Catalytic pyrolysis of biomass with thermal treatment products of spent lithium-ion batteries for the upgrading of bio-oil and syngas

Thermal treatment is an efficient method to recycle spent lithium-ion batteries and the thermal treatment products are rich in valuable metals with catalytic activity such as Co and Ni. Therefore, the feasibility of using the thermal treatment products (PyNCM and PyLCO) of spent ternary lithium batteries (NCM) and lithium cobalt oxide batteries (LCO) as the cheap catalysts for biomass (wheat straw) pyrolysis was explored in this study. The catalytic effect of the typical components of PyNCM and PyLCO (Ni, Co, NiO and CoO) on the biomass pyrolysis process was also investigated for comparison purposes. The results showed that PyNCM and PyLCO could promote the devolatilization process of wheat straw. The Second order model could well describe the catalytic pyrolysis process of wheat straw based on the Coats-Redfern method, and the obtained activation energy was in the range of 79.00 kJ/mol to 83.90 kJ/mol. The PyNCM and PyLCO had good catalytic activity for enhancing the cracking of bio-oil to produce more gaseous products (syngas), especially for PyNCM, whose gas yield increased significantly from 15.70% to 22.26%. As for bio-oil compositions, the PyNCM and PyLCO both promoted the formation of hydrocarbon compounds and reduce the oxygen content of the obtained bio-oils. The increase of the hydrocarbon content was mainly attributed to the NiO and CoO components in PyNCM and PyLCO. In addition, both PyNCM and PyLCO increased the content and yield of H2 in the syngas. Especially for PyNCM, the content and yield of H2 increased 1.6 times and 5.5 times respectively compared with direct pyrolysis of wheat straw without catalyst. The mechanism of biomass catalytic pyrolysis in the presence of PyLCO and PyNCM was proposed and discussed. The catalytic effect of PyNCM on wheat straw pyrolysis was more distinct than that of PyLCO, which might be attributed to the positive synergistic effect of Ni and Co compounds in PyNCM. This study demonstrated that the thermal treatment products of spent lithium-ion batteries could be used as efficient catalysts for biomass pyrolysis products upgrading.