Development of a Conceptual Process for Selective CO2 Capture from Fuel Gas Streams Using [hmim][Tf2N] Ionic Liquid as a Physical Solvent

The ionic liquid (IL) [hmim] [Tf2N] was used as a physical solvent in an Aspen Plus simulation, employing the Peng-Robinson Equation of State (PR-EOS) with Boston-Mathias (BM) alpha-function and standard mixing rules, to develop a conceptual process for CO2 capture from a shifted (undergone the water-gas shift reaction) warm fuel gas stream produced from Pittsburgh #8 coal for a 400 MWe IGCC power plant. The physical properties of the IL, including density, viscosity, surface tension, vapor pressure, and heat capacity were obtained from literature and modeled as a function of temperature. Also, available experimental solubility values for CO2, H-2, H2S, CO, and CH4 in this IL were compiled, and their binary interaction parameters (delta(ij) and l(ij)) were optimized and correlated as functions of temperature. The Span-Wager EOS was also employed to generate CO2 solubilities in [hmim] [Tf2N] at high pressures (up to 10 MPa) and temperatures (up to 510 K). The conceptual process developed consists of four adiabatic absorbers (2.4 m inner diameter (ID), 30 m high) arranged in parallel and packed with Plastic Pall Rings of 0.025 m for CO2 capture; 3 flash drums arranged in series for solvent (IL) regeneration with the pressure-swing option; and a pressure-intercooling system for separating and pumping CO2 up to 153 bar to the sequestration sites. The compositions of all process streams, CO2 capture efficiency, and net power were calculated using the Aspen Plus simulator. The results showed that, based on the composition of the inlet gas stream to the absorbers, 95.12 mol % of CO2 was captured and sent to sequestration sites; 98.37 mol % of H-2 was separated and sent to turbines; and the solvent exhibited a minimum loss of 1.23 mol %. These results indicate that the [hmim][Tf2N] IL could be used as a physical solvent for CO2 capture from warm shifted fuel gas streams with high efficiency.