Optimized preparation of biochar from large-particle biomass: analysis of process characteristics and structural evolution

Abstract

This study designed an online thermogravimetric analysis system to carry out pyrolysis investigation of large-particle biomass. The response surface method (RSM) was adopted for systematically exploring the influences of the particle size, pyrolysis temperature and residence time on the production and the heating properties of the biochar. The results reveal that the pyrolysis temperature has the most pronounced influence on the yield and the higher heating value (HHV) of the biochar, and the optimal biochar preparation condition is obtained with the particle size, pyrolysis temperature and residence time being 24 mm, 446 °C and 9 min separately. The real-time heating process and mass change of the large-particle biomass was revealed during the pyrolysis process. Different heating profiles are reported inside the biomass with the heating rate in the axial direction being faster than that of the radial direction. Moreover, the structural characteristics of the biochar granule at both axial and radial cross sections were analyzed with the Fourier Transform Infrared Spectroscopy (FTIR), Raman and Scanning Electron Microscopy (SEM). The produced biochar granule shows obvious non-uniformity. The I_D/I_G values in the axial and the radial quarter cross section are 3.72 and 3.56, respectively. Compared with the radial direction, more aromatic structures are formed in the axial direction. The results provide valuable insights for the preparation and practical application of biochar from large-particle biomass.