Macroporous Particles As Adsorption Agents

In the photoresist segment of the semiconductor process a very low concentration of VOC is generated. These low concentration VOCs can be removed by a concentration step followed by a catalytic oxidation process. The industrial application of this method is discussed below. Dilute VOC is fed to the rotating zeolite concentrator discussed in Section 22.2.2 (honeycomb rotor) where it is concentrated to 10 times of the original concentration and burned on catalysts at relatively low temperature. This saves fuel cost. The VOC is a mixture of IPA, acetone, MEK, toluene, ethyl acetate, n-hexane, propylene glycol monoethyl ether, propylene glycol monoethyl ether acetate, and tetramethyl ammonium hydroxide. The mix-

Ethyl Acetate Process Flow Diagram

Exhaust

Figure 22.2.3. Flow diagram of continuous air cleaning process by zeolite concentrator.

Block Diagram Pre Mix DispenmserAcryl Block Flow Agram

Figure 22.2.5. Block diagram. Continuous air cleaning process by zeolite concentrator.

ture is exhausted from the photoresist at approximately 100 Nm3/min, 20°C and 60% RH. Figure 22.2.3 shows the process flow diagram. The VOC laden feed gas (exhausted from the photoresist) is pre-treated by filters in two steps, first by a bag filter and then by activated carbon. The former removes dusts and the latter removes any readily polymerizable vapors such as, acrylic acid, organic silicon compounds e.g. hexamethylene disilazane (HMDS), phosphorous-compounds and halogen-compounds which are all catalyst poisons. The pretreated gas is fed to the zeolite honeycomb rotor for concentration. (Figure 22.2.4)

Table 22.2.3 shows measurements at the designated points in the block diagram (see Figure 22.2.5). VOC removal reached 91 % at outlet of the rotor and 98 % at outlet of the catalytic oxidation unit.

Table 22.2.3. Measurements according to block diagram (Figure 22.2.5). Continuous air cleaning process by zeolite concentrator

Figure 22.2.5. Block diagram. Continuous air cleaning process by zeolite concentrator.

Table 22.2.3. Measurements according to block diagram (Figure 22.2.5). Continuous air cleaning process by zeolite concentrator

No.

Point of detection

Temp., °C

Conc., ppm

Flow rate, Nm3/min

1

Concentrator, inlet

26

430

102

2

Concentrator, outlet

33

40

116

3

Cat. oxidation, inlet

450

3,700

4

Cat. oxidation, outlet

490

83

5

Exhaust

39

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