Emissions purification

Catalytic incineration (complete air oxidation) for the purification of gas streams is now quite commonly used in many applications (1-7), being preferred in these over thermal (non-catalytic) incineration and adsorption methods. It can offer advantages over thermal incineration in terms of costs, size, efficiency of destruction, and minimization of thermal NOx by-product formation. The catalytic incineration systems are now commonly employed in such applications as exhaust emission purification from a variety of industrial processes (including manufacture of organic chemicals and polymers) and air-stripping catalytic processes used to clean contaminated water or soil. 

The problems encountered with catalysts for auto emission purification are of the same type but of a totally different magnitude. Superior mechanical properties and, specifically, exceptional resistance to attrition are required. Furthermore, these properties should be unaffected by exposure to 1000°C and even 1100°C. Furthermore, a surface area of 50-80 m2/g and porosity of 0.6-0.8 cm3/g must remain after heating. Naturally the carrier must also withstand thermal shocks, offer the least possible diffusional limitation to reagents, and react as little as possible —or at least without unfavorable results—with the catalytically active oxides and metals deposited on its surface. 

Absorption is widely used as a raw material and/or product recovery technique in separation and purification of gaseous streams containing high concentrations of VOC, especially water-soluble compounds such as methanol, ethanol, isopropanol, butanol, acetone, and formaldehyde. Hydrophobic VOC can be absorbed using an amphiphilic block copolymer dissolved in water. However, as an emission control... 

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Extraction and purification of luciferin and luciferase (Viviani etal., 2002a) To isolate luciferin, the lanterns of the Australian A. flava were homogenized in hot 0.1 M citrate buffer, pH 5, and the mixture was heated to 95°C for 5 min. The mixture was acidified to pH 2.5-3.0 with HCl, and luciferin was extracted with ethyl acetate. Upon thin-layer chromatography (ethanol-ethyl acetate-water, 5 3 2 or 3 5 2), the active fraction of luciferin was fluorescent in purple (emission Lav 415 nm when excited at 290 nm). To isolate the luciferase, the cold-water extract prepared according to Wood (1993 see above) was chromatographed on a column of Sephacryl S-300. On the same... 

Its fluorescence showed two emission peaks, 564 nm and 626 nm the excitation peaks for the former emission peak were at 305 nm and 374 nm, and those for the latter were at 332 nm and 392 nm, indicating the presence of two different components in the preparation. It appears that the characteristics of the fluorescent proteins were altered by isolation and purification. 

Daubner, S. C., Astorga, A. M., Leisman, G. B., and Balwin, T. O. (1987). Yellow light emission of Vibrio barveyi strain Y-l purification and characterization of the energy-accepting yellow fluorescent protein. Proc. Natl. Acad. Sci. USA 84 8912-8916. 

Catalytic incineration has been appHed in the abatement of chlorinated VOC emissions in the pharmaceutical industry. The major compounds in the emission mixture are dichloromethane, perchloroethylene, dimethylformamide, oxitol, and toluene. The incinerator operates normally at 400-500 °C, but when emissions contain perchloroethylene the temperature is increased up to 500-600 °C. The emission mixture also contains water, which pushes the selectivity further toward HCl formation instead of formation of CI2. After oxidation, the product gases are washed with NaOH scrubbers. The purification level of over 99% can be achieved with the incinerator, the activity of which has been shown to be very stable after one year of continuous operation [69-71]. 

The fact that Fischer-Tropsch fuels contain neither sulfur nor aromatics may become a strong selling point for the process. Less sulfur in the fuel has, of course, a direct effect on the sulfur oxides in the emissions, and the newly developed exhaust purification systems for lean burning engines that can be introduced means that all emissions, including GO2 and NOx, will diminish. Aromatics promote particulate formation in the combustion of diesel fuels and are therefore undesirable. We discuss this further in Ghapter 10. 

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