Isolation and purification of concentrated and non-concentrated hemicellulose alkaline extracts

The membrane used in the concentration step, UFX5pHt, (MWCO 5 kDa), has an average flux of 30 L/h/m2 for previously optimized conditions of cross flow velocity (1 m s−1) and operating pressure (6 bar). Xylans were isolated from the concentrated filtrate using two different methods: neutralization/precipitation with HNO3 (7.5 N), and precipitation with methanol (20, 30, and 50 wt/wt%). For the concentrated filtrate a reduction of up to 61% in the consumption of nitric acid for the precipitation was achieved. On the other hand, products of lower purity were obtained with methanol as precipitating agent. The molecular weights of the obtained xylans were determined by SEC leading to values between 24,100 and 31,000 Da.