In recent years, an overproduction capacity of paper-grade pulps, coupled with the global economic crisis, has resulted in the closure of many pulp mills in Europe and North America, where production costs are too high compared to those in Asian and Latin American countries. Simultaneously, the demand for dissolving pulps, mainly for their conversion to cellulose regenerated fibers, has more than doubled over the last decade. The removal of hemicelluloses to upgrade paper pulps may be accomplished by several methods, i.e., enzymatic, caustic extraction, ionic liquids. Recently, we have also suggested that water extraction of paper pulps (water post-hydrolysis) in a flow-through reactor could be used for their conversion to high-purity cellulosic pulps and for the recovery of the extracted hemicelluloses. Our experimental work with birch Kraft pulp shows that up to 240 °C, increasing post-hydrolysis temperature favors the removal of xylan over the degradation of cellulose. Above 240 °C, however, increasing temperature has negligible effects on the selectivity of xylan removal, and thus it would not be recommended due to increased energy requirements. Under selected process conditions, the properties of post-hydrolyzed pulp are similar to those required in viscose pulps. Moreover, the xylan in the aqueous hydrolysates can be quantitatively recovered as xylo-oligosaccharides, but the total recovery yield increases with flow rate. Currently, the structural characterization of the pulps and their performance during conversion to viscose and IONCELL-F fibers is being investigated. The degree of polymerization of the XOS is also determined for their potential use as prebiotics. Finally, the effects of post-hydrolysis on the energy requirements and quality of nanofibrillated cellulose (NFC) produced from the pulps are being assessed.

Post-hydrolysis of birch paper-grade pulp to produce high-purity cellulosic fibers and xylo-oligosaccharides

251st National Meeting (2016)

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