G/L/S reactions

The aforementioned discussion was general in nature and also included conventional contactors such as tray and packed columns. In the case of three-phase (G-L-S) reactions, such conventional contactors are not used. The stirred reactor is the workhorse of the fine chemicals industry. The gas-inducing reactor can be considered as an alternative to stirred reactors when a pure gas is used. However, this reactor has several drawbacks (Chapter 9). In view of this, the venturi loop reactor has been widely used as a safe and energy-efficient alternative to the conventional stirred reactor. Table 3.3 summarizes the preceding discussion in the form of a multiphase reactor selection guide. 

In the fabrication of FIFMMRs, the porous hollow fiber membranes with asymmetric structures are first prepared through a phase-inversion/ sintering technique, which has been described in Chapter 2 of this book and in many recent publications [31]. The microstructure of the hollow fibers can be tailored as expected for different applications by modulation of the suspension composition and the spinning parameters [32, 33]. Aran et al. [5,21] developed porous AI2O3 FIFMMRs with various geometrical parameters for gas-liquid-solid (G-L-S) reactions. The Pd-AhOa catalyst... 

Kinetic data are reported as reaction rates (mol g l s 1) calculated assuming first order kinetics. Selectivities are calculated based on the carbon number of the original hydrocarbon. 

Nontheless, such a reaction course occurs only very infrequently in chemical reaction engineering. Most chemical reactions take place in heterogeneous material systems (G/L, L/L, G/S, L/S, G/L/S) and generate considerable amounts of reaction heat. Consequently, the genuine chemical action is accompanied by mass and heat transfer processes ( macro-kinetics ) which are scale-dependent. The course of such chemical reactions will be similar on a small and large scale, if the mass and heat transfer processes are similar and the chemistry remains the same. 

In most cases, the key reactions from bio-based educts to chemicals are gas/liquid/ solid (G/L/S) systems. 

The information presented in this chapter allows the construction of such a mathematical model for a G/S or L7S BSR, provided the kinetics of the reaction are known. In most instances in this chapter, the fluid phase is referred to as a gas unless stated otherwise, the relations presented are expected to be also valid for liquids. As was mentioned in the previous section, the development of the BSR concept for G/L/S applications is in a very early stage, and no suitable engineering relations have been developed yet. 

In microbiological processes foam problems occur therefore more often than in chemical reactions, because many metabolic processes produce surface-active substances, the process taking place in a 3- or 4-phase system (G-L-(S)-micro-... 

Petrov, V.A. Belen kii, G.G. German, L.S. Reaction of higher perfluorinated amines with antimony pentafluoride. Izv. Akad. Nauk SSSR, Ser. Khim. 1985, (8), 1934-1935. 

Sylvester, Kulkarni, and Carberry (1975) introduced a strategy in which a judicious estimate of certain physical parameters permits estimation of the intrinsic reaction rate coefficients in G L S processing. An overall effectiveness factor f is defined as... 

It is possible to apply the concept of pseudohomogeneity in cases where the diameter of small particles is slightly less than the film thickness d, which, in the two-film theory, corresponds to the transport resistance. This situation is illustrated in Fig. 4.29. In this example of a three-phase process, the S phase particles are suspended in the L phase. Five different concentration profiles are shown at the G [ L interface (cf. curves a-e) for various ratios of the reaction rate coefficient to the transport coefficient /cjr. In the case of a L S reaction with a large dp, only profiles a-c apply (cf. Fig. 4.28). 

Figure 4.29. Pseudohomog neous model approach for a heterogeneous G L S process. The solid phase, S, is homogeneously suspended in the liquid phase as small particles (floes with ds < li)- It affect mass transport through the G L interface, as shown in curve a-e in case of, for example, a reaction occurring in the liquid phase (or inside the floes) consuming O2.

Henrici-Olive G, Olive S Reactions of carbon monoxide with transition metal-carbon bonds, Transition Met Chem l(2) 77-93, 1976. 

