Fractional evaporation

Water hydrolyzes diethyl phosphorochloridate [chloro-diethoxyphosphorus(V) oxide] readily but does not affect the diene. Alternatively, the reaction mixture can be processed by fractionation. Evaporation of the petroleum ether and fractionation of the residue through a 25-cm. x 2.2-cm. column of glass helices yields 170 g. (98.5%) of diethyl phosphorochloridate, b.p. 34-36°/0.2 mm., d 1.4210-1.4250 (the refractive index indicates that it contains 5-10% of the title compound), and 240-255 g. (90-96%) of l,2,3,4,5-pentachloro-5-ethylcyclo-pentadiene, b.p. 51-53°/0.2 mm., 1.5398. 

Prepare a silica gel column as mentioned in Section 3. Transfer the solution derived from Section 6.1.1 to the column. Wash the flask with a small volume of n-hexane-ethyl acetate (9 1, v/v) mixture and elute with the same solvent mixture. Discard the first 50 mL of eluate and collect the next 110 mL of eluate in a 200-mL round-bottom flask (mepanipyrim fraction). Then, elute the column with 100 mL of n-hexane-ethyl acetate (1 1, v/v) mixture and collect the eluate (propanol form the metabolite fraction). Evaporate the solvents under reduced pressure and dissolve the residue in an appropriate volume of acetone for analysis. 

The probable impurities in radioactive phosphorus trichloride are hydrogen chloride and phosphorous acid the trichloride is, therefore, purified by fractional evaporation and fractional condensation in the high-vacuum system. Pure ethylphosphonous dichloride is prepared according to the equation ... 

Fig. 6. LNG composition as a function of fraction evaporated of initial LNG 85% methane, 10% ethane, 5% propane.

Stripping.. ..Removal of the light gases from a liquid stream using a fractionator, evaporation, or passing steam or hot air through it. 

The differential volatilization of neat kerosene components from a liquid phase, directly into the atmosphere during volatilization up to 50% (w/w), is presented in Fig. 8.8. Ten kerosene components were selected, and their composition was depicted as a function of gas chromatograph peak size (%), which is linearly related to their concentration. It may be seen that the lighter fractions evaporate at the beginning of the volatilization process. Increasing evaporation causes additional components to volatilize, which leads to a relative increase in the heavier fractions of kerosene in the remaining liquid. 

Dexamethasone 21-acetate [9-a-fluoro-16-a-methylprednisolone-21-acetate) [1177-87-3] M 434.5, m 215-225°, 229-231°, [a]2D5 +77.6° (c 1, dioxane), +73 (c 1, CHCI3). Purified on neutral Al203 using CHCI3 as eluent, fraction evaporated, and recrystd from CHCI3. UV has A,max at 239nm. [Oliveto et al. JACS 80 4431 1958]. 

C) lf the sample is a propellant, treat 1-2 g in a tared crucible (porcelain or platinum) with a few drops of coned nitric acid and heat on a steam bath, under the hood, until the evolution of nitrogen oxides subsides. Continue heating until the liquid fraction evaporates, thus leaving a gummy mass. Transfer the crucible to a triangle, and using a low flame heat carefully until most of the carbonaceous matter has been burned off. Finish the combustion at ca 600° for ca 1 hr, cool in a desiccator and weigh (Refs 1 2)... 

Sulphur Hexafluoride, SF6.—Sulphur hexafluoride, the first hexahalide to be discovered, is prepared by submitting sulphur to the action of fluorine in a copper tube. The issuing gas on condensation in a spiral tube of the same metal at —80° C. becomes partly solidified by allowing the solid to vaporise gradually and passing the vapours through potassium hydroxide solution and solid potassium hydroxide successively, the substance is rendered purer, complete purification being effected subsequently by re-solidification followed by fractional evaporation.4... 

Since there are N0 molecules in a completely covered layer, and the number evaporating per second from such a layer is v, the fraction evaporating per second is v/N0) and the average time elapsing between condensation and re-evaporation, or the average life5 of a molecule in the adsorbed layer, is NJv ... 

All tests for purity are made easier if a comparison sample of authentic purity is available. If such a sample is not available, it can be prepared by careful purification of a portion of the product itself. One bothersome, but generally applicable, method of testing for purity is carried out by recrystallizing a sample of the product being tested, and comparing the recrystallized material with that retained in the mother liquor. To this end, the mother liquor may be fractionally evaporated, whereupon the impurities, as a rule, will become so concentrated in the last mother liquor that they are easily detected. 

Hewins R. H., Yu Y., Zanda B., and Bourot-Denise M. (1997) Do nebular fractionations, evaporative losses, or both, influence chondrule compositions Antarct. Meteorit. Res. 10, 275-298. 

Vengosh A., Starinsky A., Kolodny Y., Chivas A. R., and Raab M. (1992) Boron isotope variations during fractional evaporation of sea water new constraints on the marine vs. nonmarine debate. Geology 20, 799-802. 

The small area irradiated by a CW laser would continuously melt and the spatial composition in the liquid would change with time because of fractional evaporation and mixing in the liquid phase. Furthermore, the plasma above the sample would be continuously heated and, if the intensity is not low enough, it would shield the sample from the laser beam because of absorption by the plasma can be reduced by the choice of a laser with a shorter wavelength, a different kind of gas or a lower gas pressure. 

The application of lasers with shorter pulses (e.g. in the picosecond or even femtosecond range) reduces heat dissipation by collisions of the high-energy electrons with the atoms in the solid, thereby minimizing melting of the laser crater region, as shown in Fig. 9.3, and fractional evaporation from the liquid phase. On the other hand, there is also less energy deposited in the gas plasma this usually facilitates atomization of the material ablated from the sample. 

There is also a simple graphical procedure for estimating the T h fraction vaporized on a Txy diagram. Suppose you are given a feed composition and (instead of specifying the fraction evaporated) the final temperature of the mixture at equilibrium. Then you can locate a point xp, T) on the Txy diagram. A horizontal line through this point intersects the vapor and liquid curves at the composition of those phases (xp, T) and (yp), T). 

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