Experimental Investigation of Methane Separation from Low-Concentration Coal Mine Gas (CH₄/N₂/O₂) by Tetra-n-butyl Ammonium Bromide Semiclathrate Hydrate Crystallization

Abstract

In this work, tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrate was employed in a batch operation to separate CH4 from low-concentration coal mine methane (CMM) gas with a mole composition of 30% CH4, 60% N2, and 10% O2. TBAB semiclathrate hydrate formed from the low-concentration CMM gas has more favorable incipient equilibrium conditions than gas hydrates formed from the same gas mixture. The experiments were carried out at a fixed pressure of 4.0 MPa, three TBAB mole concentrations of 0.29, 0.62, and 1.38 %, and in the temperature range of 274.75–283.35 K. The effects of TBAB concentrations and subcoolings (ΔT sub) on CH4 separation from the low-concentration CMM gas were investigated. The results indicated that CH4 was preferentially incorporated into the hydrate crystals rather than N2 and O2 in the presence of TBAB. The experimental conditions of the TBAB concentration of 1.38%, 4.0 MPa, and ΔT sub = 7.0 K were most favorable for TBAB semiclathrate hydrate to separate CH4 from the low-concentration CMM gas. The CH4 recovery obtained at these conditions was approximately 27%. Compared with CH4 content in the low-concentration CMM gas, the mole fraction of CH4 in TBAB semiclathrate hydrate was increased to 41%.

Equilibrium Conditions for Semiclathrate Hydrates Formed with CO2, N2, or CH4 in the Presence of Tri-n-butylphosphine Oxide

“…In other words, SCHs are capable of selectively incorporating small gas guest molecules within the small cavities of the SCHs. Unlike ordinary hydrates having well defined structures (Structure I, Structure II, and Structure H), SCHs have diverse structures and have hydrogen-bonding interaction between guests and hosts molecules, which is much stronger than the van der Waals force in ordinary hydrates 5 SCHs have drawn increasingly more interest from researchers for their potential applications in hydrogen storage 8 , carbon dioxide storage 9 , and gas separation [10][11][12][13][14] . The thermodynamic data of SCHs are limited, and the majority of them are for TBAB 8,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] .…”

Phase Equilibria and Methane Enrichment of Clathrate Hydrates of Mine Ventilation Air + Tetrabutylphosphonium Bromide

“…11,[16][17][18][19][20][21][22] TBAB has also been examined for its potential to separate methane from coal methane gas. 23,24 However, the methane concentrations in these studies were relatively high, over 25 vol%.…”

Hydrate‐Based Gas Separation for Methane Recovery from Coal Mine Gas using Tetrahydrofuran

“…Separation of gas mixture by using a hydrate is based on the difference between gas-solid (hydrate) phases during the formation of the hydrate. [15] Gas mixture hydrates crystallizing from gas mixtures differ in composition from the gas phase. It was suggested [16,17] to use this property of gas hydrates in separating and concentrating noble gases and components of natural gas.…”