Surface Characterization and Classification of Slow and Fast Pyrolyzed Biochar Using Novel Methods of Pycnometry and Hyperspectral Imaging

Abstract

The birchwood biochar produced by slow as well as fast pyrolysis was analyzed and compared according to physical characteristics of porosity and reflectance. A relation between char porosity and the reflectance of the biochar structure was found wherein porosity was found to be inversely proportional to reflectance. The wavelengths providing images with maximum clarity were established for classification through hyperspectral imaging technique. The wavelengths that were found to be optimum for both slow and fast pyrolysis biochars were 947 nm and 1685 nm, which fall in the near-IR and short-IR wavelength ranges, respectively. The results of the hyperspectral imaging support the findings of the porosity evaluations from pycnometric analysis, which showed that the biochar sample treated at 350°C for slow pyrolysis and 400°C for fast pyrolysis for a holding time of 20 min had the highest porosity and in turn showed the lowest reflectance mean values. The theory that reflectance of biochar samples decrease with increasing porosity of the char structure was substantiated through this qualitative study.