The Catalytic Oxidation of Hydrocarbon Volatile Organic Compounds

The Catalytic Oxidation of Hydrocarbon Volatile Organic Compounds 

Tomas GARCIA, Benjamin SOLSONA f and Stuart H. TAYLOR  

Hydrocarbons are present in many VOCs whose abatement is required for environmental reasons. After having presented the main processes used for air clean-up, the catalytic systems developed for hydrocarbon oxidation (alkanes, olefins, aromatics) are reviewed. 

The term volatile organic compound (VOC) refers to a chemically diverse and wide-ranging class of compounds which can be difficult to define, and in fact many definitions currently exist. VOCs are defined by the US Environmental Protection Agency as  

Tomas Garcia, Benjamin Solsona and Stuart H. Taylor 

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The GEiM-lOOO low-temperature thermal desorption unit is an ex situ technology that treats soils contaminated with volatile organic compounds (VOCs). This process involves a countercurrent drum, pulse-jet baghouse, and a catalytic oxidizer mounted on a single portable trailer. As the soil is heated in the GEM-1000 unit, contaminants are vaporized. The contaminants are then directed to the system s catalytic oxidizer, which is designed to convert virtually all of the VOCs to carbon dioxide and water vapor. The oxidizer contains approximately 4.9 ft of noble metal catalyst and can destroy between 95 and 99% of the hydrocarbons when operating between 600 and 1250°F. 

Complete oxidation of hydrocarbons in air is a useful method for atmospheric purification, and has been sucessfully applied in automotive exhaust control. An important new area is the catalytic control of the emissions of volatile organic compounds (VOC) in a more general sense [1]. Many sources, low concentrations and wide temperature ranges can be involved. 

Catalytic total oxidation of volatile organic compounds (VOC) is widely used to reduce emissions of air pollutants. Besides supported noble metals supported transition metal oxides (V, W, Cr, Mn, Cu, Fe) and oxidic compounds (perovskites) have been reported as suitable catalysts [1,2]. However, chlorinated hydrocarbons (CHC) in industrial exhaust gases lead to poisoning and deactivation of the catalysts [3]. Otherwise, catalysts for the catalytic combustion of VOCs and methane in natural gas burning turbines to avoid NO emissions should be stable at higher reaction temperatures and resists to thermal shocks [3]. Therefore, the development of chemically and thermally stable, low cost materials is of potential interest for the application as total oxidation catalysts. 

Afterburning processes enable the removal of pollutants such as hydrocarbons and volatile organic compounds (VOCs) by treatment under thermal or catalytical conditions. Combinations of both techniques are also known. VOCs are emissions from various sources (e.g. solvents, reaction products etc. from the paint industry, enaml-ing operations, plywood manufacture, printing industry). They are mostly oxidized catalytically in the presence of Pt, Pd, Fe, Mn, Cu or Cr catalysts. The temperatures in catalytic afterburning processes are much lower than for thermal processes, so avoiding higher NOx levels. The catalysts involved are ceramic or metal honeycombs with washcoats based on cordierite, mullite or perovskites such as LaCoOs or Sr-doped LaCoOs. Conventional catalysts contain Ba-stabilized alumina plus Pt or Pd. 

Concerning depollution strategies, the invesdgadon of Pd-only TWCs is possibly one of the hot topics in the most recent literature, " together with the study of total oxidadon processes hydrocarbon combustion, " selective soot particulate removal, " volatile organic compound (VOC) elimination and catalytic wet-air oxidation of organics (CWAO) " " and NO abatement. " ... 

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