Electrical conductivity-based assessment method for semi-clathrate hydrate conversion and phase change characteristics in gas capture and energy storage

Abstract

In gas capture/storage and energy storage, tetrabutylammonium bromide (TBAB) hydrates have been regarded as superior carriers owing to their unique molecular selectivity and high latent heat. Hydrate conversion amount is a significant parameter in evaluating gas selection and cold storage characteristics. This study proposes a method for calculating hydrate conversion amount proposed based on the correlation between electrical conductivity and solution concentration. The correlation index (R2) between electrical conductivity and TBAB solution concentration was above 0.99 at concentrations less than below 5 wt%. The conversion amounts of different hydrate types were obtained using a unique hybrid calculation method. The differences in hydrate conversion amount, conversion ratio, and memory effect were compared at different mass fractions. The results indicated that the hydrate morphology and accumulation patterns were influenced by the TBAB solution ionization degree. Regular hexagonal TBAB hydrate crystals were observed at a low ionization degree. The maximum conversion ratio of TBAB hydrate reached 96% (1 °C/30 wt%). The variation trend of TBAB hydrate phase equilibrium temperature was consistent with that of the electrical conductivity of the solution. The investigation of the memory effect revealed that the phase change process of TBAB hydrate is more predictable in high-concentration initial solutions.