New Technology Could Lead To More Energy-Efficient Ethanol Production

Ethanol to fuel cars, trucks and other vehicles might tomorrow take less energy to produce, thanks to a device invented by Agricultural Research Service scientists in California.

Chemical engineers Richard D. Offeman and George H. Robertson at the ARS Western Regional Research Center in Albany, Calif., think it may be possible to cut energy costs by using a series of specially designed permeable plastic sheets, or membranes, to produce ethanol from fermented broths of corn, or straw and other kinds of biomass feedstocks.

Bioethanol is taken out of an incoming fermentation broth using this spiral-wound liquid membrane module. The broth flows across the surface of specially designed permeable plastic membranes that are wrapped around the module's perforated collection tube. Ethanol in the broth is separated by the membranes, using a vacuum, then sent to other equipment to be condensed into liquid. The leftover broth could be processed into byproducts.

The technology will help to address the serious concern regarding the energy efficiency of bioethanol production, according to Robert L. Fireovid, ARS national program leader for process engineering and chemistry, Beltsville, Md. The researchers' invention, called a spiral-wound liquid membrane module, could potentially replace the widely used process of distilling ethanol from fermentation broths.

The module offers ethanol producers the important advantage of combining two separation processes, extraction and membrane permeation, in one piece of equipment. With further research and development, the module would require less energy than distillation.

Today, energy costs are ethanol producers' second largest expense; feedstocks are first. In brief, the fermentation broth -- typically containing about 5 to 12 percent ethanol -- would travel through a sandwich-like configuration of membranes and mesh sheets, called spacers that keep the membranes separate from each other. One membrane has a solvent in its pores that extracts the ethanol from the broth. A second membrane, with the help of a vacuum, pulls the ethanol out of the solvent. The ethanol-and-water vapor that results is then, in other equipment, condensed into an ethanol-rich liquid.

The scientists have applied for a patent. They now plan to build and fine-tune a prototype, then turn it over to a membrane manufacturer for further development before commercialization.

(USDA Agricultural Research Service, June 26, 2007)