Exploring nucleation of H2S hydrates

Abstract

Crystal nucleation is a rare event process, typically characterized by long induction times. The direct observation of nucleation of a gas hydrate in molecular simulations has been rather challenging, where recent work has focused primarily on CH₄ hydrate systems. Here we show that a H₂S hydrate can nucleate very rapidly within two-phase H₂O/H₂S systems under relatively modest (i.e., 15–20% undercooling) thermodynamic driving forces. In agreement with observations for CH₄ hydrates at high supersaturations, the homogenous nucleation process features the initial formation of amorphous hydrate-like structures, which then slowly anneal into more crystalline forms. The present results demonstrate that increased gas concentration significantly increases the probability of gas molecules exhibiting a high degree of second-neighbor coordination, thereby dramatically reducing the (average) induction time for nucleation. We confirm that the composition of aqueous solution is critical in determining its susceptibility to nucleation.