Hydrothermal carbonization of Calotropis procera leaves as a biomass: Preparation and characterization

Abstract

Hydrothermal carbonization (HTC) is a biowaste treatment process and a promising technology for many applications. The use of Calotropis procera (CP), found in the Egyptian desert, as a biosource feedstock for the HTC process. In the present work, different process conditions were applied during the HTC process. The influence of temperature, time, and particle size was studied to produce hydrochar using CP leaves as biomass. The hydrochar samples were characterized by many analytical techniques. The temperature and time controlled the severity of the reaction; they caused a significant decrease in the yield (wt.%) and caused an increase in the carbon content of the hydrochar product, with a value of 57.03 % at 240 °C and a time of 180 min. Although time in this case has a more significant effect than temperature, a long reaction time influences the hydrochar yield. FTIR showed the formation on hydrochar with high content of lignin at high temperature and longtime. The O/C decrease with increase the temperature and time as evidence of decarboxylation reaction occurs and the reaction move toward carbonization and increase the HHV of hydrochar than raw biomass that recorded 40.2 MJ/Kg at 240 °C, time 180 min and biomass particle size 150 μm. The hydrochars produced under all condition have negative surface charge in wide range of pH and all have negative charge over pH 4–5 and most suitable pH value is between 6 and 7. The best conditions recorded were temperature 200–240 °C and reaction time 120–180 min at this conditions hydrochar has a stable negative charge in slightly acidic and basic media which let it able to use in applications of removing the cationic pollutants from wastewater, and the high heating value give opportunity to use in energy production applications.