基于离子液体吸收法的气体分离研究进展

摘要

近年来,温室气体减排及利用已成为全球化低碳经济发展的关键问题.化石燃料(煤、石油、天然气等)燃烧以及矿产开采活动所排放的有毒有害气体严重污染大气环境.与此同时,这些气体又是重要的工业生产原料,因此有必要捕捉这些污染气体,并加以分离和再利用.为克服传统有机溶剂和碱液吸收法存在的污染、腐蚀等问题,有“液体分子筛”之称的离子液体(ILs)逐渐成为学者们用来代替传统气体吸收剂的绿色溶剂,由此综述了ILs在气体分离方面的研究进展.分析了影响气体溶解选择性的内外因素以及适用于不同气体混合物分离的ILs结构特征.对于CO2与难溶气体的分离,可在阴、阳离子结构中引入碱性基团(如羧酸类、氨基酸类、非质子型的含氮杂环和酚羟基等),通过强化ILs对CO2的化学吸收能力,提高CO2与难溶气体的吸收分离效果.由于碱性较强ILs对CO2,SO2,H2S都具有化学吸收作用,合理调节ILs碱性强弱和碱性基团位置以弱化ILs与CO2的结合,是提高SO2/CO2及H2S/CO2溶解选择性的有效途径.此外,结构紧凑的相对分子量较低的ILs通常具有较高的理想溶解选择性.通过分子动力学模拟计算,认为混合气体的实际溶解选择性受进气浓度比、ILs含量、温度、压力等因素综合影响.为获得较高的气体溶解选择性应正确选择ILs类型,并确定合理的使用量及操作温度和压力.%In order to meet the requirements of low-carbon economy,the reduction and utilization of global-warming gases have become the focus of attention.There are a large amount of toxic and harmful gases being emitted from the combustion of fossil fuels and syngas,as well as being released during mining activities.It is therefore necessary to trap and separate these gases for eliminating their environmental contamination,also increasing the feedstocks for industrial production.For avoiding the contamination and safety problems raised from the conventional alkali absorbents,the ionic liquids,namely "liquid molecular sieve",have become green alternatives to absorb and separate different gases.Accordingly,the research progress about separating gases by pure ionic liquids is reviewed in this paper.The influencing factors including temperature,pressure,the properties of gas and ionic liquids,and the functional groups of ionic liquids,were analyzed.It is stated that the ionic liquids with alkali groups on cation and anion are promising CO2 solvents and competent separator for removing CO2 from some sparsely soluble gases.In order to separate CO2 from strongly acidic SO2 and H2S,moderate basicity exhibits much better separating ability because strong alkali group could strongly bind with both SO2(or H2S) and CO2,leading to low SO2/CO2 and H2S/CO2 selectivities.Ionic liquids with small molecular weights and compact structures usually perform better selectivity,and low temperature and pressure are favorable for increasing the separation.Additionally,combining experimental results and molecular dynamic simulation,the real selectivity of binary gases in ionic liquids was calculated based on Equations of State.It is concluded that feed gas ratio,ionic liquid contents,temperature and pressure are significant factors required to be adjusted to approach a great real gas selectivity.