Alumina adsorption process

Adsorption processes use a solid material (adsorbent) possessing a large surface area and the ability to selectively adsorb a gas or a liquid on its surface. Examples of adsorbents are silica (Si02), anhydrous alumina (AI2O3), and molecular sieves (crystalline silica/alumina). Adsorption processes may be used to remove acid gases from natural gas and gas streams. For example, molecular sieves are used to dehydrate natural gas and to reduce its acid gases. 

Aluminum oxide (alumina), AI2O3, has lugh technological value. Sol-gel processing of alumina has created novel applications and improved some of its properties. Products such as catalyst earners, abrasives, fibers, films for electronic applications, aerogels, and membranes for molecular filtration have been developed based on sol-gel processing. See also Alumina Adsorption (Process) and Bauxite Aluminum and Aluminum Alloys and Engineered Materials. 

The use of adsorbents in conjunction with appropriate conditions for supercritical CO2 extraction enhances the efficiency of cholesterol extraction. Selective removal of 97% of cholesterol has been achieved with the use of silica gel as an in-line adsorbent (Huber et ah, 1996). Removal of 96% of cholesterol in milk fat fractions can be achieved by a combined supercritical C02 extraction and an alumina adsorption process (Mohamed et al., 1998). 

Bakhtiar 114 adsorbed toluene and iso-octane vapours from a vapour-laden air stream on to the surface of synthetic alumina microspheres and followed the change of concentration of the outlet gas with time, using a sonic gas analyser. It was found that equilibrium was attained between outlet gas and solids in all cases, and therefore transfer coefficients could not be calculated. The progress of the adsorption process was still followed, however. 

Fig. 43 Schematic representation of the adsorption process of pyrene labeled polyacrylic acid on alumina at different pH...

Most of the adsorbents used in the adsorption process are also useful to catalysis, because they can act as solid catalysts or their supports. The basic function of catalyst supports, usually porous adsorbents, is to keep the catalytically active phase in a highly dispersed state. It is obvious that the methods of preparation and characterization of adsorbents and catalysts are very similar or identical. The physical structure of catalysts is investigated by means of both adsorption methods and various instrumental techniques derived for estimating their porosity and surface area. Factors such as surface area, distribution of pore volumes, pore sizes, stability, and mechanical properties of materials used are also very important in both processes—adsorption and catalysis. Activated carbons, silica, and alumina species as well as natural amorphous aluminosilicates and zeolites are widely used as either catalyst supports or heterogeneous catalysts. From the above, the following conclusions can be easily drawn (Dabrowski, 2001) ... 

Separation of gas streams by adsorption is becoming increasingly popular as improved technology comes on the market. Some examples of commercially practiced adsorption processes are shown in Table 1. These processes take advantage of the selective adsorption properties of a number of microporous adsorbents, including activated carbon, silica, alumina, and various synthetic and natural zeolites. 

Complexation by metal oxides and clays. The adsorption processes of metals on silica, alumina, hydrated ferric oxide and a range of other minerals are well documented for laboratory studies performed with synthetic materials (Buffle, 1988 Dzombak and Morel, 1990 Stumm, 1992). The approaches described for major sites are applicable in this case. Nevertheless, the relevance of these data to natural water... 

It is a mass transfer between a mobile, solid, or liquid phase, and the adsorption bed packed in a reactor. To carry out adsorption, a reactor, where a dynamic adsorption process will occur, is packed with an adsorbent [2], The adsorbents normally used for these applications are active carbons, zeolites and related materials, silica, mesoporous molecular sieves, alumina, titanium dioxide, magnesium oxide, clays, and pillared clays. 

Reiger and Ballschmiter [43] described a multistep method for PCA analysis in sewage sludge by cyclohexane-isopropanol extraction and cleanup on silica gel column chromatography. Fractionation on silica gel was achieved by eluting with hexane (FI), which desorbed hexachlorobenzene, 4,4 -DDE, PCB, PCDD, and PCDF. PCAs were then desorbed from the column with (90 10) hexane/di-ethyl ether. The recovery of PCAs by this method was 86%. These authors also noted that cleanup chromatography on activated alumina should be avoided because PCAs were either totally or partially destroyed by dehydrochlorination during the adsorption process. 

To obtain individual phospholipids of greater than 50-60% purity, some form of selective adsorption process is usually required. Adsorption and distribution chromatography present these options. Treatment of the alcohol-soluble lecithin with alumina yields a fraction very rich in phosphatidylcholine and free of phosphatidylethanolamine and phosphatidylinositol (167). Although these products are available only in very limited quantities for highly specialized markets, products such as a lecithin containing up to 95% PC can be obtained commercially. 

Many existing water purihcation processes not enhanced by an electrical held are potential interesting helds of research. Li et al. described promising results for the adsorption of huorine on amorphous alumina supported on carbon nanotubes [72]. It is possible that their method can be enhanced by the use of electric held, as other researchers have shown with other electrically enhanced adsorption processes. 

An excellent review and detailed coverage on commercial adsorbents and new adsorbent materials has been presented by Yang in his newly published monograph on adsorbents.A very brief overview of existing commercial adsorbents is given here. Commercial sorbents that have been used in large-scale adsorptive separation and purification processes include activated carbon, zeolites, activated alumina, silica gel, and polymeric adsorbents. Although the worldwide sales of sorbent materials are relatively small as compared with other chemical commodities, sorbents and adsorption processes play a very important role in many process industries. The estimated worldwide sales of these sorbents are as follows ... 

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