Study on the solubilization capacity of bio-oil in diesel by microemulsion technology with Span80 as surfactant

Bio-oils obtained from liquefaction/pyrolysis of biomass have undesired properties such as high water content (15-25 wt.%), high oxygen content (low heating value), high corrosiveness (acidity) and instability. Therefore, they cannot be directly adopted for fuel applications. Solubilizing bio-oil in diesel by microemulsion technology is one of the most convenient approaches for further upgrading bio-oil. In this work, a synthetic bio-oil was prepared to overcome the limitation posed by complex nature and instability of crude bio-oil. Effects of several microemulsion parameters on the solubilization capacity of bio-oil in diesel were evaluated, including initial bio-oil/diesel volume ratio (B/D ratio), surfactant concentration (Span80), cosurfactant type (n-butanol, n-pentanol, n-hexanol, n-heptanol and n-octanol) and the mass ratio of cosurfactant/surfactant (C/S ratio). The optimum bio-oil/diesel volume ratio was 5:5. The proper concentration of Span80 was 0.36 M. N-octanol was certified as an ideal cosurfactant. A proper C/S ratio of 0.40 was suggested. Meanwhile, fuel properties of bio-oil/diesel microemulsion were examined, including heating value, density, kinematic viscosity, cloud point, pour point, water content, corrosivity and stability. Elemental analysis and thermogravimetric analysis of bio-oil/diesel microemulsion were conducted. Compared with the original synthetic bio-oil, the bio-oil/diesel microemulsion had more desirable fuel properties close to diesel.