Multiphase extraction application

Before leaving ionic liquids it is worth mentioning their potential value in separation processes. Organic solvents are frequently used in multiphase extraction processes and pose the same problems in terms of VOC containment and recovery as they do in syntheses, hence ionic liquids could offer a more benign alternative. Interesting applications along this line which have been studied include separation of spent nuclear fuel from other nuclear waste and extraction of the antibiotic erythromycin-A. 

When producing high value biochemicals, the economic analysis is, generally, more favorable for the MBR systems, when compared with the more conventional units. Often selectivity rather than conversion may be the key, since higher selectivities typically result in the elimination of some of the purification steps which have a strong influence on the total production costs. The application of the multiphase/extractive enzyme membrane reactor for the production of a diltiazem chiral intermediate was reported in Chapter 4... 

Obviously, there are many good reasons to study ionic liquids as alternative solvents in transition metal-catalyzed reactions. Besides the engineering advantage of their nonvolatile natures, the investigation of new biphasic reactions with an ionic catalyst phase is of special interest. The possibility of adjusting solubility properties by different cation/anion combinations permits systematic optimization of the biphasic reaction (with regard, for example, to product selectivity). Attractive options to improve selectivity in multiphase reactions derive from the preferential solubility of only one reactant in the catalyst solvent or from the in situ extraction of reaction intermediates from the catalyst layer. Moreover, the application of an ionic liquid catalyst layer permits a biphasic reaction mode in many cases where this would not be possible with water or polar organic solvents (due to incompatibility with the catalyst or problems with substrate solubility, for example). 

Flowever, information concerning the characteristics of these systems under the conditions of a continuous process is still very limited. From a practical point of view, the concept of ionic liquid multiphasic catalysis can be applicable only if the resultant catalytic lifetimes and the elution losses of catalytic components into the organic or extractant layer containing products are within commercially acceptable ranges. To illustrate these points, two examples of applications mn on continuous pilot operation are described (i) biphasic dimerization of olefins catalyzed by nickel complexes in chloroaluminates, and (ii) biphasic alkylation of aromatic hydrocarbons with olefins and light olefin alkylation with isobutane, catalyzed by acidic chloroaluminates. 

This indicates that polymeric stabilizers having M > 800 have high resistance against extraction by components of foods, and, moreover, they do not enter into the metabolic cycle. Public concern over the contamination of the human environment can be thus satisfied. As a consequence, stabilizers like Poly AO-79 (97), Chimassorb 944 (161a) or Tinuvin 622 (146) may be legally used in stabilization of polymers in contact with food. Possibilities for application of other polymeric stabilizers for articles used in the home are open. Extractability problems may be thus overcome. Articles made from weather resistant butadiene based multiphase systems like ABS, MBS or MABS [84] stabilized in the most sensitive BR phase with polymer bound stabilizers may serve as an example. 

The transfer of mass within a fluid mixture or across a phase boundary is a process that plays a major role in various engineering and physiological applications. Typical operations where mass transfer is the dominant step are falling film evaporation and reaction, total and partial condensation, distillation and absorption in packed columns, liquid-liquid extraction, multiphase reactors, membrane separation, etc. The various mass transfer processes are classified according to equilibrium separation processes and rate-governed separation processes. Fig. 1 lists some of the prominent mass transfer operations showing the physical or chemical principle upon which the processes are based. 

It is possible to extend the procedure developed above to certain multiphase applications in which the power requirement has to be estimated. In the case of low-viscosity liquid/liquid systems, as encountered in solvent extraction, and for coarse solids suspended in low-viscosity liquids at low concentrations, the operation is likely to be carried out in the turbulent region. The single-phase power curves can be used in such instances with the mean density being used in both the power number and Reynolds number. However, such an approach must not be used for gas/liquid systems where predictions based on average density values can lead to gross over-estimates of the power requirement. This is considered in detail in Chapter IS. 

Electrokinetic and electrohydrodynamic instability mixing in microsystems is a complex phenomenon which researchers are only beginning to exploit and understand. Future work requires a further development of experimental models and expansion of computational simulations to better understand how the instabilities form and grow. Specific applications of electrokinetic and electrohydrodynamic instabilities are still limited. The application of these instabilities to improve mixing between components should be explored. One example is through the use of multiphase systems where electrohydrodynamic instabilities are utilized to improve component partitioning for liquid extraction devices. 

For the applications involving multiphase reactions and separations, the mass transfer of a solute from one phase to the other or of a pure phase into another is necessary. The mass transfer rates are different in nonreactive and reactive chemical systems. In nonreactive (separation/extraction) case, the mass is transferred from the phase with higher chemical potential (partial pressure or concentration) to the lower until the equilibrium is reached. In reactive systems, the mass transfer is enhanced because of the consumption of transferring species from one phase to the other. 

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