Effect of Sulphur Dioxide and Sulphuric Acid on Steam Explosion of Aspenwood

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Abstract
The use of steam explosion as a pretreatment for woody biomass prior to enzymatic hydrolysis has been proposed in the past. In this study the effect of SO2 impregnation (1.6% SO2 on dry wood input) and H2SO4 impregnation (0.58% H2SO4 on dry wood input) on the exploded substrates produced are compared with the case where no acid was added. Both acid catalysts substantially improve the survival of pentose sugars when treatments of equal severity are compared. H2SO4 however reduces the extent to which lignin may be extracted from the water washed exploded substrates with caustic. The mode of action of the SO2 has been examined and, at the levels used in this work, approximately 50% of the input sulphur is shown to bind to the substrate forming, most likely, ligno-sulphonates. The enzymic digestibilities of the acid impregnated steam exploded substrates are compared with those of the non-acid impregnated material and are shown to be more easily saccharified.