Bulk foam fractionation

Excess collector can also reduce the separation by forming micelles in the bulk which adsorb some of the colhgend, thus keeping it from the surface. This effect of the micelles on Ki for the colhgend is given theoretically [Lemhch, Principles of Foam Fractionation, in Periy (ed.). Progress in Separation and Purification, vol. 1, Interscience, New York, 1968, chap. 1] by Eq. (22-44) [Lemlich (ed.). Adsorptive Bubble Separation Techniques, Academic, New York, 1972] if F, is constant when C, > C-... 

The distribution of counterions at the charged surface and in the bulk solution was studied combining the radiotracer technique with foam fractionation technique. The relative adsorbability of counterions was determined from the ratio of mole ratios in an adsorbed and in the solution phases. The relative adsorbability was CT CH3COO Br ClOf NOs = 1 0.7 1.5 3.0 4.1 in solution of dodecylammo-nium(0.011 mole/liter), Cl Br ClOf NOf SO/2 = 1 1.2 2.8 1.6 2.3 in solution of dodecyltrimethylammo-nium(0.015 mole/liter), and Na+ Ca2+ = 1 210 in solution of sodium dodecylsulfate(0.006 mole/liter). 

Bikerman [46] describes studies of the specific conductivity of individual foam lamellae. For bulk foams, the specific conductivity of the foam, kf, is proportional to the volume fraction of liquid in the foam and its conductivity, kl ... 

This chapter will focus on the stability of foams flowing in porous media when in the presence of crude oil. Many laboratory investigations of foam-flooding have been carried out in the absence of oil, but comparatively few have been carried out in the presence of oil. For a field application, where the residual oil saturation may vary from as low as 0 to as high as 40% depending on the recovery method applied, any effect of the oil on foam stability becomes a crucial matter. The discussion in Chapter 2 showed how important the volume fraction of oil present can be to bulk foam stability. A recent field-scale simulation study of the effect of oil sensitivity on steam-foam flood performance concluded that the magnitude of the residual oil saturation was a very significant factor for the success of a full-scale steam-foam process (14). 

One approach to determining the influence of an oil phase involves bulk foam stability tests conducted in the presence and absence of specified volume fractions of oil. An example of this kind of testing, in the... 

Excess collector can also reduce the separation by forming micelles in the bulk which adsorb some of the colligend, thus keeping it from the surface. This effect of the micelles on for the colligend is given theoretically [Lemlich, Principles of Foam Fractionation, in Perry... 

Due to the peculiarities of surfactant synthesis, many surfactants contain trace impurities of higher surface activity than the main component. These trace impurities do not influence most bulk properties. However, at the surface they are enriched and impurities may even dominate the properties of the interface. This behaviour was first recognized by Mysels [15] and a purification scheme using foam fractionation was proposed [16]. A detailed discussion on artifacts caused by impurities can be found in [17]. 

Perhaps the most important and striking features of high internal phase emulsions are their rheological properties. Their viscosities are high, relative to the bulk liquid phases, and they are characterised by a yield stress, which is the shear stress required to induce flow. At stress values below the yield stress, HIPEs behave as viscoelastic solids above the yield stress, they are shear-thinning liquids, i.e. the viscosity varies inversely with shear rate. In other words, HIPEs (and high gas-fraction foams) behave as non-Newtonian fluids. 

Those who have studied the stability of masses of foam on solutions of surface-active substances find rather different results according to whether evaporation can, or cannot, take place. Bartsch3 examined the durability of foams on an extensive range of solutions, in closed cylinders, where the air space was saturated with water vapour the maximum of stability occurred at concentrations where there was some depression of surface tension, but far below those at which the maximum depression of tension was obtained. With moderately surface-active substances such as amyl alcohol, the maximum stability of the foams occurred at a reduction of tension roughly 12 dynes per cm. naturally the bulk concentration required to reach this varied with the length of hydrocarbon chain in the compound, but it was always only a small fraction of saturation. The stability of the foams rose very rapidly, as the bulk concentration increased from zero up to that at which the maximum fall of tension was obtained ... 

The most important property for insulation is thermal conductivity. The following transport types participate in the transmission of heat heat conduction in PS, heat conduction in the filling gas (air), radiation heat transfer and heat convection by convection flows in the closed cells. The thermal conductivity of the air in the cells contributes the most to the total heat transport. The radiation fraction depends on the diameter of the cells formed. The thermal conductivity depends on the density of the foamed PS material. Thermal conductivity decreases with increasing bulk density, reaches a minimum and then rises again (Figure 9.15). The following processes are responsible for this characteristic. 

The different temperature dependences of Ti in weak and strong magnetic fields are undoubtedly associated with the effect of the phenolic adsorbent matrix, since the weight fractions of water in the foam bulk are equal. The adsorbent effect is also revealed by the two-component character of relaxation curves (Fig. 13). Thus, the short component has a relaxation time of Ti = 0.15 — 0.20 s and is practically independent of temperature. The authors explain its existence by the presence of water in 20-100 A large cells which is strongly bonded to the matrix ... 

In the coke drum, foaming occurs. As the bulk viscosity of the resid increases and solids form, a stable foam front forms, and it rises higher in the drum as the coke level rises. If left unchecked, the foam will reach near the top of the coke drum and potentially go overhead, or foam-over . The consequences of a foam-over are immediate and disastrous. The transfer line from the coke drum to the fractionator becomes fouled with coke particles. As the solids reach the fractionation tower, the suction screens in the bottom of the tower become plugged. Finally, the finer particles of coke that pass through the suction screens will... 

Barnes (6) and Tadros and Vincent (7) demonslrated die importance of a number of factors on emulsion properties and stability, among them the relative volume of flic dispersed phase, i.e., the volume fraction, and the average size of the droplet, flic bulk viscosity of each phase, and also flic nature and concentration of the emulsifier. The latter must be of vital importance as there are no stable emulsions or foams known wifliout the presence of surface-active compounds. Sometimes fliis becomes not immediately visible in some systems as stabilizers may be inherent in many natural emulsions or foams. 

A completely different method involves use of down-pumping impellers to enhance entrainment of air from the foam into the bulk liquid phase. This produces an increase in the gas hold-up, < ip (gas volume fraction in the liquid phase). The precise mechanism involved is, however, apparently unclear [35]. The approach was first described by Hoecks et al. [3] who labeled it stirring as foam disruption. It would appear to have application mainly in control of foam during fermentation in stirred vessels. The relative performance of various impellers in this context is also described in later papers [35,36]. 

For very dry foams, the rheological properties are determined solely by the films separating the bubbles. The rheological properties of a set of randomly oriented films were determined first by Deijaguin (54) and later independently by Stamenovic and Wilson (55). These models set the scale for the elastic modulii of a foam. In the dry limit (when the gas fraction equals 1), the bulk modulus of the foam is dominated by that of the gas in... 

The void fraction was used to characterize the foam samples. The foam density was determined by the water displacement method (ASTM D792-00). Samples were taken from regions near the gate, at the center, and near the end of the injection-molded part. The expansion ratio O is equal to the ratio of the bulk density of HDPE/talc compounds, po, to the measured density of the foam sample, Pf. The void fraction was calculated as follows ... 

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