Possible errors in microporosity in chemically activated carbon deduced from immersion calorimetry

The microporosity of granular and disc-shaped activated carbons prepared by both ZnCl2 and H3PO4 activation has been evaluated by adsorption of nitrogen at −196 °C and immersion calorimetry into liquids of different molecular dimensions (dichloromethane, benzene, 2,2-dimethylbutane, carbon tetrachloride and α-pinene). Experimental results show that immersion calorimetry into dichloromethane provides values of surface area more similar to nitrogen adsorption (BET equation) than benzene. No such effect is found for physically activated carbon. Some apparent anomalies have also been detected for the enthalpy of immersion of carbons activated with H3PO4 into α-pinene due to a small amount of phosphorous remaining in the carbon after washing. This is not the case for carbons activated with ZnCl2, because the washing was more effective in the removal of the chemical.