Process economic considerations for production of ethanol from biomass feedstocks

Ethanol's future role as a fuel hinges on several factors including feedstock availability, processing costs and supportive political framework. There is growing international consensus that fuel ethanol may serve a multitude of socially, environmentally, and politically desirable goals. As a result, political incentives are expanding, from Brazil and the United States to other countries in Europe and Asia. With all of the new government programs in America, Asia, and Europe in place, total worldwide fuel ethanol demand could grow to exceed 125 billion liters by 2020.

Can worldwide agricultural systems sustain future ethanol demand? One answer may be lignocellulosic biomass, which has potential as a low-cost fermentation substrate for making ethanol. Over one billion tons per year of lignocellulosics, much of it corn stover, is potentially available in the United States. Asia is also a large potential producer of bioethanol from crop residues, primarily rice straw.

SRI Consulting's Process Economics Program (PEP) has undertaken independent techno-economic evaluation of ethanol production from biomass. This evaluation indicates that both feedstock cost and capital cost are high-impact factors, with hurdles yet to be overcome. We estimate the total fixed capital costs to be nearly $260 million for a 50-million-gallon-per-year grass-roots plant, including an enzyme unit and power plant.

An ethanol price of $2.75 per gallon would be required to support investment in a risky, first-of-a-kind ethanol-from-biomass plant. Yield improvements in all major steps of the process would enable lower capital requirements, thus improving the economics and lowering investment risk. Significant improvement in the process economics could result if revenue were to be generated by sale of the residual lignin for uses more valuable than combustion.