Key factors influencing the kinetics of tetra-n-butylammonium bromide hydrate formation as a cold storage and transport material

Abstract

Cold energy storage by semi-clathrate hydrates is highly advantageous as they have large latent heat and appropriate phase change temperatures for cooling applications. The knowledge of semi-clathrate hydrate formation kinetics is essential to the process design and optimization for cold storage and transportation. This work investigated the kinetics of tetra-n-butylammonium bromide (TBAB) hydrate formation as a cold storage material using a quantitative method based on electrical resistance measurement. The effects of the initial TBAB concentration in solution (10 wt%−30 wt%) and mixing rate (250 rpm–550 rpm) were examined. As the initial TBAB concentration was increased from 10 wt% to 30 wt%, the induction time was shortened by 89% and the hydrate growth rate was enhanced by more than 5.6 times. Increase of mixing rate from 250 rpm to 550 rpm showed an 84.9% reduction of induction time and more than 44% increase of average hydrate growth rate. The addition of pre-produced hydrate seed into the subcooled TBAB solution immediately induced hydrate nucleation. The type of TBAB hydrates formed was dependent on the type of pre-produced seed. Type B TBAB hydrate seed is recommended to achieve faster hydrate formation kinetics, higher final hydrate fraction and avoid the structural transition from type A to type B hydrates. Finally, an artificial neural network model was developed for sensitivity analysis and revealed that TBAB concentration, temperature and type of seed were the three major contributors to the kinetic performance of TBAB hydrates formation. These results would provide valuable insights for optimizing the hydrate formation process for cold storage and transport applications.