Adsorption characteristics of organic solvent vapor on activated carbon under fluctuating vapor concentrations

Air containing organic solvent vapor was introduced into a glass column packed with activated carbon particles under the conditions of rectangularly fluctuating vapor concentration. All the experiments were started from an adsorption cycle and were succeeded by a nonadsorption cycle. These cycles were repeated at the same intervals under a constant flow rate. The experimental breakthrough curves and the breakthrough times were compared with those obtained under a constant vapor concentration. The breakthrough curves at the fluctuating vapor concentration were oscillated and the breakthrough times were sometimes significantly shorter than those at the constant vapor concentration when the designed average vapor concentration, i.e., the concentration averaged over an equal number of on and off cycles, was equal. This tendency was greater for the solvents that have higher saturated vapor pressures, such as acetone, methyl acetate, and methyl chloroform, especially when the fluctuating time interval was long. Because the vapor concentrations in the work environments are fluctuating, the effective time of charcoal tubes and respirator cartridges may become shorter than the expected values, which are based on the constant vapor concentration laboratory studies.