Production of microporous biochars by single-step oxidation: Effect of activation conditions on CO2 capture

• Published in: Applied energy Vol. 114; pp. 551 - 562
• Main Authors: Plaza, M.G., González, A.S., Pis, J.J., Rubiera, F., Pevida, C.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-02-2014; Elsevier
• Subjects: Adsorption; Applied sciences; Biochar; Carbon; CO2 capture; Energy; Exact sciences and technology; Olea; Prunus dulcis; CO2 capture; Adsorption; Biochar; Carbon; CO2 sequestration; capture; Oxidation; CO
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2013.09.058

•Low-cost microporous biochars are obtained by single-step activation with oxygen.•This process entails energy savings compared to conventional two-step activation.•Activation at high temperatures with low oxygen content favours narrow porosity.•Biochars obtained in these conditions present high CO2/N2 selectivity.•These biochars present CO2 working capacities competitive to that of zeolite 13X.
There is an urgent need to develop materials and processes that reduce the energy penalty associated to the CO2 capture step. Biochars are appealing adsorbents for post-combustion CO2 capture applications due to their low cost, stability in moisture conditions and microporous nature. Series of carbon adsorbents were prepared from almond shells and olive stones by single-step activation with air at 400–500°C, and with lower O2 concentration in the activating gas, 3–5%, at higher temperatures (500–650°C). This process entails energy savings compared to conventional activation with carbon dioxide or steam. It has been found that the pore size distribution can be tailored by adequately selecting the activating conditions. Carbons obtained under lower oxygen partial pressures and higher temperatures present narrow microporosity, which is essential for the adsorption of CO2 at low partial pressures. These appealing low-cost adsorbents have competitive CO2 working capacities and high CO2/N2 equilibrium selectivity in conditions that can be considered representative for post-combustion CO2 capture, thus showing potential for this application.