Ionic Liquid Mixed Solvent Extractive Distillation Separation IPAC/IPOH/Water Mixture Ionic Liquid Mixed Solvent Extractive Distillation Separation IPAC/IPOH/Water Mixture Research

Research background and significance Research background and significance

Isopropyl alcohol (IPOH) is an important organic substance that can be used as a solvent, extractant or chemical intermediate. Isopropyl acetate (IPAC) is an esterification product of isopropyl alcohol with good solubility and miscibility with most organic solvents such as ethanol, ethers and esters. These two compounds are widely used in medicine, coatings, printing inks, fragrances, electronic products and other fields. Due to the limitation of reversible reaction, IPOH is not completely consumed in the process of esterification into IPAC, so the reaction is usually accompanied by the formation of a ternary azeotrope of IPAC/IPOH/water. Efficient recovery of IPOH and IPAC from wastewater is of great significance. Isopropyl alcohol (IPOH) is an important organic substance that can be used as a solvent, extractant or chemical intermediate. Isopropyl acetate (IPAC) is the esterification product of isopropanol. It has good solubility and can be miscible with most organic solvents such as ethanol, ether and ester. These two compounds are widely used in medicine, coatings, printing inks, fragrances, electronic products and other fields. Due to the limitation of reversible reaction, IPOH is not completely consumed in the process of esterification to IPAC, so the reaction is usually accompanied by the formation of IPAC/IPOH/water ternary azeotrope. It is of great significance to efficiently recover IPOH and IPAC from wastewater.

Extractive distillation (ED) is widely used for separation of azeotrope in chemical and pharmaceutical processes due to its simple operation and high separation efficiency. High-performance solvents are the key to efficient and energy-saving separation of multi-component azeotrope in ED. Conventional organic solvents have the advantages of low cost, low viscosity and easy industrial implementation, but these solvents are volatile and high energy consumption. Ionic liquids are used in ED due to their low saturation vapor pressure, high selectivity, low toxicity and non-flammability. However, high viscosity and high cost limit its industrial application. Mixed extractant composed of organic solvents and liquefied gas can reduce the viscosity of liquefied gas and has stronger selectivity than pure organic solvents. Extractive distillation (ED) is widely used for separation of azeotrope in chemical and pharmaceutical processes because of its simple operation and high separation efficiency. High performance solvents are the key to high efficiency and energy saving for ED separation of multi-component azeotrope. Traditional organic solvents have the advantages of low cost, low viscosity and easy industrial implementation, but these solvents are volatile and high energy consumption. Ionic liquids are used for ED because of their low saturation vapor pressure, high selectivity, low toxicity and non-flammability. However, high viscosity and high cost limit its industrial application. Mixed extractant consisting of organic solvent and liquefied gas can reduce the viscosity of liquefied gas and has stronger selectivity than pure organic solvents.

Core Difficulties and Process Pain Points of Ternary Azeotrope Separation Core Difficulties and Process Pain Points Analysis

IPAC/IPOH/water system belongs to the typical IPAC/IPOH/water system belongs to the typical multi-component non-ideal strong azeotropic system multi-component non-ideal strong azeotropic system , which is different from the conventional binary azeotrope, its separation difficulty increases exponentially, and it is also a long-standing technical bottleneck for industrial esterification waste liquid recovery. There are multiple intermolecular force coupling in the system, IPOH and water can form a strong hydrogen bond association, IPAC and IPOH have a polar near-miscibility effect, and the three components cross to form a stable ternary azeotropic system under normal pressure. Conventional ordinary distillation cannot break through the azeotropic equilibrium and cannot achieve high-purity separation of components., different from conventional binary azeotrope, its separation difficulty is exponentially improved, and it is also a long-standing technical bottleneck for the recovery of industrial esterification waste liquid. There are multiple intermolecular force coupling in the system, IPOH and water can form a strong hydrogen bond association, IPAC and IPOH have a polar near-miscibility effect, and the three components cross to form a stable ternary azeotropic system under normal pressure. Conventional ordinary distillation cannot break through the azeotropic equilibrium and cannot achieve high-purity separation of components.

