Solvent loss

Thermal Stability. At processing temperatures in both the extraction and recovery plants the solvent should be completely stable to avoid expensive solvent losses contamination of the solvent by any solvent breakdown products must be avoided. 

Cost. The cost of fresh solvent is reflected in the operating costs in the form of solvent make-up charges. Avoidance of solvent losses, and hence a reduction of operating costs, may be obtainable through better plant design which is usually associated with increased capital costs. 

Finish removers are manufactured in open or closed ketdes. Closed ketdes are preferred because they prevent solvent loss and exposure to personnel. To reduce air emissions from the solvents, condensers are employed on vent stacks. Mild steel or black iron ketdes are used for neutral or basic removers stainless steel (316 or 317) or reinforced polyethylene ketdes are used for acidic removers. The ketdes are heated to increase dispersion of paraffin waxes and aid in the mixing of other ingredients. Electric or air driven motors drive either sweeping blade or propeller mixers that give sufficient lift to rotate and mix the Hquid. Dispenser-type mixers are used to manufacture thick and viscous removers. Ketde, fittings, mixer, and fill equipment must be fabricated with materials resistant to the chemicals in remover formulas. 

The second principal advantage is that CYANEX 272 is the only one of the three above-mentioned compounds that extracts cobalt in preference to calcium (52). This property can minimise or eliminate the solvent losses that are associated with calcium extraction and the subsequent precipitation of gypsum cmds in the scmbbing or stripping circuits. This is illustrated in Eigure 1 where calcium extraction is shown as a function of pH for the three subject reagents. 

Solvent Extraction. Extraction processes, used for separating one substance from another, are commonly employed in the pharmaceutical and food processing industries. Oilseed extraction is the most widely used extraction process on the basis of tons processed. Extraction-grade hexane is the solvent used to extract soybeans, cottonseed, com, peanuts, and other oilseeds to produce edible oils and meal used for animal feed supplements. Tight specifications require a narrow distillation range to minimize solvent losses as well as an extremely low benzene content. The specification also has a composition requirement, which is very unusual for a hydrocarbon, where the different components of the solvent must be present within certain ranges (see Exthaction). 

Solvent Extraction. Solvent extraction has widespread appHcation for uranium recovery from ores. In contrast to ion exchange, which is a batch process, solvent extraction can be operated in a continuous countercurrent-fiow manner. However, solvent extraction has a large disadvantage, owing to incomplete phase separation because of solubihty and the formation of emulsions. These effects, as well as solvent losses, result in financial losses and a potential pollution problem inherent in the disposal of spent leach solutions. For leach solutions with a concentration greater than 1 g U/L, solvent extraction is preferred. For low grade solutions with <1 g U/L and carbonate leach solutions, ion exchange is preferred (23). Solvent extraction has not proven economically useful for carbonate solutions. 

Film thickness is an important factor iu solvent loss and film formation. In the first stage of solvent evaporation, the rate of solvent loss depends on the first power of film thickness. However, iu the second stage when the solvent loss is diffusion rate controlled, it depends on the square of the film thickness. Although thin films lose solvent more rapidly than thick films, if the T of the dryiug film iucreases to ambient temperature duriug the evaporation of the solvent, then, even iu thin films, solvent loss is extremely slow. Models have been developed that predict the rate of solvent loss from films as functions of the evaporation rate, thickness, temperature, and concentration of solvent iu the film (9). 

An important characteristic of solvents is rate of evaporation. Rates of solvent loss are controUed by the vapor pressure of the solvent(s) and temperature, partial pressure of the solvent over the surface, and thus the air-flow rate over the surface, and the ratio of surface area to volume. Tables of relative evaporation rates, in which -butyl acetate is the standard, are widely used in selecting solvents. These relative rates are deterrnined experimentally by comparing the times required to evaporate 90% of a weighed amount of solvent from filter paper under standard conditions as compared to the time for -butyl acetate. The rates are dependent on the standard conditions selected (6). Most tables of relative evaporation rates are said to be at 25°C. This, however, means that the air temperature was 25°C, not that the temperature of the evaporating solvent was 25°C. As solvents evaporate, temperature drops and the drop in temperature is greatest for solvents that evaporate most rapidly. 

However, this difference would not seem to be large enough to account for the very large differences in solvent losses that have been reported. Another factor may be that high solids coatings may reach a stage where solvent loss is controUed by diffusion rate much eadier than is the case in low solids coatings (8,43). 

