Illustration of hydrate-based methane gas separation in coal bed methane type gas composition at lower pressures

摘要

Coal bed methane is an emerging and prosperous unconventional energy source, encompassing highly variable (10-70%) mole fractions of methane gas along with other higher hydrocarbon and nonhydrocarbon gases. The gas pressure at the source is typically low, posing technical constraints in the gas separation process. In particular, separation of methane gas from this source is a topic of wider scientific interest. The present study demonstrates the ability of hydrate-based technology in trapping methane gas, in nitrogen (N-2) + methane (CH4) gas mixture, using tetrahydrofuran (THF)-based hydrate-forming system at lower operating pressures (1.0 MPa). It is observed that the gas trapping is efficient and rapid. All the experiments were conducted at non-stirred condition, which is technically easy to achieve. Mole fraction of CH4 was increased in proportion with N2, and it was found that methane gas uptake capacity in hydrate cages, increased progressively with increasing CH4 concentration. Gas uptake kinetics was also found to be extremely fast and 90% of the gas consumed in hydrates within 50-60 min from hydrate nucleation.