There are significant technical shortcomings in the traditional single separation process: pure water extraction can only achieve dehydration, and cannot effectively split IPAC and IPOH azeotropic systems; single organic solvent extractive distillation has large solvent volatilization losses, poor system selectivity, and is prone to component entrainment, making it difficult for product purity to meet standards; although pure ionic liquid extractive distillation has excellent selectivity, high viscosity will lead to a sharp increase in vapor-liquid mass transfer resistance in the tower, deterioration of hydrodynamic properties, and problems such as deflection, liquid flooding, and mass transfer efficiency in the tower. Moreover, ionic liquid procurement costs are high, the regeneration process is complex, and the industrial economy is extremely poor. In addition, the traditional process only focuses on a single indicator of separation effect, ignores the collaborative control of energy consumption, carbon emissions, and operating costs, and is difficult to adapt to the current chemical green and low-carbon production requirements. This is also the core industry rigid demand for the innovation of mixed solvent coupled heat pump heat integration process in this study. The traditional single separation process has significant technical shortcomings: pure water extraction can only achieve dehydration, and cannot effectively split IPAC and IPOH azeotropic systems; single organic solvent extraction and distillation has large solvent volatilization losses, poor system selectivity, and is prone to component entrainment, making it difficult for product purity to meet standards; although pure ionic liquid extraction and distillation has excellent selectivity, high viscosity will lead to a sharp increase in vapor-liquid mass transfer resistance in the tower, deterioration of hydrodynamic properties, and problems such as deflection, liquid flooding, and mass transfer efficiency in the tower. Moreover, the procurement cost of ionic liquids is high, the regeneration process is complicated, and the industrialization economy is extremely poor. In addition, the traditional process only focuses on a single indicator of separation effect, ignores the collaborative control of energy consumption, carbon emissions, and operating costs, and is difficult to adapt to the current green and low-carbon production requirements of the chemical industry.

In-depth analysis of research methods innovation logic and construction-activity relationship In-depth analysis of research methods innovation logic and construction-activity relationship

Based on this, Yang Jingwei's research team from Qingdao University of Science and Technology proposed an efficient method for separating IPAC/IPOH/water mixtures by ionic liquid mixed solvent extractive distillation (MSED). And the structure-activity relationship between the separated azeotrope and the ionic liquid was studied by MD simulation. Based on this, Yang Jingwei's research team from Qingdao University of Science and Technology proposed an efficient method for separating IPAC/IPOH/water mixtures by ionic liquid mixed solvent extractive distillation (MSED). And the structure-activity relationship between the separated azeotrope and the ionic liquid was studied by MD simulation.

First, the selectivity of 169 ionic liquids was calculated using a COSMO-segmental activity coefficient-based pre-screening model. Ionic liquids with AC- have the highest selectivity and can achieve effective separation of IPAC/IPOH/water azeotropic systems. Compared with pyridyl, quaternary ammonium, pyrrolidine and piperidine ionic liquids, the synthesis of imidazolyl ionic liquids is relatively simple and inexpensive. However, alkyl chain length and substituents on imidazole rings have a significant impact on the properties and price of ionic liquids. Therefore, the researchers selected [EMIM] [AC], [EMMIM] [AC], [BMIM] [AC], [BMMIM] [AC], [HMIM] [AC] and [HMMIM] [AC] with high selectivity for further analysis. By further exploring the effect of ionic liquid structure on separation performance through molecular dynamics, the researchers determined that 1-ethyl-3-methylimidazole acetate ([EMIM] [AC]) was the best solvent. First, the selectivity of 169 ionic liquids was calculated using a COSMO-based segmental activity coefficient pre-screening model. Ionic liquids with AC- have the highest selectivity and can achieve effective separation of IPAC/IPOH/water azeotropic systems. Compared with pyridyl, quaternary ammonium, pyrrolidyl and piperidinyl ionic liquids, the synthesis of imidazolyl ionic liquids is relatively simple and inexpensive. However, the length of the alkyl chain and the substituents on the imidazole ring have a significant impact on the properties and price of ionic liquids. Therefore, the researchers chose [EMIM] [AC], [EMMIM] [AC], [BMIM] [AC], [BMMIM] [AC] with high selectivity for further analysis. By further exploring the effect of ionic liquid structure on separation performance through molecular dynamics, the researchers determined that 1-ethyl-3-methylimidazole acetate ([EMIM] [AC]) was the best solvent.

