Determination of clathrate hydrates stability conditions and water activity in aqueous solutions containing natural amino acid and its blend with ionic liquid, alcohol, and salt using a thermodynamic approach

Owing to the necessity of precise calculations in gas hydrates systems comprised of novel environmentally friendly materials such as natural amino acids (NAAs), as well as their blends with ionic liquids (ILs), alcohols, and salts, the present study reports a new method concerning the water activity computation coupled with the van der Waals-Platteeuw (vdW-P) model. The developed activity model consists of two terms, namely Free-Volume modification of the Flory-Huggins (FVFH) equation taking into account the molecular (short-range) interactions, and the extended Debye-Hückel (EDH) equation considering the ionic (long-range) interactions. The model's performance is then assessed against a comprehensive databank (11 NAAs, 9 blends, 475 data points) collected from open literature and data of 3 gaseous hydrate formers (CH₄, CO₂, and natural gas). The overall deviation of the determined gas hydrates dissociation temperatures for the whole databank is found to be 0.40 K (0.14%), while the most significant individual deviation does not exceed 1.76%, proving the remarkable performance of the developed calculation procedure. Not only does not the model benefit from parameter regression, but it also offers accurate predictions in the complex systems of the inhibitors’ blends. When NAAs are employed solely (409 data points), the deviations of the model results from real data of gas hydrates dissociation temperatures are 0.39 K. On the other hand, in the presence of NAAs mixtures with ILs, alcohols, and salts (66 data points), which represent highly complex systems, the deviation is 0.41 K.