Gas-liquid mass transfer in laboratory oxygen-delignification reactors

Liquid-phase mass-transfer coefficients were measured in two laboratory reactors used widely to estimate kinetic data for oxygen delignification. The liquid-phase mass-transfer coefficients were determined using a variant of the sulphite-oxidation method. The variables pulp consistency, stirring speed and pulp suspension mass were studied. Values for the volumetric mass-transfer coefficients were determined to range between similar to 0.001 and 0.01 s(-1) depending upon the reactor geometry and process conditions. A new mass transfer term named specific mass-transfer coefficient is introduced to account for the partial filling of the reactors with pulp. It is based on the oxygen-transfer rate per unit mass of the pulp and allows comparison between the laboratory reactors and industrial towers. A pseudo-steady-state analysis showed that the oxygen-delignification experiments reported previously were not mass transfer limited.