Pyrolysis of Switchgrass (Panicum virgatum L.) at Low Temperatures within N2 and CO2 Environments: Product Yield Study

Bioproducts and biofuels production from pyrolysis might benefit from recycling CO2, within the process instead of using conventional inert gases such as N-2. In this study switchgrass (Panicum virgatum L.) was pyrolyzed within CO2, and N-2 environments at 300, 400, and 500 degrees C for 2.5 min in a labscale fixed-bed reactor of 25 g/batch capacity. Chars, liquids, and noncondensable gases were monitored and characterized and yields were compared. A significantly lower liquid yield was observed at 300 degrees C-CO2, in comparison to a 300 degrees C-N-2, environment, which was reflected with the char volatile content being higher under 300 degrees C-CO2, and within the elemental composition of the solid and liquid products. Carbon dioxide also showed an effect at 500 degrees C, where liquid and gas yields significantly reduced and increased, respectively. At 400 degrees C-CO2, CO concentrations were lower and CO2, was higher compared to the levels at 400 degrees C-N-2, while at 500 degrees C-CO2, CO concentrations were higher, CO2, was lower, and CH4 was lower compared to levels at 500 degrees C-N-2. At 500 degrees C, a significant ash content reduction with respect to original biomass was observed only in the CO2, environment, suggesting that CO2, may effect inorganic content and subsequently the feedstock conversions since some feedstock inorganic elements are known to play a catalyst role along these reactions. Additional tests were conducted by following regular 500 degrees C tests with a char air quench. This resulted in a char specific surface increase of about 20 times; CO2, and N-2 initial environments confounded.