Research On Some Key Fundamental Problems In The Photocatalytic Oxidation Of Indoor Volatile Organic Compounds

In recent years, indoor air quality (IAQ) problems are being paid more and more attention in China. The high concentrations of volatile organic compounds (VOCs) in indoor air lower IAQ. Photocatalytic oxidation (PCO) by employing UV irradiation is an innovative and promising approach to eliminate indoorVOCs. However, some key issues of applying this technique, such as the performance enhancement of a PCO reactor, the identification and control of its harmful by-products, have not been fully investigated. These unsolved problems restrict the wide use of PCO technique in indoor air purification. Considering those, the following investigations have been carried out as my Ph.D thesis reaserach:Firstly, a wide-range applicable model has been developed for analyzing the removal performance of VOCs by PCO reactors. The dimensionless relationship between the decomposition efficiency and its influence facts was derived based on the non-dimensional analysis:ε=1-exp(-NTUm),NTUm= A* Stmη. A* stands for the geometric and structural characteristic of a PCO reactor; the Stanton number of mass transfer (Stm) shows the synergistic degree of fluid and mass flow fields, and reflects the convective mass transfer ability of the reactor and the reaction effectiveness (η) describes the relative intensity between the PCO reaction rate and the mass transfer rate.Two new methods for enhancing PCO decomposition of VOC were developed: (1) applying fins was not only to enhance the reaction area, but also to increase the air velocity field and concentration field synergy, thereby the Stm was increased. (2) The hybrid photocatalyst by mixing adsorbent into photocatalyst supported a larger reaction area than the pure photocatalyst, which improved the VOC removal efficiency.The ppb-level by-products were studied during PCO decomposition of toluene in a plate-type reactor. Some of the by-products have not been reported in the literature. Possible photocatalytic oxidation pathways of toluene were analyzed and proposed.A series of parameters were put forward to evaluate the health effects of a PCO reactor: the HRI efficiency (εHRI), the health-related effectiveness (εeff_HRI), the conversion rate of by-product (ζB,i) and coefficient of benefit (COBHRI). Based on these parameters, a health-effect-based performance evaluation method for PCO reactors was also introduced.