Abstract :
[en] Volatile Organic Compounds (VOCs), being one of the main contributors to air pollution, are responsible for several environmental problems, such as the ozone layer depletion, the formation of tropospheric ozone, and ground level smog. Moreover, some of them are also dangerous to human health.
VOC emissions can be controlled through two types of techniques: destructive and recovery techniques. The destructive techniques for VOC abatement are, among others, thermal oxidation and catalytic oxidation, the latest being the aim of this work. In both cases, VOC is oxidized into CO2 and water, but for catalytic oxidation the required temperature to eliminate the VOC is lower, due to the catalyst, making it an energetically attractive option. Furthermore, it leads normally to the formation of less noxious by-products. The catalyst can be of two types: supported noble metal and metal oxide-based catalysts. Although supported noble metal-based catalysts have higher activity, the availability and low cost of the metal oxide-based catalysts makes them a suitable alternative.
Although many studies are conducted in the development and catalytic test of new materials, the majority is performed in laboratory scale only [1], of which only a few study mixtures of VOCs [2]. To assess the catalyst viability for industrial applications further tests are required namely, tests of mixtures in pilot scale, which could then be extrapolated for industrial scale conditions.
In this context, the aim of this work is to evaluate the performance of a mixed oxide catalyst Co-Al-Ce (pellets), tested previously in powder form on a micro-pilot scale (100 mg) [3], on a pilot scale unit (reactor volume : 0.5 L ; 400.7g of catalyst) for the oxidation of n-Butanol, Toluene and of their respective mixtures. These components are representative of automobile manufacture industry emissions, typically resulting from painting and coating processes.
Single component experiments were obtained for concentrations between 1000 and 2000 ppm and air flowrates between 22 and 44 NL/min. Three mixtures (1000 ppm of Toluene and 1000 ppm of n-Butanol, 1000 ppm of Toluene and 500 ppm of n-Butanol and 500ppm of Toluene and 1000 ppm of n-Butanol), were studied using an air flow rate of 44 NL/min. The catalyst enables complete oxidation of n-Butanol at low temperature (230°C), however several by-products are formed, indicating a poor selectivity for this VOC (the average difference between the curves of conversion of n-Butanol and CO2 formation is of 25°C). In contrast while requiring a higher temperature (250°C) to reach complete oxidation of toluene, the catalyst provides a very good selectivity for this VOC (the average difference between the curves of conversion of Toluene and CO2 formation is below 10°C).
Furthermore, it was found that the presence of n-Butanol favours the oxidation of Toluene at lower temperatures (temperature is 34°C lower in the presence of 1000ppm of n-Butanol). References
[1] H. Sedjame, C. Fontaine, G. Lafaye, and J. B. Jr, 'Applied Catalysis B : Environmental On the promoting effect of the addition of ceria to platinum based alumina catalysts for VOCs oxidation,' 'Applied Catal. B, Environ., vol. 144, pp. 233-242, 2014.
[2] A. T.-B. Bosko Grbic, Nenad Radic, 'Kinetics of deep oxidation of n-hexane and toluene over Pt/Al2O3catalysts: Oxidation of mixture,' Appl. Catal. B Environ., vol. 50, no. 3, pp. 161-166, 2004.
[3] J. Brunet et al., 'Co-Al-Ce Mixed Oxide Materials Prepared by Hydrotalcite Way for VOCs Total Oxidation in Micro- and Semi-Pilot Scale,' Mater. Today Proc., vol. 3, no. 2, pp. 188-193, 2016.
