Liquid fuel production from mixed municipal solid waste by catalytic co-pyrolysis: Optimization, energy-carbon balance, and circular economy potential

This study presents an innovative integrated two-step co-pyrolysis approach for heterogeneous multi-component municipal solid waste (MC-MSW) using natural dolomite as a dual-function CaO–MgO catalyst in an integrated two-step co-pyrolysis system (ITSC). The effects of temperature (450–550 ℃), residence time (120–180 min), and feedstock-to-catalyst ratio (1:2–1:2.5) were optimized through the Box–Behnken design and desirability function approach. The MC-MSW consisted of 32% biomass, 54% mixed plastics, 9% paper, 3% textiles, and 2% rubber. Natural dolomite was selected for its abundance, low cost, and balanced acid‒base catalytic activity, enhancing cracking and deoxygenation. Under optimal conditions (500 ℃, 158 min, 1:2.5 ratio), the process yielded 34.2 wt% liquid fuel with a higher heating value (HHV) of 41.8 MJ/kg, dominated by C₅–C₁₂ hydrocarbons (78.3%) and aromatics (66.5%). In contrast, the non-catalytic run produced only 25.6 wt% liquid with 36.9 MJ/kg HHV and a higher oxygenated volatile fraction. These findings demonstrate that natural dolomite significantly enhances conversion efficiency and product quality while supporting circular carbon valorization through reduced emissions and improved energy recovery from heterogeneous urban waste streams. The process supports sustainable development goals (SDGs 7, 11, and 12) by enabling clean energy generation, sustainable urban waste valorization, and circular economy integration through reduced emissions and efficient energy recovery from heterogeneous municipal waste streams.