Negative Air Ion Technology for Control of VOCs Emission from Semiconductor Industry

Although negative air ionizers have been
used in air cleaning, little study have been
done on removal of volatile organiccompounds (VOCs) by negative air ions
(NAI). This study investigated the reactions of
NAI and VOCs in a batch reactor. Three
species of VOCs - chloroform, toluene and
1,5-hexadiene - were selected to react with
NAI at relative humidity of 0, 25 and 70%.
The NAI was generated by a negative electric
discharge at 15.0 kV. The reaction chamber
was designed as a dark discharge to prevent
the generation of O3 and NOx. The NAI
concentrations were 1.34×106 to 1.24×106 ion
cm-3 at relative humidities between 0 and 70%.
The results indicate that the order of the
reactions of chloroform and toluene with NAI
was zero, and 0.433 order for 1,5-hexadiene.
The reaction rate constants of chloroform,
toluene and 1,5-hexadiene were 1.74 − 3.07
ppb min-1, 1.07 − 2.66 ppb min-1 and 0.463 −
0.478 ppb0.567 min-1 at relative humidity from
0 to 70%. The effect of relative humidity on
the reaction kinetics was obvious for
chloroform and toluene but not for
1,5-hexadiene. The reaction between
1,5-hexa- diene and NAI generated a
relatively stable intermediate species,
4-pentenal. The oxidation of chloroform,
toluene and 1,5-hexadiene by NAI proceeded
slowly.