Comparative Removal of Hemicelluloses from Paper Pulps Using Nitren, Cuen, Naoh, and Koh*

Xylans were selectively removed from paper grade pulps by nitren extraction in order to produce dissolving pulps. The impact of nitren charge on the removal of hemicelluloses was demonstrated for a birch and mixed softwood kraft pulp. The 95% purity level could easily be reached for the birch kraft pulp. Softwood glucomannans were almost insoluble under the investigated extraction conditions applying nitren. Accordingly softwood pulps seem to be less suited for the nitren process. Furthermore, the selectivity of nitren extraction was compared with cuen. Nitren turned out to be much more selective in xylan removal, whereas cuen also dissolved part of the cellulose, when this solvent was applied at concentrations, which were needed to reach dissolving pulp purity. Nitren was also tested in its xylan extraction capability in comparison with sodium and potassium hydroxide. Extraction of a xylan-rich birch kraft pulp with nitren resulted into a pulp of highest purity (96% cellulose content), which could not be obtained applying KOH and NaOH. In the case of a eucalyptus kraft pulp, however, nitren and sodium hydroxide extraction resulted into a product of more or less the same cellulose content (97%). With a beech sulfite pulp as the starting material highest purities with regard to the cellulose content were obtained applying 10% sodium hydroxide (97.5%), whereas the nitren procedure yielded into a pulp of 96.5% cellulose content. This was due to the inability of the nitren procedure to remove 2.7% mannan, which was present in the initial paper pulp from beech. The residual nickel content in all pulps could be removed by a special washing procedure applying lactic acid.