A mass transfer study of the wet oxidation of cellulose

Abstract

The wet oxidation (WO) process is currently receiving attention as a promising solution to increasing levels of waste production. Although this process has been investigated from different perspectives, the importance of mass transfer as one the main influencing parameters in the design and development of the process has largely been ignored. This study employed a classical Shrinking Core Model to study WO of cellulose (as a model compound). The relative contributions of mass transfer and reaction kinetics to the overall reaction rate were studied in experiments performed at different temperatures and mixing rates, ranging from 220 to 260 °C and 350–700 rpm respectively. The dimensionless Hatta number was used as the criterion for determining the contribution of reaction kinetics and mass transfer to the overall reaction rate. Contrary to the assumption that mass transfer is insignificant, mass transfer was found to contribute up to 37% of the overall rate of the WO process, with higher contribution seen at higher temperatures and lower mixing rates. The Hatta number of >0.02 at higher temperatures (≥250 °C) confirmed this finding, indicating an undeniable role for mass transfer. The model presented in this paper provides an opportunity for predicting limiting steps of the WO process and can be applied in the design and optimisation of the process.