Purification of air

R.A. Khaydarov, O.U. Gapurova, R.R. Khaydarov, S.Y. Cho, Fibroid sorbents for purification of air, waste water and drinking water, Proceedings of the First International Conference on Environmental Researche and Assessments, Bucharest, Romania, March 23-27,2003, p.153-163. 

Purification of Air Prior to Liquefaction. Separation of air by cryogenic fractionation processes requires removal of water vapor and carbon dioxide to avoid heat exchanger freeze-up. Many plants today are using a 13X (Na-X) molecular sieve adsorbent to remove both water vapor and carbon dioxide from air in one adsorption step. Since there is no necessity for size selective adsorption, 13X molecular sieves are generally preferred over type A molecular sieves. The 13X molecular sieves have not only higher adsorptive capacities but also faster rates of C02 adsorption than type A molecular sieves. The rate of C02 adsorption in a commercial 13X molecular sieve seems to be controlled by macropore diffusion 37). The optimum operating temperature for C02 removal by 13X molecular sieve is reported as 160-190°K 38). 

This system can be applied to purification of air at underground parking places, offices, homes and other areas. For example, Daikir Industry Co. developed an air purifier using thin honeycomb type Ti02 photocatalysts irradiated by small UV lamps. The purifier consists of the photocatalvst and an electric precipitator tor removing both aii pollutants of formaldehyde, odorous species, etc., and particulate matter. 

The purification of air from matters in suspension has been discussed by... 

Fibrous filters are the most economical and effective devices for the purification of air from suspended particles. This purification is achieved with minimal loss of pumping energy associated with flow resistance, compared with other types of filters. The porosity of such materials is 85-99%, and fiber diameter varies from 102 to 10 2 /um. 

Another feature of these AOTs is that they are destructive types of water pollution removal processes because they eliminate compounds rather than transfer them to another medium. Thus, carbon adsorption or stripping transfers pollutants from one phase (water) to another phase such as a solid phase (carbon) or a gas phase (air). In the latter case, purification of air is required so that an additional step (i.e., carbon adsorption) is also needed, which implies higher processing costs. 

Table 2 Examples of commercially available semiconductor photocatalytic systems for purification of air ...

Semiconductor particles and films have been found to act as heterogeneous photocatalysts in a number of environmentally important reactions. Materials such as Ti02 and CdS have been found to be efficient in laboratory-scale pollution abatement systems, reducing both organic and inorganic pollutants/impurities to harmless species (see [1-35] and references therein). Photocatalysts have been shown to be useful for decomposition of O3 [36], destruction of bacteria [37-39] and viruses [40], purification of air [41], photosplitting of water [42,43] and clean-up of oil spills [44,45]. Photocat-... 

One of the activated carbons applications is purification of air and removal of odoriferous substances, hazardous to human health, from the atmosphere. Acetaldehyde can be considered as such a compound. Adsorption of formaldehyde on activated carbons was studied by Domingo-Garcia et al. [10]. They found that it is strongly adsorbed and the retention volumes obtained in that study increased with an increase in the surface areas of activated carbons. 

When a product has been isolated from a reaction the next step is to purify it. The degree of purity required will depend on the use for which the sample is intended, a synthetic intermediate might only require rough purification, whereas a product for elemental analysis would require rigorous purification. This section describes the most important purification techniques, crystallization, distillation, sublimation, and chromatography. It is assumed that the reader is familiar with the basic principles of these methods, so the emphasis is on more demanding applications such as the purification of air-sensitive materials, and purifications on a micro-scale. 

Strong-base ion-exchange fibrous materials (SBF) were tested as sorbents for purification of air from acid impurities exemplified by S02- The SBF exchangers were prepared by amination with the trimethylamine of chloromethylated polystyrene grafted on polypropylene fibres. 

Despite the elegant nature of this chemistry, the sequence is cumbersome, since two steps are required in the chain growth step and the synthesis and purification of air-sensitive materials is time-consuming and lowers the overall yield of oligomeric products. A simple modification of the above synthetic strategy leads to the systematic construction of oligostannanes up to 15 tin atoms in the linear chain as shown in Scheme 3.8.2. ... 

The first natural microporous aluminosilicate, i.e., natural zeolite, was discovered more than 200 years ago, and after long-term practical applications, the intrinsic properties of natural zeolites such as reversible water-adsorption capacity were fully recognized.13 41 By the end of the 19th century, during exploitation of ion-exchange capacity of some soils, it was found that natural zeolites exhibited similar properties some cations in natural zeolites could be ion-exchanged by other metal cations. Meanwhile, natural chabazite could adsorb water, methanol, ethanol, and formic acid vapor, but could hardly adsorb acetone, diethyl ether, or benzene. Soon afterwards, scientists began to realize the importance of such features, and use these materials as adsorbents and desiccants. Later, natural zeolites were also used widely in the field of separation and purification of air. 

Examples of molecular contaminants to be removed and carbon impregnating chemical used for purification of air for semiconductors production processes... 

The movement of charged aerosol particles in electric fields has many important technological applications, including electrodeposition (especially for painting metalhc surfaces such as automobiles) and electrophotography. It is also very important for the purification of air in critical situations. 

Environmental applications of CNTs include the purification of air, water, soil, etc., by using various properties of CNTs. For instance, properties such as high surface area, chemical stability and low density of CNTs make them suitable for applications such as adsorption of heavy ions, salts, etc., for wastewater purification [202]. CNT-based filters can be designed for such applications. 

Another early convert was Count Carlo Lodovico Morozzo (Mouroux) (Turin 5 August 1744-2 July 1804), general in the army of Piedmont, who published on the purification of air by plants, the composition of air, the colours of flowers and other vegetables, eudiometry of pure air and air vitiated by animal respiration, the gases obtained from dew, animal colours, the absorption of air by charcoal, and the respiration of oxygen. ... 

However, PSA is also used for drying of air and industrial gases. More applications continue to be discovered for PSA, including air prepurification (i.e., purification of air prior to cryogenic distillation by removal of carbon dioxide, water, and hydrocarbons see Rege et al., 2000). For air prepurification, PSA has been used only after ca. 1990. TSA and PSA are both currently being used. 

The gas-phase applications of polymeric resins are primarily used for gas chromatography and purification of air by removal of contaminants. The work of Hollis (1966) laid the foundation for the use of resins as packing materials for GC analysis. Hollis reported relative retention times of over 50 gas molecules on different EVB/styrene/DVB resins, using beads packed in a column. The same beaded forms are used today. The water vapor isotherm on the styrene/DVB resin... 

Actions for decrease in gas exhausts of flares in synthetic rubber production are developed. The device is developed for wet purification of the gas exhausts, confirmed high degree of purifieation both in laboratory, and in industrial conditions. The packaging scheme of gas purifying for synthetic rubber production is implanted. The complex of the made researches has formed the basis for designing of system of purification of air of industrial premises. Burning of gas exhausts on flares has allowed reducing pollution of air basin by toxic substances considerably. 

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