Biomass-to-liquids seen as key to biofuels future

Different ways to make biofuels can be grouped in 'generations', according to the type of technology they rely on and the biomass feedstocks they convert into fuel.

• 'first generation' biofuels, such as ethanol made from corn or sugarcane and biodiesel made from rapeseed, make use of the well established processes of starch and sugar fermentation (in the case of ethanol) and transesterification (in the case of biodiesel). For both types of fuel, easily extractible parts of plants are used, such as starch-rich corn kernels, grains or the sugar in canes; for biodiesel, oilseeds are used. The residues of the plants are not utilized.
• 'second generation' biofuels can use a far wider range of feedstocks, including biomass waste streams that are rich in lignin and cellulose, such as wheat straw, grass, or wood. In order to breakdown this biomass, two different processes are currently used: (1) the first one, a biochemical conversion technique, consists of using specialty enzymes that succeed in breaking down the ligno-cellulose and release the sugars, which can then be fermented into alcohol. This technology is best known as 'cellulosic ethanol' and will become efficient and cost-effective over the coming years, many hope. (2) The second technique, a thermochemical process (often called 'biomass-to-liquids'), relies on gasification, and consists of using high temperatures to turn biomass into a synthetic gas ('syngas'), consisting mainly of carbon monoxide and hydrogen. This gas can further be processed into different types of liquid fuel via Fischer-Tropsch synthesis. Fuels from this route are then called 'synthetic biofuels'. Alternatively, the syngas can be converted into hydrogen.
• 'third generation' biofuels rely on biotechnological interventions in the feedstocks themselves. Plants are engineered in such a way that the structural building blocks of their cells (lignin, cellulose, hemicellulose), can be managed according to a specific task they are required to perform. For example, plant scientists are working on developing trees that grow normally, but that can be triggered to change the strength of the cell walls so that breaking them down to release sugars is more easy. In third generation biofuels, a synergy between this kind of interventions and processing steps is then created: plants with special properties are broken down by functionally engineered enzymes.

The latter generation of biofuels is only gradually being explored. But the second one is receiving full attention and research funds. Of this type of biofuels, the biochemical conversion route - using specialty enzymes and micro-organisms - has received most attention. But the thermochemical route - biomass gasification and synthesis into liquid fuels - has become equally important (see picture, click to enlarge).

Testifying to this, is the U.S. government's US$385 million worth of grants announced last week (earlier post) and distributed amongst six companies. Mainstream media did not take not of the surprising fact that half of the six projects chosen will use this thermochemical process, which was first discovered almost a century ago to turn coal into a gas:
biomass :: bioenergy :: biofuels :: energy :: sustainability :: gasification :: syngas :: Fischer-Tropsch :: synthetic biofuels :: biomass-to-liquids ::

Long hailed as a more environmentally friendly way to turn coal into electricity, the gasification process might provide a faster and eventually cheaper way to produce ethanol from a variety of renewable sources collectively known as biomass, some scientists say.

For corn-based ethanol plants, the process of producing ethanol is as simple as brewing beer: sugars are extracted from the corn kernels and then enzymes are added to ferment it into alcohol. But biomass feedstocks don't easily give up their starches, so more expensive steps are needed to ferment cellulose in high-pressure chambers that have limited amounts of oxygen, according to Lanny Schmidt, a University of Minnesota chemical engineer.

Energy Secretary Samuel Bodman pegged the current cost of gasification as being about twice as much as the average $1.10 per gallon cost at corn-based ethanol plants.

A gasifier turns plant material into a synthesis gas consisting mostly of carbon monoxide and hydrogen. The "syngas" then could be turned into a variety of fuels including ethanol, hydrogen and environmentally friendly versions of diesel or gasoline, Schmidt said.

"These gasifiers are some high-tech stuff with high pressures and some more complexities," he said. "But they're probably more versatile at the end of the day to modify them as the demand and supplies change."

Gasification is a fairly simple process, based on chemistry developed in the 1920s, said Robert Brown, an Iowa State University chemical engineering professor and director of the school's Office of Biorenewables Programs.

The syngas produced during gasification mixes more readily with chemical catalysts, so it could be more easily turned into other fuels, chemicals and materials. Just add steam and you could produce hydrogen to power a fuel-cell vehicle, Brown said.

Of the six companies awarded U.S. Department of Energy grants, three will use versions of fermentation technology. But two others will use gasification and one will use a hybrid of both technologies:

• Alico Inc., a LaBelle, Fla.-based agribusiness company, would get up to $33 million to turn yard waste, wood waste and citrus peel into syngas, which would then be converted into ethanol, electricity and hydrogen.
• Range Fuels Inc., of Broomfield, Colo., would get up to $76 million for a plant near Soperton, Ga., to convert timber scraps into syngas to make ethanol and methanol.
• Abengoa Bioenergy, a St. Louis-based division of Spain's Abengoa SA, would receive up to $76 million for an 11.4 million gallons-per-year plant in Colwich, Kan., that would use both biochemical and thermochemical processes to convert corn stalks, wheat straw and switchgrass.

The Energy Department helped demonstrate the viability of gasification in the mid-1990s when it awarded Georgia-based FERCO $9.2 million to help build a power plant running on wood chips. By 2001, the $18 million plant in Burlington, Vt., was generating more than 200 megawatt-hours of electricity a day.

To compete in the marketplace, companies will have to make sure their feedstock supplies are consistent, do more research into catalysts that turn syngas into fuels, and develop better materials to contain the thermochemical reactions, according to the Energy Department.

The syngas would have to be cleaned and conditioned to remove contaminants, which is an expensive task. Energy officials say companies will have to bring down those costs if they're to compete in the market.

Mark Paster, a U.S. Department of Energy technology development manager who's studying ways to turn biomass into hydrogen, said both fermentation and gasification "are very viable and both routes continue to be researched and developed."

Paster said biomass helps reduce greenhouse gasses, so any method that can reach commercial viability will be better than one based on fossil fuel.

"There may not be a single winner, just like there's no winner in how we produce electricity," he said. "We do it in a variety of ways."