Ethanol removal using activated carbon: Effect of porous structure and surface chemistry

Activated carbons with increasing porosity have been prepared by chemical activation of olive stones using ZnCl2 followed by physical activation with CO2. The development of porosity and surface area with burn-off favours the adsorption capacity for ethanol. However, the total amount adsorbed (g/100 g AC) achieves a maximum for the sample with 30% burn-off, this amount decreasing thereafter. Apparently, for a low boiling point alcohol such as ethanol there is a critical pore size which allows an optimum packing of the adsorbed ethanol molecules. A further broadening of the porosity becomes detrimental due to the decreased overlapping adsorption potential inside the micropores. Incorporation of surface functionalities (oxygen surface groups) on the activated carbon enhances the adsorption capacity through the development of specific interactions between the ethanol molecule and the oxygen surface groups.