Separation of Hemicelluloses from NNGL Extract using Ultrafiltration

Materials and methods The extraction in the present research was carried out using North Eastern USA (NE) mixed hardwood chips at 160 °C for 2 hours, a liquor-to-wood ratio of 4 L/kg, and green liquor charge of 2.25% (as Na2O on dry wood). Pilot scale rotating digesters were used in the extraction. The extract was characterized by pH, dry solids matter, sugar composition and organic acids concentration after hydrolysis using a Shimadzu SCL-10A High Performance Liquid Chromatography (HPLC). The molar mass distribution was determined using an HPLC modified for Gel Permeation Chromatography (GPC). However, it was not possible to separate hemicellulose polymers from lignin in the chromatogram. Soluble lignin concentration was determined using UV analysis at 280 nm, particle size and zeta potential using a Malvern ZetaSizer. Zeta potential of NNGL extract was measured both in permeate and deionized water. Results and discussion The NNGL extract fouled the membrane severely and the fluxes were very low compared to that with pure water. The flux halved in an hour even at the low transmembrane pressure. Fouling seemed to arise from solutes adsorbed in the membrane pores rather than from cake build up on the membrane. The fluxes were lower at 80°C than at 40°C, especially at high pressures. This was unexpected since the liquid viscosity decreases with increasing temperature. The membrane behaved normally when increasing the temperature but filtering pure water. Increasing temperature increased fouling tendency when filtering NNGL extract possibly due to increased movability of foulants in the membrane. The temperature also worsened somewhat the permeate quality. VTT TECHNICAL RESEARCH CENTRE OF FINLAND www.vtt.fi