Ultrasound assisted Peroxone, a novel air pollution control technique

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Air pollution is an ongoing concern for many industrial processes. Volatile organic compounds (VOCs) form an important class of air pollutants because of their involvement in smog formation (trophospheric ozone), and the toxic and/or carcinogenic nature of some VOCs. While effective strategies exist to treat large and concentrated VOC emissions, small and dilute emissions are often untreated although their aggregate emission is substantial. An example is benzene emissions from glycol dehydration units in the natural gas sector, with an annual emission of about 2000 tons in Canada, spread over several thousands of small sources.A waste gas treatment technique that received interest in the past is the peroxone technique, which is the combination of hydrogen peroxide and ozone for the chemical oxidation of pollutants. What limits the effectiveness of this technique is the low solubility of ozone, because the reactions leading to pollutant degradation occur in the water phase. In addition, ozone is highly reactive in peroxone systems, with reaction times of less than a millisecond. As a result, only a very thin layer near the liquid surface is chemically active. However, ozone and hydrogen peroxide are known to be effective pollutant oxidizers in clouds, thanks to the finely dispersed nature of cloud droplets. It follows that the peroxone process can be made substantially more effective by using it in the form of a mist.Mists with a mean droplet size of 20 micrometer or less can be created with ultrasonic waves, similar to the droplet size in clouds. Hence, it is expected that a peroxone system will be substantially more effective if the hydrogen peroxide solution is delivered as an ultrasonic spray. The objective of the proposed project is to test this hypothesis experimentally and through modeling, and to use it as a basis for developing a new class of efficient advanced oxidation techniques for waste gas treatment.This project fits into an overall research programme with the long-term objective of developing a suite of waste gas treatment techniques capable of treating air pollutants emitted by the oil and gas sector and the manufacturing sector. Other techniques that are currently being studied by my group are biofiltration and ultraviolet degradation. All the required equipment for this project is available in my lab, with the exception of an ultrasonic spray generator. Experiments will be carried out with benzene as the pollutant, in a wide range of experimental conditions. Benzene degradation will be measured by gas chromatography analysis of influent and effluent samples. On the modeling side, a comprehensive chemical mechanism will be developed to help interpret the experimental data, and to aid the optimization of the process with the objective of scaling up. My research group has extensive experience with modeling these reactions in the gas phase. The liquid phase system is different due to the presence of ions, and to the different reaction rate constants and concentrations. We will carry out a comprehensive literature search on the kinetics of all the relevant reactions, and include the reactions in the model.By means of mass transfer modeling we will verify the assumption that the mass transfer equilibration time is sufficiently short to justify the assumption of complete mixing. Additional calculations on droplet evaporation and coalescence will be carried out to determine the eventual fate of the mist droplets. This consideration would be of importance in the eventual scale-up of the process to industrial scale.If the research is successful, participation of industrial partners will be sought to develop and build a pilot scale version of the process, and test it at an actual industrial site.