Thin film enzyme - poly(ionic liquid) – free ionic liquid composite membranes for enhanced CO2 absorption with carbonate aqueous solutions

Molina Fernandez, Cristhian;Luis Alconero, Patricia
(2019) ILSEPT - 4th International Conference on Ionic Liquids in Separation and Purification Technology — Location: Sitges, Spain. (8.September.2019)

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Abstract
Carbonic anhydrase (CA) has been extensively studied in literature as CO2 hydration kinetics enhancer in CO2 absorption since the hydration reaction is the limiting step when using aqueous benign solvents. To protect the enzyme from the harsh conditions in the stripper, CA is usually immobilized. However, depending on the immobilization method, this procedure can lead to the reduction of enzyme activity or the increase of mass transfer limitations. Room temperature ionic liquids (ILs) have been proven as potential solvents in biochemical reactions, increasing in many cases the enzyme activity and stability. Furthermore, polymerized ILs (PIL) present high CO2 solubility. The present study focus on the elaboration, characterization and testing of CA integrated poly(ionic liquid) – free ionic liquid composite membranes in CO2 absorption using aqueous benign solvents. To reduce diffusional mass transfer limitations, thin film PIL-IL membranes with high free IL content were prepared by bulk free radical polymerization on top of a porous PVDF support. The enzyme was dissolved in the free IL before polymerization ensuring immobilization by physical entrapment inside of the cross-linked polymeric matrix. The PIL studied was poly(1-Vinyl-3-hexylimidazolium bis(trifluoromethylsulfonyl)imide) while different amounts (0, 30 and 75 %w) and types of free ILs (1-butyl/hexyl/octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and biocompatible choline based ILs) were analysed to see the effect on enzyme activity/stability and separation performance. Furthermore, the effect of CA concentration was also addressed. Experiments were performed in a membrane contactor set-up using water and potassium carbonate solutions as absorbent. The presence of CA should produce a significant increase of permeability compared to the case without CA. It is also expected to see a trade-off between enzyme activity/stability and diffusion of CO2 in the membrane when free ILs of different hydrophobic character are compared. Finally, this study aims to expand the use of enzymes in CO2 absorption by placing them in the broader context of membrane contactors.
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Molina Fernandez, C., & Luis Alconero, P. (2019). Thin film enzyme - poly(ionic liquid) – free ionic liquid composite membranes for enhanced CO2 absorption with carbonate aqueous solutions. ILSEPT - 4th International Conference on Ionic Liquids in Separation and Purification Technology, Sitges, Spain. https://hdl.handle.net/2078.5/125137