Surface active fraction

Gum arabic is widely used as an emulsifier in the beverage industry to stabilize cloud and flavor emulsions [98]. It is derived from the natural exudate of Acacia Senegal, and consists of at least three high molecular weight biopolymer fractions The surface-active fraction is believed to consist of branched arabinogalactan blocks attached to a polypeptide... 

An important industrial example of W/O emulsions arises in water-in-crude-oil emulsions that form during production. These emulsions must be broken to aid transportation and refining [43]. These suspensions have been extensively studied by Sjoblom and co-workers [10, 13, 14] and Wasan and co-workers [44]. Stabilization arises from combinations of surface-active components, asphaltenes, polymers, and particles the composition depends on the source of the crude oil. Certain copolymers can mimic the emulsion stabilizing fractions of crude oil and have been studied in terms of their pressure-area behavior [45]. 

Emulsives are solutions of toxicant in water-immiscible organic solvents, commonly at 15 ndash 50%, with a few percent of surface-active agent to promote emulsification, wetting, and spreading. The choice of solvent is predicated upon solvency, safety to plants and animals, volatility, flammabiUty, compatibihty, odor, and cost. The most commonly used solvents are kerosene, xylenes and related petroleum fractions, methyl isobutyl ketone, and amyl acetate. Water emulsion sprays from such emulsive concentrates are widely used in plant protection and for household insect control. 

Gas turbine fuels can contain natural surfactants if the cmde fraction is high in organic acids, eg, naphthenic (cycloparaffinic) acids of 200—400 mol wt. These acids readily form salts that are water-soluble and surface-active. Older treating processes for sulfur removal can leave sulfonate residues which are even more powerful surfactants. Refineries have installed processes for surfactant removal. Clay beds to adsorb these trace materials are widely used, and salt towers to reduce water levels also remove water-soluble surfactants. In the field, clay filters designed as cartridges mounted in vertical vessels are also used extensively to remove surfactants picked up in fuel pipelines, in contaminated tankers, or in barges. 

Since catalyst activity is dependent on how much catalytically active surface is available, it is usually desirable to maximi2e both the total surface area of the catalyst and the active fraction of the catalytic material. It is often easier to enlarge the total surface area of the catalyst than to increase the active component s surface area. With proper catalyst design, however, it is possible to obtain a much larger total active surface area for a given amount of metal or other active material in a supported catalyst than can be achieved in the absence of a support. 

Foam Fractionation. An interesting experimental method that has been performed for wastewater treatment of disperse dyes is foam fractionation (88). This method is based on the phenomenon that surface-active solutes collect at gas—Hquid iaterfaces. The results were 86—96% color removal from a brown disperse dye solution and 75% color removal from a textile mill wastewater. Unfortunately, the necessary chemical costs make this method relatively expensive (see Foams). 

T] Use with log mean mole fraction differences based on ends of column, t = rise time. No continuous phase resistance. Stagnant drops are likely if drop is very viscous, quite small, or is coated with surface active agent. A.y uiean dispersed liquid M.T. coefficient. 

Leaching is the removal of a soluble fraction, in the form of a solution, from an insoluble, permeable sohd phase with which it is associated. The separation usually involves selective dissolution, with or without diffusion, but in the extreme case of simple washing it consists merely of the displacement (with some mixing) of one interstitial liquid by another with which it is miscible. The soluble constituent may be solid or liquid and it may be incorporated within, chemically combined with, adsorbed upon, or held mechanically in the pore structure of the insoluble material. The insoluble sohd may be massive and porous more often it is particulate, and the particles may be openly porous, cellular with selectively permeable cell walls, or surface-activated. 

Scale-Up on Actual Area The nominal area of a filter as used by equipment manufacturers is based upon the overall dimensions of the filtering surface. The fraction of this total area that is active in filtration is a function of the filterability of the material being handled and any special treatment which the surface may receive. 

Albertsson (Paiiition of Cell Paiiicle.s and Macromolecules, 3d ed., Wiley, New York, 1986) has extensively used particle distribution to fractionate mixtures of biological products. In order to demonstrate the versatility of particle distribution, he has cited the example shown in Table 22-14. The feed mixture consisted of polystyrene particles, red blood cells, starch, and cellulose. Liquid-liquid particle distribution has also been studied by using mineral-matter particles (average diameter = 5.5 Im) extracted from a coal liquid as the solid in a xylene-water system [Prudich and Heniy, Am. Inst. Chem. Eng. J., 24(5), 788 (1978)]. By using surface-active agents in order to enhance the water wettability of the solid particles, recoveries of better than 95 percent of the particles to the water phase were obsei ved. All particles remained in the xylene when no surfactant was added. 

A hand calculation method that can be used to take into account two-phase relief when the materials m the vessel are natural" surface active foamers. To account for disengagement, the vessel void fraction at disengagement should be evaluated (i.e.. the point at which the vent flow ceases to be two-phase and starts to be vapor only). ... 

This is very similar to the flotation procedure described under basic physical treatments. In the case of foam fractionation, not only are the pollutants raised to the surface where they can be skimmed off, but a froth, like beer foam, is produced in which the pollutants become concentrated. The key to the process is the adsorption of the pollutants onto the surface-active agents that cause the froth to form. Sometimes a surfactant is added so that non-surface-active components can be removed. 

The current research objective is to evaluate the surface activity of the subfractions obtained from the solvent fractionated crude oil and shale oil samples as they are passed through the separation process developed for this work. The columns used are anion exchange resin,... 

The results of experiments with crude oil fractions in this study also suggest that several species were present in reaction interface. There are mainly long chain carboxylic acids. The difference in size and structure is expected to give them different pka values. As a result, different surface activity (i.e., IFT value) is obtained with different levels of alkali concentration. Crude oil fractions with lower surface activity only yield surface inactive salts that may appear as precipitates at the interface. 

The highest surface activity of fraction A3 extracted from shale oil needs to be explored in detail in order to understand this very unique phenomena. The benchmark experiments performed by Lee et al. (22) in studies of dissociation phenomena of Stuart oil shale in an alkaline environment proved the formation of carboxylic acids as it was verified from GC results. In another study by Lee et al. (23), it was shown that the hydroxyl ions from an alkaline solution could decompose the silicate and aluminasilicate structures in oil shale samples, provided that ultrasonic radiation and electrolytic current were simultaneously applied. 

Mehdizadeh et al. exploited the separability of current distribution on different scales to model the macroscopic current distribution on patterns made up of lines or points distributed over a large workpeice [136], They solved the secondary distribution of the superficial current density sup using a boundary condition which captures the density of small features but not their geometry. The boundary condition is based on a smoothly varying parameter representing the Faradaically active fraction of surface area. 

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