Influence of feed flow velocity on pervaporative aroma recovery from a model solution of apple juice aroma compounds

Abstract

Pervaporation is a membrane separation technique being developed for aroma recovery from various aqueous solutions. This study concerns pervaporative aroma recovery from apple juice. The objective was to study the concentration polarisation phenomenon in this application and to find a possible relationship between the relative composition of the permeate, i.e. the aroma concentrate, and the feed flow conditions (Re. 50–1000). The study was based on a model solution of apple juice aroma compounds. The relative content of esters and aldehyde, trans-2-hexenal, increased as the hydrodynamic conditions were improved at the expense of the alcohols. For the alcohols, the membrane resistance dominated over the feed boundary layer resistance to mass transfer. For most of the esters, the opposite relation was found. For the aldehyde and ethyl acetate, the resistances were of the same order. The Sherwood correlation was found to overestimate the mass transfer coefficient of the feed boundary layer in cases of severe concentration polarisation.