Non-isothermal pyrolysis of de-oiled microalgal biomass: Kinetics and evolved gas analysis

•Non-isothermal pyrolysis of de-oiled microalgal biomass were evaluated by TGA-MS.•Iso-conversional and model-fitting kinetics were applied for thermal decomposition.•Evolved gas analysis were evaluated during pyrolysis.•Three-stage thermal decomposition & three-zone volatilization of organic matters.•Pyrolysis involved multi-step reactions & 3D growth rate with random nucleation.

Non-isothermal (β = 5, 10, 20, 35 °C/min) pyrolysis of de-oiled microalgal biomass (DMB) of Chlorella variabilis was investigated by TGA-MS (30-900 °C, Argon atmosphere) to understand thermal decomposition and evolved gas analysis (EGA). The results showed that three-stage thermal decomposition and three volatilization zone (100-400 °C, 400-550 °C and 600-750 °C) of organic matters during pyrolysis. The highest rate of weight-loss is 8.91%/min at 302 °C for 35 °C/min heating-rate. Kinetics of pyrolysis were investigated by iso-conversional (KAS, FWO) and model-fitting (Coats-Redfern) method. For Zone-1 and 3, similar activation energy (Ea) is found in between KAS (α = 0.4), FWO (α = 0.4) and Avrami-Erofe'ev (n=4) model. Using the best-fitted kinetic model Avrami-Erofe'ev (n=4), Ea values (R2 = >0.96) are 171.12 (Zone-1), 404.65 (Zone-2) and 691.42 kJ/mol (Zone-3). EGA indicate the abundance of most gases observed consequently between 200-300 °C and 400-500 °C. The pyrolysis of DMB involved multi-step reaction mechanisms for solid-state reactions having different Ea values.

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