Impurities solubility

The process of extraction with solvents is generally employed either for the isolation of dissolved substances from solutions or from solid mixtures or for the removal of undesired soluble impurities from mixtures. The latter process is usually termed washing. 

The above considerations apply also to the removal of a soluble impurity by extraction (or washing) with an immiscible solvent. Several washings with portions of the solvent give better results than a single washing with the total volume of the solvent. 

Purification of anthracene. Dissolve 0-3 g. of crude anthracene (usually yellowish in colour) in 160-200 ml. of hexane, and pass the solution through a column of activated alumina (1 5-2 X 8-10 cm.). Develop the chromatogram with 100 ml. of hexane. Examine the column in the hght of an ultra-violet lamp. A narrow, deep blue fluorescent zone (due to carbazole, m.p. 238°) will be seen near the top of the column. Immediately below this there is a yellow, non-fluorescent zone, due to naphthacene (m.p. 337°). The anthracene forms a broad, blue-violet fluorescent zone in the lower part of the column. Continue the development with hexane until fluorescent material commences to pass into the filtrate. Reject the first runnings which contain soluble impurities and yield a paraffin-hke substance upon evaporation. Now elute the column with hexane-benzene (1 1) until the yellow zone reaches the bottom region of the column. Upon concentration of the filtrate, pure anthracene, m.p. 215-216°, which is fluorescent in dayhght, is obtained. The experiment may be repeated several times in order to obtain a moderate quantity of material. 

The methyl ethyl ketazine forms an immiscible upper organic layer easily removed by decantation. The lower, aqueous phase, containing acetamide and sodium phosphate, is concentrated to remove water formed in the reaction and is then recycled to the reactor after a purge of water-soluble impurities. Organic by-products are separated from the ketazine layer by distillation. The purified ketazine is then hydrolyzed under pressure (0.2—1.5 MPa (2—15 atm)) to give aqueous hydrazine and methyl ethyl ketone overhead, which is recycled (122). The aqueous hydrazine is concentrated in a final distillation column. 

Soluble impurities can be extracted by washing with deionized or distilled water foUowed by filtration (1,12,26). Powders prepared by wet chemical synthesis are often washed and filtered for purification prior to use. The dewatering (qv) process can be enhanced by pressure filtration. Organic solvents can be used to remove water-insoluble impurities and wash-water sensitive materials. 

Lime-Sulfuric. Recovery of citric acid by calcium salt precipitation is shown in Figure 3. Although the chemistry is straightforward, the engineering principles, separation techniques, and unit operations employed result in a complex commercial process. The fermentation broth, which has been separated from the insoluble biomass, is treated with a calcium hydroxide (lime) slurry to precipitate calcium citrate. After sufficient reaction time, the calcium citrate slurry is filtered and the filter cake washed free of soluble impurities. The clean calcium citrate cake is reslurried and acidified with sulfuric acid, converting the calcium citrate to soluble citric acid and insoluble calcium sulfate. Both the calcium citrate and calcium sulfate reactions are generally performed in agitated reaction vessels made of 316 stainless steel and filtered on commercially available filtration equipment. 

There are numerous solubility data in the literature the standard reference is by Seidell (loc. cit.). Valuable as they are, they nevertheless must be used with caution because the solubihty of compounds is often influenced by pH and/or the presence of other soluble impurities which usually tend to depress the solubihty of the major constituents. While exact values for any system are frequently best determined by actual composition measurements, the difficulty of reproducing these solubility diagrams should not be underestimated. To obtain data which are readily reproducible, elaborate pains must be taken to be sure the system sampled is at equihbrium, and often this means holding a sample at constant temperature for a period of from 1 to 100 h. While the published cui ves may not be exac t for actual solutions of interest, they generally will be indicative of the shape of the solubility cui ve and will show the presence of hydrates or double salts. 

Washing in a continuous decanter is fairlv effective on solid particles larger than 80 jlrn (200 mesh), provided the particles are reasonably uniform in size with porous structure, Othenvise, the vv ash tlovvvs across the cake surface with little penetration because the pores at the cake surface are plugged bv fines. Rinsing efficiency, the proportion of soluble impurities displaced from the solids, is in the range of 50 to 80... 

Hydroxynaphthol Blue tri-Na salt [63451-35-4] M 620.5, m dec on heating, pKE,t <0. Crude material was treated with hot EtOH to remove soluble impurities, then dissolved in 20% aqueous MeOH and chromatographed on a cellulose powder column with propanol EtOH water (5 5 4) as eluent. The upper of three zones was eluted to give the pure dye which was ppted as the monosodium salt trihydrate by adding cone HCl to the concentrated eluate [Ito and Ueno zfna/ysr 95 583 1970. ... 

Neodymium oxide [1313-97-9] M 336.5, m 2320°. Dissolved in HCIO4, ppted as the oxalate with doubly recrystd oxalic acid, washed free of soluble impurities, dried at room temperature and ignited in a platinum crucible at higher than 850° in a stream of oxygen [Tobias and Garrett J Am Chem Soc 80 3532 1958]. 

