(120b) Alternative Separation Methods for Bioethanol Purification

Authors: 
Hadjitheodorou, A., University of the Witwatersrand
Peters, M., Wits University


The environmental impacts of fossil fuel usage along with the depletion of available reserves have led scientists and engineers to seek greener and more renewable sources of energy. Bioethanol has proven to be one of the most promising alternatives to fossil fuel-derived petroleum as a transport fuel. Typical ethanol concentrations of fermentation from microorganisms are around 15%. This product is a very dilute solution therefore a large portion of the energy expenditure in the production of bioethanol is used to extract ethanol from the bioreactor effluent. Currently distillation is the most commonly used method of separation, however, it is ineffective in this situation as a large amount of energy is utilised in vapourising water which exits the column mainly as a bottoms product. Distillation is also limited as an azeotrope forms at 95%wt ethanol.  Thus it is of significant interest to investigate other common separation methods in bioethanol purification, either as an alternative to distillation or as an addition, in an effort to reduce overall energy consumption. Column Profile Maps (CPM), originally developed for distillation systems, offers a graphical method for rapidly synthesizing complex separation configurations. The CPM technique, which is directly applicable to stripping and absorption processes, has been extended to other separation processes, such as membrane permeation and reactive distillation and can be developed for others (i.e. solvent extraction). Thus feasible hybrid systems can easily be synthesized from a similar basis and compared to the traditional method of distillation in terms of their ‘ease of separation’ and overall work efficiency.