Sorbents, commercial activated alumina

Defluoridation processes can be classified into four main groups Adsorption methods, in these methods sorbents such as bone charcoal, activated alumina and clay are used in column or batch systems. Ion-exchange methods, these methods require expensive commercial ion-exchange resins. Coprecipitation and... 

There are only four types of sorbents that have dominated the commercial use of adsorption activated carbon, molecular-sieve zeolites, sihca gel, and activated alumina. Estimates of worldwide annual sales of these sorbents are as follows (Humphry and Keller, 1997) ... 

The commercial alumina and silica gel sorbents are mesoporous, i.e., with pores mostly larger than 20 A (see Fig. 1). Activated alumina is produced by thermal dehydration or activation of aluminum trihydroxide, A1 (OH)3 (Yang, 1997), and is crystalline. Commercially, silica is prepared by mixing a sodium silicate solution with a mineral acid such as sulfuric or hydrochloric acid. The reaction produces a concentrated dispersion of finely divided particles of hydrated Si02, known as silica hydrosol or silicic acid ... 

During the last decade, there have been several published accounts on using adsorption for liquid fuel desulfurization. Commercially available sorbents (i.e., zeolites, activated carbon and activated alumina) were used in all of these studies. Weitkamp et al. 

First results on n-complexation sorbents for desulfurization with Ag-Y and Cu(I)-Y zeolites have been reported recently [3,4]. In this work, we included the known commercial sorbents such as Na-Y, Na-ZSMS, H-USY, activated carbon and activated alumina (Alcoa Selexsorb) and made a direct comparison with Cu(l)-Y and Ag-Y which were the sorbents with n-complexation capability. Thiophene and benzene vapors were used as the model system for desulfurization. Although most of these studies can be applied directly to liquid phase problems, Cu-Y (auto-reduced) and Ag-Y zeolites were also used to separate liquid mixtures of thiophene/benzene, thiophene/n-octane, and thiophene/benzene/n-octane at room temperature and atmospheric pressure using fixed-bed adsorption/breakthrough techniques. These mixtures were chosen to understand the adsorption behavior of sulfur compounds present in hydrocarbon liquid mixtures and to study the performance of the adsorbents in the desulfurization of transportation fuels. Moreover, a technique for regeneration of the adsorbents was developed in this study [4]. 

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 ... 

Physical sorbents for carbon dioxide separation and removal were extensively studied by industrial gas companies. Zeolite 13X, activated alumina, and their improved versions are typically used for removing carbon dioxide and moisture from air in either a TSA or a PSA process. The sorption temperatures for these applications are usually close to ambient temperature. There are a few studies on adsorption of carbon dioxide at high temperatures. The carbon dioxide adsorption isotherms on two commercial sorbents hydrotalcite-like compounds, EXM911 and activated alumina made by LaRoche Industries, are displayed in Fig. 8.F23,i24] shown in Fig. 8, LaRoche activated alumina has a higher carbon dioxide capacity than the EXM911 at 300° C. However, the adsorption capacities on both sorbents are too low for any practical applications in carbon dioxide sorption at high temperature. Conventional physical sorbents are basically not effective for carbon dioxide capture at flue gas temperature (> 400°C). There is a need to develop effective sorbents that can adsorb carbon dioxide at flue gas temperature to significantly reduce the gas volume to be treated for carbon sequestration. 

Fig. 8 Adsorption isotherms of carbon dioxide on commercial sorbents. (A) Hydrotalcite-like compound, EXM911 (B) LaRoche Industries activated alumina at 20, 200, and 300°C. (From Refs. -i l)...

Existing commercial sorbents including activated carbon, zeolites, activated alumina, and silica gels will 2. 

Table 7.1 lists the typical sorbents used their uses as well as strengths and weaknesses. The four major commercial adsorbents are the following zeolite molecular sieves (zms), activated alumina, silica gel, and activated carbon. The surfaces of activated alumina and most molecular-sieve zeolites are hydrophilic, and will preferentially adsorb water over organic molecules. Silicalite, which is a hydrophobic zeolite, is the main exception. Activated carbon, on the other hand, preferentially adsorbs organic and non-polar or weakly polar compounds over water. The surface of silica gel is somewhere in between these limits and has affinity for both water and organics. Detailed information about each of these classes of adsorbents can be found in Refs. [1,4, 6, 7]. 

Purification of aliphatics by the removal of aromatics is important in the petrochemical industry as well as for pollution control. In a typical benzene removal process, a combination of extraction and distillation is used (Meyers, 1986). Improvements by other processes have been considered, such as pervapora-tion (Hao et al., 1997), liquid membranes (Li, 1968 Li, 1971a and 1971b), and adsorption by temperature swing adsorption (TSA) in the liquid phase (Matz and Knaebel, 1990). In the work of Matz and Knaebel, commercially available sorbents were used silica gel, activated alumina, activated carbon, zeolite 13X,... 

The commercial sorbents (activated carbon, activated alumina, and zeolites) have all been studied for sulfur removal. The zeolites included 5A 13X (Salem, 1994 Salem and Hamid, 1997) various ZSM s, including ZSM-5 and silicalite (Weitkamp et ah, 1991) and ion-exchanged zeolites (Michlmayr, 1980 Vansant et al., 1988). The ion exchange was intended for the exchanged cation to form a bond with the sulfur atom in thiophene. Although some of these sorbents showed... 

The Alkalized Alumina process was developed by the U.S. Bureau of Mines and carried through the pilot-scale testing phase (Bienstock et al., 1964 1967). It has not been applied commercially. The process uses dawsonite [NaAl(C03)(OH)2]/sodium aluminate [NaA102] as the sorbent. Ihe material is activated at 1,200°F to form a high surface area, high porosity, dry solid, which removes sulfur dioxide from flue gas at temperatures between 300° and 650°F. This process is no longer being pursued due primarily to an excessive sorbent attrition rate. 

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