Adsorption of carbon dioxide using a biochar produced from mangaba seeds (Hancornia speciosa)

Abstract

The concentration of greenhouse gases has increased considerably in the Earth's atmosphere due to human actions, intensifying global warming and triggering climate change. Because of this scenario, actions are being taken to reduce emissions of these pollutants, especially carbon dioxide, CO₂. The Kyoto Protocol (Kyoto, 1997) and the 21st Conference of the Parties, COP21 (Paris, 2015), are examples of global agreements to reduce climate change. In this context, advanced technologies for the sequestration of carbon dioxide are under development, especially those based on the physical adsorption. This study integrates this class of processes and used a biochar produced through the pyrolysis of mangaba seeds (Hancornia speciosa) as adsorbent material. Biochar was characterized in terms of surface area, pore diameter, morphology and determination of functional groups. The adsorption of CO₂ was performed using the static volumetric technique, by varying the initial pressure of the system, which consisted of a fixed-bed column on a semi-pilot scale. The experimental data were adjusted to models in the literature. The Freundlich model was the best fit, thus confirming the adsorption in multilayers. The adsorption kinetics followed the intraparticle diffusion model, indicating that diffusion is the limiting step of the process. The higher adsorption capacity was verified, with a maximum value of 5.21 mol CO2 / kg of bioadsorbent.