(656g) CO2 Capture Using Nanoporous Carbon Adsorbents Derived from Biomass Pyrolysis

The substantial rise in CO₂ emissions from fossil fuels has significantly contributed to global warming and climate change. One promising strategy to tackle this challenge is to employ biomass-derived carbon (BDC) adsorbents for CO₂ capture, thanks to its benefits such as sustainability, cost-effectiveness, facile scalability to industrial scale, and non-toxicity. However, it is unclear how the structures and properties of BDC affect its CO₂ adsorption, limiting its CO₂ uptake performance.

In this study, we focus on developing effective BDC adsorbents using spent coffee grounds (SCG) as carbon precursors for CO₂ capture, by establishing crucial relationships between structure-property-CO₂ uptake performance of the resultant materials. Nanoporous carbon derived from SCG was prepared by the pyrolysis of SCG with metal activating agents, forming metal oxide particles distributed on nanoporous carbon matrices. Various synthetic parameters for SCG-derived carbon have been investigated in terms of carbon’s structure and properties, and its CO₂ adsorption behaviors. Key synthetic parameters examined include the type and amount of metal activating agents (e.g., Zn²⁺, Ca²⁺, and Mg²⁺) and precursors, the impregnation method for preparing SCG-metal mixtures, and the pyrolysis temperature and duration. Moreover, the CO₂ and N₂ uptake performances at different temperatures, the selectivity of CO₂ over N₂, and the cyclic stability of the prepared carbon were also evaluated. Our findings showed that all prepared SCG-derived carbon adsorbed CO₂ under physisorption mechanisms. SCG-derived carbon with ZnO, pyrolyzed with 40% ZnCl₂ at pyrolysis temperature of 600°C for 1 h, achieved high CO₂ adsorption capacity of ~60 cm³/g and high CO₂/N₂ selectivity of 13.7 at CO₂ adsorption temperature of 20°C, outperforming all other carbon samples prepared in this study. This is primarily attributable to high microporosity and surface area of the 40% ZnCl₂-activated carbon. Future research will be directed toward complete understanding of the underlying mechanism for carbon’s structural formation during pyrolysis as well as its interaction with CO₂.