In pyrolysis reactions, methanol arises from the breakdown of methyl esters and/or ethers from the decomposition of pectin-like plant materials 137.38]. Methanol also arises from the methoxyl groups of the uronic acid. The acetic acid, formed in the thermal decomposition of all three main components of biomass, comes from the elimination of acetyl groups originally linked to the xylose units, while furfural is formed by dehydration of the xylose units. Quantitatively and 1-hydroxy-2-propanone 1-hydroxy-2 butanone are present in high concentrations in the liquid prod- ucts. These two alcohols are partly esterified by the acetic acid. other compounds are formic and propionic acids, 1-hydroxy-2 and 2-furfuradeyde. In addi- 1-hydroxy-2-butanone propanone, tion to water, other low-molecular weight polar compound such as hydroxy acetaldehyde, acting also as solvent is present.