Membrane distillation and pervaporation for ethanol removal: are we comparing in the right way?

ABSTRACT

A new glance on the comparison between membrane distillation (MD) and pervaporation is performed. There is a difficulty in this comparison, mainly due to different hydrodynamic conditions reported in the literature. Pervaporation and MD are similar although the comparison between these two processes can be tricky. In that way, how can we make a proper comparison between results of these two processes? This study proposes a reasonable comparison between MD and pervaporation for ethanol–water separation. Two very distinct regions of results in terms of selectivity and flux are presented. Feed temperature and composition and concentration polarization effects were also investigated.

KEYWORDS:

• Membrane distillation
• vacuum membrane distillation
• pervaporation
• concentration polarization
• ethanol recovery

Acknowledgements

The authors gratefully acknowledge Dr Cristina Cardoso Pereira for the PVDF membrane fiber fabrication. This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

Highlights

• Pervaporation and membrane distillation (MD) were compared for ethanol/water separation;

• MD would be more adequate by considering the experimental condition;

• Concentration polarization cannot be neglected;

• Literature data cannot be directly compared due to different hydrodynamics.

Nomenclature

J	=	mass flux (kg/m2 h)
C0	=	concentrations by mass fraction on the membrane interface
Cb	=	concentrations by mass fraction on the feed bulk phase
Cp	=	concentrations by mass fraction on the permeate
δ	=	thickness of the concentration polarization layer
α	=	selectivity
αVLE	=	theoretical selectivity