Effect of ammonium hydroxide-based ionic liquids' freezing point and hydrogen bonding on suppression temperature of different gas hydrates

The study presents the effect of freezing point depression and hydrogen bonding energy interaction on four ammonium hydroxide-based ionic liquids (AHILs) of gas hydrate systems. The AHILs investigated are tetrame-thylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabuty-lammonium hydroxide. The considered hydrate system includes methane (CH4), carbon dioxide (CO2), and three binary mixed gas hydrates (70-30 CO2 + CH4, 50-50 CO2 + CH4, 30-70 CO2 + CH4), which are often encoun-tered in the flow assurance pipelines. The experimental temperature range is between 274.0 and 285.0 K, cor-responding to pipeline pressures for different gas systems. The thermodynamic influence, i.e., average suppression temperature (& UDelta;T) of the studied system, was reported for different mass concentrations (1, 5, and 10 wt%) and correlated with the freezing point depression and hydrogen bonding energy interaction of AHILs. The study also covers the structural impact of AHILs (in the form of alkyl chain variation) on the thermodynamic hydrate inhibition (THI) behaviour via freezing point and hydrogen bonding energy interactions. Findings revealed that the increased alkyl chain length of AHILs reduced the & UDelta;T due to a decrease in hydrogen bonding ability. The highest THI inhibition (& UDelta;T = 2.27 K) is attained from the lower alkyl chain AHIL, i.e., TMAOH (10 wt %) for the CO2 hydrate system. The freezing point depression of AHILs is a concentration-dependent phenomenon. Increased concentration of the AHILs in the system yielded lower freezing point temperature, positively influencing hydrate mitigation. Although the study provided the initial insight between the freezing point tendency and hydrogen bonding energies of AHILs on thermodynamic inhibition (& UDelta;T). Based on the freezing point depression and hydrogen bonding energy interaction, a more generalized correlation should be developed to predict any potential ionic liquids regarded as promising hydrate inhibitors.

Automated summary

This study focuses on the effect of four ammonium hydroxide-based ionic liquids (AHILs) on gas hydrate systems, specifically freezing point depression and hydrogen bonding energy interaction. The findings reveal that increasing the alkyl chain length of AHILs reduces the freezing point depression due to a decrease in hydrogen bonding ability. Higher concentrations of AHILs result in lower freezing point temperatures, positively influencing hydrate mitigation. Further research is needed to develop a more generalized correlation to predict the potential of other ionic liquids as hydrate inhibitors.