Emulsification droplet coalescence

Tornberg and Ediriweera, 1987). Phase inversion temperature (Shinoda and Saito, 1969) and emulsifying capacity (Swift et al., 1961) have been used to evaluate the effects of low molecular weight and protein emulsifiers, respectively. Unfortunately, it is not possible to measure the size of the large droplets present in unhomogenized water-in-oil emulsions because the droplets coalesce very quickly. The phase inversion temperature is not a relevant test, as it may not be related directly to the stability to inversion at the emulsification temperature. Furthermore, it has been stated (Matsumoto and Sherman, 1970) that water-in-oil emulsions do not exhibit a true phase inversion temperature, unlike oil-in-water emulsions. 

Emulsification and coalescence are related to spontaneously formed unstable W/0 emulsion (Castor et al., 1981b) or mixed emulsion. Isolated oil droplets are emulsified after contacting with alkaline solution. The emulsified droplets coalesce with each other to become larger droplets while they move in the... 

De-emulsiftcation one of the stumbhng blocks in the construction of a continuous liquid membrane process plant is de-emulsification and recovery of the solvent. De-emulsification involves coalescence of dispersed droplets into larger droplets with subsequent phase separation by gravity. The most popular method to augment this process is by apphcation of an electric field. This indicates that hquid membrane plants will be energy intensive. 

A type of emulsion formed by mechanical emulsification is largely determined by volume ratio of liquids the liquid present in a much greater quantity usually forms a continuous phase, i.e. dispersion medium. In the case of approximately equal volumes of two liquids both direct and inverse emulsions are formed among these two the emulsion that survives is the one with higher stability against droplet coalescence and further phase separation. The stability relationship between direct and inverse emulsions depends in this case on the nature of stabilizer, which, consequently, determines the final type of emulsion that forms. 

The size distribution of emulsions is controlled by the rate of diffusion of functional molecules to the interface [4]. Emulsifier molecules diffuse to the interface while coalescence is occurring [4]. If the coating of fat globules were instantaneous, the emulsion would have a particle size distribution identical to that at the moment of emulsification. In actuality, emulsifier molecules require a finite time to reach the interface and be adsorbed. The rate of droplet coating is determined by (1) the rate of fat droplet coalescence, (2) the rate at which emulsifiers reach the interface, and (3) their rate of absorption. The... 

Emulsification and coalescence The possibility of enhancing oil recovery from porous media by a spontaneous emulsification mechanism has been examined by Schechter and coworkers (6). These researchers postulated that residual oil, which is entrapped after a conventional waterflood, can be mobilized by spontaneous emulsification and subsequent coalescence of small droplets with other... 

The kind and concentration of emulsifier molecules applied have a big influence on the coalescence process during the emulsification process itself and during prolonged shelf-life. In emulsification (droplet disruption processes), the droplets are disrupted into smaller ones. New interfacial area develops, being insufficiently covered by emulsifier molecules. Interfacial active molecules (emulsifiers) are transported by laminar and turbulent flow to the droplet subsurface, diffuse to the interface and adsorb and re-orientate at it. This stabilizes the new droplets formed. However, this process takes some time (milliseconds to minutes), depending on the emulsifier molecular stmcture. Droplets colliding with each other in the meantime will coalesce [2], A detailed study about droplet coalescence... 

Studies of flow-induced coalescence are possible with the methods described here. Effects of flow conditions and emulsion properties, such as shear rate, initial droplet size, viscosity and type of surfactant can be investigated in detail. Recently developed, fast (3-10 s) [82, 83] PFG NMR methods of measuring droplet size distributions have provided nearly real-time droplet distribution curves during evolving flows such as emulsification [83], Studies of other destabilization mechanisms in emulsions such as creaming and flocculation can also be performed. 

A well-studied example of a bioemulsifier is emulsan, a cell surface-exposed molecule that allows Acinetobacter calcoaceticus RAG-1 to attach to crude oil droplets [123]. Upon depletion of the short-chain alkanes utilised by this strain, the emulsan molecules were released from the bacterial surface, thereby allowing the cells to leave the oil droplet and to find a new substrate. Important positive side-effects of this mechanism seem to be that the remaining emulsan hydrophilises the droplet and prevents both the reattachment of A. calcoaceticus RAG-1 and the coalescence of the used oil droplet with other droplets that still contain unexploited alkanes. Bredholt et al. [124] studied the oil-emulsifying activity of Rhodococcus sp. strain 094. When exposed to inducers of crude-oil emulsification, the cells developed a strongly hydrophobic character, which was rapidly lost when crude-oil emulsification started. This indicated that the components responsible for the formation of cell-surface hydrophobi-city acted as emulsion stabilisers after release from the cells. 

Therefore, in order to keep such an emulsion stable, an emulsifier is generally required, which is suitable for the preparation of water-in-oil emulsions. Because of its surface activity, the emulsifier promotes the emulsification of the salt phase in small droplets and prevents the coalescence of the formed droplets after the emulsion has formed. 

There appeared to be some additional emulsification taking place in the test separator as evidenced from the relatively slower separation of free water from samples taken downstream of the separator. This phenomena suggests that break-out of free gas from the liquid phase can hamper effective coalescence of the water droplets, averting he dehydration efficiency. 

Perhaps the most difficult of the requirements is the emulsification and contacting. For efficient operations the emulsion characteristics must be uniform throughout the reactor. An excess of acid is preferred, since this results in a hydrocarbon-in-acid emulsion. In these mixtures the viscosity and surface tension of the continuous acid phase are effective in minimizing the tendency of the dispersed hydrocarbon droplets to coalesce and separate, acting under the influence of the very large specific gravity differential between the light and heavy phases. 

With cetyl alcohol, there is the complication that the polarity of the molecule may cause it to reside at the surface of the droplet, imparting additional colloidal stability. Here, the surfactant and costabilizer form an ordered structure at the monomer-water interface, which acts as a barrier to coalescence and mass transfer. Support for this theory lies in the method of preparation of the emulsion as well as experimental interfacial tension measurements [79]. It is well known that preparation of a stable emulsion with fatty alcohol costabilizers requires pre-emulsification of the surfactants within the aqueous phase prior to monomer addition. By mixing the fatty alcohol costabilizer in the water prior to monomer addition, it is believed that an ordered structure forms from the two surfactants. Upon addition of the monomer (oil) phase, the monomer diffuses through the aqueous phase to swell these ordered structures. For long chain alkanes that are strictly oil-soluble, homogenization of the oil phase is required to produce a stable emulsion. Although both costabilizers produce re-... 

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