In situ sensing of adsorbed water in activated carbon using impedance measurements

It is demonstrated that a resistor–capacitor circuit equipped with a dielectric cavity can be used to measure the capacitance of granular carbon by monitoring the voltage change across a charging–discharging capacitor. Using simple electrical theory for the time-dependent voltage, the capacitor capacitance is determined from the decay rate of the discharging voltage cycle. By passing humidified air with a specific dew point through the capacitor cavity, the capacitance is shown to increase with dew point increases indicating water sorption is occurring. Conversely as the dew point decreases, the carbon capacitance decreases in a manner that is consistent with hysteresis giving further credibility to the capacitance measurements. Further studies are planned to measure the effect of contaminants such as volatile organic compounds on the sorption of water vapor by activated carbon.