This work presents new data to further develop the hydrate-based process for the separation of CH 4 from the lowconcentration coal mine methane gas (30 mol % CH 4 /N 2 ) through the formation of tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrate. The TBAB semiclathrate hydrate formed from the 30 mol % CH 4 /N 2 gas mixture has more favorable equilibrium conditions than the gas hydrate formed from the same gas mixture. The incipient equilibrium conditions at 0.17, 0.29, and 0.62 mol % TBAB were experimentally determined and reported. The experiments of forming TBAB semiclathrate hydrate from the 30 mol % CH 4 /N 2 gas mixture were performed in both semibatch and batch operation under a fixed driving force of 3.5 MPa. The results indicate that CH 4 is preferentially encaged into the TBAB hydrate. The use of a 0.29 mol % TBAB solution is preferred over the 0.17 and 0.62 mol % TBAB solutions. The semibatch operation is more effective than the batch operation for the separation of CH 4 from the 30 mol % CH 4 /N 2 gas mixture. The CH 4 recovery was found to be approximately 25% at 0.29 mol % TBAB concentration in the semibatch operation and the corresponding CH 4 concentration released from the TBAB hydrate was nearly 43 mol %. A CH 4 -rich stream (70 mol % CH 4 /N 2 ) was obtained after two stages of TBAB semiclathrate hydrate formation.

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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%.

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In this work, we reported an investigation of using a fixed bed of zeolite 13X (FBR) for hydrate-based CO2 capture from a CO2/CH4 gas mixture (40 mol % CO2 and 60 mol % CH4). The experiments were carried out at a fixed temperature of 277.15 K and in the pressure range of (5.2 to 6.7) MPa. The effects of the driving force (overpressure), surfactant sodium dodecyl sulfate (SDS), and the fixed bed saturations on hydrate formation and CO2 selectivity were elucidated. The results indicated that hydrate growth in the fixed zeolite 13X was enhanced as the driving force was increased from 2.5 to 4.0 MPa, but the final gas uptake, CO2 recovery, and CO2 separation factor were reduced. Hydrate formation in the fixed zeolite 13X was promoted in the presence of SDS as compared to that in the absence of SDS. When the initial driving force was fixed at 2.5 MPa, the final gas uptake, CO2 recovery, and separation factor obtained at 75% saturation of the fixed bed were higher than those obtained at 100% and 50% saturations. The comparison between the fixed bed of zeolite 13X and the stirred tank reactors shows that CO2 selectivity obtained in the fixed bed of zeolite 13X was lower than those obtained in the stirred tank reactors. Therefore, zeolite 13X can be used to enhance hydrate formation but may not be a proper candidate for CO2 capture from the CO2/CH4 gas mixture.