Extraction of xylan from wood pulp and brewer’s spent grain

• Alkaline extraction of pure xylan from birch kraft pulp was optimized.
• The best conditions yielded 16.1 wt.% xylan and 82.4 wt.% extracted pulp.
• 90% of applied sodium hydroxide was recycled by ultrafiltration.
• In the extraction of BSG, lipids and protein were co-extracted with arabinoxylan.

Hemicelluloses are potential raw materials for different types of biobased materials. Alkaline extraction of bleached birch kraft pulp yields pure, high molecular weight hemicellulose (xylan) and hemicellulose-poor pulp. In this work, the concentration of alkali and the extraction temperature were studied as parameters for xylan yield and mass balance in the extraction. Extraction at room temperature using 1 molar aqueous sodium hydroxide (NaOH) showed the highest value for the mass balance with 98.5 wt.% on dry matter of pulp – 16.1 wt.% xylan in the extract and 82.4 wt.% extracted pulp. Recycling of 90% of the NaOH used for the extraction was demonstrated by ultrafiltration. The ultrafiltration process is thus a highly potential tool offering an economical way to simultaneously recycle chemicals and separate products from process liquids in xylan extraction and other biorefinery processes. The concept of alkaline extraction was also demonstrated for brewer’s spent grain (BSG). Arabinoxylan comprised 80% of the carbohydrates in the alkaline extract of BSG. However, the selectivity of the extraction was poor as proteins, lipids and some lignin were also efficiently extracted from BSG in alkaline conditions.