Other Sorbents

From these results, it is seen that olefins can be recovered at high purities and reasonably high recoveries. The sorbent prodnctivities are higher than that obtained in air separation by PSA/VSA. As mentioned, for air separation, a single PSA/VSA can produce over 200 tons/day of oxygen. Thus, it is feasible to recover olefins at that scale with a single PSA nnit. 

4A zeolite and carbon molecular sieves (CMS) have been examined for N2/CH4 separation. A process using 4A zeolite for this separation was developed by Habgood (1958), but this process was limited to low temperatures (—79 to 0°C) and a high-methane feed content ( 90%). Ackley and Yang (1990) have demonstrated the use of carbon molecular sieve (CMS) for separation of N2/CH4 mixtures in pressure swing adsorption (PSA) processes but have also shown that the potential for CMS to achieve the desired pipeline quality (90% methane) is doubtful. The only two promising sorbents are clinoptilolites and titanosilicates, as discussed below. 

Clinoptilolite is a member of the heulandite group, and is the most abundant of the natural zeolites. Using Na+ as the only charge-compensating cation, the 

Frankiewicz and DonneUy (1983) showed the promise of a calcium-exchanged clinoptilolite for N2/CH4 separation by a PSA process, but the product was below pipeline quality. This work stimulated a good deal of interest in further investigation. Two Japanese patent applications (61-255,994, in 1986, and 62-132,542 in 1987, see Chao, 1990) disclosed the use of natural clinoptilolite and Ca-exchanged forms for nitrogen removal from methane. Chao (1990) suggested the use of Mg-exchanged clinoptilolite for N2/CH4 separation. 

The high-pressure N2 isotherms showed that the N2 capacity is still increasing noticeably with pressure at 7 atm. This trend reflects the large pore volnmes of clinoptilolites. Using a conservative valne of 0.138 cm /g for the pore volnme, the N2 capacity would be 4 mmol/g (assuming pore filling with liquid nitrogen 

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Characteristics of attrition and adsorption were investigated to remove CO2 in fluidized hed using activated carhon, activated alumina, molecular sieve 5 A and molecular sieve 13X. For every dry sorbent, attrition mainly still occurs in the early stage of fluidization and attrition indexs(AI) of molecular sieve 5A and molecular sieve 13X were higher than those of activated carbon and activated alumina. Percentage loss of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but that of activated carbon and activated alumina were 8.3% and 8.1%, respectively. Overall attrition rate constant (Ka) of activated alumina and activated carbon were lower than other sorbents. 

Table 2 summaries overall attrition rate constants (Ka) and physical properties for each dry sorbent. As shown in Table 2, Ka of activated alumina was the lower than any other sorbent, but was similar to activated carbon. However, we used activated carbon as dry sorbent to control CO2 because it is the most cost-effective among others.

Plates with 0.5- to 2-mm layer thickness are normally nsed for increased loading capacity. Layers can be self-made in the laboratory, or commercially precoated preparative plates are available with silica gel, alumina, cellulose, C-2 or C-18 bonded siliea gel, and other sorbents. Resolution is lower than on thinner analytical layers having a smaller average partiele size and particle size range. Precoated plates with a preadsorbent or eoneentrating zone faeilitate application of sample bands. 

The most-nsed stationary phase in PLC is sihca gel, with type 60 taking preference. In the fnture, other sorbents snch as the RP materials will also most probably be increasingly nsed. This will also be trae for the case of special PLC plates consisting of layer combinations snch as precoated plates with concentrating zones, resnlting in simphfication of sample application as well as an increase in the efficiency of separation. 

The bioassay results are given in Table II. Mutagenic activity was detected in eleven of the finished and six of the corresponding raw waters. These results indicate mutagenic agents can be accumulated from water using XAD-2 resin. Additional investigations have been performed to compare XAD-2 with other sorbents. 

Other sorbent tubes are designed to trap vapors by a chemical mechanism. Chemical sorption is almost always accomplished by coating a solid sorbent or support with the desired reactant. In this way, the substance of interest is not only removed from the gas stream being sampled, but is altered chemically. This type of sorption has the advantages of being more selective and rendering reactive substances stable. Many variables may affect the ability of a sorbent to collect an analyte. Some of the relevant factors are discussed below. 

