Fractionation of Liquid Mixtures

Fractionation of liquid mixtures with supercritical carbon dioxide in counter-cur-rent columns can be operated continuously, because liquids can be easily pumped into and out of a column. This represents a big advantage over extrachon from solid materials, as it allows real process intensification - large quantities of feed can be processed with only a small volume under high pressure at any given time. Frac-tionahon, mostly of natural products or extracts, has been extensively studied at the laboratory and pilot-plant scale. The design principles of this type of column have been established, and scale-up procedures devised [1,6]. They can be operated with reflux, as in distillation, and frachonahon can therefore become an extremely se-lechve process. Difficult separahons can be effechvely carried out. 

The fractionation of extracts previously obtained by water-ethanol extraction was described in detail by Brunner and Budich [7]. This development suggests that frac-tionahon with carbon dioxide can be advantageously used as a secondary separation process to obtain highly pure, high-value-added compounds from natural products. 

In any case, it may be said that this is a well-studied process, waiting for a first appHcation to go commercial. Once this happens, it can safely be predicted that many others will follow the same route. 

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Aptel P, Cuny J, Jozefowiczz J, Morel G, and Neel J. Liquid transport membranes prepared by grafting polar monomers onto poly(tetra fluoro ethylene) films I. Some fractions of liquid mixtures by pervaporation. J. App. Poly. Sci. 1972 16 1061-1076. 

J. Neel, Fractionation of Liquid Mixtures by Pervaporation through Artificial Membranes , publ. as[ll ]. 

Countercurrent multistage extraction is the application of SFE to the fractionation of liquid mixtures and the purification of liquid substances. SFE in the modification of countercurrent multistage operation extends the possibilities of separation processes, such as fractional distillation, absorption and liquid-liquid extraction to the isolation and purification of components of low volatility. The separation of volatile liquid components is also possible at tempera-... 

The diagram (Fig. 5.21) shows that as the pressure is reduced below the dew point, the volume of liquid in the two phase mixture initially increases. This contradicts the common observation of the fraction of liquids in a volatile mixture reducing as the pressure is dropped (vaporisation), and explains why the fluids are sometimes referred to as retrograde gas condensates. 

Distillation is probably Ihe most widely used separation (mass transfer) process in the chemical and allied industries. Its applications range from the rectification of alcohol, which has been practiced since antiquity, lo the fractionation of crude oil. The separation of liquid mixtures by distillation is based on differences in volatility between the components. The greater the... 

The supercritical fluid and liquid solubilities reported in Figs. 9-12 suggest that diamondoids will preferentially partition themselves into the high-pressure, high-temperature, and rather low-boiling fraction of any mixture including crude oil. 

The adsorption plateaus on this solid, determined with each of the surfactants (Table II) and the individual CMC values, were used to calculate the adsorption constants input in the model. Figure 3 compares the total adsorption (sulfonate + NP 30 EO) of the pseudo-binary system investigated as a function of the initial sulfonate fraction of the mixtures under two types of conditions (1) on the powder solid, batch testing with a solid/liquid ratio, S/L = 0.25 g/cc (2) in the porous medium made from the same solid, for which this solid ratio is much higher (S/L = 4.0 g/cc). 

Figure 15.7. Adsorption of liquid mixtures on charcoal. Chloroform + acetone and benzene + ethanol. The ordinate gives the amount of each individual substance that is adsorbed, the abscissa the mol fraction of chloroform (mixed with acetone) or the mol fraction of benzene (mixed with ethanol). (Data gathered by Kipling. Adsorption from Solutions of Non-Electrolytes, 1965).

Unless the boiling points of the components of a mixture are widely different it is usual to employ a fractionating column to attempt the separation of liquid mixtures by distillation. Apparatus for precision fractionation, which can successfully separate mixtures in which the components have boiling points which differ by only a few degrees, is available, although careful operation and an appreciation of the factors which influence the efficiency of the fractionating column chosen are needed. 

C, supercooled liquid, calculated-mole fraction of Aroclor mixtures, Murphy et al. 1987)... 

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