Non-isothermal decomposition kinetics of lipids recovered from oleaginous microbial biomass ( C. vulgaris and L. starkeyi ): reaction mechanism and TGA-MS analysis

Oleaginous microorganisms and the thermal decomposition of their recovered lipids are new attractive research fields for the sustainable production of biofuels from actual biomass. In this work, the thermal decomposition of lipids from C. vulgaris and from L. starkeyi was investigated using a thermogravimetric analyzer coupled to a mass spectrometer (TGA-MS) under non-isothermal conditions. Thermal decomposition was examined using the one-step reaction model. Integral, differential, and advanced isoconversional methods were implemented to analyze the conversion-dependent activation energy. The Friedman method resulted in an accurate and reliable estimation of the kinetic parameters. The activation energy showed a strong dependence on conversion from 123.5 to 246 kJ mol -1 for lipids from C. vulgaris and from 80.3 to 299.9 kJ mol -1 for lipids from L. starkeyi. The generalized master plot approach evidenced that the thermal decomposition of lipids from C. vulgaris proceeds via three-dimensional diffusion (D 3 —Jander’s equation). Also, the kinetic analysis indicated that Valensi’s equation (D 2 ), controlled by a two-dimensional diffusion model, is the most likely mechanism for the thermal decomposition of lipids from L. starkeyi . The rate parameters were evaluated via a kinetic compensation plot. Ion temperature evolution was investigated by TGA-MS revealing many of the functional groups evolved in the range of 350–500 °C as C1–C7 aliphatic hydrocarbons, aromatic hydrocarbons, aldehydes, carboxylic acids, and furan derivatives. All these aspects favor the lipid biosynthesis from microbial biomass to potential lipid-based building blocks.