An efficient model for the prediction of CO<inf>2</inf> hydrate phase stability conditions in the presence of inhibitors and their mixtures

A thermodynamic model for the prediction of CO2 hydrate phase stability conditions in the presence of pure and mixed salts solutions and various ionic liquids (ILs) is developed. In the proposed model van der Waals and Platteeuw model is used to compute the hydrate phase, Peng-Robinson equation of state (PR-EoS) for the gas phase and the Pitzer-Mayorga-Zavitsas-Hydration model is employed to calculate the water activity in the liquid water phase. This model is an extension of the model developed by Tumba et al. (2011) for the prediction of methane and CO2 hydrate phase stability conditions in the presence of tributylmethylphosphonium methylsulfate IL solution. Shabani et al. (2011) mixing rule is modified by incorporating the water-inhibitor (salt/IL) interaction parameter to calculate the water activity in mixed salt solutions. The model predictions are also calculated using the Pitzer-Mayorga model separately and compared with predictions of the developed model. The model predictions are compared with experimental results on the phase stability of CO2 hydrate in the presence of ILs, pure and mixed salts as reported in literatures. The ILs are chosen from imidazolium cationic family with various anion groups such as bromide (Br), tetrafluoroborate (BF4), trifluoromethanesulfonate (TfO), and nitrate (NO3) and the common salts such as NaCl, KCl and CaCl2. Good agreement between the developed model predictions and the literature data is observed. The overall average absolute deviation (AARD%) with Pitzer-Mayorga-Zavitsas-Hydration model is observed to be within ±1.36% while Pitzer-Mayorga model accuracy were about ±1.44 %. Further, the model is extended to calculate the inhibition effect of selected inhibitors (ILs and salts) on CO2 hydrate formation.