ABSTRACT
The objective of this study was to assess the impact of removing hemicelluloses from chips of eucalyptus wood by self-hydrolysis treatment (H O) on the subsequent ‘kraft’ process behavior and pulps bleachability and quality. The self-hydrolysis treatments were conducted at temperatures of 152°C (30, 45 and 60 minutes); 160°C (15, 30 and 45 minutes); and 170°C (5, 10, 15, 20 and 30 minutes); water: wood ratio of 4:1 m3/t. Normal chips (reference) and self-hydrolyzed chips at 170°C during 5, 15 and 30 minutes were submitted to ‘kraft’ cooking up to kappa number 16 - 18 and the resulting pulp was bleached using the O/OD (EPO) DD sequence. According to the results obtained, self-hydrolyzing the chips at 170°C for 30 minutes allowed the removal of up to 60% hemicelluloses. Cooking yield of the self-hydrolyzed chips for 30 minutes was around 6% smaller and pentosan content 88% lower than that of the normal chips. The efficiency of delignification with oxygen of the pulp derived from self-hydrolyzed chips for 30 minutes was of 75%, compared to 43.6% of the reference-pulp, and the bleaching cost using the O/OD (EPO) DD sequence was US$ 7/adt per pulp, lower that of the reference-pulp. The effluent originated from bleaching the pulp derived from the self-hydrolyzed chips presented lower values of COD (39.6%), color (21.3%) and AOX (51.6%), compared to that of the reference-pulp
Keywords:
self-hydrolysis; hemicellulose removal; xylans; cooking yield