Anionic surfactants salinity scans

Figure 2 shows the test tube aspect of a salinity scan with an anionic surfactant at a concentration about 1 wt. % and for WOR = 1. hi all test tubes the surfactant, oil, alcohol, and temperature are the same, i.e., in Eq. 4 all values are set but sahnity. The test tube that exhibits three-phase behavior corresponds to the salinity S = 2.2% NaCl, so-called optimum sahnity in this case, which satisfies HLD = 0 according to Eq. 4. 

The characteristic parameter of the surfactant can be estimated by the use of the corresponding correlations (Eqs. (3.3) and (3.4)). For anionic surfactants for instance, salinity scans with a given oil, alcohol type and concentration and temperature, would allow to determine the optimum salinity (S in wt.% NaCl) for each tested surfactant, and thus estimate the value of the surfactant characteristic parameter a from Eq. (3.3). Another way to characterise a surfactant is by using the double-scan technique (see Fig. 3.7). A first scan, e.g. a salinity scan, is carried out with a given set of (not-to-be changed) variables such as oil phase, alcohol type and concentration and temperature. With the first (known) surfactant (subscript 1), the optimum salinity Sj is such that... 

The third alternative to determine a component characteristic parameter is to interpolate between known systems. If for instance the EACN of a crude oil has to be estimated, the best way is to carry out base experiments with a few -alkanes for instance from heptane to tetradecane as in Fig. 3.8, in order to plot the variation of the optimum value of the scanned variable (S) versus ACN, then to carry out a scan with the unknown oil and to identify the alkane mixture that matches the optimum formulation. Figure 3.8 illustrates the determination of the EACN of an unknown crude oil by scanning the salinity of an anionic surfactant system. Such technique could also be used by extrapolating instead of interpolating, provided that the trend is linear and the extrapolation is not too far away, as for unknown paraffinic oil in Fig. 3.8. 

All types of micro emulsions were obtained in salinity scans with mixtures of Aerosol MA (sodium dihexyl sulphosuccinate) and twin-tailed (Guerbet and Exxon type) alcohol ethoxy and propoxy sulphates for perchloroethylene (PCE), carbon tetrachloride, 1,2-dichlorobenzene and trichloroethylene [59] at 25°C. At lower temperatures, however, stable macro emulsions are formed. Chloroform, 1,2-dichloroethane and other chlorinated hydrocarbons were found to be too polar for those anionic surfactants. Extremely hydrophilic and temperature-insensitive surfactants are necessary for effective solubilisation of chlorinated hydrocarbons yielding Winsor III systems. N-methyl-N-D-glucalkaneamide surfactants showed good performance for DNAPL solubilisation even at 16°C [56]. 

Figure 8 Unidimensional formulation scan. Typically observed phase behavior for a system containing 2% anionic surfactant, 49% brine, and 49% alkane, versus the brine salinity.

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