A method and apparatus for separating acetonitrile-isopropyl alcohol-water ternary azeotrope by vapor permeation coupled with pressure swing distillation

Abstract

The present application relates to the technical fields of chemical azeotropic separation and pharmaceutical solvent refining, and discloses a method and device for separating acetonitrile-isopropyl alcohol-water ternary azeotrope by steam permeation coupling variable pressure rectification, wherein the raw material is sent into a NaA type molecular sieve membrane steam permeation unit after being vaporized and overheated to perform gas phase predehydration, and the ternary azeotropic system is converted into an acetonitrile-isopropyl alcohol binary system with low water content; the binary mixed liquid enters a pressurized rectification tower, high-purity acetonitrile is output from the tower kettle, the overhead azeotrope is sent into an atmospheric pressure rectification tower, the overhead water-containing stream of the atmospheric pressure rectification tower is refluxed to a vaporization overheater to close-loop dehydrate, the side-line azeotrope is extracted and refluxed to the pressurized rectification tower, and high-purity isopropyl alcohol is output from the tower kettle; the present application eliminates an independent deep dehydration unit, does not need to add a third type of auxiliary agent, the water content of the product is not more than 0.02%, and the pharmaceutical industry solvent recovery requirements are met.

Description

Technical Field

[0001] This invention relates to the field of chemical azeotropic separation and pharmaceutical solvent refining technology, and in particular to a method and apparatus for separating acetonitrile-isopropanol-water ternary azeotropes by vapor permeation coupled with pressure swing distillation. Background Technology

[0002] Acetonitrile and isopropanol are widely used polar organic solvents in the pharmaceutical industry. During processes such as active pharmaceutical ingredient synthesis, pharmaceutical intermediate purification, and formulation equipment cleaning, these two solvents are continuously consumed, generating large amounts of mixed waste solvents that readily form a stable acetonitrile-isopropanol-water ternary azeotropic system. This system exhibits characteristics of both a ternary minimum azeotrope and multiple binary azeotropes, with extremely low relative volatility between components. Conventional atmospheric distillation cannot overcome the azeotropic limitation, making high-purity separation and recovery difficult.

[0003] Existing separation processes all have inherent defects: 1. Extractive distillation processes require the introduction of extractants such as ethylene glycol, glycerol, and ionic liquids to disrupt the azeotropic system. The process is lengthy and necessitates a regeneration system for the extractant, resulting in significant equipment investment and high operating costs. Furthermore, trace amounts of the extractant can remain in the finished solvent, failing to meet the high-purity solvent standards required for pharmaceutical raw material production. Additionally, the regeneration process generates substantial amounts of waste, which does not comply with green production control requirements.

[0004] 2. Traditional three-tower pressure swing distillation process typically adopts a three-tower configuration of "one dehydration tower + one set of two-tower pressure swing distillation" for this system, relying on pressure changes to control the azeotropic composition to achieve separation. Even with the addition of inter-tower thermal integration, it still needs to bear the high reflux circulation load of the dehydration tower itself and its reboiling and condensation energy consumption. The equipment configuration is redundant, the footprint is large, the load of water-containing material circulation processing is large, the solvent recovery rate is low, the overall economic efficiency is insufficient, and it is difficult to meet the continuous large-scale solvent recycling needs of pharmaceutical companies.

[0005] 3. Existing vapor permeation coupled distillation processes generally use superheated gas-phase feed, which can effectively isolate liquid-phase impurities and avoid membrane damage. However, this type of process still has significant shortcomings: the membrane unit is only used for shallow pre-dehydration, and deep dehydration requires a separate dehydration unit at the back end or a significant increase in membrane area, neither of which is economically viable. Furthermore, conventional dual-tower circulation systems lack directional moisture discharge channels, leading to moisture accumulation within the system and unstable product purity.

