Novel insight into VOC removal performance of photocatalytic oxidation reactors

Abstract

A general model has been developed for analyzing the removal of volatile organic compounds (VOCs) by photocatalytic oxidation (PCO) reactors, taking into consideration of the photocatalytic (surface) reaction and the convective mass transfer coefficients including allowance for their spatial dependence. On this basis, a novel insight into VOC removal performance of PCO reactors is presented. The key parameter for evaluating PCO reactor VOC removal performance is the number of the mass transfer unit (NTU(m)), which is shown to be a simple linear product of three dimensionless parameters: the ratio of the reaction area to the cross-sectional area of the flow channel (A*), the Stanton number of mass transfer (St(m)), and the reaction effectiveness (eta). The A* represents the geometric and structural characteristic of a PCO reactor. The St(m) shows the synergistic degree of alignment between the fluid and mass flow fields, and reflects the convective mass transfer rate of the reactor. The eta, describes the relative intensity between the PCO reaction rate and the mass transfer rate. By using the relationship and the parameters, the influence of various factors on the VOC removal performance, the bottleneck for improving the performance and design of a PCO reactor can be determined. Three examples are used to illustrate the application of our proposed model. It is found that the VOC removal bottleneck is the reaction rate for honeycomb type reactor, while mass transfer rate for light-in-tube type reactor. With six fins the fractional conversion of a light-in-tube reactor increases about 70% relative to the one without any fins. Indoor air quality problem caused by volatile organic compounds (VOCs) have annoyed people for many years. Photocatalytic oxidation (PCO) appears to be a promising technique for destroying VOCs in indoor air. With the model and the novel insight presented in this paper, the influence of various factors on the VOC removal performance can be determined. And the bottleneck for improving the performance of a PCO reactor can be easily identified. These are helpful for designing high performance PCO reactors and optimizing their operative performance.