Investigation Of Nano TiO₂ Composites For Photocatalytic Oxidation Removal Of Mercury Vapor

Mercury is a toxic heavy metal with a property of bioaccumulation along the food chains. The emission of mercury into the atmosphere increases day by day due to the great demand of coal consumption in the global power and energy resource, resulting to severe harms to human beings and the environment. Our research focuses on the exploitation of novel photo catalysts——nano TiO₂ composites, and its application to the mercury vapor control.A process by sol-gel method has been developed to synthesize the catalysts of activated carbon (AC) and aluminium silicate fibers (fibers) coated with nano-scale TiO₂ particulates (TiO₂-AC, TiO₂-fiber). X-ray diffraction spectroscopy (XRD) and other testing methods were utilized to characterize the catalysts. Photocatalytic oxidation experiments with the catalysts for mercury vapor removal were carried out in a photoreactor with on-line monitor under ultraviolet (UV) irradiation at the wave length of 253.7nm. And then the catalysts after removal experiments were tested to determine the mercury species and its behavior during photocatalytic reaction. At last, simulate the chemical dynamics equation on the base of the results to identify the reaction grade.The results show that it is effective to load TiO₂ particulates at the size of 10 30nm on AC and fibers by sol-gel method. The composites loaded with TiO₂ in anatase phase indicates remarkably high photocatalytic removal rate of mercury vapor, exhibiting synergistic adsorption and photo-oxidation ability, and achieving the removal rate high up to 86%. When the proportion of the ethanol and acetic acid in the sol reaches 2/1, the catalysts demonstrate the most active photocatalytic ability. In the reaction, the O2 concentration of 5% in simulated flue gas has been abundant for the catalytic capture, further enhancement of O2 has no impact on the removal rate. With the increase of the water vapor concentration in the ambience, the retention rate of mercury gets promoted first, and then maintains steadily. While with the irradiation intensity of 3.3 mW/ cm2, the reaction gets enough UV to get rid of the mercury, and further increase of the irradiation won't stimulate the removal. With the elevation of temperature in the range of 30⁷0℃, firstly, the removal rate keeps still, while growing to 100℃, the catalytic removal got stunted obviously, showing that relatively high temperature restrains the catalytic reaction.The mercury species determination experiments show that all of mercury oxide proportions in the catalysts maintain up to 83%, validating the existence of the photocatalytic oxidation of mercury vapor directly. On one side, O2 with the content of 5% in the simulated flue gas is adequate to catalyze the oxidation of Hg, and the HgO proportion doesn't change with the increase of O2. On the other side, the oxidation will be stimulated with the increase of moisture at low level. While reaching 2.5%, the further increase of water vapor concentration will stunt the reaction. In addition, all of the oxidation rates in 5 conditions exceed 84%, elucidating obvious oxidation effect. And at last, the simulation results show that the catalytic removal follows the dynamic equation of grade 1.