Experimental study on growth characteristics of CO2 hydrates in quartz sand
Injecting carbon dioxide(CO2)into seabed sediment layers to form CO2 hydrates is an effective method of carbon sequestration.However,this approach faces challenges such as long induction times and slow growth rates of hydrate formation.Using quartz sand as the porous medium,the effects of quartz sand grain size,initial water saturation and additives on the kinetics of CO2 hydrate growth and the evolution of its macroscopic morphology were studied under isothermal and isochoric conditions at the experimental temperature of 273.65 K and the initial pressure of 3.5 MPa.The study results indicate that in a 3.4%NaCl solution(percentage is by mass,same below),with an initial water saturation of 75%,when the quartz sand grain size is 26 mesh to 40 mesh,the CO2 hydrate growth rate is the fastest,and the formation amount is the highest.And the final gas consumption is 0.0285 mol,with a water conversion rate of 7.27%.With a quartz sand grain size of 10 mesh to 18 mesh,when the initial water saturation is 50%,the CO2 hydrate formation amount is the highest,with a final gas consumption of 0.0384 mol and water conversion and conversion amount of 17.17%and 4.29 g,respectively.In a 1%L-methionine solution,the CO2 hydrate growth rate accelerates,and the formation amount increases significantly,with a final gas consumption 3.6 times higher than in pure water and the conversion rate of water increases by 5.7 times.Compared to pure water,the CO2 hydrate formation amount in the 3.4%NaCl solution does not show significant changes.In the mixed solution(3.4%NaCl+1%L-methionine),the promoting effect of L-methionine is weakened,resulting in a slower CO2 hydrate growth rate and a reduced formation amount,though still better than in the 3.4%NaCl solution.Morphological experiments indicate that the CO2 hydrate film coverage time is the shortest in pure water(5.33 s)and the longest in the mixed solution(14.33 s).Adding L-methionine can alter the macroscopic morphology of the hydrates,making them loose and porous.
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