Critical flux of colloidal foulant in microfiltration: Effect of organic solvent

Abstract

As membrane technology becomes more popular for separation and purification in the aqueous phase, the advantages have increasingly attracted attention for organic solvent filtration applications. However, although the knowledge base on the inevitable membrane fouling in water is rich by now, the understanding for organic solvents is limited. Accordingly, this study was targeted at providing insights on the fouling behavior of the same colloidal foulant (namely, silica) and microfiltration membrane (namely, Anopore) in four different solvents (namely, DI water, ethanol, hexane and formamide). The direct observation through the membrane (DOTM) technique was used to characterize critical flux (Jcrit), which affirmed the distinctly different values in the four solvents at various Reynolds numbers. The shear-induced diffusion model predicted well for water and formamide only, indicating the model has to be enhanced to account for solvent effects. To quantify the interfacial interactions, the Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended (XDLVO) models were used. Both models agreed in that silica-membrane and silica-silica interactions were the most attractive in hexane, which underlies the immediate membrane fouling and extensive clumping, respectively. For the other three solvents, the relative DLVO interaction energies agreed with the relative Jcrit values at fixed Re, indicating the greater relevance of the DLVO (rather than XDLVO) model and Re (rather than crossflow velocity). Because the greatest silica-silica repulsion in ethanol was mis-predicted by both DLVO and XDLVO models, the solvation film effect was additionally harnessed to provide an explanation. The understanding gained from this study on membrane fouling in organic solvents are expected to be beneficial in the design and operation of such emerging membrane filtration systems.