New method finds shortcut to produce fuel from crop wastes

Source: Umair Irfan, E&E reporter • Posted: Friday, May 3, 2013

Cellulose is an appealing raw material for fuels. Several chemical processes can turn this long sugar chain into fuel precursors for cars, trucks and aircraft. It’s abundant in crop waste, like leaves and stalks from corn, so it’s cheap and won’t raise food prices.

But making it efficiently is tricky. Most of the common ways to break cellulose down involve finicky enzymes or microbes, which will only work with high-quality cellulose sources and require a strictly controlled environment. These exacting standards increase the cost of building a biofuel plant and the unit cost of the products.

Some of the traditional cellulose processing steps, like fermentation, can take days, and up to one-third of the carbon from the cellulose dissipates as carbon dioxide.

Mercurius Biorefining Inc. is working on a way around these obstacles, building a pilot cellulosic biofuel plant in Indianapolis that will process 10 tons of biomass daily to produce jet and diesel fuel. The facility, expected to go online within a year, will use a novel chemical pathway that acts quickly and is a bit more easygoing when it comes to its feedstock and operating conditions.

“The big advantage is that this is a purely chemical-catalytic process that works under mild conditions (about 100 degrees Celsius),” Mark Mascal, a chemistry professor at the University of California, Davis, who developed the system, explained in an email. The catalyst, hydrochloric acid, doesn’t foul and acts fast. Depending on the kind of cellulose used, the reaction can take between a few minutes and a couple of hours, according to Mascal.

Making ‘biocrude’ at the farm

The resulting product is a compound called 5-(chloromethyl)furfural, or CMF for short. With some additional processing, CMF can turn into fuels, plastics or even pharmaceuticals.

Using this process, biofuels become more economical. “The capital costs are lower than competing technologies because [chemical] reaction times are lower,” said Karl Seck, CEO of Mercurius. He added that many of the processing steps are well-understood, particularly in the petroleum sector and the paper industry, so the necessary hardware is easier to get and cheaper to install than, say, an anaerobic digester.

Chemically processing cellulose could also introduce a new biofuel workflow. Rather than trucking raw biomass to a single plant, farmers could build on-site chemical reactors that turn leaves, stalks and husks into an energy-dense liquid “biocrude,” which they could then pump to a central plant for further refining.

“It has been demonstrated to work exceptionally well on the bench scale,” Mascal said. “It is now a matter of getting expert engineers to bring it to pilot and commercial scale.”

To this end, the Department of Energy announced a $4.6 million grant for Mercurius’ pilot plant last week. Seck said he expects to bring the plant construction costs down, ranging from $3 to $5 per annual gallon of production.