Synergistic effects of low-/medium-vacuum carbonization on physico-chemical properties and stability characteristics of biochars

Vacuum carbonization is considered to be an effective and promising thermochemical-tool for resource and energy recovery by collecting and reusing pyrolysis products and volatiles. In this study, thermochemical conversion of orange peel to biochar under low-and medium-vacuum pyrolysis conditions were investigated for product distribution and stability characteristics of biochar. The pyrolysis experiments were executed under three different conditions i.e., N-2 atmosphere (without vacuum), low-vacuum (1013.2 Pa) and medium-vacuum (101.3 Pa) in the temperature range of 300-700 degrees C. The derived biochars were characterized for its aromaticity, polarity, elemental composition, pH, electrical conductivity, surface area, thermal decomposition, FTIR spectroscopy and chemical oxidation properties. Results revealed that low and medium-vacuum pyrolysis had an overriding effect on the H/C (aromaticity) and O/C (polarity) ratios, surface functional groups, as well as on the chemical oxidation potential of derived biochars. A significant reduction in biochar yield (1.1-1.9 folds), increased aromaticity with low H/C (1.3-2.0 folds) and O/C (1.95-4.75 folds) values was observed with increased pyrolysis temperature, under low-and medium-vacuum pyrolysis compared to the N-2 atmosphere. It was also found that biochar produced in the temperature range of 300-700 degrees C, under low and medium-vacuum pyrolysis were comparatively preferable to biochar stability. It is concluded that biochar produced at low-medium vacuum pyrolysis conditions shows higher carbon sequestration potential compared to the N-2 atmosphere.