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

Abstract

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 technical-economic assessment of integrated kraft pulp biorefineries.

Keywords

• Kraft cooking
• Hemicellulose
• Xylan pre-extraction
• Green liquor extraction
• White liquor extraction
• NaOH extraction
• Sulfur balance
• Sodium balance