Oil and Hydrocarbon Spills II, C.A. Brebbia & G.R. Rodriguez (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-828-7
Gel-like protective coating for keeping oil and
petroleum products from evaporation
M.S. Vilessova*, L.Ye. Gendlin*, L.A. Rubinchik*,
A.A. Bespalov^ & B.I. Tkachev*
^Russian Scientific Center "AppliedChemistry", Russia.
^Chelyabinsky Polytechnical University, Russia.
Abstract
The problem of reducing the losses of petroleum products due to evaporation,
and the related problem of environmental protection are currently considered to
be crucial. We have developed a new method which produces a substantial
decrease in the surface evaporation rate of hydrocarbon liquids and can be used
successfully instead of the traditional unreliable, bulky and expensive pontoons
and condensers. The suggested method uses a lightweight powder-like material,
designed to spread throughout the surface of the liquid in order to form a
semipermeable layer, separating liquid and air volumes from each other. When
particles produced on the basis of a sufficiently lightfiller(having closed-cell or
closed inner space structure) are placed on the surface of a liquid with the
appropriate solubility parameter (gasoline, kerosene, etc.), they swell and float
on the surface in the form of a gel-like mobile film. Owing to its thixotropy, the
coating is capable of spontaneously restoring its continuity if damaged. The
material, based on hollow glass microspheres encapsulated into shells of slightly
cross-linked hexyl-acrylate rubber, named KOMPOZAM, have been applied in
storage tanks for petroleum products which operate in the "filling in - pumping
out" mode. Full-scale tests of KOMPOZAM have been carried out and delivered
good results.
Data obtained in measurements of hydrocarbon vapour
concentrations above the surface of the liquid in an industrial tank of 1,000 m^
capacity demonstrate a 10-15 fold decrease of oil products losses. The service
life of the KOMPOZAM layer exceeds 5 years. KOMPOZAM consumption rate
is 1-2 kg per m^.
Oil and Hydrocarbon Spills II, C.A. Brebbia & G.R. Rodriguez (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-828-7
140 Oil and Hydrocarbon Spills II: Modelling, Analysis and Control
1 Introduction
The problem of reducing the losses of petroleum products due to evaporation,
and the related problem of environmental protection are currently considered to
be crucial. Losses of petroleum products stored in tanks, caused by their
evaporation, reach up to hundreds of thousand of tons every year. In addition,
evaporation of petroleum products results in considerable pollution of the
environment around the storage area.
At present, to protect petroleum products against evaporation, pontoons
floating on the surface of the liquid are used. However, even though there is a
great variety of designs used in constructing these protective elements, they all
have a number of essential drawbacks, consisting mainly in difficulties of their
erecting and operating, insufficient reliability and high cost. The present study is
devoted to the development of low-density dispersed composite material (named
KOMPOZAM) designed to cut down the evaporation losses of petroleum and
petroleum products in storage and to protect the environment. As a basis for
development of the KOMPOZAM formulation the author's technical solution
has been used, according to which, KOMPOZAM should be some light
dispersed material consisting of hollow particles, for example, micro-spheres
non-soluble in hydrocarbons and coated (micro-encapsulated) with a shell of
loosely cross-linked polymer, which has good compatibility with hydrocarbons.
When introduced into petroleum and petroleum products the KOMPOZAM
forms an even layer on the liquid surface and after swelling it transforms itself
into a thin continuous gel-like protective coating which prevents mass transfer at
the liquid - gas interface and results in a considerable decrease in the rate of
petroleum or petroleum products evaporation.
The novelty of the idea results from the fact that the shell around the solid
particle is created from partially cross-linked latex particles, which are in a
rubber-like state. Latex particles were previously partially cross-linked either by
chemical methods or by dosed y-irradiation (Vilessova et al., [1]). This leads to a
decrease in their solubility and to limited swelling ability, which is determined
by the degree of cross-linking. It was shown that the latex particles coat the
solid particle to form a granular envelope since the cross-links prevent their
complete coalescence. This envelope is clearly demonstrated in the electron
micrograph (Fig.l).
When such a dispersed product is placed in a suitable solvent, limited
swelling of latex particles of the envelope occurs, and gels having interfaces are
formed. The diagram of material formation is shown in Fig.2.
Oil and Hydrocarbon Spills II, C.A. Brebbia & G.R. Rodriguez (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-828-7
141
Figure 1: Hollow glass microspheres coated with rubber particles.
LATEX +
FILLER
SPRAY
DRYING
SOLVENT
SWELLING
{\ r
-
Figure 2: Diagram of the gel-like material formation.
Oil and Hydrocarbon Spills II, C.A. Brebbia & G.R. Rodriguez (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-828-7
142 Oil and Hydrocarbon Spills II: Modelling, Analysis and Control
A visco-elastic system is formed which constitutes an aggregate of
autohesive-bound gel particles, and is characterised by very pronounced nonnewtonian rheological behaviour. As can be seen in Fig. 3, the system features a
presence of ultimate shear stress and its effective viscosity depends sharply on
the flow speed gradient.
800 -
*~~^
^—•*
600 •
400 •
- —
X^^
200 • /
(a)
100
200
300
Flow speed gradient, 1 /&
400
10000
\3 1000
.•£'
% 100
10
(b)
0,001
0,1
10
Flow speed gradient, 1/s
1000
Figure 3: Flow curves of the swollen material.
