Two-step pyrolysis of corncob for value-added chemicals and high quality bio-oil: Effects of pyrolysis temperature and residence time

The effects of the first step pyrolysis temperature (T1) and residence time (RT1) on the two-step pyrolysis (TSP) were investigated by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and thermogravimetric analyzer coupled with FTIR spectrophotometer (TG-FTIR) was used to analyze the pyrolysis characteristics of corncob. T1 was classified into low temperature (T1-L: 250 °C, 300 °C and 350 °C), medium temperature (T1-M: 400 °C and 450 °C) and high temperature (T1-H: 500 °C and 550 °C). Compared with one-step pyrolysis (OSP), T1-M was the optimal condition in TSP to increase the selectivities of value-added chemicals such as acetic acid, furfural, 4-vinylphenol, 2-methoxy-4-vinylphenol and guaiacol, etc. Few acids and more hydrocarbons with content of 10.54% were acquired in the second step at T1-M, which was conducive to improving the quality of bio-oil. Different RT1 at T1-M could further increase the selectivities of specific products such as furfural at T1 of 450 °C with 10 s, toluene at T1 of 450 °C with 20 s, and acetic acid, 4-vinylphenol, 2-methoxy-4-vinylphenol and vanillin at T1 of 450 °C with 5 s, etc. Based on the results, a new polygeneration approach of TSP for efficient utilization of biomass was proposed.