Experimental Investigation of the Oxidative Pyrolysis Mechanism of Pinewood on a Fixed-Bed Reactor

Abstract

Oxidative pyrolysis of pinewood was studied on a bench-scaled fixed-bed reactor. The qualitative and quantitative analysis of oxidative pyrolysis products, including permanent gases (CO, CO2, and CH4), water, char, and tar, was conducted. Two important parameters (temperature and oxygen concentration) were taken into consideration. Results showed that oxygen improved the yields of permanent gas and water but decreased the yields of char and tar. In comparison to char and water, oxidative pyrolysis had a greater effect on permanent gas and tar yields. CO and CH4 were mostly released between 300 and 400 °C, while CO2 was produced at all of the temperature investigated. CO2 was always the dominant gas in all cases. At a relatively low temperature (300 °C), the adsorption of an oxygen molecule on the reactive center and the subsequent decarbonylation reaction lead to the production of CO2. Little CO and CH4 generated when the temperature was higher than 400 °C. Gravimetric results of pyrolysis tar indicated that the tar yield decreased from 0.3321 g/g of biomass (700 °C and 0% O2) to 0.1901 g/g of biomass (700 °C and 21% O2). Gas chromatography/mass spectrometry results showed that, under an oxidative atmosphere, primary tar components tended to be converted to secondary tar. The phenols would also be converted by the partial oxidation reaction under high oxygen concentrations. Oxygen promoted the development of the pore structure when the oxygen concentration was no more than 15%. However, oxygen would restrict the further development of the char pore under ultimate conditions, resulting from the high char combustion rate at high oxygen concentrations.