Monday, July 28, 2008

Boosting Cellulosic Biofuels

A catalytic process could improve thermochemical routes to ethanol.

By Duncan Graham-Rowe

Biofuel pact: NREL and Dow Chemical are collaborating on improving thermochemical processes to make ethanol biofuel from cellulosic biomass, such as wood waste. The groups hope to use a Dow catalyst to improve the conversion of syngas into ethanol. Credit: NREL

The Department of Energy's National Renewable Energy Laboratories (NREL) is to begin work testing a catalyst developed by Dow Chemical, the industrial giant based in Midland, MI, to see if it can be used to massively boost the production of ethanol made from biomass.

The partnership will attempt ways to make ethanol biofuel from cellulosic biomass, such as waste from corn or wood, using thermochemical processes. Specifically, NREL is looking to use a Dow catalyst to convert syngas--a mix of hydrogen and carbon dioxide made from the gasification of the biomass--into a mixture of alcohols, including ethanol. The joint agreement calls for the partners to demonstrate the process on a pilot scale and evaluate the feasibility of an integrated commercial-scale facility.

The hope is that a molybdenum sulphate catalyst developed by Dow in the 1980s will improve the syngas-conversion process. If successful, a catalytic process could theoretically achieve production rates of 130 gallons of alcohol per ton of biomass, a significant improvement on the 60-to-80-gallon yields produced by existing biochemical fermentation plants, says Mark Jones, a technology strategy development scientist with Dow.

NREL is already developing thermochemical reactions, such as gasification, to make ethanol from biomass. Compared with biochemical ethanol fermentation plants, thermochemical production is much faster, says Stephen Gorin, a senior scientist with NREL, in Golden, CO. "The throughput is very high," he says. "Front to back, you're talking orders of seconds as opposed to five to six days using biochemical production."

The high temperatures used in gasification can break down just about any form of biomass and easily handles the high lignin content that can make up as much as 25 percent of many forms of biomass. This means that nonedible feedstocks, such as wood waste and the stalks and leaves from crops, can be used.

But one problem with thermochemical production lies in the final stages of the synthesis, where catalysts are used to convert the syngas into a mixed blend of alcohols containing ethanol. NREL wants to make the process more selective for the synthesis of ethanol and increase the yields.

It makes sense for NREL to join forces with Dow, says Gorin, because the chemical company has had a long track record of knowing how to produce the catalyst, as well as expertise in scaling up industrial processes to sizes necessary for commercial production.

Dow has been working on its catalyst for quite some time, says Paul Dauenhauer, a chemical engineer at the University of Minnesota, in Minneapolis. With the thermochemical approach to making biofuel, the catalytic step converting syngas into alcohols is the limiting factor in terms of cost and design, he says. The other limiting factor is scaling. It is far from straightforward taking a pilot plant and trying to get the same results on an industrial scale, says Dauenhauer.