Application of COSMO-RS in Gas Hydrate Mitigation

Formation of gas hydrate in oil and gas pipelines has resulted in flow assurance problem. Ionic liquid (IL), due to its dual functionality has been considered as a very promising hydrate inhibitors. However, experimental testing of IL alone is insufficient to examine all potential ILs combinations due to high number of cation and anion to form ILs. Therefore, in order to screen potential ILs prior to narrow down the amount of potential ILs for experimental work, it is helpful to have a predictive model that could satisfactorily pre-screen ILs or to validate experimental work just by considering the fundamental properties.
In this context, four fundamental properties of IL-hydrate system namely sigma profile, hydrogen bonding energies, activity coefficient, and solubility were stimulated through Conductor-Like Screening Model for Real Solvent (COSMO-RS). They were then analyzed to determine if they could be correlated with IL inhibition ability. Among them, sigma profile and hydrogen bonding energies, which later upgraded to total interaction energies exhibit significant relationship with IL inhibition ability. Sigma profile graph in general gives a qualitative understanding in whether certain IL is hydrophobic or hydrophilic. Total interaction energies of ions, on the other hand, have successfully been applied to develop a model that could predict IL thermodynamic inhibition ability in terms of average temperature depression. The correlation was validated with experimental values from literature with an average error of 20.49%. Findings also suggest that this correlation is not suitable to be used for substituted cations, due to the extra H-bonding provided by substituted functional group such as hydroxyl group. Finally, through the use of sigma profile graph and developed correlation, the inhibition ability of 20 ammonium based ILs have been predicted. TMA-OH, due to its short alkyl chain length cation and highly electronegative anion has shown the most promising inhibition ability among 20 of them. It is predicted to be able to depress temperature of IL-hydrate system by 1.97oC, whereas the widely studied EMIM-Cl can only experimentally depress the system by 1.22oC.