Table I shows some of the characteristics of the commonly used sorbents. The charcoals are by far the most frequently used solid sorbent for organic vapors. Over 130 methods have been validated in our five-year study using coconut, petroleum, and synthetic charcoal. The other sorbents include silica gel, used primarily for amines, and porous polymers, used for substances not amenable to collection on charcoal or silica gel. Other researchers have used other sorbents, including Florisil, alumina, and molecular sieves.

Adsorption of mercury. All chemicals used were Merck or Baker analytical quality reagents, unless stated otherwise. From the commercially available adsorbents the following were used silica gel 60 A porosity, 0.063-0.200 mm particle size (Merck) charcoal 0.3-0.5 mm particle size, gas-chromatographic quality (Merck) alumina R Woelm hydrous zirconium oxide HZ0-1, 100-200 mesh, (Bio-Rad). Except for zirconium phosphate, which was prepared according to Amphlett ( ), all other sorbents were prepared by coating (precipitation) on acid-purified silica gel, as described in (1 ). The Si0 -NH was prepared according to Leyden et al (11). L... 

Although some hydrotalcites can remove As(III) to less than 20(igL-1 in water (Jiang et al., 2007), most of them, as with many other sorbents, are not very effective with As(III). Therefore, any As(III) should be oxidized before treatment with these compounds (Yang et al., 2005 Bhaumik, Samanta and Mai, 2005). 

Flue gas desulfurization The injection of calcium or other sorbents to remove sulfur from flue gases. Fluorescent probe A chemical that can produce light when being acted upon by a source of energy. Fluvial A term used to describe structures, organisms, sediments, and other features associated with rivers. 

Brown (1996) reported the results of a multi-laboratory study concerning the suitability of different sorbents for the measurement of VOCs in the workplace environment. In this study 20 test compounds were used and the sorbents had to fulfill a number of test criteria. Chromosorb 106 was found to be the most versatile sorbent and especially useful for the sampling of very volatile and polar compounds. Other sorbents which satisfied the acceptance criteria were Carbotrap, Tenax TA, Tenax GR and Carbopack B. 

MIP-SPE sorbents are stable in both aqueous and organic solvents and are very selective for the analyte of interest. Increased selectivity relative to other sorbents produces increased sensitivity because larger sample volumes can be extracted. Also, increased selectivity results in efficient sample cleanup of the analyte in the presence of complex biological or environmental matrix... 

Numerous examples of the ulitity and selectivity of these sorbents are. given below. Table 2.3 lists nine steroids that were tested for their retentiveness on five different sorbents [31]. The steroid standards at 1 mg/ml were dissolved in methanol-water for the evaluation of a C,8 sorbent. For all the other sorbents, the steroids were dissolved in methylene chloride. At the polarity extremes for these steroids, cholesterol (the least polar) is retained only on C18, whereas hydrocortisone (most polar) is retained on all five of the sorbents tested. 

Silica gel 60, the most versatile and most frequently used TLC sorbent, was taken as a basis. The mean particle size of this sorbent was optimized simultaneously, the particle size distribution was brought to within as narrow limits as possible (L- ) The sorbent material thus obtained was used t prepare HPTLC pre-coated plates silica gel 60, being followed subsequently by the development of other sorbents for processing into HPTLC pre-coated layers. The materials chosen were largely "reversed phase" sorbents, that is to say, chemically modified silica gels with a non-polar surface (, 8), as well as microcrystalline cellulose ( )""... 

VII. Other Sorbents and Their Unique Adsorption Properties Carbon Nanotubes, Heteropoly Compounds, and Pillared Clays 118... 

Activated carbon is the most widely used sorbent. Its manufacture and use date back to the 19th century (Jankowska, Swiatkowski, and Choma, 1991). The pore-size distribution of a typical activated carbon is given in Fig. 1, along with several other sorbents. Excellent reviews on activated carbon are available elsewhere (Jankowska, Swiatkowski, and Choma, 1991 Rouquerol, Rouquerol, and Sing, 1999 Barton et al, 1999). 

Because of its large accessible internal surface, it adsorbs more nonpolar and weakly polar organic molecules than other sorbents do. 

The heat of adsorption, or bond strength, is generally lower on activated carbon than on other sorbents. Consequently, stripping of the adsorbed molecules is easier and results in lower energy requirements for regeneration of the sorbent. 

It is not correct, however, to regard activated carbon as hydrophobic. The equilibrium sorption of water vapor on an anthracite-derived activated carbon is compared with that of other sorbents in Fig. 2. The sorption of water vapor on activated carbon follows a Type V isotherm (according to... 

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