Pyrolysis of pine and eucalyptus wood residues for production of biofuels and biochar

Abstract

Uganda produces 180,000 m3 of forestry wood residues of which, only 10% is utilised by the local companies while the rest are left to rot and/or openly burnt posing environmental and health risks. These underutilised residues have chemical characteristics that qualify them to be a potential source of sustainable biofuels and biochar by pyrolysis technology. Pyrolysis of these wood residues may provide an opportunity to address the energy needs of Uganda and also reduce the problems associated with the inappropriate disposal. The objective of this study was to examine the potential of eucalyptus and pine forestry wood residues in bio-fuels and biochar production through pyrolysis. The specific objectives were; (1) characterising the feedstock, (2) characterising the products, (3) investigating the effect of the pyrolysis temperature and feedstock type on the distribution and yield of products and (4) carrying out energy balance for the pyrolysis process. Eucalyptus, pine and a blended mixture of eucalyptus and pine residues were fed in a 37.6 L batch reactor and pyrolysed at final pyrolysis temperature ranges of 300-350, 400-450 and 500-5500C at a heating rate of 10 0C/min. Characterisation of tar and wood vinegar was carried out using a gas chromatograph (GC) model 7820A fitted with a flame ionization detector (FID). The chemical composition of pine and eucalyptus residues showed significant difference (p<0.05) as depicted by proximate and ultimate analysis. The results showed that the most notable compounds in the bio-oils were alcohols, acids, furans, phenols, aldehydes and ketones. The yield of biochar, tar and vinegar reduced significantly (p<0.05) with increase in temperature with the maximum (48, 12 and 6.5% respectively) produced at 300-3500C. On the other hand, the yield of non-condensable gases increased with temperature and the maximum (62%) was produced at 500-5500C. Analysis of variances revealed that the feedstock type used had no significant effect (p>0.05) on the distribution and yield of products. Results of the energy balance showed that the reactor efficiency was 78% whereas that of the pyrolysis process was 100%. The presence of the oxygenated aliphatic and aromatic hydrocarbons makes the bio-oils a potential source of transportation fuels and chemicals. The results of this study showed that pyrolysis technology can be applied to the underutilised wood residues in Uganda so as to reduce the problems associated with their inappropriate disposal and also boost the energy industry through production of biofuels.