Experimental Study On Promoting Methane Hydrate Formation With The Addition Of Tetrahydrofuran

Gas hydrate is a nonstoichiometric crystalline compound with the advantages of high storage capacity,environmental protection,safe operation conditions,so it has been regarded as a potential technology for natural gas storage and transportation.However,it still needs to moderate the condition and enhance the kinetics of the hydrate formation for the further industrial production.Therefore,the objective of this paper was to study the formation of methane hydrate with the addition of tetrahydrofuran as the promoter.The process of methanetetrahydrofuran hydrate formation was recorded from the perspective of kinetics and morphology to investigate the effect of temperatures on hydrate growth behavior,so as to clarify the mechanism of tetrahydrofuran promoting hydrate formation.In view of this,this paper uses tetrahydrofuran as an additive to conduct experimental research on methane hydrate formation,and analyzes the formation characteristics of methane-tetrahydrofuran hydrate under different experimental temperatures from the perspective of kinetics and morphology,so as to clarify the mechanism of additives promoting hydrate formation.The major contents are as follows:In order to study the kinetic characteristics of methane-tetrahydrofuran hydrate,the variation of methane storage and the time-dependent temperature-pressure curves during the hydrate formation were analyzed under different experimental temperatures.As the experimental temperature increased,the multiple nucleation and the effective heat diffusion increased the methane uptake.Raman spectroscopy was used to analyze the structural characteristics of methane-tetrahydrofuran hydrate and the cage occupants of guest molecules.It was confirmed that the structure of methane-tetrahydrofuran hydrate is s II structure.The proportion of tetrahydrofuran in large cages decreased as the temperature increased,while the proportion of methane in small cages increases by about 11.63%.Therefore,increasing the experimental temperature increased the methane uptake by about19.85%,which is conducive to improving the methane storage in hydrate.The macroscopic and microscopic morphology of methane-tetrahydrofuran hydrate were observed,and the macroscopic formation process of hydrate was summarized as follows: firstly,the hydrate film is formed at the gas-liquid interface,and the hydrate film grows on the wall under the action of capillary force,and then grows along with the liquid phase until the reaction ends.The porous hydrate structure on the wall was conducive to the continuous contact between gas and liquid to form more hydrates.Based on the degree of subcooling,the morphology distribution of methane-tetrahydrofuran crystal was as follows: when the degree of undercooling is above 3.0 K,hydrates grow in three-dimensional polyhedron crystals and wedge crystals,while when the degree of undercooling is below 3.0 K,hydrates grow in the two-dimensional hexagonal,quadrangle,and triangular plate crystals.As the experimental temperature increased,the hydrate grew slowly and loosely,which was conducive for a complete reaction.And the low-viscosity hydrates with stable structure were beneficial to save the energy consumption during the separation and transportation of hydrates.Comparing the formation kinetics characteristics of methane hydrate with and without the addition of tetrahydrofuran and analyzing the energy consumption,the results showed that the presence of tetrahydrofuran greatly reduced the energy consumption about 98.62%.Therefore,tetrahydrofuran could moderate the methane hydrate formation conditions,reduce the induction time,increase the gas storage to reduce the energy consumption in the process of hydrate formation,which had a better economic efficiency.The conclusions obtained in this paper could provide a theoretical basis for natural gas storage and transportation by solid hydrate method to realize the improvement of gas storage with low energy consumption.