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April 07, 2008

More details on the Coskata process for converting garbage into fuel (Cellullostic ethanol)

Costaka's process combines both biological (i.e., microbes) and thermochemical (heat and chemicals) processing. This could potential convert existing biomass sources in the United States to provide 35% of current fuel usage.

Coskata can use a wide variety of feedstocks for making fuel: wood chips, weeds and non-food crops like miscanthus, human waste, and carbon-heavy garbage (such as tires). Biomass, ideally easy-to-grow crops that don't require much water, will likely be the primary feedstock. The ability to exploit various feedstocks reduces exposure to crop failures or shortages. Coskata, which has received an investment from General Motors, also makes fuel from the lignin in biomass. Some companies making ethanol from strictly biological processes can't use lignin to make fuel.

Conceivably, Coskata could even produce fuel from the carbon monoxide from steel mills. If you could capture all of the carbon monoxide that comes out of mills worldwide, you could make 50 billion gallons of fuel a year, or close to a third of the U.S. annual consumption of fuel.


I had a prior article on the Coskata process and company.

The first stage in Coskata's process revolves around converting the feedstocks into synthetic gases. The different feedstocks can be segregated and processed differently. Waste can be converted to gas with plasma technology, for instance, while plant matter can be gasified with less energy-intensive methods. This allows the company to optimize on different gasification processes.

Once the syngas is produced, it is fed to microbes that convert it to liquid fuels. The microbes live in large colonies that collect on membranes. Fuel is produced when the gas passes through the membrane. Part of the company's intellectual property revolves around coming up with a way to let the microbes live as colonies and form slimes.

Less distillation. Microbes can create a fluid that is 15 percent alcohol or so by volume but can't get it to 99 percent purity on their own. That's why distilled spirits are stronger than beer.

Rather than fully distill the fluid, Coskata will distill to about 50 percent and then employ a membrane from Membrane Technology Research in Menlo Park to purify it the rest of the way. This cuts processing costs and energy. Coskata actually doesn't need the membrane to get to $1 a gallon. "This is gravy," Roe said.

Coskata primarily wants to earn revenue and profits from licensing the technology to big companies. like large forestry concerns, petroleum producers, and chemical manufacturers.

The Cosksta process cuts greenhouse gas emissions by 90 percent (complete fuel lifecycle) compared with gas. It also uses less water than most ethanol processes, which rely on food crops.

The Coskata $1 a gallon figure is how much the fuel will cost to produce. It includes the cost of the feedstock, the cost of the energy required to convert raw materials into fuel, and labor. It does not include paying off the capital of the facilities, taxes, retail mark-ups, or other expenses that can be added as the fuel wends its way through distribution. An adjusted price is around $1.50 a gallon.

FURTHER READING
Zeachem combines thermochemical and biological processes in a different manner.

Popular Mechanics description of the process

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