ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 8, pp. 1286!1290. + Pleiades Publishing, Inc., 2006.
Original Russian Text + V.V. Tarasov, N.F. Kovalenko, N.E. Kruchinina, S.A. Shilin, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79,
No. 8, pp. 1300!1304.
PROCESSES AND EQUIPMENT
OF CHEMICAL INDUSTRY
Model of Heterogeneous Hydrodynamic Coagulation
V. V. Tarasov, N. F. Kovalenko, N. E. Kruchinina, and S. A. Shilin
Mendeleev Russian University of Chemical Technology, Moscow, Russia
Received October 5, 2005; in final form, January 2006
Abstract-The Eley3Rideal and Langmuir concepts of surface reactions were used to develop a model of
heterogeneous hydrodynamic coagulation of diluted [oil-in-water] emulsions (0.132.0 vol %). The math-
ematical model was verified, and factors that govern the coagulation rate were revealed.
Coagulation and flocculation  are widely used
in practice for purification of wastewater to remove
dispersed particles. Recently, the method of hetero-
geneous hydrodynamic coagulation (HHC) has been
receiving a large development effort because its use
can markedly raise the drop size in emulsions stable
against sedimentation and accelerate their separation
by a factor of 1003200. The HHC procedure and
the apparatus used were described in [2, 3]. The same
publications described a method for preparation of
emulsions comparatively stable against sedimentation,
whose light absorption decreased by no more than
10315% per day. In , basic kinetic data, used in
the present study to verify the model developed,
The HHC mechanism is based on the Deryagin3
Landau3Verwey3Overbeek (DLVO) theory . The
kinetic energy of correctly organized emulsion flows
favors overcoming of potential barriers in the DLVO
curve , which accelerates the coagulation process.
Adsorption of droplets on the apparatus walls prob-
ably leads to formation of large droplet aggregates
(clusters). A part of a cluster grown is split-off under
the action of incident vortices (pulsations). In our
opinion, the maternal part of the cluster is smaller
in size than the split-off daughter part. Having be-
come not attached to wall, the latter comes under
the influence of the Archimedes force and ascends
into the comparatively [quiet] part of the fluid in
the apparatus. As a result, a certain part of coars-
ened clusters is removed from the HHC process in
the form of transparent (in the case of coalescence) or
nontransparent (in the absence of coalescence) drops.
The walls and other immobile parts of the apparatus
[work] as size converters: small drops arrive to leave
The aim of our study was to develop a mathemat-
ical model of HHC and verify its validity.
We used as fluids being dispersed Midel 7131 trans-
former oil, I-40 machine oil, olive oil, and decane .
It is reasonable to assume that the stage of adsorp-
tion of microdrops on a solid surface is a necessary
stage of HHC. Coagulation becomes a rather probable
process because flows of droplets attack at a high
velocity the surface of a solid, especially in the case
when they have a considerable affinity to this surface.
Presence of coarse drops of a second organic solvent
facilitates coagulation. Coarse drops can even lead to
disappearance of the latent period frequently accom-
panying the development of HHC. In this study, we
considered the process of surface coagulation without
any additional solvent. In our opinion, the mechanism
suggested includes the following stages : formation
of guiding (nucleating) centers from microdrops, sur-
face coagulation of fine drops with the guiding centers,
interaction of the guiding centers with coarse drops
(coalescence) or with pulsations of the moving fluid,
detachment of coarsened drops or drop clusters from
the solid surface, and secondary disintegration of
coarsened drops or decomposition of drop clusters.
The last of the processed listed above is undesirable
and should be minimized.