Research On Nucleation And Formation Of Natural Gas Hydrate Loaded On Activated Carbon

The excellent gas storage capacity and high safety of natural gas hydrate make it show great application value in natural gas storage and transportation,peak regulation and other industries,and is considered to be the most promising natural gas storage and transportation alternative technology.However,the slow nucleation and growth kinetics and low gas storage rate of hydrates limit the large-scale industrial applications.Porous materials have been proved to greatly enhance hydrate kinetics due to the rich specific surface area and pore structure.However,the promotion of hydrates by porous materials is affected by multiple factors such as the amount of pre-adsorbed water,driving force,and gas-solid contact area.Hydration kinetics under the action of porous materials and enhanced hydration performance(nucleation and growth kinetics,gas storage rate)are the keys to the application and promotion of this technology.Based on this,this paper mainly conducts the following research:In this paper,the formation kinetics of methane hydrates loaded by activated carbon were first explored,and parameters such as hydrate induction time,gas storage capacity,and reaction rate were evaluated.The results showed that the introduction of activated carbon greatly enhanced the hydrate kinetics,the induction time was significantly shortened from tens of hours to within 1 h,and the storage capacity could be improved ideally from ?20 V/V to 156.88 V/V,while the growth rate was significantly enhanced.Based on the observation of hydrate morphology and the adsorption kinetics of activated carbon influenced by pre-adsorbed water,the mechanism of activated carbon to enhance hydrate nucleation and growth kinetics named "adsorption-induced two-way nanoconvection" was proposed.In addition,through the recycle experiments of hydrate formed on activated carbon,it was found that activated carbon has excellent recycling performance,stable gas storage capacity and further shortened induction period,which reflects the good application prospect of activated carbon in this technical field.Although activated carbon greatly enhances methane hydrate nucleation and growth kinetics,its promoting effect is greatly reduced under the conditions of high ratio of liquid to carbon and low pressure.Improving the hydration performances of hydrate loaded by activated carbon under these conditions can help promote the application of hydrate-based natural gas storage and transportation technology.Based on this,in this paper,activated carbon was used to compound amino acids and halogen salts,respectively.And the kinetics of hydrate formation under the action of activated carbon/amino acid and activated carbon/halogen salt compound systems were explored.What's more,nano-silver particles coated activated carbon(Ag@AC)was prepared via impregnation reduction,and its promoting effect on hydrate nucleation and growth kinetics was evaluated.Finally,activated carbon containers were printed by 3D printing technology,and the gas-solid contact effect was evaluated.The effect of the kinetics of hydrate loaded by activated carbon was explored,and the feasibility of the "rechargeable" gas storage mode of hydrate canning was explored.The results showed that the addition of amino acids further shortened the hydrate induction period and increased the gas storage capacity.The compounding of 0.2 wt.% L-methionine and 0.5wt.% L-leucine showed a high liquid-to-carbon ratio.Excellent hydrate formation promoting effect.In contrast,the activated carbon compounded with halogen salt systems did not improve the nucleation kinetics of hydrates,but the compounding of 0.1wt.% Na Cl solution significantly improved the gas storage capacity of hydrates,and this promotion effect existed on higher ratio of liquid to ratio.When the hydrate experiments were carried out on the activated carbon immobilized by the silver nanoparticles,the nucleation kinetics of the hydrate was significantly enhanced on the basis of maintaining the stable gas storage capacity.Under the conditions of low pressure(5 MPa)and high ratio of liquid to carbon(1.4),the induction time of hydrate was shortened by 96.88%and 86.90%,respectively.The nucleation and growth kinetics of hydrate loaded by activated carbon depend on gas-solid contact.Setting vent holes in the activated carbon containers could improve the gas-solid specific contact surface area,thereby increasing the heat and mass transfer of the system,and enhancing hydrate nucleation and growth kinetics.This discovery made it possible for activated carbon beds to store and release natural gas in a "rechargeable" manner,and provided a new idea for the application of hydrate-based gas storage technology loaded by activated carbon beds.