Isolation of xylans from bleached Eucalyptus kraft pulp by antisolvents precipitation

The present work is focused on alkaline extraction of xylans from bleached Kraft pulp of Eucalyptus globulus, and its isolation from the alkaline extract, aiming high purity product and yields. Alkaline extraction was optimized, through the stirring speed and extraction time. A higher stirring speed increased extraction yields which varied between 65 and 85%. However, extraction time did not have influence on extraction yields. Xylans isolation was performed by precipitation with diluted acids and with various alcohol concentrations. Washing of the precipitates, to remove impurities, was performed either with water and/or with methanol. Water washing yielded xylans with purity values up to 99%, while with methanol those values were lower, in the range of 36–84%. Xylans characterization indicated average molecular weights of 16.8–22.7 kDa. The isolated xylan yields varied between 43 and 97%. Nitric acid showed to be the most adequate solvent to get pure xylan. On the other hand, in alcohol experiments lower yields were obtained due to the losses in the subsequent water washing process.