Solubilization of hydrocarbons

Optimizing the formulation of micellar surfactant solutions used for enhanced oil recovery consists of obtaining interfacial tensions as low as possible in multiphase systems, which can be achieved by mixing the injected solution with formation fluids. The solubilization of hydrocarbons by the micellar phases of such systems is linked directly to the interfacial efficiency of surfactants. Numerous research projects have shown that the amount of hydrocarbons solubilized by the surfactant is generally as great as the interfacial tension between the micellar phase and the hydrocarbons. The solubilization of crude oils depends strongly on their chemical composition [155]. 

M. Baviere and T. Rouaud. Solubilization of hydrocarbons in micellar solutions Influence of structure and molecular weight (solubilisation des hydrocarbures dans les solutions micellaires influence de la structure et de la masse moleculaire). Rev Inst Franc Petrol, 45(5) 605-620, September-October 1990. 

Boehm, P.D. and Quinn. J.G. Solubilization of hydrocarbons by the dissolved organic matter in sea water, Geochim. Cosmochim. Acta, 37(ll) 2459-2477. 1973. 

H. Saito and K. Shinoda, The solubilization of hydrocarbons in aqueous solutions of nonionic surfactants, J. Colloid Interface Sci. 24 (1967) 10-15. 

School the interaction corresponds only to the formation of a colloidal suspension of hydrocarbon particles, stabilized to some extent by DNA. This situation diminishes the significance of such an interaction for carcinogenesis. On the other hand, it does not touch upon the reality of the solubilization of hydrocarbons by free purines and upon the significance of the factors considered as being involved in this phenomenon. Generally speaking, the possibility exists that the nature of the interaction of the aromatic hydrocarbons with the nucleic acids is quite different from the nature of their interaction with the free constituents of these acids. Such a situation has been recently brought into evidence for actinomycin (Reich, E., Science 143, 684 (1964) Pullman, B. Biochim. Biophys. Acta 88, 140 (1964).)... 

Micelles are molecular aggregates formed in solutions of surface-active agents (surfactants compounds that orient at an interface such as between oil and water) (McAulifFe, 1980). Micelles may contain up to 100 or more surfactant molecules with a nonpolar (hydrophobic) end on the inside and a polar (hydrophilic) end on the outside. In 1959, Baker first advanced the concept of solubilization of hydrocarbons in (soap) micelles as a possible primary migration mechanism. The possible role of soaps, i.e. salts of organic acids, in primary migration was supported by Cordell (1973). The concept was considered attractive because it also explains how the practically water-insoluble hydrocarbons can solubilize in groundwater at relatively low temperatures. However, the likelihood of micellar solution as an effective primary migration mechanism has been seriously questioned by many authors (for instance Price, 1976 Hunt, 1979 Tissot and Welte, 1984). The main problems associated with micellar solution are ... 

Information concerning solubilization of hydrocarbons in ionic surfactant micelles was obtained from 2H NMR relaxation and H NMR paramagnetic relaxation measurements. The location of the hydrocarbons (benzene naphthalene, triphenylene cyclohexane, cyclododecane and tert-butylcyclohexane) in micelles... 

Nonaqueous microemulsions with nonionic surfactants have been studied. The C12E4 surfactant was found to stabilize microemulsions of formamide and dodecane [138], The ternary phase diagrams were studied at different temperatures and the solubilization of hydrocarbon was shown to be very temperature dependent (Figure 6.7). It was also observed that the temperature intervals of the three-phase regions are dependent on the hydrocarbon used larger aliphatic hydrocarbons... 

The solubilization of hydrocarbons in the interior of the micelle (Chapter 4, Section I) increases the value of Vh-... 

The effect of the curvation of the micelle on solubilization capacity has been pointed out by Mukerjee (1979, 1980). The convex surface produces a considerable Laplace pressure (equation 7.1) inside the micelle. This may explain the lower solubilizing power of aqueous micellar solutions of hydrocarbon-chain surfactants for hydrocarbons, compared to that of bulk phase hydrocarbons, and the decrease in solubilization capacity with increase in molar volume of the solubilizate. On the other hand, reduction of the tension or the curvature at the micellar-aqueous solution interface should increase solubilization capacity through reduction in Laplace pressure. This may in part account for the increased solubilization of hydrocarbons by aqueous solutions of ionic surfactants upon the addition of polar solubilizates or upon the addition of electrolyte. The increase in the solubilization of hydrocarbons with decrease in interfacial tension has been pointed out by Bourrel (1983). 

