| Summary: | A redox cycle involving a manganese gluconate complex and oxygen in an aqueous alkaline media was investigated for its ability to delignify chemical pulp. Current applied at a cathode was used to reduce the higher oxidation states of the manganese complex. The reaction of the manganese (II) and (III) complex forms with oxygen is believed to produce hydrogen peroxide. Evidence presented in this study suggests a redox cycle was operating involving the manganese III and IV oxidation states of the manganese complex, oxygen and sufficient current. It is thought hydrogen peroxide produced in this redox cycle was responsible for the larger Kappa number and viscosity reductions observed in experimental runs employing the manganese gluconate complex/oxygen redox cycle, than in corresponding runs in the absence of the manganese complex/oxygen redox cycle. For a pulp consistency of 1 %, in 1 M sodium hydroxide, with oxygen purge, for 3 hours at 50°C and atmospheric pressure, the presence of the manganese gluconate complex and sufficient current on a platinised titanium cathode reduced the pulp Kappa number from 29 --> 17 and the viscosity from 33 --> 20 cP. In the absence of the complex and current the pulp Kappa number was reduced from 29 -- > 20 while the viscosity was reduced from 33 -- > 29 cP. The manganese complex/oxygen redox cycle did not significantly enhance the delignification or cellulose degradation reactions in factorial experiments at 20 °C or 90 °C. At 20 °C it is believed that increased peroxide stability prevented the delignification and cellulose degradation reactions. The formation of free radical species being necessary in peroxide delignification. At 90 °C it is believed the increased activity of the hydroxide ions and oxygen mask any effect of peroxide produced in the manganese complex/oxygen redox cycle. Abstract
The presence of a contaminant, likely copper or iron ions, in the reactor is believed to cause the larger viscosity drop in experimental runs where the contaminant was present. It is thought that the copper and iron ions increased the production of free radical species in the bleaching mixture, thus promoting cellulose degradation. === Applied Science, Faculty of === Chemical and Biological Engineering, Department of === Graduate
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