In the past, oxygen delignification studies were mostly performed in batch reactors, whereby the caustic and dissolved oxygen concentrations are changing during the reaction. 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, a differential reactor system (called Berty reactor) has been adopted. 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 spectroscopy. The delignification rate is found to be first-order in HexA-free residual lignin content. The delignification rate reaction order in [NaOH] and oxygen pressure are 0.412 ± 0.060 and 0.305 ± 0.260 respectively. The activation energy is 54.5 ± 6.8 kJ/mol. © 2007 American Institute of Chemical Engineers AIChE J, 2007
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