The core methodological innovation of this study lies in the three-level precision R & D system of "theoretical pre-screening - molecular dynamics mechanism verification - multi-objective parameter optimization" "theoretical pre-screening - molecular dynamics mechanism verification - multi-objective parameter optimization" The three-level precision R & D system completely abandons the traditional solvent screening blind trial and error R & D model, and greatly improves the R & D efficiency and process accuracy. The core advantage of the COSMO model is that it does not require a lot of experimental data, and can accurately anticipate the hydrogen bonding, polarity matching and dissolution selectivity of ionic liquids and components of the system based on the molecular surface charge density distribution. Quickly lock the acetate anion system from more than 100 ionic liquids, and clarify that the anion is the core factor that determines the separation selectivity of the ternary system., completely abandoning the traditional solvent screening blind trial and error research and development model, greatly improving the R & D efficiency and process accuracy. The core advantage of the COSMO model is that it does not require a large amount of experimental data, and can accurately anticipate the hydrogen bonding, polarity matching and dissolution selectivity of ionic liquids and components of the system based on the molecular surface charge density distribution. Quickly lock the acetate anion system from more than 100 ionic liquids, and clarify that the anion is the core factor determining the separation selectivity of the ternary system.

The differential screening of alkyl chain length verifies the regulation law of ionic liquid physical properties: the longer the alkyl chain, the higher the viscosity of ionic liquids, the greater the mass transfer resistance, and the higher the cost. The short URL [EMIM] [AC] can retain the strong hydrogen bond recognition ability of acetate while taking into account the advantages of low viscosity, low cost and high fluidity. Combined with molecular dynamics simulation, the separation mechanism can be revealed from the microscopic level: the acetate anion of [EMIM] [AC] can form a strong hydrogen bond association with IPOH and water molecules, which greatly improves the relative volatility of recombinant components. At the same time, imidazole cation can produce a weak polar interaction with IPAC, accurately realize the differentiated separation of three components, and consolidate the scientific nature of solvent screening from the microscopic structure-activity level. The differential screening of alkyl chain length verifies the regulation law of ionic liquid physical properties: the longer the alkyl chain, the higher the viscosity of ionic liquid, the greater the mass transfer resistance, and the higher the cost. The short URL [EMIM] [AC] can retain the strong hydrogen bond recognition ability of acetate while taking into account the advantages of low viscosity, low cost and high fluidity. Combined with molecular dynamics simulation, the separation mechanism can be revealed at the microscopic level: the acetate anion of [EMIM] [AC] can form a strong hydrogen bond association with IPOH and water molecules, which greatly improves the relative volatility of recombinant components. At the same time, imidazole cation can produce a weak polar interaction with IPAC, accurately realize the differentiated separation of three components, and consolidate the scientific nature of solvent screening from the microscopic structure-activity level.

By measuring the vapor-liquid balance of the system under the influence of [EMIM] [AC], the researchers validated the calculation model used. Taking the annual total cost and gas emission as the objective function, the multi-objective genetic algo was used to optimize the process parameters. They proposed an energy-saving heat pump-assisted integrated heat extraction and distillation (HPHIED) process to achieve heat recovery of MSED. The technological breakthrough in this link is to break the limitation of traditional process single-parameter optimization, couple the economic index with the environmental protection index in both directions, and introduce the heat pump thermal integration technology to solve the industry pain point of high energy consumption of mixed solvent extraction and distillation, and realize the three-dimensional collaborative optimization of process performance, economy and environmental protection. By measuring the vapor-liquid equilibrium of the system under the influence of [EMIM] [AC], the researchers validated the calculation model used. Taking the annual total cost and gas emission as the objective function, the multi-objective genetic algo was used to optimize the process parameters. They proposed an energy-saving heat pump-assisted heat integrated extraction and distillation (HPHIED) process to achieve heat recovery of MSED. The technological breakthrough in this link is to break the limitation of traditional process single-parameter optimization, couple economic indicators and environmental protection indicators in both directions, and introduce heat pump heat integration technology to solve the industry pain point of high energy consumption of mixed solvent extraction and distillation, and realize the three-dimensional collaborative optimization of process performance, economy and environmental protection.

