Experimental study on CO2 sorption capacity of the neat and porous silica supported ionic liquids and the effect of water content of flue gas

In this research, absorption of CO2 in different ionic liquids (ILs) is studied. Thus four ILs were synthesized containing 1-butyl-3-methylimidazolium as the cation and nitrate [NO3]−, thiocyanate [SCN]−, dicyanamide [N(CN)2]− and hydrogen sulfate [HSO4]− as the anions, respectively. The resulting ILs were then immobilized into activated silica support in a 1/1 IL/SiO2 weight ratio via the impregnation-vaporization method. CO2 sorption behavior of both neat and silica supported ILs (ILs-SiO2) were investigated at different temperatures and flow rates under atmospheric pressure, while their desorption process were carried out under 20 mm Hg at 70 °C. In both sorbents, the best results were obtained at 25 °C with a flow rate of 12 mL/min, where [bmim][N(CN)2] with 1.85 (wt%) or 0.42 mmol CO2 per gram of sorbent and [bmim][HSO4]-SiO2 with 2.33 (wt%) or 0.53 mmol CO2 per gram of sorbent showed the highest sorption capacities. The effect of water on CO2 absorption capacity of the neat and silica supported ILs were also studied by transmission of CO2 gas flue containing 400 ppm water. The results indicated that the mass gain was higher when wet CO2 was passed through the sorbents, opposed to passing dry CO2. Because of the existence of a weak coulombic intraction between the sorbents and CO2, desorption occurs rapidly and a readily reuse of the sorbents is therefore provided.