Influence of different pyrolysis temperatures on chemical composition and graphite-like structure of biochar produced from biomass of green microalgae Chlorella sp

There is a great demand for environmentally friendly carbon materials as an alternative to fossil raw materials in industrial production. Microalgae biomass can be a valuable renewable source for the production of biochar. The study examined the effect of the pyrolysis temperature on the chemical composition, morphological features and the degree of order of the carbon structure of biochar based on green microalgae – Chlorella sp. Thermochemical conversion was carried out at 400÷900 oC in a CO2 atmosphere. The obtained biochar material had a porous structure. It was found that as the temperature increased, the biochar yield decreased from 38.4 to 21.9 wt%, while its aromaticity and stability, determined by the H/C molar ratio, increased. Based on the results of FTIR and Raman spectroscopy, it was evidenced that the biochar produced at 400÷500 oC was distinguished by the presence of functional groups and double bonds (i.e. –NH2, C–O, C=C, C=N, N=O) as well as a high degree of order in the carbon structure (ID/IG=0.2). As the temperature increases, the amorphous nature of biochar began to develop. This study could provide data for the proper selection of temperature for pyrolysis of green algae to obtain biochar with the desired graphite-like structure and properties.