Performance And Kinetic Model Of Thermal-catalytic Oxidization Technology For Indoor Formaldehyde Removal

Formaldehyde is a major indoor chemical pollutant and the removal of indoor formaldehyde is important for protecting occupants’health. The performance of traditional adsorption technology is not satisfactory in formaldehyde removal due to its low molecular weight and high vapor pressure. The thermo-catalytic oxidation (TCO) has a great potential in terms of efficiency and lifetime without added energy. However, its performance and removal model under indoor environmental condition, which presents relatively low temperature and low concentration level, are not sufficiently studied. Traditional researches on TCO rarely considered humidity, which is very important in the indoor formaldehyde purification field.This study investigated the performance and kinetic model of thermal-catalytic oxidation technology for removal indoor formaldehyde. An air cleaning media test system was set up before experiments. The concentrations of formaldehyde were measured by acetylacetone spectrophotometry method. At first, the typical transition metal catalyst hopcalite (CuO-MnO2) was determined through selection among more than six materials. To explore the catalytic reaction mechanism, the effects of internal diffusion and external diffusion were eliminated by using small size catalyst and increasing face velocity. The effects of inlet formaldehyde concentration (200-1000ppb) and humidity (6-98%RH at25℃) on the reaction rate were studied at25℃,60℃,120℃,180℃. The reaction kinetic models of First order, L-H, E-R and MVK model considering single paratemter (formaldehyde surface concentration) were applied to fit the experimental data. The L-H model considering two paratemeters (formaldehyde surface concentration and humidity) was applied to fit the experimental data. The three parameters model was determined by adding temperature influence.We have had the following findings:(1) the formaldehyde conversion tested at typical room environment is about20-30%, which shows great potential of application;(2) the conversion increases significantly when the temperature increases and keeps more than95%when the temperature is180℃;(3) the formaldehyde conversion was markedly influenced by the inlet concentration and humidity especially at low temperature;(4) the kinetic model that best describes the reaction mechanism is L-H model, which considers competitive adsorption;(5) the prediction model considering concentration, humidy and temperature was determined and the prediction accuracy was acceptable. The conclusions will be useful for evaluating the application possibility of TCO air cleaners at typical indoor environment and designing TCO air cleaners based on packed-bed reactor.