The influence of polarity on flux and rejection behaviour in solvent resistant nanofiltration—Experimental observations

Abstract

The separation characteristics of a dense polydimethylsiloxane (PDMS) membrane were studied using mixtures comprising xylene, cyclohexane or n-heptane with oxygenate components at concentrations up to 75%. The effects of polarity on flux and rejection performance were determined through a test matrix of solvent type, concentration, filtration pressure, crossflow rate and the degree of membrane crosslinking.In all cases involving alcohols, the more polar compound in the feed mixture was partially rejected by the membrane and the extent of rejection was dependent on the polarity as quantified by solubility parameter. The rejection-concentration profiles for several alcohol/solvent mixtures exhibited a maximum, with the highest rejection around 30%. Mixtures containing MTBE did not separate, i.e. no rejection was observed.Rejection increased with increasing pressure and crossflow rate but was largely unaffected by the degree of membrane crosslinking. Component flux was affected by the oxygenate concentration in the mixture, which was attributed in part to changes in the degree of membrane swelling with composition. Experimental findings suggest that the separation is primarily governed by multicomponent solvent/oxygenate/membrane swelling equilibria, and results compare favourably with swelling isotherms available in the open literature.

Solvent-induced swelling of membranes — Measurements and influence in nanofiltration

“…Flux and steady state rejection are the principal measures and Figures 6-10 illustrate the salient features of swelling on these two parameters as well as representative swelling data for ethanol mixed with a second, lower polarity, solvent. For fuller descriptions the reader is directed to previous papers by the authors [11][12][13][14][15] where experimental arrangements and some of the data reported in Figures 6-10 are discussed in greater detail along with applications of nanofiltration models. All crossflow nanofiltration data reported in this paper were obtained with a DESAL membrane module (wetted surface area = 75 cm 2 ) at a crossflow rate of circa 1 l/min.…”

Analysis of solvent flux through nanofiltration membranes by mechanistic, chemometric and hybrid modelling

“…The Hildebrand solubility descriptor is used in the model proposed by Bhanushali et al [7]. Other authors also report its possible importance for describing solvent-membrane affinity [3,5,6,8,39]. The results presented in Fig.…”

Recent Advances in Polymeric Solvent‐Resistant Nanofiltration Membranes

“…However, some studies have shown that membrane swelling dramatically increased the flux of the solution without obvious changes in the solute rejection. 160 The difference may be caused by the difference of selective layer structure of the SRNF membranes. For the dense membranes, the free volume plays main role in rejecting of solutes, whereas the pores between the selective layer molecules determine the rejections to solutes for the porous membranes.…”