Diluents aromatic

The anionic exchange reagents commonly employed in these processes are tris-alkyl ammonium cations, generally dissolved in an aromatic diluent such as xylene. Tris-isooctylamine has been used at Falconbridge Nikkeiverk in Kristiandsand, Norway for the purification of solutions derived from HC1 leaching of Ni—Cu matte for over 30 years.103... 

Diluent Tendency to form third phases with aliphatic hydrocarbons. Long-chain alcohols as phase modifiers or aromatic diluents are necessary Many diluents can be used... 

Cobalt is then extracted into a 0.3 M solution of the tertiary amine Adogen 381 in an aromatic diluent ... 

Among these examples, a general trend is always observed third-phase formation is favored by larger alkane diluent molecules, the LOC is lower with a linear alkane chain diluent than with branched alkanes, and, generally, the third phase is prevented when aromatic diluents are used. In the language of surface wetting, short-chain solvents better wet the protruding chains. 

In contrast, in the TBP-aromatic diluent system, G(HDBP), G(H2MBP), and G(gaseous products) decreased (88), due to the aromatic diluents protective effect (23, 26, 39, 73, 88-90). 

The radiation resistance of TBP-aliphatic compound solutions could be improved by the introduction of aromatic derivatives the addition of only 10% of aromatic diluents or 0.1 mol L 1 mono-fvo-propyldiphcnyl reduced the global concentration of the degradation products by half (91, 94). 

In conclusion, despite their protective effect as regards degradation, the use of aromatic diluents has been avoided because of their low flash point. The classical diluents selected for PUREX process operations were hydrocarbons, either pure compounds (i.e., n-dodecane), or mixtures of different products (i.e., hydrogenated polypropylene tetramer, odorless kerosene, etc.) (93). Halocarbon diluents had two major drawbacks linked to their radiolytic behavior sensitization of TBP degradation and the production of extremely corrosive chloride ions (89, 93, 95). 

The protective effect of aromatic diluents has encouraged authors to test the radio-lytic stability of TODGA derivatives possessing an aromatic moiety. Two molecules were synthesized A,/V,/V7V -tctra(/j-octylphcnyl)diglycolamidc (T(OPh)DGA) and A,A,A,A -tetra-octylfuran-2,5-diamide (TOFDA) (183). The order of radiolytic stability was T(OPh)DGA > TOFDA > TODGA, which indicates that the presence... 

However, no significant effect was observed with other aromatic diluents such as tert-butyl benzene, 2,4-dinitrophenol, 2-nitrobiphenyl, or 2,2-dinitrobiphenyl (241). 

The nature of the diluent has an important role on the degradation rate of calix-arene (see Table 8.7). In dodecane, the loss of calixarene was very high, compared with measurements in the aromatic NPOE diluent. As already mentioned with other ligands (like TBP), aromatic diluents had a protective effect, explained by a lower ionization potential. However, serious radiolytic damage (e.g., a considerable rise in viscosity) has been observed with NPOE alone (68). Therefore, authors, such as Lamouroux, have suggested the use of a mixture NPOE-dodecane (72). 

The stabilizing effect of aromatic diluents has already been discussed (Section 8.4.2 on the mechanism), but the presence of an aromatic moiety inside the extractant also improves its radiolytic stability. 

Even so, aromatic diluents could cause important damage, as in the case of NPOE, a diluent proposed to solubilize calixarenes. In particular, a considerable increase in the viscosity of the organic phase was observed after radiolysis (68). 

Because aromatic diluents are more expensive and more toxic than aliphatic ones, the latter are preferably used in industrial practice (see earlier). Aromatic diluents, with equivalent molecular weights comparable to those of aliphatic ones, are more polar and thus more water soluble. The degradation of the diluent is usually negligible in comparison with that of the ion exchanger. The latter one can be chemically and thermally degrading and also can be poisoned by an irreversibly extracted compound. 

A process for the recovery of Am (and Pu) from these concentrates, based on solvent extraction with tricapryl methyl ammonium nitrate, TCMAN (Aliquat-336, nitrate form), was developed (30), and was operated for some time in a small-scale facility equipped with pulsed glass columns at the Alkem company to produce multi-gram amounts of americium dioxide. In its final version (3JU the process worked as follows The concentrated effluents were made up to 6 to 7 moles/1 nitric acid, and the U and Pu were extracted in the first column by 0,5 moles/1 TCMAN dissolved in Solves-so-100, a high-boiling aromatic diluent. U and Pu... 

Baroncelli, F., and G. Grossi Chemical Degradation of Aromatic Diluents Exposed to Nitric Acid Attack, in Solvent Extraction of Metals, H. A. C. McKay (ed.), Macmillan, London, 1965. 

Baroncelli et al. also determined the separation factors for Pu from initially 1.5 M U ion and 4 M HNOg by amine extractions with tri-n-dodecyl amine ("tri-lauryl-amine," TLA) in an aromatic diluent ("Solvesso 100") and a paraffinic diluent ("Shellsol T"), and found them to be similar, around 40. The TLA-Shellsol mixture had about... 

Solubility Characteristics Soluble in esters, ketones, ether/alcohol mixtures, glycol ethers. Excellent tolerance for aromatic diluent (toluene), le.ss tolerant for aliphatic diluents Formulating Considerations Avoid drying out during processing Supplier Aqualon... 

Nitrocellulose lacquers can be formulated with a large number of ketone solvents. Acetone, a fast evaporating solvent, will tolerate large additions of cheaper aromatic diluents to the nitrocellulose lacquers. The low viscosity of acetone and the hydrocarbon additions affords low solution viscosities. Other ketones that are useful as nitrocellulose solvents and that have high aliphatic and aromatic dilution ratios include MEK and MIBK. Additional ketones that find use in nitrocellulose lacquers include methyl /i-amyl ketone, methyl isoamyl ketone, dipropyl ketone, diisobutyl ketone, and cyclohexanone. Selection of the ketone often will depend on the desired evaporation rate. 

Most western countries have legislated reductions of hydrocarbon emissions. In SX plants, this means a tendency away from the use of aromatic components. In Africa, Australia, and South America, diluents containing 20 to 25% aromatic contents are still common, while in North America, diluents seldom contain more than 5% aromatics. Some processes, however, require 100% aromatic diluents because of their solvation properties. The uranium and precious metals industries often employ aromatic diluents, while cobalt, nickel, and zinc systems can anploy 100% aliphatic diluents. 

Most extraction procedures are useful for separating californium from americium/curium or from lighter actinides, but are limited for separating it from other transcurium elements. For example, HDEHP dissolved in an aromatic diluent has been used to separate Cf and Cm (separation factor 50). Efforts continue to find new and better extractants with the aim of improving separation factors and selectivity. It is unlikely that a specific extractant for californium will be developed but new materials may provide improved separation factors. Recent reviews that discuss californium extraction chemistry are available [32-34]. 

Trade name of extracting agent from Henkel Co. Ltd. Contains 2-hydroxy-5-nonylbenzophenone oxime and 40 volume percent inert aromatic diluent (Rltcey and Ashbrook, 1984a) (Table 5.2.4). 

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