Customizing high-performance molten salt biochar from wood waste for CO₂/N₂ separation

Engineered biochar derived from wood waste pyrolysis in molten salts were developed for effective CO₂/N₂ separation. The production conditions were customized to obtain the biochar with high CO₂ capture capacity and CO₂/N₂ selectivity by tuning the type of molten salts (MgCl₂-KCl, ZnCl₂-KCl, ZnCl₂-NaCl-KCl, and K₂CO₃-Na₂CO₃-Li₂CO₃), salt/feedstock ratios (1:1 and 3:1) and pyrolysis temperatures (600 and 800 °C). High temperature (800 °C) and moderate salt loading (salt/feedstock ratio of 1:1) benefited the CO₂ adsorption by providing an increased surface area and highly dispersed metal species as adsorption sites. PSL-3-800 and PSL-3-600 (K₂CO₃-Na₂CO₃-Li₂CO₃ biochar) showed the highest CO₂ capacity (4.5 mmol g⁻¹, 0 °C, 100 kPa) and the highest CO₂/N₂ selectivity (28.5), respectively, among the engineered biochar developed in this study. In addition, ZP-3-600 showed the highest selection parameter (S) in both PSA and VSA processes, indicating the promising CO₂ capture performance under PSA/VSA conditions. A high recovery rate (89%) of molten salts was achieved. These results suggest a new pathway for upcycling biowaste as eco-friendly and effective adsorbents for gas adsorption and separation.