Petroleum sulfonates solubility

The equivalent weight distribution of natural petroleum sulfonates depends on the boiling range of the aromatic components in the feedstock, but generally consists of a broad continuum of molecular weight components (139). For many appHcations it is precisely this property of derived petroleum sulfonates that provides the unique properties, such as emulsification. Conversely, most oil-soluble synthetic sulfonates have much more limited components and molecular weight distribution. 

Amoco developed polybutene olefin sulfonate for EOR (174). Exxon utilized a synthetic alcohol alkoxysulfate surfactant in a 104,000 ppm high brine Loudon, Illinois micellar polymer small field pilot test which was technically quite successful (175). This surfactant was selected because oil reservoirs have brine salinities varying from 0 to 200,000 ppm at temperatures between 10 and 100°C. Petroleum sulfonate apphcabdity is limited to about 70,000 ppm salinity reservoirs, even with the use of more soluble cosurfactants, unless an effective low salinity preflush is feasible. 

An assessment of the toxicity potential of chemicals used in EOR has been reviewed (181). A series of first-intent petroleum sulfonates derived from petroleum fractions were synthesized along with a series of od-soluble synthetic sulfonates. Their properties and preliminary od recoveries have been reported (182). 

It has also been shown [254] that a commercial petroleum sulfonate surfactant which consists of a diverse admixture of monomers does not exhibit behavior typically associated with micelle formation (i.e., a sharp inflection of solvent properties as the concentration of surfactant reaches CMC). These surfactants exhibit gradual change in solvent behavior with added surfactant. This gradual solubility enhancement indicates that micelle formation is a gradual process instead of a single event (i. e., CMC does not exist as a unique point, rather it is a continuous function of molecular properties). This type of surfactant can represent humic material in water, and may indicate that DHS form molecular aggregates in solution, which comprise an important third phase in the aqueous environment. This phase can affect an increase in the apparent solubility of very hydrophobic chemicals. 

Petroleum sulfonic acids may be divided roughly into those soluble in hydrocarbons and those solnble in water. Because of their color, hydrocarbon-soluble acids are referred to as mahogany acids, and the water-soluble acids are referred to as green acids. The composition of each type varies with the nature of the oil sulfonated and the concentration of acids produced. In general, those formed during light acid treatment are water soluble oil-soluble acids result from more drastic sulfonation. 

Brown acid oil-soluble petroleum sulfonates found in acid sludge that can be recovered by extraction with naphtha solvent. Brown-acid sulfonates are somewhat similar to mahogany sulfonates but are more water soluble. In the dry, oil-free state, the sodium soaps are light-colored powders. 

Soluble cutting oils are mineral oils containing 10 to 50% emulsifiers such as sodium petroleum sulfonates, sodium naphthenates, or sodium rosinates. These compounds allow emulsification of 5 parts or less of the oil in 95 parts or more of water. The emulsion acts as a coolant and, to some extent, as a lubricant (11). 

I Burner fuel stabilized with an oil-soluble petroleum sulfonate (Witco Petronate CR) in 1% NaCI was studied. Table 1 lists the variables and their ranges for the single-stage kinetic studies. A detailed description of the equipment, materials, and procedures has been presented by Byeseda.8... 

Temperature limitations are also important. In order for the surfactant to be effective it should be soluble at the temperature of the reservoir. Materials, such as some of the petroleum sulfonates, have very low solubilities in brines at temperatures below about 150 F (71 C). Consequently, they produce almost no foam below this temperature. Other surfactants, e.g., ethoxylated alcohols, become less soluble as the temperature is increased. These materials become limited in their effectiveness in higher temperature applications. An increase in temperature may also decrease the surface-active property of some surfactants. 

High-performance liquid chromatography is performed using a Hewlett-Packard 1090 chromatograph equipped with a ternary-solvent delivery system, an autoinjector with a 0 -20- u.L injection loop, an oven compartment, and a diode-array UV detector. An ELS detector (Alltech Associates, Deerfield, IL) is connected in series to the UV detector. Hexane, 2-propanol, and water were used for the analysis of nonionic surfactants. Water and tetrahydrofuran (THF) are used for the analysis of anionic surfactants. No preliminary sample preparation is used other than dilution. The nonionic surfactants are diluted 1 40 (v/v) with hexane. The anionic surfactants (alkyl ether sulfates and synthetic and petroleum sulfonates) are diluted 1 20 (v/v) with water-THF (50 50). The calcium sulfonate surfactants were diluted 1 20 (v/v) with a THF-38% hydrochloric acid solution of pH 1. Hydrochloric add is required to prevent salt precipitation by converting any excess water-insoluble caldum carbonate into water-soluble calcium chloride. All diluted samples are... 

Soluble oils that include mineral oils [L] as well as petroleum sulfonates, amine soaps, sodium naphthenates, triazines, chloro-phenols amines, and sodium nitrite, all [H]. 

