Other Alternatives

A variety of other ingenious schemes have been developed which could be applied to large-scale chromatography. In this section these methods are reviewed briefly. 

In the search to develop continuous chromatographic processes, a variety of two-dimensional designs have been developed. The most popular design has been the rotating annulus shown in Fig. I4.S-1. An annulus packed with sorbent is rotated slowly past the feed point. Solvent or carrier gas flows continuously downward in the remainder of the annulus. Solutes flow downward with the carrier and are carried around by 

RGURE 14.4-3 Schematic of appanms for moving-port chn niatt gnpliy F F, S B Solvent, P = Pnxfacts. Reprinted vrith permission fiom lEC Process Des. Dev., 23, 256 (1984). Cofiyright 1984 American Chemical Society. 

A rather different application of rotating equipment is to do normal elution chromatography in a centrifuge (chromatoftige). For example, in a basket type centrifuge first a layer of packing is laid down by 

Rotating annulus system for steady-state, two-dimensional 

FIGURE 14.5 1 Rotating annulus system for steady-state, two-dimensional chromatography. 

Recently proposed web-based assay sharing systems provide similar benefits, but without the confidence on the availability of the required crude at the required time. 

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Since (A) does not contain any other functional group in addition to the formyl group, one may predict that suitable reaction conditions could be found for all conversions into (A). Many other alternative target molecules can, of course, be formulated. The reduction of (H), for example, may require introduction of a protecting group, e.g. acetal formation. The industrial synthesis of (A) is based upon the oxidation of (E) since 3-methylbutanol (isoamyl alcohol) is a cheap distillation product from alcoholic fermentation ( fusel oils ). The second step of our simple antithetic analysis — systematic disconnection — will now be exemplified with all target molecules of the scheme above. For the sake of brevity we shall omit the syn-thons and indicate only the reagents and reaction conditions. 

The iaterpretation of the spectroscopy of SBSL is much less clear. At this writing, SBSL has been observed primarily ia aqueous fluids, and the spectra obtained are surprisiagly featureless. Some very interesting effects are observed when the gas contents of the bubble are changed (39,42). Furthermore, the spectra show practically no evidence of OH emissions, and when He and Ar bubbles are considered, continue to iacrease ia iatensity even iato the deep ultraviolet. These spectra are reminiscent of blackbody emission with temperatures considerably ia excess of 5000 K and lend some support to the concept of an imploding shock wave (41). Several other alternative explanations for SBSL have been presented, and there exists considerable theoretical activity ia this particular aspect of SBSL. 

Cost. It is necessary to produce the feedstock from which the monomer is generated, viz, the dimer, at a cost which can be supported by the commercial appHcation, and yet allow it to be economically competitive with all other alternative ways to achieve the same end result. This factor often, but not always, seriously limits the amount of effort that can be put iato dimer synthesis and purification. 

M. A. DeLuchi, "Emissions of Greenhouse Gases from the Use of Gasoline, Methanol, and Other Alternative Transportation Puels," ia W. Kohl, ed.. Methanol as an yiltemativeFuel Choice yin yissessment, ]oim. Hopkias Poreiga PoHcy lastitute, Washiagtoa, D.C., 1990, pp. 167—199. 

In certain brilliantine compositions, vegetable and animal oils are used as substitutes for mineral oil. In these systems, because of their potential for rancidity, antioxidants must be included. Other alternatives to mineral oils that have found utiHty in brilliantines are the polyethylene glycols which come in a variety of solubiHties and spreading properties. Use of these materials offers the advantage of chemical stabiHty to rancidity. Other additives found in brilliantines to improve their aesthetics include colorants, fragrance, medicated additives, lanolin, and fatty acid esters. 

Without other alternatives, the carboxyalkyl radicals couple to form dibasic acids HOOC(CH)2 COOH. In addition, the carboxyalkyl radical can be used for other desired radical reactions, eg, hydrogen abstraction, vinyl monomer polymerization, addition of carbon monoxide, etc. The reactions of this radical with chloride and cyanide ions are used to produce amino acids and lactams employed in the manufacture of polyamides, eg, nylon. 

Engineering design, then, involves many considerations (Fig. 1.7). The choice of a material must meet certain criteria on bulk and surface properties (strength and corrosion resistance, for example). But it must also be easy to fabricate it must appeal to potential consumers and it must compete economically with other alternative materials. In the next chapter we consider the economic aspects of this choice, returning in later chapters to a discussion of the other properties. 

The other alternative is to attempt to increase K -. Pure ceramics have a fracture toughness between 0.2 and 2 MPa m. A dispersion of particles of a second phase can increase this a little the advancing crack is pinned by the particles and bows between them, much as a dislocation is pinned by strong second phase particles (Chapter 10). 