[0006] In summary, the existing process has significant shortcomings in terms of equipment configuration, energy consumption control, moisture management, and product stability. There is an urgent need for a new separation process that is streamlined, has low energy consumption, and provides stable product purity. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies by proposing a method and apparatus for separating acetonitrile-isopropanol-water ternary azeotropes through vapor permeation coupled with pressure swing distillation. This method relies on a superheated vapor-phase permeation process to ensure high membrane flux and membrane operational stability. Combined with a dual-tower pressure swing distillation coupled with a dual-branch closed-loop circulation structure, it eliminates the need for traditional independent deep dehydration units. No third-party additives are required throughout the process, and the purity and moisture content of the produced solvent meet the standards for use in the pharmaceutical industry. This achieves low-energy consumption, high recovery rate, and high-purity resource-based separation and recycling of pharmaceutical waste solvents.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for separating acetonitrile-isopropanol-water ternary azeotrope by vapor permeation coupled with pressure swing distillation, comprising the following continuous processing steps: (1) Superheated vaporization of raw materials: The azeotropic material collected from the top of the atmospheric pressure distillation column of the acetonitrile-isopropanol-water ternary mixed system is used as raw material. The raw material is vaporized and superheated to obtain a stable superheated gaseous raw material without liquid entrainment. (2) Steam permeation gas phase pre-dehydration: The superheated gas phase feed is fed into the steam permeation membrane unit, and water molecules are selectively removed by relying on the transmembrane partial pressure difference. The water vapor on the permeate side of the steam permeation membrane unit is condensed and the permeate is discharged. At the same time, the exhaust gas of the vacuum unit is discharged. After the gas phase on the feed side of the steam permeation membrane unit is condensed, an acetonitrile-isopropanol binary mixture with a water content of no more than 0.1% is obtained. (3) Pressure swing coupling distillation for deep separation: The binary mixture is fed into a pressurized distillation column for pressurized distillation separation. High-purity acetonitrile product is collected from the bottom of the pressurized distillation column. The azeotropic material with trace water content at the top of the pressurized distillation column is fed into an atmospheric distillation column with a side-stream collection structure. The azeotropic material with trace water content at the top of the atmospheric distillation column is refluxed to the feed end for deep dehydration. The acetonitrile-isopropanol azeotropic material with low water content is collected from the side stream of the atmospheric distillation column and refluxed to the feed end of the pressurized distillation column. High-purity isopropanol product is collected from the bottom of the atmospheric distillation column.

[0009] Furthermore, the raw material is a ternary azeotropic material produced from the top of an atmospheric distillation column in a pharmaceutical process. By mass fraction, the raw material contains 65%–70% acetonitrile, 10%–20% isopropanol, and 10%–20% water.

[0010] Furthermore, the vapor permeation membrane unit is composed of 2 to 4 NaA type molecular sieve membrane modules connected in series. The operating gauge pressure on the feed side of the unit is 0.1 to 0.2 MPa, the overall superheat of the material is controlled at 2 to 10°C, and a stable superheated gas phase condition is maintained throughout the process. The permeation side is maintained at an absolute pressure of 300 to 2000 Pa by a vacuum unit.

[0011] Furthermore, the pressurized distillation column operates at a gauge pressure of 0.4–0.7 MPa, has 25–40 theoretical plates, a feed position at the 12th–22nd theoretical plate, and an operating reflux ratio of 1.5–3:1.

[0012] Furthermore, the atmospheric distillation column is operated at atmospheric pressure, with 30 to 45 theoretical plates. The feed position is located on the 12th to 22nd theoretical plates, and the number of theoretical plates in the stripping section accounts for no less than 50% of the total number of plates. The side stream outlet is located on the 4th to 8th theoretical plates above the feed plate, and the operating reflux ratio is 1 to 2.5:1.

