Soda delignification of mixture of spruce and pinewood chips with the catalytic effect of anthraquinone.

Abstract

A semilogarithmic dependence of the effect of the anthraquinone (AQ) addition level within 0.05-1.0% on the weight of spruce and pinewood chips mixture (75:25) has been verified in soda process. The following resulting pulp characteristics are involved: Kappa number, Kappa number reduction, lignin content, lignin content reduction, carbohydrate content, and viscosity. The quality characteristics of soda-AQ-based pulps are affected vitally by the AQ addition level and alkali concentration. At an equal AQ charge a higher delignification selectivity will be obtained through the application of an increased active alkali charge (18% Na2O on wood), this being expressed in the yield-to-lignin unit ratio in contrast to a lower active alkali charge (16% Na2O on wood). At an identical delignification selectivity during soda pulping with the catalytic effect of AQ a higher degradation of carbohydrates will occur, expressed in the viscosity reduction, than during kraft delignification.Mechanical properties expressed in the tear index to breaking length relationship of the soda-AQ based pulps delignified by 16% Na2O active alkali with 0.3-1.0% AQ addition are identical with or even better than those present in kraft pulps. Pulps produced by delignification with 18% Na2O active alkali and 0.3-1.0% AQ addition give mechanical properties similar to those of kraft pulp.