SORPTIVE RECOVERY OF DILUTE ETHANOL FROM DISTILLATION COLUMN BOTTOMS STREAM

Modern ethanol distillation processes are designed to ensure removal o f all ethanol from the column bottoms, i.e., to levels <100 ppm ethano l and utilize substantial stripping steam to achieve this result. An a lternate approach using sorption was attempted as a means to reduce en ergy requirements in the stripping section, and thereby reduce cost. A dsorbents tested for use in such an application showed that carbonaceo us supports, in particular Ambersorb XEN 572, gave alcohol-free water as effluent when a 1% (w/w) starting ethanol concentration was passed downflow at 1 bed vol/h over a fixed-bed adsorber at 70 degrees C. Reg eneration was readily achieved at 70-90 degrees C using hot air, vacuu m, superheated steam, or hot water to strip the ethanol from the colum n, and yielded ethanol streams containing a maximum of 5.9% alcohol, w ith average concentrations of 2.5-3.5% depending on the regeneration m ethod used. These experimentally determined operating conditions combi ned with distillation energy calculations have enabled development of a process concept for sorptive concentration of dilute ethanol which i s more energy efficient than distillation alone. The combination of ex isting distillation and corn grit drying technologies, with sorptive r ecovery of dilute ethanol (from the column bottoms) shows promise of r ecovering a fuel grade, 99.4% ethanol product from a 4.5% ethanol brot h with an energy requirement of 23,100 BTU/gal. The potential energy s aving of 3600 BTU/gal over distillation alone corresponds to 1.8 c/gal , and provides motivation for further examination of this approach in reducing costs of ethanol production from biomass.