Application Of A Group Contribution Equation Of State For The Thermodynamic Modeling Of CO₂+Ionic Liquids

Nowadays, the alternative refrigerant is a global problem, and the carbon dioxide as a nature refrigerant has a series of advantages, they are economic, environmental, safe, non-toxic, non-flammable, chemical and thermal stability etc, so it must be a long-term development. The main problem that restrict the development of the carbon dioxide absorpt refrigeration system is the choice of refrigerant and absorbent. The basic principle of absorption refrigeration is to take the advantage of the working pairs which have special quality, the refrigerant could absorpt and release heat by evaporation and condensation the whole way in the system. The absorbent have the ability to absorb the carbon dioxide as much as possible in one condition, and the ability to release the carbon dioxide in other condition. The ionic liquid is the substance that has a good salvation, the ionic liquids as absorbent will be a hot research in the future.The absorpt refrigeration mainly uses Low-grade heat source instead of mechanical to provide working power, the refrigerat system has many advantages such as being quiet, simple energy-saving and friendly to the environment etc. Suitable ionic liquid and natural refrigerant carbon dioxide are selected to be the working pairs, which is much miniaturized and efficient than conventional absorption refrigeration. The group contribution equation of state(GC-EoS) was applied to predict the solubility of gas in binary or ternary ionic liquids. It is known that the properties of ionic liquids(ILs) can be modified by appropriate selection of cations and anions. Even if an infinite number of ionic liquids can be generated, only a limited number of families of anions and cations are used. The GC-EoS is a promising method by selecting the cations and anions. The ionic liquids are divided to many functional groups according to the group contribution principle, the gas itself is an independent functional group. for calculating the solubility of gas in ionic liquids.The GC-EoS is based on the concept of group contribution, bombined with the generalized van der Waals partition function, the Carnahan-Starling expressiong for hard spheres, mixing rules based on an NRTL-like expressiong for the excess Helmholtz function. It is used to calculated binary or ternary vapor-liquid equilibria of nonideal mixtures. The calculation need to divide the ionic liquids into a certain functional groups,We could enter the parameters to calculate according to the group contribution equation of state and the Vissual C++program, these parameters include the pure component parameters, the parameters of functional groups and binary interaction parameters. The paper introduces these parameters in detail and tries to sort out the parameters. The paper describes the comparation between the simulate results and experimental values, the error is very small, so the GC-EoS is a good method for describing the thermal conditions of the gas in ionic liquid. The article also simulate data by drawing figures, it introduces the factors that influence the solubility of CO2in pure ionic liquid or immiscible ionic liquids and the relationship between them.