Extraction and Isolation of Hemicelluloses from Agricultural and Forestry Waste Streams

Abstract: New methods and products must be developed to reduce our dependency on fossil fuels, to reduce global warming. In this work, methods of extracting and isolating hemi¬celluloses from agricultural and forestry waste streams have been studied. Hemi¬celluloses are biodegradable polymers that can replace fossil-fuel-based products for use in various applications, such as barrier films and hydrogels. Arabinoxylan was extracted from barley husks, wheat straw and barley straw, by steam pretreatment, and then further concentrated and purified by conventional filtration, microfiltration and ultrafiltration. Xylan yields of 25 to 50 wt%, based on the content in the raw material, were achieved in the steam pretreatment stage by optimizing the operating conditions. The pH should be kept above 8 and a severity factor of about 4 used to obtain a high yield of arabinoxylan with large molar mass. The extraction of hemicelluloses from agricultural residues can be combined with ethanol production, which could be of great interest in future biorefineries. Galactoglucomannans were extracted from process water from a thermo¬mechanical pulp mill. These hemicelluloses were isolated by common filtration combined with membrane filtration. Drum filtration and microfiltration were used to remove solids and ultrafiltration to concentrate and purify the hemicelluloses. A hemicellulose concentration above 60 g/l was achieved with a purity of about 80%. The process developed is very promising, indicating that hemicelluloses could be produced at a cost of roughly €600 per tonne, although further work is required to prove the concept on a larger scale.