Page 401 - Air Pollution Control Engineering

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Catalytic Oxidation 375

Table 2
Destruction Efficiencies of Common VOC Contaminants in Fluidized-Bed
Combustor
Destruction efficiency at 650ºF Destruction efficiency at 950ºF
mean mean

Cyclohexane 99 99+
Ethylbenzene 98 99+
Pentane 96 99+
Vinyl chloride 93 99
Dichloroethylene 85 98
Trichloroethylene 83 98
Dichloroethane 81 99
Trichloroethane 79 99
Tetrachloroethylene 52 92
Source: ref. 2.

as platinum. However, certain metal oxide catalysts can be used in the oxidation of
chlorinated VOCs.
The control efficiencies of some common VOC contaminants are shown in Table 2
at two different operating temperatures for the fluidized-bed catalytic combustor dis-
cussed previously. As the data show, the destruction efficiency of a catalytic oxidation
system can vary greatly for different contaminant types. The lowest DEs typically are
seen for chlorinated compounds.

1.3. Applicability to Remediation Technologies
The applicability of catalytic oxidation depends primarily on emission stream com-
position. As described in Chapter 8 on thermal oxidation, waste gas composition will
determine the auxiliary air and fuel requirements for combustion controls. These
requirements in turn will have a strong influence on whether catalytic oxidation is an
economical approach for controlling air emissions. The waste gas composition is also
important in that for catalytic oxidation to be effective, the waste gas cannot contain
catalyst poisons that would limit system performance.
Although catalytic oxidation has traditionally not been widely used to control halo-
genated hydrocarbons, improved catalysts make this application more feasible.

2. PRETREATMENT AND ENGINEERING CONSIDERATIONS
2.1. Air Dilution Requirements
In general, catalytic incineration (catalytic oxidation) is applied to dilute emission
streams. If emission streams with high VOC concentrations are treated by catalytic
incineration, they may generate enough heat upon combustion to deactivate the catalyst.
Therefore, dilution of the emission stream with air is necessary to reduce the concen-
tration of the VOCs. Dilution will be required if the heat content of an emission stream
is greater than 10 Btu/scf for an air and VOC mixture and above 15 Btu/scf for inert and
VOC mixture (2).