Comparison of the slow, fast, and flash pyrolysis of recycled maize-cob biomass waste, box-benhken process optimization and characterization studies for the thermal fast pyrolysis production of bio-energy

Abstract

Developing an effective cleaner process technology for maize-cob biomass wastes is of utmost importance. This work involved the comparison of products yield (bio-oil, biogas, and biochar) from the fast, slow, and flash pyrolysis of maize-cob biomass wastes using a fixed-bed reactor; evaluation of the individual and combined influences of pyrolysis temperature, biomass particle size, and residence time on the yield of product, and the determination of the optimum pyrolysis conditions/products yield of fast pyrolyzed maize-cob. The fast pyrolysis was performed according to the Box-Behnken Design of Experiment with three variables and three levels of the response surface methodology. The bio-oil fuel properties were determined utilizing ASTM methods and chemically characterized using CHNS elemental analyzer, GC/MS, and FTIR. The performance of the three pyrolysis techniques in terms of their product yield is in the following order: Flash pyrolysis > Fast pyrolysis > Slow pyrolysis (for bio-oil); Slow pyrolysis > Fast pyrolysis > Flash pyrolysis (for biochar and biogas). An optimum bio-oil yield of 43.13% with a high heating value (HHV) of 30.59 MJ/kg, biochar yield of 37.18% with HHV of 20.41 MJ/kg, and biogas yield of 26.05% (HHV = 13.19 MJ/kg) was respectively obtained at an optimum temperature of 567.72, 463.71, and 593.17 °C; biomass particle size of 0.51, 3.83, and 2.58 mm; and residence time of 10.01, 15.28, and 18.92 min. The determined physicochemical characterized properties of the maize-cob-derived-bio-oil revealed that the bio-oil can potentially be valued as a biofuel and as a more promising feedstock for value-added chemical production.