Bio-processing of Gas-to-Liquids: A Report Card

If finding microbes that can convert cellulose plant material into ethanol is of the holy grails of biofuels, an equally elusive goal is using microbes to make liquid fuels out of natural gas.

Almost everyone agrees that the best way to apply our now-abundant natural gas resources to transportation would be to convert it into a “drop-in” liquid fuel that would fit easily into our current gas-station infrastructure. T. Boone Pickens’ CleanFuels Corp. and others are trying to supply compressed natural gas to diesel trucks, but the effort has obvious impediments and will require a whole new infrastructure.

Much easier would be the direct conversion of natural gas to methanol, the simplest alcohol, which is now produced at a rate of 33 billion gallons per year for industrial purposes. But methanol still suffers from its Prohibition-Era reputation as poisonous “wood alcohol” (although gasoline is equally poisonous) and has run into stiff EPA regulations on converting contemporary engines to burn alternative fuels. (See “Making the Case for Mars and Methanol”) And so the vision has arisen that a golden gas-to-liquids pathway can be carved by the nation’s laboratories working with nature’s existing microbial stock.

A year ago, ARPA-E, the fast-track research funding agency modeled on the Defense Department’s Advanced Research Project Agency, announced a new initiative: REMOTE – the Reduced Emissions Using Methanotrophic Organisms for Transportation Energy.  Methanotrophic organisms are microbes that feast on methane, the simplest carbohydrate, and can convert it into more complex molecules such as butane or formaldehyde, which can in turn be synthesized by other microbes into butanol, methanol or other liquids that can be cleanly burned as fuels.  As the agency wrote in its Funding Opportunity Announcement (FOA):

The benefits of converting natural gas to liquid fuels for use in transportation have long been recognized. First, the existing transportation infrastructure is based on liquids, and such fuels can be conveniently “dropped in” without substantial changes in vehicles. Second, liquid fuels from methane have lower emissions than petroleum-based fuels. Liquid fuel produced from methane decreases emissions by up to 50%, compared to unconventional petroleum, and decreases particulate matter by up to 40%, compared to combustion of conventional diesel. Further, methane is responsible for 10% of the nation’s greenhouse gas emissions (on a CO2 equivalent basis), in part because its global-warming potential is 20 times greater than that of CO2 over a 100-year period. Technologies capable of capture and conversion of methane will help mitigate the global-warming potential of these emissions.

There are several interesting things going on here. First, ARPA-E has chosen the goal of reducing emissions rather than reducing dependence on foreign oil as the motivating force of the project. Alcohols do burn cleaner than gasoline. In fact, the whole California effort that put 15,000 methanol cars on the road in the 1990s was aimed at reducing air pollution, not replacing oil imports. This may satisfy environmentalists, who tend to see natural gas as just another fossil fuel and would prefer to pursue cellulosic ethanol in order to remain “carbon neutral.”

Second, although the chemical synthesis of methanol, butanol and other potential fuels is already economical, employing biotechnology gives the whole plan a “green” tinge. Chemical processes are regarded as “old economy” and unlikely to attract investment from Silicon Valley and other centers of venture capital, whereas biotechnology has a New Age sheen to it. Already ARPA-E has handed out $20 million to small startups and others have been forthcoming.

Finally, by latching onto natural gas flaring, ARPA-E is addressing a problem that is gaining more and more attention, particularly the publication of a paper in Science last week claiming that will be no climate benefits in switching from diesel and other crude-oil-based fuels to natural gas derivatives. Indeed, flaring is now said to consume the equivalent of one-third of America’s consumption of crude oil. Obviously, anything that addresses this will get attention.

So how are thing going?  Last week Robert J. Conrado and Ramon Gonzalez, two researchers in the Department of Energy, issued a progress report in Science. Basically, the news is that while there’s still lots of optimism about the idea, nothing much has been accomplished yet.

Conrado and Gonzalez note that the process of biological conversion involves three steps:   1) the “activation” of the stable methane molecule so it becomes chemically receptive; 2) the conversion of methane to formaldehyde and other intermediates; and 3) the synthesis of these intermediates into alcohols and other fuels through bioreactors. All three steps need improvement. “To access small-scale and time-varying resources [i.e., flared gas at remote wells], process intensification leading to an order-of-magnitude increase in volumetric productivities is needed and will require technological breakthroughs in [all] three areas.”

One institution that is working on the problem is the Sandia National Laboratory in New Mexico. Blake Simmons, manager of the lab’s biofuels and biomaterial science group, says the challenges are daunting but he remains optimistic. “There have been plenty of investigations into this in the past since there are plenty of organisms in nature that thrive and multiply off natural gas,” he said in an interview with Phys.org. “The problem, though, is that they exist in unique, tailored environments and are typically very slow at what they do. People have been trying to express this class of enzymes for a couple of decades, so this won’t be a slam dunk. But we have the collective experience and capabilities at Sandia to figure it out.”

And so the search for a clean, green conversion of methane to a liquid fuel goes on. In the meantime, however, it might be worth opening the door to methanol and other chemically synthesized products just as a placeholder.

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