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Quaternary salts can form semi-clathrate hydrates, caging gas molecules in the empty small cages, which have the potential for the separation of mixtures, such as the simulated flue gas [CO 2 (17 mol %)/N 2 mixtures]. To enhance the CO 2 separation from CO 2 /N 2 binary mixtures, three quaternary salts, tetra-n-butylammonium bromide (TBAB), tetra-nbutylphosphonium bromide (TBPB), and tetra-n-butylammonium nitrate (TBANO 3 ), are investigated at different operating conditions by a one-stage hydrate separation process. The results indicate that the induction time for each quaternary salt system can be shortened to less than 5 min under the optimal operating condition. Meanwhile, each quaternary salt can significantly promote the CO 2 separation under its optimal condition. TBANO 3 displays the strongest capability in terms of gas consumption and CO 2 separation with the pressure drop of 0.72 MPa and the highest split fraction of 67% and separation factor of 15.54 compared to the other two salts. Besides, CO 2 can be further removed from 17 to 7 mol % in the presence of TBANO 3 . TBPB also has a potential effect on CO 2 separation with the pressure drop of 0.57 MPa and the separation factor of 14.06. The result demonstrates that TBANO 3 and TBPB are two better additives for efficient hydrate capture of CO 2 .

In this work, the dissociation behavior of methane hydrate in quartz sand sediment by injecting a thermodynamic inhibitor, methanol (MeOH), was investigated using a one-dimensional experimental apparatus. The experimental results indicated that the hydrate dissociation process included four stages: free gas production, methanol dilution, major hydrate dissociation, and residual gas production. The overall liquid production rate was smaller than the injection rate during the whole production process. The cumulative gas produced from hydrate under methanol solution injection was adjusted with the reference experiment. A new strategy of the adjustment of the experimental runs was introduced, which was based on the ratio of the water and methanol solution injection rates. In general, with the increase of the methanol injection rate and the methanol concentration, the cumulative hydrate-originating gas produced increased. During the major hydrate dissociation stage, the production efficiency was enhanced continuously with the increase of the injection rate and concentration of the methanol solution, while the methanol efficiency increased and reached a maximum value when the concentration was 60 wt % and then gradually decreased.

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