Optimum salinity

Effect of Aqueous Phase Salinity and pH on Interfacial Tension. Comparison of the first two entries in Table 14 shows that an increase in AOS 2024 solvent salinity from 0 to 3% NaCl results in a significant decrease in IFT. This suggests that the optimum salinity of this AOS 2024 sample is closer to 3% NaCl than to 0%. 

Some effort has been directed toward understanding the growth requirements of the alga of interest, allelopathic alga (13), the optimum salinity (14), the distribution of allelopathic agents (15), and the temperature optimum (16). This paper reviews the approaches taken to separate the allelopathic agents from the other materials and the methods used to characterize the biological activity of aponin from Nannochloris sp. 

For instance, if the surfactant in Fig. 3 (left) scan is an alkyl-benzene sulfonate with a 14 carbon atom alkylate, and it is changed for a 12 carbon atom alkylate, then another scan with the same oil, alcohol, and temperature shows that the optimum salinity becomes S2 = 4.5 wt. % NaCI (Fig. 3 right). It follows that In S has increased by 0.72 unit, hence a should have decreased by 0.72 unit according to... 

Since partitioning is altered by the total concentration of surfactant [44], the optimum formulation for three-phase behavior or for minimum interfacial tension is likely to change with concentration [8,48]. Thus, optimum salinity, optimum ACN, or optimum EON change with the concentration of surfactant if it is a mixture, whereas it is independent of the concentration for an isomerically pure surfactant, as shown in Fig. 10 left and center plots. 

The optimum salinity variation does not follow a straight line on a In S scale (nor with a S scale), but exhibits a downward deviation, i.e., it displays a value of optimum salinity which is systematically lower than expected from the use of Eqs. 4 and 5 [33]. This indicates that the anionic-nonionic association tends to reduce the hydrophilicity of the mixture, and it has been... 

Fig. 13 Plot of optimum formulation (as optimum salinity) versus nonionic-ionic mixtiue composition. After [33]...

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... 

Optical Brighteners Optimum Salinity Oriented-Wedge Theory... 

Optimum Salinity In microemulsions, the salinity for which the mixing of oil with a surfactant solution produces a middle-phase microemulsion containing an oil-to-water ratio of 1. In micellar enhanced oil recovery processes, extremely low interfacial tensions result, and oil recovery tends to be maximized when this condition is satisfied. 

Diffusion studies were made using an Isopar M/Heavy Aromatic Naptha (IM/HAN) 9 1 oil mixture (Exxon). Isopar M and HAN are refined paraffinic and aromatic oils, respectively. Figure 3 shows equilibrium salinity scans measured in the laboratory for equal-volume mixtures of the surfactant solution and oil. Since room temperature varied somewhat, the effect of temperature on phase behavior was determined. As Figure 3 shows, there is a small temperature effect, especially at the lower salinities. However, it is not large enough to have influenced the basic results of the contacting experiments. Optimum salinity, where equal volumes of oil and brine are contained in the middle phase, is approximately 1.4 gm/dl. 

The dynamic behavior of the PDM system in the salinity range between optimum salinity and the upper-phase microemulsion region was similar to that below optimum in that intermediate brine and microemulsion phases formed. Figure 13 shows these phases for the 1.5 gm/dl-salinity PDM system. The middle-phase type of microemulsion, being high in oil content at these salinities, grew more rapidly in the direction of the oil phase than it did at low... 

At approximately optimum salinity, spontaneous emulsification of brine drops in the oil phase began in both systems. This phenomenon resulted from local supersaturation of the oil phase, as explained in the discussion section below. The amount of emulsification tended to increase with increasing salinity. As a result, the cloud of emulsion drops began to obscure the interface between the microemulsion and oil, making interface position measurements difficult. These observations of spontaneous emulsification confirm the results of the earlier contacting experiments performed in the horizontal configuration ( 4). 

Theoretical diffusion path studies were made with a model system for comparison to the experimentally observed phenomena. A pseudoternary representation was chosen for modeling the phase behavior, and brine and oil were chosen as the independent diffusing species. For simplicity and because their exact positions and shapes were not known, phase boundaries in the liquid crystal region were represented as straight lines. Actually, studies indicate a rather complex transition from liquid crystal to microemulsions as system oil content is increased, especially near optimum salinity (15-16). A modified Hand scheme was used to model the equilibria of binodal lobes (14,17). Other assumptions are described in detail elsewhere (13). 

In the three-phase regime of equilibrium phase behavior, the diffusion path studies were based on a dimensionless parameter S which indicates the position of the system within the regime. Thus, S = 0 corresponds to the salinity where the three-phase region first appears via a critical tie line (14), and S = 1 corresponds to the salinity where it disappears into another critical tie line. The optimum salinity occurs at S 0.5. 

Figure 21. Calculated diffusion path at optimum salinity.

Calculated diffusion paths also successfully predicted the occurrence of spontaneous emulsification in the systems. Near optimum salinity where this phenomenon first appeared, brine drops spontaneously emulsified in the oil but were isolated from the bulk brine phase by a microemulsion. At high salinities, a more common type of spontaneous emulsification was seen with brine emulsifying in the oil directly above a brine layer. 

Figure 22. Expanded view of the oii corner showing the onset of spontaneous emulsification at optimum salinity.

Phase behavior studies of oil-brine-surfactant systems have shown that the ultralow interfacial tension (less than 0.01 dyne/cm) necessary for EOR is very sensitive to salinity changes (2 3). Such low tensions are obtained only within a small range of salinity near the point of "optimum salinity" where equal amounts of oil and brine are solubilized. The tolerance of ultralow tensions to divalent ions is still less. 

In alkaline-related chemical processes, the addition of alkalis such as sodium carbonate increases ionic strength (salinity). As alkaline concentration is increased, the optimum salinity is decreased. The order to decrease the optimum salinity is (Martin and Oxley, 1985)... 

If the solution is clear up to this salinity, any problem mentioned previously would not appear because the solution will be more stable after mixing with the oil in situ. If the solution is hazy or any precipitation appears, chemicals must be reselected. Such a test is an aqueous stability test. Generally, the salinity limit in an aqueous stability test is close to the optimum salinity of microemulsion. When an alkali is added for screening ASP formula, sometimes precipitation is seen. This result is probably due to an alkali reaction with the glass tube so that silicate forms (Sheng et al., 1994). Figure 7.5 shows an example of an aqueous stability test. 

We ht the data with two lines one with Cse < Cseop (optimum salinity) and the other one with Cse > Cseop. Ah can be simply interpolated at any Csei... 

At the optimum salinity (normalized salinity CseD = 1), C13 = C23 = (1 - C33)/2 for j = 3 in Eq. 7.12, which means the binodal curve is symmetric. Thus, Eq. 7.14 is readily derived at the optimum salinity, and Cssmaxi can be calculated from Eq. 7.14 using Ahi. The physical meaning of Cssmaxi is the maximum height of the binodal curve at the optimum salinity. At the zero optimum salinity (practically very low salinity, Cseo = 0) and twice optimum salinity (CseD = 2), we also assume the binodal curves are symmetric and use Eq. 7.14 to calculate Cssmaxo and C33max2 Corresponding to Aho and Ah2, respectively. 

Based on material balance, at the optimum salinity (CseD = 1). we have... 

We know that at a very low salinity or at a high salinity, the microemulsion is usually Winsor type I or Winsor type II. The microemulsion volumes (S3) at these salinities are generally higher than that at the optimum salinity. Then according to Eqs. 7.15 through 7.17, and will be lower than... 

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