Formulating noncovalent interactions to predict structural transition in mixed guest hydrates

Abstract

This work aims at formulating the noncovalent interactions of the mixed guest hydrate lattices of sI and sII structures. The reduced density plots obtained at the B3LYP level with 6‐31G(d) split valence set unveil the crucial contributions of hydrogen bonding, dispersion, van der Waals interaction, and steric effects toward lattice stability. These contributions are rather unreported in the hydrate phase equilibrium modeling. With this research gap, we attempt to formulate the natural regularity in the nonstoichiometric hydrates by the spherical harmonics shape descriptor. The van der Waals and hydrogen‐bond interactions are described with Kihara spherical cell potential and ab initio based calculations, respectively. Further, the ionization potential and polarizability of the guest molecule describe the dispersion interactions. Combining these contributions, we introduce a theoretical framework for the phase equilibrium modeling of mixed guest hydrates. This novel formulation offers various appealing advantages as: significantly reduced parametric structure, standardization of the parameter value for host–host pair, and generalized model framework. Despite of making the proposed theory so simple, it consistently outperforms the existing latest models, which employ various state equations, ab initio based calculations and CSMGem, for a wide variety of systems (total 26 systems tested) with reference to the experimental data.

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

“…Consequently, when the CO 2 and CH 4 molecules share a hydrate lattice, a nonuniform distribution of the lattice stericity is observed. A similar dependence of steric hindrances on the guests occupying the hydrate lattice is also reported by Dongre and Jana …”

“…A similar dependence of steric hindrances on the guests occupying the hydrate lattice is also reported by Dongre and Jana. 70 A slight shift in the distribution of the RDG is observed when salt is introduced in the vicinity of a hydrate lattice. Grouped sign (λ 2 )ρ is used to quantify the variations in RDG distribution.…”

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

“…45 Such coexistence of sIItype cage leads to catalyzing structural transition in the copresence of ethane. In Figure 5d, the structural transition boundary predicted by our model with accommodating the correlations of Peyrovedin et al 31 is compared with the boundaries reported by Klauda and Sandler, 17 Dongre and Jana, 21 and Chen and Li. 36 It is evident that above the ice point (i.e., T > 273 K), there are similarities in the predicted composition vs temperature profiles, which are also reasonably close to the experimental data.…”

“…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.…”