The 1S,2R stereoisomer 17 has been obtained via the Baker s yeast reduction of the unsaturated bromoketone 18 in 99% e.e. and 75% yields at 3 g/L. The reaction occurs presumably through the reduction of the initially formed saturated ketone 19. The fact that racemic bromoketone 20 is also reduced by yeast to the same enantiomer with complete stereoselectivity is evidence that the intermediate bromoketone 19 rapidly racemizes in the reaction medium. The efficiency of the latter biotransformation makes it preferable to the corresponding yeast reduction of the unsaturated compound (Scheme 7). The preparation of such enantiomerically pure compounds found significance in the preparation of optically active l-amino-2-indanol as ligand in the human immunodeficiency virus (HIV) protease inhibitor indinavir [47]. 

Vibrational motion is thus an important primary step in a general reaction mechanism and detailed investigation of this motion is of utmost relevance for our understanding of the dynamics of chemical reactions. In classical mechanics, vibrational motion is described by the time evolution and l t) of general internal position and momentum coordinates. These time dependent fiinctions are solutions of the classical equations of motion, e.g. Newton s equations for given initial conditions and I Iq) = Pq. 

In analogy with the peracid attack on steroidal double bonds, the formation of the bromonium ion, e.g., (81a), occurs from the less hindered side (usually the a-side of the steroid nucleus) to give in the case of the olefin (81) the 9a-bromo-l l -ol (82). Base treatment of (82) provides the 9 5,1 l S-oxide (83). Similarly, reaction of 17/3-hydroxyestr-5(10)-en-3-one (9) with A -bromosuccinimide-perchloric acid followed by treatment with sodium hydroxide and sodium borohydride furnishes the 3, 17 5-dihydroxy-5a,l0a-oxirane. As mentioned previously, epoxidation of (9) with MPA gives the 5, 10 -oxirane. °... 

Preparation and Reactions of Polyfluorinated Aromatic Heterocyclic Compounds Yakobson G G, Petrova, T D, Kobnna, L S Fluorine Chem Rev 7, 115-223 285... 

A -methyl-5//,7//-dibenzo[d,.g][l,5]telluroazocine 65, its thiooxide 67a (X=S, R= Me) (95JA6388). The same type of reaction with benzylamine and sodium selenide gives A-benzyl-5//,7//-dibenzo[d,g][l,5]telluroazocine selenoxide 67b (X = Se, R = CH2Ph). Reaction of the tellurium dibromide 66 with sodium sulfide carried out in the absence of the primary amines affords the eight-member Te,S-containing heterocycle 5//,7//-dibenzo[d,g][l,5]telluroazocine (92CL151). 

In most of the successful Diels-Alder reactions reported, dienes containing no heteroatom have been employed, and enantioselective Diels-Alder reactions of multiply heteroatom-substituted dienes, e.g. Danishefsky s diene, are rare, despite their tremendous potential usefulness in complex molecular synthesis. Rawal and coworkers have reported that the Cr(III)-salen complex 15 is a suitable catalyst for the reaction of a-substituted a,/ -unsubstituted aldehydes with l-amino-3-siloxy dienes [21] (Scheme 1.28, Table 1.12). The counter-ion of the catalyst is important and good results are obtained in the reaction using the catalyst paired with the SbFg anion. 

A half-reaction in which the oxidation number of an element is increased. Examples 2 Mg(s) + 02(g) — 2MgO(s) (2, 3) Mg(s) - Mg2+(s) + 2 e. oxidation number The effective charge on an atom in a compound, calculated according to a set of rules (see Toolbox K.l). An increase in oxidation number corresponds to oxidation a decrease corresponds to reduction. 

Tilney, L.G. Inoue, S. (1982). Acrosomal reaction or Thyone sperm. 11. The kinetics and possible mechanism of acrosomal process elongation. J. Cell Biol. 93, 820-827. 

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