heat exchange module is connected to the top steam outlet of the distillation and concentration module, the discharge port on the permeate side of the membrane separation and dehydration module, the raw material inlet of the raw material receiving and pretreatment module, and the feed inlet of the membrane separation and dehydration module, respectively. It is used to recover the latent heat of the top steam of the distillation and concentration module and the waste heat of the high-temperature material on the permeate side of the pervaporation membrane module, and to preheat the raw material and / or heat the feed of the membrane separation and dehydration module.

[0055] Furthermore, the raw material receiving and pretreatment module includes a raw material storage tank, a dual precision filter, and a raw material preheater; The raw material storage tank is used to store waste isopropanol raw materials with a water content of 5wt%-30wt% generated in the electronics industry, and the discharge end is connected to the feed end of the dual precision filter. The discharge end of the dual precision filter is connected to the feed end of the raw material preheater, and is used to filter, preheat and pretreat the raw material.

[0056] Specifically, the raw material storage tank is made of 304 or 316L stainless steel, and its volume is determined according to the processing scale (e.g., 20-100 m³). A nitrogen sealing device is installed at the top to maintain a slight positive pressure (0.5-2 kPa) to isolate air and prevent IPA oxidation and secondary moisture absorption. The tank is equipped with a level gauge and thermometer, and is fitted with a stirrer or circulating pump to prevent material stratification.

[0057] Dual precision filters: Two filters are installed in parallel, one in use and one on standby, and can be switched and cleaned online. The filtration accuracy is 0.45μm or 1μm, and the filter element material is polytetrafluoroethylene (PTFE) or polypropylene (PP). It is used to remove mechanical particles, photoresist fragments, microorganisms, etc. from the raw materials, protecting the subsequent tower internals and membrane modules from clogging.

[0058] Feed preheater: Plate heat exchanger or spiral plate heat exchanger. Its hot-side medium is the overhead vapor from a high-efficiency distillation column. By adjusting the bypass flow rate of the overhead vapor, the feed temperature is precisely preheated to 5-10°C below the bubble point temperature (usually 65-75°C) to reduce the flash evaporation effect of the feed entering the column and stabilize the gas-liquid distribution inside the column.

[0059] Furthermore, the distillation and concentration module includes a high-efficiency distillation column, a reboiler, a top condenser, a reflux tank, and a reflux pump; The discharge end of the raw material preheater is connected to the feed inlet of the high-efficiency distillation column; The reboiler is located outside the bottom of the high-efficiency distillation column and is used to provide rising steam for the high-efficiency distillation column. The top vapor outlet of the high-efficiency distillation column is connected to the heat integration and heat exchange module and the top condenser, respectively. The discharge end of the top condenser is connected to the reflux tank; The bottom discharge end of the reflux tank is connected to a reflux pump. The outlet of the reflux pump is divided into two branches. One branch is a reflux branch connected to the top of the high-efficiency distillation column for distillation reflux. The other branch is a collection branch connected to the membrane separation and dehydration module for conveying the azeotropic isopropanol-water mixture to the membrane separation unit.

[0060] Specifically, high-efficiency distillation columns: Tower body: Made of 316L stainless steel, with the inner wall electrochemically polished to a surface roughness Ra≤0.4μm, to prevent metal ion leaching and microbial adhesion.

[0061] Internal components: High-efficiency structured packing is used, such as CY700 or BX500 type metal wire mesh corrugated packing, with a theoretical plate count of 45-55. The packing section is equipped with a liquid distributor (trough or tubular type) and a liquid redistributor to ensure uniform gas-liquid distribution. The high-efficiency distillation column is used to increase the IPA concentration from 5%-30% of the feed to 87.5wt%~87.9wt% (slightly lower than the azeotropic composition), while simultaneously enriching impurities with boiling points higher than IPA (such as photoresist resin, plasticizers, and high-boiling-point organic compounds) in the bottom of the column, which are periodically discharged.

[0062] Operating parameters: The operating pressure at the top of the column is atmospheric pressure (101.3 kPa), the temperature at the top of the column is 80-82℃, and the temperature at the bottom of the column is 85-95℃.

[0063] Reboiler in the column bottom: A forced circulation or thermosiphon reboiler is used, with saturated steam at 0.3-0.6 MPa as the heating medium. A steam regulating valve is installed to automatically adjust the steam flow rate according to the column bottom temperature or pressure difference.

[0064] Tower reboiler: A forced circulation or thermosiphon reboiler is adopted, and the heating medium is saturated steam at 0.3-0.6MPa. The steam feed pipeline is equipped with a PID automatic regulating valve. The system dynamically adjusts the steam feed rate in small amplitudes based on the tower bottom temperature and the IPA concentration signal collected from the top of the tower. Under all operating conditions, the steam regulation range is constrained to a narrow range by thermal integration coupling, eliminating the need for large-scale start-stop / large-range load change operations due to fluctuations in the moisture content of the raw materials.

[0065] Tower top condenser: Shell-and-tube or plate heat exchanger, with circulating cooling water (32℃ / 38℃) as the cooling medium. It condenses the tower top vapor into liquid.

[0066] Reflux tank and reflux pump: The reflux tank has a volume sufficient to hold reflux liquid for 5-10 minutes. The tank is nitrogen-sealed. The reflux pump is a variable frequency centrifugal pump that sends a portion of the condensate back to the top of the column as reflux, controlling the reflux ratio; the other portion is pumped from the top of the column to the membrane separation module.

