Solvent flux through dense polymeric nanofiltration membranes

Abstract

Citation: ROBINSON, J.P. ... et al, 2004. Solvent flux through dense polymeric nanofiltration membranes.Journal of Membrane Science, 230 (1-2), pp. [29][30][31][32][33][34][35][36][37] Additional Information:• ABSTRACTThis work examines the flux performance of organic solvents through a polydimethylsiloxane (PDMS) composite membrane. A selection of n-alkanes, i-alkanes and cyclic compounds were studied in deadend permeation experiments at pressures up to 900 kPa to give fluxes for pure solvents and mixtures between 10 and 100 l m -2 h -1. Results for the chosen alkanes and aromatics, and subsequent modelling using the Hagen-Poiseuille equation, suggest that solvent transport through PDMS can be successfully interpreted via a predominantly hydraulic mechanism. It is suggested that the mechanism has a greater influence at higher pressures and the modus operandi is supported by the non-separation of binary solvent mixtures and a dependency on viscosity and membrane thickness. The effects of swelling that follow solvent-membrane interactions show that the relative magnitudes of the Hildebrand solubility parameter for the active membrane layer and the solvent(s) are a good indicator of permeation level. Solvents constituting a group (e.g. all n-alkanes) induced similar flux behaviours when corrections were made for viscosity and affected comparable swelling properties in the PDMS membrane layer.

Non-aqueous nanofiltration: solute rejection in low-polarity binary systems

“…Such behaviour is indicative of the selective PDMS layer rejecting low-polarity, minimally interacting solutes on the basis of size-exclusion. The data in Figures 3-6, and other data 7,10 , suggest viscous solvent transport to an extent dependent on the degree of swelling induced porosity. Increasing solute rejection with molecular weight has previously been reported by Gibbins et al 9 for an MPF-50 membrane where solute molecular weights ranged from 250 to 400 g mol -1 .…”

“…The PAN substrate has previously been shown to be inactive 7 whilst the radiation crosslinked and selective PDMS layer exhibited a nominal thickness of 2 μm. A single membrane was used to obtain the reported data and no preconditioning of the membrane was required prior to an experiment (repeat experiments with nominally identical membranes yielded similar results to those shown).…”

“…A single membrane was used to obtain the reported data and no preconditioning of the membrane was required prior to an experiment (repeat experiments with nominally identical membranes yielded similar results to those shown). No appreciable deterioration in flux/rejection performance was observed over the duration of the study and individual experiments were deliberately conducted in a random order to ensure that the membrane was not conditioned by any previous solvent, solute and/or handling procedure; see also 7,10 . The solvent induced swelling of the composite membrane layers was completely reversible as evidenced by the sequential nature of the data presented here, periodic flux measurements with a chosen 'standard' n-heptane solvent and in-situ determinations of PDMS/PAN layer thickness to be reported at a later date.…”

“…Figures 3 and 4 also clearly show that solute rejection is dependent on solvent type and is a consequence of the degree of solvent induced swelling in the selective PDMS layer of the membrane. Previous work by the authors has shown how the level of solvent flux can be directly related to membrane swelling properties 7,10 and the relative magnitudes of δ for the permeating solvent and membrane. The current work extends this finding whereby solvents inducing a larger amount of swelling yield lower solute rejection than poorer-swelling solvents.…”

“…This relatively robust polymer is stable in the presence of many organic solvents, although the passage of solvent(s) induces physical, but reversible, swelling. The Hildebrand solubility parameter, δ, is reported to be a good indictor of the extent of swelling to be expected for a particular solvent/PDMS membrane combination 6,7 , solvents with a solubility parameter similar to that of PDMS (i.e. δ =15.5 MPa 0.5 ) induce more swelling.…”