Impacts of the surfactant sulfonated lignin on hydrate based CO2 capture from a CO2/CH4 gas mixture

In the present work, we report an investigation of using an anionic surfactant sulfonated lignin (SL) to promote gas hydrate formation for CO2 capture from a CO2/CH4 gas mixture. The experiments were performed at 277.15 K in a stirred tank reactor. The initial overpressure (driving force) for hydrate formation was fixed at ΔP = 2.5 MPa. The impacts of the SL presence on hydrate growth behavior and CO2 separation efficiency were elucidated. The results indicated that hydrate nucleation was prolonged in the presence of SL but this stage was accelerated when adding 1.0 mol% tetrahydrofuran (THF) into the SL solution. Compared to THF/SL and sodium dodecyl sulfate (SDS) solutions, CO2 recovery obtained in SL solutions was increased to 63.5 ± 2.9% and the separation factor was 4.0 ± 0.8. Gas consumption obtained in SL solutions was higher than that obtained in other systems like liquid water, SDS solution, THF solution, and tetra-n-butyl phosphonium bromide (TBPB) solution. Therefore, sulfonated lignin can be used as a promising surfactant to improve hydrate formation kinetics as well as the efficiency of CO2 capture from CO2/CH4 gas mixture, but there still exists a space to increase the CO2 selectivity in the presence of SL.