Elemental loss, enrichment, transformation and life cycle assessment of torrefied corncob

Elemental loss, enrichment, and transformation are crucial to evaluate the fuel properties of torrefied biomass, and life cycle assessment (LCA) can reflect the environmental impact of torrefaction operation. The corncob is selected as the feedstock for the exploration of fuel properties variation during the torrefaction process. The obtained result implies that torrefaction operation obviously changes the macroscopic and microscopic morphologies of torrefied corncob, and leads to a higher calorific value and bigger surface area. With the increase of torrefaction temperature and torrefaction duration, the loss of weight percentage of elemental C, H, and O occurs and is in the order of O > C > H. The relative content of elemental C gradually increases and leads to better fuel properties. The forms of elemental N and O are stable and do not change during the torrefaction process, but the form of C gradually changes from a combined state to an elemental state. These results are confirmed by Fourier transform infrared (FT-IR) spectra, contact angle detection, and thermogravimetric and derivative thermogravimetric analysis. The LCA result infers that the light torrefaction process (200 °C) possesses the lowest environmental impact, whereas the mild torrefaction condition of 250 °C appears to be the optimal choice for corncob upgrading. [Display omitted] •The color of torrefied corncob is correlated to the torrefaction severity and calorific value.•The elemental C, H, and O gradually removed in the order of O > C > H during the torrefaction process.•The elemental C gradually accelerates during torrefaction process and related to the calorific value.•XPS spectra illustrates the elemental transformation of C and the stability of N and O.•Mild torrefaction condition seems like the optimal choice for corncob upgrading.