[0067] Furthermore, the membrane separation and dehydration module includes a membrane feed heater, a pervaporation membrane assembly, a vacuum unit, and a permeate-side condensation and collection unit; The feed end of the membrane feed heater is connected to the outlet branch of the reflux pump. This outlet branch is a pipeline connecting the distillation concentration module to the membrane separation and dehydration module, used to transport the material from the reflux pump to the membrane separation and dehydration module. The discharge end of the membrane feed heater is connected to the feed end of the pervaporation membrane module; The permeate side of the pervaporation membrane assembly is connected to the product output and quality control module, and the permeate side of the pervaporation membrane assembly is sequentially connected to the vacuum unit and the permeate side condensation collection unit.

[0068] Specifically, the membrane feed heater is a plate heat exchanger. The heat source preferentially utilizes the latent heat of the overhead steam from the high-efficiency distillation column (through series or parallel connection with the overhead steam system), or low-pressure steam / hot water. The material from the top of the high-efficiency distillation column (IPA content 87.5wt%–87.9wt%) is heated to the optimal operating temperature of the pervaporation membrane, i.e., 95-110℃. Precise temperature control is crucial; too low a temperature will reduce membrane flux, while too high a temperature may damage the membrane structure or exacerbate membrane fouling. During production, the pervaporation membrane module's permeate flux data is collected online in real time. When the membrane flux decays to below 85% of the initial flux, the feed temperature is slightly increased by 5–10℃ via the membrane feed heater. Once the flux recovers, the temperature is adjusted back down, with the feed temperature controlled to not exceed 120℃ throughout the process. Impurities adsorbed on the membrane surface are stripped and membrane flux is restored through small temperature variations online, eliminating the need for shutdown and membrane element cleaning.

[0069] Pervaporation membrane module: Membrane material: NaA-type zeolite molecular sieve membrane. This inorganic membrane has uniform sub-nanometer pores (approximately 0.42 nm), allowing water molecules (kinetic diameter 0.29 nm) to pass through rapidly, while IPA molecules (kinetic diameter 0.47 nm) are effectively retained. Its separation factor (α) can reach 5000-10000, and its flux can reach 0.5-2.0 kg / (m²·h).

[0070] Pervaporation membrane module structure: Utilizing a multi-channel tubular membrane module, each membrane tube contains 19 or 37 channels, resulting in a large effective membrane area. The membrane tubes are made of a porous α-Al₂O₃ support, with the NaA-type zeolite molecular sieve membrane located on either the inner or outer surface of the support. The module housing is made of 316L stainless steel and sealed using O-rings or graphite gaskets. The module is designed to withstand temperatures up to 150℃ and pressures up to 1.0 MPa.

[0071] Operating procedure: The material flows inside (or outside) the membrane tube, and a high vacuum (absolute pressure 1-5 kPa) is maintained on the downstream side (permeate side) by a vacuum pump system. Driven by both concentration and pressure differences, water molecules selectively permeate through the membrane and vaporize on the permeate side; the water content of the concentrated IPA (permeate side) is reduced to below 100 ppm.

[0072] Vacuum unit: A two-stage unit consisting of a Roots vacuum pump and a liquid ring vacuum pump, or a dry screw vacuum pump, is used to ensure a stable low vacuum downstream of the membrane over a long period. A condenser is installed before the vacuum system to condense permeated water vapor and prevent it from entering the vacuum pump and damaging the equipment.

[0073] Permeate-side condensation and collection unit: This unit consists of a condenser and collection tank on the membrane permeate side, which condenses water vapor into liquid water, which is periodically discharged into the wastewater treatment system. The collection tank is equipped with a level gauge and interlocked with the vacuum unit to prevent the liquid level from becoming too high.

[0074] Furthermore, the product output and quality control module includes a product cooler, an online trace water analyzer, an automatic three-way switching valve, and a finished product storage tank; The feed end of the product cooler is connected to the permeate side of the pervaporation membrane module, and the discharge end is connected in series with the online trace water analyzer and the automatic three-way switching valve. The automatic three-way switching valve has a first outlet and a second outlet. The first outlet is connected to the finished product storage tank; the second outlet is connected to the raw material storage tank and the high-efficiency distillation column, forming a closed loop for the return of unqualified products.

[0075] If the online trace water analyzer detects that the water content of the deeply dehydrated isopropanol is ≤100ppm, it will be output as electronic-grade ultra-high purity isopropanol product to the finished product storage tank through the first outlet of the automatic three-way switching valve; if the water content is >100ppm, it will be returned to the raw material storage tank for recirculation through the second outlet of the automatic three-way switching valve. Specifically, the product cooler is a plate heat exchanger with circulating cooling water as the cooling medium, which cools the dehydrated high-purity IPA (95-110℃) to room temperature (≤40℃) for easy storage.

[0076] Online trace water analyzer: Installed after the product cooler, it uses tunable diode laser absorption spectroscopy (TDLAS) or Fourier transform infrared spectroscopy (FTIR) technology to monitor the water content in the product in real time, with a measurement accuracy of ±10ppm.

