Optimization of bio-oil production using response surface methodology and formation of polycyclic aromatic hydrocarbons (PAHs) at elevated pressures

This paper aims at the optimization of bio-oil yield obtained from poplar sawdust pyrolysis. A response surface methodology was carried out to optimize the experimental conditions. The factors investigated were temperature, pressure and heating rate. Five levels, which were low level, upper level, center point and two axillar points, were considered for each of the factors. Statistical analysis shows that these factors significantly affect bio-oil yield. According to the model, bio-oil yield is maximized when the following conditions are utilized; a pyrolysis temperature of 528.44 °C, pressure of 1 bar, and a heating rate of 750 °C/min. Bio-oil yield decreased with increased pressure, and the maximum bio-oil yield obtained was 30.45%. The physical properties of char and chemical compositions of the produced bio-oil were then characterized. These included SEM (Scanning Electron Microscope) and GC/MS (Gas chromatography/mass spectrometry) characterization. The formation of polycyclic aromatic hydrocarbons (PAHs) from the pyrolysis of poplar sawdust was observed, taking into account the influence of pressure. Pressurized pyrolysis of poplar sawdust generated a tar range of 2-4 ring PAHs. PAHs were the dominant products at 21 and 41 bars.