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Solvent extraction of organic acids from stillage for its re-use in ethanol production process

¹ Chemical Engineering Department, Universidad Nacional de Colombia (Sede Bogotá)
² Inborn Errors of Metabolism Institute, Pontificia Universidad Javeriana
³ Chemical Engineering Department, Design Group of Process and Products, Universidad de Los Andes

^* To whom correspondence should be addressed. E-mail: osanchez{at}uniandes.edu.co.

	Abstract

Stillage re-use in the fermentation stage in ethanol production is a technique used for the reduction of water and fermentation nutrients consumption. However, the inhibitory effect on yeast growth of the by-products and feed components that remains in stillage increases with re-use and reduces the number of possible recycles. Several methods such as ultrafiltration, electrodialysis and advanced oxidation processes have been used in stillage treatment prior its re-use in the fermentation stage. Nevertheless, few studies evaluating the effect of solvent extraction as a stillage treatment option have been performed. In this work, the inhibitory effect of serial stillage recycling over ethanol and biomass production was determined, using acetic acid as a monitoring compound during the fermentation and solvent extraction process. Raw palm oil methyl ester showed the highest acetic acid extraction from the aqueous phase, presenting a distribution coefficient of 3.10 for a 1:1 aqueous phase mixture:solvent ratio. Re-using stillage without treatment allowed up to three recycles with an ethanol production of 53.7 ± 2.0 g L^–1, which was reduced 25% in the fifth recycle. Alternatively, treated stillage allowed up to five recycles with an ethanol final concentration of 54.7 1.3 g L^–1. These results show that reduction of acetic acid concentration by an extraction process with raw palm oil methyl ester before re-using stillage improves the number of recycles without a major effect on ethanol production. The proposed process generates a palm oil methyl ester that contains organic acids, among other by-products, that could be used for product recovery and as an alternative fuel.

First published on September 11, 2009
Waste Management & Research 2009, doi:10.1177/0734242X09335701


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