Thermogravimetric analysis on combustion behavior of marine microalgae Spirulina platensis induced by MgCO3 and Al2O3 additives

Abstract

The impact of MgCO3 and Al2O3 additives on the thermal behavior of Spirulina platensis (SP) biomass during combustion in a thermal analyzer was evaluated to understand their catalytic effect in the decomposition process. The samples were pure SP and a mixture of SP and additives at mass fractions of 3, 6, and 9 (wt, %). Each sample of around 8.5 mg was mounted in a thermobalance and subjected to a furnace on a heating program of 10°C/min. The 100 ml/min air atmosphere was kept continuously flowing during the combustion process from 30-1200°C. The thermal behavior of the sample was then characterized from the thermogravimetric (TG) and derivative thermogravimetric (DTG) curves, those were recorded by a computer during the experiment. The Horowitz-Metzger method was used to evaluate the impact of additives on the kinetic parameters of the samples. The results indicated that the presence of additives shifted the main decomposition stage toward a lesser temperature. The rate of mass loss (ML) in the main decomposition zone decreased in the 1st peak and increased in the 2nd, in accordance with the increase in the fraction of additives. This indicates that additives play different roles during the decomposition process. The mass mean activation energy (Em) increased at the additive fraction of 3% for both MgCO3 and Al2O3, as well as at 6% MgCO3 compared to combustion with no additives. Conversely, the presence of greater additives promoted a shift in Em toward smaller values. These results confirm that both additives significantly influenced the thermal behavior and kinetics of the SP combustion.