Process synergy mechanism and research results Deep analysis of process synergy mechanism and research results Deep analysis

The results show that compared with the single organic solvent extraction distillation process, the TAC and gas emissions of the MSED process are 26.83% and 25.32%, respectively. The TAC and gas emissions of the HPHIED process are 11.02% and 35.83% lower than those of the MSED process, respectively, indicating that the use of mixed extractants significantly reduces the TAC and gas emissions of the traditional ED. The combination of thermal integration and heat pump technology further improves the autothermal recovery ability of MSED and significantly reduces energy consumption. In addition, the researchers obtained the optimal mixing ratio (0.334 [EMIM] [AC] + 0.666 DMSO) and related process parameters through MOGA optimization. The results show that compared with the single organic solvent extraction distillation process, the TAC and gas emissions of the MSED process are 26.83% and 25.32%, respectively. The TAC and gas emissions of the HPHIED process are 11.02% and 35.83% lower than those of the MSED process, respectively, indicating that the use of mixed extractants significantly reduces the TAC and gas emissions of traditional ED. The combination of heat integration and heat pump technology further improves the self-heat recovery capacity of MSED and significantly reduces energy consumption. In addition, the researchers obtained the optimal mixing ratio (0.334 [EMIM] [AC] + 0.666 DMSO) and related process parameters through MOGA optimization.

The synergistic core of the optimal mixed solvent system originates from the synergistic core of the optimal mixed solvent system originates from the coupling effect of the synergistic complementarity of the two solvents. The coupling effect of the synergistic complementarity of the two solvents is not a simple physical compounding. Among them, DMSO, as a traditional polar organic solvent, has the advantages of low viscosity, good fluidity, low mass transfer resistance and low cost, which can effectively improve the hydrodynamic properties of the pure ionic liquid system and solve the problems of low mass transfer efficiency and excessive pressure drop in the tower; while [EMIM] [AC], as a functional auxiliary, makes up for the shortcomings of DMSO's weak selectivity, volatility and low separation accuracy by virtue of its characteristics of extremely low saturated vapor pressure and high component selectivity. The optimal ratio of the two is 0.334:0.666, which is not a simple physical compounding. Among them, DMSO, as a traditional polar organic solvent, has the advantages of low viscosity, good fluidity, low mass transfer resistance and low cost, which can effectively improve the hydromechanical properties of pure ionic liquid systems and solve the problems of low mass transfer efficiency and excessive pressure drop in the tower; while [EMIM] [AC], as a functional auxiliary, makes up for the shortcomings of DMSO's weak selectivity, volatile and low separation accuracy by virtue of its extremely low saturation vapor pressure and high component selectivity. The optimal ratio of the two is 0.334:0.666 to achieve the optimal balance of selectivity, mass transfer efficiency, energy consumption, and cost. The optimal balance of selectivity, mass transfer efficiency, energy consumption, and cost not only eliminates the solvent loss and high emission problems of pure organic solvents, but also avoids the high viscosity and high cost disadvantages of pure ionic liquids., not only eliminates the solvent loss and high emission problems of pure organic solvents, but also avoids the high viscosity and high cost disadvantages of pure ionic liquids.