[0077] Automatic three-way switching valve: a pneumatic or electric three-way ball valve interlocked with an online trace water analyzer. When the water content is ≤100ppm (and other online indicators such as conductivity are normal), the valve switches to the product tank direction; when the water content is >100ppm or fails to meet the standard for any reason, the valve automatically switches to the non-conforming product return pipeline, returning the product to the raw material storage tank or the feed inlet of the high-efficiency distillation column for reprocessing.

[0078] Furthermore, the heat integration and heat exchange module constructs a multi-stream cascade heat exchange network to collect the waste heat from the top steam of the high-efficiency distillation column and the waste heat from the high-temperature material on the permeate side of the membrane module, providing a heat source for the raw material preheater and the membrane feed heater, thereby realizing the recovery and utilization of heat throughout the system.

[0079] Specifically, a multi-stream cascade heat exchange network: Heat source 1: Top steam of the high-efficiency distillation column. Its temperature is approximately 80-82℃, and its latent heat is approximately 400kJ / kg. This heat source first enters the feed preheater to heat the feed; if there is still excess heat, it can be connected in series to the membrane feed heater for supplementary heating.

[0080] Heat source 2: Product exiting the membrane module on the permeate side. Its temperature is approximately 95-110℃ (depending on the feed temperature and the temperature drop inside the membrane). This heat source can be used for preheating demineralized water, plant heating, or other low-grade hotspots, achieving cascaded utilization of heat.

[0081] Control logic: Temperature sensors are installed at the outlets of the raw material preheater and the membrane feed heater. By adjusting the bypass valve of the steam / heat source, precise PID control of the temperature is achieved to ensure stable thermal balance.

[0082] Workflow: 1. Raw material preparation and pretreatment stage: The collected waste IPA (5%-30% moisture content) is pumped into the feed storage tank, where it is nitrogen-sealed and allowed to settle. Then, it is pumped to a dual precision filter to remove particles ≥0.45μm. The filtered liquid then enters the feed preheater, where it exchanges heat with the overhead vapor from the high-efficiency distillation column, raising its temperature to 65-75℃. It then enters the middle section of the high-efficiency distillation column.

[0083] 2. Distillation Concentration and Heavy Removal Stage: In a high-efficiency distillation column, rising vapor and falling liquid undergo multi-stage gas-liquid mass transfer.

[0084] At the top of the column: an azeotropic mixture of isopropanol and water is obtained. The vapor at the top of the column first enters the feed preheater to release some heat, and then enters the top condenser to condense into liquid, which is collected in the reflux tank. Part of the reflux liquid is pumped back to the top of the column as reflux (to control the composition at the top of the column), and the other part is used as feed for the membrane unit.

[0085] Reboiler: High-boiling-point impurities such as photoresist monomers, etching byproducts, metal ions, particulate matter, and high-boiling-point polymers accumulate in the reboiler and are periodically discharged through the reboiler drain outlet for hazardous waste disposal. The reboiler continuously provides the power for the rising steam.

[0086] 3. Membrane separation deep dehydration stage: The azeotropic feed collected from the top of the high-efficiency distillation column is pressurized by a pump and then enters the membrane feed heater, where it is heated to 95-110°C (preferably utilizing the residual heat of the steam at the top of the column). It then enters the feed side of the pervaporation membrane module. Under the suction of the vacuum pump system, the pressure on the permeate side of the membrane is maintained at 1-5 kPa. Water molecules preferentially permeate through the NaA molecular sieve membrane, vaporize on the permeate side, and condense into water in the permeate side condenser, which is collected in the permeate collection tank and then discharged. The IPA retained by the membrane flows out on the effluent side, with its water content reduced to below 100 ppm, becoming electronic-grade high-purity IPA. The entire membrane unit utilizes the above-mentioned variable temperature control method to activate the membrane surface online, allowing the device to operate continuously without interruption.

[0087] 4. Product cooling and quality control stage: High-purity IPA (95-110℃) flowing out from the permeate side of the membrane module enters the product cooler, where it exchanges heat with circulating cooling water and is cooled to ≤40℃. An online trace water analyzer reads the product water content in real time.

[0088] Qualified path: If the water content is ≤100ppm, the automatic three-way switching valve is turned on to the product tank, and the high-purity IPA enters the product tank for storage.

[0089] Non-conforming path: If the water content is >100ppm (e.g., membrane performance degradation, excessive raw material fluctuations, etc.), the automatic three-way switching valve instantly switches to the non-conforming product return pipeline, sending the material back to the raw material storage tank or the inlet of the high-efficiency distillation column for reprocessing, ensuring that the product in the product tank is 100% qualified.

[0090] 5. Thermal integration cycle: In this system, the overhead vapor from the high-efficiency distillation column is preferentially used to heat the feed in the feed preheater before entering the overhead condenser, achieving the initial recovery and utilization of the latent heat at the top of the column. Simultaneously, the membrane feed heater also preferentially uses the waste heat from the overhead vapor as a heat source. Thus, after completing its mass transfer mission, the latent heat of the overhead vapor is fully utilized, significantly reducing the cooling load on the overhead condenser and the heating load on the reboiler.

