Combination Of Imidazolium Bromine And Tetrabutylammonium Bromide For Ch4 Purification From Simulated Biogas By Hydrate-Based Gas Separation

Biogas is one of the green energy resources. To enhance usage of biogas (64.0 mol % CH4/CO2) and reduce the greenhouse effect, CH4 purification by the hydrate-based gas separation (HBGS) technology was studied in this work. Green solvent ionic liquid [BMIm] Br and thermodynamic promoter tetrabutylammonium bromide (TBAB) were added as hydrate additives to investigate their influence on hydrate formation. [BMIm] Br has an inhibition effect on CH4 and CH4/CO2 hydrate phase equilibrium. The combination of [BMIm] Br and TBAB decreased CH4/CO2 hydrate phase equilibrium pressure under identical temperature. Kinetics of CH4 and CO2 hydrate formation in [BMIm] Br solution were investigated. Gas uptake in the hydrate phase increased when [BMIm] Br concentrations changed from 1000 to 2000 and 3000 ppm. The influence factors of gas liquid ratio, temperature, pressure, and concentration on biogas hydrate separation were studied. Separation results were analyzed based on CH4 mole fraction in the residual gas, CH4 recovery, separation factor, phase equilibrium constant, and hydrate ratio of CH4 and CO2. CH4 in residual-phase gas can be enriched from initial 64.00 to 79.13 mol %, and the maximum CH4 recovery was 85.19%. For the combination of TBAB and [BMIm] Br on simulated biogas hydrate separation study, the CH4 value in residual gas was enhanced to 76.96 mol % and CH4 recovery was above 90%. The synergistic effect of TBAB + [BMIm] Br was not obvious compared to the result in pure [BMIm] Br solution, and gas storage in the hydrate phase decreased on the whole.