Ceramic ultrafiltration membranes for non-solvent vegetable oil degumming (phospholipid removal)

Abstract

Crude vegetable oils mainly contain triacyl-glycerols but also various minor substances suchas phospholipids (PLs), free fatty acids (FFAs),waxes and colouring pigments. These sub-stances may affect the quality of the refined oiland are removed from the crude oil by severalsteps of refining. The conventional method toremove PLs (e.g. lecithin) is called degumming.Generally, this process consumes large amountof energy and additives as well. Membranefiltration primarily is a size-exclusion-basedpressure-driven process and often mentioned as apossible alternative method for water-degummingin the literature. Zhang et al. [1] with polyimidemembranes, Subramanian [6] with flat-sheet sili-con active layer membranes experiencedPL retention of 93–96% when filtrated crudesoybean and rapeseed oils. They concentratedthe soybean oil micelles to volume concentra-tion ratio of 10. PLs could be rejected above90%. Alicieo et al. [2] clarified crude soybeanoil through a ceramic tubular membrane (poresize 0.01mm) and a polysulphone hollow fibermembrane (MWCO 100 kDa) in a cross-flowapparatus. They demonstrated that ceramicmembrane showed higher rejection of phospho-rous. Hafidi et al. [3] tested sunflower, soyaand rapeseed oil-refining by a cellulose microfil-tration membrane. At 25°C, the PL retentionreached 84–98%, whereas it was only of 46–78%at 60°C. Moura et al. [4] studied degumming ofsoybean oil using UF membrane prepared frompolyethersulphone (MWCO 101.9 kDa). Theremoval of up to 89% of PLs was reached. Dry (non-solvent) membrane degummingwas studied in this paper with several ceramictube membranes. To achie ve satisfying PL sepa-ration in non-solvent environment with UFmembrane requires relatively small (6 kDa orsmaller) MWCO. Koris and Vatai [5] reachedPL retention of 70–77% by flat sheet UF mem-brane (MWCO 15 kDa). Because of its highviscosity the vegetable oil permeates throughthe membrane with slow velocity. Thus low-ratepermeate flux seems to be the main disadvan-tage of this novel degumming method.