[0091] Example 2: A membrane-coupled distillation dehydration method for the recovery of electronic-grade ultra-high purity isopropanol, implemented using the membrane-coupled distillation dehydration system described in Example 1, includes the following steps: S1. Raw material pretreatment: Waste isopropanol raw material is sent to the raw material receiving and pretreatment module for storage and filtration pretreatment; S2. Distillation Concentration: The pretreated material is fed into the distillation concentration module, and isopropanol is concentrated to near but not above its azeotropic composition through distillation separation to obtain an azeotropic isopropanol-water mixture; at the same time, the main water and high-boiling-point impurities are separated and discharged. S3. The azeotropic isopropanol-water mixture is fed into the membrane separation and dehydration module in liquid form for pervaporation separation; the membrane separation and dehydration module is equipped with a NaA type zeolite molecular sieve membrane for selectively removing water, thereby breaking through the azeotropic limitation of isopropanol-water and deeply dehydrating isopropanol. S4. Product Output and Quality Control: The deeply dehydrated isopropanol is sent to the product output and quality control module for online water content detection. If the water content is ≤100ppm, it is output as electronic-grade ultra-high purity isopropanol. If the water content is >100ppm, it is returned to the raw material receiving pretreatment module or the distillation and concentration module for recirculation. The latent heat of vapor from the distillation and concentration module and the waste heat from the high-temperature material on the permeate side of the membrane separation and dehydration module are recovered and used to preheat the waste isopropanol feedstock in step S1, and / or to heat the azeotropic isopropanol-water mixture in step S3. Furthermore, in step S2, the waste isopropanol raw material is waste isopropanol raw material generated in the electronics industry, with a water content of 30wt% and an isopropanol mass fraction of 87.9wt% in the azeotropic isopropanol-water mixture. This composition is close to but not higher than its azeotropic composition. The high-boiling-point impurities are photoresist monomers, etching by-products, metal ions, particulate matter, and high-boiling-point polymers.

[0092] Furthermore, the NaA-type zeolite molecular sieve membrane has a pore size of 0.45 nm, a separation factor of 5000-10000, a flux of 2.0 kg / (m²·h), an operating temperature of 110 °C, and an absolute pressure on the membrane permeation side of 1-5 kPa.

[0093] Furthermore, in step S3, a variable temperature operation is adopted: the permeate flux of the membrane separation and dehydration module is monitored in real time, and the feed temperature of the membrane module is dynamically adjusted according to the change of permeate flux; when the permeate flux drops to below 85% of the initial value, the feed temperature is increased by 10°C to restore the flux, and the temperature is adjusted back after the flux is restored, with the maximum feed temperature not exceeding 120°C.

[0094] Example 3: A membrane-coupled distillation dehydration method for the recovery of electronic-grade ultra-high purity isopropanol, implemented using the membrane-coupled distillation dehydration system described in Example 1, includes the following steps: S1. Raw material pretreatment: Waste isopropanol raw material is sent to the raw material receiving and pretreatment module for storage and filtration pretreatment; S2. Distillation Concentration: The pretreated material is fed into the distillation concentration module, and isopropanol is concentrated to near but not above its azeotropic composition through distillation separation to obtain an azeotropic isopropanol-water mixture; at the same time, the main water and high-boiling-point impurities are separated and discharged. S3. The azeotropic isopropanol-water mixture is fed into the membrane separation and dehydration module in liquid form for pervaporation separation; the membrane separation and dehydration module is equipped with a NaA type zeolite molecular sieve membrane for selectively removing water, thereby breaking through the azeotropic limitation of isopropanol-water and deeply dehydrating isopropanol. S4. Product Output and Quality Control: The deeply dehydrated isopropanol is sent to the product output and quality control module for online water content detection. If the water content is ≤100ppm, it is output as electronic-grade ultra-high purity isopropanol. If the water content is >100ppm, it is returned to the raw material receiving pretreatment module or the distillation and concentration module for recirculation. The latent heat of vapor from the distillation and concentration module and the waste heat from the high-temperature material on the permeate side of the membrane separation and dehydration module are recovered and used to preheat the waste isopropanol feedstock in step S1, and / or to heat the azeotropic isopropanol-water mixture in step S3. Furthermore, in step S2, the waste isopropanol raw material is waste isopropanol raw material generated in the electronics industry, with a water content of 5wt% and an isopropanol mass fraction of 87.5wt% in the azeotropic isopropanol-water mixture. This composition is close to but not higher than its azeotropic composition. The high-boiling-point impurities are photoresist monomers, etching by-products, metal ions, particulate matter, and high-boiling-point polymers.

[0095] Furthermore, the NaA-type zeolite molecular sieve membrane has a pore size of 0.40 nm, a separation factor of 5000, a flux of 0.5 kg / (m²·h), an operating temperature of 95 °C, and an absolute pressure on the membrane permeation side of 1 kPa.

[0096] Furthermore, in step S3, a variable temperature operation is adopted: the permeate flux of the membrane separation and dehydration module is monitored in real time, and the feed temperature of the membrane module is dynamically adjusted according to the change of permeate flux; when the permeate flux drops to below 85% of the initial value, the feed temperature is increased by 5-10℃ to restore the flux, and the temperature is adjusted back after the flux is restored, with the maximum feed temperature not exceeding 120℃.

