Microfluidic devices as gas – Ionic liquid membrane contactors for CO₂ removal from anaesthesia gases

This work proposes a microfluidic gas – ionic liquid contactor for CO₂ removal from anaesthesia gas, containing Xe. The working principle involves the transport of CO₂ through a polymer flat membrane followed by its capture and enzymatic bioconversion in the ionic liquid solvent. Microfluidic devices enable a rapid and inexpensive screening of potential CO₂ absorbers. The alveolar – type design of the ionic liquid chamber was adopted to reduce mass transfer limitations of CO₂ through the liquid phase. Polydimethylsiloxane (PDMS) was the chosen polymer for dense membrane, as well as for the microfluidic device fabrication, mainly due to the high permeability of gases, O₂ and CO₂, and low cost. The selected ionic liquid was cholinium propionate (CP) with a water activity of 0.753, due to its high affinity towards CO₂ and biocompatibility with the enzyme used for CO₂ conversion to bicarbonate, carbonic anhydrase (CA). The CO₂ and Xe permeability and CO₂/Xe selectivity were determined in the microfluidic devices developed and compared to those exhibited by free standing PDMS membranes mounted on a standard permeation cell. The performance of the microfluidic devices as gas – ionic liquid contactors was evaluated for a given solvent flow rate with pure gas streams of CO₂ and Xe. The obtained results show that cholinium propionate with or without the enzyme has no effect on the Xe transport, but remarkably enhances the affinity towards carbon dioxide leading to enhancement factor up to 1.9 in the presence of 0.1 mg CA/gIL.