Effect of Integrating Xylan Extraction from E. grandis into the Kraft Pulping Process on Pulp Yield and Chemical Balance

Kraft mills have the potential to pre-extract hemicellulose from wood as another value added product. The impacts of pre-extracting xylan on pulp and handsheet properties, sodium and sulfur balances, and chemical make-ups in the kraft pulping process of Eucalyptus grandis were assessed. Xylan extractions using white liquor, green liquor, and NaOH were done under varying extraction times, temperatures, and alkaline concentrations; residues were subsequently pulped at 170 C for 45 min. The highest xylan yield (15.15% w/w) was obtained with 2 M NaOH, at 120 C for 90 min followed by white liquor (13.27% w/w), utilizing 20% AA at 140 C for 90 min. Green liquor extraction with 2% total titratable alkali (TTA), at 160 C and an H-factor of 800 produced the lowest yield (7.83% w/w). However, the green liquor extractions were the most practical for integration into the kraft process due to their limited effect on pulp yield and properties of handsheets produced from the pre-extracted woodchips and the sulfur and sodium make-up increase. White liquor extractions would favour high pulp yield with low kappa number and reduced chemical charge and cooking time. These results are important for technicaleconomic assessment of integrated kraft pulp biorefineries.