Oxidation‐reduction reactions in stirred liquid‐liquid systems

Abstract

An extremely interesting special class among heterogeneous reaction systems is that of liquid-liquid electron exchange. Scibona, Danesi, and Orlandini (13) recently pointed out the possible application of this type of system in the processing of aqueous solutions. Thus, for example, aqueous solutions of multivalent metallic ions can be reduced or oxidized by their contact with an immiscible organic phase containing, appropriately, an organic-soluble reductant or oxidant. The result is a change in the valence state of a species in the aqueous phase without introduction of extraneous components, except for the addition or removal of a proton. For this to be effectively achieved the reactants (and their oxidation or reduction products) must be substantially insoluble in the opposite phase.As these authors pointed out, the same result can be accomplished by using solid electron-exchange polymers ( 5 ) but the use of a liquid-liquid system offers the possibility of faster oxidation-reduction rates. Their proposal, in essence, suggests an analogous development in the general area of heterogeneous electron exchange reactions to that which has occurred in the field of ion exchange. In that area liquid ion exchange (9) has assumed an important processing role in recent years, particularly in nuclear technology for recovering uranium and related values from ore-leach liquors (4, 6). Since the technique for conducting liquid ion exchange operations is identical to that employed for general solvent extraction, the same advantages would accrue to liquid electron exchange operations. In particular, the ease of adaptation to continuous, countercurrent contacting would be a noteworthy operational advantage.The study of Scibona, Danesi, and Orlandini (13) was No information was given, however, as to how the reaction rates might be affected by changes in the degree of agitation, the relative volumes of the two phases or the temperature. In this study rates of reduction of tetravalent cerium ions I: Ce (IV) ] by tetrachlorohydroquinone (TCH) in stirred liquid-liquid systems were investigated quite extensively. The aqueous phase was the continuous phase, contained the Ce(1V)' oxidant ions and was in all cases made 1N with respect to sulfuric acid. The immiscible organic dispersed phase (an equivolume mixture of carbon tetrachloride and 2-octanone) served as the solvent for the solid reductant, TCH. Dispersion was accomplished by stirring the two-phase system in a baffled beaker with a flat-blade, turbine impeller rotating at a constant speed. The influence of several variables on the kinetics of reduction of ceric ions [Ce (IV) ] to cerous ions [Ce(III) ] was considered. Among these were the concentrations of Ce( IV) and TCH in their respective phases, the volume of the dispersed organic phase, the rotational speed of the stirrer and the temperature. An interesting deduction of the present work is that the rate of reduction of Ce (IV) by TCH appears to be directly proportional to the interfacial area of the stirred two-phase 9 Throu...

Liquid-Liquid Extraction with Interphase Chemical Reaction in Agitated Columns. 1. Mathematical Models

“…An extremely interesting special class among heterogeneous reaction systems is that of liquid-liquid electron exchange. Scibona et al (1966) and later Mansoori and Madden (1969) noted the potential of this type of system in the processing of aqueous solutions. For example, aqueous solutions of multivalent metallic ions can be reduced or oxidized by contact with an immiscible organic phase containing, appropriately, an organic soluble re- during or oxidizing species, the result being a change in the valence state of a species in the aqueous phase without introducing extraneous components, except for the addition or removal of a proton.…”

Process Studies on Indirect Electrosynthesis of 1,4‐Naphthoquinone

“…Figure 4 shows experimental data (7,26) for which concentrations were measured in the organic phase. Since the reaction was expected to occur in the aqueous phase (29), the overall rate constant was thus a combination of a kinetic rate constant (k2) and a partition coefficient (Kp)…”

A contactor for studying mass transfer with reaction in liquid‐liquid systems

“…In the kinetic regime the reaction proceeds in the entire bulk of the phase and the concentration of the transferred reactant is a t its saturation value ; this is the highest rate possible for the reaction (for given concentrations and temperature). In an attempt to resolve this discrepancy some runs were made under conditions similar to those 0f (14,16).…”