Assessing the Alkyl Chain Effect of Ammonium Hydroxides Ionic Liquids on the Kinetics of Pure Methane and Carbon Dioxide Hydrates

• Main Authors: Muhammad Saad Khan, Cornelius Borecho Bavoh, Mohammad Azizur Rahman, Bhajan Lal, Ato Kwamena Quainoo, Abdulhalim Shah Maulud
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: Energies
• Subjects: ammonium hydroxide ionic liquids (AHILs); CH₄ hydrate; CO₂ hydrate; alkyl chain; ionic liquids; kinetic hydrate inhibition (KHI)
• Online Access: https://www.mdpi.com/1996-1073/13/12/3272

In this study, four ammonium hydroxide ionic liquids (AHILs) with varying alkyl chains were evaluated for their kinetic hydrate inhibition (KHI) impact on pure carbon dioxide (CO₂) and methane (CH₄) gas hydrate systems. The constant cooling technique was used to determine the induction time, the initial rate of hydrate formation, and the amount of gas uptake for CH₄-AHILs and CO₂-AHILs systems at 8.0 and 3.50 MPa, respectively, at 1 wt.% aqueous AHILs solutions. In addition, the effect of hydrate formation sub-cooling temperature on the performance of the AHILs was conducted at experimental temperatures 274.0 and 277.0 K. The tested AHILs kinetically inhibited both CH₄ and CO₂ hydrates at the studied sub-cooling temperatures by delaying the hydrate induction time and reducing the initial rate of hydrate formation and gas uptake. The hydrate inhibition performance of AHILs increases with increasing alkyl chain length, due to the better surface adsorption on the hydrate crystal surface with alkyl chain length enhancement. TPrAOH efficiently inhibited the induction time of both CH₄ and CO₂ hydrate with an average inhibition percentage of 50% and 84%, respectively. Tetramethylammonium Hydroxide (TMAOH) and Tetrabutylammonium Hydroxide (TBAOH) best reduced CH₄ and CO₂ total uptake on average, with TMAOH and Tetraethylammonium Hydroxide (TEAOH) suitably reducing the average initial rate of CH₄ and CO₂ hydrate formation, respectively. The findings in this study could provide a roadmap for the potential use of AHILs as KHI inhibitors, especially in offshore environs.