Polyamidoamine-facilitated poly(ethylene glycol)/ionic liquid based pressure swing membrane absorption process for CO₂ removal from shifted syngas

Pre-combustion capture of CO₂ from shifted syngas is a major route for carbon capture and sequestration from integrated gasification combined cycle for coal as the fuel. Conventional Selexol absorption-based processes involve cooling the gas to near-ambient temperature. A novel cyclic 5-valve pressure swing membrane absorption (PSMAB) process is being developed for CO₂ removal from lower-temperature shifted syngas at ∼100 °C in hollow-fiber membrane contactors using ionic liquid (IL) absorbent, 1-butyl-3-methyl-imidazolium dicyanamide ([bmim][DCA]). Separation performance is considerably enhanced by adding nonvolatile polyamidoamine (PAMAM) dendrimer Generation 0 to the IL at higher temperatures for a 40% CO₂, 60% He (surrogate for H₂) feed. Absorption performance in the cyclic process depends on selective sorption and other absorbent properties especially viscosity and hollow-fiber membrane contactor module design employing microporous hydrophobized polyether ether ketone (PEEK) hollow fiber-based membranes. Equilibrium CO₂ solubility and CO₂–He selectivity for IL, [bmim][DCA], has been compared with those for poly(ethylene glycol) (PEG) 400 which yields improved equilibrium CO₂–He selectivity and CO₂ absorption with/without 20 wt% PAMAM dendrimer over the temperature range 50–100 °C. The PSMAB process separation performance has been explored using PEG 400-based absorbent in two hollow-fiber membrane contactor modules with improved designs in series at temperatures up to 100 °C and feed-gas pressures up to 1720 kPag. This performance has been compared with that of the system using IL, [bmim][DCA]. The dendrimer-IL system performance for two modules-in-series with reduced dead volume considerably enhanced separation yielding >95% CO₂ in the CO₂-enriched product; further this performance exceeded easily that of the PEG 400-based system.