Separation in Two Distillation Fields

The feed must be sufficiently close to the distillation boundary, but on the concave side. 

Both products A and B must belong to the same residue curve, either on the same side with the feed, or on the other side of the boundary when this can be crossed. 

The selection of an entrainer with boundary crossing is based on the observation that in a RCM both A and B must be nodes, stable or unstable. By consequence the pure components are separated either as overhead or bottom products. Table 3.17 gives a list of recommended heuristics [13, 14]. In all cases, tbe distillation boundary must be highly curved, although how curved cannot be specified theoretically. In this case the simplest entrainer choice is a low-boiler entrainer for minimum AB azeotrope, and a high-boiler entrainer for maximum AB azeotrope, again not easy to meet in practice. 

Low boiler The entrainer has to boil lower than the minimum AB azeotrope. New maximum azeotropes with both A and B. At least one has to boil higher than the AB azeotrope. 

Medium boiler New minimum azeotrope with A, the low-boiling component. New maximum azeotrope with B, the high-boiling component. 

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Figure 9.16 Separation of acetone and chloroform with toluene (Alternative 1). Three columns sequence for separation in two distillation fields. The first split is sharp.

Three columns sequence for separation in two distillation fields. First split sloppy. 

Examples of suitable RCMs for azeotropic separation in a single field are given in Fig. 9.11. For a feasible sequence, A and B but not both must be a saddle, except in extractive distillation, when both A and B are saddles. Two columns are sufficient for... 

In membrane distillation, two liquids (usually two aqueous solutions) held at different temperatures are mechanically separated by a hydrophobic membrane. Vapors are transported via the membrane from the hot solution to the cold one. The most important (potential) applications of membrane distillation are in water desalination and water decontamination (77-79). Other possible fields of application include recovery of alcohols (e.g., ethanol, 2,3-butanediol) from fermentation broths (80), concentration of oil-water emulsions (81), and removal of water from azeotropic mixtures (82). Membrane (pervaporation) units can also be coupled with conventional distillation columns, for instance, in esterifications or in production of olefins, to split the azeotrope (83,84). 

The NMR spectrum of the product shows that two species are present. Both show two 3H triplets at about Sh = 1 and two 2H quartets at about 8 -3, One has a very low field proton and an ABX system at 2.1-2.9 with /AB 16 Hz, /ax 8 Hz, and /BX4 Hz. The other has a 2H singlet at 2.28 and two protons at 5,44 and 8.86 coupled with /13 Hz. One of these protons exchanges with D20, Any attempt to separate the mixture (for example, by distillation or chromatography) gives the same mixture. Both compounds, or the mixture, on treatment with ethanol in acid solution give the same product. What are these compounds ... 

Fig. 2 Fractograms were obtained with a Sd-FFF apparatus (77 X 1 X 0.0125 cm), (a) RBC elution profile on a new or properly washed FFF channel. Elution conditions flow injection of 5 X 10 RBCs (1/20 dilution of total blood in phosphate buffer saline pH 7.4/0.1 % of bovine albumin) external field 9.45g (1 g = 9.81 cm/s ) flow rate 0.7 mL/min, photometric detection at A = 313 nm. (b) Channel poisoning effect observed after 47 identical injections Idescribed in (A)], (c) Two sequences of RBC elution and channel cleaning procedure. Each sequence is RBC fractogram (flow injection of 5 X 10 RBCs (1/20 dilution of total blood in phosphate buffer saline pH 7.4), external field 25.7g, flow rate of 1.02 mL/min, photometric detection at A = 313 nm), external field stopped (S.R.), hypo-osmolar shock with doubly distilled water, cleaning agent (C.A.) signal, second water washing, (d) Example of fragile nucleated cells eluted in Sd-FFF neuroblasts (NB) case. Elution conditions flow injection of 1.5 X 10 neuroblasts in phosphate buffer saline pH 7.4/0.1 % of bovine albumin), external field 60.0g, flow rate of 1.25 mL/min, photometric detection at A = 254 nm. (e) Separation of components from an artificial mixture of neuroblasts and RBC. Elution conditions flow injection of 1.5 X 10 neuroblasts and 5 X 10 RBC in phosphate buffer saline pH 7.4/0.1 % of bovine albumin, external field 50.0g, flow rate of 1.25 mL/min, photometric detection at A = 254 nm.

Extraction of Essential Oils from Plants. Essential oils are aromatic substances widely used in the perfume industry, the pharmaceutical sector, and the food and human nutrition field. They are mixtures of more than 200 compounds that can be grouped basically into two fractions a volatile fraction, which constitutes 90-95% of the whole oil, and a nonvolatile residue, which constitutes the remaining 5-10%. The isolation, concentration, and purification of essential oils have been important processes for many years, as a consequence of the widespread use of these compounds. The common methods used are mainly based on solvent extraction and steam distillation. SFE has been used for the extraction of essential oils from plants, in an attempt to avoid the drawbacks linked to conventional techniques (57). Such is the case with the extraction of flavor and fragrance compounds, such as those from rose (58), rosemary (59), peppermint (60), eucalyptus (61), and guajava (62). The on-line coupling of the extraction and separation ietermi-nation steps (by SFE-GC-FID) has been proposed successfully for the analysis of herbs (63) and for vetiver essential oil (64). 

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