[0097] Example 4: A membrane-coupled distillation dehydration method for the recovery of electronic-grade ultra-high purity isopropanol, implemented using the membrane-coupled distillation dehydration system described in Example 1, includes the following steps: S1. Raw material pretreatment: Waste isopropanol raw material is sent to the raw material receiving and pretreatment module for storage and filtration pretreatment; S2. Distillation Concentration: The pretreated material is fed into the distillation concentration module, and isopropanol is concentrated to near but not above its azeotropic composition through distillation separation to obtain an azeotropic isopropanol-water mixture; at the same time, the main water and high-boiling-point impurities are separated and discharged. S3. The azeotropic isopropanol-water mixture is fed into the membrane separation and dehydration module in liquid form for pervaporation separation; the membrane separation and dehydration module is equipped with a NaA type zeolite molecular sieve membrane for selectively removing water, thereby breaking through the azeotropic limitation of isopropanol-water and deeply dehydrating isopropanol. S4. Product Output and Quality Control: The deeply dehydrated isopropanol is sent to the product output and quality control module for online water content detection. If the water content is ≤100ppm, it is output as electronic-grade ultra-high purity isopropanol. If the water content is >100ppm, it is returned to the raw material receiving pretreatment module or the distillation and concentration module for recirculation. The latent heat of vapor from the distillation and concentration module and the waste heat from the high-temperature material on the permeate side of the membrane separation and dehydration module are recovered and used to preheat the waste isopropanol feedstock in step S1, and / or to heat the azeotropic isopropanol-water mixture in step S3. Furthermore, in step S2, the waste isopropanol raw material is waste isopropanol raw material generated in the electronics industry, with a water content of 20wt% and an isopropanol mass fraction of 87.5wt% in the azeotropic isopropanol-water mixture. This composition is close to but not higher than its azeotropic composition. The high-boiling-point impurities are photoresist monomers, etching by-products, metal ions, particulate matter, and high-boiling-point polymers.

[0098] Furthermore, the NaA-type zeolite molecular sieve membrane has a pore size of 0.43 nm, a separation factor of 8000, a flux of 0.8 kg / (m²·h), an operating temperature of 100 °C, and an absolute pressure on the membrane permeation side of 3 kPa.

[0099] Furthermore, in step S3, a variable temperature operation is adopted: the permeate flux of the membrane separation and dehydration module is monitored in real time, and the feed temperature of the membrane module is dynamically adjusted according to the change of permeate flux; when the permeate flux drops to below 85% of the initial value, the feed temperature is increased by 8°C to restore the flux, and the temperature is adjusted back after the flux is restored, with the maximum feed temperature not exceeding 120°C.

[0100] Comparative Example 1: The process flow of this comparative example is as follows: a distillation column and a membrane separation unit are simply connected in series, but the steam at the top of the distillation column is not recovered for latent heat and is directly condensed in the top condenser by circulating cooling water. The membrane feed heater uses electric heating to heat the material to the operating temperature without any thermal integration measures. The remaining equipment configuration is the same as in Example 4 of this invention.

[0101] Comparative Example 2: In the distillation and concentration step of this comparative example, isopropanol is concentrated to just reach the azeotropic composition, and isopropanol is collected from the top of the column to reach the upper limit of the azeotropic composition of the system. The remaining steps are the same as those in Example 4 of this invention.

[0102] Comparative Example 3: In the membrane separation and dehydration step of this comparative example, the membrane module operates continuously at a constant temperature of 100°C, without employing the variable temperature operation of this invention. The remaining steps, including distillation and concentration, and thermal integration, are the same as in Example 4 of this invention.

[0103] Experimental section: Experiment 1: Comparative Examples 1-3 and Examples 2-4 of the present invention were run respectively. The steam consumption of the reboiler of the distillation column, the heat load of the top condenser, the power consumption of the membrane feed heater, and the total energy consumption of the system were recorded under each process condition. All energy consumption data were uniformly converted into equivalent power consumption (kWh / ton of product).

[0104] The experiment ran continuously for 72 hours, and the average value of the stable operation phase (i.e., from 24 hours to 72 hours after startup) was taken as the final data. All experiments were based on the same baseline conditions: a processing capacity of 1000 kg / h of waste isopropanol feedstock, and a product target of water content ≤100 ppm.

[0105] Measurement methods and instruments: Steam consumption of the reboiler in the distillation column: A vortex flow meter (accuracy ±1.0%) is installed on the saturated steam inlet pipe of the reboiler to continuously record the instantaneous steam flow rate and cumulative mass flow rate, which are then converted into the consumption per unit time (kg / h). Heat load of the condenser at the top of the column: A platinum resistance thermometer (accuracy ±0.1℃) and an electromagnetic flow meter (accuracy ±0.5%) are installed on the cooling water inlet and outlet pipes of the condenser, respectively. The heat load is calculated based on the cooling water temperature rise and flow rate: Q = C × m × Δt, where C is the specific heat capacity of the cooling water (4.18 kJ / (kg·℃)), m is the mass flow rate of the cooling water (kg / s), and Δt is the temperature difference between the inlet and outlet water (℃). Power consumption of the membrane feed heater: A multi-function meter (accuracy ±0.5%) is installed at the power inlet of the membrane feed heater to continuously record the active power (kW), and the average value during the stable operation phase is taken. Comprehensive energy consumption conversion: saturated steam is converted at 1kg steam = 0.7kWh (corresponding to the enthalpy value of 0.4MPa saturated steam); cooling water circulation energy consumption is calculated at 0.1kWh / ton of water; the power consumption of the membrane feed heater is calculated based on the actual meter reading. The experimental results are shown in Table 1.