Chemical and physical solvent losses can render a process uneconomical. Desirable solvents are good solvents for urea, poor solvents for CA, high boiling, and stable to pyrolysis intermediates, ammonia, oxygen, and heat. Although no perfect solvent has been identified, some solvents, eg, dinitriles (94), pyrrohdinones (95,96), and sulfones (97) largely meet these requirements. 

Selection of Solvent When choice is possible, preference is given to liquids with high solubilities for the solute a high solubility reduces the amount of solvent to be circulated. The solvent should be relatively nonvolatile, inexpensive, noncorrosive, stable, nonviscous, nonfoaming, and preferably nonflammable. Since the exit gas normally leaves saturated with solvent, solvent loss can be costly and may present environmental contamination problems. Thus, low-cost solvents may be chosen over more expensive ones of higher solubility or lower volatility. 

Solvent solubility. A low solubility of extrac tion solvent in the raffinate generally leads to a high relative volatihty in a raffinate stripper or a low solvent loss if the raffinate is not desolventized. A low solubility of feed solvent in the extract leads to a high relative separation and, generally, to low solute-recovery costs. 

These characteristics combine to yield a system that has low heat and pumping requirements, is relatively noncorrosive, and suffers only minimal solvent losses (less than 1 Ib/MMscf). 

Flow coating Suitable for use on most articles. Gives good penetration into pores of castings Similar to dipping, but the defects not so marked. Tendency for greater solvent loss. 

Defined as everything produced except the desired product (including all inorganic. salts, solvent losses, etc.). 

Put in another way, the E factor represents the ratio of kilos in to kilos out i.e. it is the mass balance or the weight ratio of all the raw materials, including solvent losses, to the amount of desired product. It can be readily calculated for a particular product line, production site, or even a whole company. It is quite amazing, therefore, that so few... 

Phase ratio is given by the volume ratio of the two phases, and its significance is in the solvent extraction process. A small organic to aqueous ratio although beneficial ideally, it is sometimes unwelcome because it may result in high solvent losses. A raised organic to aqueous ratio, on the other hand, needs a large reservoir of solvent, and this may imply a financial burden. 

Solvent extraction carried out in conventional contactors like mixer-settlers and columns has certain limitations, including (a) controlling optimum dispersion and coalescence, (b) purifying both phases to ensure that stable emulsions are avoided (c) temperature control within a narrow band (d) high entrained solvent losses and related environmental and process economic effects and (e) large equipment dimensions and energy requirements when the density differential or selectivity is low. 

Estimated solvent loss 10 kg/d price 400/t. Plant attainment 95 per cent. 

Examples illustrating the reactions 21-23 are given in Figures 10-12. Shown in Figure 10 is the CID mass spectrum for the desolvation of Ni2+(H2O)10. The sequence of product ions Ni2+(H20) where n = 9 to n = 4 illustrates the sequential solvent loss represented by equation 21. The CID spectra in Figure 11 demonstrate that for the n = r = 4, charge reduction via internal proton transfer (see equation 23)... 

Table 2 gives a summary of results70,71 which provide the solvent number r at which simple solvent loss and charge reduction become competitive. Charge reduction becomes dominant for solvent numbers lower than r. Ion clusters for... 

An exothermic reaction with the stoichiometry A 2B takes place in organic solution. It is to be carried out in a cascade of two CSTR s in series. In order to equalize the heat load on each of the reactors it will be necessary to operate them at different temperatures. The reaction rates in each reactor will be the same, however. In order to minimize solvent losses by evaporation it will be necessary to operate the second reactor at 120 °C where the reaction rate constant is equal to 1.5 m3/kmole-ksec. If the effluent from the second reactor corresponds to 90% conversion and if the molal feed rate to the cascade is equal to 28 moles/ksec when the feed concentration is equal to 1.0 kmole/m3, how large must the reactors be If the activation energy for the reaction is 84 kJ/mole, at what temperature should the first reactor be operated ... 

The need for multiple desolvation of the metal ion in some systems may provide a barrier to complex formation which is reflected by lower formation rates - especially for inflexible macrocycles such as the porphyrins. Because of the high energies involved, multiple desolvation will be unlikely to occur before metal-ion insertion occurs rather, for flexible ligands, solvent loss will follow a stepwise pattern reflecting the successive binding of the donor atoms. However, because of the additional constraints in cyclic systems (relative to open-chain ones), there may be no alternative to simultaneous (multiple) desolvation during the coordination process. 

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