Effects of By-products of Co-pyrolysis on Biochar for Benzene Vapor Adsorption Performance

To explore the effects of the components in the raw materials and by-products of co-pyrolysis on the physicochemical properties of biochar，rice husk（RH，which has a high percentage of lignin and a low content of N）and sawdust（SD，which has a high percentage of both cellulose and N）were used as typical raw materials to prepare co-pyrolysis biochar. The benzene vapor adsorption performance of the obtained biochar was then tested on a fixed-bed device. At the same time，the by-product components generated during pyrolysis were analyzed using thermogravimetric（TG），scanning electron microscopy（SEM），and gas chromatography-mass spectrometry（GC-MS）. Several characteristic methods such as X-ray diffraction（XRD），Fourier transform infrared spectroscopy（FT-IR），and Raman spectroscopy were used for the structural analysis of biochar. The effect mechanism of the by-products of co-pyrolysis on the structure of biochar and the adsorption efficiency of biochar for benzene vapor was discussed. The results showed that the crystal structures of the prepared samples were not significantly different. The specific surface area of SD with a high cellulose content was 1.6 times higher than that of RH with a high lignin content after pyrolysis. The oleic acid in the raw material had a synergistic effect with the intermediate product，ammonia，from the decomposition of N-containing amino acids during co-pyrolysis. The by-product oleic amide was generated and aggregated to block the pores. The specific surface areas of RC1 was 134.28 m2·g−1. The benzene vapor adsorption capacity of co-pyrolysis biochar（RCn）was worse than that of pyrolysis biochar（RC and SC）and mixing pyrolysis biochar（RC-mSC）. Furthermore，the generation of oleic acid amides decreased with an increase in the amount of sawdust during pyrolysis. Thus，the adsorption capacity and specific surface area of RC4 increased to 238.78 mg·g−1 and 367.37 m2·g−1，respectively. The fitting k value from the Yoon Nelson kinetic equation of RCn was 0.060-0.084 min−1，which was higher than the value of 0.039 min−1 of SC. Thus，the co-pyrolysis improved the adsorption rate. In summary，the by-products of co-pyrolysis had an inhibitory effect on the benzene vapor adsorption capacity of the biochar. As the sawdust ratio increased，the inhibitory effect decreased. Furthermore，the adsorption process was fitted to a pseudo-first-order kinetic model，which mainly consisted of physical adsorption. The regeneration efficiency of RC3 exceeded 85% after five cycles，indicating its potential for industrial applications. The results revealed the key factor in the benzene adsorption performance of co-pyrolysis biochar from the composition of raw materials and by-products and provided a reference for the reduction，resource utilization，and harmless utilization of biomass. © 2025 Science Press. All rights reserved.