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Characterization of bio-oil, syn-gas and bio-char from switchgrass pyrolysis at various temperatures

Imam, Tahmina, Capareda, Sergio
Journal of analytical and applied pyrolysis 2012 v.93 pp. 170-177
Panicum virgatum, biofuels, biomass, carbon, carbon dioxide, carbon monoxide, carbon sequestration, coproducts, elemental composition, emissions, energy, ethane, ethylene, gas chromatography-mass spectrometry, heat, hydrogen, lignocellulose, methane, nitrogen content, oils, oxygen, ozone, pyrolysis, soil quality, sulfur, surface area, temperature, transportation, viscosity
Pyrolitic conversion of lignocellulosic biomass, such as switchgrass and other agricultural residues, to bio-fuels is being considered for national energy security and for environmental advantages. Bio-oil, syn-gas and bio-char were produced and characterized from switchgrass at 400, 500 and 600°C by pyrolysis. Bio-oil yield increased from 22 to 37%, syn-gas yield increased from 8 to 26%, and bio-char yield decreased from 48 to 25% with increases of pyrolysis temperatures from 400 to 600°C. Bio-oil heating value was 36.3MJ/kg, density was 920kg/m³ and viscosity was 10 cST. GC–MS study indicated that the bio-oil contained 37% oxygenates that can be upgraded to transportation fuel in future research. Syn-gas compositional analysis shows that, with increasing pyrolysis temperature, CO₂, CO, C₂H₄ and C₂H₆ contents increased, whereas H₂ and CH₄ contents decreased. Part of the syn-gas consisting of H₂, CO and CO₂, when converted to syn-fuel, can be beneficial to the environment; sulfur free, presence of oxygenates results in less CO emissions and ozone to the atmosphere. Bio-char may be used as a co-product to enhance soil quality, and for carbon sequestration. Analysis of elemental composition and physical properties of bio-char show increase in carbon content, decrease in oxygen, hydrogen, and nitrogen content, and increase in surface area and pore volume with increases of pyrolysis temperature. The optimized pyrolysis process for bio-oil production in this study will help meet future goals of oil upgrading to produce transportation fuel.