Pre-extraction of hemicelluloses and subsequent kraft pulping Part I: alkaline extraction

A mild alkaline treatment was applied to aspen chips prior to kraft pulping in order to extract hemicelluloses for use as biofuels. The extraction was performed at 50-90° C, and did not require costly pressurized reaction vessels. It resulted in a recovery of 40-50 kg of hemicellulose per ton of chips, and yielded the same amount of pulp after subsequent pulping of the extracted chips residue, as compared to a control cook. The pre-extraction process requires careful optimization of the pulping process, and allows shorter cooking time and lower chemical charges. Kraft pulps obtained from pre-extracted chips have a slightly higher cellulose/hemicellulose ratio, and demonstrate a small decrease in tensile index (~10%), but improved brightness and shive content. While the hemicellulose yield for this process is low, this problem is outweighed by the fact that pulp properties and pulping yield can be maintained at a high level. The recovered hemicellulose can be concentrated/isolated more easily than furfural-containing smaller fragments obtained by autohydrolysis or dilute-acid treatment.