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Impact of design parameters on the performance of ultraviolet photocatalytic oxidation air cleaner Donya Farhanian a , Fariborz Haghighat a, * , Chang-Seo Lee a , Ness Lakdawala b a Department of Building, Civil and Environment Engineering, Concordia University, Montreal, Quebec, Canada b DECTRON International Inc., Montreal, Quebec, Canada article info Article history: Received 4 January 2013 Received in revised form 11 April 2013 Accepted 14 April 2013 Keywords: Photocatalytic oxidation By-products UVC lamps VUV lamps Ozone Airflow rate abstract Ultraviolet photocatalytic oxidation (UV-PCO) is regarded as one of the promising technologies for air purification. Previous studies on UV-PCO of ethanol were performed in an ideal bench top reactors. However, this research is focused on UV-PCO of ethanol in full-scale open test rig which closely re- sembles the real application of this technology. Ethanol mineralization was investigated under several conditions including two types of UV-lamps (UVC and VUV) for two different photocatalysts under varied concentrations, airflow rate and relative humidity. In each case, removal efficiency and by-products yield were compared. Furthermore, possible mechanism for by-product formation is presented. Experimental results show that acetaldehyde and formaldehyde are the main by-products of ethanol. VUV lamps in- crease photocatalytic oxidation of ethanol compared to UVC lamps. The increase of relative humidity decreases UV-PCO of ethanol using both VUV and UVC lamps; however, the yield of by-products in the presence of VUV lamps increases while it decreases in the presence of UVC lamps. Higher flow rate results lower removal efficiency and consequently formation of less by-products. Improvement of re- action section by increasing the number of reactors leads to higher ethanol removal efficiency, less partial oxidation, lower amount of by-products and the complete mineralization of acetaldehyde. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Ultraviolet photocatalytic oxidation is one of the recent tech- nologies for mineralization of pollutants especially volatile organic compounds (VOCs) and it has many advantages compared to other existing methods [1e5]. Unlike other methods, UV-PCO could be used for mineralization of all groups of VOCs and applicable for indoor environment condition with no need for additional chem- icals injection. In this method, pure or doped metal oxide semi- conductors, mainly TiO 2 , used as a photocatalyst and UV-lamps as the energy source are exploited for the generation of electron/hole pairs. CO 2 and H 2 O are the main products of complete degradation of VOCs [6e8]. However, despite these advantages, the formation of by-products is one of the main constraints of the application of this technology in the gas-phase, especially for indoor air purification. These by-products can be either desorbed in air or accumulated in the catalyst surface. In the former, the effects of noxious by- products are the concern while in the latter concerns include catalyst deactivation hence decrease of process efficiency. Alcohols with C n H 2nþ1 OH formulation are one of the major groups of VOCs in indoor environments. Ethanol with 100% indoor environment frequency detection and 89 mg/m 3 has the highest concentration among all VOCs [9]. Based on the previous studies, two types of by-products mechanisms are possible in alcohol photocatalytic degradation: first, production of aldehyde or ketone as a result of direct oxidation or hydrogenation and second, the formation of olefins due to dehydration [10]. Muggli et al. [11] and Nimlos et al. [12] detected acetaldehyde, acetic acid, formaldehyde and formic acid as by-products of ethanol while Wisthaler et al. [13] identified methanol, and Kozlov and his colleague detected acetic acid, acetaldehyde, carboxylates, and carbonate as intermediate products [14]. Most of the previous parametric studies with respect to by- products formation are devoted to UV-PCO of toluene [2,3,5e8,15]. Zhao and his coworkers studied UV-PCO of toluene in a bench top reactor using two types of photocatalysts (P25 and N-doped TiO 2 ) and two types of UV-lights (UV and VUV), and different levels of relative humidity [2]. Quici et al. [16] investigated UV-PCO of toluene in the presence of VUV and UVC lamps in low concentration. They did parametric studies under presence of ozone for evaluation of toluene decomposition using two types of UV lamps. However, they did not investigate the by-products formation and they used small * Corresponding author. Tel.: þ1 415 848 2424x3192; fax: þ1 514 848 7965. E-mail addresses: [email protected], [email protected] (F. Haghighat). Contents lists available at SciVerse ScienceDirect Building and Environment journal homepage: www.elsevier.com/locate/buildenv 0360-1323/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.buildenv.2013.04.010 Building and Environment 66 (2013) 148e157
