Research On UV Mineralization Of Organic Compounds For TVOC Detection

Volatile organic compounds(VOCs)have became a very important class of air pollutants.At present,there are three main methods for VOCs' detection: colorimetric tube detection,portable detector detection and chromatography.For these types of measurement methods,the colorimetric tube detection's accuracy is too low,portable detector detection method's measurement range is too small and the chromatographic steps are too complex and the measurement cost is relatively high.This project's target is to develop a measurement method which is low in cost and effective in measuring the concentration of VOCs.The principle of this method is that VOCs is irradiated in a reactor equipped with a UV lamp,The carbon dioxide's concentration of the inlet and outlet of the reactor is measured by a carbon dioxide sensor,and the concentration differential of carbon dioxide before and after of the reator is proportional to the concentration of the VOCs in the detected air.Thereby,the concentration of the VOC is obtained.This detection method is simple in principle,easily to operate and with wide application range.When with toluene as the experimental object,the vacuum ultraviolet(VUV)lamp and the short-wave UV lamp all could degrade the toluene.But only the VUV lamp could mineralize the toluene.The initial concentration and the retention time are the two main factors affecting the mineralization of toluene.The mineralization rate of toluene increases with the residence time when the concentration is constant.When the theoretical residence time is 576 s,the average mineralization rate in the concentration of toluene so can reach above 95%.When the residence time is low,the mineralization rate of toluene decreases with the increase of the initial concentration,but with the increase of residence time,initial concentration 's effect on toluene mineralization will be smaller.The mineralization rate of toluene can maintain as constant within a certain concentration range.When several representative volatile organic com VOCs,such as acetone,benzene,styrene,etc.,were subjected to UV mineralization experiments,the average mineralization rate of these substances at a theoretical residence time of 576 s,within a certain concentration range can reach more than 95%.This project also created two other measurement methods,mixed-chamber recirculation flow measurement method and mixed-chamber-free recirculation flow measurement method.with this two measurement methods,mineralization rate of n-butyraldehyde,n-hexane,toluene and styrene can reach more than 95%.When the detected air contains a variety of VOCs,these VOCs can be completely mineralized,with this three measurement methods when the residence time is sufficient.The concentration of carbon dioxide produced is substantially equal to the sum of the concentrations of carbon dioxide produced by the mineralization of all the organic substances in the gas to be detected in theory.