The addition of neutral electrolyte to solutions of nonionic POE surfactants increases the extent of solubilization of hydrocarbons at a given temperature in those cases where electrolyte addition causes an increase in the aggregation number of the micelles. The order of increase in solubilization appears to be the same as that for depression of the cloud point (Section IIIB, below) (Saito, 1967) K+ > Na+ > Li+ Ca2+ > Al3+ SO4 > Cl-. The effect of electrolyte addition on the solubilization of polar materials is not clear. 

Let us now turn to the discussion of main trends in solubilization process using on the results of studies carried out by Z.N. Markina [19]. Let us use the direct solubilization of hydrocarbons and alcohols in aqueous surfactant solutions as an example. It is well known that the solubility of hydrocarbons in water is very small, e.g. for octane it is about 0.0015% by weight. At the same time, one may prepare 2% solution of octane in 10% sodium oleate solution, i.e., the effective solubility of this hydrocarbon increases by more than three orders of magnitude. Solubilization can be described quantitatively by characteristic referred to as the relative solubilization, s, given by the ratio of the number of moles of solubilized... 

According to the studies carried out by V. N. Izmailova et al, the molecules of some proteins and enzymes reveal high capability to solubilize hydrocarbon molecules, which can incorporate into different segments of macromolecules. The solubilization studies, and in particular those of solubilization of hydrocarbons in aqueous solutions of proteins, allows one... 

Nagarajan R, Ganesh K. Comparison of solubilization of hydrocarbons in (PEO-PPO) diblock versus (PEO-PPO-PEO) triblock copol3uner micelles. J Colloid Interface Sci 1996 184 489-499. 

The third effort in the early development in microemulsion science originated with Saito and Shinoda [18,19] in Japan. In their studies on the temperature-dependent behavior of water-hydrocarbon-polyethylene glycol alkyl (aryl) ether systems, a relationship was observed between the cloud point of the surfactant and the solubilization of the hydrocarbon. For aliphatic hydrocarbons it was found that the solubilization of hydrocarbon... 

Unlike the experiments carried out below the cloud point temperature, appreciable solubilization of oil was observed in the time-frame of the study, as indicated by upward movement of the oil-microemulsion interface. Similar phenomena were observed with both tetradecane and hexadecane as the oil phases. When the temperature of the system was raised to just below the phase-inversion temperatures of the hydrocarbons with C12E5 (45°C for tetradecane and 50°C for hexadecane), two intermediate phases formed when the initial dispersion of Li drops in the water contacted the oil. One of these was the lamellar liquid crystalline phase L (probably containing some dispersed water). Above this was a middle-phase microemulsion. In contrast to the studies carried out below the cloud point temperature, there was appreciable solubilization of hydrocarbon into the two intermediate phases. A similar progression of phases was found at 35 C when using / -decane as the hydrocarbon. At this temperature, which is near the phase-inversion temperature of the water-C12E5-decane system, the... 

An additional argument for a distinction between micelles and microemulsions is that in all the literature on the solubilization of hydrocarbons, dyes, and other substances in micellar solutions, the ratio of solubilized molecules to surfactant molecules very rarely exceeds, or even approaches, 2. Many microemulsion systems, on the other hand, have been described in which the dispersed phase surfactant (and cosurfactant) ratio exceeds 100 Because of the relatively low ratios of additive to surfactant obtainable in micellar systems, it is clear that there can exist no oil phase that can be considered separate from the body of the micelle. In many microemulsions, however, the size of the droplet and the high additive surfactant ratio requires that there be a core of dispersed material that will be essentially equivalent to a separate phase of that material. The seemingly obvious conclusion is that microemulsion systems (in the latter case, at least) possess an interfacial region composed primarily of surfactant (and cosurfactant), analogous to that encountered in macroemulsions. 

FIGURE 7. The solubilization of hydrocarbon is small in normal micelles (A) and so is the case for the cosurfactant (B). A combination of hydrocarbon and cosurfactant will give a microemulsion from an aqueous solution of optimum concentration of surfactant (C). 

The solubilization of hydrocarbons in normal micelles (Vide ante) was not sufficient to justify the name microemulsion and a role of the cosurfactant was envisioned as necessary. This is also the case (Ranee, 1977). These microemulsions are found in the plane that connects the hydrocarbon and cosurfactant corners with one point on the water/surfact-ant axes. Fig. 7. The concentration of surfactant in the aqueous solution is the critical factor higher and lower concentrations fail to produce the large solubilization area. 

---