Recently a large amount of interest has developed around separating out impurities of
small size; pertinent examples are found within fuel and solvent processing. For such
applications a leading candidate process is nanofiltration. This thesis focuses on SRNF
(solvent resistant nanofiltration) composite membranes consisting of a dense polymer
active layer bonded to a stronger, but ultimately more porous, support layer. The
composite membranes that have been produced during the course of this work consist
of a PDMS (polymdimethylsiloxane) active layer bonded to a commercially available
support layer of PAN (polyacrylonitrile). To create the membrane a monomer was
spread over the support layer and then polymerised to form the matrix which was
responsible for separation. Commercially, either heat or radiation is often applied to
cause polymerisation, however the membranes in the current work have been formed
by the used of a homogeneous catalyst. This thesis investigates the transport and
separation dynamics of the produced membranes for a series of fuel simulants
composed of organometallics and poly-nuclear aromatic solutes dissolved in aromatic
and alkane solvents.
Membrane composition and the extent of polymer swelling were found to be the two
key factors which had the greatest influence on solvent flux and solute rejection. By
increasing catalyst concentration it was found that the dual effects of increased
rejection and reduced flux occurred, with the converse also being true. The effective
pore size of the membrane could also be controlled by varying the catalyst amount
during manufacture as this directly affected the limit of crosslinking which formed.
Polymer swelling was the most pronounced using solvents with a solubility parameter
close to that of the polymer. The membrane transport mechanism was most accurately
forecast by the solution diffusion model for flux predictions and the convection diffusion
model for rejection predictions, however all the models tried were in close agreement.
This was postulated to be due to the swelled polymer matrix which allows for both
convective and diffusive transport to occur.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.