(2b) Controlled Particle Deposition by Design of An Electrochemical Adsorption Cell | AIChE

(2b) Controlled Particle Deposition by Design of An Electrochemical Adsorption Cell

Authors 

Bakhshi, E. - Presenter, R&D Center of PIDMCO ,National Petrochemical Company
Abniki, F. - Presenter, National Iranian Petrochemical Company,Ghadir Group


Deposition of colloidal particles substrate is encountered in a variety of naturally occurring processes such as particulate fouling of heat exchangers, thrombus formation in vascular prostheses and other artificial organs and aerosols entering the lungs. Deep bed filtration of waste waters is perhaps the most prominent example of importance to industry.

Design of an electrochemical adsorption cell utilizing reticulated vitreous carbon (R.V.C.) as the working electrode ,stainless steel as the counter electrode and a cellulose acetate membrane ,for separating the anodic and cathodic, is described for the separation of polystyrene latex colloidal particles from a KCI solution.

The experimental results are compared with the Derjaguin-Landau-Verwey-Ovdrbeek (D.L.V.O.) prediction for the occurrence of favorable and unfavorable deposition conditions.

In the theoretical section of this work it will be assumed that the main energies contributing adsorption interaction between the surfaces will be due to electrical double layer to Van der Waals attraction . The some of these energies provides the total interaction energy between surfaces and this constitutes the underlying assumption for the classical D.L.V.O. theory of colloidal stability.

The polystyrene latex particles used in this study were 5.4 µm and hence effect of diffusion becomes negligible. For reasonably low flow rates, Re was less than l, inertial impaction is usually assumed negligible compared to the bulk flow. The highest particle Reynolds number employed in this study was 2800 and hence the contribution due to inertial impaction can be ignored . Therefore only the effect of gravity and electrostatic forces need to be considered in any theoretical analysis of the experimental results. Once the particles are in the vicinity of the collector. In order to observe solely the effect of these forces the effect of hydrodynamic interactions has to be kept at a minimum. Therefore experiments carried out were directed mainly at finding out the dividing line between hydro dynamically-controlled and electro statically-controlled processes.

In this way , for the present experimental conditions the main forces contributing to deposition process are the surface forces and hydrodynamics . At the highest flow rate of 34 cubic meter/min the colloidal forces were shown to be negligible compared to the hydrodynamics . Indeed the effect of surface at the KCl concentration of 0.001 mol/cubic dm apparently only became significant at the flow rate.

At this flow rate and KCl concentration of 0.001 mol/cubic dm experimental results show Clear evidence of conditions governing the of favorable and unfavorable deposition conditions . The variation of collector potential under unfavorable deposition condition does not produce large changes in the deposition rate whereas variation collector potential under favorable condition produce significant change in the deposition state.