Low-temperature pyrolysis of CCA-treated wood: thermogravimetric analysis

A thermo-analytical study of untreated and chromated copper arsenate (CCA) treated wood samples is performed in order to obtain a better understanding of the low-temperature pyrolysis of CCA-treated wood waste in an inert atm osphere. The type of wood used in this study is Finns sylvestris sapwood. T he influence of the presence of CCA and the heating rate on the pyrolytic b ehaviour of wood samples is studied, as well as the release of volatile com pounds and metals (Cr, Cu, As) during the pyrolysis process. This paper sho ws that CCA has a significant influence on the thermal behaviour of wood sa mples, which is more pronounced the higher the CCA concentration of the sam ple is. The temperature at the onset of pyrolysis, as well as the temperatu re where the maximum rate of decomposition occurs, are lowered by the CCA t reatment. The final char yield (including the metals) is higher and the rat e of weight loss is much more peaked for CCA-treated wood. It could be post ulated that the CCA compounds act as promoters of the pyrolysis reactions f avouring the formation of char. For higher heating rates, there is a shift of the DTG peak to higher temperatures for both untreated and CCA-treated w ood samples. Within the accuracy of the evolved gas analysis (EGA) method a pplied, it is observed that the presence of CCA does not significantly infl uence the type and relative amount of measured volatiles. The volatilisatio n of metal compounds is shown to be strongly dependent on temperature and r esidence time of the wood sample at a given temperature. A critical point ( 10 min at 400 degrees C) exists, below which the release of Cr and Cu is ne gligible and the release of As is below 10%. Above this critical point (lon ger times at 400 degrees C), there is a dramatic increase in metal release for all three metals. The CCA concentration itself also has an influence in the sense that higher concentrations in the original sample give higher re lative concentrations of metals in the resulting pyrolysis residue. (C) 199 9 Elsevier Science B.V. All rights reserved.