Feedstock-Dependent Thermogravimetric Kinetic Screening across Six Representative Biomass Types and Apparent Kinetics of a Volcanic-Derived Iron-Rich Mineral for Biomass Chemical Looping Applications

Natural iron-rich minerals are potential low-cost alternatives for biomass direct chemical looping (BDCL) systems, but their interactions with different biomass feedstocks remain poorly understood. This study evaluated Badar stone, a volcanic iron-rich natural mineral from Indonesia, against synthetic Fe2O3 using six representative biomass feedstocks, consisting of three lignocellulosic biomasses, namely rice husk, sawdust, and sago waste, and three microalgal biomasses, namely Aurantiochytrium, Euglena, and Spirulina. Thermogravimetric analysis (TGA) under N2 was employed to examine devolatilization behavior and interactions between char and OC. A mass balance-based multistep kinetic model was used to assess thermal decomposition and apparent kinetic behavior across 400–800, 800–1000, and 1000–1300 K. Biomass devolatilization dominated the TG response at low and intermediate temperatures, while clearer biomass–oxygen carrier differences appeared at higher temperatures. Rice husk showed limited sensitivity to Badar stone loading, with sums of fitted apparent activation energies of 367.1–369.5 kJ/mol. Sawdust showed stronger oxygen carrier dependence, with the corresponding value decreasing from 371.1 kJ/mol with Badar stone to 307.2 kJ/mol with Fe2O3. Spirulina exhibited the highest values among the microalgal biomasses, reaching 416.2 kJ/mol with Badar stone and 429.3 kJ/mol with Fe2O3. Badar stone produced broader and more gradual high-temperature TG responses, whereas Fe2O3 produced sharper responses. These results demonstrate that the apparent thermochemical behavior depends strongly on both biomass type and oxygen carrier composition, providing a basis for selecting biomass–mineral combinations for subsequent cyclic and reactor-scale evaluation.