The energy-saving logic of the heat pump-assisted heat integration process has strong engineering innovation: the high-temperature waste heat of the tower kettle and the low-temperature cooling capacity at the top of the tower are completely lost in the traditional extractive distillation process, and the energy cascade utilization rate is extremely low. The HPHIED process recovers the latent heat of the steam at the top of the tower through the heat pump system, and after the pressure is raised, it provides heat to the reboiler of the tower kettle to achieve a closed-loop heat cycle within the system, which greatly reduces the consumption of external steam heat sources and cooling media. From the data perspective, the two-stage process optimization shows the characteristics of layer efficiency: the mixed solvent replaces the single solvent to achieve the basic energy saving and cost reduction of the separation system, while the blessing of heat pump thermal integration further taps the potential of process waste heat recovery, realizes the second large pressure drop of energy consumption and carbon emissions, and forms a dual strengthening system of "solvent optimization + energy optimization". The energy-saving logic of the heat pump-assisted heat integration process has strong engineering innovation: the high temperature waste heat of the tower kettle and the low temperature cooling capacity at the top of the tower are completely dissipated in the traditional extractive distillation process, and the energy cascade utilization rate is extremely low. The HPHIED process recovers the latent heat of the steam at the top of the tower through the heat pump system, and supplies heat to the reboiler after the pressure is raised, so as to realize the closed-loop circulation of heat inside the system and greatly reduce the consumption of external steam heat source and cooling medium. From the data perspective, the two-level process optimization presents the characteristics of layer efficiency: the mixed solvent replaces a single solvent to achieve basic energy saving and cost reduction of the separation system, while the blessing of heat pump heat integration further exploits the potential of process waste heat recovery, and realizes the secondary large pressure drop of energy consumption and carbon emission, forming a dual strengthening system of "solvent optimization + energy optimization".

At the same time, the application of MOGA multi-objective genetic algo solves the problem of multi-variable coupling conflict of process parameters. Parameters such as solvent ratio, reflux ratio, theoretical tray number, and feed position restrict each other in the process of extractive distillation, and single-objective optimization is prone to the drawbacks of "energy saving is not economical, and the economy is not environmentally friendly". The multi-objective optimization can accurately balance the two core indicators of total annual cost (TAC) and gas emissions, and output the optimal parameter combination suitable for industrial production, avoiding the problem of disconnection between the optimal parameters in the laboratory and the actual working conditions of industry. At the same time, the application of MOGA multi-objective genetic algo solves the problem of multi-variable coupling conflict of process parameters. In the process of extractive distillation, parameters such as solvent ratio, reflux ratio, theoretical tray number, and feed position restrict each other, and single-objective optimization is prone to the drawbacks of "uneconomical energy saving, economic and environmental protection". Multi-objective optimization can accurately balance the two core indicators of total annual cost (TAC) and gas emissions, and output the optimal parameter combination suitable for industrial production to avoid the problem of disconnection between the optimal parameters in the laboratory and the actual working conditions of the industry.

Technology innovation highlights and industry differentiation advantages Technology innovation highlights and industry differentiation advantages

Compared with the traditional azeotrope separation process and the existing ionic liquid extraction and rectification technology, this study has four core innovation advantages, filling the technical gap of the green separation of the ternary ester-alcohol-water composite system. First, compared with the traditional azeotrope separation process and the existing ionic liquid extraction and rectification technology, this study has four core innovation advantages, filling the technical gap of the green separation of the ternary ester-alcohol-water composite system. First, the ionic liquid-organic solvent mixed synergistic extraction system is constructed. The ionic liquid-organic solvent mixed synergistic extraction system breaks through the bottleneck of single solvent performance, realizes the two-way balance of selectivity and mass transfer efficiency, and solves the pain point of low separation accuracy and large solvent loss of the traditional technology. Second, a systematic solvent screening method of "simulated pre-screening + mechanism verification + experimental check" is established to avoid the high cost and low efficiency problems of traditional experimental trials and errors, and to provide a standardized methodology for the screening of extractants in multi-component azeotropic systems., break through the bottleneck of single solvent performance, achieve both selectivity and mass transfer efficiency, and solve the pain points of low separation accuracy and large solvent loss of traditional technologies. Second, a systematic solvent screening method of "simulated pre-screening + mechanism verification + experimental check" is established to avoid the high cost and low efficiency problems of traditional experimental trials and errors, and provide a standardized methodology for the screening of extractants in multi-component azeotropic systems.

Third, the first heat pump-assisted heat integrated coupling mixed solvent extraction and rectification process, the process enhancement technology and energy system optimization and deep integration, breaking the shackles of high energy consumption in the industrialization of ionic liquid extraction and rectification, and greatly improving the practicality of process engineering. Fourth, to achieve the synergistic optimization of economic and environmental protection indicators, which is different from the design logic of heavy separation, light energy consumption, and light environmental protection in traditional processes. It is suitable for the development trend of green and low-carbon transformation in the chemical industry, and has both engineering landing and policy adaptability. Third, the first heat pump-assisted heat integrated coupling mixed solvent extraction and rectification process, the process enhancement technology and energy system optimization and deep integration, breaking the shackles of high energy consumption in the industrialization of ionic liquid extraction and rectification, and greatly improving the practicality of process engineering. Fourth, to achieve the synergistic optimization of economic and environmental indicators, which is different from the design logic of traditional processes that are heavy separation, light energy consumption, and light environmental protection, and is suitable for the development trend of green and low-carbon transformation in the chemical industry.

