More About the Coskata Process



As you’ve almost certainly already heard by now, General Motors has announced a partnership with Coskata, Inc. to produce ethanol less expensively and without using food materials as feedstock for the process. This is exciting for a number of reasons. First of all, Coskata is close to completing a continuous demonstration stream at their laboratory. They also expect to have a pilot demonstration plant in place by the end of the year that will produce 40,000 gallons of ethanol. And later this year, they expect to announce the site for their first full-scale plant which will be capable of annual production of 100 million gallons of ethanol. The process also consumes less water resources (less than one gallon of water per gallon of ethanol produced) and delivers 7.7 units of energy per unit of energy used in the process.

The process relies on using anaerobic microbes that consume carbon monoxide and hydrogen and produce ethanol. Because the process uses specially bred strains of microbes, they produce ethanol exclusively, unlike other fermentation processes, which often produce a range of alcohols and which require further distillation. Furthermore, the flexibility of the Coskata process allows for other microbes to be used in the same process setup (or even a parallel setup). Other strains of microbes that produce other useful alcohols, including some used as precursors for plastic production, so that the same technology could be used in other applications to provide a petroleum replacement.

To feed these microbes, the feedstock (which can come from an amazingly wide range of sources) is turned into synthesis gas (or syngas), a mixture of carbon monoxide and hydrogen. This is just the diet the microbes in the Coskata process are hungry for. There are a number of methods that can be used for producing syngas. The basic process of gasification has been known since the 1800s. Wood gas, air gas, holzgas, and blue gas are all related products and processes. This is also the same gasification process that has gotten some discussion when talking about so-called ‘clean coal’ technology. But with a wealth of other potential feedstocks, it is likely that coal will remain on the sidelines with this proces. Still, it is part of the great flexibility of this development that so many primary sources are available to help produce ethanol.

Some recent developments have led to new processes that could also serve as a front-end for the Coskata process bioreactors. Sandia Labs’ Counter Rotating Ring Receiver Reactor Recuperator (or CR5) would use solar energy to convert carbon dioxide sources into syngas. An even more exotic method known as plasma gasification could be used even with hazardous waste sources, and would reduce those materials to inert slag (which can be safely disposed of) and syngas. Plasma gasification uses high energy plasma inside a containment vessel to break down any materials fed into it to their constituent atoms. The plasma gasification process is particularly interesting because, once it is started, the process is self-sustaining, using the high temperature output from the reactor vessel to power an electrical generator that powers the plasma lance. As long as materials continue to be fed into the vessel, the process can go on indefinitely, and it even produces a surplus of electricity. Plasma gasifiers are not cheap, but this is a technology that the Coskata founders are particularly interested in seeing paired with their system, as well.

With the variety of methods for producing syngas to feed the microbial process, the system can be tailored according to the kind of raw materials that are going to be used at a particular facility. If the feedstock is going to be agricultural waste, then a simple gasifier is all that is needed at the front end of the process. But, if a more variable and uncertain waste stream (such as factory or municipal solid waste) are going to be used, then a plasma gasifier is likely a better choice.

The Coskata process is also very scalable. It would be possible, for example, for a retrofit coal-fired power plant to install cleaner coal technology, and use off-peak periods (when the syngas being produced was not needed for electrical generation) to feed Coskata bioreactors and produce ethanol. This dual use is another way in which the Coskata process may be a very flexible and useful technological development in the next few years.

Note: GM paid for my travel to attend a background briefing about this program before the official announcement.

About the Author

Philip Proefrock is an architect and photographer in southeast Michigan. He is also a LEED Acredited Professional.

His professional involvement with green building includes working as project architect for the award-winning Malletts Creek Branch Library for the Ann Arbor District Library, which received the 2005 AIA Michigan Sustainable Design Award, and which was the first completed commercial vegetated roof (green roof) in the state of Michigan.

He is an active member of Green Drinks Michigan/o2 Network. In addition to being lead writer for Green Building Elements, he is also a contributing writer for and for

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