Electrical fields, emulsion breaking

A number of techniques are used commercially to accelerate emulsion breakdown. Mechanical methods indude centrifugal separation, freezing, distillation and filtration. Another method is based on the principle of antagonistic action - i.e. the addition of O/W-promoting emulsifiers tends to break W/O emulsions, and vice-versa. Emulsions can also be broken by the application of intense electrical fields, the principal factors involved being electrophoresis in the case of O/W emulsions and droplet deformation in the case of W/O emulsions. 

A vessel used to break emulsions by promoting coalescence through the application of an electric field. See... 

Extraction can be enhanced by the application of a dc or pulsed electric field, typically on the order of 1 kV/cm. This requires that the aqueous phase be dispersed and the organic phase be of low conductivity. The improvement in mass transfer rate is due to the breakup of large drops by the action of the field and to the increase of drop velocity resulting in increased mass transfer coefficients. It has also been found that low-frequency pulsed fields are effective in breaking up emulsions in the settler stage of mixer-settler units. 

Electrical Methods. The principle of electrostatic dehydration in emulsion breaking for both refinery desalting and oil-field production is essentially the same. The electric field produced disturbs the surface tension of each droplet, probably by causing polar molecules to reorient themselves. This reorientation weakens the film around each droplet because the polar... 

There are some important advantages of splitting emulsions by means of an electrical field in contrast to the usual breaking processes (3). 

KRIECHBAUMER and MARR Emulsion Breaking in Electrical Fields... 

When decreasing the electrode length from 160 mm to a few mm -that means, that the contact time of the emulsion with the electrical field decreases from about 10 seconds to less than 1 second - the emulsion breaking coefficient does not decrease very steep. 

Figure 8. Effect of breaking time on emulsion breaking efficiency electrical field strength 1000 V/mm.

Further on, we shall be studying reverse water-oil emulsions of the w/o type. The continuous phase - the oil - is a substance with very low conductivity (10 -10 1/ohm-M). The disperse phase (water) contained in the oil output has many soluble mineral salts that causes its high conductivity (10 -10 1/ohm-M). Therefore a reverse water-oil emulsion can be considered as a disperse system, in which the disperse phase (water droplets) is conductive, and the continuous phase (oU) is dielectric. It means that we can always act selectively on the disperse phase of a w/o emulsion with external electric field. Under the action of electric field, water drops become polarized, get drawn to eacti other, colUde and coalesce. Thus the external electric field promotes integration of the emulsion. Later on, it will be shown that a high intensity of the electric field may also cause droplets to break. 

An electrostatic field applied across an emulsion will place a limit on the maximum stable droplet size. The electrostatic field has a polarizing effect which creates charges of opposite polarity at opposing sides of the droplet. This elongates the droplet, in the direction of the applied electric field, and may result in break-up if the disruptive electro-statie foree exceeds the cohesive interfaeial foree. 

The influence of electrical fields on hydrodynamics and thus on mass transfer has been excellently reviewed by Yamaguchi [77,78]. It is thus possible to produce monodispersed droplet swarms up to extreme viscosities in the nanoscale (Figure 18.22). Here, the force balance on a nozzle leads to a dismpture of drops [79]. Under similar electrical but different geometrical conditions, breakage of an emulsion will occur, when due to polarization droplets form chains and will coalesce to bigger droplets as is technically used in secondary oil recovery, breaking down the water in oil emulsions [80]. Thus, coalescence and droplet formation in the electric field is sensitive to minor... 

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