Retort Co-carbonization of Daniellia oliveri Leaves: Effect of Cow Dung Co-feed on Biochar Properties

Daniellia oliveri sheds a large quantity of leaves in the dry season in sub-Saharan Africa. Retort carbonization is a recent biomass conversion technique where the flue gas generated in the product zone is re-combusted in the heating zone to produce BC. This work shows that good-quality biochar (DO-BC) can be obtained from the retort carbonization of these leaves. We also show that the utilization of cow dung as co-feed improves the quality of the BC obtained (DC-BC).

The process was conducted at ambient pressure and 100 min of process time. The BC yield for DO-BC was 28.01% at a peak temperature of 382.2 °C and 38.69% for DC-BC at a peak temperature of 361.6 °C. The BCs were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive Xray Spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), Differential Thermal Analysis/Thermogravimetric Analysis (DTA/TGA), and Brunauer–Emmett–Teller (BET) analysis.

The specific surface increased from 114 m²/g for DO-BC to 174 m²/g for DC-BC respectively. Cow dung co-feed led to significant morphological differences in the BC. DC-BC had more surface heterogeneity and more inorganic elements. The average roughness was 31.25 × 10³ μm for DO-BC and 29.21 × 10³ μm for DC-BC respectively. Functional groups like C–H, C–O, C=C, O–H, and C–N were observed in the BCs and the cow dung co-feed led to more C–O and C–H functional groups in the BC. The BCs showed similar thermal characteristics with a maximum thermal degradation temperature of around 400 °C.

It was surmised that the systematic addition of a secondary component to the feedstock can improve the yield and surface properties of the final BC obtained.