A decision support method for biochars characterization from carbonization of grape pomace

Highlights: • Grape pomace carbonization and assesses the impact of the temperature on the biochars properties. • Multi-criteria decision analysis to evaluate the best application of biochar produced. • Biochar yields decrease from ~51% to ~30% as the carbonization temperature increases from 300 to 800 °C. • Biochar obtained at 400 and 500 °C could be used as biofertilizer and 400 °C as biocatalyst. • To biofuel application the best temperature for biochar production was 500 and 600 °C. Grape pomace can be used to produce several products, such as, biofuels, fertilizers, or catalysts. This work focuses on the carbonization of grape pomace assessing the impact of the carbonization temperature and temperature rate on the properties of the resulting biochars. The potential use of the produced biochars were analyzed by a multiple criteria decision method. To this end, grape pomace particles of 250 μm were carbonized in a nitrogen atmosphere using a horizontal electrically heated tube furnace. The experiments were carried out for temperatures between 300 and 800 °C and residence times between 30 and 75 min. The resulting biochars were characterized by thermogravimetric analysis, scanning electron microscopy, and energy dispersive x-ray spectroscopy. The results reveal that i) the biochar yields decrease from ~51% to ~30% as the carbonization temperature increases from 300 to 800 °C; ii) the biochar produced at higher temperature presents the lowest H/C and O/C ratios; iii) for raw biomass the thermal degradation of hemicellulose, cellulose and lignin occurred at temperatures below 600 °C, while for the biochars only cellulose and lignin decomposition happened; iv) the biochars present ashes with high contents of magnesium, phosphorus, potassium and calcium; and v) the biochar obtained at 400 and 500 °C is adequate for biofertilizer and 400 °C for biocatalyst application. For the biofuel application the best temperature was 500 and 600 °C.