Fast pyrolysis of pretreated wood

During the 1980`s, several research groups reported the fact that pyrolysis in a non-oxidizing atmosphere of wood that had been prehydrolyzed with dilute acid allowed a substantial depolymerization of the cellulose to occur to give anhydrosugars. More recent work has shown that only deionization of the wood is necessary, and not necessarily a partial hydrolysis. The indigineous alkaline inorganic cations contained in the wood (principally calcium and potassium) have a profound effect on the mechanism of thermal decomposition of the cellulose and hemicellulose fractions. Also, it has been known for many years that alkaline cations are efficient oxidation catalysts for biomass. We have explored the possibility that oxidation reactions in fast pyrolysis of prehydrolyzed, or of deionized, biomass may be altered much more for carbohydrates than for lignins. Results obtained show that fast pyrolysis of pretreated biomass with controlled levels of oxygen will selectively oxidize lignins with relatively little effect on anhydrosugar yields. This partial oxidation approach generated needed heat in situ. As well, by removing a substantial fraction of the lignin-derived material from the pyrolysis liquid, the recovery of anhydrosugars for use as fermentable sugars or as chemicals is simplified.