Paraffin water interface

Fowkes and Harkins reported that the contact angle of water on paraffin is 111° at 25°C. For a O.lAf solution of butylamine of surface tension 56.3 mJ/m, the contact angle was 92°. Calculate the film pressure of the butylamine absorbed at the paraffin-water interface. State any assumptions that are made. 

As a result of a number of experiments the mean areas of paraffin-water interface occupied by a molecule of the emulsifying soaps were obtained as follows. For comparison Langmuir s values for the actual areas of the fatty acids are appended whilst Adam s value for the —CO OH head is 25 1 A. 

Since the streaming potential determination is easier to carry out and is less subject to corrections than microelectrophoresis, it was used in the present work to study the behavior of the solid paraffin-water interface. 

Tadros [133] predicted an increase in the thickness of adsorbed polyvinyl alcohol layer at the paraffin-water interface with increasing bulk concentration from 3.5 nm at 1 ppm to 67.7 nm at 20 ppm. It is doubtful, however, whether it is possible solely on the evidence of results from application of Equation 8.35, to confirm multilayer formation. Kayes [134] has calculated using this equation, adsorbed layer thicknesses on solid particles for alkyl polyoxyethylene monoethers of 3.2 and 9.2 nm for derivatives with 30 and 60 ethylene oxide residues, respectively, which approximates to monolayer coverage. 

Fanta GF, Felker FC, Shogren RL, Knutson CA. 2001a. Starch-paraffin wax compositions prepared by steam jet cooking. Examination of starch adsorbed at the paraffin-water interface. Carbohydr Polym 46 29-38. 

Furthermore from the computed area of the cross-section of the interface occupied by one soap molecule it is clear that the molecules of the soap are relatively close together and orientated in a plane at right angles to the interface. As has already been noted in the case of the air-water interface the fatty acids are orientated with their polar carboxyl groups in the water phase we would consequently anticipate that in the oil-water interface the same orientation would occur, the hydrocarbon chain being immersed in the paraffin phase and the polar —OOONa or —COOK group in the aqueous phase. Such orientation is an important factor in the... 

Discussion. We can now propose a coarse description of the paraffinic medium in a lamellar lyotropic mesophase (potassium laurate-water). Fast translational diffusion, with D 10"6 at 90 °C, occurs while the chain conformation changes. The characteristic times of the chain deformations are distributed up to 3.10"6 sec at 90 °C. Presence of the soap-water interface and of neighboring molecules limits the number of conformations accessible to the chains. These findings confirm the concept of the paraffinic medium as an anisotropic liquid. One must also compare the frequencies of the slowest deformation mode (106 Hz) and of the local diffusive jump (109 Hz). When one molecule wants to slip by the side of another, the way has to be free. If the swinging motions of the molecules, or their slowest deformation modes, were uncorrelated, the molecules would have to wait about 10"6 sec between two diffusive jumps. The rapid diffusion could then be understood if the slow motions were collective motions in the lamellae. In this respect, the slow motions could depend on the macroscopic structure (lamellar or cylindrical, for example)... 

More than a century ago, Pickering [2] and Ramsden [3] investigated paraffin-water emulsions contains solid particles such as iron oxide, silicon dioxide, barium sulfate, and kaolin and discovered that these micron-sized colloids generate a resistant film at the interface between the two immiscible phases, inhibiting the coalescence of the emulsion drops. These so-called Pickering emulsions are formed by the self-assembly of colloidal particles at fluid-fluid interfaces in two-phase liquid systems (Fig. 1). 

Fig. 14. Schematic depiction of selected physical and chemical events during fat digestion. The 1- and 3-ester linkages of triglyceride (upper left) are cleaved by lipase, forming 2-monoglyceride and fatty acid. These lipolytic products leave the oil-water interface and are dispersed in the aqueous phase as mixed bile acids-lipolytic product micelles. A proposed molecular arrangement of the bile acid-lipolytic product micelle is shown in cross-section this model is based on studies of the bile acid-lecithin micelle (65). In this model, the hydrophobic back of the bile acid molecule apposes the paraffinic chains of the lipolytic products, and the hydroxy groups of the bile acid molecule are toward the aqueous phase. The paraffin chains of the interior of the micelle are liquid, thus permitting other water-insoluble molecules such as cholesterol and fat-soluble vitamins to dissolve in the micelle. Indeed, the solvent capacity of the bile acid-lipolytic product micelle is contributed chiefly by the paraffin chains of the lipolytic products.

