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Making valuable chemicals out of methane

Viral nanowires: Catalyst developer Siluria uses viruses to create novel nanowire catalysts. Shown here is a single nanowire
Viral nanowires: Catalyst developer Siluria uses viruses to create novel nanowire catalysts. Shown here is a single nanowire.
Image Credit: Siluria.

Converting methane directly to valuable chemicals and liquid fuels is an industrial challenge that has defied the best minds in chemistry. Now catalyst developer Siluria Technologies claims to have solved the problem.

Siluria's solution is a catalyst that efficiently turns methane into ethylene, the feedstock underpinning more than two-thirds of global chemical production. The Menlo Park, California-based firm, which raised $3.3 million from venture capital firms last year and expects to announce further financing this month, says it succeeded with a brute-force trial-and-error process that tested novel compounds with catalytic potential. "The problem is too difficult to analyze your way out of. We're overwhelming the problem instead with a simple, sturdy experimental technique," says Alex Tkachenko, Siluria's CEO.

A cheap and efficient way of turning methane into liquid chemicals and fuels could free the chemical industry from its dependence on pricier and dirtier petroleum. But knocking off one of the four hydrogen atoms arrayed around methane's sole carbon atom requires so much energy that the process tends to run out of control, burning up the entire gas molecule. "If you can't stop it, you end up with CO2," says Charles Musgrave, a computational chemist at the University of Colorado.

The quest to activate methane's chemical potential has left a path of unrequited chemists. Catalysis design firm Catalytica spent five years and over $10 million to develop a sophisticated catalyst and process to turn methane into methanol, but its process proved too costly. And in 2008, Dow Chemical put up over $6.4 million for methane activation research led by teams at Northwestern University and the U.K.'s Cardiff University. "Dow had gone as far as they could. It's a sign of how hard this problem really is that they're going out and funding others in this way," says Musgrave.

How might Siluria have outsmarted the chemists? By enlisting mindless viruses to handle the catalyst design. Its workhorse is a virus that's 900 nanometers long and just nine nanometers in diameter. The virus can serve as a template for the formation of equally small nanowires when it's exposed to metals and other elements under the right conditions. Siluria can create an endless variety of potential catalysts by mutating the virus's protein coat so its surface guides nanowire formation, selecting the ratio of elements introduced to that template, and tweaking the timing and conditions of the process. To detect efficient methane activation catalysts, Siluria then subjects these structures to screening.

Siluria's discovery system was invented by MIT bioengineer Angela Belcher, who developed it further in a startup called Cambrios Technologies, which she cofounded. The system was then spun out into Siluria in 2008, when Cambrios focused in on commercializing a transparent electrode for solar cells and other electronic devices. Tkachenko says 95 percent of Siluria's effort is now devoted to the methane-to-ethylene process.

The company came out of stealth mode this summer because it had identified a novel nanowire catalyst that it believes could be commercially viable. Erik Scher, Siluria's vice president for R&D, says that Siluria's nanowire catalyst can activate methane at "a couple of hundred degrees" cooler than the best existing catalysts, which he says operate between 800 °C and 950 °C.

Relatively mild conditions should deliver two benefits, he says. Not only should they keep the methane from burning up, they also mean that the resulting methyl radicals are more likely to stay on the surface of the nanowire in the company of other methyl radicals, which can then react with each other to form ethylene rather than flying off the nanowire to engage in other reactions--including ones that degrade the precious ethylene product.

Tkachenko says the catalyst, if applied widely to ethylene production, could cut costs to the chemical industry by tens of billions of dollars annually and reduce global carbon-dioxide emissions by over 100 million tons per year. The company hopes to use its anticipated financing to move into the pilot process next year. Validation with a lab scale reactor running continuously for thousands of hours would then lead to commercial demonstration plants, hopefully in less than five years--an aggressive pace for a major chemical process.

Experts such as Musgrave say there are plenty of potential pitfalls. Even if Siluria's catalyst selectively converts methane to ethylene at high yield, he says, it may fail to generate ethylene fast enough to make the process commercially viable. "They might have solved the selectivity problem, but might end up sacrificing the turnover," says Musgrave.

Roy Periana, director of the Scripps Research Institute's Energy and Materials Laboratories in Juniper, Florida, and the chemist who led Catalytica's methane activation effort, says throughput is critical to pay for the multibillion dollar cost of a chemical plant. And the impact has to be "revolutionary," says Periana. "They're not about to get rid of their billion dollar plant for a 5 to 10 percent improvement," he says.

Source: Siluria Technologies via Technology Review /...

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