To enhance the energy efficiency of biogas and reduce environmental pollution, impurities such as CO2 and N2 must be removed. In this context, hydrate-based gas separation (HBGS) is a novel technology that has been utilized in gas purification. As such, the hydrate phase equilibrium data of the CH4/CO2/N2 gas mixture are crucial for application of the HBGS process in biogas separation. This study presents our investigation into the phase equilibrium conditions for the hydrates of synthesized ternary CH4/CO2/N2 biogas mixtures. All experiments were conducted at 276.2–286.3 K and 2.59–8.84 MPa using an isochoric method with different ternary CH4/CO2/N2 gas concentrations. The results obtained herein indicated that the hydrate phase equilibrium conditions shifted to lower pressures and higher temperatures with increasing CO2 contents. In addition, with a N2 content of about 10%, the hydrate phase equilibrium data of the ternary gas mixtures approached that of pure CH4.

The dissociation behaviors of propane hydrate by high concentration alcohols inhibitors injection were investigated. Methanol (30.0, 60.1, 80.2, and 99.5 wt %) and ethylene glycol (30.0, 60.1, 69.8, 80.2, and 99.5 wt %) solution were injected, respectively, as alcohols inhibitors in 3.5 L transparent reactor. It is shown that the average dissociation rates of propane hydrate injecting methanol and ethylene glycol solution are 0.02059-0.04535 and 0.0302-0.0606 mol • min -1 • L -1 , respectively. The average dissociation rates increase with the mass concentration increase of alcohols solution, and it is the biggest when 99.5 wt % ethylene glycol solution was injected. The presence of alcohols accelerates gas hydrate dissociation and reduces the total need of external energy to dissociate the hydrates. Density differences act as driving force, causing the acceleration effects of ethylene glycol on dissociation behaviors of propane hydrate are better than that of methanol with the same injecting flux and mass concentration.

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To reveal the kinetic performance of gas molecules in hydrate growth, hydrate formation from pure CO2, flue gas, and biogas was measured using in-situ Raman and macroscopic methods at 271.6 K. In the in-situ Raman measurements, Raman peaks of gases in the hydrate phase were characterised and normalised by taking the water bands from 2800 to 3800 cm−1 as a reference, whose line shapes were not found to have a noticeable change in the conversion from Ih ice to sI hydrate. The hydrate growth was suggested to start with the formation of unsaturated hydrate nuclei followed by gas adsorption. In hydrate formed from all tested gases, CO2 concentrations in hydrate nuclei were found to be 23–33% of the saturation state. In the flue gas system, the N2 concentration reached a saturation state once hydrate nuclei formed. In the biogas system, competitive adsorption of CH4 and CO2 molecules was observed, while N2 molecules hardly evolved in hydrate formation. Combined with micro- and macroscopic analysis, small molecules such as N2 and CO2 were suggested to be more active in the formation of hydrate nuclei, and the preferential adsorption of CO2 molecules took place in the subsequent gas adsorption process.

Hydrate-based gas separation(HBGS) technology based on tetran-butyl ammonium bromide (TBAB) semiclathrare hydrate can be utilized in CO 2 separation from biogas. The phase equilibria of semiclathrate hydrates are crucial for the successful industrial application of HBGS technology. In this work, the phase equilibrium data of TBAB semiclathrate hydrate with a synthesized binary CO 2 /CH 4 mixed gas (0.5 CO 2 and 0.5 CH 4 in mole fraction) were reported at five different TBAB concentrations (0.001, 0.01, 0.05, 0.1, and 0.2 mass fraction). The experiments were conducted in the temperature range (278.1 to 292.6) K and pressure range (2.17 to 8.16) MPa using an isochoric method. The agreement between the experimental data and the data reported in the literature indicated the reliability of the apparatus and method. The results showed that there were no obvious thermodynamic promotion effects on the CO 2 /CH 4 mixed gas hydrate phase equilibrium conditions when the mass fraction of TBAB was less than 0.01, while there was a significant affect on the CO 2 /CH 4 mixed gas hydrate phase equilibrium conditions when the mass fraction of TBAB was greater than 0.05. In addition, the results also indicated that the promotion effect of TBAB on the CO 2 /CH 4 gas hydrate formation may be varied as the concentration of TBAB in the aqueous solutions changes.

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Pipeline blockage by gas hydrates is a serious problem in the petroleum industry. Low-dosage inhibitors have been developed for its cost-effective and environmentally acceptable characteristics. In a 1.072-L reactor with methane, ethane and propane gas mixture under the pressure of about 8.5 MPa at 4 °C, hydrate formation was investigated with low-dosage hydrate inhibitors PVP and GHI1, the change of the compressibility factor and gas composition in the gas phase was analyzed, the gas contents in hydrates were compared with PVP and GHI1 added, and the inhibition mechanism of GHI1 was discussed. The results show that PVP and GHI1 could effectively inhibit the growth of gas hydrates but not nucleation. Under the experimental condition with PVP added, methane and ethane occupied the small cavities of the hydrate crystal unit and the ability of ethane entering into hydrate cavities was weaker than that of methane. GHI1 could effectively inhibit molecules which could more readily form hydrates. The ether and hydroxy group of diethylene glycol monobutyl ether have the responsibility for stronger inhibition ability of GHI1 than PVP. gases, hydrate, low dosage hydrate inhibitors, formation time