Interfacial tension temperature effects

The interfacial tension-temperature relationships at various CaCL concentrations for Karamay crude in a Sun Tech IV (5 g/L) and NaCI (10 g/L) solution are shown in Figure 9. For 0, 0.025 and 0.1 g/L Ca, an increase in interfacial tension with temperature was observed. The interfacial tension values above 150°C were about the same for these concentrations. At temperatures below 100°C, the effect of Ca was to increase interfacial tension, probably by hindering the formation of a surfactant-rich phase. This is consistent with the detrimental effect or light oil/brine interfacial tensions (increase from about 10 3 to about 10 1) reported by Kumar et al. T371. ... 

Thermodynamic and Kinetic Effects on Polymorphic Outcome Because of the interplay between thermodynamic factors (free energies, solubilities, concentrations, interfacial tensions), temperature, and molecular recognition in determining nucleation of a new phase, it is essential to consider the effects of thermodynamic and kinetic factors when using solvents to selectively nucleate polymorphs. Threlfall (2000) has thoroughly considered thermodynamic and kinetic factors and the conditions in which the solvent may or cannot affect polymorphic outcomes. The analysis is briefly summarized here. 

PA-12 or PA-1212 or PA-612 or PA-610 or PA-69 or PA-46 /SEES (0-20) / SEBS-g-MA (1.8% MA) (0-20) properties / TEM / ductile-brittle transition temperatures / interfacial tension estimates / effects of PA amine end-group concentration on copolymer formation (titration before and after extrusion) / torque rheometry ... 

Chemicals (demulsifiers) are normally used to reduce the interfacial tension. Chemical effectiveness is enhanced by mixing, time, and temperature. Adequate mixing and sufficient time are required to obtain intimate contact of the chemical with the dispersed phase. A certain minimum temperature is required to ensure the chemical accomplishes its function. Both viscosity reduction and effectiveness of chemical are dependent on the attainment of a certain minimum temperature. It may well be that the increase in chemical effectiveness is a result of the decrease in viscosity of the oil phase. 

Assume that an aqueous solute adsorbs at the mercury-water interface according to the Langmuir equation x/xm = bc/( + be), where Xm is the maximum possible amount and x/x = 0.5 at C = 0.3Af. Neglecting activity coefficient effects, estimate the value of the mercury-solution interfacial tension when C is Q.IM. The limiting molecular area of the solute is 20 A per molecule. The temperature is 25°C. 

The diffusion current Id depends upon several factors, such as temperature, the viscosity of the medium, the composition of the base electrolyte, the molecular or ionic state of the electro-active species, the dimensions of the capillary, and the pressure on the dropping mercury. The temperature coefficient is about 1.5-2 per cent °C 1 precise measurements of the diffusion current require temperature control to about 0.2 °C, which is generally achieved by immersing the cell in a water thermostat (preferably at 25 °C). A metal ion complex usually yields a different diffusion current from the simple (hydrated) metal ion. The drop time t depends largely upon the pressure on the dropping mercury and to a smaller extent upon the interfacial tension at the mercury-solution interface the latter is dependent upon the potential of the electrode. Fortunately t appears only as the sixth root in the Ilkovib equation, so that variation in this quantity will have a relatively small effect upon the diffusion current. The product m2/3 t1/6 is important because it permits results with different capillaries under otherwise identical conditions to be compared the ratio of the diffusion currents is simply the ratio of the m2/3 r1/6 values. 

Eq. (132) states that the interfacial tension has to be balanced by a pressure difference between the two phases. The terms containing derivatives of crin Eqs. (133) and (134) are non-zero only if there are local variations of the interfacial tension, which might be due to differences in concentration or temperature. The flow induced by such an effect is known as Marangoni convection. 

The B. licheniformis JF-2 strain produces a very effective surfactant under conditions typical of oil reservoirs. The partially purified biosurfactant from JF-2 was shown to be the most active microbial surfactant found, and it gave an interfacial tension against decane of 0.016 mN/m. An optimal production of the surfactant was obtained in cultures grown in the presence of 5% NaCl at a temperature of 45° C and pH of 7. TTie major endproducts of fermentation were lactic acid and acetic acid, with smaller amounts of formic acid and acetoin. The growth and biosurfactant formation were also observed in anaerobic cultures supplemented with a suitable electron acceptor, such as NaNO3[1106]. 

