Combination of Imidazolium Bromine and Tetrabutylammonium Bromide for CH₄ Purification from Simulated Biogas by Hydrate-Based Gas Separation

Abstract

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.

Enrichment of gas storage in clathrate hydrates by optimizing the molar liquid water–gas ratio

“…52 Thermodynamic promoters such as tetrahydrofuran, cyclopentane, tetra-n-butyl ammonium bromide, and epoxycyclopentane increase the hydrate stability conditions to higher temperatures. 11,[53][54][55][56][57][58][59][60] The use of packed beds, porous materials, nanoparticles, dry water, foams, and hydrogels proved to accelerate the growth kinetics and higher gas uptake by increasing the surface area. Studies report that the micelle formation and the decreased surface tension offer higher gas water interaction and enhance mass transfer.…”

Effect of Cyclooctane and l-Tryptophan on Hydrate Formation from an Equimolar CO2–CH4 Gas Mixture Employing a Horizontal-Tray Packed Bed Reactor

“…In recent years, there have been few studies related to the separation of CO 2 –CH 4 gas mixtures. − Most of the hydrate formation studies on CO 2 –CH 4 gas mixtures were done with a primary focus on the separation of CO 2 . A recent study on the CO 2 –CH 4 gas mixture focused on storage and transport of the CO 2 containing natural gas from stranded gas fields that may consist of a high concentration of CO 2 .…”