Nanofiltration: a method for improving the purity of fuels and non-aqueous solvents

This paper describes some of the principal features of solvent resistant nanofiltration and its potential in fuel processing. Experimental data for both fuel simulants and a petrol fuel are presented. The solute rejection mechanism for low polarity mixtures was size exclusion with a membrane cut-off in the region of 1-2 nm. The extent of solute rejection was dependent on the degree of membrane crosslinking, the membrane swelling induced by the feed and the filtration pressure. Nanofiltration experiments with the petrol fuel showed a good correlation with the data obtained for the fuel simulants, both in terms of permeate flux and solute rejection. Provided that higher polarity oxygenates were not present in the fuel, it was possible to remove undesirable polynuclear aromatic and organometallic solutes to an extent that was sufficient to significantly reduce valve deposits and emissions gases in engine tests.