Blends of sodium hypochlorite with 15% HC1 and with 12% HCl/3% HF have been used to stimulate aqueous fluid injection wells(143). Waterflood injection wells have also been stimulated by injecting linear alcohol propoxyethoxysulfate salts in the absence of any acid (144). The oil near the well bore is mobilized thus increasing the relative permeability of the rock to water (145). Temperature effects on interfacial tension and on surfactant solubility can be a critical factor in surfactant selection for this application (146). 

Oil/water interfacial tensions were measured for a number of heavy crude oils at temperatures up to 200°C using the spinning drop technique. The influences of spinning rate, surfactant type and concentration, NaCI and CaCI2 concentrations, and temperature were studied. The heavy oil type and pH (in the presence of surfactant) had little effect on interfacial tensions. Instead, interfacial tensions depended strongly on the surfactant type, temperature, and NaCI and CaCL concentrations. Low interfacial tensions (<0.1 mN/m) were difficult to achieve at elevated temperatures. 

Isaacs and Smolek [211 observed that low tensions obtained for an Athabasca bitumen/brine-suIfonate surfactant system were likely associated with the formation of a surfactant-rich film lying between the oil and water, which can be hindered by an increase in temperature. Babu et al. [221 obtained little effect of temperature on interfacial tensions however, values of about 0.02 mN/m were obtained for a light crude (39°API), and were about an order of magnitude lower than those observed for a heavy crude (14°API) with the same aqueous surfactant formulations. For pure hydrocarbon phases and ambient conditions, it is well established that the interfacial tension behavior is dependent on the oleic phase [15.231 In general, interfacial tension values of crude oiI-containing systems are considerably higher than the equivalent values observed with pure hydrocarbons. 

Effect of NaCI Concentration. The presence of surfactant in brine can have a dramatic effect on crude oil-aqueous surfactant tensions even at elevated temperatures r5,211. Figure 5 shows that the effect of sodium chloride concentration on Athabasca bitumen-D20 interfacial tensions measured at constant surfactant... 

Figure 4 Effect of temperature on the interfacial tension of an Alberta heavy oil in produced water containing LTS-18 surfactant. Data are from three separate replicate experiments conducted under the same conditions.

Effect of Temperature. In the absence of surfactant, interfacial tensions of the Athabasca 1 211. Karamay 1 51, and other heavy oils 1 321 show little or no dependence on temperature. For surfactant-containing systems, Figure 6 shows an example of the effect of temperature (50-200°C) on interfacial tensions for the Athabasca, Clearwater and Peace River bitumens in Sun Tech IV solutions containing 0 and 10 g/L NaCI. The interfacial tension behavior for the three bitumens was very similar. At a given temperature, the presence of brine caused a reduction in interfacial tension by one to two orders of magnitude. The tensions were seen to increase substantially with temperature. For the case of no added NaCI, the values approached those observed T211 in the absence of surfactant. 

Effect of pH. Interfacial tensions between heavy crude oils and alkaline solutions were measured at temperatures up to 180°C by Mehdizadeh and Handy T341. They observed that tensions increased with an increase in temperature. However, recovery efficiencies obtained at high temperatures were comparable to those obtained at lower temperatures, apparently because the ease of emulsification at high temperatures counteracted the increase in tens i on. 

Effect of Ca2. In many reservoirs the connate waters ontain substantial quantities of divalent ions (mostly Ca . In alkaline flooding applications at low temperatures, the presence of divalent ions leads to a drastic increase in tensions r35,36]. Kumar et al. f371 also found that Ca and Mg ions are detrimental to the interfacial tensions of sulfonate surfactant systems. Detailed studies at elevated temperatures appear to be non-existent. 

Figure 9 Effect of CaCI2 concentration and temperature on the interfacial tension of the Karamay crude/D20 system containing Sun Tech IV and NaCI. Dashed line represents data in the absence of CaCI2 (reference [5]).

In precipitation studies (4 7, 4 ) it has been shown that, below a certain Mg/Ca concentration ratio in the aqueous solution, the rate of nucleation of calcite was faster than that of aragonite. Above that Mg/Ca ratio the order was reversed. This was explained by the effect of Mg2+ ions on the interfacial tension between the solution and precipitate, which apparently is larger for calcite than for aragonite (49). At still higher Mg/Ca ratios dolomite can be formed (50). Such low temperature precipitates of dolomite contain ordering defects. The number of defects increases when precipitation proceeds in a shorter time interval or at lower temperatures C51 ). 

