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Effects of Various Reactive Gas Atmospheres on the Properties of Bio-Oils Produced Using Microwave Pyrolysis

Tarves, Paul C., Mullen, Charles A., Boateng, Akwasi A.
ACS Sustainable Chemistry & Engineering 2016 v.4 no.3 pp. 930-936
BTEX (benzene, toluene, ethylbenzene, xylene), Panicum virgatum, activated carbon, ammonium nitrogen, biochar, biofuels, biomass, calorimetry, carbon dioxide, gas chromatography-mass spectrometry, lignocellulose, methane, models, naphthalenes, nuclear magnetic resonance spectroscopy, oxygen, pyrolysis, synthesis gas
Fast pyrolysis of lignocellulosic biomass produces organic liquids (bio-oil), biochar, water, and noncondensable gases. The noncondensable gas component typically contains syngas (H₂, CO, and CO₂) as well as small hydrocarbons (CH₄, C₂H₆, and C₃H₈). To understand the influence of reactive gas in various pyrolysis processes, we have employed a laboratory scale microwave reactor and performed pyrolysis of switchgrass under varying gaseous atmospheres and characterized the bio-oils obtained. The batch (100 g of biomass) microwave pyrolysis was performed at 900–1000 W over the course of 7 min in the presence of a microwave absorber (10 g of activated charcoal). The products formed were quantified and the bio-oils were characterized by GC–MS, elemental analysis, Karl Fischer and TAN titrations, bomb calorimetry, and ¹³C NMR spectroscopy. Pyrolysis experiments performed under a N₂ atmosphere were used as the control and then compared to experiments performed under various reactive gases (CO, H₂, and CH₄) and a model pyrolysis gas mixture (“PyGas”). The use of a CO atmosphere had a negligible effect on the quantity and quality of bio-oils produced, whereas the use of H₂, CH₄, and PyGas atmospheres each provided more deoxygenated products (i.e., BTEX, naphthalenes, etc.) and lower oxygen content. The use of different particle sizes also displayed a pronounced effect on the product distribution and the composition of the bio-oils obtained.