INFLUENCE OF GREEN LIQUOR AND HOT WATER PRE-EXTRACTION OF HARDWOODS ON KRAFT PULPING

摘要

Mixed hardwood chips were pre-extracted with green liquor and hot water prior to kraft pulping. The hot water extraction rate was higher by a factor of 1.3 compared to extraction with green liquor solution corresponding to 3 % Na2O charge on ODW. The total monosaccharides content in hydrolysed hot water extract was approximately twice higher than in hydrolysed green liquor extract at the same wood weight loss. The total kraft pulp yield decreased with increase of wood weight loss in pre-extraction. Pulp yield from green liquor pre-extracted chips was approximately the same as from original chips, while pulp yield from hot water pre-extracted chips at 10 % wood weight loss was by about 4 % lower. Addition of 0.1 % AQ in kraft pulping of pre-extracted chips increased total pulp yield by about 1%. Effective alkali charge in kraft pulping was reduced by 3 % in kraft pulping of green liquor pre-extracted chips, and by 1 % of hot water pre-extracted chips in comparison with original chips. The fibre characteristics of kraft pulps from green liquor pre-extracted chips at 10 % wood weight loss were only slightly lower as of kraft control pulps at the same kappa number. Fibre strength (FS number), length (L number) and bonding ability (B number) of pulps from hot water pre-extracted chips were lower by about 3 %, and by about 6 % respectively for bonding ability as fibre characteristics of kraft control pulps. Strength properties of pulps from pre-extracted chips showed similar dependencies. Tensile index of pulps from hot water pre-extracted chips decreased by about 12 %, burst index by about 15 % and tear index by about 5.5 % in comparison with kraft control pulps at a same kappa number.