기체상 유동층 반응기에서 TiO₂/SiO₂ 광촉매를 이용한 BTEX와 악취성 황화합물질 제거특성 연구

Abstract

Indoor air quality (IAQ) is of interest in term of impact on public health as a result of the growing number of complaints linked to poor air quality and of the recognized influence of environmental factors on the appearance of some pathological affections. The characterization of air pollution sources is mainly based on physico-chemical analytical methods for assessing emission of pollutants such as volatile organic compounds(VOCs). In this study, photodegradation of BTEX (benzene, toluene, ethylbenzene and xylene) and odorous sulfur compounds (H2S, CH3SH methyl mercaptan, dimethyl sulfide DMS and dimethyl disulfide; DMDS) havebeen examined in the fluidized bed gaseous reactor. Silica gel (particle diameter = 40~63㎛ surface area = 561 ㎡/g, MERCK), is used as a substrate to improve fluidization performance of TiO₂particles since TiO₂ powder is classified into Geldart C Group having poor fluidization characteristics. Precursor solutions for TiO₂coating on the silica gel are prepared using tetraisopropoxide (98.0% Junsei Chemical, Japan), hydrochloric acid (36%, Junsei Chemical Co., Ltd., Japan), isopropyl alcohol (for ACS analysis, CARLO ERBA REAGENTI) and deionized water. After mixing this solution for 180 minutesat room temperature, silica gel is added to the colloidal suspensions of TiO₂ and then it is dried at 100℃ for 24 hours. It is calcined at 500℃for 1 hour. A small Pyrex glass tube(60mm O.D. × 1000mm Height) is located inside at the middle of a large Pyrex glass tube(70mm O.D × 1000mm Height). The Gas distributor is also used to provide gas stream for uniform fluidization of TiO₂/SiO₂ photocatalyst. The UV lamp (Philips, F15TBLB, Ultraviolet Output=2.6watt, Ultraviolet rays range; 315nm~ 400nm, Ultraviolet rays peak; 352nm, 368nm) is installed inside the small Pyrex tube for effective ultraviolet light irradiation, which is similarly to visible ray. The BTEX were analyzed with a gas chromatography (QP2010, Shimadzu., Japan)equipped with a flame ionization detector and a mass spectrometry which is interlocked an automatic thermal desorption System (ATD400, Perkin Elmer., USA). The measurement system includes highly purified N₂ as a carrier gas and AT1 column. And the odorous sulfur compounds were analyszed GC-FPD(GC17A, Shimadzu., Japan) with automatric cryo injection system(TOP treading CO., LTD.,Korea). Structural characterization by XRD was carried out to verify the effect of hydrothermal treatments on the crystallographic structure and crystallite size of TiO₂/SiO₂. The TiO₂/SiO₂ photocatalysts were made by a sol-gel method and calcined at 500℃ for 1 hour. The different characteristics between rutile and anatase are attributed to the different position of the conduction band (more positive for rutile) and to the higher recombination rate of electron-hole pairs in rutile. The best experimental conditions of Ug based on the maximum BTEX removal efficiency are found at 2.0 of Umf and 1.43 of the bed height/diameter ratio. About 76.3%, 78.4%, 99.6%, 99.8% and 99.9% of removal efficiencies have been achieved for benzene, toluene, ethylbenzene, m, p-xylene, and o-xylene, respectively. And 87.5%, 80.4%, 89.2%, 94.2% and 93.4% of removal efficiencies with 60-mesh TiO₂/SiO₂ photocatalysts have been achieved for benzene, toluene, ethylbenzene, m, p-xylene, and o-xylene, respectively with BTEX initial concentration of 100±5ppbv and RH of 0%. The 99.8% of removal efficiency with 60-mesh TiO₂/SiO₂ photocatalysts has been achieved for methyl mercaptan. Concentrations of hydrogen sulfide, dimethyl sulfide and dimethyl disulfide stayed below detection limit after 10 minutes of operation time.