List of 7 Next-Gen Biofuels According to Popular Mechanics

celluosic ethanol biological method

Process*: Raw biomass is typically ground up and pretreated in an acid steam bath before soaking in a massive hot tub for several days. Enzymes break down rigid cellulose into simple sugars like xylose, similar to the sweetener in toothpaste, which can be fermented by yeast or bacteria; it is then distilled into fuel-grade ethanol.
Bottom Line: Fermenting cellulose currently involves a lot of water and several time-consuming steps, adding to expense. The first commercial facility is expected to open in Iowa by late 2011.
Innovators: Iogen (backed by Shell), POET, SunEthanol, Verenium
Freshwater Usage:** 3 gallons
Energy Yield***: 66%


celluosic ethanol biological method

Process*: Cornstalks, garbage and even old tires are blasted with several-thousand-degree heat in an anaerobic chamber. With no oxygen, biomass can’t combust. Instead, feedstocks break down into carbon monoxide, hydrogen and carbon dioxide. This synthesis gas, or syngas, is cleaned, cooled and either ingested by bacteria or mixed with catalysts to produce ethanol and other alcohols.
Bottom Line: This method uses substantially less water and provides greater yields, but it has yet to be scaled to levels that compete with the ethanol fermentation industry. Plants are set to open in Pennsylvania and Georgia in late 2009.
Innovators: Coskata (backed by GM), Range Fuels
Freshwater Usage:** 1 gallon
Energy Yield***: 66%


algal biodiesel

Process*: Specially selected or genetically modified strains of algae are grown in enclosed bioreactors—tubes or plastic bags filled with water—and fed waste CO2 from heavy emitters like coal-fired power plants, cement kilns or breweries. The algae are then separated from water by centrifuge, and the oil is extracted with a solvent. It is then processed in
Bottom Line: Algae produce thousands of gallons more oil per acre than crops such as soy or palm, but growing and processing them at scale still present challenges. A number of U.S. facilities are slated to come on line by 2012.
Innovators: GreenFuel, HR Biopetroleum (backed by Shell), Solazyme, Solix
Freshwater Usage:** None
Energy Yield***: 103%


green gasoline

Process*: Simple sugars—either derived from breaking down tough, cellulosic feedstocks or from sources such as sugarcane—are reacted over solid catalysts to remove the oxygen locked inside their molecules and form high-energy hydrocarbons. Like crude run through traditional refineries, raw sugar feedstocks are separated to create the range of molecules in the fuels we know as gasoline, diesel and jet.
Bottom Line: Green incarnations of today’s fuels are the holy grail, but until cellulose can be cheaply converted to simple sugars, domestic potential will be limited. Virent hopes to have its gas in car tanks by 2012.
Innovators: Virent (backed by Shell and Honda)
Freshwater Usage:** None
Energy Yield***: 100%


biobutanol

Process*: Like ethanol, biobutanol is fermented by microorganisms from sugars, which are broken down from raw feedstocks and mixed with water. But for this process, the microbes have been genetically modified to produce an alcohol with a longer chain of hydrocarbons. Since butanol doesn’t mix with water at high concentrations, the finished fuel can be stored easily and transported within existing gasoline pipelines.
Bottom Line: Butanol is the rocket fuel of alcohols, but it has traditionally been derived from petroleum. Plants to produce it cheaply from renewable sources by 2012 are in the works in the U.S. and U.K.
Innovators: Cobalt Biofuels, Dupont (backed by BP), Gevo, Tetravitae Bioscience
Freshwater Usage:** N/A
Energy Yield***: 90%


designer hydrocarbons

Process*: By swapping out natural genes for synthetic ones, scientists trick microorganisms such as E. coli and yeast into converting simple sugars to diesel, gasoline and jet fuel instead of into fats or alcohols. As in traditional ethanol production, microbes ferment the sugars (in this case, from sugar cane) in a slurry, but since finished fuels don’t mix with water, the hydrocarbons are easily separated by centrifuge without expensive distillation.
Bottom Line: Designer fuels are ready to drop into engines, but unless they’re made in a closed-loop system, they’re water-intensive. The first commercial plant will be located in Brazil and is expected to start producing diesel in 2010.
Innovators: LS9, Amyris
Freshwater Usage:** 3 gallons
Energy Yield***: 106%


fourth gen fuels

Process*: Scientists have genetically engineered algae not just to turn CO2 into oil, but to continuously excrete that oil directly into the surrounding water. Since oil floats, harvesting it becomes simple work compared with the energy-intensive drying and extraction traditionally used for typical algae, which store oil within their cell walls. As with second-generation methods, the oil can then be processed into biodiesel.
Bottom Line: If they can perform at scale, these mutant algae may well be game changers. Synthetic Genomics hopes to have commercial amounts of biodiesel on the market within five years, though no plants have been built yet.
Innovators: Synthetic Genomics
Freshwater Usage:** None
Energy Yield***: 103%

* May vary slightly from company to company.
** Gallons per gallon of fuel, based on early projections; amount may vary depending on final production process.
*** Compared to a gallon of gasoline.