Submitted to: Biofuels, Bioproducts, & Biorefining (Biofpr)
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/20/2010
Publication Date: 1/15/2011
Citation: Robertson, G.H., Offeman, R.D., Cao, T., Orts, W.J. 2011. Ethanol in biorefining and dehydration of agricultural materials: energy, capital cost, and product quality implications. Biofuels, Bioproducts, & Biorefining (Biofpr). 5:37-53. Interpretive Summary: Ethanol production in biorefineries continues to make use of energy consuming methods for dehydrating water-containing products. The availability of aqueous ethanol in the refining arena suggests its use as a separation aid. This manuscript describes many of the biorefinery-germane uses of ethanol and develops criteria for its use in the removal of water from solids. Very significant reduction of process energy related to drying biorefinery solids are revealed as possible. In special cases, material properties of the dehydrated solids may also be enhanced. This strategy has potential for improving energy use in variety of biomass refining technologies that also make ethanol.
Technical Abstract: The production of aqueous ethanol from biorefining operations suggests the availability and possibility for its use within the refinery to aid in separations prior to and after fermentation. A variety of uses that have been considered are described here. In general these rely on biomass constituent solubility enhanced by ethanol concentration and temperature so that lipids, proteins, and lignin may be dissolved and recovered. Additionally, ethanol may also be applied to remove water from solids such as wet starch, wet gluten, and distillers wet grains. This technology has been described in the past as extractive or displacement drying and replaces conventional solids dehydration with solvent drying plus solvent regeneration. Materials as diverse as wood, peat, coal, and starch have been dried in this way. General criteria using best-case assumptions for this replacement are developed here. Applied to ethanol, these suggest significant potential energy savings for a system that combines low-load solvent drying with distillation. Distillation energy for regenerating ethanol solvent to 90%v or less and producing water is equivalent to a 3-4 effect evaporation of water when compared on separation energy / unit-of-water-removed basis. Material properties of the dehydrated substance may be enhanced since the solvent drying is at a lower temperature and leaves the matrix without structural collapse. The parameters for capital cost comparison are delineated with important considerations and economies identified that result from the use of a low cost solvent as well as compatible technologies in the biorefinery setting.