Selectivity and efficiency of biomimetic catalysts in a model system for pulp bleaching

Three biomimetic systems were evaluated for their selectivity in a model system for pulp. FeSO4, Fe-EDTA and hemoglobin, in the presence of H2O2, constituted the biomimetic systems. Sodium lignosulfonate and hydroxyethyl cellulose (HEC) were used as a model system to represent lignin and carbohydrate fractions in pulp. A simple kinetic model was used to determine kinetic parameters for depolymerization of each substrate. Point selectivities at two different H2O2 concentrations were evaluated on the basis of the resulting expressions. Hemoglobin demonstrated superior selectivity for lignosulfonate degradation at a high H2O2 level. The production of hydroxyl radicals from each of the biomimetic systems was measured using a chemiluminescence assay. For the FeSO4 and Fe-EDTA systems, depolymerization was related to the amount of radicals generated. The fate of reacted H2O2 was evaluated using a specially designed reactor to measure H2O2 consumed by reaction and that decomposed. To achieve a given number of chain scission in lignosulfonate, the hemoglobin system consumed the least amount of H2O2.