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][Tf 2 N] was used as a physical solvent in an Aspen Plus simulation, employing the Peng–Robinson Equation of State (PR-EOS) with Boston–Mathias (BM) α-function and standard mixing rules, to develop a conceptual process for CO 2 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 CO 2, H 2, H 2 S, CO, and CH 4 in this IL were compiled, and their binary interaction parameters (δ ij and l ij ) were optimized and correlated as functions of temperature. The Span–Wager EOS was also employed to generate CO 2 solubilities in [hmim][Tf 2 N] 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 CO 2 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 CO 2 up to 153 bar to the sequestration sites. The compositions of all process streams, CO 2 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 CO 2 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][Tf 2 N] IL could be used as a physical solvent for CO 2 capture from warm shifted fuel gas streams with high efficiency.