Review of VOC Oxidation Catalysts

Catal3Ttic oxidation has been established as one of the most appropriate technologies for VOC abatement. An assessment of the suitability of catalytic oxidation for hydrocarbon control, along with competing processes, is given in Table 3.2. In the literature there are many studies focusing on the catalytic oxidation of VOCs, however, it is beyond the scope of this work to comprehensively review these studies. Rather we will concentrate on the catalytie total oxidation of simple short-chain alkanes and aromatic compounds as illustrative examples of VOC abatement. 

Parameter Condensation Absorption Adsorption Regenerative Incineration oxidation Catalytic oxidation Flameless oxidation BIF combustion Biofiltration Flares 

Rating A = Excellent B = Good C = Satisfactory D = Poor F = Unacceptable Table adapted and shortened from Refs. 21, 22. 

The reactivity of an alkane can be related inversely to the energy of its constituent C-H bonds. More specifically, the reactivity will be linked to the energy of the weakest C-H bond. The C-H bond energy of tertiary carbons is lower than those of secondary carbons and these are lower than primary carbons (Table 3.3). Consequently, -butane, which contains two secondary carbons, is more reactive than propane, which only contains one, and propane is more reactive than ethane, which has two primary carbon atoms. Finally methane is the least reactive, since it has the strongest C-H bond of the alkanes.  

Although it is always difficult to generaUse, olefins are easier to oxidise than alkenes, but still more difficult than oxygenates. The relationship between the energy of the weakest C-H bond and reactivity is also applicable to olefins. Thus ethylene only presents vinylic C-H bonds, meanwhile propylene and butylenes have both vinylic and allylic C-H bonds. Since the aUylic C-H bonds (Table 3.3) are weaker than vinylic C-H bonds, it is reasonable to assume that the oxidation of propylene and butylenes is more facile than that of ethylene, and indeed it is. 

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