Pore volume upgrade of biochar from spent coffee grounds by sodium bicarbonate during torrefaction

Y A novel approach for upgrading the pore volume of biochar at low temperatures using a green additive of sodium bicarbonate (NaHCO3) is developed in this study. The biochar was produced from spent coffee grounds (SCGs) torrefied at different temperatures (200-300 degrees C) with different residence times (30-60 min) and NaHCO3 concentrations (0-8.3 wt%). The results reveal that the total pore volume of biochar increases with rising temperature, residence time, or NaHCO3 aqueous solution concentration, whereas the bulk density has an opposite trend. The specific surface area and total pore volume of poreforming SCG from 300 degrees C torrefaction for 60 min with an 8.3 wt% NaHCO3 solution (300-TP-SCG) are 42.050 m(2) g(-1) and 0.1389 cm3. g(-1), accounting for the improvements of 141% and 76%, respectively, compared to the parent SCG. The contact angle (126 degrees) and water activity (0.48 aw) of 300-TP-SCG reveal that it has long storage time. The CO2 uptake capacity of 300-TP-SCG is 0.32 mmol g(-1), rendering a 39% improvement relative to 300-TSCG, namely, SCG torrefied at 300 degrees C for 60 min. 300-TP-SCG has higher HHV (28.31 MJ.kg(-1)) and lower ignition temperature (252 degrees C). Overall, it indicates 300-TP-SCG is a potential fuel substitute for coal. This study has successfully produced mesoporous biochar at low temperatures to fulfill "3E", namely, energy (biofuel), environment (biowaste reuse solid waste), and circular economy (bioadsorbent). (C) 2021 Elsevier Ltd. All rights reserved.