(673e) Kinetics of Oxygen Delignification from Cstr and Batch Reactor Data

Many studies of the kinetics of oxygen delignification have been reported. In the past these studies were mostly performed in batch reactors whereby the hydroxide and dissolved oxygen concentrations are changing during the reaction. This makes it difficult to determine the reaction order of the different reactants in the rate expressions. Also the lignin content and cellulose degradation of the pulp are only established at the end of an experiment when the sample is removed from the reactor. To overcome these deficiencies, we have adopted a differential reactor system used frequently for fluid-solid rate studies (so-called Berty reactor). In this continuous stirred tank reactor (CSTR), the dissolved oxygen concentration and the alkali concentration in the feed are kept constant, and the rate of lignin removal is determined from the dissolved lignin concentration in the outflow stream measured by UV-VIS equipped with a flow cell. Experiments were performed at different temperatures (80¢ªC, 90¢ªC, 100¢ªC and 110¢ªC), oxygen pressures (35psig, 55psig, 75psig and 95psig) and alkali concentrations (1.1g/l, 3.3g/l, 5.5g/l and 7.7g/l). Analysis of the product stream of the CSTR provides the exact liquid composition inside the pulp sample at any given time. In addition to the dissolved lignin concentration, the TOC and methanol of the spent liquor were also measured at different reaction times. This information was used to provide further support for the concept of "peeling delignification" resulting from peeling of hemicelluloses to which lignin fragments are covalently bonded.