Optimization of conditions for the production of biochar from maize residues without using carrier gas

Abstract

Maize residue is one of the most available crop residues worldwide which can be converted into biochar for simultaneously addressing agricultural, environmental, and energy issues. In the present study, biochar was produced from maize residues (cob, husk, leaf) in a lab-scale pyrolysis reactor without a carrier gas. The physico-chemical properties of each feedstock were analyzed. The microstructures of the biomass and the biochar were assessed and compared by using scanning electron microscope. A Box-Behnken design was used to find the optimum operational conditions to produce maximum biochar from each of the biomass and eventually, identify a suitable feedstock. Three levels of the operational conditions i.e. temperature (300, 450, 600°C), heating rates (5, 10, 15°C/min), and the holding time (30, 60, 90 min) were evaluated. Multivariate correlations of biochar yield were established using reduced quadratic models with 0.9949, 0.9776 and 0.9876 R2 for cob, husk and leaf, respectively. A significant decrease in biochar yield was observed with increased temperature while the heating rate was found to have the least effect. The holding time did not have major effect on the yield of biochar. Under optimized conditions, the maximum biochar yield from husk, cob and leaf were 30.7, 33.4, 37.9%, respectively. The highest biochar yield (37.91%) from maize leaf was obtained at 300°C, 30 min holding time and 15°C/min as heating rate. Further research is required to evaluate the quality of the biochar produced from each feedstock under optimized conditions.