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.