Organic solvents in varnish can easily cause volatile organic compounds (VOCs) and odorous problems in manufacturing plants of enamel insulated wire. In general, the related process exhaust gases are treated by catalytic incinerators. However, the slight odors in the incinerated exhausts may induce uncomfortable feels to the inhabitants in the vicinity of the plants. Main components of odors are reported to be xylenes and to a lesser extent ketones. This study intended to oxidize the odorous compounds by chemical scrubbing method with either sodium hypochlorite or ozone as an oxidant and hydrogen peroxide as a reducing agent for the elimination of residual chlorine or ozone emitted from the oxidation scrubber. An additional study was the oxidation of aqueous mixed xylenes by sodium hypochlorite.
The first part of the study was the chemical oxidation of aqueous xylenes by sodium hypochlorite. Results indicated that more than 95 % of 20 mg/L xylenes could be converted to some oxygenated hydrocarbons with an initial effective chlorine concentration of 180 mg/L at pH 6.5 over a prolonged reaction time of over 120 min. With pH < 3 and a reaction time of 120 min, xylenes could be oxidized to benzene carboxylic acid that precipitated as organic crystalline solids to the reactor bottom.
The second part was chemical scrubbing of the odorous gases emitted from the catalytic incinerator. Operation conditions were an effective chlorine concentration of 1,500 mg/L and pH 6.5 for the oxidative scrubbing liquor, and a hydrogen peroxide concentration of 700 mg/L and pH > 12 for the reductive one. Results indicated that on an average, around 59 % of the influent xylenes could be removed, and the scrubbed gas was nearly odorless. 65.0 - 98.5 % of the influent non-aromatic compounds could be removed with trace amounts of chlorinated compounds in the gas were detected.
The third one was the treatment of the odorous gases by using ozone as an oxidant and followed by activated carbon adsorption. 18 - 34 mg/m3 of ozone was added to the test gas with initial xylene concentrations of 25 - 55 mg/m3. Results indicated that only around 35 % of the added xylene was removed with ozone contact times of 0.15 - 0.6 min. Although 99.9 % of the residual ozone and odors were removed by the activated carbon, a longer operation time should be tested to verify the performance. Trace amounts of ring cleavage precursors of 2.4-dimethylphenol and ring cleavage products were found in the ozonized gas.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0809111-192629 |
| Date | 09 August 2011 |
| Creators | Lai, Han-Chang |
| Contributors | Wen-Hsi Cheng, Ming-Shean Chou, Mei-Juan Xu |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0809111-192629 |
| Rights | user_define, Copyright information available at source archive |
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