Emulsion destabilization processes

Many dairy emulsions destabilize by flocculation and networking. Hib-berd et al, (1997a, b) obtained the ultrasonic response to flocculation showing that floe size increased during the experiment. The experiment was repeated with a higher level of hydroxyethyl cellulose (0.1%, v/v) with the result that flocculation occurred more rapidly with the formation of a densely connected network of particulate material. The residual root-mean-square error associated with fitting the ECAH model to the ultrasonic data at various points in the flocculation reaction increased rapidly at the onset of network formation and could, in principle, be used to detect such phenomena in a process context. 

The chemical treatment method is the most effective method to break very stable emulsions. This process usually destabilizes dispersed oil or emulsified oil as the first stage, followed by the removal of the separated oil as the second stage. Acidification and coagulation are the common processes for chemical treatment. 

Direct and inverse emulsions are found in everyday-life products. For instance, both types of emulsion are common in food oil-in-water emulsions include milk, cream, and mayonnaise butter and margarine are examples of water-in-oil emulsions. Furthermore, recent studies were carried out, with the help of professional sensory panelists, to determine the influence of emulsion type on the perception of taste [36], In relation to the breakdown mechanisms of emulsions (creaming/sedimentation, flocculation, coalescence, and Ostwald ripening), controlling emulsion type can be regarded as a key parameter to design stabilization/destabilization processes. In cosmetic... 

Emulsion Stability. An emulsion is defined as a macroscopic dispersion of two liquids, one of which forms the continuous phase of the system and the other forms the discrete phase. An emulsion of two liquids without a stabilizer will quickly break into two liquid layers. Emulsions destabilize by three distinct processes breaking, creaming, and flocculation (Figure 14). When emulsions break, the initial small droplets of the emulsion spontaneously join to form larger droplets. This process is termed coalescence , and it ultimately leads to two separate liquid layers. 

Direct investigation of the coalescence subprocess in emulsions is difficult. Instead, the entire destabilization process is usually investigated. Meanwhile, the rate of the destabilization process depends on the rates of both flocculation and disaggregation and on the floe structure as well. All these characteristics vary in a broad range. At a given unknown value for the time of the elementary act of coalescence T(. the different times can be measured for the integrated process and different evaluations of x. are possible. 

The mechanical properties of fire protecting interfacial film are essential for the final stability level of the W/0 emulsions. Concentrated polymeric interfacial films may display either elastic or viscous properties that make the destabilization process difficult and time consuming. The aromatic asphaltene molecules will normally undergo a stacking into sandwich-like structures as a consequence of tire molecular association. The presence of other nanosized-particles like organic wax particles and inorganic clay particles will further enhance the stability level. However, fliese compounds are not further dealt wifli in the present chapter. 

In the offshore produetion of petroleum, technical problems are sometimes eneountered with emulsions which are formed at different stages of the production and transportation processes. These have to be taken into consideration at an early stage of the planning and construction of a platform. Enough space must be reserved for emulsion destabilization equipment such as coalescers and separators. With effective methods of emulsion separation, based on reliable information about crude oil and its tendency to form emulsions, much of fliis space could be reserved for other more useful purposes. 

Since Ostwald ripening is a diffusive process, it cannot be accelerated by centrifugation. Nevertheless, analytical centrifugation was able to trace emulsion destabilization... 

As part of the dispersed phase, lipids in a state of incipient or advanced crystallization may substantially increase emulsion destabilization. During processing and/or storage, intraglobular fat (e.g., in cream, margarines) may solidify, form-... 

Concerning the barrier effect, Capek [69], in a review where the destabilization processes of emulsions is extensively analyzed, explains that the presence of a fatty alcohol can form with an ionic surfactant a denser inter facial layer that can increase the resistance to transfer of the dispersed component from small droplets to the continuous phase and from the continuous phase to the big droplets. 

Rubber processed in latex form accounts for about 10% of new mbber consumption. Rubber latex is a Hquid, oil-in-water emulsion which is used to make foam or thin-walled mbber articles. The same accelerators and antidegradants used in dry mbber are used in latex, with longer-chain versions preferred for greater oil solubiHty. To prepare these and other additives for addition to latex, they must be predispersed in water and the surface of the powder or oil droplet coated with a surface-active agent to prevent destabilization (coagulation) of the latex. 

Before determining the degree of stabiUty of an emulsion and the reason for this stabiUty, the mechanisms of its destabilization should be considered. When an emulsion starts to separate, an oil layer appears on top, and an aqueous layer appears on the bottom. This separation is the final state of the destabilization of the emulsion the initial two processes are called flocculation and coalescence (Fig. 5). In flocculation, two droplets become attached to each other but are stiU separated by a thin film of the Hquid. When more droplets are added, an aggregate is formed, ia which the iadividual droplets cluster but retain the thin Hquid films between them, as ia Figure 5a. The emulsifier molecules remain at the surface of the iadividual droplets duiing this process, as iadicated ia Figure 6. 

The stabilization of an emulsion iavolves slowiag the destabilization, primarily the flocculation process. This may be achieved ia two principal manners by reduciag the mobiHty of droplets through enhanced viscosity or by inserting an energy barrier between them (see also Dispersants Flocculating agents). 

In a recycling system, the aqueous discharge effluent from both centrifiiges is returned to the extractors for additional oil recovery, the water being reused. During this extraction process the viscosity of the emulsions increases because peel polysaccharides, mainly pectins, are transported with the emulsion. Enzymatic breakdown of the internal links of the pectin, catalysed by endopolygalacturonase activity, produces an important decrease in the viscosity of the emulsion [16]. In addition, enzymatic treatment removes pectins from the emulsion and contributes to it destabilization [17]. 

The fact that these phospholipids-stabilized emulsions are sterilized by heat may be surprising since most emulsions stabilized by almost any other surfactant is readily destabilized by heat. Indeed, the fact that the droplet size of phospholipids-stabilized emulsions actually decreases on the application of thermal stress is probably due to the behavior of the phospholipids which move from the aqueous phase to the oil phase, especially to the interfacial mesophase, during the heating process. 

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