Developing almond shell-derived activated carbons as CO2 adsorbents

Two series of carbon dioxide adsorbents were prepared from almond shells, by carbonisation followed either by activation with CO2 or by heat treatment in the presence of ammonia gas (amination). Both procedures gave carbons with high CO2 adsorption capacities in pure CO2 as well as in a binary mixture of 15% CO2 in N2. Activation with carbon dioxide significantly developed porosity in the samples, mostly in the micropore domain, while amination at 800 °C moderately developed narrow microporosity in the char and incorporated stable nitrogen functionalities, which enhanced CO2 selectivity. Amination showed two additional advantages over conventional activation with CO2: a greater carbon yield and a shorter soaking time.