Carbon activation with KOH as explored by temperature programmed techniques, and the effects of hydrogen

The effects of hydrogen produced upon KOH activation of an anthracite precursor were investigated by temperature programmed reaction (TPR) and post-carbonization temperature programmed desorption (TPD). TPR experiments performed with and without added hydrogen in the sweep gas for different KOH/anthracite ratios demonstrate that the greater this ratio, the greater the amount of hydrogen evolved during the activation process. It is also shown that hydrogen concentration during the activation process can significantly affect porosity development of the resultant activated carbon (AC). A series of post-activation TPD experiments was carried out for AC samples prepared under different conditions. The behavior of oxygen surface complexes in the TPD experiments also supports significant interaction between hydrogen and oxygen surface groups and/or inhibition of their formation. Post-activation gas evolution via thermal desorption is demonstrated to be an indicator of the hydrogen evolution during the activation process. These results explain earlier findings that porosity development correlates with hydrogen evolution, and is favored for high KOH/anthracite ratios, high sweep gas flow rates (up to a maximum value), and high activation temperatures. The effect of the “inert” sweep gas flow rate is attributed to the mass transfer rate of gas phase species, especially hydrogen and potassium vapor.