Subcritical hydrothermal liquefaction of cattle manure to bio-oil: Effects of conversion parameters on bio-oil yield and characterization of bio-oil

In this study, cattle manure was converted to bio-oil by subcritical hydrothermal liquefaction in the presence of NaOH. The effects of conversion temperature, process gas, initial conversion pressure, residence time and mass ratio of cattle manure to water on the bio-oil yield were studied. The bio-oil was characterized in terms of elemental composition, higher heating value, ultraviolet–visible (UV/Vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). Results showed that the bio-oil yield depended on the conversion temperature and the process gas. Higher initial conversion pressure, longer residence time and larger mass ratio of cattle manure to water, however, had negative impacts on the bio-oil yield. The higher heating value of bio-oil was 35.53 MJ/kg on average. The major non-polar components of bio-oil were toluene, ethyl benzene and xylene, which are components of crude oil, gasoline and diesel.