Conclusion and Outlook Conclusion and Outlook

Overall, this work provides theoretical guidance for the conceptual design, solvent screening and process optimization of ionic liquids in ED, which is expected to promote the realization of environmental protection and sustainable utilization of resources. Overall, this work provides theoretical guidance for the conceptual design, solvent screening and process optimization of ionic liquids in ED, which is expected to promote the realization of environmental protection and sustainable utilization of resources.

From the perspective of theoretical value, this study clarified the structure-activity relationship between the structure of imidazole acetate ionic liquids and the separation performance of ternary azeotropic systems, revealed the microscopic mechanism of synergistic effect of mixed solvents and heat pump heat integration and energy saving, and improved the theoretical system of ionic liquid mixed extraction and distillation separation of multi-component strong non-ideal systems. From the perspective of theoretical value, this study clarified the structure-activity relationship between the structure of imidazole acetate ionic liquids and the separation performance of ternary azeotropic systems, revealed the microscopic mechanism of synergistic effect of mixed solvents and integrated energy saving of heat pump heat, and improved the theoretical system of ionic liquid mixed extraction distillation separation of multi-component strong non-ideal systems, providing general theoretical support for the research and development of similar ester-alcohol water azeotrope separation processes.

From the perspective of industrialization landing and technology iteration, there is still room for optimization in the current process. First, targeted research on ionic liquid modification can be carried out to synthesize low-viscosity, high-stability, and low-cost functionalized ionic liquids, further reducing the proportion of ionic liquids added to the mixed solvent and compressing operating costs; Second, heat pump coupling matching mode can be optimized, combined with pinch technology to complete global energy integration, and further tap the energy-saving potential of the system; Third, high-efficiency regeneration processes for mixed solvents can be developed to solve the problems of solvent trace loss and impurity accumulation during long-term operation, and improve the stability of long-term operation of the device. From the perspective of industrialization landing and technology iteration, there is still room for First, it can carry out targeted research on ionic liquid modification to synthesize low-viscosity, high-stability, and low-cost functionalized ionic liquids, further reducing the proportion of ionic liquids added to the mixed solvent and compressing operating costs; second, it can optimize the coupling matching mode of the heat pump, combine pinch technology to complete global energy integration, and further tap the energy-saving potential of the system; third, it can develop a high-efficiency regeneration process for mixed solvents to solve the problems of trace solvent loss and impurity accumulation during long-term operation, and improve the stability of the long-term operation of the device.

At the industrial application level, this process can be widely adapted to IPAC/IPOH waste liquid recovery scenarios in the pharmaceutical, coatings, and fine chemical industries. Compared with traditional processes, it can simultaneously realize the triple benefits of high-value resource recovery, energy consumption pressure drop, and carbon emission reduction, which is in line with the development concept of circular economy. In the future, with the large-scale production of ionic liquids and the continuous reduction of costs, the mixed solvent extraction and rectification coupled thermal integration process is expected to gradually replace the traditional high-consumption and low-efficiency separation process, and become the mainstream industrial technology for green separation of ester-alcohol-water ternary azeotropes. It has a strong prospect for industrialization promotion. At the industrial application level, this process can be widely adapted to IPAC/IPOH waste liquid recovery scenarios in the pharmaceutical, coatings, and fine chemical industries. Compared with traditional processes, it can simultaneously achieve the triple benefits of high-value resource recovery, energy consumption pressure drop, and carbon emission reduction, which is in line with the development concept of circular economy. In the future, with the large-scale production of ionic liquids and the continuous reduction of costs, the mixed solvent extraction and distillation coupled thermal integration process is expected to gradually replace the traditional high-consumption and low-efficiency separation process, and become the mainstream industrial technology for green separation of ester-alcohol-water ternary azeotrope.

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