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Theair temperature before entering the rotor was controlled in the rangeof either 90–120 or 130–160 ◦C.The photocatalytic reactor has a parallel array of nine UV lightsources (Shiraishi et al., 2005b). The blacklight fluorescent lamp wasinserted and fixed in the center of each glass tube whose inside sur-face was coated with a thin film of titanium dioxide. These reac-tion tube units were arranged in parallel in a plastic transparent box(215mm in length and width and 295mm in height). The air wassucked up through the annulus of each glass tube from the bottomof the box by the rotation of an electric fan (13W in electric powerconsumption) fixed at the upper part of the box, and then dischargedfrom the top. This photocatalytic reactor (and its arrangement) hasseveral advantages described in the introduction section.The air purifier was set up in a 1m3 closed room using a frame-work of angle bars covered with vinyl chloride sheets. The electri-cally heated plate for volatilizing toluene and two electric fans formixing the air were placed inside the closed room. All the experi-ments were performed according to the following procedures:(1) A small amount of toluene was dropped on a metal plate and theroom was immediately closed.(2) The metal plate was heated electrically to instantaneously vola-tize toluene.(3) The electric fans were switched on to sufficiently mix the air inthe closed room.(4) After 2min, the air purifier was switched on to start the decom-position experiment.(5) At time intervals, 10 cm3 of the air was sampled with a syringefrom 1m3 room and 0.022m3 reactor box and then injected to the gas chromatograph (GC-8A; Shimadzu Co. Ltd., Kyoto, Japan)equipped with a flame ionization detector (GC-FID) and a sepa-ration column (packing: Bentone 34+DNP on Shimalite 80–100NAW; Shinwa Chemical Industries Ltd., Kyoto, Japan) at 80 ◦Cand a N2 gas flow rate of 50cm3 min−1. The limit of detection(LOD) and limit of quantitation (LOQ) are 0.13 and 0.26mgm−3,respectively.(6) After each experiment, the air purifier was subsequently oper-ated for 12 h to remove toluene from the rotor.3. Results and discussion3.1. Air purification using only a continuous adsorption/desorption unitPurifications of air containing toluene at concentrations of 3.4,7.8, and 10.6mgm−3 were performed using only the continuousadsorption/desorption unit where the desorption temperature wascontrolled in the range of 90–120 ◦C. Fig. 2 shows the time courses oftoluene concentrations in the closed room and reactor box in thesepurification experiments. Fig. 3 shows the results of the same ex-periments except for the desorption temperature controlled in therange of 130–160 ◦C. In all the experimental results, the toluene con-centrations in the closed room are lowered to almost a zero valuewithin 10min.
The rates of change are not remarkably dependent onthe desorption temperature. On the other hand, the toluene concen-trations in the reactor box increase quickly, reaching their respectivemaximums by 10min and almost levelling off. The toluene concen-tration becomes constant at its higher level, when a larger amount oftoluene is initially volatized, and when the desorption temperatureis higher. The maximum concentration is almost doubled when thedesorption temperature is increased from the range of 90–120 ◦Cto the range of 130–160 ◦C. It should be noted that the tolueneconcentration in the closed room does not become completelyzero because of the adsorption equilibrium between the air androtor.The equilibriumconcentrations of toluene in the reactor box, CSeq,were determined from Figs. 2 and 3. Fig. 4 shows plots of these val-ues against the equilibrium concentration of toluene adsorbed onthe rotor, CReq for two ranges of desorption temperature. It is appar-ent that there is a linear relationship between CSeq and CReq.Also,CSeq is increased by about two times by increasing the desorptiontemperature from the range of 90–120 ◦C to the range of 130–160 ◦C.For these desorption temperatures, the percentages of desorptionof toluene into the reactor box were estimated to be about 1% and2.3%, respectively, implying that toluene is strongly adsorbed ontozeolite particles and is not easily desorbed even at such temperatureconditions. 3.2. Air purifications using a combination of continuousadsorption/desorption unit and photocatalytic reactorPurifications of air containing toluene at concentrations of 3.4,7.2, and 9.5mgm−3 were performed using the air purifier, i.ethe photocatalytic reactor combined with the continuous adsorp-tion/desorption unit, where the desorption temperature was con-trolled in the range of 90–120 ◦C. Fig. 5 shows the time courses oftoluene concentrations in the closed room and reactor box in thesepurification experiments