Abstract
During this work, an original study of the CO2 and SO2 competitive gas absorption in three superbase ionic liquids (ILs), namely, trihexyltetradecylphosphonium 1,2,4-triazolide ([P66614][124Triz]), and trihexyltetradecylphoshonium benzimidazolide ([P66614][Benzim]), is reported for the first time. To initiate such a comprehensive study, the CO2 and SO2 mixed gas solubility in selected ILs was determined by using an original and accurate dynamic method coupled with mass spectrometry after several absorption and desorption cycles. This method has been validated by comparing the gravimetric uptake of CO2 with the mass spectrometry data using trihexyltetradecylphosphonium benzotriazolide, 1,2,4-triazolide, and benzimidazolide ILs and shown to be consistent within 10% in mole ratio units. Solubility results clearly show that the presence of SO2 in the gas stream decreases the CO2 capture capability of the investigated ILs. Furthermore, the viscosity, chemical analysis (water content and sulfur content), and sp...
Highlights
The CO2 capture of ionic liquids (ILs) has been widely investigated as an alternative sorbent to the industrial standard, aqueous monoethanolamine (MEA) solution
0fl.u1e5−ga0s.2i5s%10N−O15x %anCd Op2a,rt1ic0u%latwesa.t1e0r−,120.0T5h−e utilization of MEA as an industrial CO2 capture agent has been further disadvantaged by pilot scale studies, which have shown that the addition of small amounts of SO2 to a CO2 feed decreases the CO2 removal efficiency and increases the amine degradation rate.[13]
ILs previously studied were selected to be tested using the breakthrough method developed where the exit gas is analyzed by a mass spectrometer
Summary
The CO2 capture of ionic liquids (ILs) has been widely investigated as an alternative sorbent to the industrial standard, aqueous monoethanolamine (MEA) solution. As already mentioned in the case of CO2 uptake, higher SO2 solubility is reported for ILs with structures allowing a chemical reaction between this acidic gas and the IL. This chemical reaction could occur on the anion (e.g., phosphonium-based superbase ILs reported and in the literature14−21) or on the cation in the case of the guanidinium-22,23 or ammonium-based ILs.[24] In the case of ILs absorbing SO2 physically, one can appreciate that anion selection seems more important than the cation.[25,26] For example, according to Zeng et al.,[25,26] the higher SO2 uptake capacity of the [C4Py][SCN] versus [C4Py][BF4] is mostly
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