Pierre Saumagne

Kinetics and instabilities in the extraction of Co(II) by sodium di-(2-ethylhexyl) phosphate at the water/toluene interface. II. Spontaneous turbulence induced by interfacial reactions

Abstract Spontaneous turbulences induced by interfacial reactions in liquid/liquid systems (STIR) and their accelerating effects on the total reaction rate are examined. A model of the mechanism of STIR and of its kinetic effects on the nonagitated system H 2 O/CoBr 2 /NaD2EHP/toluene (where NaD2EHP is sodium di-(2-ethylhexyl) phosphate) is proposed. STIR arise from inhomogeneous accumulation of the Co(D2EHP) 2 complex in a layer B which appears between the aqueous and the organic bulk phases. This surfactant-rich layer offers strong resistance to the diffusion of Co 2+ ions from the aqueous phase toward the interfacial reaction site. The STIR intensity I is equal to the product v 2 × E between the superficial reaction rate v 2 and the intensity E of the emulsification (represented by the ratio s e / S mi between the overall droplet area s e in layer B and the surface s mi of the macroscopic water/toluene interface). The v 2 reaction rate is also influenced by STIR according to v 2 = C m /[1/ k c + E /( k ′ + k ″ I )], where k c is a chemical rate constant, and k ′ and k ″ are actual rate constants. The ratio E /( k ′ + k ″ I ) represents the mass transfer resistance and C m the metal-ion concentration in the aqueous phase. The model is in good agreement with the experimental dependence I ( C m ) and v ( C m ).

Kinetics and instabilities in the extraction of Co(II) by sodium di-(2-ethylhexyl) phosphate at the water/toluene interface. I. Kinetics and mechanism

Abstract A toluenic solution of sodium di-(2-ethylhexyl) phosphate (NaD2EHP) was allowed to react with an aqueous solution of Co(II) in a nonagitated system. Two layers of NaD2EHP emulsions in water appeared: a dilute emulsion A and an opaque emulsion B located below the toluenic phase. Furthermore, spontaneous convective motions were observed. The kinetics of complexation was investigated by spectrophotometry. The influence of four factors was studied: the Co 2+ concentration C m , the NaD2EHP concentration C d , the inert anti-emulsifier (KBr) concentration C e , and the hydration degree I h of the surfactant. When C m was increased, the reaction rate w exhibited a maximum at C m = 15 moles m −3 and then a minimum at C m = 30 moles m −3 . The whole dependence w ( C m , C d , C e , I h ) is explained by a double location of a superficial reaction with proper reaction orders of 1 relative to Co 2+ and 0 relative to NaD2EHP. The results show that, in the absence of forced convection, the rate w of the Co(II) extraction is the sum w 1 + w 2 where w 1 is the reaction rate at the surface of the droplets in layer B and w 2 represents the reaction rate at the macroscopic W/O interface. An increase in C m resulted in a strong reduction of the intensity E of the emulsification. Conversely, an increase in E led to an increase in the droplet area and therefore an increase in w 1 , while w 2 was reduced via an increase in the resistance to the diffusion of Co 2+ through the aqueous interstices of emulsion B.

Infrared study of the adsorption of non-ionic surfactants on silica

An infrared study of the adsorption of octylphenolethoxylates with an average of 1, 10 and 70 oxyethylenic groups at the silica–carbon tetrachloride interface is reported. The adsorption occurred mainly via hydrogen bonding between the oxygen atoms of the hydrophilic chain and the free silanols. No chemisorption was found to take place. The surfactant molecules presented a flat configuration at low coverage, but at increasing coverage they were adsorbed in a more upright configuration as fewer oxyethylenic groups were able to interact with surface silanols owing to steric crowding. Finally, at saturation, the last molecules were adsorbed vertically through the terminal hydroxy group.

Spectroscopic determination of association constants of water with organic bases

The formation constants of 1–1 complexes of water with proton acceptors are determined in carbon tetrachloride at 25°C by infrared spectroscopy. Water is classified according to its proton-donor power and is found to be similar to phenols rather than alcohols.

Infra-red spectroscopic studies of the bending modes of water. Detection of 1:1 and 1:2 complexes in organic solutions

We have analyzed the ν2 vibration of H2O dissolved in organic solvents over the whole concentration range. For water dissolved in small amounts in some basic solvents, the band is asymmetric or split. A study of ternary mixtures and a temperature effect allow the assignment of the two components to the bending vibration of 1:1 and 1:2 water–basic solvent complexes. The ν2 region is very useful for the observation of the 1:1 complexes.

Etude par Spectroscopie Infrarouge et par Spectroscopie Raman des Fluctuations Orientationnelles de la Molecule de Furanne en Solution

A study of reorientational motions by infrared spectroscopy and Raman scattering is undertaken for the molecule of furan in solution. This molecule is a near oblate top molecule: the values of its moments of inertia are:

Infrared study of the desorption of polycondensed aromatic compounds by non-ionic surfactants at the silica–carbon tetrachloride interface

The desorption of two polycondensed aromatic compounds (9,10-diphenylanthracene and 3-acetylphenanthrene) by octylphenolethoxylates (type Triton X) at the silica–carbon tetrachloride interface has been studied by infrared spectroscopy. A correlation has been found between the adsorption of the surfactant on the free hydroxyl groups of silica and the desorption of the aromatic species. The results show that the adsorption mechanism of the Tritons is not deeply modified by the compound to be desorbed. The desorption process occurs when one or more surfactant segments are adsorbed on the sites, thus retaining the aromatic molecule. Then complete desorption can only be obtained if the surfactant is able to cover every surface site. This is achieved at increasing coverage by a decrease in the number of oxyethylenic segments per molecule which adsorb on the vacant and non-vacant sites.