Effect of convective mass transfer on beer diafiltration

Abstract

The industrial application of dialysis for the de-alcoholization of beer is based on a diafiltration method, because a small positive transmembrane pressure an the beer side of the membrane is necessary to prevent ingress of water by osmosis and resulting dilution of the beer. This pressure difference introduces the new driving and convective mass transfer mechanism, which takes place simultaneously with the diffusive mechanism (specific for dialysis). The question is the influence which it has on the overall mass transfer phenomenon and selectivity of the alcohol/extract separation. An experimental investigation of beer diafiltration using two different membranes (cellulose based Cuprophane and polysulfone) was performed at different transmembrane pressure differences and flow rates. On the basis of the experimentally measured inlet and outlet concentrations the convective components of the alcohol and extract mass fluxes as well as the overall separation factor were determined. This data was analysed and compared. The results indicate that convective mass transfer stimulated extract transfer and losses and thus diminished the efficiency of selective alcohol/extract separation in beer dialysis.