Fractionation of hemicelluloses by membrane filtration

Hemicellulosic materials are among the most abundant renewable resources on earth, but have not yet found any broad application. However, if a cost effective extraction method is developed, hemicelluloses have the potential to be utilized to a much larger extent in the future. Ultrafiltration (UF) is a low energy demanding separation process that can be used to concentrate and purify hemicelluloses from industrial process water. In this investigation the performance of six UF membranes was studied, when treating process water from thermo-mechanical pulping (TMP) of spruce. Four membranes were hydrophobic and two hydrophilic and the cut-off was 1-5 kDa. The hydrophobic membranes were subject to severe fouling problems and had a much lower flux than the hydrophilic membranes. The hydrophilic membrane C005F, from Microdyn Nadir GmbH with cut-off 5 kDa, had the highest flux and showed the best separation capability with respect to hemicelluloses and contaminants (salts and monosaccharides). The flux was 140 l/m2.h at 0.8 MPa and 40°C. The retention of hemicelluloses was 90% and the retention of monosaccharides 3%. High flux and efficient separation of product and contaminants reduce the investment costs of a hemicellulose extraction plant.