Pretreatment of wood and cellulose for production of sugars by fast pyrolysis

Abstract

The liquid products (tars or sirups) obtained from the fast pyrolysis of cellulosics show a wide variation in composition depending on the cellulosic feedstock used. Native cellulose in wood gives significant yields of hydroxyacetaldehyde and other low molecular weight oxygenated compounds but low yields of anhydrosugars, while highly altered microcrystalline cellulose gives the reverse. Experimental results from fluidized bed fast pyrolysis are given for poplar wood and for a number of types of cellulose produced by different processes. It is shown that high anhydrosugar yields can be obtained by fast pyrolysis at atmospheric pressure. The effect on product nature and yields as a result of different pretreatments of the wood or cellulose before pyrolysis is also reported. From these observations, as well as from the variation of product yields with temperature for one cellulose product, possible mechanisms for the primary decomposition of cellulose are proposed. Two major parallel pathways appear to account for the yields of major products. The content and nature of inorganic salts and the degree of polymerization of the cellulose play an important role in determining the relative importance of these two decomposition pathways, at least in the medium temperature range, 400 to 550°C.