Formulating Noncovalent Interactions for Gas Hydrates with Electrolytes: A New Approach of Stability Analysis

Abstract

Understanding of gas hydrate stability is crucial for the prediction of hydrate equilibrium pressures in the presence of electrolytes. In this contribution, a new theoretical framework is conceptualized to describe the hydrate phase precisely. For this, a noncovalent interaction analysis is proposed to be performed on a unit hydrate lattice composed of pure and mixed guests in the vicinity of salts at the B3LYP-D3+def2-SVPD level of theory. It is seen that the guests affect the steric and hydrogen bond interactions, while salts influence the van der Waals and dispersion interactions. Energies associated with these noncovalent interactions are quantified using the fundamental molecular properties and then consolidated to comprehensively describe the hydrate phase. Finally, the proposed approach is widely tested for hydrate systems (total 30) with pure or mixed guests in the presence of single or multiple salts. Our model secures better predictions of the phase equilibria data compared with the existing methodologies.

Proposing Crystallographic Theory to Deparameterize Hydrate Phase Description: Physical Insights and Validation

“…In fact, the vdWP model requires the identification of the same number of adjustable parameters (i.e., 3) per guest, but the model of Chen and Guo involves three to six adjustable parameters per guest. A few studies have leveraged quantum mechanical calculations to evaluate hydrate phase properties , and gain insights into their stability. , The observations obtained from such simulations are then used to reduce the parametric dependencies of the phase equilibrium estimates. Others choose to directly use these quantum mechanical calculations and directly simulate the phase equilibrium conditions of different hydrate structures. – However, these methodologies remain convoluted and highly computationally expensive, making the regression-based models more suitable for use.…”

“…A few studies have leveraged quantum mechanical calculations to evaluate hydrate phase properties 19,20 and gain insights into their stability. 21,22 The observations obtained from such simulations are then used to reduce the parametric dependencies of the phase equilibrium estimates. Others choose to directly use these quantum mechanical calculations and directly simulate the phase equilibrium conditions of different hydrate structures.…”