Toward a carbon-negative strategy for syngas production via CO2-assisted catalytic pyrolysis of natural loofah residues

초록

Pyrolysis is a promising technique for biomass valorization; however, its sustainability is constrained by its high energy requirements and associated CO2 emissions. Here, CO2 was employed as a reaction atmosphere for the Ni/Al2O3-catalyzed pyrolysis of natural loofah residues (NL) to enhance syngas production while enabling process-level carbon mitigation. Three reactor arrangements (conventional, in-line non-catalytic, and in-line catalytic) were compared to dissect the mechanistic function of CO2. CO2 became reactive at ≥ 490 °C, where it promoted the conversion of oxygenated volatile species into CO. This effect was further enhanced by Ni/Al2O3, increasing CO production from 54.25 mmol under N2 to 96.14 mmol under CO2, while decreasing the bio-oil fraction from 7.10 to 4.91 wt%. Reducing the heating rate to 5 °C min−1 improved the overlap between NL devolatilization and CO2 activation, resulting in a syngas selectivity of 98.54 %. The resulting biochar showed an equilibrium CO2 uptake of 77.39 mg g−1, comparable to that of post-activated biochars. Within the defined gate-to-gate system boundary, carbon accounting that included CO2 utilization during catalytic pyrolysis and subsequent CO2 uptake by the resulting biochar indicated a net CO2 balance of −0.24 g CO2 g−1 NL. This carbon mitigation performance corresponds to an estimated benefit of 368.15 USD per ton of NL compared to conventional incineration. These results suggest that CO2-assisted catalytic pyrolysis can be a viable strategy for converting biomass waste into syngas while contributing to circular carbon management. However, the carbon-negative implication should be interpreted within the defined system-boundary, as a full life-cycle assessment was beyond the scope of this study.

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