Distillation coupling

Solid-phase microextraction has also been used for to determine volatile organic compounds in soil [26]. Target compounds were adsorbed directly from a head-space sample above a soil layer onto a fused-silica fibre. Vacuum distillation coupled with gas chromatography-mass spectrometry [27], head-... 

The development of a commercial mass spectrometer and its application to hydrocarbon gas analysis by the method of Washburn et al. (63) made gas analysis rapid, economical, and, what is even more important, inspired a confidence in the results of routine hydrocarbon gas analysis which was badly lacking. A complex gaseous mixture comprising the atmospheric gases, carbon monoxide, and Ci to C6 hydrocarbons required more than 20 hours of applied time by the previous methods of low temperature fractional distillation coupled with chemical absorption methods. With the mass spectrometer such an analysis is completed in 2 hours or less, about 15 minutes of which is consumed in the... 

The environmental site investigated for this study was at the US Environmental Protection Agency s National Exposure Research Laboratory on the University of Nevada Las Vegas (UNLV) campus. The VOCs monitored in this study were those that are persistent in the environment, that tended to bioconcentrate in an organic phase (hydrophobic), and that could easily be detected in air and leaves. Nine different plant species found on the UNLV campus were analysed by using vacuum distillation coupled with GC-MS to determine concentrations of VOCs. Grab air samples were taken before and immediately after collection of leaves to determine the concentration of VOCs in air. 

The various components of LPG streams are used in a variety of processes. Propane, butane and isobutane are used as cracker feedstock for the production of olefins which is discussed in later chapters. In addition n-butane is used for the production of 1,3-butadiene. This compound can also be extracted from the C4 cracked gases by extensive distillation coupled with a selective absorption process. 

Membrane processes are versatile and flexible they can be combined with other methods in hybrid processes. Adapted to actual needs they can treat various process streams of different compositions and concentrations. Membrane distillation coupled with evaporation or reverse osmosis may improve the purification efficiency and increase decontamination factors. The flow chart of such hybrid processes is presented in Figure 30.21. In Figure 30.21a, the combination of MD unit with evaporator is shown. 

Figure 11.4 Ethanol purification via distillation coupled with pervaporation. Adapted from Huang, Baker, et al. (2010). 

A critical assessmentof methods available for the measurement of aggregation number concludes that isopiestic distillation coupled with sedimentation equilibria provides accurate data, but that the results of quasi-elastic light scattering are difficult to interpret and that luminescence quenching data are not soundly evaluated. 

The advantages of coupling a permeation membrane on a distillation-based propylene/propane fractionation were first evaluated in a study carried out at University of Colorado, Boulder, and sponsored by BP. Various membrane/ distillation coupling scenarios (membrane unit located on the top stream or on the bottom stream or on the side stream of the column, all cases with a recirculation of the propylene-enriched permeate inside the column) were compared with a reference case based on a propylene/propane splitter column operated with 152 theoretical stages, a reflux ratio equal to 24.1 and a feed... 

Triantafyllou, C., and Smith, R., The Design and Optimization of Fully Thermally Coupled Distillation Columns, Trans. IChemE, Part A, 70 118, 1992. 

Introduce complex distillation configurations. Introduce prefractionation arrangements (with or without thermal coupling), side-rectifiers, and side-strippers to the extent that operability can be... 

Acetone in conjunction with benzene as a solvent is widely employed. With cyclohexanone as the hydrogen acceptor, coupled with toluene or xylene as solvent, the use of higher reaction temperatures is possible and consequently the reaction time is considerably reduced furthermore, the excess of cyclohexanone can be easily separated from the reaction product by steam distillation. At least 0 25 mol of alkoxide per mol of alcohol is used however, since an excess of alkoxide has no detrimental effect 1 to 3 mols of aluminium alkoxide is recommended, particularly as water, either present in the reagents or formed during secondary reactions, will remove an equivalent quantity of the reagent. In the oxidation of steroids 50-200 mols of acetone or 10-20 mols of cyclohexanone are generally employed. 

Electrolysis, under similar conditions, of a mixture of two carboxylic acids RCOOH and R COOH leads, in addition to normal coupling products R—R and R —R, to cross coupling R—R. If a mixture of a saturated carboxylic acid and a half ester of an ato-dicarboxylic acid is electrolysed, there are three main products, viz., a hydrocarbon (I), a mono-ester (II), and a di-ester (HI) and these are readily separable by distillation. Some unsaturated ester (IV) is often present in small quantity. 

The chemist can try to separate the two isomers by careful fractional distillation but it will be next to impossible to do because both the cis and the trans have practically the same boiling point. There are a few things that the chemist can do or hope for to get rid of that cis isomer. The cis configuration is less stable than the trans and may switch over to the trans configuration with a little help. The chemist can gently heat the isosafrole oil to about 150°C for an hour or so. She can also try the same heating except have the oil mixed with some acetic acid. Also, the isosafrole can be fractionally distilled to ultra purity and then be allowed to simply sit for a couple of days. Trans isosafrole may spontaneously crystalize out while the cis form remains as an oil. They can then be separated by filtration. 

You know how just a couple of paragraphs ago where the chemist first filtered the crude crystals from the chilled reaction mixture, then washed them with water or acetic acid Well, all that liquid filtrate has a lot of valuable, unreacted piperonal or benzaldehyde in it. To rescue the stuff the chemist dilutes the mixture with 500ml dHaO and extracts it with DCM. The DCM is washed with 100ml 5% NaOH solution then vacuum distilled to give a dark oil which is unreacted aldehyde. Hey That s a lot of good material that can be put through the process again. 

Process Concepts. Hybrid systems involving gas-phase adsorption coupled with catalytic processes and with other separations processes (especially distillation and membrane systems) will be developed to take advantage of the unique features of each. The roles of adsorption systems will be to efficiently achieve very high degrees of purification to lower fouUng contaminant concentrations to very low levels in front of membrane and other separations processes or to provide unique separations of azeotropes, close-boiling isomers, and temperature-sensitive or reactive compounds. 

Electrochemical fluorination leads to fragmentation, coupling, and rearrangement reactions as well as giving the perfluorinated product. In addition, small amounts of hydrogen can be retained in the cmde product. The products are purified by treatment with base to remove the hydrogen-containing species and subsequently distilled. 

Hydroxyisoquinolines. Hydroxy groups in the 5-, 6-, 7-, and 8-position show phenoHc reactions for example, the Bucherer reaction leads to the corresponding anainoisoquinolines. Other typical reactions include the Mannich condensation, azo-coupling reactions, and nitrosation. Both 0-methyl and /V-methyl derivatives are obtained from the methylation of 1-hydroxyisoquinoline, indicating that both tautomeric forms are present. Distillation of various hydroxy compounds, eg, 1- and 4-hydroxyisoquinoline, with zinc dust removes the oxygen. Treatment of 1-isoquinolinol with phosphoms tribromide yields 1-bromoisoquinoline [1532-71 -4] (178). 

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