[0013] The present invention also provides an apparatus for separating acetonitrile-isopropanol-water ternary azeotrope via vapor permeation coupled with pressure swing distillation, comprising a vaporization superheating unit, a vapor permeation dehydration unit, and a pressure swing distillation separation unit; the vaporization superheating unit includes a vaporization superheater, the vapor permeation dehydration unit includes a vapor permeation membrane unit, a permeate condenser, a feed-side condenser, and a vacuum unit, and the pressure swing distillation separation unit includes a pressurized distillation column and an atmospheric distillation column; The material inlet of the vaporization superheater is connected to the azeotropic material outlet at the top of the atmospheric distillation column in the pharmaceutical distillation section, and the vapor phase outlet of the vaporization superheater is connected to the feed side of the vapor permeation membrane unit. The vapor permeation membrane unit is provided with a feed side and a permeation side. The feed side of the vapor permeation membrane unit is connected to the feed side condenser. The liquid phase outlet of the feed side condenser is connected to the feed inlet of the pressurized distillation column. The permeation side of the vapor permeation membrane unit is connected in sequence to the permeate condenser and the vacuum unit. The top outlet of the pressurized distillation column is connected to the feed inlet of the atmospheric distillation column; the top material pipeline of the atmospheric distillation column is connected to the feed end of the vaporization superheater; a side-stream outflow pipeline is installed in the middle and upper part of the atmospheric distillation column and flows back to the feed end of the pressurized distillation column; the bottom of the pressurized distillation column is the acetonitrile product outflow end, and the bottom of the atmospheric distillation column is the isopropanol product outflow end.

[0014] The present invention has the following beneficial effects: 1. This invention features a highly streamlined process structure, making engineering implementation convenient and efficient. It eliminates the need for traditional independent deep dehydration units, reducing the core distillation equipment from three units to two, resulting in a more compact process. The membrane equipment utilizes a skid-mounted modular design, ready for immediate use upon arrival, eliminating the need for separate equipment foundations and enclosure buildings. In contrast, distillation columns require supporting civil engineering works such as concrete foundations and steel frame structures, leading to complex on-site hoisting and internal component installation procedures. It should be noted that the initial investment for NaA-type molecular sieve membrane elements and complete membrane units is not low; however, this invention, by reducing the number of distillation columns and compressing the system's cyclic load, achieves superior overall life-cycle economics compared to traditional multi-tower plus independent dehydration solutions, making it more suitable for the cost reduction and efficiency improvement needs of pharmaceutical companies.

[0015] 2. The present invention has excellent moisture control capabilities, and the product purity is stable and controllable over a long period of time. The present invention constructs a unique drainage channel for the system by directional reflux of the water-containing stream at the top of the atmospheric distillation column into a vapor permeation membrane unit, which completely solves the technical problem of continuous accumulation of trace moisture and easy exceedance of product moisture in existing coupled processes. No adsorbents, extractants or other third-class components are required throughout the process. The water content of the obtained acetonitrile and isopropanol products is stably controlled within 0.02%, with no external impurities remaining, and all indicators meet the solvent use standards of the pharmaceutical industry.

[0016] 3. The system of the present invention has a significantly reduced circulating load and outstanding energy-saving benefits. The present invention adopts a dual-flow circulation mechanism of water-containing material and main azeotropic material, with only a small amount of high water-containing material participating in the membrane unit circulation treatment, which greatly reduces the system distillation and membrane dehydration load, resulting in significant long-term economic benefits and reducing steam and electricity consumption in pharmaceutical plants.

[0017] 4. The membrane of this invention operates stably and has an extended service life. This invention adopts the industry-mature superheated gas phase feeding mode, the core function of which is to isolate the membrane pore blockage and irreversible damage caused by liquid phase impurities. At the same time, it relies on the high-temperature gas phase system to increase the diffusion rate of water molecules and obtain higher membrane permeation flux. It is adapted to the characteristics of NaA type inorganic molecular sieve membrane material, and there is no problem of organic membrane swelling failure. The membrane operates stably, the replacement cycle is extended, and the maintenance frequency and spare parts cost are reduced.

[0018] 5. The present invention has a wide operating condition adaptability range and high solvent recovery efficiency; the tower structure parameters and operating parameters of the present invention cover a wide operating condition range, which can be adapted to waste solvent raw materials with different pharmaceutical process outputs and component fluctuations, and the system has strong anti-interference ability; the whole process material closed loop circulation, organic component loss is extremely low, the total recovery rate of acetonitrile is ≥96%, the total recovery rate of isopropanol is ≥92%, which greatly reduces the amount of fresh organic solvents purchased.

