5. Conclusion
Concentration of ethanol from fermentation broth up to fuelgrade
quality can be carried out energetically by more efficient
hybrid process than a single distillation or one- or multi-stage
pervaporation process. Application of pervaporation with hydro-
philic membrane module in a hybrid process can especially be
advantageous to further concentration of overhead product of
distillation with 50–70 wt% ethanol, by even relatively low
selectivity membrane, namely if separation factor, j, is less than
0.02 (j* > 50). It was shown, how strongly the outlet concentration
and, the energy demand of the pervaporation process depend on
the feed concentration and separation coefficient of the membrane
applied. Even in this case a multi-stage pervaporation device is
needed to reach the fuel-grade quality. Applying hydrophobic and
hydrophilic membranes with j = 50 and j* = 50, respectively, a fuel
grade quality can be reached by a three-stage process with two
hydrophilic and one hydrophobic membrane modules, starting
with ethanol concentration of 5 wt%, while in case of membranes
with j = 100 and j* = 100, a two-stage process, using consecutively
switched hydrophobic and hydrophilic membranes, fulfills this
requirement. For widespread economic application of the perva-
poration as standalone or hybrid process, membrane modules with
high separation coefficient, larger than 50, are needed. Commer-
cially available industrial membranes do not offer more economic
ethanol recovery process than the distillation, at present