Toluene removal from indoor air using a miniaturized photocatalytic air purifier including a preceding adsorption/desorption unit

The performance of the miniaturized photocatalytic air purifier including a continuous adsorption/desorption unit with a zeolite particles-loaded honeycomb rotor was investigated in the photocatalytic purification of 1 m(3) air containing toluene at concentrations of 3-11 mg m(-3) (about 1-3 ppmv). While operating the continuous adsorption/desorption unit only, and for desorption temperatures controlled within the range of 90-120 and 130-160 degrees C, the unit took approximately 10min to reduce the toluene concentration in a 1m(3) room, to a value of almost zero. Almost the same time courses of toluene concentrations were obtained when the photocatalytic reactor was switched on. This result clearly shows that the rapid decrease in the toluene concentration in the 1 m(3) room is mainly due to the adsorption of toluene onto the zeolite rotor. When the reactor was switched off, the concentration of toluene desorbed into the 0.022 m(3) reactor box increased rapidly and then levelled off in 10min. On the other hand when the reactor was switched on, the toluene concentration in the reactor box increased rapidly, passing through a maximum in 10-150min, and then decreasing to a value near zero, leading to the toluene concentration in the 1 m(3) room becoming negligible. The apparent rates of decomposition determined from the decreasing toluene concentration in the reactor box were 10-fold smaller than the intrinsic rate constant in the Langmuir-Hinshelwood equation, which would suggest that the desorption process of toluene from the rotor is the rate-limiting. All the decomposition experiments were performed using the same zeolite rotor and photocatalytic reactor over a six month period: and the runs were repeated more than one hundred times. Nevertheless, there was no distinct decrease in decomposition activity of the photocatalyst or any significant loss in ability for the zeolite rotor to adsorb toluene could be seen, indicating that these materials can perform constantly over a long period of time. However, as the rotor will sooner or later become saturated with toluene, it may become necessary to introduce a regeneration procedure in order to periodically remove toluene from the rotor. (C) 2009 Elsevier Ltd. All rights reserved.