(684d) Experimental Determination of the Physicochemical and Structural Evolution of Biomass Particles during Combined Pyrolysis and CO2 Gasification

Physicochemical and structural evolution characteristics of biochar and its precursor poplar wood sawdust biomass, using a novel approach of combined pyrolysis-CO₂ gasification, was investigated. A prominent feature of this study is the recycling of CO₂ in using it as a gasifying agent, an approach which is not widely investigated in the past compared to char gasification in other environments such as air, steam and oxygen. The study was performed at a temperature range of 100°C to 800°C, with the aim of investigating the behavior at the seldom investigated lower temperatures and then progressing gradually to higher temperatures. Different analytical techniques that include thermogravimetric (TGA) analysis, ultimate analysis, elemental analysis, Fourier transform infrared (FTIR) spectroscopy, X-Ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface analysis and scanning electron microscopy (SEM) were carried out in an effort to bring insight and new understandings in this area. The combined pyrolysis-CO₂ gasification at 800^oC led to a final char weight of 9.82 % compared to 15.57 % for a pyrolysis-only study in the TGA analysis. This conformed to the findings from the gasification with a tubular reactor. The gasification with the tubular reactor showed further that the combined pyrolysis-CO₂ gasification led to the production of more syngas and less char. SEM analysis showed the existence of well-defined pores distributed on biochars surface, which increased from 100^oC to 800^oC. FTIR spectroscopy was characterized by functional groups absorption bands of cellulose and hemicelluloses in the low temperature biochars which gradually disappeared in biochars generated at higher temperatures. The pyrolysis-gasification temperature from 100°C to 300^oC did not yield a significant increase in BET surface area, however, at 400^oC, the BET surface area increased drastically to 37.438 m²/g and continued the upward trend up to 800^oC. XRD confirmed the presence of two narrow pronounced and intense peaks at the 2θ angles of 20.86° and 26.60° for the biochars generated at 200°C and 400°C. As the pyrolysis-gasification temperature increased, the biochar displayed distinctive amorphous characteristics. The results of this study clearly show the influence of temperature changes and combined pyrolysis and CO₂ gasification on the physicochemical and structural evolution of poplar sawdust biomass and derived biochar.