Phase splitting extraction processes

Adrian et al. (2000) have reported a novel high-pressure liquid-liquid extraction process with reference to processing in biotechnology the example of cardiac glycosides (digitoxin and digoxin) is cited. A completely miscible, binary system of water and a hydrophobic organic solvent like ethanol can split into two liquid phases when a near-critical gas (e.g. CO2) is added. The near-critical C02/water/l-propanol system is reported, for which possibilities for industrial exploitation exist. 

The phenomenon of TPF is a disturbing one to be avoided for an application of liquid-liquid extraction. For the PUREX process, the conditions of TPF as functions of concentrations of HN03, U(VI), U(IV), and Pu(IV) diluent and temperature were investigated thoroughly (86-88). The conditions are commonly expressed in terms of LOC. The scientific elucidation, however, of the TPF, dealing with compo-sitions/speciation and structure of the phases, causes of the phase splitting and its mechanism, thermodynamic features of TPF, reasons for difference of the LOCs with respect to metals and acids, had been deficient. 

With increasing content of solute B, the states of raffinate and extract approach each other and, finally, coincide at the critical point. In consequence, density difference Ap and interfacial tension cr approach zero as shown in Fig. 6.1-2. Low values of Ap and cr make the phase splitting more difficult or even impossible. Therefore, the region near the critical point cannot be utilized in solvent extraction processes. 

One of the most cmcial problems of extraction processes is the splitting of the phases after completion of the inteifacial mass transfer. Phase splitting is very diffi-... 

Mutual solubility of polymers and volatile organic substances are of importance for many applications in polymer chemistry and polymer engineering. Polymerizations, which should be performed in homogeneous phase, require the complete miscibility of monomer, polymer, solvent (liquid or supercritical) and other additives. Subsequently, the extraction of the polymer product from the reaction mixture requires a phase split (into two liquid phases or into a vapor and a liquid phase) to obtain a polymer product of high purity on one side and the remaining monomer on the other side. In this context, the devolatilization of polymers is of particular interest. Another example is the use of polymer membranes for the separation of two volatile organic compounds. Here, besides the knowledge of diffusivity, the solubility (sorption) of the different components in the polymer membrane is also an important prerequisite for an efficient process. 

LC-NMR can be used to identify natural products in crnde plant extracts that usually consist of complex mixtnres. The crnde natural product extracts normally contain a great nnmber of closely related and difficult-to-separate compounds. The classical separation approach may become very tedious and time-consuming. The directly conpled HPLC-NMR presents an efficient separation techniqne together with a powerfnl spectroscopic method to speed up the identification process. LC-NMR has been nsed extensively for characterization of natnral prodncts. More recently, the combination of LC-NMR and LC-MS has been further developed in this field. Eor example, Wilson et al. have nsed combined on-flow NMR and electrospray ionization MS to characterize ecdysteroids in extracts of silene otites. After reversed-phase HPLC nsing D2O in acetonitrile-dj and UV detection, the LC flow was split 95 5 for the simnl-taneous detection by NMR and MS. The peaks of interest were analyzed by stop-flow NMR to give better quality spectra for structural assignment. 

In phase separation two immiscible fluids are physically separated. Microchannels offer the ability to separate phases in an orientation-independent manner, since capillary and surface tension forces are more dominant in these high-surface-area devices. Various microchannel phase separators have been developed to separate organic and aqueous phases for use in unit processes such as solvent extraction or reactions conducted at an aqueous organic interface [185-188]. The approach is to hydrophobize half of the channel with a non-polar agent so that the organic phase is constrained to the hydrophobic half and the aqueous phase to the hydrophilic half Phase separation is simply then a matter of splitting the flow at the hydrophobic-hydrophilic junction of the flow. 

---