In a similar study, Exxon describes an onshore plant where once again gas processing with a turboexpander was chosen over the other alternatives. The results of that report are detailed in Table 3-7. 

Probably the most widely used capacity control for the centrifugal compressor is speed control. The capacity curve when used with speed control covers a wide range. While electric variable speed motors offer a continuation to the speed control practice, there are some other alternatives available. Suction throttling has been widely used and offers a r sonable control range for a relatively low cost. 

Note that we refer to a process as inherently safer, when compared to some other alternative, but not as "inherently safe. All materials and processes have hazards, and it is not realistic or practical to propose that we can eliminate all of them. In many cases we can identify material and process alternatives which clearly reduce hazards, and we can consider those alternatives to be inherently safer. 

The ultimate goal of inherently safer design is elimination of all hazards with no need for controls. However, some control systems are always required. The working logic of a specific control system can make it inherently safer than other alternatives. 

Seek alternatives to chlorine for water treatment and disinfecting applications. For example, sodium hypochlorite has been used both in industrial and municipal water treatment applications (Somerville, 1990). Other alternatives include calcium hypochlorite, ozone, ultraviolet radiation and heat treatment (Negron, 1994 Mizerek, 1996). 

For other CERCLA sites the proeess ean be very different from the typieal DOE site. The proeess may start with various phases of site assessments. The intermediate step may be a pilot study, followed by a pilot plant operation, or possibly a removal aetion or other alternative. The final steps may vary widely. However, just as in DOE sites, the appropriate rule or requirement depends on the site-speeifie faeility or operation, the assoeiated hazards, and the potential for worker exposure to the hazards. For the Army Corps of Engineers eleanup or oversight, the rules will most likely be even more stringent than for OSHA or DOE. 

All processes potentially generate contaminants i.e., they act as sources. Often the contaminant is spread into and with the air around the process. Control of the contaminants is thus often the same as control of the contaminated air. Other alternatives to control contaminant sources are described in Chapter 3. 

As mentioned before, the efficiency of an exterior hood may be low, which is a disadvantage of this type of system. Before an exterior hood is chosen other alternatives should be investigated regarding efficiency, suitability, and cost. 

The recommendation is to start with Method A, if possible. If this is not possible Method C can be used, but it is recommended that the equations given in Method A, together with approximations of the contaminant s properties, be used to check and/or verify the manufacturer s data. Method B could be used if no other alternative exists. If the design is for a noncommercial or nonstandard exhaust, it is not possible to use Method C and it is strongly recommended to use Method A, even if only approximate values are available. 

In almost all cases the molecules have a higher value as liquid than as gas. Crude oil streams typically contain a low percentage of intermediate components. Thus, it is not normally economically attractive to consider other alternatives to multistage separation to stabilize the crude. In addition, the requirement to treat the oil at high temperature is more important than stabilizing the liquid and may require the flashing of both intermediate and heavy components to the gas stream. 

Inhibited THF is problematic for semipreparative separations. Because small quantities of polymer are being collected along with larger volumes of solvent, more inhibitor, usually butylated hydroxytoluene (BHT), than sample is often collected in each fraction. Thus, one must carefully consider if the BHT will cause a problem in the subsequent analysis of the isolated fractions. If it does, uninhibited THF or other alternate solvents should be used. It must be remember that if uninhibited THF is used, the analyst must pay careful attention to the inevitable peroxide formation in the solvent/fractions. 

Compared with other alternative motor fuel options (reformulated gasoline, compressed or liquefied natural gas, ethanol from corn or coal, methanol and electricity), propane has the lowest greenhouse gas emissions except for natural gas. According to a 1998 study by the Institute of Transportation Studies, greenhouse emissions from propane vehicles arc 21.8 percent less than from gasoline or diesel. 

The synthesis of aziridines through reactions between nitrenes or nitrenoids and alkenes involves the simultaneous (though often asynchronous vide supra) formation of two new C-N bonds. The most obvious other alternative synthetic analysis would be simultaneous formation of one C-N bond and one C-C bond (Scheme 4.26). Thus, reactions between carbenes or carbene equivalents and imines comprise an increasingly useful method for aziridination. In addition to carbenes and carbenoids, ylides have also been used to effect aziridinations of imines in all classes of this reaction type the mechanism frequently involves a stepwise, addition-elimination process, rather than a synchronous bond-forming event. 

These operations often select for impurity removal as well as further product concentration. Approaches include fractional precipitation. Other alternatives such as chromatography and adsorption are also considered as methods of process purification. 

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