Investigation on the pyrolysis of cow bone as a catalyst for ozone aqueous decomposition: Kinetic approach

Abstract

In this study, the feasibility of using pyrolysis of cow bone (PCB) as a catalyst for ozone aqueous decomposition was investigated. PCB, a new catalyst prepared under laboratory conditions, was used for ozone aqueous decomposition in a fluidized bed reactor (FBR) with liquid recirculation using a pump. The catalytic effect of PCB and the relevant parameters of this heterogeneous catalyst on ozone decomposition were investigated. The chemical composition of PCB samples was analyzed by X-ray fluorescence (XRF), which showed that the PCB was composed of CaO, P2O5, MgO, SiO2, Na2O, K2O and MnO. Results of ozone aqueous decomposition indicated that ozone decay rates, for both self and heterogeneous ozone decomposition, accelerated with increasing the pH of the solution. A first-order kinetic model fit the self and heterogeneous decays of ozone the best. tert-Butyl alcohol (TBA) was employed as a radical scavenger during the experiments. In heterogeneous catalytic ozone decay, results indicated that the ozone decay rate was less affected by TBA at an alkaline pH. The contribution of a radical reaction mechanism on the ozone decay rate was subsequently determined. Results showed that the ozone decay rate increased due to surface catalyzed radical reactions. At pH values higher than the pH of the point of zero charge (pHPZC) of the PCB, ozone interactions with strong Lewis acids (LA) on metal oxide surface sites of the PCB, as well as rates of aqueous ozone decay, increased. These findings suggested that the ozone decomposition reaction mainly took place on the PCB surface and that the surface chemistry of the PCB played a key role in the performance of the catalytic process.