IN-SITU ELECTROCHEMICALLY MEDIATED OXYGEN DELIGNIFICATION OF WOOD PULP WITH A MANGANESE(III) AMINOPOLYCARBOXYLATE COMPLEX

The manganese complex Mn(III)CyDTA [(trans-1,2- -hexane-1,2-diamine-N, N,N',N'-tetraaceto)manganate (III)] was used as the redox catalyst for the in situ electrochemically mediated oxygen bleaching of softwood k raft pulp. Three hour bleaching runs at 101 kPa oxygen pressure, pH 9. 0, 80 degrees C, 6 mM manganese, with 1 L of pulp suspension at 1% con sistency gave the following results: in the presence of an initial con centration of 1.4 mM Mn(III)CyDTA employing a graphite plate anode (A = 58 cm(2)) with a current density of 102 A/m(2), the kappa number dro pped from 30.0 to 15.0, while the viscosity decreased from 34.6 cP to 20.5 cP. Under similar conditions the ''blank'' run, i.e., without MnC yDTA and current, brought about only a 9.4% decrease in kappa number, from 30.0 to 27.2, while the viscosity dropped slightly, from 34.6 cP to 30.3 cP. The effects of Mn concentration, CyDTA/Mn molar ratio, oxy gen, temperature, pH and current on delignification and carbohydrate d egradation, were studied in parametric and factorial experiments. The results show that Mn(III) promotes delignification mainly through seco nd- and third-order interaction with oxygen and a temperature, while C yDTA is working as a carbohydrate protecting agent. The anodic current continuously regenerates the Mn(III) to support the delignification p rocess.