Effect Of Nanoparticle And Its Surface Wettability On Phase Equilibrium And Kinetics Of Hydrate Formation

As the main greenhouse gas,carbon dioxide emission reduction has attracted more and more attention.Carbon dioxide capture and storage(CCS)is one of many carbon emission reduction schemes,but its conventional capture technology is faced with the problems of high energy consumption and low efficiency.Hydrate-based carbon dioxide capture is considered as a kind of greenhouse gas capture technology with application prospect.It is reported that adding nanoparticles into the solution as additives can effectively promote the formation of hydrate and reduce the energy consumption in the process.However,there are few studies on the influence of nanoparticles with modified surface wettability on hydrate formation.Therefore,this paper studied the thermodynamic and kinetic characteristics of hydrate formation process in CO₂-pure water system with Al₂O₃ nanoparticle added,and analyzed the influence of the main controlling factors on the induction time of hydrate formation and gas consumption,such as hydrophilicity and hydrophobicity of Al₂O₃ nanoparticles,addition amount,particle size,stirring rate and so on.The surface wetting characteristics of hydrophilic and hydrophobic modified Al₂O₃nanoparticles are obviously different from each other.According to the analysis of infrared spectrum,it is determined that the hydrophilicity of Al₂O₃ nanoparticles is mainly generated by the hydroxyl functional groups on its surface.Through the experiment of CO₂ hydrate formation,it is found that the Al₂O₃ nanoparticles with different surface wetting characteristics have no obvious effect on the thermodynamic characteristics(phase equilibrium temperature and pressure)of hydrate formation,but have a significant influence on the kinetics of hydrate formation.Compared with non-modified Al₂O₃ nanoparticles,hydrophilic and hydrophobic Al₂O₃ nanoparticles can effectively increase the final gas consumption of CO₂ hydrate formation,but hydrophobic Al₂O₃ nanoparticles slightly increase the nucleation induction period of CO₂ hydrate formation.Under the same particle size and rotating speed,compared with 0.01 wt%non-modified Al₂O₃ nanoparticle suspension,0.01 wt%hydrophile Al₂O₃nanoparticle suspension can increase the final gas consumption of CO₂ hydrate formation by99%,and shorten the induction time required for hydrate nucleation by 10.3%.Compared with non-modified Al₂O₃ nanoparticle,hydrophilic and hydrophobic modified Al₂O₃ nanoparticles can effectively improve the final gas conversion rate of CO₂ hydrate formation,but hydrophobic Al₂O₃ nanoparticles slightly increase the nucleation induction period of CO₂ hydrate formation.It can be considered that the hydrophilic and hydrophobic modification of the surface of nanoparticle as additives in the hydrate formation process is an effective means to study the methods of hydrate formation promotion.Through comparison,it is found that smaller particle size and larger stirring rate can effectively increase the gas consumption and shorten the induction time.Under the same conditions,compared with the static state,the final gas consumption of CO₂ hydrate formation can be increased by 116.2%at 800 rpm,and the induction time required for hydrate nucleation can be shortened by 78.5%.Finally,it is determined that when the particle size is 30 nm,the concentration of hydrophilic modified Al₂O₃ nanoparticle suspension is 0.01 wt%,and the stirring speed of the rotor in the reactor is800 rpm,the promotion effect on the formation of CO₂ hydrate is the best.This study shows that surface modification of Al₂O₃ nanoparticles can effectively improve the final gas consumption of CO₂ hydrate formation and shorten the induction time required for hydrate nucleation under certain conditions,with high efficiency and simple operation.Therefore,this method can be used as one of the auxiliary options to improve the efficiency of carbon dioxide capture in hydrate formation,and can also provide a basis for the application of hydrate in other technical fields.