Slow pyrolysis of CCB-treated wood for energy recovery: Influence of chromium, copper and boron on pyrolysis process and optimization

This paper investigates the effect of copper, chromium and boron on the slow pyrolysis of CCB-treated wood. A mixture of softwood has been impregnated with several inorganic salts (individually CuSO4, KCr(SO4)2, B4Na2O7) and with salt of CCB (mixture of CuSO4, KCr(SO4)2 and H3BO3). The weight loss of samples is identified by thermogravimetric analysis (TGA). The results show a higher mass of final residue and a decrease in degradation temperature on treated wood compared to untreated wood. TGA results also show that, the maximum degradation of CCB treated wood occurs at 300 °C. In addition, slow pyrolysis experiments were carried out in a laboratory scale reactor. The pyrolysis products were quantified using analytical balance whereas gases were analyzed by gas chromatography. The trends of weight loss obtained by TGA and by laboratory scale pyrolysis are similar. Furthermore, it is observed that CCB salts inhibit the formation of CO and CO2 but promote that of H2. In the second part of this work, yield of solid pyolysis residue (charcoal) with a high metal content (Cu, Cr, B) has been carried out at 300 °C and 370 °C during residence time of 20 and 30 min. Metals in charcoal are analyzed using Inductively Coupled Plasma Mass Spectrometry. Taking into account the energy recovery of by-products, slow pyrolysis at 300 °C and 30 min appears to be optimal conditions with a high yield of charcoal about 45% and the element recovery is up to 94% of Cu, 100% of Cr and 88% of B.