Ionic liquid screening for desulfurization of coke oven gas based on COSMO-SAC model and process simulation

1305 ionic liquids (ILs) involving 45 cations and 29 anions were computationally screened to search the optimal solvents for deep desulfurization of coke oven gas (COG) based on the combination of the COSMO-SAC model and process simulations. Firstly, the molecular structures, including those of independent ions and solutes, were constructed and geometrically optimized using density functional theory (DFT) calculation with the VWN-BP functional of generalized gradient approximation (GGA) and DNP basis set (v4.0) in DMol3 software. The σ-profiles of ion pairs for COSMO-SAC model were calculated through summation of σ-profiles of cations and anions. Secondly, Henry’s constant of various gas solutes such as H2S, COS, TS, CH4 in each ion pair was estimated by COSMO-SAC model. In order to balance the trade-off between the solubility and selectivity of various sulfides in ionic liquids, the mass-based Absorption-Selectivity-Desorption index (ASDI) combined with physical properties was employed as the evaluation metrics. Four ILs with high values of ASDI and appropriate melting point and viscosity were screened out for further process simulation. Finally, sensitivity analysis and central composite experimental design were performed to optimize the input parameters of process simulations on COG desulfurization, while total annual cost and specific energy consumption of the desulfurization processes were used to evaluate the economic and energy efficiency of various ILs. It is indicated that [C1mpyr][Oac] exhibits the high total sulfur removal ratio of 99.05% and the CH4 recovery ratio of 94.65%. In addition, its specific energy consumption and total annual cost were 5 kWh/kg Sulfides and $9 million/year, respectively. In short, we proposed the combined COSMO-SAC and process simulation method that provide a comprehensive perspective of large-scale IL design for COG or similar gas mixture desulfurization.