Oil-soluble surfactants

AH corrosion inhibitors in use as of this writing are oil-soluble surfactants (qv) which consist of a hydrophobic hydrocarbon backbone and a hydrophilic functional group. Oil-soluble surfactant-type additives were first used in 1946 by the Sinclair Oil Co. (38). Most corrosion inhibitors are carboxyhc acids (qv), amines, or amine salts (39), depending on the types of water bottoms encountered in the whole distribution system. The wrong choice of inhibitors can lead to unwanted reactions. Eor instance, use of an acidic corrosion inhibitor when the water bottoms are caustic can result in the formation of insoluble salts that can plug filters in the distribution system or in customers vehicles. Because these additives form a strongly adsorbed impervious film at the metal Hquid interface, low Hquid concentrations are usually adequate. Concentrations typically range up to 5 ppm. In many situations, pipeline companies add their own corrosion inhibitors on top of that added by refiners. 

Asphalts and waxes can be removed by dissolving in hot naphtha for 3 to 4 hours. The naphtha benefits from the addition of 0.1% of a water-soluble surfactant (HLB value of 15-20, such as polyethylene glycol 600 monolaurate) and 0.1% of an oil-soluble surfactant (HLB value of 0-5, such as propylene glycol monstearate). The solution must be circulated fill-and-soak methods are unsatisfactory. 

The preparation of a ferrofluid emulsions is quite similar to that described for double emulsions. The starting material is a ferrofluid oil made of small iron oxide grains (Fe203) of typical size equal to 10 nm, dispersed in oil in the presence of an oil-soluble surfactant. The preparation of ferrofluid oils was initially described in a US patent [169]. Once fabricated, the ferrofluid oil is emulsifled in a water phase containing a hydrophilic surfactant. The viscosity ratio between the dispersed and continuous phases is adjusted to lie in the range in which monodisperse fragmentation occurs (0.01-2). The emulsification leads to direct emulsions with a typical diameter around 200 nm and a very narrow size distribution, as can be observed in Fig. 1.33. 

Detergent In relationship to fuel technology, a detergent is an oil-soluble surfactant added to fuel aiding in the prevention and removal of deposits. Examples include anionic alkyl aryl sulfonates, cationic fatty acid amides, or nonionic polyol condensates. 

Microemulsions are transparent or translucent, thermodynamically stable emulsion systems (Griffin 1949). Forming a middle phase microemulsion (MPM) requires matching the surfactant system s hydrophobicity with that of the oil. The HLB (hydrophilic-lipophilic balance) number reflects the surfactant s partitioning between water and oil phases higher HLB values indicate water soluble surfactants while lower values indicate oil soluble surfactants (Kunieda et. al. 1980, Abe et. al. 1986). While a balanced surfactant system produces middle phase microemulsions, an underoptimum surfactant system is too water soluble (high HLB) while an over-optimunTSystem is too oil soluble (low HLB). 

Water solubilization also allows solubilization of inorganic salts not otherwise taken up by the micelle. The water solubilized by the soft-core reverse micelles of the oil soluble surfactant can subsequently solubilize inorganic salts which were originally oil-insoluble. This phenomenon is known as "secondary solubilization". This is defined as the solubilization of a material which the micelle can take up only when another solubilizate such as water is already present (Aebi and Wiebush, 1959 Arkin and Singleterry, 1949 Baker et al., 1954 Fulton et al., 1953 Inoue and Nose, 1987 Kon-no and Kitahara, 1972 Mathews and Hirschhom, 1953). 

Addition of chemicals without careful consideration may break an emulsion. An emulsion prepared with ionic surfactants should not be mixed with chemically incompatible materials of opposite charge. The pH of the emulsion should be alkaline if the emulsion is made with alkali soaps. At an acidic pH, the carboxylate ion of the soap is converted to the carboxylic acid, which is not water-soluble and an emulsifying agent. An alkali-soap stabilized O/W-type emulsion may be inverted to a W/O-type emulsion by adding a divalent electrolyte. The carboxylate ion reacts with the divalent electrolyte to form an alkali earth soap that is an oil-soluble surfactant. Addition of a common electrolyte to an emulsion prepared with ionic surfactants suppresses the ionization according to the Le Chatelier rule (e.g., ammonium oleate and ammonium chloride). The presence of noninteractive electrolytes in the emulsions alters the polar nature of the interfacial film. For example, the... 

Anti-sludge agents. During acid treatment, sludge, consisting of asphaltenes, resin, paraffin and other high molecular weight hydrocarbons is formed. Addition of oil-soluble surfactants can prevent the formation of insoluble film. 

The physical or chemical crosslinking of polymers can be also realized in water-in-oil (W/O) emulsion systems. In this case, aqueous droplets of prepolymers are stabilized by oil-soluble surfactants in a continuous oil phase. Hyaluronan-based microgels were prepared by crosslinking of carboxylic units of hyaluronan with adipic dihydrazide in aqueous droplets [19]. Chitosan-based microgels were prepared by crosslinking of chitosan chains with glutaraldehyde in aqueous droplets [20-25],... 

An oil soluble surfactant, can be used as a co-emulsifier and lubricant in self-emulsifiable textile and industrial oils, as a mold release agent, and as a viscosity control agent. EMEREST 2622 is also used in specialty paper coatings. 

An oil-soluble surfactant and co-emulsifier, is used in combination with water-soluble surfactants as a defoaming agent. 

