Separation and Purification Technology vol:136 pages:144-149
Bio-ethanol, as a clean and renewable fuel, is gaining increased attention. Biochemically produced by fermentation of an aqueous broth of different feedstock, it is purified by distillation (till the water/ethanol azeotropic mix of ∼95 wt% ethanol). A further removal of water to obtain >99.5 wt% ethanol is commonly performed using molecular sieves, however with the drawback of a high steam consumption (∼0.5 kg steam/kg ethanol). Hydrophilic membranes can be a valid alternative, without steam addition, and with a minimum electrical power required in pumping and in creating the permeate vacuum. The present paper assesses the current molecular sieve operation. It experimentally investigates the separation performance of a commercially available hydrophilic membrane, and finally compares both techniques. The initial experiments demonstrate the high flux obtained and the acceptable selectivity. At a feed temperature of ∼60 °C, a membrane unit of ∼120 m2 can replace the current 160 ton molecular sieve unit in a 200,000 ton/year plant.