Co-pyrolysis behavior of spent bleaching clay and dealkaline lignin: An investigation into TG-FTIR, kinetics, and interaction mechanisms

Spent bleaching clay (SBC) and lignin wastes are generated from oil refining and paper industries, respectively. The complementary properties of these two types of waste enable synergistic effects in co-pyrolysis, thereby mitigating limitations characteristic of single-component pyrolysis. In this study, the co-pyrolysis behavior of the two wastes was explored at the microscopic molecular level using simultaneous TG-FTIR technology, coupled with fixed-bed pyrolysis experiments. The co-pyrolysis behavior was systematically investigated at the mass ratio of lignin and SBC (0 %L, 30 %L, 50 %L, 70 %L, and 100 %L) and different reaction temperatures (450, 500, 550, 600, and 650 °C). The results showed that the activation energy required for co-pyrolysis decreased at 50 %L and 70 %L ratios, as determined using FWO and KAS methods. The Ea required for co-pyrolysis decreased at 50 %L and 70 %L ratios. Specifically, the addition of 30 % SBC reduced the activation energy of lignin from 141.67 kJ/mol (KAS) and 146.41 kJ/mol (FWO) to 120.25 kJ/mol (KAS) and 126.04 kJ/mol (FWO), respectively. Furthermore, the 50 %L radio infrared absorbance of CH 4 and CO 2 was relatively strong due to the enhanced decarboxylation and demethoxylation reactions. Meanwhile, the fixed-bed co-pyrolysis experiment showed that the relative content of non-methoxy phenolics increased from 7.0 % to 10.6 % with bio-oil yield increasing from 27 % to 40 %, after adding 50 % SBC. Additionally, the interaction mechanism was proposed based on the TG-FTIR and fixed-bed pyrolysis experimental results. SBC served as a hydrogen donor to promote the thermal decomposition of lignin and improved the yields of phenol and alkylphenols. This work offers guidance for the synergistic conversion of renewable carbon sources with oily solid wastes.