Biochar from Cocoa Shell Pyrolysis: Potential Sorbent for CO₂Capture

Biochar produced from slow pyrolysis of cocoa shells was studied as a sorbent for CO2 capture. Three cocoa shell samples obtained from Papua New Guinea, Peru, and Colombia were studied. Thermogravimetric analysis showed that the first three stages of degradation were quite similar for different cocoa shell sources. However, the fourth stage was different, which could be due to the different lignin content in the cocoa shell sources. Chemical analysis showed that the cocoa shell biochar had a lower content of carbon and oxygen, and a higher content of magnesium, potassium, and calcium compared with the cocoa shell. CO2 uptake performance of the cocoa shell biochar was examined and compared with a commercial activated carbon using a thermogravimeter at atmospheric pressure and ambient temperature. The final CO2 uptake after 30 min 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.