THE KINDS OF BIOFUELS

Biofuels Battle: Chemistry Versus Biology; What's the best way to turn plants into fuel?
Jonathan Fahey, April 29, 2009 (Forbes)

"There are 1,865 biofuels companies out there…[Take] agricultural waste, easy-to-grow non-food crop or just sunshine; add water and carbon dioxide and turn it into some type of fuel, like ethanol, butanol, gasoline, diesel or jet fuel…The entrants: enzymes, algae, yeast, bacteria and plain old chemistry.

"The winners will be the methods that use the least amount of energy to produce a fuel that stores the most amount of energy, at the best cost. Since the beginning of 2007, $1.8 billion has been invested worldwide in the race to these so-called next generation biofuels…[T]he finish line is not close. Helena Chum, a research fellow at the National Renewable Energy Laboratory, estimates that next-generation biofuels now cost anywhere between $5 and $1,000 a gallon, with a median of about $25…"

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"Current generation biofuels work because yeast likes the same food we do. Yeast thrives on the loads of sugar found in corn kernels and sugar cane, and they happily turn out lots of ethanol as a waste product…[T]he hope is that the parts of plants that aren't so easy to digest can be turned into fuel. Cellulose, which comprises cell walls; hemicellulose, polymers found in plant walls; and lignin, the stiff stuff in cell walls that gives plants, such as trees, their support.

"All the methods (except for the algal approach) first require that the plant matter be busted up, usually violently…The approach that is most straightforward, and furthest along, is to use a mild acid to pre-treat the plant material, then use enzymes to break down the constituents, then use yeast to ferment the sugars, then distill the output into ethanol…Companies like Iogen, POET, Verenium and Abengoa are working on pilot plants to develop this method…"

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"Companies like Range Fuels and Virent… cut the bugs out. Range Fuels uses heat and pressure…Virent takes a slurry of sugars from broken-down plant matter and, like an oil refinery, uses metal catalysts…[C]ompanies like LS9, Amyris, Mascoma and Qteros [are] trying…to engineer bacteria and yeast that will chew up the broken-up plant material and spit out ethanol, gasoline or diesel….

"Finally, there's algae. The algae people argue that growing a plant just to break it down is a waste of energy. Algae don't have to grow leaves or stalks; they can be trained to just turn out ethanol (…Algenol…) or diesel (Solazyme).

"So who's going to win? Certainly not all 1,865 companies. And maybe none will. Maybe the science will be too hard to scale up cheaply…."