Towards the potential of trihexyltetradecylphosphonium indazolide with aprotic heterocyclic ionic liquid as an efficient absorbent for membrane-assisted gas absorption technique for acid gas removal applications

Abstract The present study deals with complex experimental evaluation of a unique hybrid technique – membrane-assisted gas absorption, which is proposed as an alternative approach to natural gas sweetening, and explores the ionic liquid with aprotic heterocyclic anion – trihexyltetradecylphosphonium indazolide as a component of the combined absorbent system. The synthesized ionic liquid was analyzed by 13C and 1H NMR in order to validate its formation and structure, afterwards the physicochemical properties, namely, density, viscosity, and absorption loading with respect to CH4, CO2 and H2S were determined, as well as the mass transfer properties of the combined membrane-absorbent system (permeability, diffusivity and sorption coefficients). The trihexyltetradecylphosphonium indazolide characterized by almost equimolar absorption loading for CO2 at elevated pressure, and the combined membrane-absorbent system provides selectivity up to 62 and 106.9 for the CH4/CO2 and CH4/H2S pairs respectively. Further, the efficiency of the proposed technique was evaluated experimentally on the example of separation of two binary CH4-based mixtures with CO2 and H2S as impurities. As a result of treatment, the purified product stream contains up to 93.34 and 99.998 vol.% of CH4 in the case of CO2 and H2S removal, respectively.