[0019] 6. This invention is green and low-carbon, with no secondary pollution. This invention does not introduce any external components such as organic extractants or azeotropic agents throughout the entire process, resulting in small amounts of waste and no secondary pollution. It aligns with the regulatory guidelines for green production and the recycling of hazardous waste solvents in the pharmaceutical industry. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall process flow structure of the present invention; Legend: 1. Vaporization superheater; 2. Steam permeation membrane unit; 3. Permeate condenser; 4. Vacuum unit; 5. Feed-side condenser; 6. Pressurized distillation column; 7. Atmospheric distillation column; a. Feed; b. Permeate; c. Tail gas; d. Acetonitrile product; e. Isopropanol product. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Reference Figure 1 This invention provides a method for separating acetonitrile-isopropanol-water ternary azeotrope using vapor permeation coupled with pressure swing distillation, comprising the following continuous processing steps: (1) Vaporization and superheating of raw material a: Using the azeotropic material collected from the top of the atmospheric pressure distillation column of the acetonitrile-isopropanol-water ternary mixed system as raw material, raw material a is vaporized and superheated to obtain a stable superheated gaseous raw material without liquid entrainment; (2) Steam permeation gas phase pre-dehydration: The superheated gas phase feed is fed into the steam permeation membrane unit 2. Water molecules are selectively removed by relying on the transmembrane partial pressure difference. The water vapor on the permeate side of the steam permeation membrane unit 2 is condensed and the permeate b is discharged. At the same time, the tail gas c of the vacuum unit 4 is discharged. After the gas phase on the feed side of the steam permeation membrane unit 2 is condensed, an acetonitrile-isopropanol binary mixture with a water content of no more than 0.1% is obtained. (3) Pressure swing coupling distillation for deep separation: The binary mixture is fed into the pressurized distillation column 6 for pressurized distillation separation. High-purity acetonitrile product d is collected from the bottom of the pressurized distillation column 6. The azeotropic material with trace water enriched at the top of the pressurized distillation column 6 is fed into the atmospheric distillation column 7 with a side-stream collection structure. The azeotropic material with trace water enriched at the top of the atmospheric distillation column 7 is refluxed to the feed end for deep dehydration. The acetonitrile-isopropanol azeotropic material with low water content is collected from the side stream of the atmospheric distillation column 7 and refluxed to the feed end of the pressurized distillation column 6. High-purity isopropanol product e is collected from the bottom of the atmospheric distillation column 7.

[0023] The raw material a is a ternary azeotropic material produced from the top of an atmospheric distillation column in a pharmaceutical process. By mass fraction, the raw material contains 65%–70% acetonitrile, 10%–20% isopropanol, and 10%–20% water.

[0024] The vapor permeation membrane unit 2 is composed of 2 to 4 NaA type molecular sieve membrane modules connected in series. The operating gauge pressure on the feed side of the unit is 0.1 to 0.2 MPa, and the overall superheat of the material is controlled at 2 to 10°C, maintaining a stable superheated gas phase condition throughout the process. The permeation side is maintained at an absolute pressure of 300 to 2000 Pa by the vacuum unit 4.

[0025] The pressurized distillation column 6 operates at a gauge pressure of 0.4–0.7 MPa, has 25–40 theoretical plates, and the feed is located at the 12th–22nd theoretical plate. The operating reflux ratio is 1.5–3:1.

[0026] The atmospheric distillation column 7 operates at atmospheric pressure, with 30 to 45 theoretical plates. The feed is located on the 12th to 22nd theoretical plates, and the number of theoretical plates in the stripping section accounts for no less than 50% of the total number of plates. The side stream outlet is located on the 4th to 8th theoretical plates above the feed plate, and the operating reflux ratio is 1 to 2.5:1.

