Cost-effective alkylammonium formate-based protic ionic liquids for methane hydrate inhibition

Abstract In light of current concerns about environmental impact, ionic liquids have been tested in a number of industrial applications, including gas purification, lubrication, and catalysis. In this work, cost-effective alkylammonium-based protic ionic liquids (PIL) were utilized as high-dosage gas hydrate inhibitors in order to achieve an inexpensive feedstock. Three structurally different PILs, ethylammonium formate ([EA][Of]), dimethylammonium formate ([DMA][Of]), and dimethylethylammonium formate ([DMEA][Of]), were studied to determine their inhibitory effect on methane gas hydrates. All of the studied PILs were initially tested for thermodynamic gas hydrate inhibition at 5 wt% and at 10 wt% to understand the effect of concentration by increasing the dosage. These PILs were produced by adding primary, secondary, and tertiary amines to formic acid, which is mildly acidic in nature and has biological significance. The PILs showed similar thermodynamic hydrate inhibition (THI) effects at the studied concentrations. The THI trend ([EA][Of] ≥ [DMA][Of] ≥ [DMEA][Of]) reflects the small effect of the structural variation of the cation, with the common formate anion providing the dominant inhibitory action due to presence of a carboxylic group. The pressure-temperature ( P-T ) equilibrium curve data of the investigated PILs were compared with the existing literature data for ILs including [TBMA][Of] at 10 wt% and 5 wt%. The comparison plots reveal that the THI effects of the studied PILs are better than or comparable to the other ILs, which is the matter of discussion over cost effective operation. Additionally, experimental kinetic hydrate inhibition (KHI) data were collected for 5 wt% PIL systems using polyethylene oxide (1 wt%) as an additive to demonstrate its synergistic effect.