Extractant loss

However, the quantity of Pa produced in this manner is much less than the amount (more than 100 g) that has been isolated from the natural source. The methods for the recovery of protactinium include coprecipitation, solvent extraction, ion exchange, and volatility procedures. AH of these, however, are rendered difficult by the extreme tendency of protactinium(V) to form polymeric coUoidal particles composed of ionic species. These caimot be removed from aqueous media by solvent extraction losses may occur by adsorption to containers and protactinium may be adsorbed by any precipitate present. 

Third Monomers. In order to achieve certain property improvements, nitrile mbber producers add a third monomer to the emulsion polymerization process. When methacrylic acid is added to the polymer stmcture, a carboxylated nitrile mbber with greatly enhanced abrasion properties is achieved (9). Carboxylated nitrile mbber carries the ASTM designation of XNBR. Cross-linking monomers, eg, divinylbenzene or ethylene glycol dimethacrylate, produce precross-linked mbbers with low nerve and die swell. To avoid extraction losses of antioxidant as a result of contact with fluids duriag service, grades of NBR are available that have utilized a special third monomer that contains an antioxidant moiety (10). FiaaHy, terpolymers prepared from 1,3-butadiene, acrylonitrile, and isoprene are also commercially available. 

EtOH extraction was the most efficient way to improve the flavour of the phloem. A solvent/solid ratio of at least 10 1/kg was needed to achieve a significant change in the taste. The loss of catechins was approximately 27% and that of lignans was 35%. All the catechins and lignans were found from the EtOH extract. Losses of lignans and catechins were smaller with other sovents, but either the taste was not modified or the cost of solvent treatment would be too high. Phenolic compounds like lignans and catechins also have a bitter taste and some improvement in flavour may have occurred because of the lower concentration of these. The disappearance of the characteristic... 

Table 7.90 shows the main characteristics of the polymer/additive analysis procedure, consisting of dissolution followed by p. SEC-GC. An advantage of this approach is the minimisation of the extraction losses inherent in conventional sample preparation techniques. The determination of higher-molecular-weight additives is restricted, due to the upper interface temperature attainable in the GC-MS system. The usefulness of the tool for quantitative analysis has been ascertained [948,976],... 

Table 7.6 shows some typical reported extractant losses occurring in solvent extraction processes. Most of these data were obtained from inventory calculation and, hence, represent total loss from the several ways, by which solvent components may be lost from the system [3,15,16,58-69]. 

Table 7.6 Extractant Losses Reported for Some Processes... 

Membrane instability results in partial mixing of feed and stripping phases, which deteriorates the selectivity. In addition, raffinate and product are contaminated by the extractant, leading also to extractant losses. Economy of separation and hence industrial application of LM for separation of cephalosporins are strongly dependent on membrane stabilization. 

L = extraction loss or yield of extract, % of feed S = solvent dosage, % of feed VI = viscosity index a, b = constants... 

The strainmaster is a rectangular vessel construction fitted with a conical shaped bottom. The vessel is equipped with straining pipes horizontally orientated in the lower part. The advantage is that the pipes represent a larger filtration area compared to what is possible in a lauter tun yields are up to 13 brews/24 h. The higher capacities in all three alternatives are gained, however, at the expense of higher extract losses and water consumption. 

A chromatographic analysis that suffers from variation due to extraction losses, incomplete derivatization, column losses, extraneous peaks, and so on, will probably not be greatly aided by automatic integration. The precision enhancement comes largely from elimination of elements of manual methods that tend to reduce precision. 

The crown ethers were investigated mainly for the removal of Sr or Cs from nuclear-waste streams (246-250), and some studies reported their interest as selective extractants of plutonium (251). Different crown ether derivatives with the addition of alkyl chains have been examined, in order to increase the lipophilicity of the molecule and prevent major extractant losses due to high solubility in aqueous phases. These extractants were described as radiolytically resistant, and their stability increased in the order benzocrown > dicyclohexanocrown > crown (44). 

Environmental contaminants are present as complex mixtures, so that if toxicity is found, procedures known as toxicity identification evaluation may be carried out. This procedure identifies toxic components by systematically treating the effluent, elutrate, or pore water to remove various fractions - hydro-phobic ( fat soluble ) chemicals, metals, acids, volatile compounds, etc. - and retesting the toxicity after each extraction. Loss of toxicity after an extraction implicates the chemical that was extracted. This is confirmed by chemical analysis and toxicity tests on... 

Hengen and Hengen developed a method for the determination of nicotine and cotinlne in 1 ml samples of plasma. Nicotine was extracted from alkalinized plasma (NaOH) with diethyl ether, and cotinlne from the same sample with dichlbromethane. Modaline was used as internal standard for nicotine, lidocaine for cotinine. Analytical recovery of nicotine added to the plasma was 80 - 6 %, for cotinine 95 - 5 56. The internal standards were directly added to the plasma to monitor extraction losses. The sensitivity was such that less than 0.1 pg of nicotine and 0.1 pg of cotinine could be detected per liter. Day-to-day reproducibility for nicotine was within 14 % and within 6 % for cotinine. Narrow peaks for the gas chromatographed compounds were obtained on the very stable SP-2250 column (3 %) on Supelcoport at 155°C for... 

C morphine to correct for extractive losses. Morphine conjugates were hydrolyzed by B-gluc-uronidase and morphine extracted with ether. Nalorphine was used as an internal standard and... 

Treatment of contaminated wastewater by pervaporation is superficially attractive, however, only a few commercial installations have been built. Phenol, which azeotropes with water at around 10wt%, is typically recovered by extraction in large plants, where measures to eliminate extractant loss can be economically applied. Pervaporation is an attractive and cost competitive alternative for small plants. Organophilic membranes in spiral wound modules are used in these applications. 

The economics of the recovery are further affected by recovery yield (which also determines the cost of final effluent treatment), by the concentration and the purity of the recovered acid and by extractant losses and the cost of pretreatment of the feed, if required. 

The volatilities of ABC extractants are low, and they are practically insoluble in the aqueous streams (lower than those of the corresponding amine). As a result, extractant losses are low, and contamination of the exiting streams is avoided. Low volatility becomes a drawback in the purification of the extractant from impurities that may accumulate in it. Unlike in the case of volatile solvents, such as C4—C5 alkanols, that can be purified through distillation, in the case of ABC extractants, some feed pretreatment or partial treatment of the regenerated extractant by NaOH might be required. 

Figure 6. The effects of cytosol and microsome enzymes from a rat liver S9 preparation on the mutagenicity of nitropyrenes and diesel particle extracts. Loss of activity is also described as a percent decrease in the residual direct-acting mutagenicity.

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