Potential effect of the membrane potting on the long-term performance during hydrolysis of edible oil

For both the hydrolysis of vegetable oils and the esterification of glycero l and fatty acids hollow fibre membrane bioreactors are developed. In these bioreactors, hydrophilic membranes are used as immobilization carrier for the enzyme as well as phase separator. In this paper, the membrane reactor is scaled up from a 0.8 m(2) lab scale module to a 22.5 m(2) bench scale un it. In spite of cleaning, hardly any oil flow was possible through the fibr e lumen within 3 months of operation. To study these phenomena, a series of lab scale experiments hydrolyzing sun flower oil was performed. During 40 days the cross-sectional area of the fi bres decreased to 20% of its initial value. As a result, the hydrolysis act ivity of the bioreactor decline for 94%. Two possible fibre blocking mechanisms could be eliminated: enzyme coagulat ion and substrate/product polymerization. We found that fibre blocking was caused by swelling of the polyurethane potting. Swelling led to a decrease of the available volume for the membrane fibres embedded in the polyurethan e potting, hence the how resistance in the lumen increased. Potting material immersed in short chain fatty acids gave a more rapid swel ling than immersed in longer chain fatty acids. Similar to this, in a react or running with a short tail fatty acid, oil flow was not possible any more after 5 days, while the use of oleic acid gave no fibre blocking, on the s ame time scale. In many types of hollow fibre membrane modules, polyurethane is used as pot ting resin. The use of these modules in membrane bioreactors or in any othe r two-phase membrane system could lead to flow problems. (C) 2000 Elsevier Science B.V. All rights reserved.