[0027] The present invention also provides an apparatus for separating acetonitrile-isopropanol-water ternary azeotrope by vapor permeation coupled with pressure swing distillation to implement the above method, characterized in that it includes a vaporization superheating unit, a vapor permeation dehydration unit, and a pressure swing distillation separation unit; the vaporization superheating unit includes a vaporization superheater 1, the vapor permeation dehydration unit includes a vapor permeation membrane unit 2, a permeate condenser 3, a feed-side condenser 5, and a vacuum unit 4, and the pressure swing distillation separation unit includes a pressurized distillation column 6 and an atmospheric distillation column 7; The material inlet of the vaporization superheater 1 is connected to the azeotropic material outlet at the top of the atmospheric distillation column in the pharmaceutical distillation section, and the vapor phase outlet of the vaporization superheater 1 is connected to the feed side of the vapor permeation membrane unit 2. The vapor permeation membrane unit 2 is provided with a feed side and a permeation side. The feed side of the vapor permeation membrane unit 2 is connected to the feed side condenser 5. The liquid phase outlet of the feed side condenser 5 is connected to the feed inlet of the pressurized distillation column 6. The permeation side of the vapor permeation membrane unit 2 is connected in sequence to the permeate condenser 3 and the vacuum unit 4. The top outlet of the pressurized distillation column 6 is connected to the feed inlet of the atmospheric distillation column 7; the top material pipeline of the atmospheric distillation column 7 is connected to the feed end of the vaporization superheater 1; a side-stream outflow pipeline is arranged in the middle and upper part of the atmospheric distillation column 7 and flows back to the feed end of the pressurized distillation column 6; the bottom of the pressurized distillation column 6 is the outflow end of acetonitrile product d, and the bottom of the atmospheric distillation column 7 is the outflow end of isopropanol product e.

[0028] Example 1

[0029] In this embodiment, the raw material a is a ternary azeotropic material of acetonitrile-isopropanol-water. The mass composition of raw material a is: acetonitrile 68.237%, isopropanol 11.894%, and water 19.869%.

[0030] Raw material a is vaporized and superheated to 109°C by vaporization superheater 1. The operating gauge pressure on the feed side is 0.13 MPa, and the material superheat is 8°C, maintaining a stable superheated gas phase state throughout the process. The superheated gas phase is fed into a 3-stage series NaA-type molecular sieve membrane unit. The operating gauge pressure on the feed side of the membrane unit is 0.13 MPa, and the absolute pressure of 980 Pa is maintained on the permeate side by vacuum unit 4. Water vapor on the permeate side is condensed by permeate condenser 3, and permeate b is discharged to remove it. At the same time, exhaust gas c from vacuum unit 4 is discharged. The gas phase on the raw material side is condensed by raw material side condenser 5 to obtain an acetonitrile-isopropanol binary mixture with a water content of 0.083 wt%.

[0031] The binary mixture is fed into pressurized distillation column 6, which operates at a gauge pressure of 0.55 MPa, has 33 theoretical plates, and the feed is located on the 17th theoretical plate. The operating reflux ratio is 2.3:1, the top temperature is 139.2°C, and the bottom temperature is 141.8°C. The azeotropic feed from the top of pressurized distillation column 6 is fed into atmospheric distillation column 7, which has 35 theoretical plates, with the feed on the 15th theoretical plate. The side feed outlet is located on the 6th theoretical plate above the feed plate. The operating reflux ratio is 1.5:1, the top temperature is 76.4°C, and the bottom temperature is 80.6°C. The aqueous stream from the top of atmospheric distillation column 7 is refluxed to the vaporization superheater 1 for dehydration. The main azeotropic feed from the side feed is refluxed to the feed end of pressurized distillation column 6. High-purity isopropanol product e is collected from the bottom of pressurized distillation column 6.

[0032] Results: Acetonitrile product d had a purity of 99.930 wt%, isopropanol content of 0.052 wt%, and water content of 0.018 wt%; isopropanol product e had a purity of 99.614 wt%, acetonitrile content of 0.372 wt%, and water content of 0.014 wt%; the total recovery rate of acetonitrile was 96.7%, and the total recovery rate of isopropanol was 93.2%.

[0033] Example 2

[0034] In this embodiment, the raw material a is a ternary azeotropic material of acetonitrile-isopropanol-water. The mass composition of raw material a is: acetonitrile 66.873%, isopropanol 18.415%, and water 14.712%.

