Ozone-catalytic Oxidation System and Process Optimization for Indoor Air Purification

Description

In recent years, indoor air quality has become an important issue in Hong Kong and in many other countries. Numerous indoor sources emit a low concentration of toluene (0.5-3 ppm), which causes adverse health effects such as allergic reactions, tiredness, and even cancer. To attain the tighter indoor environmental quality standards adopted by governments, a considerable amount of energy is consumed in buildings.Operating at a moderate temperature (300-400oC), ozone-catalytic oxidation (OCO) is a relatively new energy-efficient technology for achieving 70-95% removal efficiency of a high concentration of toluene (500-1000 ppm) in outdoor applications. To apply this OCO technology, which operates at room temperature for indoor toluene removal, a breakthrough development of this OCO technology must be achieved. This result is due to the very low reaction rate of toluene oxidation by the OCO processes at room temperature. A high-performance OCO reactor must be developed and optimized for indoor toluene removal. Key issues associated with the OCO technology, including the formation of intermediate species (which lead to environmental toxicity), the release of low-level ozone, and the deactivation of the catalysts after prolonged use at room conditions, must be resolved.This proposal aims at resolving the key problems of the current form of the OCO system for indoor toluene removal. First, a novel OCO reactor will be fabricated for this study. Highly active and stable nano-sized catalysts (e.g., Pd or Pt) will be uniformly dispersed and confined on the wall of the hydrophobic substrate (e.g., MCM-41 or SBA-15), which will then be coated on the aluminum foam reactor. This highly active foam reactor can greatly enhance the heat and mass transport and reduce the pressure drop across the OCO system compared with the conventional reactor designs. Thus, a lower operating cost of the system can be achieved.Second, factorial and response surface experiments will be designed and conducted sequentially to develop statistical models to study simultaneously the main effects and possible interactions of several operating parameters of the OCO system. With these models, the operational conditions of the OCO system can be characterized and optimized with respect to nuisance environmental factors.Third, based on the results of the statistical models, the experimental setting for the optimal and the worst-case scenarios will be used to investigate and understand the mechanism of toluene decomposition through OCO technology under dry and humid conditions. In situ analysis will be conducted to detect the formation of intermediate species on the catalysts’ surface. The obtained results can guide the design of efficient catalysts for a complete oxidation of toluene.Fourth, with detailed experimental data, a theoretical model that includes mass transport and chemical kinetics will be developed to describe the OCO process on the foam reactor. This model helps researchers in better understanding the OCO process, guiding the development of reactor configurations, and providing the necessary engineering scale-up data for full-scale operation.Fifth, an accurate bias-corrected predictive model will be developed for future prediction and process optimization by combining the theoretical model and physical experiments. Thus, the merits of the OCO system’s high-energy efficiency and cost effectiveness can be achieved. This research will provide additional information on designing an energy-efficient system for indoor air purification, which can be used to maintain a healthier built environment.