Extraction systems, reactive

In the mechanism of an interfacial catalysis, the structure and reactivity of the interfacial complex is very important, as well as those of the ligand itself. Recently, a powerful technique to measure the dynamic property of the interfacial complex was developed time resolved total reflection fluorometry. This technique was applied for the detection of the interfacial complex of Eu(lII), which was formed at the evanescent region of the interface when bathophenanthroline sulfate (bps) was added to the Eu(lII) with 2-thenoyl-trifuluoroacetone (Htta) extraction system [11]. The experimental observation of the double component luminescence decay profile showed the presence of dinuclear complex at the interface as illustrated in Scheme 5. The lifetime (31 /as) of the dinuclear complex was much shorter than the lifetime (98 /as) for an aqua-Eu(III) ion which has nine co-ordinating water molecules, because of a charge transfer deactivation. 

When using any solvent extraction system, one of the most important decisions is the selection of the solvent to be used. The properties which should be considered when choosing the appropriate solvent are selectivity distribution coefficients insolubility recoverability density interfacial tension chemical reactivity viscosity vapour pressure freezing point safety and cost. A balance must be obtained between the efficiency of extraction (the yield), the stability of the additive under the extraction conditions, the (instrumental and analyst) time required and cost of the equipment. Once extracted the functionality is lost and... 

TABLE 4 Some Processes Studied in Reactive Extraction Systems... 

Figure 2 illustrates the concentration profiles of various species (lactic acid, amine, and lactic acid-amine complex) in the extraction system. Both reactive and physical extractions of lactic acid take place at the interface between the aqueous and organic phases or at the outer membrane surface of the hollow fiber, and the solute flux owing to the extraction, /, can be described by Eq. 1 ... 

Two main criteria for the membrane selection are pore size and material. As peroxidases usually have sizes in the range of 10-80 kDa, ultrafiltration membranes with a molecular cutoff between 1 and 50 kDa are the most adequate to prevent enzyme leakage [99]. The materials commonly applied to ultrafiltration membranes are synthetic polymers (nylon, polypropylene, polyamide, polysulfone, cellulose and ceramic materials [101]. The adequate material depends on a great number of variables. When enzyme is immobilized into the matrix, this must be prepared at mild conditions to preserve the enzymatic activity. In the case of enzyme immobilization onto the membrane, this should be activated with the reactive groups necessary to interact with the functional groups of the enzyme. If an extractive system is considered, the selection of the hydrophilicity or hydro-phobicity of the membrane should be performed according to the features of reactants, products, and solvents. In any case, the membrane should not interfere with the catalytic integrity of the enzyme. 

Laboratory experiments, transport modeling, field data, and engineering cost analysis provide complementary information to be used in an assessment of the viability of an MNA approach for a site. Information from kinetic sorption/ desorption experiments, selective extraction experiments, reactive transport modeling, and historical case analyses of plumes at several UMTRA sites can be used to establish a framework for evaluation of MNA for uranium contamination (Brady et al, 1998, 2002 Bryan and Siegel, 1998 Jove-Colon et al, 2001). The results of a recent project conducted at the Hanford 100-N site provided information for evaluation of MNA for a °Sr plume that has reached the Columbia River (Kelley et al, 2002). The study included strontium sorption-desorption studies, strontium transport and hydrologic modeling of the near-river system, and evaluation of the comparative costs and predicted effectiveness of alternative remediation strategies. 

A reactive extraction system usually consists of a LEX diluted in a solvent. The latter is used to adjust rheological or physicochemical properties because most of the ion exchangers are highly viscous or even solid. The solvent should be nonmiscible with water and with a high boiling point (e.g., 500 K) to avoid losses. If kerosene-like solvents are used sometimes a modifier (e.g., isododecanol) is necessary in order to prevent the formation of a third phase and so to help to solubilize the ion-exchanger-solute complex. The regeneration and reextraction of the extract... 

Lee J.W., Hauan S., Lien K. and Westerberg A. (2000a). Difference points in extractive and reactive cascades. II. Generating design alternatives by the lever rule for reactive systems. Chemical Engineering Science 55, 3161-3174. 3.2.9... 

Pai RA, Doherty MF, Malone MF. (2002). Design of reactive extraction systems for bioproduct recovery. AIChE Journal, 48, 514—526. 

Thermodynamically and kinetically complex systems like azeotropic, extractive, and reactive systems pose additional bottlenecks in design and operation of batch columns. The following sections describe the methods for analyzing these complex systems. These methods also provide heuristics for synthesis of these columns especially in terms of the different cuts obtained in a single column or performance comparison of the complex columns. 

In spite of the importance of reaction prediction, only a few systems have been developed to tackle this problem, largely due to its complexity it demands a huge amount of work before a system is obtained that can make predictions of sufficient quality to be useful to a chemist. The most difficult task in the development of a system for the simulation of chemical reactions is the prediction of the course of chemical reactions. This can be achieved by using knowledge automatically extracted from reaction databases (see Section 10.3.1.2). Alternatively, explicit models of chemical reactivity will have to be included in a reaction simulation system. The modeling of chemical reactivity is a very complex task because so many factors can influence the course of a reaction (see Section 3.4). 

Methyl acetate-methanol Minimum boiling azeotrope None Element of recovery system for alternative to production of methyl acetate by reactive distillation alternative to azeotropic, extractive... 

Reactive distillation is one of the classic techniques of process intensification. This combination of reaction and distillation was first developed by Eastman Kodak under the 1984 patent in which methyl acetate was produced from methanol and acetic acid. One of the key elements of the design is to use the acetic acid as both a reactant and an extraction solvent within the system, thereby breaking the azeotrope that exists within the system. Likewise, the addition of the catalyst to the system allowed sufficient residence time such that high yields could be obtained, making the process commercially viable. Other examples in which reactive distillation may enhance selectivity include those of serial reactions, in which the intermediate is the desired product, and the reaction and separation rates can be systematically controlled to optimize the yield of the desired intermediate. ... 

Intelligent engineering can drastically improve process selectivity (see Sharma, 1988, 1990) as illustrated in Chapter 4 of this book. A combination of reaction with an appropriate separation operation is the first option if the reaction is limited by chemical equilibrium. In such combinations one product is removed from the reaction zone continuously, allowing for a higher conversion of raw materials. Extractive reactions involve the addition of a second liquid phase, in which the product is better soluble than the reactants, to the reaction zone. Thus, the product is withdrawn from the reactive phase shifting the reaction mixture to product(s). The same principle can be realized if an additive is introduced into the reaction zone that causes precipitation of the desired product. A combination of reaction with distillation in a single column allows the removal of volatile products from the reaction zone that is then realized in the (fractional) distillation zone. Finally, reaction can be combined with filtration. A typical example of the latter system is the application of catalytic membranes. In all these cases, withdrawal of the product shifts the equilibrium mixture to the product. 

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