Ethanol in biorefining and dehydration of agricultural materials: energy, capital cost, and product quality implications

The production of aqueous ethanol from fermentation-based 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 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 (a unit operation) with solvent drying plus solvent regeneration (a system of unit operations). Materials as diverse as wood, peat, coal, and starch have been dried experimentally 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 to 4 effect evaporation of water when compared on a separation-energy per 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 low-cost solvent and compatible technologies in the biorefinery setting. Published in 2010 by John Wiley & Sons, Ltd This article is a US Government work and is in the public domain in the USA