Abstract: The highly efficient and low-cost recovery of ionic liquid from the solution remains an issue to realize the reuse of ionic liquid. This work proposes the coupling process combining nanofiltration and vacuum flash evaporation for recovery of ionic liquid in solution. The lower concentration of ionic liquid aqueous solution is concentrated through nanofiltration technology, and then the higher concentration of ionic liquid aqueous solution is treated by the vacuum flash evaporation process to obtain the pure ionic liquid and realize the efficient separation and recovery of ionic liquid. 1-methyl-3-octylimidazolium tetrafluoroborate ([C8Mim][BF4]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2Mim][BF4]) were used as model compounds to explore the recovery effect of the coupling technology by process simulation. Based on the literature reported data on the previous researches, the main physical properties of ionic liquid and ionic liquid-water thermodynamic models were constructed by the regression method. A model of the coupled process of the separation and recovery technology for ionic liquid was established by Aspen Plus simulation software. The influences of different operating conditions on the process separation performance were investigated by the parametrical sensitivities analysis. Then the optimal scenario could be obtained. At the same time, the heat exchanger network of the coupling process was modified which could increase the energy efficiency and reduce the cooling and heating utilities consumption. Moreover, the energy consumption of different processes were analyzed and evaluated to clarify the separation and recovery advantages of the novel coupling process. The results showed that the heating utilities of [C8Mim][BF4] and [C2Mim][BF4] were 11% and 13% of those of the initial scenarios, and the cooling utilities were 15% and 19% of those of the initial scenarios after the heat exchanger network modification. The lowest comprehensive energy consumption of the 2 stage membrane separation-flash evaporation coupling process was 3.9 GJthermal-eq/t IL ([C8Mim][BF4]) and 4.5 GJthermal-eq/t IL ([C2Mim][BF4]), which was only 20% ([C8Mim][BF4]) and 27% ([C2Mim][BF4]) of the direct vacuum flash evaporation process. The results of this study can provide theoretical basis and guidance for the future industrial application of ionic liquid recovery process.

Key words: ionic liquid, nanofiltration, vacuum flash evaporation, energy consumption, process simulation, recovery and separation

摘要： 从混合溶液中高效、低能耗地回收离子液体，一直是实现其再利用的难点。本研究提出纳滤、闪蒸回收溶液中离子液体的耦合工艺，即先将较低浓度的离子液体水溶液通过纳滤提浓，获得较高浓度的离子液体水溶液通过减压闪蒸工艺获得纯离子液体并实现离子液体的高效分离回收。在模拟研究过程中，以1-辛基-3-甲基咪唑四氟硼酸盐([C8Mim][BF4])和1-乙基-3-甲基咪唑四氟硼酸盐([C2Mim][BF4])作为模型化合物，来探究耦合工艺的离子液体回收效果。基于文献报道数据，采用回归方法构建起离子液体主要物性和离子液体-水之间的热力学模型，采用Aspen Plus模拟软件建立分离回收过程的耦合新工艺模型，考察不同操作条件对工艺分离效果的影响变化规律，获得工艺最佳操作方案。同时，对回收过程进行换热改造，提高回收工艺的热效率，降低公用工程消耗量。对不同分离过程的能耗进行分析评价，以明确耦合新工艺的分离回收优势。研究结果表明，经过换热改造后，[C8Mim][BF4]和[C2Mim][BF4]的回收工艺热公用工程分别为改造前的11%和13%，冷公用工程分别为改造前的15%和19%。2级膜分离-闪蒸耦合工艺的综合能耗最低为3.9 GJ thermal-eq/t IL([C8Mim][BF4])和4.5 GJthermal-eq/t IL([C2Mim][BF4])，仅为直接闪蒸工艺的20% ([C8Mim][BF4])和27% ([C2Mim][BF4])。本研究结果可为未来离子液体回收工艺的工业化应用提供理论依据和指导。

关键词: 离子液体, 纳滤, 闪蒸, 能耗, 工艺模拟, 分离回收