MEMBRANE MODIFICATION TO AVOID WETTABILITY CHANGES DUE TO PROTEIN ADSORPTION IN AN EMULSION MEMBRANE BIOREACTOR

This study addresses problems encountered with an emulsion/membrane bi oreactor. In this reactor, enzyme- (lipase) catalyzed hydrolysis in an emulsion was combined with two in-line separation steps. One is carri ed out with a hydrophilic membrane, to separate the water phase, the o ther with a hydrophobic membrane, to separate the oil phase. In the ab sence of enzyme, sunflower oil/water emulsions with an oil fraction be tween 0.3 and 0.7 could be separated with both membranes operating sim ultaneously. However, two problems arose with emulsions containing lip ase. First, the flux through both the hydrophilic and the hydrophobic membranes decreased with exposure to the enzyme. Second, the hydrophob ic membrane showed a loss of selectivity demonstrated by permeation of both the oil phase and the water phase through the hydrophobic membra ne at low transmembrane pressure. These phenomena can be explained by protein (i.e. lipase) adsorption to the polymer surface within the por es of the membrane. It was proven that lipase was present at the hydro philic membrane and that this, in part, explains the flux decrease of the hydrophilic membrane. To prevent the observed loss of selectivity with exposure to protein, the hydrophobic polypropylene membrane (Enka ) was modified with block copolymers of propylene oxide (PO) and ethyl ene oxide (EO). These block copolymers act as a steric hindrance for p roteins that come near the surface. The modification was successful: A fter 10 days of continuous operation the minimum transmembrane pressur e at which water could permeate through an F 108-modified membrane was 0.5 bar,the same value as that observed in the beginning of the exper iment. This indicates that loss of selectivity due to protein adsorpti on is prevented by the modification of the membrane.