Semiclathrate-based CO2 capture from fuel gas in the presence of tetra-nbutyl ammonium bromide and silica gel pore structure

Pre-combustion CO2 capture technology was investigated via a hydrate-based gas separation process. Semiclathrate phase equilibria were measured for the simulated fuel gas from the integrated gasification combined cycle (IGCC) consisting of 40 mol% CO2 and balanced H-2 in the presence of tetra-n-butyl ammonium bromide (TBAB) and porous silica gel particles containing water inside. The basic idea is an extension of our previous work [34], that is, using a porous silica gel structure made it possible to get rid of stirring the content inside the hydrate reactor and ensure the rapid hydrate formation with relatively short induction. TBAB was introduced to confined aqueous solution in silica gel pore structure, having nominal pore diameter of 100 nm, as a thermodynamic promoter and formed semiclathrate with the gas mixture under milder temperature and pressure conditions. Compositional analysis of semiclathrate and coexisting gas phases was also performed at various temperatures and TBAB concentrations. The highest CO2 concentration obtained from the dissociated semiclathrate was 94 mol% formed at 277.15 K and 3.0 MPa, with 20 wt% TBAB solution in 100 nm silica gel. To demonstrate the highly-concentrated CO2 outlet stream from the single-stage semiclathrate reactor, the kinetic study of CO2 distribution through fixed-bed type reactor charged with silica gel particles containing aqueous TBAB solution was also investigated. Utilization of porous silica gel makes it possible to capture higher concentration of CO2 in the semiclathrate phase, but it also reduced the total amount of gas consumed for semiclathrate conversion. However, the use of silica gel particles with TBAB enabled formation of semiclathrate hydrate under milder conditions and unstirred continuous method to a high extent and a high rate.