Effects of concentration, temperature, and coupling on pervaporation of dilute flavor organics

Abstract

Pervaporation is a novel method to extract flavor organics from dilute distillates and extracts. Selection of operating conditions and membranes is critical for the process design and scale-up. In the current study, the effects of feed concentration and operating temperature on membrane separation performance were investigated. Four polydimethyl siloxane (PDMS) membranes and one polyoctylmethyl siloxane (POMS) membrane were tested for pervaporation and their separation performances were compared. Flavor loss rate due to evaporation was determined from a batch operation experiment. Experimental study was extended from single component to multicomponent (ethyl butyrate, trans-2-hexenal, benzaldehyde, cis-3-hexenol, phenethyl alcohol, and methyl anthranilate) mixtures that resembled real flavor systems. The total mass transfer resistance was divided into two parts: one in the liquid boundary layer and the other in the membrane. Specific mass transfer driving forces and resistances were defined based on the nonequilibrium thermodynamic formalisms. Using the concentration polarization model, the liquid boundary layer thickness on the feed side and the intrinsic membrane permeance were calculated for various pervaporation systems. The effects of operating conditions and membrane properties on concentration polarization were analyzed. It was concluded that the boundary layer thickness was affected not only by the bulk flow parallel to the membrane surface, but also by the permeation flow perpendicular to the membrane surface. When separation performances of multicomponent systems were compared to those obtained from single component systems, no obvious coupling effects were detected for the pervaporation of dilute multiple flavor organics. It was, thus, concluded that no coupling terms need to be included in the mass transfer equations for dilute flavor pervaporation. Therefore, same flux equations and concentration polarization models can be applied to both single- and multi-component pervaporation systems.