I missed this story when it came out last week:
Hydrocarbon biofuels’ promise tops that of ethanol, gasoline
John Regalbuto, a chemical engineer at the University of Illinois, Chicago, and director of the NSF catalysis and biocatalysis program, wrote in Science that biomass-derived fuels are not far from being part of the energy mix as a replacement for gasoline, diesel and jet fuel.
Hydrocarbon fuels can be directly produced from the sugars of woody biomass — forest waste, cornstalks or switchgrass — through microbial fermentation or liquid-phase catalysis, he wrote. They can be produced by pyrolysis or gasification directly from the woody biomass. And they can be produced by converting the lipids of nonfood crops and algae.
“The drawback to using ethanol as a complete replacement for gasoline … is not only the high cost of its production from cellulose but also its lower energy density,” Regalbuto wrote. “Ethanol has two-thirds the energy density of gasoline, and cars running on E85 (85 percent ethanol and 15 percent gasoline) get about 30 percent lower gas mileage.”
I am not so concerned about the energy density as I am the prospects for ever being able to produce ethanol from cellulose at a reasonable energy efficiency. By that, I mean this: If I start with biomass with the energy content of a million BTUs, how much ends up as usable energy?
And the money quote, which has been my argument all along:
“I’m not a lobbyist but a scientist, but if I were, I would argue for a subsidy for all biofuels and not just ethanol,” he said in an e-mail. “It’s too early to tell which route — pyrolysis, aqueous phase processing, gasification or synthetic biology — will win out; we may well have versions of all four contributing to the mix. I would simply say that lignocellulosic hydrocarbons appear to give far more promise than cellulosic ethanol.”
Without any subsidies at all, fossil fuels would kill pretty much all biofuels except for sugarcane ethanol from the tropics. If you subsidize all biofuels equally, corn ethanol can compete as a 1st generation fuel, but gasification or pyrolysis will win out over cellulosic ethanol. The energy efficiency of cellulosic ethanol relative to gasification is far too low for it to compete in the long run. I am not naive enough to think that corn ethanol is going away – it has too much support in Congress. But the 2nd generation will only see cellulosic in niche applications. Gasification is where I am placing my bet.