Lewis cell

Some of the earliest attempts to address the difficulties associated with making kinetic measurements at immiscible liquid-liquid interfaces were made by Lewis [16,17] using the stirred cell design illustrated in Fig. 2. The Lewis cell employs direct contact between the two immiscible liquids, and reaction rates are evaluated by measuring concentration changes in the bulk of one of the two phases, usually by a batch extraction technique. The rate of change of concentration, dc/dt, is related to the interfacial reaction flux, 7, by... 

Although the Lewis cell was introduced over 50 years ago, and has several drawbacks, it is still used widely to study liquid-liquid interfacial kinetics, due to its simplicity and the adaptable nature of the experimental setup. For example, it was used recently to study the hydrolysis kinetics of -butyl acetate in the presence of a phase transfer catalyst [21]. Modeling of the system involved solving mass balance equations for coupled mass transfer and reactions for all of the species involved. Further recent applications of modified Lewis cells have focused on stripping-extraction kinetics [22-24], uncatalyzed hydrolysis [25,26], and partitioning kinetics [27]. 

A significant advance in this area was recently made by Li and coworkers [30,31], who developed a laminar flow technique, that allowed the direct contact of two liquids with better-defined mass transport compared to the Lewis cell. Laminar flow of the two phases parallel to the interface was produced through the use of flow deflectors. By forcing flow parallel to, rather than towards, the interface, it was proposed that the interface was less likely to be disrupted. Reactions were followed by sampling changes in bulk solution concentrations. 

The technique offers a known interfacial area under convective flow conditions that are quite well-defined, with mass transport rates that are enhanced compared to the Lewis cell and its analogs. However, in common with many other approaches, interfacial fluxes must be determined indirectly from bulk solution measurements. 

Of the methodologies considered, the Lewis cell, employs direct contact of the two liquids, but does not have well-defined hydrodynamics. The constant interface cell with laminar flow has better-defined hydrodynamics, but the interfacial flux is not measured... 

Several experiments using different organic solvents in different biphasic media are necessary to find the adequate distribution of the reaction components. A series of experiments are essential for the choice of a process and for scaling-up. Experiments using Lewis cells [44] may yield useful results for understanding equilibrium, kinetics, and interactions between organic solvent-substrate and/or organic solvent-biocatalyst. A study of two-liquid phase biotransformation systems is detailed below in Sections II-IX. 

FIG. 4 Modified Lewis cell macroheterogeneous biphasic medium. (From Ref. 25.)... 

In our previous work [63], we studied the hydrolysis kinetics of lipase from Mucor javanicus in a modified Lewis cell (Fig. 4). Initial hydrolysis reaction rates (uri) were measured in the presence of lipase in the aqueous phase (borate buffer). Initial substrate (trilinolein) concentration (TLj) in the organic phase (octane) was between 0.05 and 8 mM. The presence of the interface with octane enhances hydrolysis [37]. Lineweaver-Burk plots of the kinetics curve (1/Uj.] = f( /TL)) gave straight lines, demonstrating that the hydrolysis reaction shows the expected kinetic behavior (Michaelis-Menten). Excess substrate results in reaction inhibition. Apparent parameters of the Michaelis equation were determined from the curve l/urj = f /TL) and substrate inhibition was determined from the curve 1/Uj.] =f(TL) ... 

We previously described [25] the function of soybean lipoxygenase-1 in a biphasic system (modified Lewis cell) composed of an aqueous phase (borate buffer) and octane. The substrate of the reaction is linoleic acid (LA) and the main product is hydro-peroxyoctadecadienoic acid (LIP). The system involves two phenomena LA transfer from the organic to the aqueous phase and lipoxygenase kinetics in the aqueous medium. 

However, in the two-phase system described here the reaction progress has an influence on substrate transfer [Eq. (9)] and steady-state changes continually during the evolution of the system. Interaction between the reactant transfer and lipoxygenase-catalyzed reaction is therefore studied in octane-aqueous biphasic medium (modified Lewis cell). 

Recently [63], we studied the behavior of two-enzyme system catalyzing two consecutive reactions in a macroheterogeneous medium (modified Lewis cell). The system consisted of lipase-catalyzed hydrolysis of trilinolein and subsequent lipoxygenation of liberated fatty acids (Fig. 3). Our approach compared the kinetic behavior of coupled enzymes in the Lewis cell with the sequential study of separated phenomena presented before ... 

The kinetic constant, ki can be calculated from Lewis cell experiments [46] under the condition of higher carrier concentration compared to that of solute in aqueous phase, so that the mass transfer rate is controlled by the transport of the solute to the interface and the rate of reaction at the interface. 

Figure 8.4 Reactor types used in organic-aqueous biphasic systems (a) Emulsion reactor, (b) Lewis cell, (c) passive membrane reactor, (d) active membrane reactor. E represents enzyme molecules.

J. M. Woodley, A. J. Brazier, and M. D. Lilly, Lewis cell studies to determine reactor design data for two-liquid-phase bacterial... 

The simplest device providing rudimentary control of hydrodynamics is the Lewis cell [ 19 ], of which a variation by the present author is easier to construct. It consists of a reactor containing two contra-rotated agitators positioned on either side of a liquid-liquid interface, Fig. 5.16. 

Fig. 10.U. Stirred Lewis cell with two independent stirrers and a planar interphase.

There are many classical methods to investigate the chemical reaction and kinetics at the liquid-liquid interface, which include a Lewis cell, a single drop method, and rotating disc method [22]. All of these methods however could not measure both the extraction rate and interfacial concentration of extractant, simultaneously. Modern experimental methods of interfacial reaction can determine the interfacial species, interfacial concentration, and interfacial chirality of an extractant or complex as a function of time. 

Stirred (Lewis) cell Impellers gently stir the two phases Irreproducible, undefined boundaries... 

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