Gas separation by absorption in pure ionic liquids

In order to meet the requirements of low-carbon economy,the reduction and utilization of global-warming ga- ses 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 ion- ic liquids,namely “liquid molecular sieve”,have become green alternatives to absorb and separate different gases. Ac- cordingly,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 liq- uids,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 H2 S,moderate basicity exhibits much better separating ability because strong alkali group could strong- ly bind with both SO2(or H2 S) and CO2 ,leading to low SO2 / CO2 and H2 S / CO2 selectivities. Ionic liquids with small molecular weights and compact structures usually perform better selectivity,and low temperature and pressure are fa- vorable 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.