Morphological Study of Tetra-n-Butylammonium Bromide Semi-Clathrate Hydrate in Confined Space

Abstract

Tetra-n-butylammonium Bromide (TBAB) finds extensive use in diverse applications. An in-depth investigation into the effects of the formation conditions on TBAB hydrate is necessary to optimize the application process. This work focuses on examining the influence of the mass concentration of TBAB solution and the cooling rate on TBAB hydrate formation through optical microscopy and Raman spectroscopy. The TBAB hydrate formation process occurs in a confined space created by an optical sheet with a 0.03 mm deep groove. Four TBAB solutions of 13. 8 wt%, 18 wt%, 32 wt%, and 40 wt% are investigated, and the supercooling required for hydrate nucleation increases with concentration at a cooling rate of 0.5 K/min. Notably, Type A TBAB hydrate preferentially forms in all of the solutions, although type B hydrate is thermodynamically stable in the two dilute solutions. At a larger cooling rate of 2 K/min, two distinct crystal growth patterns are observed: one controlled by mass transfer and the other regulated by heat transfer. Increasing the cooling rate not only alters the optical morphology, but also reduces the supercooling due to a decrease in the Gibbs free energy barrier caused by a larger temperature gradient. This is beneficial for practical applications as it helps to alleviate the supercooling degree.