*Solvents, Ionic Liquids and Solvent Effects*

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**143**

**Chapter 8**

**Abstract**

methane hydrate

**1. Introduction**

be captured by structure H hydrates [3].

Pre-Screening of Ionic Liquids

Application of COSMO-RS for

Ionic liquids (ILs) due to their potential dual functionality to shift hydrate equilibrium curve and retard hydrate nucleation are considered as a very promising gas hydrate inhibitor. However, experimental testing alone is insufficient to examine all potential ILs combinations due to a high number of cation and anion to form ILs. 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). ILs were then analyzed to determine if they can be correlated with IL inhibition ability. Among them, sigma profile and hydrogen bonding energies, which later upgraded to total interaction energies, exhibit a significant relationship with IL inhibition ability. Total interaction energies of ions, on the other hand, have successfully been applied to develop a model. The model can predict the thermodynamic inhibition ability in terms of average temperature depression. The correlation was further validated with experimental values from literature with an average error of 20.49%. Finally, using sigma profile graph and developed correlation, the inhibition ability of 20 ammonium-based ILs (AILs) have been predicted. Tetramethylammonium hydroxide (TMA-OH), due to its short alkyl chain length cation and highly electronegative anion, has shown the most promising inhibition ability among the considered system.

**Keywords:** ionic liquids, gas hydrate, thermodynamic inhibitors, COSMO-RS,

Gas hydrates are icelike crystalline solid compounds that could form in the presence of water and gas under favorable thermodynamic temperature-pressure condition [1]. At low-temperature and high-pressure conditions, water molecules (host) will surround the gas molecules (guest) and encapsulate the gas in a hydrogenbonded solid lattice [2]. Depending on the gases trapped, different structures of gas hydrates can be formed. The structure I hydrate trapped methane (CH4), ethane (C2H6), and carbon dioxide (CO2) gases. Structure II usually forms for propane (C3H8) gas, while a mixture of CH4 and butane (C4H10) and other hydrocarbons can

as Gas Hydrate Inhibitor via

Methane Hydrate

*Muhammad Saad Khan and Bhajan Lal*
