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Catalytic ozonation of VOCS over different porous materials

Authors Kwong, Chi Wai
Issue Date 2009
Summary Adsorption is widely used in pollution treatment systems for Volatile Organic Compounds (VOCs) decontamination. However, it is only able to transfer gaseous pollutants from one phase to another. Ozone is a strong oxidization agent with catalytic properties that can eliminate VOCs completely with sufficient residence time. The use of ozonation with porous materials exploits the strong oxidizing capability of ozone with porous adsorbents that contain contaminants and extend the residence time for the reactions. Some porous materials such as zeolite have catalytic features which further enhance ozonation reactions. These porous materials can serve as reservoirs to contain the intermediate species and the residual ozone by holding them in the adsorbed phase. In this thesis, the basic mechanism of the ozonation process over various porous materials such as zeolite, MCM-41 and fly-ash products from biomass combustion, were investigated in fixed bed reactor. Low concentration VOCs was employed (0.3- 4ppmv) to correlate the pollutant removal characteristics with the change of ozone concentrations (6- 80ppmv). Results showed that around 20- 40% of the removed VOCs were contributed by catalytic ozonation and the rest was done by adsorption. Fourier Transform Inferred (FT-IR) techniques were employed to identify the in-situ surface reaction species and the intermediate species. It was found that the atomic oxygen was one of the active species for pollutant destructions and Aldehydes were the major intermediate species for ozonation reactions. Experimental results showed that the Lewis acid sites in the porous material played a key role for the decomposition of ozone for subsequent catalytic reactions. Besides those investigations, a series of specific adsorption-desorption experiments and the mass balance analysis were conducted to quantify the rate determining steps, reaction kinetics and the overall performance of the ozonation reactions. It was found that the apparent activation energy of ozonation process over biomass fly-ash products was around 44kJ/mol. It was significantly lower than the process with the use of molecular oxygen as oxidant at 97kJ/mol.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2009
Language English
Format Thesis
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