Identification of volatile organic compounds in the gaseous fraction from soybean residue pyrolysis.

GABRIEL IMWINKELRIED,; CARLA FERMANELLI; CLARA SAUX; BLANCO MARÍA BELÉN

Simposio; 26th International Symposium on Gas Kinetics and Related Phenomena; 2022

The depletion of non-renewable raw materials has motivated biomass valorization for energy production. Some agro-industrial wastes, including soybean hulls, are processed through a thermochemical transformation process at high temperatures and in an inert atmosphere -pyrolysis- leading to the formation of biochar, bioliquid and a gas fraction as products1. The identification of volatile organic compounds (VOCs) in the gas fraction is essential to predict air quality impacts by the study of their gas-phase reactions with atmospheric oxidantsIn this work, the experiments were performed by triplicate in a temperature range of 400-600 °C for 10 min with N2 flow of 60 ml/min into a fixed-bed glass tubular reactor located inside an oven. The gases were captured in a collapsible Tedlar chamber of 5 liters capacity in order to capture and preconcentrate the gas sample through the solid-phase microextraction (SPME) technique to finally be desorbed in a mass chromatograph coupled to mass spectrometry (GC-MS). Figure 1 depicts the predominance of aromatic hydrocarbons (such as toluene, ethylbenzene, phenol), oxygenated compounds (such as 2-methylpropanal, 2-methylbutanal, 3-methylbutanal), alkanes (heptane and octane), alkenes (such as 1-hexene, 1-octene, 2-octene) and furans (2-methylfuran and 2,5-dimethylfuran) as the main chemical compounds for the range of reaction temperatures.The highest relative chromatographic area (RCA) is represented by aromatic hydrocarbons with methylbenzene as the major compound with 22% RCA at 500 °C. Figure 2 illustrates the performance of the three pyrolysis reaction products, where the maximum production of bioliquid (44%) and syngas (34%) is achieved at 600 °C. In contrast, the production of biochar is maximized at 400 °C (62%) over the other two fractions. This performance has been previously demonstrated for the pyrolysis of this biomass.2Finally, soybean residues pyrolysis causes a great diversity of VOC's, where methylbenzene is the most prevalent compound for all temperatures, an aromatic hydrocarbon of high relevance due to human health and environmental hazards. On the other hand, the increase in pyrolysis temperature is directly proportional to the production of the bioliquid and gas fractions.