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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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The formation and mechanism of CH4 hydrate intercalated in montmorillonite are investigated by molecular dynamics (MD) simulation. The formation process of CH4 hydrate in montmorillonite with 1 ~ 8 H2O layers is observed. In the montmorillonite, the "surface H2O" constructs the network by hydrogen bonds with the surface Si-O ring of clay, forming the surface cage. The "interlayer H2O" constructs the network by hydrogen bonds, forming the interlayer cage. CH4 molecules and their surrounding H2O molecules form clathrate hydrates. The cation of montmorillonite has a steric effect on constructing the network and destroying the balance of hydrogen bonds between the H2O molecules, distorting the cage of hydrate in clay. Therefore, the cages are irregular, which is unlike the ideal CH4 clathrate hydrates cage. The pore size of montmorillonite is another impact factor to the hydrate formation. It is quite easier to form CH4 hydrate nucleation in montmorillonite with large pore size than in montmorillonite with small pore. The MD work provides the constructive information to the investigation of the reservoir formation for natural gas hydrate (NGH) in sediments.

An energy-efficient hydrate-based warm brine preparation method in situ seafloor was first proposed for marine natural gas hydrates (NGH) exploitation. The detailed preparation process and key technologies are discussed. The optimal hydrate-former, cyclopentane + CH4, is viable for preparing warm brine under various seawater depths. The heating coefficient of the warm brine preparation reaches 3.0. The NGH production performance by depressurization in conjunction with the prepared warm brine stimulation was studied by numerical simulation. The warm brine stimulation accelerates gas production. The gas production behavior performs better with the higher salinity and temperature. However, these positive effects are limited by the direct seepage of the brine from the injection well to the production well. The massive water production from the overburden and underburden layers causes low R GW and energy efficiency. Compared to the conventional hot brine injection, the good performance of the warm brine injection confirms the feasibility of the new method.

In this work, the formation kinetics of cyclopentane (CP) + methane hydrate is studied. CP is used as a promoter to accelerate the hydrate formation. The total methane consumption, the induction time, and the formation rate were investigated under different hydrate formation conditions in NaCl solution. The results indicated that the pressure driving force could increase the gas consumption and shorten the induction time. Meanwhile, the induction time could be greatly influenced by the pressure driving force at a lower temperature. Especially, it could be shortened to a minimum value of 110 s with the increase of the pressure driving force at a fixed operating condition (CP concentration, 7.45%; NaCl solution concentration, 3.50%; and temperature, 298.15 K). Moreover, the hydrate formation rate would be accelerated with the increase of the stirring rate by its promotion in the dissolution and dispersion of methane. Finally, a higher CP concentration was favorable for the rapid hydrate formation of CP + CH4 binary hydrates. The amount of CP used could determine the amount of methane incorporated into the hydrate phase.