An improved model for the kinetics of non-oxidative hydrothermal process

Abstract

Hydrothermal processing as a post-treatment technology for sludge has attracted great interest globally as it could reduce the amount of sludge considerably. This experimental study developed a comprehensive kinetic model of cellulose degradation via non-oxidative hydrothermal processing at various temperatures (ranges 180-260 °C). Values of activation energies and pre-exponential factors were determined using chemical oxygen demand (COD)-based lumped concentrations. In this study, a new reaction pathway between solid, soluble matter and gaseous products was proposed which not only enables prediction of solid phase degradation but also can predict the formation of various types of products (in liquid and gas phase) during the reaction time. The results show that the reaction rate of cellulose to liquid products (k₁=2.7×10⁹exp(-102810RT)) were fast compared to that of for liquid products to gaseous products (k₂=4.4×10³exp(-64629RT)). Moreover, the model infers that the major part of solid degradation leads to the formation of the gaseous product with the reaction rate constant of k₃=5.7exp(-12905RT). The proposed model can provide an opportunity to predict the performance of the non-oxidative hydrothermal processing of organic solid waste.

Keywords: Kinetics; Non-oxidative hydrothermal process; Organic solid; Reaction pathway.