Impact of torrefaction on the composition, structure and reactivity of a microalga residue

The impact of torrefaction upon the composition, structure, and reactivity of a microalga residue, which was obtained from Chlamydomonas sp. JSC4 (C. sp. JSC4) undergoing oil-extraction, is studied. Three indices of decarbonization (DC), dehydrogenation (DH), and deoxygenation (DO) are defined to account for the mass losses of carbon, hydrogen, and oxygen in the biomass from torrefaction. The results indicate that these indices are characterized by the order of DO > DH > DC, as a result of dehydration and devolatilization mechanisms occurred during biomass torrefaction, and the calorific value of torrefied biomass linearly increases with increasing the indices. The thermogravimetric analysis (TGA) and Fourier transforminfrared (FTIR) spectra clearly suggest that carbohydrate is first destroyed with increasing torrefaction severity, followed by protein consumption. When the torrefaction degree is not severe, the ignition temperature of the biomass is governed by the thermal degradation of carbohydrate and is insensitive to the torrefaction severity. Once the residue is torrefied at 250 degrees C for 60 min or at 300 degrees C for 30 min, most of the carbohydrate and protein in the biomass are depleted, but part of the lipid is retained. As a result, the ignition and burnout temperatures of the biomass are raised to a certain extent, thereby reducing its reactivity. The obtained results have provided a useful insight into applications of using upgraded microalgae residues as fuels in industry. (C) 2016 Elsevier Ltd. All rights reserved.