Kraft Pulping Integrated with Mild Alkaline Pre-Extraction of Southern Mixed Hardwoods, 2008 Engineering, Pulping and Environmental Conference

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Fresh southern mixed hardwood chips were extracted with alkaline solutions containing sufficient alkalinity to approximately neutralize the acids released upon treatment of the chip-liquor mass at various elevated temperatures. The effect of alkali charge in the form of NaOH, Na₂CO₃ or green liquor and the time and temperature of the pretreatment on the extract yield and composition was investigated. The mild alkaline extraction with 3% NaOH or 3% Na₂CO₃ at 140^oC and 90 minutes led to the removal of about 6 - 8% of wood substance from the hardwood chips. When the extracted chips were pulped at different reduced effective alkali charges (12-13% EA), the pulp yield was approximately 1% lower than that of the kraft control at 15% EA. A modified pre-extraction by addition of 0.05% AQ with 3% Na₂CO₃ or 3% GL, however, increased the yield increase by up to about 1% higher than conventional kraft pulp. No significant difference in paper strength was found in handsheet tests except for a minor change in tear resistance.