Novel pressure and temperature swing processes for CO2 capture using low viscosity ionic liquids

Abstract

For gas sweetening, physical solvents (e.g. Selexol, Rectisol and Fluor) are favored over chemical solvents when the partial pressure of CO2 in the flue gas is high. The CO2 rich solvent is usually regenerated by reducing the pressure without adding heat. The current work presents a comparative study of the low-viscous ionic liquid (IL) 1-hexyl-3-methylimidazolium tricyanomethanide ([C6mim][TCM]) versus the established physical solvent Selexol (DEPG, a mixture of dimethyl ethers of polyethylene glycol) used as a benchmark. The process being investigated is the sweetening of synthetic natural gas mainly consisting of CO2 and CH4 (about 13 kton·y−1). The parameters used for the fair comparison include: (i) the CO2 solubility (removal capability and solvent efficiency), (ii) the energy needed for solvent regeneration and (iii) the required equipment to achieve the same performance in terms of separation selectivity and specification of the purified gas. Besides the pressure swing process configuration commonly used in the absorption/desorption processes involving physical solvents, novel temperature swing and a combination of the two are evaluated including their impact on the primary energy requirement and investment costs for CO2 capture. In this work, it is concluded that a combination of pressure- and temperature swing is the most feasible configuration for solvent regeneration. The pressure in this novel concept is reduced to only 0.92 MPa in the lowest pressure flash tank as compared to 0.1 MPa in the conventional pressure swing process, reducing the recompression costs considerably as the absorber operates at 2.8 MPa.