Comparative evaluation of autohydrolysis and acid-catalyzed hydrolysis of Eucalyptus globulus wood

Three different acids (acetic, oxalic and sulfuric acid) were tested for their catalytic activity during the pretreatment of Eucalyptus globulus wood comparatively to autohydrolysis in order to extract valuable products prior to kraft pulping and to reduce lignin precipitation in the pretreatment step. The utilization of oxalic and sulfuric acid reduces treatment temperatures at a given wood yield as compared to autohydrolysis and acetic acid addition and thus decreases the insoluble lignin content in the hydrolyzates. Due to the high temperatures of autohydrolysis xylose dehydration to furfural occurs at high wood yield losses, while during acid catalyzed hydrolysis degradation of cellulose to glucose is more pronounced. The main difference between the acid catalyzed and non-catalyzed reaction constitutes the ratio of monomeric xylose and xylooligosaccharides in solution.

► Autohydrolysis of Eucalyptus globulus releases water soluble xylooligomers.
► Oxalic and sulfuric acid catalyze consecutive hydrolysis to monomeric xylose.
► Pretreatment intensity is not affected by the addition of acetic acid.
► Less insoluble lignin during acid hydrolysis. Soluble lignin is not that affected.
► Soluble lignin in hydrolyzate derives from acid-soluble lignin in wood.