Catalytic pyrolysis of spirulina platensis residue (SPR): Thermochemical behavior and kinetics

Abstract

The pyrolysis characteristics of Spirulina platensis residue (SPR) with silica-alumina catalysts were investigated using thermogravimetric analysis (TGA). The effects of differing amounts of catalysts on thermochemical behavior and kinetics parameters (pre-exponential factor in Arrhenius equation [A] and activation energy [Ea]) were studied. The experiment was carried out from 30 to 1000° at a heating rate of 20°/min for the case of non-catalytic and catalytic pyrolysis (silica-alumina). For the catalytic pyrolysis, also of interest were the catalyst-to-SPR weight ratios of 1:1 and 1:2. The TGA curve and differential thermogravimetric peak analysis results suggest that the use of catalysts in pyrolysis (particularly at a catalyst-to-SPR weight ratio of 1:1) reduces both pyrolysis time and temperature range to 14.68 min and 230-555°, respectively. The kinetic parameters were then calculated in a one-step global non-isothermal model and solved using a least squares method in MATLAB. The presence of catalyst was able to reduce Ea to the lowest value from 41.10 kJ/mol (without catalyst) to 40.77 kJ/mol (weight ratio of 1:2) and 39.46 kJ/mol (weight ratio of 1:1) in Zone 1. However, the increase of catalyst quantity was not in line with the increase of reaction rate constant (k) and resulted in reasonably low A of, respectively, 593.30, 406.31, and 266.37.