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Energy & Fuels 2004, 18, 188-201
Colloidal Properties of Bio-Oils Obtained by Vacuum Pyrolysis of Softwood Bark. Storage Stability Tuya Ba, Abdelkader Chaala, Manuel Garcia-Perez, and Christian Roy* De´ partement de Ge´ nie Chimique, Universite´ Laval, Sainte-Foy, Que´ bec G1K 7P4, Canada Received June 6, 2003
Bio-oil obtained via the vacuum pyrolysis of softwood bark residues is a multiphase, viscous, unstable system composed of water-soluble and water-insoluble fractions. Using centrifugation, the bio-oil can be separated into an upper layer (ca. 16 wt %) and a bottom layer (ca. 84 wt %). The upper layer exhibits low contents of water, solid, and ash, as well as a low density, a low acidity, a high content of methanol-insoluble materials, a high viscosity, and a high calorific value. The physicochemical properties of the bottom layer are similar to those of the whole biooil, except the bottom layer contains greater contents of ash and water. Microscopic analysis of the bio-oil has revealed a multiphase complex colloidal system that is composed of solid particles, three-dimensional structures, and droplets. The upper layer represents the dispersed droplet phase, which is rich in waxy materials (fatty and resin acids) and water-insoluble compounds. It is the upper layer that, overall, provides the unique colloidal properties to this type of bio-oil. The morphology of the bottom layer is similar to that of the bio-oil matrix. The presence of microstructures in the whole bio-oil has been revealed by differential scanning calorimetry and rheology. The microstructures (e.g., waxy materials) in the bio-oil matrix are, in part, responsible for the bio-oil high viscosity and non-Newtonian behavior that is observed at low temperature (50 °C before it can be stored, handled, processed, and burned. Acknowledgment. This project has been supported by NSERC. The authors wish to thank Pyrovac International for the pyrolysis tests, as well as Mrs. Micheline Gingras and Mrs. Joanne Lagace´ for the laboratory analyses. Thanks are also due to Dr. X. Lu for the DSC analysis, Dr. J. Yang for the TGA tests, and Dr. H. Pakdel for the GC-MS analysis. EF0301250
