Optimization and life-cycle assessment of biochar production through microwave–assisted pyrolysis of industrial hemp hurd

Industrial hemp hurds (HH) are the biomass residues following bast separation from inner core of hemp plant for fibre extraction. Current research emphasized on microwave-assisted pyrolysis (MAP) of HH for the optimization of hemp biochar (HB) production, its characterization and cradle to gate life cycle analysis (LCA) to explore its application as fossil fuels alternate. Utilizing central composite design (CCD), MAP was optimized for two operational parameters: microwave power (P) and pyrolysis time (T) with HB yield and higher heating value (HHV) as output parameters. The highest HB yield of 75.3% was obtained at P and T of 600 W and 10 min respectively with model Eq. 325.1 -0.37P -12.17T + 0.004PT + 1.3×10-4P ² +0.18T ² , validated with an average error of 4.8%. The maximum HHV of 29.5 MJ/kg prevailed at 1000 W and 25 min with model Eq. 71.91 -0.18P -0.11T + 1.3×10-4P ² and an average error of 5.2%. The negative greenhouse gas (GHG) emission of -10.06 t CO ₂ e/yr suggested the sustainability of MAP for HB production through carbon capture. The life cycle assessment (LCA) using ReCiPe Midpoint (H) indicated that the HB production process significantly impacts several environmental categories, with the highest impact being on global warming potential, at 167.3 kg CO ₂ eq. It is followed by human non-carcinogenic toxicity, at 3199.9 kg 1, 4-DCB, and terrestrial ecotoxicity, at 2380.1 kg 1, 4-DCB. The sensitivity analysis evaluated the environmental impacts derived from four distinct impact assessment methodologies, facilitating the identification of overarching trends in environmental impacts. Novelty statement The current study employed microwave-assisted pyrolysis (MAP) technique for biochar production from industrial hemp hurds. Biochar production was optimized using response surface methodology for maximizing heating value and yield emphasizing its applicability as a potential and sustainable fuel alternative. Detailed characterization studies like scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Energy-dispersive X-ray spectroscopy, BET surface area analysis, etc., were performed to examine the quality of the obtained biochar. Apart from biochar production through advanced technology like MAP, this study also focused on the environmental impact of such process through a thorough investigation on negative emission technology potential and life-cycle assessment using cradle-to-gate approach. This research highlighted the negative greenhouse gas (GHG) emission of -10.06 t CO ₂ e/yr suggesting the sustainability of MAP for biochar production through carbon capture. Therefore, this research presents novel contributions to the field of waste valorization and renewable and clean energy production through biofuel production from MAP of waste biomass.