THE EFFECTS OF LOW-LEVEL RELATIVE HUMIDITY ON THE CARBON
ADSORPTION EFFICIENCY OF A VOLATILE ORGANIC HYDROCARBON
1
J. Sipple, R. Putnam, and A. Ramaswami
13226 E. Kansas Dr., K183, Aurora, CO 80012; 1Phone: (303) 338-5390; 1E-mail:
Jefrey.Sipple@uchsc.edu.
The removal of volatile organic hydrocarbons (VOCs) is extremely important to the
protection of human health and the environment. Carbon adsorption is one such technology
which is used to remove these contaminants with greater than 99% efficiency. The removal
is facilitated by Van Der Waal forces, which enhance the stability of the bonds between
carbon atoms which make up the contaminant and the elemental carbon atoms comprising
the carbon bed. Though this removal efficiency is slightly lower than incineration, it also
has a lower overall environmental impact. However, the literature suggests that under
humid conditions (i.e. somewhere between 30 and 70% or above), solvent bonding to
activated carbon is impaired, decreasing the overall carbon adsorption efficiency. Practical
experiences indicate that even a one percent decrease in the overall removal efficiency by
activated carbon can be significant, especially in instances that cleanup goals cannot be
achieved. It is generally accepted that under humid conditions, water molecules in some
way interfere with the binding sites available to the carbons of the contaminant, but what
effects, if any, low relative humidity may have on carbon adsorption is unknown. In fact, all
experimental models and data are currently based on the recovery of pure solvents or
combinations of pure solvents, so a model incorporating the effects of any relative humidity
on recovery is unavailable. The major goal of our project is to test the hypothesis that a
decrease in the carbon adsorption efficiency of a pure VOC occurs under conditions of low
relative humidity. If this decrease in carbon adsorption efficiency is a statistically significant
one, we will propose a theoretical, mathematical model which could explain these changes.
Key words: VOCs, humidity, solvents