Cation surfactant precipitation

It has been reported by Celik and Somasundaran T381 that the interaction of divalent (and trivalent) cations with sulfonate surfactants causes surfactant precipitation followed by dissolution of the precipitate at higher concentrations. The precipitate redissolution phenomenon is not observed with monovalent ions. Indeed, some surfactant precipitation in the spinning drop tube was observed above concentrations corresponding to the first minimum of Figure 8 it is not known whether redissolution took place at higher concentrations resulting in the second tension minimum. 

Other methods start from crude indanthrone, which is dissolved in sulfuric acid or oleum (sometimes mixed with organic solvents). The product may be precipitated with water. It is more advantageous to separate the precipitated crude pigment, to reslurry it in water, and to heat the resulting aqueous suspension in the presence of a cationic surfactant. Subsequent treatment of the sulfuric acid solution with nitric acid, manganese dioxide, or chromium trioxide is followed by transfer into a solution containing sodium sulfite or iron(II)sulfate. 

The phase behavior of anionic-cationic surfactant mixture/alcohol/oil/ water systems exhibit a similar effect. First of all, it should be mentioned that because of the low solubility of the catanionic compound, it tends to precipitate in absence of co-surfactant, such as a short alcohol. When a small amount of cationic surfactant is added to a SOW system containing an anionic surfactant and alcohol (A), three-phase behavior is exhibited at the proper formulation, and the effect of the added cationic surfactant may be deduced from the variation of the optimum salinity (S ) for three-phase behavior as in Figs. 5-6 plots. Figure 16 (left) shows that when some cationic surfactant is added to a SOWA system containing mostly an anionic surfactant, the value of In S decreases strongly, which is an indication of a reduction in hydrophilicity of the surfactant mixture. The same happens when a small amount of anionic surfactant is added to a SOWA system containing mostly a cationic surfactant. As seen in Fig. 16 (left), the values of In S at which the parent anionic and cationic surfactant systems exhibit three-phase behavior are quite high, which means that both base surfactants, e.g., dodecyl sulfate... 

Generally speaking, for a stable emulsion a densely packed surfactant film is necessary at the interfaces of the water and the oil phase in order to reduce the interfacial tension to a minimum. To this end, the solubility of the surfactant must not be too high in both phases since, if it is increased, the interfacial activity is reduced and the stability of an emulsion breaks down. This process either can be undesirable or can be used specifically to separate an emulsion. The removal of surfactant from the interface can, for example, be achieved by raising the temperature. By this measure, the water solubility of ionic surfactants is increased, the water solubility of non-ionic emulsifiers is decreased whereas its solubility in oil increases. Thus, the packing density of the interfacial film is changed and this can result in a destabilisation of the emulsion. The same effect can happen in the presence of electrolyte which decreases the water solubility mainly of ionic surfactants due to the compression of the electric double layer the emulsion is salted out. Also, other processes can remove surfactant from the water-oil interface - for instance a precipitation of anionic surfactant by cationic surfactant or condensing counterions. 

Gas hydrate inhibitors. Gas hydrates, solid water clathrates containing small hydrocarbons, are problematic for oil and gas production because they can precipitate and cause line blockage. Simple cationic surfactants containing at least two butyl groups were previously developed to inhibit formation of gas hydrate precipitates in gas production lines [87]. However, similar to the situation with cationic drag reduction additives, poor toxicity profiles prevent widespread commercial acceptance. Ester quaternaries with structures somewhat similar to those used in fabric care have been claimed as hydrate inhibitors [88 ]. Additionally, certain alkylether quaternary compounds, e.g. C12-C14 alkyl polyethoxy oxypropyl tributyl ammonium bromide, were shown to have hydrate inhibition properties [89]. 

Franklin et al. studied the in-situ anodic oxidation of barium peroxide (Ba02) in aqueous sodium chloride solutions containing cationic surfactants. An active intermediate, barium superoxide (BaO ), was formed which in turn converted carbon tetrachloride to soluble barium chloride and barium carbonate precipitate [45]. This work was extended to the destruction of 1,2-dibromomethane in aqueous solutions... 

Sodium lauryl sulfate reacts with cationic surfactants, causing loss of activity even in concentrations too low to cause precipitation. Unlike soaps, it is compatible with dilute acids and calcium and magnesium ions. 

Xanthan gum is an anionic material and is not usually compatible with cationic surfactants, polymers, or preservatives as precipitation occurs. Anionic and amphoteric surfactants at concentrations above 15% w/v cause precipitation of xanthan gum from a solution. 

Figure 3. Variation of pH of the supernatant as a function of adsorption (pH not adjusted) (a) systems presented in Fig.2 (b) adsorption of cationic surfactant, BDDAB, and its polar head, BTAB, onto precipitated silica at 298 K.

Fig.5. Differential molar enthalpies of displacement onto precipitated silica (a) cationic surfactant and its polar head at 298 K (b) cationic surfactant, BDDAB, at 298 and 308 K.

A diluted aqueous solution of either sodium salicylate, sodium benzoate, or sodium succinate can precipitate cationic surfactants. 

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