As we can sense from Figure 9.1, bio-oil is free-flowing. Its low viscosity is
due to its high water content. Also, it has an acrid, smoky smell that can irritate
eyes with long-term exposure. With a specific gravity of ~1.2, bio-oil is heavier
than water or any oil derived from petroleum. A comparison of its physical
and chemical properties with those of conventional fossil fuels is given in
Table 9.3.
An important feature of bio-oil not reflected in Table 9.3 is that some of
its properties change with time. For example, its viscosity increases and its
volatility decreases (Mohan et al., 2006) with time. Some phase separation and