[0035] Raw material a is vaporized and superheated to 115°C by vaporization superheater 1. The feed side operating gauge pressure is 0.18 MPa, and the material superheat is 5°C, maintaining a stable superheated gas phase state throughout the process. The superheated gas phase is fed into a 3-stage series NaA-type molecular sieve membrane unit. The feed side operating gauge pressure of the membrane unit is 0.18 MPa, and the absolute pressure of 520 Pa is maintained on the permeate side by vacuum unit 4. Water vapor on the permeate side is condensed by permeate condenser 3, and the permeate b is discharged to remove it. At the same time, the exhaust gas c of vacuum unit 4 is discharged. The raw material side gas phase is condensed by raw material side condenser 5 to obtain an acetonitrile-isopropanol binary mixture with a water content of 0.069 wt%.

[0036] The binary mixture is fed into pressurized distillation column 6, which operates at a gauge pressure of 0.61 MPa, has 38 theoretical plates, feeds onto the 20th theoretical plate, operates at a reflux ratio of 2.6:1, has a top temperature of 142.0°C, and a bottom temperature of 144.7°C. The azeotropic feed from the top of pressurized distillation column 6 is fed into atmospheric distillation column 7, which has 41 theoretical plates, feeds onto the 18th theoretical plate, and a side-stream outlet located on the 5th theoretical plate above the feed plate. It operates at a reflux ratio of 2.2:1, has a top temperature of 76.9°C, and a bottom temperature of 81.5°C. The aqueous stream from the top of atmospheric distillation column 7 is refluxed to the vaporization superheater 1 for dehydration, while the main azeotropic feed from the side stream is refluxed back to the feed end of pressurized distillation column 6. High-purity isopropanol product e is collected from the bottom of pressurized distillation column 6.

[0037] Results: Acetonitrile product d had a purity of 99.914 wt% and a water content of 0.018 wt%; isopropanol product e had a purity of 99.571 wt% and a water content of 0.015 wt%; the total recovery rate of acetonitrile was 95.8%, and the total recovery rate of isopropanol was 94.3%.

[0038] Example 3

[0039] In this embodiment, raw material a is a ternary azeotropic material of acetonitrile-isopropanol-water. The mass composition of raw material a is: acetonitrile 69.784%, isopropanol 15.206%, and water 15.010%.

[0040] Raw material a is vaporized and superheated to 101°C by vaporization superheater 1. The feed side operating gauge pressure is 0.12 MPa, and the material superheat is 4°C, maintaining a stable superheated gas phase state throughout the process. The superheated gas phase is fed into a 3-stage series NaA type molecular sieve membrane unit. The feed side operating gauge pressure of the membrane unit is 0.12 MPa, and the absolute pressure of 1360 Pa is maintained on the permeate side by vacuum unit 4. Water vapor on the permeate side is condensed by permeate condenser 3, and the permeate b is discharged to remove it. At the same time, the exhaust gas c of vacuum unit 4 is discharged. The gas phase on the raw material side is condensed by raw material side condenser 5 to obtain an acetonitrile-isopropanol binary mixture with a water content of 0.086 wt%.

[0041] The binary mixture is fed into pressurized distillation column 6, which operates at a gauge pressure of 0.46 MPa, has 27 theoretical plates, feeds onto the 14th theoretical plate, operates with a reflux ratio of 1.9:1, has a top temperature of 136.8°C, and a bottom temperature of 139.6°C. The azeotropic feed from the top of pressurized distillation column 6 is fed into atmospheric distillation column 7, which has 32 theoretical plates, feeds onto the 16th theoretical plate, and a side-stream outlet located on the 6th theoretical plate above the feed plate. It operates with a reflux ratio of 1.4:1, has a top temperature of 76.3°C, and a bottom temperature of 80.2°C. The aqueous stream from the top of atmospheric distillation column 7 is refluxed to the vaporization superheater 1 for dehydration, while the main azeotropic feed from the side stream is refluxed back to the feed end of pressurized distillation column 6. High-purity isopropanol product e is collected from the bottom of pressurized distillation column 6.

