Oxidation characteristics of fluorine-, nitrogen-, and sulfur-containing organic compounds by UV/O3

by Chang, Ken-Lin

Abstract (Summary)
DMSO (dimethyl sulfoxide) is a liquid with a high boiling point (189 oC) that has been extensively utilized in various industries owing to its ability to dissolve various organic and inorganic compounds. DMSO is increasingly being adopted as a detergent or a photo-resistant stripping solvent in manufacturing semiconductors and liquid crystal displays (LCD). Therefore, DMSO is now a major component of wastewater. The biological treatment of DMSO-containing wastewater generates noxious DMS (dimethyl sulfide) and other compounds that may cause odor problems. Also having a high water solubility and a moderate boiling point (110 oC), tetrafluoro propanol (TFP) has been extensively applied in the manufacture of CD-R and DVD-R, due to its ability to dissolve organic dyes. The spin coating process produces a large amount of wastewater containing TFP. No reports have been written on the biodegradability of TFP to the authors¡¦ knowledge. Additionally, HMDS (hexamethyldisilazane) has been extensively used in life science microscopy and material science. For instance, the semiconductor industry employs HMDS to promote the adhesion of photo-resistant material to oxide(s). HMDS is classified as a carcinogen, and has an ammonia odor. Condensing incinerators have been found to be unsuitable for treating HMDS-containing waste gases, because of the formation of silicon dioxide, which blocks porous adsorbents. Biological treatment also appears to be unpromising due to its low water solubility and limited biodegradability. This investigation evaluates the feasibility, effectiveness and oxidation characteristics of aqueous DMSO, TFP and gaseous HMDS (hexamethyldisilazane) by UV/O3 processes. A reactor made entirely of acrylic plastic with an effective volume of 10 L was employed for the reactions. The tested VOCs concentrations were adjusted to 400¡V890mg/L and 772¡V887 mg/L for DMSO and TFP, respectively, and the gas (ozone-enriched air) flow rate was controlled at 3L/min. The effects of various solution pH values (acidic, alkaline, uncontrolled), solution temperatures (26 oC, 37 oC, 48 oC and 60 oC), and UV wavelengths (254 nm and 185+254 nm) on the removal of tested VOCs were studied . Additionally, the operation costs of treating DMSO and TFP by UV/O3 were estimated. Experimental results demonstrate that acidic conditions (pH = 3.6) favored the degradation of DMSO, and that the removal efficiency could reach 95% at a volumetric UV intensity P/V of 2.25 W/L and a reaction time of 120 min. However, alkaline conditions (pH = 9.5) favored the decomposition of TFP, with the removal efficiency reaching 95% at P/V = 2.5 W/L and a reaction time of 60 min. Both DMSO and TFP exhibited zero-order degradation kinetics when sufficient ozone was supplied. Raising the oxidation temperature did not increase the UV/O3 oxidation of TFP in the tested concentration and temperature ranges. Operation costs of the UV/O3 per unit volume of wastewater with DMSO or TFP are comparable to those of the methods described in the literature. For the gaseous HMDS oxidation, two batch reactors with effective volumes of 1.2 and 5.8 L were used employed with the decomposition occurred under UV (185+254 nm) irradiation and UV (254 nm)/O3 processes. Tests were performed with initial HMDS concentrations of 32¡V41mg/m3 under various initial ozone dosages (O3 (mg)/HMDS (mg) =1¡V5), atmospheres (N2, O2, and air), temperatures (28 oC, 46 oC, 65 oC and 80 oC), relative humilities (20%, 50%, 65% and 99%) and volumetric UV power inputs (0.87 W/L, 1.74 W/L, 4.07 W/L and 8.16 W/L) to assess their effects on the HMDS degradation rate. Results of this study demonstrate that the decomposition rates for the UV (185+254 nm) irradiation exceeded those for the UV (254 nm)/O3 process for all conditions. UV (185+254 nm) decompositions of HMDS displayed apparent first-order kinetics. A process with irradiation of UV (185+254 nm) to HMDS in air saturated with water at temperatures of 46¡V80 oC favors the HMDS degradation. With the above conditions and a P/V of around 8 W/L, k? 0.20 s?1, and over 90% of the initial HMDS was degraded in a time of 12s. The main mechanisms for the HMDS in wet air streams irradiated with UV (185+254 nm) were found to be caused by OH free radical oxidation produced from photolysis of water or O (1D) produced from photolysis of oxygen. Economic evaluation factors of UV (185+254 nm) and UV (254 nm)/O3 processes at various UV power inputs were also estimated.
Bibliographical Information:

Advisor:Chang, Jen-Ray; Ming-Shean Chou; Jimmy C. M. Kao; Shui-Jen Chen; Mei-Jywan Syu; Chu-Chin Hsieh; Ching-Chih Lai

School:National Sun Yat-Sen University

School Location:China - Taiwan

Source Type:Master's Thesis

Keywords:advanced oxidation processes aops dimethyl sulfoxide dmso tetrafluoro propanol tfp volatile organic compounds vocs hexamethyldisilazane hmds photolysis uv o3 ozonation


Date of Publication:09/10/2007

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