(199c) Dilute Acid Prehydrolysis and Extraction of Hemicellulose Prior to Aspen Chemi-Thermomechanical Pulping

Dilute acid hydrolysis of aspen wood chips and their bleached chemi-termomechanical pulping (BCTMP) were investigated. Aspen chips were impregnated in the pilot plant by 0.05 mol/L sulphuric acid at 60ºC. The impregnated chips were cooked at 130ºC for 10 minutes. In addition to the pilot scale study, BCTMP mill pressate samples were also collected for further chemical composition analysis and purification. Filtrate samples were analyzed and purification methods were tested for the removal of impurities and separation of saccharides in different molecular weight fractions. Acid prehydrolysis resulted in a release of higher level of xylans than glucans compared to steam impregnation. Both steam impregnation and acid prehydrolysis processes resulted in acetic acid/xylose ratios around 25-30%. Acid prehydrolyzed wood chips were refined and bleached in the pilot plant at mill operating conditions. The pre-extraction of aspen wood chips significantly reduced refining energy to a given freeness. The current drawbacks of prehydrolysis are lower brightness ceiling of 79%, lower strength and higher shives content at a given freeness. Unaffected pulp properties are bulk, surface roughness, and air resistance.