[0106] Table 1 Comparison of energy consumption under different process conditions Comparative Example 1 198.4 220.6 45.7 661.6 Comparative Example 2 176.2 115.7 18.8 552.8 Comparative Example 3 125.3 105.4 18.9 427.3 Example 2 141.4 121.0 22.3 465.4 Example 3 113.5 95.3 15.6 393.9 Example 4 124.7 104.9 18.4 424.3 As shown in Table 1, Comparative Example 1 did not employ thermal integration measures. All the steam at the top of the distillation column was condensed by cooling water, resulting in complete waste of latent heat. The heat load of the top condenser reached a staggering 220.6 kW. Simultaneously, the membrane feed heater required additional electric heating, consuming 45.7 kW of electricity. The overall energy consumption was as high as 661.6 kWh / ton of product. The simple series coupling scheme without thermal integration is extremely energy-intensive and uneconomical.

[0107] Comparative Example 2 employed thermal integration measures, recovering the latent heat of the overhead vapor for preheating the feed and heating the membrane feed. Therefore, the heat load of the overhead condenser and the power consumption of the membrane feed heater were significantly reduced compared to Comparative Example 1, resulting in a lower overall energy consumption. However, Comparative Example 2 precisely controlled the isopropanol composition at the azeotropic point of 87.7 wt% at the top of the distillation column, leading to an increased reflux ratio and a reboiler steam consumption as high as 176.2 kg / h. Compared to Example 4 of this invention (with the same feed water content of 20 wt%), Comparative Example 2 showed a 51.5 kg / h increase in reboiler steam consumption and a 128.5 kWh / ton of product increase in overall energy consumption. This demonstrates that controlling the distillation endpoint to near but not above the azeotropic composition (87.5 wt%-87.9 wt%) effectively reduces the difficulty of distillation and energy consumption.

[0108] Comparative Example 3 employed both thermal integration and distillation endpoint control. The reboiler steam consumption (125.3 kg / h), the overhead condenser heat load (105.4 kW), and the membrane feed heater power consumption (18.9 kW) were all at low levels, resulting in a comprehensive energy consumption of 427.3 kWh / ton of product. This was lower than Comparative Examples 1 and 2, and essentially the same as Example 4 of this invention (424.3 kWh / ton of product), demonstrating that thermal integration and distillation endpoint control can achieve good energy-saving effects. However, Comparative Example 3 operated the membrane at a constant temperature of 100°C without cleaning or temperature recovery. While this method resulted in low energy consumption in the short term, the membrane flux gradually decreased over time, leading to a gradual increase in the product's water content.

[0109] Example 3 (feed moisture content 5 wt%) had the lowest overall energy consumption at 393.9 kWh / ton of product, with reboiler steam consumption of 113.5 kg / h, overhead condenser heat load of 95.3 kW, and membrane feed heater power consumption of 15.6 kW. Example 4 (feed moisture content 20 wt%) had an overall energy consumption of 424.3 kWh / ton of product, with reboiler steam consumption of 124.7 kg / h, overhead condenser heat load of 104.9 kW, and membrane feed heater power consumption of 18.4 kW. Example 2 (feed moisture content 30 wt%) had an overall energy consumption of 465.4 kWh / ton of product, with reboiler steam consumption of 141.4 kg / h, overhead condenser heat load of 121.0 kW, and membrane feed heater power consumption of 22.3 kW. Compared with Comparative Examples 1 and 2, Examples 2-4 of this invention showed a significant reduction in overall energy consumption and remarkable energy-saving effects. Compared with Comparative Example 3, the overall energy consumption of Example 3 of the present invention is lower, while the overall energy consumption of Example 4 is basically the same. However, Examples 2-4 all achieved a longer continuous operating cycle and a more stable product water content through temperature-changing operation, and their overall performance is significantly better than that of Comparative Example 3.

[0110] Experiment 2: Comparative Examples 1-3 and Examples 2-4 of the present invention were run respectively, and the reflux ratio, top isopropanol composition, and final product water content of the high-efficiency distillation column were recorded under each process condition. The stability of product water content for each process was also investigated when the feed water content fluctuated within the range of 5 wt%-30 wt%.

[0111] The experiment ran continuously for 120 hours, and the average value during the stable operation phase (i.e., from 24 hours to 120 hours after startup) was taken as the final data. All experiments were based on the same baseline conditions: a waste isopropanol feedstock with a processing capacity of 1000 kg / h. The water content of the product was measured: the water content of the product was read by an online trace water analyzer (measurement accuracy ±10 ppm) in the product output and quality control module, and samples were taken weekly and sent to the laboratory for comparison and calibration using a Karl Fischer moisture analyzer (accuracy ±5 ppm).

