Carbon dioxide-mediated catalytic pyrolysis of lignin in syngas production

Kraft lignin (KL), a byproduct of the pulp and paper industry, is commonly combusted as a low-grade fuel. However, its high sulphur content results in the emission of sulphur oxides, which pose environmental hazards. This study explores a sustainable approach for the valorisation of waste KL into syngas via CO₂-mediated pyrolysis. In single-stage pyrolysis, CO₂ enhanced the thermal decomposition of volatile compounds (VCs) via homogeneous reactions (HRs). These HRs enhanced syngas production, particularly that of carbon monoxide (CO). Catalytic pyrolysis was conducted to further promote the HRs driven by CO₂. The synergistic effects of CO₂ and a Ni catalyst significantly increased syngas yield, particularly for CO. In a CO₂ atmosphere, the CO concentration increased 4.3-fold compared to that in an N₂ atmosphere. Our findings indicated that CO₂-mediated catalytic pyrolysis offers an efficient and sustainable approach for the disposal and valorisation of KL and production of syngas, which can be applied as a clean energy source or feedstock in chemical synthesis.