Violuric Acid Catalyzed Electrochemical Delignification and Bleaching of Poplar Kraft Pulp
The electrochemically mediated delignification (EM) of lignocellulosic fibers is one of new methods for fiber pulp delignification and bleaching. The choice of mediator is a key to the foundation of the delignification system. In this paper, violuric acid (VIO) was selected as a mediator to catalyze this delignification process, and the catalyzing delignification was carried out as well as subsequent bleachability of delignified pulps. The catalyzing delignification efficiency was evaluated according to pulp kappa number and viscosity. The pollution loads of bleaching effuluents were discussed. The results showed that VIO is a suitable mediator for the electrochemical delignification system. At the optimum conditions, the kappa number reduces by 5.4, from 17.4 to 11.7, and viscosity decreases from 1144cm3/g to 1059cm3/g. The alkali treatment after EM can further reduce kappa number and increase brightness of resulting pulp. The kappa number of pulp treated with EME can be reduced to 8.9 with the delignification rate of 48.8% and viscosity only decreases to 1065 cm3/g. The brightness of EM E treated pulp increases from original 39.2% ISO to 50.7% ISO. The EM treated pulps can be bleached to 80%ISO with the subsequent QP or EQP bleaching sequences at 2.0% H2O2 charge. The bleaching effluents of EMQP have lower COD and BOD than that of OQP which is considered as environmental friendly bleaching sequence.
Zhenyu Du and X.B Sun
F. G. Kong et al., "Violuric Acid Catalyzed Electrochemical Delignification and Bleaching of Poplar Kraft Pulp", Advanced Materials Research, Vols. 113-116, pp. 2067-2071, 2010