Figs. 9 and 10 show the comparison of results obtained with
model mixture and fermentation broth for permeance and selectivity,
respectively. According to Luis et al. (2013), these parameters
enable better observation of the process efficiency once the effect
of the driving force and operating conditions is eliminated when
the parameters are calculated. Fig. 9 shows better results for broth
pervaporation, and an increase of both ethanol and water flux as
the feed ethanol weight fraction is increased, as observed in
Fig. 6. However, the permeance analysis shows clearly that the ethanol
flux increase has a major effect on the total flux increase,
especially for fermentation broth. This indicates that by-products
present in the multicomponent mixtures could be facilitating the
ethanol permeability, and no coupling flux is observed. In fact,
by-products of fermentation, such as carboxylic acids, aldehydes,
alcohols and other salts, may influence the separation process,
especially at lower ethanol feed mass fractions and flow rates. No
glucose was observed in the broth used for the separation, when
analyzed via high-performance liquid chromatography. Glucose
has been shown to affect the performance of pervaporation, as
reported by Chovau et al. (2011).