Thermal analysis and devolatilization kinetics of cotton stalk, sugar cane bagasse and shea meal under nitrogen and air atmospheres

Thermal degradation, reactivity and kinetics for biomass materials cotton stalk (CS), sugarcane bagasse 1 (SB1), sugarcane bagasse 2 (SB2) and shea meal (SM) have been evaluated under pyrolysis (N2) and oxidising (dry air) conditions, using a non-isothermal thermogravimetric method (TGA). In the cases of CS and SB1 the peak temperatures were 51 °C higher for pyrolysis compared with oxidative degradation, whereas for SB2 and SM the difference was ∼38 °C. However, the differences in the rates of weight loss were significantly higher under oxidising conditions for all the materials studied. Maximum rate of weight loss (% s−1) under pyrolysis conditions ranged from 0.10 to 0.18 whereas these values accelerated to the range of 0.19–0.28 under oxidising conditions, corresponding to respective peak temperatures. Samples ranked in order of reactivity (RM × 103) (% s−1 °C−1) are CS = 1.31 ≈ SM = 1.30 > SB2 = 1.14 > SB1 = 0.94 for air and CS = 0.54 > SB2 = 0.49 > SB1 = 0.45 > SM = 0.31 for nitrogen. Shea meal exhibited a complex char combustion behaviour indicating that there may be two distinct types of char derived from fibrous and woody components in the original material. Activation energy calculations were based on the Arrhenius correlation.