[0042] Results: Acetonitrile product d had a purity of 99.943 wt% and a water content of 0.011 wt%; isopropanol product e had a purity of 99.648 wt% and a water content of 0.009 wt%; the total recovery rate of acetonitrile was 97.1%, and the total recovery rate of isopropanol was 92.8%.

[0043] This invention employs an industry-standard superheated gas-phase feed method. Its core advantage lies in isolating solid impurities, salt media, acidic substances, colloids, and other contaminants carried by the liquid phase material, preventing membrane pore blockage and irreversible membrane damage. Furthermore, the gas-phase system operates at a higher temperature, resulting in faster water molecule diffusion and mass transfer rates, effectively increasing the permeation flux of the NaA-type molecular sieve membrane. Utilizing the pore size separation and polarity selectivity of the NaA-type inorganic molecular sieve membrane, water molecules are preferentially allowed to pass through while organic components are retained. This allows for the one-step conversion of a complex ternary azeotropic system into a low-water-content acetonitrile-isopropanol binary system with a water content ≤0.1%, significantly reducing the separation load of subsequent distillation stages. Simultaneously, it eliminates the negative impact of water on pressure swing distillation operations—water not only reduces the relative volatility of acetonitrile and isopropanol, worsening the separation effect, but also accumulates within the column, leading to excessive product moisture and increasing the heat load on the reboiler, affecting the long-term stable operation of the system.

[0044] The binary mixture obtained by pre-dehydration in this invention is fed into a pressurized distillation column 6. The increased pressure can effectively control the binary azeotropic composition of acetonitrile and isopropanol and change the relative volatility of the components. Acetonitrile is an excess heavy component. After continuous enrichment in the stripping section of the pressurized distillation column 6, it is purified by stripping in the bottom of the column to obtain a high-purity acetonitrile product. Trace amounts of water are enriched towards the top of the column with the rising vapor phase, forming a water-containing azeotropic material, which provides a basis for subsequent dehydration and separation.

[0045] The aqueous azeotropic feed from the top of pressurized distillation column 6 is fed into atmospheric distillation column 7. Under atmospheric pressure, the azeotropic composition shifts, and isopropanol, as an excess heavy component, is enriched and purified in the bottom of the column to produce high-purity isopropanol. Trace amounts of moisture continuously accumulate towards the top of the column, and the high-water-content azeotropic feed from the top is refluxed to the front-end vaporization superheater 1 for dehydration, establishing the system's only directional drainage channel and completely preventing moisture accumulation within the dual-column system. Simultaneously, the low-water-content stable azeotropic feed from the upper side stream of the rectification section of atmospheric distillation column 7 is refluxed to the feed end of pressurized distillation column 6, completing the closed-loop circulation of the main solvent. This significantly reduces the system's rectification and membrane dehydration load, eliminating the need for additional deep dehydration units or blindly expanding the membrane area, significantly improving process economy and adapting to continuous production.

[0046] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for separating acetonitrile-isopropanol-water ternary azeotrope using vapor permeation coupled with pressure swing distillation, characterized in that, The following continuous processing steps are included: (1) Superheated vaporization of raw materials: The azeotropic material collected from the top of the atmospheric pressure distillation column of the acetonitrile-isopropanol-water ternary mixed system is used as raw material. The raw material is vaporized and superheated to obtain a stable superheated gaseous raw material without liquid entrainment. (2) Steam permeation gas phase pre-dehydration: The superheated gas phase feed is fed into the steam permeation membrane unit, and water molecules are selectively removed by relying on the transmembrane partial pressure difference. The water vapor on the permeate side of the steam permeation membrane unit is condensed and the permeate is discharged. At the same time, the exhaust gas of the vacuum unit is discharged. After the gas phase on the feed side of the steam permeation membrane unit is condensed, an acetonitrile-isopropanol binary mixture with a water content of no more than 0.1% is obtained. (3) Pressure swing coupling distillation for deep separation: The binary mixture is fed into a pressurized distillation column for pressurized distillation separation. High-purity acetonitrile product is collected from the bottom of the pressurized distillation column. The azeotropic material with trace water content at the top of the pressurized distillation column is fed into an atmospheric distillation column with a side-stream collection structure. The azeotropic material with trace water content at the top of the atmospheric distillation column is refluxed to the feed end for deep dehydration. The acetonitrile-isopropanol azeotropic material with low water content is collected from the side stream of the atmospheric distillation column and refluxed to the feed end of the pressurized distillation column. High-purity isopropanol product is collected from the bottom of the atmospheric distillation column.

