Comprehensive study on pyrolysis and co-pyrolysis of walnut shell and bio-oil distillation residue

In this study, the pyrolysis and co-pyrolysis characteristics of walnut shell and bio-oil distillation residue were investigated by means of thermogravimetric analysis followed by Fourier transform infrared spectrophotometer (TGA-FTIR). Multiple reaction models were employed to fit individual pyrolysis experiment of walnut shell and bio-oil distillation residue to find the optimal model for further analysis of co-pyrolysis. The results showed that the pyrolysis behavior of bio-oil distillation residue was different from that of walnut shell. Compared to the pyrolysis of walnut shell, bio-oil distillation residue retained more biochar and a relatively lower rate of mass loss. However, the best fitting models for walnut shell and bio-oil distillation residue were all five-reaction model through comparing the fitting effect and the component complexity. Moreover, five-reaction model was introduced to analyze the co-pyrolysis of walnut shell and bio-oil distillation residue, indicating that the co-pyrolysis had good adaptability to five-reaction model. The thermal degradation of the co-pyrolysis shoulder and spike peaks could be accurately predicted. In addition, the gas products of bio-oil distillation residue and walnut shell had the same absorption band by infrared spectroscopy, indicating that the pyrolysis of two raw materials had similar products while the different absorption intensities represented different concentrations of gas products. Based on Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods, as the proportion of walnut shell in blend sample increased, the average activation energy gradually increased except for the pure walnut shell.