Extraction of products

The higher activity of the catalyst [(mall)Ni(dppmo)][SbFg] in [BMIM][PFg] (TOF = 25,425 h ) relative to the reaction under identical conditions in CFF2C12 (TOF = 7591 h ) can be explained by the fast extraction of products and side products out of the catalyst layer and into the organic phase. A high concentration of internal olefins (from oligomerization and consecutive isomerization) at the catalyst is known to reduce catalytic activity, due to the formation of fairly stable Ni-olefin complexes. 

Fermentation broths are complex, aqueous mixtures of cells, comprising soluble extracellular, intracellular products and any unconverted substrate or unconvertible components. Recovery and extraction of product is important in bioprocess engineering. In particular separation is a useful technique it depends on product, its solubility, size of the process, and product value. Purification of high-value pharmaceutical products using chromatography such as hormones, antibody and enzymes is expensive and difficult to scale up.1 Tire necessary steps to follow a specific process depend on the nature of the product and the characteristics of the fermentation broth. There are a few steps for product recovery the following processes are discussed, which are considered as an alternative for product recovery from fermentation broth. 

For desymmetrization of diesters 3 via their hydrolysis in water, pig Hver esterase [12], o -chymotrypsin [12, 13a], and Candida antarctica Hpase (CAL-B) [14] were successfully used. However, further studies showed that respective anhydrides 5 can be used as substrates for enzyme-catalyzed desymmetrization in organic solvents [15]. The desired monoesters 4 were obtained in high yield in this way, using immobilized enzymes Novozym 435 or Chirazyme L-2 (Scheme 5.3). After the reaction, enzymes were filtered off, organic solvents were evaporated, and the crude products were crystalHzed. This was a much simpler experimental procedure in which control of the reaction progress was not necessary, and aU problems associated with extraction of products from aqueous phase and their further purification were omitted [15]. 

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Removal of reaction products can shift the equilibrium, forcing the reaction to go to completion. This can be effected by evaporation of products from the reaction mixture (reactive distillations), extraction (including supercritical extraction) of products from the reaction mixture (reactive extractions), or membrane processes. Counter- and cocurrent operation also falls within this category. If the reaction is equilibrium-limited or inhibited by reaction products countercurrent operation outperforms cocurrent operation. 

The stirred batch reactors are easy to operate and their configurations avoid temperature and concentration gradient (Table 5). These reactors are useful for hydrolysis reactions proceeding very slowly. After the end of the batch reaction, separation of the powdered enzyme support and the product from the reaction mixture can be accomplished by a simple centrifugation and/or filtration. Roffler et al. [114] investigated two-phase biocatalysis and described stirred-tank reactor coupled to a settler for extraction of product with direct solvent addition. This basic experimental setup can lead to a rather stable emulsion that needs a long settling time. 

It overcomes problems of product safety. Direct extraction of product from some native biological sources has, in the past, led to the unwitting transmission of disease. Examples include the transmission of blood-borne pathogens such as hepatitis B and C and human immunodeficiency virus (HIV) via infected blood products and the transmission of Creutzfeldt-Jakob disease to persons receiving human growth hormone (GH) preparations derived from human pituitaries. 

The product of the electrochemical reaction was extracted with cyclohexane. The yields observed in the reactions of PhBr and PhCH2Br were 35 and 75%, respectively. In the reaction of PhCH2Br, no toluene was formed, indicating that the process was highly selective and that the reduction of the halogenated substrate was avoided. It was further verified that, at the end of the electrolysis, the catalytic system completely regained its reversibility. The nickel(II) catalyst remained totally in the ionic liquid after the extraction of products, and the catalyst system was reusable. 

A further technique said to be useful on an industrial scale for the ECF conversion of alkanesulphonyl fluoride and tetramethyl sulphone to form per-fluoroalkane sulphonyl fluorides involves the continuous extraction of products from the electrolyte and hydrogen gas stream. The method claims high yields (93%) without recovery problems of prior art [151]. 

Extractive batch reactors (Figure 9.2-2) [22] are used for continuous extraction of products from reaction mixtures (containing liquid substrates and an enzyme preparation), which shifts the reaction equilibrium towards formation of the product. 

In some cases continuous extraction of products allows extended operation and high volumetric efficiency. Reactors run in this mode are referred to as continuous-stirred batch reactors... 

Extraction of products arising from the chemical degradation is described as part of several procedures detailed in Chapter 6. 

Enzyme-catalyzed reactions based on such biphasic systems have been shown to be promising alternatives for developing green chemical processes because of their physical and chemical characteristics [9]. By combining these media with enzymes, the possibilities of carrying out integral green biocatalytic processes has been already demonstrated [10-12]. Such biphasic systems can be used for both the biotransformation and extraction of products simultaneously, even under extremely harsh conditions, because of the different miscibilities of ILs and SC-CO2. 

Transformations of oxiranes into thiiranes by reaction with potassium thiocyanates, carried out in mixtures of ionic liquids (l-butyl-3-methylimidazolium hexafluorophosphonate ([bmim]PF6) or tetrafluoroborate ([bmim]BF4) and water (2 1), gave the corresponding thiiranes in very good yield (up to 96% Equation 56) <2003JOC2525>. The ionic liquid may be reused after extraction of products with ether for example, treatment of 2-phenyloxirane with potassium thiocyanate in [bmim]PF6 ionic liquid afforded 2-phenylthiirane in 93%, 89%, 85%, 81%, and 78% yields over five cycles. 

The production of flavour substances by cell or tissue cultures is still a dream for the future in most cases. Today the extraction of product from intact living plants is still less expensive than the production by isolated cells and tissues. On the other hand, it is very attractive to make use of the secondary metabolism of plant cells for the synthesis of natural flavours in a controlled way to avoid contaminating by-products and thus considerably simplify downstream processing. Further advantages of such cell culture systems would be the independence from agriculture combined with the risk for possible shortage and variances in product quality, the ability to scale-up the process to create an inexhaustible source of well-defined product. 

Results shown in Figure 32 are impressive, particularly in terms of TON values. Moreover, after extraction of products with toluene/hexanes (1 1), the IL phase was recycled 5 times without loss of catalytic activity. 

Acid extraction of product from silkworm body parts... 

Recently, however, a number of studies were published which demonstrated that radical brominations [23] and polymerizations, [24, 25] can proceed providing better (or roughly equal) results than the corresponding reactions in conventional solvents. Furthermore, hydroformylations, [26] CO2 hydrogenations, [27] catalytic additions/cyclo-additions on CO2, [28, 29] and enzymic reactions [30, 31] in SC-CO2 were successful. In many cases both reaction and extraction of products can profit from the supercritical phase. 

Substances in the sc state have a unique set of physical properties that make them attractive alternatives as reaction solvents. They have high miscibility with gases, liquid-like solvating power, and better-than-liquid transport properties, which invariably provide improved reaction rates. By far, the most commonly used fluid is GO2 because it is inexpensive, nontoxic, nonflammable, environmentally benign, and has low critical constants = 304.2 K = 72.8 bar). Accordingly, it has been lauded as a replacement for volatile organic solvents. The sc fluids also offer the potential to tune the solvent properties and affect yield, rate, and selectivity with pressure. In addition, the morphology of the product can be controlled by rapid expansion of sc solutions, and selective extraction of products from complex mixtures can be achieved by careful choice of solution density. 

In spite of the low productivity of the enzymic process - the large volumes of solution with low concentration of product the long duration of reaction and the need of additional purification, filtration, and extraction of product from reaction mixture the instability of the enzyme and the impossibility of recycling the enzyme - this process is still used in practice. 

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