Gases from air

The removal of gases from air generally involves either absorption or adsorption. The absorption may be either into a liquid or solid. Often a reactant is used that forms a complex with the gas being removed. The reactant must then be regenerated and the pollutant removed in some concentrated form. The use of a reactant usually greatly increases the efficiency of the removal process.27... 

ODORGARD A process for removing odorous gases from air streams by scrubbing with an aqueous solution of sodium hypochlorite in the presence of a proprietary heterogeneous catalyst. The catalyst contains nickel and is based on the HYDECAT catalyst. Developed by ICI Katalco and F. H. H. Valentin. Nine units had been installed in the United Kingdom by 1995. World Patent WO 94/11091. 

Use information given in the text to construct a flow chart to show the processes involved in the extraction of gases from air. 

There is also the possibility of significant loss or flux of noble gases from air in the other direction (i.e., recycling back into the mantle by tectonic subduction or perhaps even just hiding of gas in some ill-studied reservoir, in quantities large enough to be important to inventory considerations). The issues here are more con-... 

The development of novel membranes for advanced, low-cost separa-tion/concentration of specific syngases is necessary. This would include H2, CO2, CO, and gaseous impurities (such as H2S). Membranes to separate other gases from air, such as O2 or N2, are also needed. Improvements could include a reduction in the number of steps or stages in a process or in processing speed. 

Fractional distillation is used for separations in many industrial processes. In this Pennsylvania plant, atmospheric air is liquefied by cooling and compression and then is separated by distillation in towers. This plant produces more than 1000 tons daily of gases from air (nitrogen, oxygen, and argon). 

Ahmed, M.S. Attia, Y.A. Multi-metal oxide aerogel for capture of pollution gases from air. Appl. Therm. Eng. 1998, 18 (9/10), 787-797. 

Effect of Noncondensables on Heat Transfer Most of the heat transfer in evaporators does not occur from pure steam but from vapor evolved in a preceding effect. This vapor usually contains inert gases— from air leakage if the preceding effect was under vacuum, from air entrained or dissolved in the feed, or from gases liberated by decom-... 

If required, relatively pure carbon monoxide can be recovered by cryogenic separation (i.e. condensation at very low temperatures), use of selective scrubbing solutions (for example CUAICI4 in toluene, the COSORB process) or solid adsorbents, and by other methods. Some CO recovery techniques are also applicable to the CO-rich (c. 70% molar) off-gases from basic oxygen furnaces and the leaner off-gases from air blast furnaces produced in steel manufacture, though operations of this type are still limited. 

Experimentally, the resistance at the interface has been shown to be negligible for most cases of mass transfer where chemical reactions do not occur, such as absorption of common gases from air to water and extraction of organic solutes from one phase to another. However, there are some exceptions. Certain surface-active compounds may concentrate at the interface and cause an interfacial resistance that slows down the diffusion of solute molecules. Theories to predict when interfacial resistance may occur are still obscure and unreliable. 

Most liquid solutions are obtained by dissolving a gas, liquid, or solid in some liquid. Soda water, for example, consists of a solution of carbon dioxide gas in water. Acetone, CsHgO, in water is an example of a liqnid—liquid solution. (Immiscible and miscible liquids are shown in Figure 12.1.) Brine is water with sodium chloride (a solid) dissolved in it. Seawater contains both dissolved gases (from air) and solids (mostly sodium chloride). 

Solutions of gases dissolved in water are common. Club soda, for example, is a solution of carbon dioxide and water, and most liquids exposed to air contain dissolved gases from air. Fish depend on the oxygen dissolved in lake or ocean water for life, and our blood contains dissolved nitrogen, oxygen, and carbon dioxide. Even tap water contains dissolved gases. The solubility of a gas in a liquid is affected by both temperature and pressure. 

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