A Lattice Distortion Theory for Promotor Containing Clathrate Hydrates.

A lattice distortion theory for promotor containing clathrate hydrates is formulated using the statistical thermodynamics based model of van der Waals and Platteeuw in association with the ab initio quantum mechanics to compute the cavity potentials. Despite of high degree of lattice distortion anticipated for large and polar molecules of liquid promotors, their variable lattice energy concept is unreported. With this intention, we estimate the lattice stabilization energy from spin-component scaled second order Møller-Plesset (SCS-MP2) perturbation theory applied with the augmented correlation-consistent polarized double zeta valence (aug-cc-pVDZ) basis set. Implementing this to compute cavity potential for different promotors, the reference properties of hydrates are harvested by regressing against the phase equilibrium conditions of their binary hydrates with methane. Our study confirms the exponential relation of reference chemical potential difference with van der Waals volume of the promotors. Moreover, using the excess Gibbs free energy theory, the higher order distortions for the multiple guests are captured. The proposed lattice distortion theory is attested with phase equilibrium conditions of eight promotors containing clathrate hydrate systems, namely propylene oxide, acetone, tetrahydrofuran, pyrrolidine, iso-butanaldehyde, cyclopentane, furan and thiophene, all having methane as a co-guest.