(437a) Gas Purification and Separation With Ionic Liquids

Gas purification and separation with Ionic liquids

Xiangping Zhang, Haifeng Dong, Ying Huang, Xin Zhang, Suojiang Zhang

Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex System, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China

Abstract

In the past decade, ionic liquids have emerged as a promising alternative to be used in the gas purification and separation due to their remarkable properties, such as negligible volatility, high chemical/physical stability, higher solubility and selectivity, and tenability which allows design of task-specific ionic liquids (TSILs). In industries, gas separation or processing was regarded as an important operation to remove harmful and toxic gas emissions from waste gas in order to reduce ecologic destroy and environmental pollution from an environmental perspective; on the other hand, purifying gases by separating impurities from mixtures can improve the quality of the gas to satisfy the requirement of gas products considering the industrial relevance. There are some typical gas separation processes with ionic liquids, such as CO₂ capture, desulfurization of flue gas, volatile organic compounds (VOCs) control, as well natural gas sweetening, have shown promising potentials for industrialization.

In this work, an Industrial Application-Oriented research framework was proposed and conducted to develop new processes to purify and separate gases taking ionic liquids as main solvents. The following studies have been focused on: 1) the structure-properties relationship of candidate ionic liquids was studied using the molecular dynamics simulation and the quantum mechanics, combining the results of spectrum characterization. Studying the interaction force between the gas and ionic liquid would be helpful to understand the absorption mechanism and then to determine the criterion of the designing and screening promising ionic liquids; 2) new thermodynamic models were developed and used to predict the physicochemical properties of ILs on the base of the fragment contribution-corresponding states (FCCS) method. The FCCS method has advantages to deal with both the molecular and ionic systems, and it is more precise than traditional method with an average absolute relative deviation less than 4% for more than 600 kinds of ILs investigated. The binary and ternary-compound gas-liquid phase equilibrium data were measured in the lab, and the SRK equation of state was used for predicting the solubility gas in ILs. The binary parameters for VLE of compounds were regressed from experimental data; 3) the transportation properties of gas and liquid were important for reactor design. The multi-bubble/single behavior in ionic liquids was studied by using high speed image pick-up system. The bubble behavior, such as bubble size distribution, gas holdup, Sauter diameter and interfacial area were investigated. New correlations based on the experimental data was proposed for the prediction of bubble Sauter diameter in gas-ionic liquid systems; 4) process simulation was used to determine the operational parameters and the flowsheet structure. The whole flowsheet of gas separation was established considering real industrial constraints. 5) techno-economic assessment procedure is also important to evaluate the new process. On the base of the models proposed and experimental data, the key parameters (e.g. solvent concentration and flow rate, stage numbers and lean loading) were optimized aiming at minimizing the energy requirement of the solvent regeneration. Capital costs and operating costs were estimated in this work to assess the economic performance.

Several ionic liquid-based gas separation processes were studies on the base of the above research framework. The possibilities and the feasibilities of the new processes would be expected to be obtained. The relevant study not only provides new gas separation technologies to replace the traditional energy-extensive and polluted ones, but also indicates the advantages and drawbacks before these new processes come into commercialization. Importantly, the obtained information will be helpful to avoid the failures of industrialization and reduce the risk of investment in the future.

Acknowledgements

We would like to acknowledge the support from Key Program of National Natural Science Foundation of China (No.21036007), the National Natural Science Foundation of China (No. 51274183) and the National High Technology Research and Development Program of China (No.2011AA050606).