I'm no chemist, but much of my work revolves around biochar. I've always understood it with the following rough approximation:
$$ \ce{CH2O (dry plant matter) + heat -> black carbon + H2 + CO + CH4 + hydrocarbons} $$
I've got two questions:
Is the above a decent approximation? In what ways is it misleading (as all approximations always are)?
A colleague recently told me that methane is only formed in this reaction when there is water vapor present -- he said that it mixes with CO at high temperature to form the methane. Is this true? Will one not get any methane from oven-dried biomass that is exposed to heat in the absence of oxygen?