Violuric Acid Catalyzed Electrochemical Delignification and bleaching of Poplar Kraft Pulp

摘要

The electrochemically mediated delignification (E_M) 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 1144cm~3/g to 1059cm~3/g. The alkali treatment after E_M can further reduce kappa number and increase brightness of resulting pulp. The kappa number of pulp treated with E_ME can be reduced to 8.9 with the delignification rate of 48.8% and viscosity only decreases to 1065 cm~3/g. The brightness of E_ME treated pulp increases from original 39.2% ISO to 50.7% ISO. The E_M treated pulps can be bleached to 80% ISO with the subsequent QP or EQP bleaching sequences at 2.0% H_2O_2 charge. The bleaching effluents of E_MQP have lower COD and BOD than that of OQP which is considered as environmental friendly bleaching sequence.