The preceding calculated surface concentration is very close to that which is found for the adsorption of K-laurate and K-palmi-tate at the air-water interface, namely, 4 x 10" moles/cm It is hence inferred that the oligomer salt exhibits the same adsorption mechanism as that of the soaps in the air-water interface, i.e. adsorption of the oligomer is due exclusively to the escaping tendency of the paraffin group introduced by way of the mercaptan regulator. 

Investigations of the effects of oil-soluble surfactants on the emulsification of paraffins in aqueous surfactant solutions led to the proposal that the formation of interfacial complexes at the oil-water interface could increase the ease with which emulsions could be formed and, possibly, explain the enhanced stability often found in such systems (Figure 9.9). By definition, an interfacial complex is an association of two or more amphiphilic molecules at an interface in a relationship that will not exist in either of the bulk phases. Each bulk phase must contain at least one component of the complex, although the presence of both in any one phase is not ruled out. The complex can be distinguished from such species as mixed micelles by the fact that micelles (and therefore mixed micelles) are not adsorbed at interfaces. According to the Le Chatelier principle, the formation of an interfacial complex will increase the Gibbs interfacial excess F/ [Eq. (9.2)] for each individual solute involved, and consequently, the interfacial tension of the system will decrease more rapidly with increasing concentration of either component. 

During storage, sediments decant with the water phase and deposit along with paraffins and asphalts in the bottoms of storage tanks as thick sludges or slurries (BS W). The interface between the water-sediment and the crude must be well monitored in order to avoid pumping the slurry into the refinery s operating units where it can cause serious upsets. 

The varying actual orientation of molecules adsorbed at an aqueous solution-CCU interface with decreasing A has been followed by resonance Raman spectroscopy using polarized light [130]. The effect of pressure has been studied for fatty alcohols at the water-hexane [131] and water-paraffin oil [132] interfaces. 

In the case of liquid/liquid interfaces we have the experiments of W. C. McC. Lewis (1908), who examined the relations at the surface of separation between an aqueous solution and paraffin oil or mercury. If o-, a are the surface tensions between paraffin oil and pure water and the solution, respectively, it was found that cr < [Pg.439]

The work of adhesion is influenced by the orientation of the molecules at the interface. For example, with the help of Table A.4.1 and Eq. (A.4.8), the work of adhesion of n-decane-water (corresponding to a paraffinic oil-water system) and of glycerol-water can be computed to be 40 10 3 J nr2 and 56x 10 3 J nr2, respectively. It requires more work to separate the polar glycerol molecules (oriented with the OH groups toward the water) from the water phase than the nonpolar hydrocarbon molecules. For paraffinic oils Woo is about 44 mj nr2, for water Www is 144 mj nr2, and for glycerol Woo is 127 mJ nr2. 

Interface control has the advantage of being easily adjustable to handle unexpected changes in oil or water specific gravity or flowrates. However, in heavy oil applications or where large amounts of emulsion or paraffin arc anticipated, it may be difficult to sense the interface. In such a case, bucket and weir control is recommended. 

Fig. 3—Bucket and weir configuration for three-phase horizontal separator eliminates interface controller and uses conventional displacement fioal lo operate oil and water dump valves This design is useful if paraffin or large volumes o emulsions that would loul interlace controllers are expected.

The presence of solids further complicates the performance requirements for a demulsifier. Emulsions stabilized by fine particles can usually be broken if the wettability of the particles is reversed. Inorganic particles, such as iron sulfides or clay minerals, can be made water-wet, causing them to leave the interface and diffuse into the water phase, or they can be made oil-wet so that they leave the interface and diffuse into the oil phase [68]. Organic particles, such as paraffins and asphaltenes, can be removed from interfaces by dissolution [461,463,466]. 

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