Flocculation oriented

Additional commercial processes are available for extraction of tea, hops, oriental herbs, tobacco leaves, and pharmaceuticals C02-enhanced oil recovery environmental appHcations such as extraction/flocculation of aqueous wastes reactions with iategrated separations such as aminations (ethylene... 

A more flexible option from an operational viewpoint is the implementation of process-oriented enhancements that intensify particle separation. This can be achieved by two different methods. In the first method, the suspension to be separated is pretreated to obtain a cake with minimal resistance. This involves the addition of filter aids, flocculants or electrolytes to the suspension. In the second method, the period during which suspensions are formed provides the opportunity to alter suspension properties or conditions that are more favorable to... 

Adsorption of the admixture on the hydrating cement grains could decrease flocculation in at least three ways (D44). The first is an increase in the magnitude of the ( -potential if all the particles carry a surface charge of the same sign and sufficient magnitude, they will repel each other. The second is an increase in solid- liquid affinity if the particles are more strongly attracted to the liquid than to each other, they will tend to disperse. The third is steric hindrance the oriented adsorption of a non-ionic polymer can weaken the attraction between solid particles. 

Somasundaran P, Xiang Y, Krishnakumar S. Role of conformation and orientation of surfactants and polymers in controlling flocculation and dispersion of aqueous and nonaqueous suspensions. Colloids Surf A 1998, 133, 125-133. 

Flocculation of charged solid particles occurs with the addition of surfactant to the suspension. If surfactant ions are adsorbed on the surface and oriented so that hydrophobic... 

Redispersion of the flocculate and other evidences for the hydrophilic character of the support coated with the adsorbed surfactant in the neighbourhood of the cmc indicate that bilayer coverage represents complete saturation of the surface. Commonly, the term bilayer is applied to an adsorbed structure in which the surfactant molecules are oriented perpendicular to the surface and fully extended [5,9,20,37,81,89]. The hydrocarbon tails of both layers form a hydrophobic core between the heads. At both sides counterions accumulate between the ionic head-groups. The result looks like a lamellar micelle. For certain physical regimes, the adsorbed amount is only a fraction of what is expected for a tightly packed bilayer [37,48] the structure which best fits the experimental data can... 

With new data for polyelectrolytes obtained with the techniques described above it should become possible to determine carefully the effects of ionic strength and externally controlled surface potential on the rate of adsorption of poly electrolytes. We hope that the effects of molar mass and charge density of the poly electrolyte, as well as the nature of that charge (annealed or quenched) can be established. This should stimulate further theoretical research aimed at constructing an adequate equivalent of the Von Smolu-chowsky-Fuchs theory for the rate of flocculation. At present, it would seem that an analysis of the adsorption process taking all complications into account necessitates a simulation-oriented approach. 

Effective compatibilization of binary polymer blends by addition of a copolymer reduces the dispersed particles size and Vj [Anastasiadis et al, 1987 Wu, 1987 Patterson et ai, 1971]. An illustration is shown on Figure 4.15. The effect of compatibilizer addition is similar to the emulsification of the classical emulsions. In the former systems, the compatibilizer effect on the drop size and Vj follows the same behavior as the emulsion drop size reduction upon addition of a surfactant. The latter behavior is usually described as the titration curve that characterizes the surfactant efficiency. The shape of the titration curve depends on the type of emulsifier and the emulsification process, e.g., mixing time and equipment. However, the amount of emulsifier to saturate the interface also depends on the affinity of emulsifier to the dispersed phase, the size of the dispersion, the orientation of the emulsifier at the interface and its ability to prevent flocculation and coalescence [Djakovic et al., 1987]. A similar behavior is to be expected for polymer blends upon addition of a compatibilizer. 

For the extreme case of parallel orientation the only eifects on flocculation are (a) the modification of the attractive force between particles which is likely to be small in most cases, and (b) the effect on the zeta potential which could be significant depending on the chemical character of the surface and polymer. When the polymer chains are extended into the liquid phase there is a major effect which arises when particles approach sufTiciently close for the adsorbed layers to interact. 

Interpretation of the adsorption isotherms indicated that for the acidic silica surface the basic resin molecules interacted strongly with the surface and adopted a parallel orientation, thus making little contribution to preventing flocculation. On the other hand, for the predominantly alumina-coated su rface, the resin only made contact with the surface with its limited number of acid groups, the rest of the molecule being extended into the medium and providing a steric barrier to flocculation. 

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