Investigation of effectiveness of KOH-activated olive pomace biochar for efficient direct air capture of CO2

Abstract

The capture of CO2 directly from the air is one of the most promising methods under investigation in recent years to reduce the environmental concentration of this pollutant in order to mitigate its effects on climate change. In this work, the activation of olive pomace biochar with potassium hydroxide, KOH, has been studied for its use as a CO2 adsorbent. The effectiveness of biochar activated with KOH at 750 °C in an inert N2 atmosphere was evaluated, using different mass ratios of biochar/KOH, 1:0.5, 1:1, and 1:2. Various characterisation analyses of the biochar were performed to determine its chemical composition, specific surface area, pore size and volume, structure, morphology, and functional groups. The adsorption isotherm was determined at atmospheric pressure and a temperature of 10 °C. The experimental equilibrium results were fitted to the Langmuir, Freundlich, and Temkin models. Additionally, the kinetic behavior of biochar/KOH as an adsorbent was studied, and dynamic experiments were conducted at atmospheric pressure and 10 °C. The experimental data were fitted to various kinetic models (pseudo-first order, pseudo-second order, Avrami, and Elovich). Furthermore, the mass transfer mechanism during the adsorption process was evaluated using the intra-particle diffusion model. Finally, biochar regeneration was investigated for its subsequent reuse as an adsorbent. For this purpose, complete desorption of the captured CO2 in the biochar was easily carried out by modifying the temperature.