Sorbents, commercial applications

Control of Juice Bitterness. A number of advances have been reported in this field since it was last reviewed (3). A commercial application of the cellulose acetate adsorption technique for the removal of limonin from citrus juices was undertaken (49). New sorbent gel forms of cellulose esters for adsorption of limonin were developed (50). Knowledge was gained that limonoids are biosynthesized in citrus leaves and translocated to the fruit (12) and that specific bioregulators can inhibit accumulation of XIV in citrus leaves (15). Additional studies were carried out on the use of neodiosmin to suppress limonin and other types of bitterness (30,51). The influence of extractor and finisher pressures on the level of limonin and naringin in grapefruit juice was reported (34). Also, further studies were conducted on the microbial sources and properties of limonoate dehydrogenase (52), the enzyme that converts XIV to XV and can be used to prevent limonin from forming in freshly expressed citrus juices (53). 

The use of commercially available preparative plates with a concentration zone will enhance separation. This zone is a layer of inert large-pore silica at the bottom of the plate onto which the sample is applied. As the solvent migrates through this zone, the mixture is unretained and focuses at the interface between the zone and normal sorbent. Uneven applications of mixtures are focused as discrete lines, and this will greatly improve separation/resolution. 

To be suitable for commercial applications, a sorbent should have a high selectivity to enable sharp separations, high capacity to minimize the amount of sorbent needed, and the capability of being regenerated for reuse. These properties depend upon the dynamic equilibrium distribution of the solute between the fluid and the solid surface. Unlike vapor-liquid and liquid-liquid equilibria where theory is often applied to estimate phase distribution of the solute, no acceptable theory has been developed to predict solid-sorbent equilibria. Thus, it is necessary to obtain... 

Table 1.1 shows examples of commercial applications of these sorbents. Both bulk separation and purification processes are given. Here bulk separation is defined (by Keller, 1983) as having the concentration of the adsorbed component above 10 wt % in the feed. For purification, the concentration of the adsorbed component is generally <2 wt % in the feed. The liquid-phase bulk separations that use the zeolites listed in Table 1.1 are accomplished with the simulated moving bed process. Not included in Table 1.1 are many liquid-phase bioseparations... 

Because the sorbent needs to be regenerated for most commercial applications, adsorption processes are necessarily cyclic. A number of cyclic adsorption processes are available, depending on the way the sorbent is regenerated. These processes have been discussed extensively elsewhere (e.g., Yang, 1987 Humphrey and Keller, 1997). 

Camell (1986) provides information on the first commercial application of the ICI zinc oxide sorbent on a North Sea oil platform. Although the material is capable of removing hydrogen sulfide from gases at low temperature, its performance does improve with tempera-... 

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 experience of application of various efferent methods of endotoxin elimination has led to the idea of creating selective anti-LPS hemosorbents with Polymyxin B as the bioUgand. The covalently immobilized Polymyxin B does not cause side effects characteristic of free Polymyxin B and keeps its therapeutic effects. G.W. Duff in 1982 demonstrated for the first time the sorption efficiency of Polymyxin B-immobilized sorbent in vitro [9]. In 1984 K. Hanasawa with co-workers developed PMX-F - a fibrous polystyrene based hemosorbent with immobilized Polymyxin B that could be used directly for blood perfusion [10]. In 1994 PMX-F sorbent was officially approved for patient treatment in Japan. Currently, there are several polymyxin immobilized (PMX-F) sorbents produced commercially for clinical use, such as Alteca - LPS Absorber (Sweden), Toray Industries hic. (Japan), etc. However these sorbents have poor hemocompatibility and are very expensive. 

Others would include the addition of materials aimed at increasing the bioavailability of the contaminant to the degrading organisms. The most studied compounds are surfactants, but cations have been reported to increase the bio availability of some oiganic compounds, and sorbents and days are also considered. The dispersion of spilled oil on water by the application of dispersants is perhaps the major commercial use of this idea. 

The following table provides a listing of the major types of sorbents used in sampling, concentrating, odor profiling, and air and water pollution research.16 These materials are useful in a wide variety of research and control applications. Many can be obtained commercially in different sizes, depending on the application involved. The purpose of this table is to aid in the choice of a sorbent for a given analysis. Information that is specific for solid phase microextraction (SPME) is provided elsewhere in this chapter. 

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