[0112] Table 2. Water content of products under different process conditions Comparative Example 1 85.5 Comparative Example 2 47.2 Comparative Example 3 48.3 Example 2 48.2 Example 3 28.4 Example 4 42.8 As shown in Table 2, the water content of Comparative Example 1 was 85.5 ppm, which did not exceed the acceptable standard of 100 ppm, but was higher than that of all the examples. The water content of Comparative Examples 2 and 3 was not much different from that of the examples, but combined with Experiment 1, the comprehensive energy consumption of Comparative Example 2 was as high as 552.8 kWh / ton of product; although the energy consumption of Comparative Example 3 was the same as that of Example 4, its constant temperature membrane operation resulted in poor long-term operational stability (see Table 3). Therefore, under the premise of ensuring the optimal level of product water content, the embodiments of the present invention are superior to Comparative Examples 2 and 3 in terms of energy consumption and long-term stability, and have better overall performance.

[0113] The water content of the products in Examples 2-4 of this invention is 28.4ppm-48.2ppm, which is at a low level. The product water content of Example 3 is the lowest. This is because Example 3 processes raw materials with low water content (5wt%), with a small distillation load. Combined with optimized distillation endpoint control, an extremely low product water content is achieved.

[0114] Each group continued to operate for 30 days, recording the product water content every 5 days. The results are shown in Table 3.

[0115] Table 3. Variation of product water content with operating time under different process conditions (unit: ppm) 0 85.5 47.2 48.3 48.2 28.4 42.8 5 87.6 48.5 52.6 48.7 29.4 43.3 10 90.4 48.7 60.3 49.6 30.5 44.1 15 94.7 48.5 75.7 49.4 30.6 44.3 20 99.8 49.7 105.3 50.3 31.7 45.1 25 105.4 50.2 130.4 50.2 31.8 45.5 30 112.2 52.8 — 51.9 32.3 46.4 As shown in Table 3, the initial water content of Comparative Example 1 was 85.5 ppm, which continued to rise over time, reaching 99.8 ppm on day 20, 105.4 ppm (exceeding the standard) on day 25, and 112.2 ppm on day 30. This may be because Comparative Example 1 did not use thermal integration, resulting in the complete waste of latent heat of vapor at the top of the distillation column, large fluctuations in the composition at the top of the column, and unstable feed conditions for membrane separation.

[0116] Although the water content in Comparative Example 2 increased, it remained within the acceptable range. Its main problem was high energy consumption (see Table 1). Comparative Example 3 used isothermal operation, with an initial product water content of 48.3 ppm. However, it rose to 75.7 ppm on day 15, 105.3 ppm on day 20, and reached 130.4 ppm on day 25, severely exceeding the standard, requiring system shutdown. This is likely because isothermal operation cannot restore membrane flux online, and membrane fouling leads to a sharp decline in separation performance and rapid deterioration of product water content.

Claims

1. A membrane coupled rectifying dehydration process for the recovery of electronic grade ultra-high purity isopropanol, characterized in that, Includes the following steps: S1. Raw material pretreatment: Waste isopropanol raw material is sent to the raw material receiving and pretreatment module for storage and filtration pretreatment; S2. Distillation Concentration: The pretreated material is fed into the distillation concentration module, and isopropanol is concentrated to near but not above its azeotropic composition through distillation separation to obtain an azeotropic isopropanol-water mixture; at the same time, the main water and high-boiling-point impurities are separated and discharged. S3. The azeotropic isopropanol-water mixture is fed into the membrane separation and dehydration module in liquid form for pervaporation separation; the membrane separation and dehydration module is equipped with a NaA type zeolite molecular sieve membrane for selectively removing water, thereby breaking through the azeotropic limitation of isopropanol-water and deeply dehydrating isopropanol. S4. Product Output and Quality Control: The deeply dehydrated isopropanol is sent to the product output and quality control module for online water content detection. If the water content is ≤100ppm, it is output as electronic-grade ultra-high purity isopropanol. If the water content is >100ppm, it is returned to the raw material receiving pretreatment module or the distillation and concentration module for recirculation. The latent heat of vapor from the distillation and concentration module and the waste heat of high-temperature material on the permeate side of the membrane separation and dehydration module are recovered and used to preheat the waste isopropanol raw material in step S1 and / or to heat the azeotropic isopropanol-water mixture in step S3.

2. The method of claim 1, wherein, In step S2, the waste isopropanol raw material is waste isopropanol raw material generated in the electronics industry, with a water content of 5wt%-30wt% and an isopropanol mass fraction of 87.5wt%-87.9wt% in the azeotropic isopropanol-water mixture. This composition is close to but not higher than its azeotropic composition. The high-boiling-point impurities are photoresist monomers, etching by-products, metal ions, particulate matter, and high-boiling-point polymers.

3. The method of claim 1, wherein, The NaA-type zeolite molecular sieve membrane has a pore size of 0.40-0.45 nm, a separation factor of 5000-10000, a flux of 0.5-2.0 kg / (m²·h), an operating temperature of 95-110℃, and an absolute pressure on the membrane permeation side of 1-5 kPa.

4. The method of claim 3, wherein, In step S3, a variable temperature operation is adopted: the permeate flux of the membrane separation and dehydration module is monitored in real time, and the feed temperature of the membrane module is dynamically adjusted according to the change of permeate flux; when the permeate flux drops to below 85% of the initial value, the feed temperature is increased by 5-10℃ to restore the flux, and the temperature is adjusted back after the flux is restored. The maximum feed temperature does not exceed 120℃.

