Multifunctional Alkaline Pulping, Delignification and Hemicellulose Extraction

In this study, multifunctional alkaline pulping was suggested to produce different pulp grades at one mill site, ranging from high-yield paper pulp to high-purity dissolving pulp. In all process modifications, sulfur was successfully replaced by anthraquinone. Autohydrolysis and alkaline pre-extraction were applied to Eucalyptus globulus wood chips, followed by kraft and soda-AQ pulping. Alkaline pre-extraction prior to soda-AQ pulping largely preserved the pulp yield, while a substantial amount of xylan could be extracted in polymeric form during the pre-treatment. The resulting pulp revealed characteristics indicating an alternate use – as paper pulp and as dissolving pulp – after further purification with cold caustic extraction (CCE). The removal of hemicelluloses from kraft or soda-AQ paper pulps by a CCE post-treatment allowed the production of high yield dissolving pulps. The hemi-rich CCE-lye was recycled to soda-AQ pulping, contributing to yield increase by xylan re-precipitation. Alternatively, the CCE-lye could be purified efficiently by ultrafiltration, by concentrating the rather pure and high molecular weight xylan in the retentate for further use. The results indicated that biorefinery concepts can be realized for alkaline pulping by adopting the proposed modification of multifunctional alkaline pulping.