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

Abstract

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-1and3, 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 691.42kJ/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.