| Natural gas hydrates are non-stoichiometric crystalline,solid inclusion compounds composed of host structure,forming a periodic cage-like structure via H-bonding,that incorporate guest molecules(such as CH4,CO2).It has the advantages of free-polution,high energy density and abundant reserves,becoming an important part of the global energy system.With the in-depth study of hydrate,the technologies of storing and transporting natural gas,gas capture and screening in clathrate hydrates have gradually shown great potential value in large-scale.However,there are some kinetic and thermodynamic bottlenecks in the process of hydrate formation,such as difficulty in nucleation and low ratio of water to hydrate conversion,and easily forming under high pressure and low temperature.In the existing research,nano-materials are usually added as promoters to improve these issues.Nevertheless,the poor dispersion stability of nano-materials in water limits the further development of its research work.Therefore,we studied the hydrate formation and growth behavior in MXene dispersed liquid with wide concentration range,and further explored the effect mechanism of two-dimensional nano-materials on the kinetics and thermodynamics of hydrate formation.In this paper,the interaction between two-dimensional MXene membranes and water was studied,focusing on the changes of wettability and permeability of MXene films under different conditions.In terms of wettability,the wettability and surface energy of MXene membranes can keeps stability for vacuum drying storage.The surface energies of different MXene films were in the range of 49.92±2.01 to 62.44±0.25 m J/m2,and organic pollution and surface oxidation were the main reasons for the fluctuation of the contact angle of the samples.It is important that the wettability of Ti2CTx MXene film was studied for the first time and the corresponding surface energy was obtained.In terms of permeability,the water permeability of MXene films was extremely sensitive to drying process,loading and deposition rate.It was found that the water permeability of MXene film was significantly enhanced by the voids generated by the disordered stacking of nanosheets,which can be effectively avoided by slowly depositing nanosheets of assembly films.Therefore,the water permeability of MXene membrane can be controlled by controlling the accumulation of nano films.The surface of MXene nanosheets can provide more nucleation sites and significantly enhance the nucleation process of hydrate formation and growth due to its good wettability and thermal conductivity.The induction time can be reduced to about 4 min(the induction time was more than 1 h in pure water).Moreover,with the increase of dispersion concentration,the water molecules with weak hydrogen bond structure in the dispersion increased,which was more conducive to the formation of hydrogen bond network of hydrate cage structure to promote the rapid formation and growth of hydrate crystals.And the gas storage capacity of MXene dispersion system can be improved by introducing other kinetic promoters.The gas storage of the mixed system of MXene and SDS showed great cycle stability,only decreasing by 4.18%after ten cycles.At the same time,MXene dispersed liquid had a slight thermodynamic promoting effect on methane hydrate formation and growth.Methane hydrate in the presence of MXene dispersed liquid was formed at a temperature highter than that in pure water at a given pressure,and it showed about max 0.54 oC shifting to the right side.The promoting effect of MXene dispersions with different sizes of nano-sheets on hydrate reaction showed differences.Among them,the dispersions with intermediate size of nanosheets(2.5T and 5T)had good promotion effect.The theoretical results obtained in this study provide a certain reference and support for the study of the effect of two-dimensional nano materials on hydrate formation,and help to enhance the kinetics and thermodynamics of hydrate formation by using related materials efficiently. |
PDF Full Text Request