The method of oxidation is essentially that of Russigd The product obtained is slightly but definitely better than that produced at a lower temperature, or by adding the sulfuric acid to the dichromate solution, or by using ferric clrloride as in A). These latter procedures give the same yield, but the product is less pure and contains a black, ether-soluble impurity which must be washed out carefully after crystallization from ether. 

Ninety-eight grams of 6-chloro-2-chloromethyl-4-phenylquinazoline 3-oxide hydrochloride were introduced into 600 cc of ice cold 25% methanolic methylamine. The mixture was initially cooled to about 30°C and then stirred at room temperature. After 15 hours the reaction product which precipitated was filtered off. The mother liquor was concentrated in vacuo to dryness. The residue was dissolved in methylene chloride, washed with water and dried with sodium sulfate. The methylene chloride solution was concentrated in vacuo and the crystalline residue was boiled with a small amount of acetone to dissolve the more soluble impurities. The mixture was then cooled at 5°C for 10 hours and filtered. The crystalline product, 7-chloro-2-methylamino-5-phenyl-3H-1,4-benzodiazepine 4-oxide, was recrystallized from ethanol forming light yellow plates, MP 236° to 236.5°C. 

In general, it is fair to state that one of the major difficulties in interpreting, and consequently in establishing definitive tests of, corrosion phenomena in fused metal or salt environments is the large influence of very small, and therefore not easily controlled, variations in solubility, impurity concentration, temperature gradient, etc. . For example, the solubility of iron in liquid mercury is of the order of 5 x 10 at 649°C, and static tests show iron and steel to be practically unaltered by exposure to mercury. Nevertheless, in mercury boiler service, severe operating difficulties were encountered owing to the mass transfer of iron from the hot to the cold portions of the unit. Another minute variation was found substantially to alleviate the problem the presence of 10 ppm of titanium in the mercury reduced the rate of attack to an inappreciable value at 650°C as little as 1 ppm of titanium was similarly effective at 454°C . 

The physical nature of the precipitate must be such that it can be readily separated from the solution by filtration, and can be washed free of soluble impurities. These conditions require that the particles are of such size that they do not pass through the filtering medium, and that the particle size is unaffected (or, at least, not diminished) by the washing process. 

Tinplate and Solder. Metallurgical studies were performed to determine the effect of irradiation at low temperature on the corrosion resistance of tinplate and on the mechanical properties and microstructure of tinplate and side-seam solder of the tinplate container. The area of major interest was the effect of low-temperature irradiation on the possible conversion of the tin from the beta form to the alpha form. In the case of pure tin, the transition occurs at 18 °C. It was feared that low-temperature irradiation would create dislocations in the crystal lattice of tin and enhance the conversion of tin from the silvery form to a powdery form rendering the tin coating ineffective in protecting the base steel. Tin used for industrial consumption contains trace amounts of soluble impurities of lead and antimony to retard this conversion for several years. 

The color requirement is intended to cover the unavoidable presence of a small amt of the red form of Explosive D in admlxt with the yel form. The requirement with respect to irritant contaminarit -represents a control of the purity of PA used in manuf when this is made by the dinitrochlorobenzene process. The chloroform soluble impurities requirement also represents a control of the nature of impurities present in PA manufd by a process other than the nitration of phenol ... 

A compound whose solubility increases with temperature can be purified by recrystallization. The impure solid is dissolved in a minimum volume of hot water. The hot solution is filtered to remove insoluble impurities, and then the solution is cooled in an ice bath. The solubility of the compound decreases as the temperature drops, causing the substance to precipitate from solution. Soluble impurities usually remain in solution. Purification by recrystallization is not restricted to aqueous solutions. An organic solid can be purified by recrystallization from an appropriate organic solvent. 

As a result of the decomposition, calcium chloride and other soluble impurities pass into solution, while tungstic acid, together with silica and undecomposed scheelite, remain in the residue. The technical grade tungstic acid thus obtained is purified using the ammonia-cal method. 

In the ultimate analysis it may be pointed that the aforesaid hydrolysis processes are no doubt technically very satisfactory and tolerable, but environmentally this is not the case. The different processes yield jarosite, goethite and hematite, all of which retain considerable amounts of other elements, especially, zinc and sulfur. The zinc originates mainly from undissolved zinc roast in the iron residues, and sulfur from sulfate, which is either embodied into the crystal lattice or adsorbed in the precipitate. As a consequence of the association of the impurities, none of these materials is suitable for iron making and therefore they must be disposed of by dumping. The extent of soluble impurities present in the iron residues means that environmentally safe disposal not an easy task, and increasing concern is being voiced about these problems. An alternative way of removing iron from... 

Several high-rate air flotation clarifiers (both DAF and dispersed air flotation) with less than 15 min of detention times have been developed for groundwater decontamination, industrial effluent treatment, resources recovery, and water reclamation. Both insoluble and soluble impurities such as... 

Example 10.2 An organic product with a flowrate of lOOOkg-h-1 contains a water-soluble impurity with a concentration of 6% wt. A laboratory test indicates that if the product is extracted with an equal mass of water, then 90% of the impurity is extracted. Assume that water and the organic product are immiscible. 

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