Experimental and numerical analysis of CO2 and CH4 hydrate formation kinetics in microparticles: A comparative study based on shrinking core model

The promotion of gas hydrate formation kinetics through mass transfer enhancement has been an important research topic, for which microparticles have been considered an effective method. In this work, carbon dioxide (CO2) and methane (CH4) hydrate formation kinetics in microparticles are investigated using "dry water" particles made of 3, 5 and 8-wt% silica. A modified shrinking-core model is established to study the CO2 and CH4 hydrates formation kinetics. It is the first model that integrates the effects of dissolved gas, the capillary effect of porous hydrate shell, and the volume change from water to hydrate. The experimental results reveal that "dry water" particles with 8-wt% silica has the highest normalized gas uptake due to their small particle size. The simulation results show an initial effective diffusion coefficient of 6.41-6.50 x 10(-)(14) m(2) s(-1) for CO2 and a slightly higher 6.83 x 10(-)(14) m(2) s(-1) for CH4 hydrate formation. The average effective diffusion coefficient of gas is higher in smaller particles. The water consumed through capillaries is more prominent in smaller particles, but it only accounts for less than 10% of water consumed at the hydrate-water interface. Furthermore, a decoupled heat transfer model was developed to quantify the effect of heat transfer in gas hydrate formation. The instantaneous temperature gradient in the hydrate shell is of a small magnitude of 10(-2) K m(-1), indicating that the impact of the heat transfer on hydrate formation kinetics is negligible. This work provides comprehensive insights into gas hydrate formation in microparticles and contributes as a theoretical basis for the improvement of gas hydrate kinetics through mass transfer enhancement.