2. The method for separating acetonitrile-isopropanol-water ternary azeotrope by steam permeation coupled with pressure swing distillation according to claim 1, characterized in that, The raw material is a ternary azeotropic material produced from the top of an atmospheric distillation column in a pharmaceutical process. By mass fraction, the raw material contains 65%–70% acetonitrile, 10%–20% isopropanol, and 10%–20% water.

3. The method for separating acetonitrile-isopropanol-water ternary azeotrope by steam permeation coupled with pressure swing distillation according to claim 1, characterized in that, The vapor permeation membrane unit consists of 2 to 4 NaA type molecular sieve membrane modules connected in series. The operating gauge pressure on the feed side of the unit is 0.1 to 0.2 MPa, and the overall superheat of the material is controlled at 2 to 10°C, maintaining a stable superheated gas phase condition throughout the process. The permeation side is maintained at an absolute pressure of 300 to 2000 Pa by a vacuum unit.

4. The method for separating acetonitrile-isopropanol-water ternary azeotrope by steam permeation coupled with pressure swing distillation according to claim 1, characterized in that, The pressurized distillation column operates at a gauge pressure of 0.4–0.7 MPa, has 25–40 theoretical plates, and the feed is located at the 12th–22nd theoretical plate. The operating reflux ratio is 1.5–3:

1.

5. The method for separating acetonitrile-isopropanol-water ternary azeotrope by steam permeation coupled with pressure swing distillation according to claim 1, characterized in that, The atmospheric distillation column operates at atmospheric pressure, with 30 to 45 theoretical plates. The feed is located on the 12th to 22nd theoretical plates, and the number of theoretical plates in the stripping section accounts for no less than 50% of the total number of plates. The side stream outlet is located on the 4th to 8th theoretical plates above the feed plate, and the operating reflux ratio is 1 to 2.5:

1.

6. An apparatus for separating acetonitrile-isopropanol-water ternary azeotrope by vapor permeation coupled with pressure swing distillation according to any one of claims 1 to 5, characterized in that, It includes a vaporization superheating unit, a steam permeation dehydration unit, and a pressure swing distillation separation unit; the vaporization superheating unit includes a vaporization superheater, the steam permeation dehydration unit includes a steam permeation membrane unit, a permeate condenser, a feed-side condenser, and a vacuum unit, and the pressure swing distillation separation unit includes a pressurized distillation column and an atmospheric distillation column; The material inlet of the vaporization superheater is connected to the azeotropic material outlet at the top of the atmospheric distillation column in the pharmaceutical distillation section, and the vapor phase outlet of the vaporization superheater is connected to the feed side of the vapor permeation membrane unit. The vapor permeation membrane unit is provided with a feed side and a permeation side. The feed side of the vapor permeation membrane unit is connected to the feed side condenser. The liquid phase outlet of the feed side condenser is connected to the feed inlet of the pressurized distillation column. The permeation side of the vapor permeation membrane unit is connected in sequence to the permeate condenser and the vacuum unit. The top outlet of the pressurized distillation column is connected to the feed inlet of the atmospheric distillation column; the top material pipeline of the atmospheric distillation column is connected to the feed end of the vaporization superheater; a side-stream outflow pipeline is installed in the middle and upper part of the atmospheric distillation column and flows back to the feed end of the pressurized distillation column; the bottom of the pressurized distillation column is the acetonitrile product outflow end, and the bottom of the atmospheric distillation column is the isopropanol product outflow end.

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