5. A membrane coupled rectifying dehydration system for use in the process of any one of claims 1-4, characterized in that, include: The raw material receiving and pretreatment module, the distillation and concentration module, the membrane separation and dehydration module, the product output and quality control module are connected in sequence, and the heat integration and heat exchange module is coupled to the raw material receiving and pretreatment module, the distillation and concentration module, and the membrane separation and dehydration module respectively. The raw material receiving and pretreatment module is used to receive waste isopropanol raw material and perform storage and filtration pretreatment. The inlet of the distillation and concentration module is connected to the outlet of the raw material receiving and pretreatment module, and is used to concentrate isopropanol to a level close to but not higher than its azeotropic composition through distillation separation, while separating and discharging the main water and high-boiling-point impurities. The feed inlet of the membrane separation and dehydration module is connected to the outlet of the distillation and concentration module to receive the isopropanol-water mixture with a near-azeotropic composition. By utilizing the preferential water permeability of the NaA-type zeolite molecular sieve membrane, the limitation of the isopropanol-water azeotropic composition is overcome, and the isopropanol is deeply dehydrated. The inlet of the product output and quality control module is connected to the outlet of the membrane separation and dehydration module. It is used to perform online water content detection on the deep dehydrated isopropanol, and output qualified products to the product tank according to the detection results, and return unqualified products to the raw material receiving and pretreatment module or the distillation and concentration module. The heat integration and heat exchange module is connected to the top steam outlet of the distillation and concentration module, the discharge port on the permeate side of the membrane separation and dehydration module, the raw material inlet of the raw material receiving and pretreatment module, and the feed inlet of the membrane separation and dehydration module, respectively. It is used to recover the latent heat of the top steam of the distillation and concentration module and the waste heat of the high-temperature material on the permeate side of the pervaporation membrane module, and to preheat the raw material and / or heat the feed of the membrane separation and dehydration module.

6. The membrane coupled rectification dehydration system of claim 5, wherein, The raw material receiving and pretreatment module includes a raw material storage tank, a dual precision filter, and a raw material preheater; The raw material storage tank is used to store waste isopropanol raw materials with a water content of 5wt%-30wt% generated in the electronics industry, and the discharge end is connected to the feed end of the dual precision filter. The discharge end of the dual precision filter is connected to the feed end of the raw material preheater, and is used to filter, preheat and pretreat the raw material.

7. The membrane-coupled distillation dehydration system according to claim 6, characterized in that, The distillation and concentration module includes a high-efficiency distillation column, a reboiler at the bottom of the column, a condenser at the top of the column, a reflux tank, and a reflux pump; The discharge end of the raw material preheater is connected to the feed inlet of the high-efficiency distillation column; The reboiler is located outside the bottom of the high-efficiency distillation column and is used to provide rising steam for the high-efficiency distillation column. The top vapor outlet of the high-efficiency distillation column is connected to the heat integration and heat exchange module and the top condenser, respectively. The discharge end of the condenser at the top of the tower is connected to the reflux tank; The bottom discharge end of the reflux tank is connected to a reflux pump. The outlet of the reflux pump is divided into two branches. One branch is a reflux branch connected to the top of the high-efficiency distillation column for distillation reflux. The other branch is a collection branch connected to the membrane separation and dehydration module for conveying the azeotropic isopropanol-water mixture to the membrane separation unit.

8. The membrane-coupled distillation dehydration system according to claim 7, characterized in that, The membrane separation and dehydration module includes a membrane feed heater, a pervaporation membrane module, a vacuum unit, and a permeate-side condensation and collection unit; The feed end of the membrane feed heater is connected to the outlet branch of the reflux pump. This outlet branch is a pipeline connecting the distillation concentration module to the membrane separation and dehydration module, used to transport the material from the reflux pump to the membrane separation and dehydration module. The discharge end of the membrane feed heater is connected to the feed end of the pervaporation membrane module; The permeate side of the pervaporation membrane assembly is connected to the product output and quality control module, and the permeate side of the pervaporation membrane assembly is sequentially connected to the vacuum unit and the permeate side condensation collection unit.

9. The membrane-coupled distillation and dehydration system according to claim 8, characterized in that, The product output and quality control module includes a product cooler, an online trace water analyzer, an automatic three-way switching valve, and a finished product storage tank. The feed end of the product cooler is connected to the permeate side of the pervaporation membrane module, and the discharge end is connected in series with the online trace water analyzer and the automatic three-way switching valve. The automatic three-way switching valve has a first outlet and a second outlet. The first outlet is connected to the finished product storage tank; the second outlet is connected to the raw material storage tank and / or the high-efficiency distillation column, forming a closed loop for the reflux of unqualified products. If the online trace water analyzer detects that the water content of the deeply dehydrated isopropanol is ≤100ppm, it will be output as electronic-grade ultra-high purity isopropanol product to the finished product storage tank through the first outlet of the automatic three-way switching valve; if the water content is >100ppm, it will be returned to the raw material storage tank or high-efficiency distillation column for recirculation through the second outlet of the automatic three-way switching valve.

10. The membrane-coupled distillation and dehydration system according to claim 9, characterized in that, The heat integration and heat exchange module constructs a multi-stream cascade heat exchange network, which collects the waste heat of the top steam of the high-efficiency distillation column and the waste heat of the high-temperature material on the permeate side of the membrane module, respectively, to provide heat sources for the raw material preheater and the membrane feed heater, thereby realizing the heat recovery and utilization of the entire system.

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