Effect of feedstock and microwave pyrolysis temperature on physio-chemical and nano-scale mechanical properties of biochar

Abstract

Abstract Biochars were produced from softwood chips (spruce–fir mix) and hemp stalk biomasses in an in-house-developed microwave pyrolysis reactor. A kilogram batch raw biomass mixed with 10 wt% microwave absorber was pyrolyzed at 60-min residence time. Microwave power levels were set at 2100, 2400, and 2700 W with optimum heating rates ranging 25–50 °C/min. The proximate analysis indicated a progressive gain in biochar carbon content with power level increase. Both biochars showed a H:C ratio of < 1.2 with a graphite-like structure, which is an important observation for their potential use as a filler in bio-composites structural strength increase. Fourier Transfer Infrared (FT-IR) spectra showed a major loss of functional groups as the power level increased. Brunauer–Emmett–Teller (BET) surface area and porosity distribution contained higher volume of smaller pores in the hemp biochar. The char hardness and Young’s modulus, obtained via nanoindentation technique and load–depth curve analysis, indicated that hemp biochar possessed a higher Young’s modulus and lower hardness than softwood chip biochar.

Keywords

• Biomass
• Microwave pyrolysis
• Pilot-scale manufacturing
• Biochar characterization
• Nanoindentation