Abstract

Biochar produced from slow pyrolysis of cocoa shells was studied as a sorbent for CO2 capture at atmospheric pressure and ambient temperature. Chemical analysis showed that the cocoa shell biochar had lower content of carbon and oxygen, and higher content of magnesium, potassium, and calcium compared to the cocoa shell. CO2 uptake performance of the cocoa shell biochar was examined and compared with a commercial activated carbon using a thermogravimeter. The final CO2 uptake after 30 minutes was slightly higher for cocoa shell biochar. However, activated carbon had a faster adsorption response and it approached equilibrium faster than the cocoa shell biochar. This could be due to differences in particle size, pore structure, and surface area of the activated carbon which allows the CO2 to be adsorbed easily in its porous structure. A pseudo-second-order model of kinetics fits the CO2 adsorption behavior of cocoa shell biochar and activated carbon indicating that the rate limiting step is chemical adsorption. Furthermore, the stability of the cocoa shell sorbent was confirmed over four adsorption/desorption cycles. By considering the simplicity of the production process and efficiency of CO2 adsorption, cocoa shell biochar can be considered a good option for CO2 capture.

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