Valorization of slow pyrolysis vapor from biomass waste: Comparative study on pyrolysis characteristics, evolved gas evaluation, and adsorption effects.

Pyrolysis vapor is an important byproduct in the production of biochar from biomass waste, and its emission may pose potential environmental risks. To achieve green production of biochar and efficient utilization of pyrolysis vapors, a novel strategy is proposed in this study to use pristine biochar as an adsorbent to adsorb the pyrolysis vapors. According to thermogravimetry-Fourier infrared spectroscopy-mass spectrometry evaluation, the evolved vapors mainly consisted of oxygenated compounds, hydrocarbons, CO2, CO, and H2O. With pyrolysis temperature increasing, ethers, phenols, hydrocarbons, acids/ketones, and CO2 were changed in the same direction based on two-dimensional correlation spectroscopy analysis. Moreover, butene, propargyl alcohol, and butane were the most abundant ionic fragments. After adsorbing pyrolysis vapors, the heating value of the biochar increased by a maximum of 3.2 MJ kg-1 with changes of physicochemical properties. This strategy provides a theoretical basis for green preparation of biochar while recovering energy from pyrolysis vapors.