Petroleum sulfonates are widely used in surfactant flooding. When there are divalents such as Ca and in the solution, however, the divalent complex is formed. The complex has limited solubility in water and precipitation occurs. When the concentration of petroleum sulfonates is increased, the precipitates redissolve. When the concentration is further increased, the precipitation occurs again. In other words, as the surfactant concentration is increased, there is a phenomenon of precipitation-dissolution-reprecipitation. This means the following reaction is reversible ... 

Surfactants used as detergents in dry cleaning must, of course, be soluble in the solvent used as the bath liquid. They are often added as solutions in some suitable solvent. Surfactants used for this purpose include solvent-soluble petroleum sulfonates, sodium and amine salts of alkylarylsulfonates, sodium sulfosucci-nates, POE phosphate esters, sorbitan esters, POE amides, and POE alkylphenols (Martin, 1965). 

We repeated the experiments above when the petroleum sulfonate is soluble in decane. The results are shown in Figs 4 and 5. We can see that the film lifetime, the IFT2min, and the To.osmN/m have almost the same change with the increasing concentration of petroleum sulfonate in decane. 

The optimum surfactant formulation for a microemulsion system is dependent on many variables (i.e., pH, salinity, temperature, etc.). References [17,49] list some of the components in a typical formulation. The surfactants and co-surfactants must be available in large amounts at a reasonable cost. In addition, they should also be chemically stable, brine soluble, and compatible with the other formulation components. Common surfactants used are petroleum sulfonates and ethoxylated alcohol sulfates [50,51]. The degree of interfacial tension lowering depends on the... 

Fig. 4. Schematic representation of and various steps involved in mass transfer of petroleum sulfonate from aqueous solution to the interface and then to the oil phase. The right hand side of the diagram illustrates the role of preferentially water soluble and oil soluble surfactant species in partitioning of the petroleum sulfonate.

The equilibrated and nonequilibrated oil/brine/surfactant systems differed in their oil displacement efficiency. The equilibrated oil rather than the equilibrated aqueous phase of the surfactant solution is responsible for the high oil displacement efficiency of dilute surfactant systems containing no alcohol. The oil soluble fraction of petroleum sulfonate is more effective in lowering the interfacial tension and in promoting the flattening of oil drops. Almost 94% oil recovery was achieved in sandpacks by a low concentration ( 0.1%) surfactant plus alcohol formulation when used in place of brine flooding. 

The importance of minimizing adsorption has provided the impetus for a number of adsorption studies of both anionic and nonionic surfactants on representative reservoir solids most of these deal with surfactant adsorption from aqueous solution. In general it has been found that the adsorption of petroleum sulfonates on mineral adsorbents increases with decreasing solubility in the solvent. Gale and Sandvik (1) have found that petroleum sulfonate adsorption from brine on clay minerals increased with molecular weight and therefore decreasing solubility in brine. 

Adsorption studies of petroleum sulfonates from aqueous solution are generally restricted, however, to dilute solutions because of the limited solubility of these surfactants in water, particularly in the presence of salt. With respect to oil-recovery systems, it is of interest to extend the study of petroleum sulfonate adsorption to microemulsions where the sulfonate concentrations are generally much higher. Glover et al. (6) have found that sulfonate adsorption from small-bank laboratory microemulsion displacement tests increased with salinity at low salt concentrations at higher salt concentrations sulfonate loss was attributed to phase trapping as proposed by Trushenski (7). 

The primary surfactants used were PDM-334, a monoethanolamine dodecyl orthoxylene sulfonate (av. MW = 427, 79.7% sulfonate), Exxon Chemical and two petroleum sulfonates, TRS 10-410 (eq. wt. = 422, 61.6% sulfonate) and TRS 18 (eq. wt. = 510, 61.3% sulfonate) from Witco Chemical. All of the sulfonates are considerably more soluble in oil than in water. 

Static petroleum sulfonate adsorption on simulated reservoir solids is affected significantly by the composition of the microemulsion from which the sulfonate is adsorbed. Petroleum sulfonates which are preferentially oil-soluble tend to be adsorbed to a lesser degree from oil-external than from brine-external microemulsions under equivalent conditions. Since the cosurfactant component can be used effectively to obtain a desired microemulsion composition, sulfonate adsorption is affected significantly by the choice of cosurfactant. If an oil-external microemulsion is to be used in a flood, it is preferable to employ a glycol ether cosurfactant, rather than a simple alcohol, because of lower surfactant adsorption in addition, the glycol ether microemulsion would exhibit enhanced salt tolerance which would affect favorably its inter- -facial tension properties. 

The fourth part includes experimental results on adsorption of pure surfactant and petroleum sulfonates on Berea sandstone. Retention of surfactants is related to their solubility limits in the brine. 

Experimental results include adsorption data for systems containing surfactant, cosurfactant, brine, and Berea sandstone. Adsorption values of pure surfactant (Texas 1) and commercially available petroleum sulfonates (TRS 10-80) are reported and the retention of surfactants in the Berea rock is related to a surfactant solubility limit in the brine. 

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