Colloidal properties of bio-oils obtained by vacuum pyrolysis of softwood bark. Characterization of water-soluble and water-insoluble fractions

Crude bio-oils obtained via the pyrolysis of bark residues are dark, viscous, and sticky materials that visually appear similar to homogeneous liquids. However, microscopic tests revealed the presence of tridimensional compounds (agglomerates) and solid particles that are dispersed in the continuous bio-oil medium. These materials are responsible for the increase in bio-oil viscosity, the non-Newtonian flow behavior, the poor combustion properties, the corrosiveness, and the increase in the plugging frequency of the nozzles. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) tests, and rheology have been used to evaluate the colloidal properties of the bio-oils. The generic composition of the bio-oil, obtained by extracting water-insoluble materials (i.e., the lignin-derivative compounds), has been determined. The extraction produced a yield of lignin-derivative compounds of 29 wt %. The chemical composition of the water-soluble materials, as well as the molecular weight distribution of the water-insoluble components, has also been determined.