Study on catalytic co-pyrolysis of physical mixture/staged pyrolysis characteristics of lignite and straw over an catalytic beds of char and its mechanism

Although the study of co-pyrolysis of coal and biomass have dominated the primary chemicals production in the field of renewable energy utilization, it is still challenging for tar to become lighter. Here we design a set of experimental programs, including the individual pyrolysis, staged catalytic pyrolysis and the co-pyrolysis of physical mixture to investigate the effects of feedstock arrangement on pyrolysis product characteristics. We demonstrated that the experimental results of co-pyrolysis of physical mixture indicate some synergetic effects on pyrolysis products rather than the superposition of individual pyrolysis process of lignite and straw, thus the subsequent tar composition and char structure were characterized. Based on the existing catalytic cracking mechanism, we obtained the staged catalytic pyrolysis have a more pronounced catalytic cracking effect on heavy components compared with the co-pyrolysis of physical mixture, which enables the formation of light oil, naphthalene oil, tar with the lower oxygen content and higher benzene. The Raman spectra of char in catalytic bed exhibits the total peak area of char and the amount of large aromatic ring formed by polymerization increased with the increase of pyrolysis temperature. Simultaneously, the role of catalytic cracking of straw char was stronger than that of lignite char remarkably has been confirmed from the point of view of the chemical structure of char.