Multi-objective optimization and techno-economic evaluation of microwave-assisted pyrolysis of hemp biomass for sustainable biochar and bio-oil production

As the world seeks sustainable alternatives to fossil-based energy and materials, microwave-assisted pyrolysis has emerged as a promising next-generation thermochemical technology, offering rapid volumetric heating, superior energy efficiency, and precise control over product formation. This study delivers a comprehensive assessment of microwave-assisted pyrolysis applied to hemp biomass, integrating experimental investigation, techno-economic analysis, and multi-objective optimization to evaluate its viability as a carbon-negative biochar and bio-oil production pathway. Experiments across varying microwave power levels revealed that methane dominated the greenhouse gas emission profile, while the optimal 1.0 kW condition achieved a remarkable 88.7% reduction in emission intensity compared to 0.8 kW. Carbon partitioning analysis demonstrated that 62–68% of biomass carbon was retained in the biochar, a testament to the process’s strong carbon-fixation capability. Elemental characterization confirmed progressive carbonization yielding stable, aromatic biochar with favorable atomic ratios for long-term carbon sequestration. Techno-economic analysis identified electricity as the primary cost driver, with biochar revenue forming the economic backbone of the process. Multi-objective optimization via a GA–TOPSIS framework identified 1.0 kW as the optimal operating condition, balancing cost, revenue, and environmental performance. Further improvements through energy recovery and carbon-credit integration could enhance the economic competitiveness of MAP for sustainable biochar production.