Influence of non-stoichiometric solutions on the THF hydrate growth: chemical affinity modelling and visualization

Tetrahydrofuran (THF) hydrate is a useful material for cold storage applications and an excellent substitute for simulating natural gas hydrates. THF also serves as a thermodynamic promoter for hydrate formation. The selection of suitable THF concentration in the aqueous solution remains a challenging task for the utilization of the THF hydrate. Present work focuses on the influence of non-stoichiometric solutions on THF hydrate growth. The THF hydrate was grown in polycrystalline form as a gross hydrate layer from the wall towards the center of a cylindrical reactor. Experiments were conducted at the three THF concentrations 19.06, 30, and 15 wt% at 276.15 K and atmospheric pressure. Transient imaging of the hydrate provided the hydrate thickness with time. Moreover, the chemical affinity model was used to analyze the hydrate formation kinetics. An increase in the concentration of the THF in bulk solution accelerated hydrate growth with time. We found that non-homogeneity in the THF hydrate front increased in the azimuthal direction if the concentration of THF in the THF-water solution deviated from stoichiometric concentration. A hypothesis was also proposed to explain the above observation. The non-homogeneity was qualitatively shown by binary images and mathematically quantified using the maximum to minimum hydrate thickness ratio. The chemical affinity model proved effective in describing hydrate growth kinetics.