If, however, they are subjected instead to pyrolysis a process of controlled burning in a low-oxygen atmosphere the result is charcoal, a substance that is mostly elemental carbon.

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Meanwhile, Kior last month said it received EPA approval for a drop-in replacement fuel from wood chips using a pyrolysis process adopted from the oil refining business.

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When heated in the absence of oxygen (a process called pyrolysis), keratin forms hollow tubular structures six millionths of a metre across and riddled with microscopic pores, much like carbon nanotubes.

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The two other possibilities, which were ruled out, were on-island heat treatment - in an incinerator, gasification or pyrolysis plant - or a further stage of processing to produce a fuel product, which would also be shipped off-island.

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