3-27: Hemicellulose hydrolysis in South America lignocellulosic biomass by steam explosion

Hemicellulose from lignocellulosic materials constitute a large potential source of fermentable sugars to be used for fuel production. Sources from the Bolivian Altiplano include e.g. Paja Brava (Stipa ichu), quinoa straw (Chenopodium quinoa Willd.) and Curupaú (Anademanthera columbrin). Those sources all have a high carbohydrate content and are already used for various purposes. The aim of the present study was to determine conditions for a good recovery of hemicellulose, primarily pentose, sugars from these materials. The three feedstocks were subjected to steam explosion using different catalyst agents. The Paja Brava and quinoa straw were SO₂-impregnated (2.0 to 2.5% w/w) and steam pretreated at temperatures between 190 and 200^oC, and holding times of 300 to 600 s. Curupaú hardwood, on the other hand, was hydrolyzed with dilute sulfuric acid (H₂SO₄ = 0.5 – 1.5 % (w/w) at a temperature of 180 to 210 °C, and a holding time between 300 and 600 s.
Acid hydrolysis gave a good recovery of pentose sugars with only minor amounts of degradation products in terms of furan compounds. Only minor proportion of the lignin was solubilized. At the conditions in the study, SO₂ was the most effective catalyst tested for extraction of xylose. The quinoa and Paja Brava gave the highest xylose yields, 62% and 65%, respectively. A reasonable xylose yield (58%) was also found from the Curupaú. Acid catalyzed steam explosion thus appears to be a suitable pretreatment process for extraction of hemicellulose sugars from these feedstocks to be used in fermentation processes.