Flocculation process continuous

Continuous flocculation in stirred tanks shows similar trends with regard to agitation/mixing conditions as for batch systems. The overall performance of continuous flocculation processes tends to be inferior to that which can be obtained in batch systems. This is attributed to a closer approach to equilibrium in the continuous case. In-line flocculation, by injection of polymer into turbulent flow in a pipe, is widely practised in industry and offers certain advantages. Multiple addition at several points along the length of a pipe is preferred to single-point addition. 

It seems that coalescence process is very delayed by the emulsifier. In order to investigate the flocculation process, a study through an optical microscopy of the droplets and flocks has been employed. Unfortunately, a little difference in the contrast (brown against pale yellow) between droplets and continuous phase has not permitted a good determination of mean droplets dimensions. Probably, mean diameter should be few microns (i-5). 

Most often, however, the primary particles are colloidally unstable , or caducous, and flocculate to a limited extent. In this process two particles upon collision adhere to each other and subsequently fuse, or coalesce, to form a single particle in which most, if not all of the surface groups remain at the interface. This is represented in Figure 6. The consequent reduction in surface-to-volume ratio leads to an increase In surface charge density, a, and surface electrical potential, 9 q, which in turn produces a rapid decline in the rate of flocculation, Rp as the process continues. [11]. Such... 

The collision theory [15] and the concept of the limited flocculation process were originally used to calculate the values of Rc and Rf, respectively. Later, the diffusion theory [17,18] was adopted by Fitch to calculate the value of Rc [31]. It was pointed out that the concentration of oligomeric radicals with chain length of j in the continuous aqueous phase, which was required to carry out the calculation, was very difficult to be determined. 

The sequence, flocculation — coalescence — separation, is compHcated by the fact that creaming or sedimentation occurs and that this process is determined by the droplet size. The sedimentation velocity is monitored by the oppositely directed forces which form the buoyancy and the viscous drag of the continuous phase on the droplet ... 

Achieving steady-state operation in a continuous tank reactor system can be difficult. Particle nucleation phenomena and the decrease in termination rate caused by high viscosity within the particles (gel effect) can contribute to significant reactor instabilities. Variation in the level of inhibitors in the feed streams can also cause reactor control problems. Conversion oscillations have been observed with many different monomers. These oscillations often result from a limit cycle behavior of the particle nucleation mechanism. Such oscillations are difficult to tolerate in commercial systems. They can cause uneven heat loads and significant transients in free emulsifier concentration thus potentially causing flocculation and the formation of wall polymer. This problem may be one of the most difficult to handle in the development of commercial continuous processes. 

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