Effects of Gas Compositions on Tuning the Kinetics of CH/CO Hydrates with 1,3-Dioxolane: Implication for Hydrate-Based Biogas Storage.

A key to the application of hydrate-based biogas storage (primary components as CH and CO) lies in elucidating the mechanism of the slow kinetics and seeking solutions to enhance the kinetics. In this study, the low-toxicity 1,3-dioxolane (DIOX) was employed to promote CH/CO hydrate formation at various DIOX concentrations ( = 5.56 mol %, 3.00 mol %, and 1.00 mol %) under different gas mixture compositions (CH/CO = 71.7 mol %/28.3 mol %, 47.5 mol %/52.5 mol %, and 23.9 mol %/76.1 mol %). The phase equilibria, cage occupancy, kinetics, and resulting morphology of CH/CO + DIOX mixed hydrates were acquired for analysis. The thermodynamic promotion of DIOX diminishes as the CO composition increases and decreases. An increase in the CO composition reduces the occupancy of CH in the sII hydrate 56 cages. Additionally, CO dissolution in DIOX solution weakens the fractionation of the gas mixture due to hydrate formation. At = 5.56 mol % and 3.00 mol %, two distinct stages of hydrate growth were identified based on morphology observation: (a) initial slow gas uptake due to the formation of hydrate film at the gas-liquid interface and (b) enhanced gas uptake stage due to the rupture of the hydrate film. Increasing the CO composition, employing solutions with a memory effect, and moderately reducing can expedite hydrate film rupture and shorten the period of hydrate film formation. The findings offer insights into technical-feasible strategies to enhance the kinetics of CH/CO hydrates for biogas and CO-rich containing natural gas storage.