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ABSTRACT:
Distribution coefficients and separation factors were determined for the partitioning of ethanol and water from aqueous mixtures into several vegetable oils and their fatty alcohol and fatty ester derivatives. Castor oil, ricinoleyl alcohol, and methyl ricinoleate all show higher ethanol distribution coefficients, and similar or reduced separation factors, relative to other oils and derivatives studied here or reported by others. Of particular interest, ricinoleyl alcohol has an ethanol distribution coefficient 50% higher than that of oleyl alcohol, a commonly studied solvent for ethanol extraction from fermentation broths.
Paper no. J11212 in JAOCS 83, 153-157 (February 2006).
KEY WORDS: Ethanol, fatty alcohols, fatty esters, solvent extraction, vegetable oils.
Interest is growing rapidly in the biorefining of ethanol, butanol, diols, and other products derived from fermentation of renewable substrates. Fuel ethanol is primarily derived from grains; as of January 2006, U.S. plant capacity was approximately 16.4 × 10^sup 9^ L/yr (4,336 MM gal/yr), with another 6.6 × 10^sup 9^ L/yr (1,746 MM gal/yr) capacity under construction (1). Much effort has been devoted to laboratory-scale fermentation for butanol (2). DuPont is pursuing 1,3-propanediol (3). A common critical problem for these water-soluble products is their recovery from dilute aqueous solutions. Though distillation is a standard method for recovering low-boiling products such as ethanol, the energy requirements for the separation can be high by this method, especially when the concentration of the product in the feed is very low. At high product concentrations, azeotropes also are a common problem in distillation and require additional processing via azeotropic or extractive distillation, adsorption, or pervaporation to yield a dry product.
Liquid-liquid solvent extraction is an attractive alternative separation process for ethanol and higher alcohols. Continuous removal of the product during fermentation is possible. This can be important, as generally these products are inhibitory to the microorganisms producing them, hence continuous removal of these products can increase fermentor productivity and substrate yield. As an alternative to distillation for ethanol, solvent extraction has the potential to be more energy efficient (4,5).
Criteria that must be considered when choosing an extraction solvent include extraction performance, chemical stability, solubility in the aqueous feed, immiscibility of phases, emulsion or foam formation, economic separation of the solvent and product, biocompatibility with the fermentation organisms, safety...