Pyrolysis of switchgrass (Panicum virgatum L.) at low temperatures in N2 and CO2 environments; a study on chemical composition of chars extracts and bio-oils

With the increasing value addition applications of biomass pyrolysis char such as a soil amendment or feedstock for subsequent thermochemical conversions, chemical composition of char extracts becomes a necessity. Along this study, switchgrass (Panicum virgatum L.) was pyrolyzed using two distinct gas vectors, N2 vs. CO2, at 300, 400 and 500 °C for 2.5 min in a 25 g/batch fixed bed reactor using a 55 °C/min preheating stage temperature ramp. Chars were extracted with dichloromethane using Soxhlet, and these mixtures, in common with pyrolytic liquids were analyzed by GC–MS. With respect to temperature, the process performed at 500 °C resulted in a significantly lesser amount of char extracts as compared to the ones produced at 300 and 400 °C respectively. Differences were observed with respect to gas environments at the 3 operating temperatures. Among the differences, the pyrolysis performed at 300 °C under CO2 lead to higher char extracts content compared to N2 environment (9 vs. 6 mg/g char). Chars obtained at 300 °C-CO2 had a significantly lower calorific value compared to those from 300 °C-N2 (22.2 vs. 24.5 MJ/kg respectively). At 400 °C, furfural was only found in char extracts from N2 gas inflow environment, while in bio-oil, it was also found at significantly higher relative content under N2 vs. CO2. The char extracts as well as condensable chemical compounds have demonstrated predominant levels of phenols, cyclopentanones derivatives and furan-derived compounds.

► Switchgrass pyrolysis was conducted within a fixed bed reactor in CO2 vs. N2 atmospheres.
► Chars were extracted by Soxhlet using dichloromethane solvent.
► Char extracts and bio-oils were analyzed by GC–MS and their content identified.
► Char extracts content was significantly higher at 300 and 400 °C than 500 °C.
► Differences in chemical compositions were observed at all temperatures studied for CO2 vs. N2 atmospheres.