STEROX ND surfactant has excellent oil-soluble surfactant properties which make it useful in grease cutting and emulsification. It is very soluble in nonpolar solvents and is miscible in water. It is often used in conjunction with higher mole ethoxylates to improve degreasing and oil-cutting efficiency. 

Griffin devised the concept of hydrophile-lipophile balance (HLB) and its additivity many years ago for selection of non-ionic emulsifiers and this rather empirical method is still widely used. The enormous literature on the HLB of surfactants has been reviewed by Becher. Each surfactant is allocated an HLB number usually on a scale of 0-20, based on the relative proportions of the hydrophilic and hydrophobic part of a molecule. Water-in-oil emulsions are formed generally from oil-soluble surfactants of low HLB number and oil-in-water emulsions from more hydrophilic surfactants of high HLB number. The method of selection is based on the observation that each type of oil will require an emulsifying agent of a specific HLB number to produce a stable emulsion. Thus, oils are often designated two required HLB numbers, one low and one high, for their emulsification to form water-in-oil and oil-in-water emulsions respectively. A series of emulsifiers and their blends with HLB values close to the required HLB of the oil are then examined to see which one forms the most stable emulsion (c.f. Fig. lA). 

In general, nonionic oil soluble surfactants were chosen for a study since they would satisfy these conditions, although many ionic surfactants with low HLB s were also evaluated. Pentane was used to simulate dense carbon dioxide. In the initial, low pressure evaluation of eighty-four commercially available surfactants which statisfied most of the criteria listed previously. Thirty-two of the samples exhibited at least 0.5 weight percent solubility in pentane (13). At weight concentrations of 0.5 - 4.0 percent surfactant (as is), none of these surfactants induced an increase in the solution viscosity above 10.0 percent. 

Emulsion stability is determined by the strength of the interfacial film and the way the adsorbed molecules in it are packed. If the adsorbed molecules in the film are closely packed, and it has some strength and viscoelasticity, it is difficult for the emulsified liquid droplets to break the film. In other words, coalescence is difficult. The emulsion is therefore stable. The molecular structure and the properties of the emulsifiers in the film affect the film s properties. The molecules in the film are more closely packed if the emulsifier has straight chains rather than branched chains. The film strength is increased if mixed emulsifiers are used rather than a single one. The reasons are that (1) the molecules in the film are closely packed, (2) mixed liquid crystals are formed between droplets, and (3) molecular complexes are formed in the interface by emnlsifier compositions. For example, an oil-soluble surfactant mixed with a water-solnble snrfactant works very well to stabilize emulsions (Kang, 2001). 

Glycerides, glucosides, saccharides, sorbitan derivatives, Tweens and Spans, etc. also belong to the class of nonionic surfactants. Mono- and diesters of fatty acids and multiatomic alcohols are oil soluble surfactants with low solubility in water. Sulfoesterification of these compounds followed by subsequent neutralization allows one to obtain water soluble surfactants. Many representatives of this group, such as sucrose esters, are non-toxic, tasteless and odorless, which makes them attractive for use in the pharmaceutical, food and perfume industries. 

The situation is different when oil-soluble surfactants dissolved in a liquid hydrocarbon adsorb at the same interface the extension of the hydrocarbon chain length results in only a small decrease in the surface activity. This is related to a small increase in the solubility of surfactants in oil upon extending the hydrocarbon chain length. The energy of surfactant adsorption from the oil phase at the water - oil interface is controlled by the hydration of the polar groups, which takes place when surfactants move to the interface from the oil bulk. 

Everything we have just said about the adsorption of water- and oil-soluble surfactants is also true (at least at low concentrations) for the surfactants soluble simultaneously in both aqueous and hydrocarbon media. In this case an equilibrium is established between surfactant solutions in the aqueous and oil phases and the adsorption layer formed at the interface. At... 

Conversely, when polar solids or powders (oxides, carbonates, silicates, alumosilicates, e.g. chalk, clays, etc.) are exposed to an oil phase containing oil-soluble surfactants, the adsorption layers in which polar heads are facing the surface and the hydrocarbon tails are floating in oil are formed (Fig. III-7, b). This process is of great importance for the incorporation of... 

The role of the interaction energy between surfactant molecules and liquids in the stabilization of emulsions is reflected in so-called Bancroft s rule [36,46]. This rule states that in the emulsification, the liquid in which the emulsifying agent is more soluble becomes the dispersion medium. Thus, water soluble surfactants stabilize direct oil-in-water emulsions, while oil soluble surfactants stabilize inverse water-in-oil emulsions. 

The methods of emulsion breaking (de-emulsification) are of importance in various areas of industry [39,61], especially in oil recovery in crude petroleum the content of highly saline water may be as high as 50 - 60%. Oil-soluble surfactants present in petroleum (asphaltenes, porphyrines, etc) and those introduced during tertiary recovery form highly developed adsorption layers at the water surface, and thus create structural-mechanical... 

Isolated emulsion films, and especially films of inverse emulsions, are important subjects of various studies [31]. Hydrocarbon films formed in aqueous medium and stabilized by surfactants constitute the simplest and at the same time representative model of biological membranes formed by mixtures of natural water- and oil- soluble surfactants, i.e. of proteins and lipids. Figure VIII-13 shows a common scheme of membrane structure [62,63],... 

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