Effect of thermo-responsive switchable solvents on microalgae cells’ disruption and non-isothermal combustion kinetics

The effect of the exposure to thermo-switchable solvent (TSS) on cell wall disruption of Chlorella sp. microalgae was investigated. The combustion and kinetic behaviors of microalgae cells treated with TSS, which was maintained at its hydrophilic state for 1.5 h to disrupt the cell wall, were analyzed and compared with those of undisrupted cells. The X-ray diffraction (XRD) results showed a clear drop in the crystallinity of the TSS-treated samples, which was mainly due to the degradation of the cellulosic material. The results were confirmed from the thermogravimetric analysis, which showed a drop in the cellulosic material from 71.9% in the untreated sample to 49% for TSS-treated sample. The activation energy of TSS-treated sample from different non-isothermal models was 44.90–157.97 (FWO), 103.09–492.19 (KAS), and 100.60–478.89 kJ mol⁻¹ (Starink). The values were lower at low conversions (x ≤ 0.5) than untreated samples whose activation energy was 70.67–152.98 (FWO), 195.38–465.58 (KAS), and 190.39–453.11 kJ mol⁻¹ (Starink). The low activation energies for all models of TSS-treated samples indicate that less energy would be required for the thermal conversion processes, as compared with the untreated samples. The tested model-free methods reduce mass transfer limitations, with Flynn-Wall-Ozawa (FWO) compensating for experimental errors, whereas Kissinger-Akahira-Sunose (KAS) and Starink for providing precision to kinetic data depending on a good constant degree of conversion. The reaction mechanism was represented well by the Malek and Popescu. The results presented in this work provide deeper understanding of the effect of TSS on microalgae cell wall disruption.