Study of breakage of main covalent bonds during co-pyrolysis of oil shale and alkaline lignin by TG-FTIR integrated analysis

Pyrolytic vapor generated over different temperature ranges can be correlated with breaking of different groups of covalent bonds. In the present study, pyrolysis of oil shale and alkaline lignin was studied by thermogravimetry coupled with fourier transform infrared spectroscopy (TG-FTIR) analysis. As the dominant fraction of pyrolytic gaseous products, methane (CH4) was selected as an entry point to track the breakage of main covalent bonds during pyrolysis of oil shale and alkaline lignin. Through applying the deconvolution method, overall CH4 evolution and differential thermogravimetric (DTG) curves of pyrolysis of oil shale and alkaline lignin could be fitted by a series of sub-curves assigned to different groups of covalent bonds. This indicated that the mass loss of oil shale was mainly caused by the fracture of three groups of covalent bonds. In contrast, mass loss of alkaline lignin was mainly caused by the fracture of two groups of covalent bonds. Furthermore, detailed influence of co-pyrolysis on the cleavage of covalent bonds was also analyzed for different blending ratios of oil shale and alkaline lignin. The results revealed that co-pyrolysis of alkaline lignin and oil shale led to the enhancement in CH4 yield by promoting the breakage of linkages. It was also found that among three groups of covalent bonds, the third was most significantly influenced due to reduction in its bond energy.