title: Solvent extraction of organic acids from stillage for its re-use in ethanol production process.
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.
authors.affiliation: Department of Chemical Engineering, Universidad Nacional de Colombia (Sede Bogotá), Bogotá, Colombia.
authors.forename: G A
authors.initials: GA
authors.lastname: Castro
authors.forename: L A
authors.initials: LA
authors.lastname: Caicedo
authors.forename: C J
authors.initials: CJ
authors.lastname: Alméciga-Díaz
authors.forename: O F
authors.initials: OF
authors.lastname: Sanchez
mesh_terms: D019342:Acetic Acid / Q000737:chemistry; D000143:Acids / Q000032:analysis* / Q000737:chemistry; D000434:Alcoholic Beverages / Q000191:economics; D005591:Chemical Fractionation / Q000379:methods*; D057168:Distillation; D004467:Economics; D000431:Ethanol / Q000737:chemistry*; D005285:Fermentation; D009930:Organic Chemicals / Q000032:analysis* / Q000737:chemistry; D000073878:Palm Oil; D010938:Plant Oils / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D018505:Waste Management / Q000379:methods*
chemical_list: D000143:Acids; D009930:Organic Chemicals; D010938:Plant Oils; D012997:Solvents; D000431:Ethanol; D000073878:Palm Oil; D019342:Acetic Acid