Gasification of chars from orange residues and wood sawdust were studied in order to compare their reactivities using thermogravimetric analysis (TGA). Char samples were obtained by pyrolysis in a tubular reactor of quartz at a temperature of 900 °C and heating rate of 250 °C/min. The gasification of the chars using CO2 was done on a thermogravimetric analyzer isothermally at temperatures up to 950 °C, and non-isothermally at temperatures up to 980 °C. Several morphological changes due to vaporization during pyrolysis were identified by comparing the SEM images of the chars and the corresponding biomass.
The biomass particle size was below 150 µm, and the sample size low enough to reduce heat and mass transfer side effects, thus ensuring that the reaction kinetics is the limiting step. The reactivity in CO2 of both biomasses increased with conversion. However, differences in reactivity were observed between the two types of biomass. The char of orange residue exhibited a higher reactivity than wood sawdust. This could be due to the catalytic effect of the inorganic content, specifically potassium, which was found in the orange residue ash but not in the sawdust ash. The activation energies found for the wood sawdust char gasification were 197.4 and 187.7 kJ/mol for the isothermal and non-isothermal methods respectively, while for the orange residue char were 126.5 and 129.3 kJ/mol.