Energy sorghum pyrolysis using a pressurized batch reactor

This paper tries to assess process yields by performing conventional pyrolysis at an elevated pressure of energy sorghum using a high-pressure batch reactor and evaluates the corresponding product characteristics, respectively. Pyrolysis was performed at 6.9 bar (100 psi) at different temperatures from 400 to 600 °C with heating rates of 4 °C/min. The changes in temperature did not affect the product distribution but significantly affected product characteristics. The H/C molar ratio of bio-oil is at 1.51 while the O/C molar ratio was six times lower than the O/C molar ratio of the sorghum biomass (0.11 vs. 0.67). About 50 % of the bio-oil is composed of aliphatic hydrocarbons (i.e., alkanes and alkenes) and aromatic compounds (i.e., phenolic and benzene derivatives). The carbon distribution lies between C₈ and C₄₄ while the distribution of straight chain alkanes exhibited a maximum in the range of C₈ to C₂₁, which is found to be in the range of gasoline and diesel fuels. The product bio-char from sorghum biomass is a carbon-rich material with C concentrations of 49 to 52 %wt and was classified under the low- to medium-volatile bituminous coal group according to ASTM standard D388. Lastly, the produced non-condensable gas consisted mainly of CH₄ and CO₂ with small amounts of CO, H₂, and C₂H₆.