Mathematical modeling of CO2 membrane absorption system using ionic liquid solutions

Abstract

This research presents a 2D mathematical modeling based on finite difference method (FDM) for absorption of CO2 into aqueous solution of ionic liquids ([bmim][BF4] and [bmim][PF6]) by means of hydrophobic polypropylene hollow fiber membrane contactor (HFMC). Governing equations with their corresponding boundary conditions were solved and the results were validated against reported experimental data and excellent agreement was found. This study has provided an opportunity to investigate the effects of various ionic liquids with different concentrations as well as liquid and gas flow rate on CO2 absorption system in membrane contactors. The results demonstrated that molar flux of carbon dioxide for 25 wt% and 50 wt% solution of [bmim][PF6] is 1.29 and 1.98 times that of pure water, respectively. Also [bmim][BF4] has a weaker performance than [bmim][PF6] due to lower carbon dioxide solubility, and the addition of 50 wt% of it to the pure water has increased the absorption rate by 32 %. Overall and liquid phase mass transfer coefficient has decreased in ionic liquid solutions. Reynolds number in tubes has been decreased by increasing of ionic liquid mass fraction and also a sharp decrease in the Reynolds number can be observed in the ionic liquids mass fractions greater than 60 wt%.