On the selective transport of nutrients through polymer inclusion membranes based on ionic liquids

Resumen

Ionic liquids are molten salts which remain liquid at temperatures below 100 °C. They are usually made of an organiccation (imidazolium, pyrrolidinium, pyridinium, etc.) and an inorganic (hexafluorophosphate, tetrafluoroborate,chloride, etc) or organic anion (dicyanamide, bistrifluoromethylsulfonylimde, tosylate, etc.) Their unique propertiesmade them very attractive for a wide variety of chemical processes such as separation or catalysis. Their vapour pressureis negligible and show good chemical and thermal stability. Their properties can be tailored by varying the anion andthe cation of their structure in order to be adapted to a specific process. ILs have successfully employed as extractionagents for metal ions, organic compounds or macromolecules, in liquid/liquid systems. However, their immobilizationas liquid phase in different kinds of matrix provide a dual benefit: i) to obtain stable materials with a minimal contentof IL and ii) the opportunity to reuse the IL at the end of the process. IL-based membranes can be mainly groupedinto: i) supported ionic liquids membranes (SILMs), ii) polymer ionic liquid inclusion membranes (PILIMs), iii)polymerized ionic liquid membranes (PyILMs) and iv) other ionic liquid/polymer composite materials. Other recentuse of PILIMs is as separator in microbial fuel cells (MFCs). Microbial fuel cells use bacteria to convert the chemicalenergy of a particular substrate contained in wastewater into electrical energy. By using organic matter in wastewateras a fuel, contaminants are removed from water while generating electricity. However, it is necessary to improve theperformance of MFCs before they can be scaled up since, to date, their practical implementation is not feasible. Oneapproach is the use of two chamber MFC. In the anodic chamber the organic matter is oxidized and in the cathodicchamber microalgae is growing and is producing the oxygen which is needed for to cathodic reduction reaction.Furthermore, microalgae is able to capture carbon dioxide and the produced biomass can be used for production ofadd value compounds. All of above could improve the power and the wastewater treatment efficiency of MFCs, whilereducing their cost. In a two chamber MFCs, the study of the transport through the membrane it not limited to protonbut also to the rest of species in the anodic and catodic chamber. Specifically, in the case of combination of microalgaegrowing in MFCs, the microalgae nutrient transport through the membrane should be analysed. The results of thistransport studies could allow to design more efficiency bioelectrochemical reactors (MFCs). In this work, for the firsttime, the selective transport of different nutrients (NaNO3, MgSO4, CaCl2 and NaH2SO4) through a polymerinclusion membrane based on ammonium-type ionic liquid is evaluated. In this case, the effect of the ionic liquidmembrane composition and the nature and concentration of the anion on the permeability of the membrane isanalyzed in-depth. Although our first objective is the application of the results to the design more efficientbioelectrochemical reactor based on microbial fuel cells, the conclusions of the present work could be applied to anyfield in which the recovery or selective separation of the studied nutrients will be of interest.