A kinetic study of the SCWO of a sulfonated lignin waste stream

The kinetics of the supercritical water oxidation (SCWO) of a sulfonated lignin waste from an industrial source was investigated using a semi-batch, continuous-flow tube reactor. Experiments were carried out at reduced pressures from 0.9 to 1.4 and reduced temperatures from 0.9 to 1.2. In addition, the feed concentration, excess oxidant, flow rate in the reactor, and reactor length were varied to obtain a wide range of experimental residence times and conversions. The residence time and conversion data were used to calculate the reaction orders and Arrhenius parameters. The kinetic model was validated by comparison of the predicted to the experimental conversions. Overall, the results of the kinetic analysis were found to compare very favorably with those from model compound studies in the literature. Based on these results, it was concluded that the overall rate-limiting step was the oxidation of the sufonated lignin ring C-C bonds.