Combustion of chlorinated hydrocarbons in catalyst-coated sintered metal fleece reactors

Incinerators emit chlorinated hydrocarbons, such as polychlorinated benzenes (PCBz) and phenols (PCPh), polychlorinated biphenyls (PCB) and polychlorinated dibenzodioxins and furans (PCDD/F), as very dilute streams. High temperatures (>1000 degreesC) are required in traditional oxidizers. From an energy-saving perspective and to avoid de novo synthesis of PCDD/F, exhaust gas clean-up must be performed at low temperatures (250-350 degreesC). Catalytic combustion can be applied in this temperature range and different reactor layouts are used (eg monoliths, honeycomb). The present investigation uses a novel catalyst-coated sintered metal fleece. Thin metal fibers are sintered (non-woven) to fleece of various thickness, structure and porosity. V-Ti-W catalysts are examined. The paper will briefly review the catalyst coating method suitable to provide a structured fleece reactor with adequate characteristics. Experiments were carried out in the temperature range of 260-340 degreesC with various hydrocarbons injected in a carrier air stream. The experimental investigations demonstrated: (i) that the conversion of the hydrocarbons (volatile organic compounds, VOC) is independent of the oxygen concentration, corresponding to a zero-order dependence of the reaction rate; (ii) that the conversion of the hydrocarbons is a first-order reaction in the VOC; (iii) that the oxidation of the VOC proceeds to a greater extent with increasing temperature, with chlorine substitution enhancing the reactivity, and (iv) that the reaction rate constant follows an Arrhenius-dependence with activation energies between 37.3 and 58.4kJ mol(-1). An assessment of the results leads to a model expression with kinetic reaction control. This model can be used in a scale-up strategy. (C) 2003 Society of Chemical Industry.