R. Aveyard, B.P. Binks, T.A. Lawless, and J. Mead Interfacial Tension Minima in Oil -I- Water - - Surfactant Systems. Effects of Salt and Temperature in Systems Containing Nonionic Surfactants. J. Chem. Soc. Faraday Trans. 1 81, 2155 (1985). R. Aveyard and T.A. Lawless Interfacial Tension Minima in Oil-Water-Surfactant Systems. Systems Containing Pure Nonionic Surfactants, Alkanes, and Inorganic Salts. J. Chem. Soc. Faraday Trans. 1 82, 2951 (1986). 

Movements in the plane of the interface result from local variations of interfacial tension during the course of mass transfer. These variations may be produced by local variations of any quantity which affects the interfacial tension. Interfaeial motions have been ascribed to variations in interfacial concentration (H6, P6, S33), temperature (A9, P6), and electrical properties (AlO, B19). In ternary systems, variations in concentration are the major factor causing interfacial motion in partially miscible binary systems, interfacial temperature variations due to heat of solution effects are usually the cause. 

The effects of many other factors, such as interfacial tension, stirring rate, phase volume ratio or temperature, in aqueous-organic two-liquid-phase media on the stability of biotransformation have been studied [36, 37]. 

Pons et al. have studied the effects of temperature, volume fraction, oil-to-surfactant ratio and salt concentration of the aqueous phase of w/o HIPEs on a number of rheological properties. The yield stress [10] was found to increase with increasing NaCl concentration, at room temperature. This was attributed to an increase in rigidity of films between adjacent droplets. For salt-free emulsions, the yield stress increases with increasing temperature, due to the increase in interfacial tension. However, for emulsions containing salt, the yield stress more or less reaches a plateau at higher temperatures, after addition of only 1.5% NaCl. 

Increasing temperature has the effect of decreasing emulsion stability this has been demonstrated by Kunieda et al. [11,14], among others, and is due to the increase of the rate of coalescence of the dispersed phase droplets with increasing thermal energy. Pons et al. [100] also noted that a temperature increase caused an increase in average droplet size due to increasing interfacial tension. 

The several sets of published interfacial tension data for gas-water systems do not agree. The data which appear to be most consistent are given in Figure 16-23.14 The data were obtained with methane and pure water. However, the data cover the pressure and temperature ranges of usual interest. Figure 16-23 can be used as a correlation for natural gas-water systems its accuracy is unknown. The effect of dissolved solids on interfacial tension is unknown. 

Jennings, H.Y., Jr. and Newman, G.H. The Effect of Temperature and Pressure on the Interfacial Tension of Water Against Methane-Normal Decane Mixtures, Trans., AIME (1971) 251, 171-175. 

In a blend of immiscible homopolymers, macrophase separation is favoured on decreasing the temperature in a blend with an upper critical solution temperature (UCST) or on increasing the temperature in a blend with a lower critical solution temperature (LCST). Addition of a block copolymer leads to competition between this macrophase separation and microphase separation of the copolymer. From a practical viewpoint, addition of a block copolymer can be used to suppress phase separation or to compatibilize the homopolymers. Indeed, this is one of the main applications of block copolymers. The compatibilization results from the reduction of interfacial tension that accompanies the segregation of block copolymers to the interface. From a more fundamental viewpoint, the competing effects of macrophase and microphase separation lead to a rich critical phenomenology. In addition to the ordinary critical points of macrophase separation, tricritical points exist where critical lines for the ternary system meet. A Lifshitz point is defined along the line of critical transitions, at the crossover between regimes of macrophase separation and microphase separation. This critical behaviour is discussed in more depth in Chapter 6. 

Interfacial tension analysis may be used to study the interaction of emulsifiers and milk protein at the oil-water interface of whippable emulsions. The interfacial activity of proteins is affected only slightly by temperature changes. In general, emulsifiers can reduce interfacial tension much more than protein, and this effect is especially pronounced at low temperatures. 

Figure 6 shows the results of the experiment on the effects of temperature and salt concentration. The supernatant was prepared as described in the Materials and Methods section, except that there was a 9-d incubation instead of overnight owing to the replacement of a bumed-out lamp in the interfacial tension instrument. There were no significant differences among all salt concentrations at 21 and 45°C. However, at 70°C, the higher salt concentrations did not increase surface tension of surfactin, as did those at the lower temperatures. At 50 g/L of NaCl and 70°C, surface tension was 31.5 1.3 mN/m compared with 50.9 0.3 and 53.4 0.2 mN/m at 50 g/L of NaCl at 21 and 45°C, respectively. 

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