Impeller emulsification

Excessive mixing Limit agitator power input and provide proper of reactants or impeller design impurities which, Return process to pilot or development to rede-promotes process to eliminate or minimize this emulsification. problem Poor phase separa- tion resulting in L it shaft speed problems in subse- Monitor shaft speed quent processing, phase separation steps or in down- stream equipment. I" " de-emulsifiers CCPS G-29 Lees 1996... 

Although low shear emulsification equipment (mechanical stirrers or impellers) can differ in the type of fluid flow imparted to the mixture (axial-flow propeller or radial-flow turbines), no subclasses have been defined. 

Flat plate impellers with sawtooth edges are suited to emulsification and dispersion. Since the shearing action is localized, baffles are not required. Propellers and turbines also are sometimes provided with sawtooth edges to improve shear. 

By selecting optimum impeller speed during emulsification, surfactant concentration, volume ratio of surfactant solution, carrier concentration, and a suitable feed phase composition, uniformly distributed stable emulsion could be obtained to provide a high separation factor and higher mass transfer rate. 

Figure 7.4 Variation of average pore size (D) with total mixing time (t) as a function of dispersed phase volume fraction (s). Dosing time is 10 min, impeller speed El = 300 rpm, emulsification temperature T = 25° C. Rare size is evaluated from the scanning electron micrographs of the polymers and the raw data are corrected to compensate for the random space distribution of the pores...

Figure 7.5 Variation of average pore size with emulsification temperature when dosing time = 40s, total mixing time = 100s, impeller speed = 300 rpm, phase volume = 90%...

Table 7.1 The variation of coalescence pore size with water-soluble polymer concentration as a function of molecular weight. The phase volume is 85%, impeller speed of 300 rpm, and dosing and homogenization times of 600 s each, temperature of emulsification is 25° C...

The choice of agitator is dictated mainly by the type of mixing required, for example heat transfer, gas absorption, or emulsification, the suspension of solid particles in a liquid and the type of material being mixed, for example its viscosity, specific gravity, heat conductivity or size of the suspended particles. Generally, paddle, impeller, and anchor agitators are rotated at lower speeds (up to 150 r.p.m.) than the propeller or turbine type (up to 2900 r.p.m. in smaller vessels). The efficiency of agitation is considerably increased by the use of... 

In emulsion polymerization, a high shear rate may cause coagulation. However, a certain amount of turbulence is required for emulsification and to avoid phase segregation. Moreover, high fluid circulation is needed in order to guarantee the macroscopic uniformity and to enhance mass and heat transfer. In this way, mixed-flow turbines with features of both radial and axial flow can be useful. The most common of these impellers is the 45° angled blade turbine. Multiple impellers on the same shaft can also be employed. 

There are four types of turbine impellers, which are characterized by the flow patterns and level of shear they create axial flow, radial flow, hydrofoil, and high-shear impellers. They have the widest use in low and medium viscosity liquid applications, solids suspension, liquid-liquid emulsification, and gas dispersion. Turbine impellers can have blades varying from 2 to 12 in number. Two blades are normally unstable mechanically, while it is difficult to install more than six blades on a hub. Axial flow impellers generally have three or four blades, and radial flow impellers are designed with six blades. 

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