The work presented in this thesis aims at developing a new separation process based
on the application of supported magnetic ionic liquid membranes, SMILMs, using magnetic ionic liquids, MILs. MILs have attracted growing interest due to their ability to
change their physicochemical characteristics when exposed to variable magnetic field
conditions. The magnetic responsive behavior of MILs is thus expected to contribute for
the development of more efficient separation processes, such as supported liquid membranes, where MILs may be used as a selective carrier. Driven by the MILs behavior, these membranes are expected to switch reversibly their permeability and selectivity by in situ and non-invasive adjustment of the conditions (e.g. intensity, direction vector and uniformity) of an external applied magnetic field.
The development of these magnetic responsive membrane processes were anticipated
by studies, performed along the first stage of this PhD work, aiming at getting a deep
knowledge on the influence of magnetic field on MILs properties. The influence of the
magnetic field on the molecular dynamics and structural rearrangement of MILs ionic
network was assessed through a 1H-NMR technique. Through the 1H-NMR relaxometry
analysis it was possible to estimate the self-diffusion profiles of two different model MILs, [Aliquat][FeCl4] and [P66614][FeCl4]. A comparative analysis was established between the behavior of magnetic and non-magnetic ionic liquids, MILs and ILs, to facilitate the perception of the magnetic field impact on MILs properties. In contrast to ILs, MILs show a specific relaxation mechanism, characterized by the magnetic dependence of their self-diffusion coefficients. MILs self-diffusion coefficients increased in the presence of magnetic field whereas ILs self-diffusion was not affected.
In order to understand the reasons underlying the magnetic dependence of MILs
self-diffusion, studies were performed to investigate the influence of the magnetic field
on MILs’ viscosity. It was observed that the MIL´s viscosity decreases with the increase
of the magnetic field, explaining the increase of MILs self-diffusion according to the
modified Stokes- Einstein equation.
Different gas and liquid transport studies were therefore performed aiming to determine
the influence of the magnetic behavior of MILs on solute transport through SMILMs.
Gas permeation studies were performed using pure CO2 andN2 gas streams and air, using a series of phosphonium cation based MILs, containing different paramagnetic anions.
Transport studies were conducted in the presence and absence of magnetic field at a
maximum intensity of 1.5T. The results revealed that gas permeability increased in the
presence of the magnetic field, however, without affecting the membrane selectivity. The increase of gas permeability through SMILMs was related to the decrease of the MILs viscosity under magnetic field conditions.(...
