Displacement Wagner mechanism

Figure 11-11. Displacement reactions of the type AX+BY = AY+BX. a) lost mechanism, schematic, b) Equipotential surfaces and the evolution of phase boundary instability, lost mechanism, c) Wagner mechanism of displacement reactions, schematic.

In 1959, Wagner and Leach (11) suggested that increased oil recovery could be obtained by changing wettability of rock material from oil-wet to water-wet. Melrose and Bradner (7) and Morrow (12) also suggested that for optimal recovery of residual oil by a low interfacial tension flood, the rock structure should be water-wet. Previous investigators (13,14) have used sodium hydroxide to make the reservoir rock water-wet. Slattery and Oh (15) have shown that intermediate wettability may be less desirable than either oil-wet or water-wet rocks. Since, chemical floods satisfy many of these conditions, they have been considered promising for enhanced recovery of oil. The mechanism of oil displacement in porous media has been reviewed by Bansal and Shah (16) and more recently by Taber (17). 

Thionyl chloride is the classical reagent for the preparation of alkyl chlorides from alcohols with retention of configuration. This reaction is known to proceed via alkyl chlorosulfinates (7 75) which decompose by an ion pair mechanism, but may be diverted to an SN2 displacement path by addition of pyridine171 Wagner-Meerwein rearrangements have been observed in the course of alkylchlorosulfinate decomposition, e.g. (176) - (777)172). The behavior of the isomeric chlorosulfinates (178) and (179) is consistent with competitive ion pair collapse and 1,2-alkyl shift173. ... 

Space charge polarization occurs when the material contains free electrons whose displacement is restricted by grain boundaries. Hence, entire macroscopic regions of the material become either positive or negative. This mechanism is often called the Maxwell-Wagner effect and it takes place in low frequency fields. 

The slightly modified differential form of Faraday s law makes it possible to describe electrode shape change due to reactions as well as mechanical displacement, By introducing the Wagner number in the classical one-dimensional examples of electrode growth and electrochemical machining, the important properties of electrode shape change were obtained. 

Fig. 6-11. Reaction mechanisms for two limiting cases of the displacement reaction AX 4- BY = = AY 4- BX according to Jost (a) and Wagner (b).

Wagner begins with the assumption that in certain cases the solubilities and mobilities of A ions in BX and of ions in AY are so low, and consequently the product layers are formed so slowly, that another reaction mechanism may predominate once nucleation has occurred. This reaction mechanism is shown in Fig. 6-11 (b). Essentially, a closed circular flow of cations occurs in the product phases such that the cations diffuse only in their own respective compounds, A quantitative approximation to the reaction rate can be made as follows. Since three phases are in simultaneous contact, it is sufficient to specify only one additional variable in addition to P and T in order to uniquely determine the problem. If the partial pressure Px2 is chosen as this variable, then it is a simple matter to calculate the activity gradient of A in AY if the free energies of formation of the individual compounds are known. This is essentially given by the standard free energy A of the reaction AX 4- BY == AY 4- BX. Then, if the diffusional resistances in AY and BX are known, it is possible to calculate the rate of the displacement reaction for this limiting case as well. 

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