Pyrolysis process of agricultural waste using CO2 for waste management, energy recovery, and biochar fabrication

This study focused on the mechanistic understanding of CO2 in pyrolysis process of agricultural waste to achieve waste management, energy recovery, and biochar fabrication. In order to scrutinize the genuine role of CO2 in the biomass pyrolysis, all pyrogenic products such as syngas, pyrolytic oil (i.e., tar), and biochar generated from pyrolysis of red pepper stalk in N2 and CO2 were characterized. Thermo-gravimetric analysis confirmed that during the thermolysis of red pepper stalk, the magnitude of exothermic reaction in CO2 from 220 to 400 °C was substantially different from that in N2, resulting in the different extents of carbonization. The physico-chemical properties of biochar produced in CO2 were varied compared to biochar produced in N2. For example, the surface area of biochar produced in CO2 was increased from 32.46 to 109.15 m2 g−1. This study validates the role of CO2 not only as expediting agent for the thermal cracking of volatile organic carbons (VOCs) but also as reacting agent with VOCs. This genuine influence of CO2 in pyrolysis of red pepper stalk led to enhanced generation of syngas, which consequently reduced tar production because VOCs evolving from devolatilization of biomass served as substrates for syngas via reaction between CO2 and VOCs. The enhanced generation of CO reached up to 3000 and 6000% at 600 and 690 °C, respectively, whereas 33.8% tar reduction in CO2 was identified at 600 °C.