A flow curve of the system can be well described by the Shulman equation
(Shulman et al., [2]) with exponent values of 1/n = 1/2 and 1/m = 1/3:
where
T - shear stress
y' - flow speed gradient
TO - ultimate shear stress
jiipi - parameter called "plastic viscosity".
Oil and Hydrocarbon Spills II, C.A. Brebbia & G.R. Rodriguez (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-828-7
Oil and Hydrocarbon Spills II: Modelling, Analysis and Control 143
A typical effect of the system composition on its rheological characteristics
is shown in Fig. 4 (it is essential in this case to what extent a polymer fraction of
the material is saturated with a solvent).
400 •
X.
^s
X
X
\
(a)
0,4
!j 1-7C.
"b
•55o 1i"
95 u
.y 75 .
rt
pZ
0,4
0,6
0,8
1
1,2
1,4
Extent of the polymer phase saturation
\
\
^
\
^^**.
— —
(b)
0,6
0,8
1
1,2
1,4
Extent of the polymer phase saturation
Figure 4: Effect of absorbed hydrocarbon on rheological properties of the
material
In contradistinction to powder-like materials containing no swellable
polymer and having the capapcity to retain liquids owing to capillary forces only,
our systems possess extremely high phase stability even when being affected by
mechanical stresses. A set of centrifuge tests used by us as a standard evaluation
procedure demonstrated that no liquid release occurs from the system "kerosene
- rubber - solid carrier" overloaded up to the factor of 30. At the same time,
exudation of kerosene from its mixture with the same powder-like stuff
containing no rubber takes place just at the level of overloading less than 2 g.
It is possible to design dispersed materials, as either floatable or sinkable in
hydrocarbons or water, by deliberately varying the density of solid filler.
Systems with "heavy" and "light"fillershave been developed. Various metal
oxides, minerals, and pigments are examples of heavy fillers. Porous dispersed
materials and hollow microspheres are example of light fillers. After
Oil and Hydrocarbon Spills II, C.A. Brebbia & G.R. Rodriguez (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-828-7
144 Oil and Hydrocarbon Spills II: Modelling, Analysis and Control
microencapsulation by the given method, the light powder-like material, when
placed on the surface of a liquid with the appropriate solubility parameter (pure
hydrocarbons, gasoline, kerosene, and other solvents), swells and floats on the
surface in the form of a gel-like mobile uniform film.
As a dispersed base for KOMPOZAM, in order to provide its high
floatability, we have chosen hollow glass micro-spheres (HGMS). The use of
HGMS in KOMPOZAM formulation was dictated by a number of specific
properties, namely: low density, high floatability, good wettability in respect to
liquids of various natures, physical and chemical inertness.
Polymer material to produce KOMPOZAM (HGMS micro-encapsulation)
had to meet the following requirements: uniform distribution of polymer on the
HGMS surface, good adhesion of polymer to HGMS, controllability of polymer
cross-linking, i.e. the degree of its swelling in hydrocarbons and polymer
properties stability in storage and service as a component of KOMPOZAM and
GPC. Following the above, the use of polymer latex produced by y-irradiation
method for HGMS micro-encapsulation has been suggested. This allows for
good reproducibility in production of highly stable latex with pre-assigned
formulation and properties and finely control polymer structure (cross-linking
factor) directly in the process of synthesis.
Microencapsulation of hollow glass microspheres into partially cross-linked
latex shells is most effectively carried out by spray drying the suspension of
microspheres in latex. The obtained product - KOMPOZAM - is a white, light,
fluffy powder, which swells easily in oil products and floats on their surfaces.
Its main properties are shown in Table 1.
Table 1: Principal technical characteristics of KOMPOZAM basic formulation.
Characteristic
Appearance
Weight ratio HGMS/polymer
Density (kg/rn^)
Moisture content (wt. %), no inore than
Degree of polymer swelling
Consumption for lm^ surface protected (kg)
Predicted service life (years), no less than
Protection factor - evaporat ion rate decrease
(times)
Value
soft white powder
3/1
500-600
1
15-20
1,5-2
5
10- 15
The laboratory data on the effect of protection against evaporation have been
confirmed under real operating conditions (Table 2). Here the experimental data
obtained in measurements of hydrocarbon vapours concentrations above the
surface of a liquid in an industrial tank of 1,000 m^ capacity are given. In one of
the tanks a film of KOMPOZAM material is floating on the surface, in the other
one the surface of liquid is unprotected. As can be seen, the decrease in oil
product losses is 10-15 fold.
Oil and Hydrocarbon Spills II, C.A. Brebbia & G.R. Rodriguez (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-828-7
Oil and Hydrocarbon Spills II: Modelling, Analysis and Control 145
Table 2: Results of the full-scale trial of KOMPOZAM.
Days after
halfemptying
0
1
4
Vapour concentration (g/nf), 1 meter above surface
without coating
151.8
240.0
393.0
with coating
10.9
17.4
13.6
Equally, as the main function of KOMPOZAM is as a floatable protective
coating, at present we are working on another application of our material:
converting spilled hydrocarbons into some pseudo-elastic state in order to
prevent their further spreading and to cut down on the release of toxic and firehazardous vapours around the spill site. In this case, some "heavy" (and cheaper
than HGMS) filler should be used as a base for the material. Dispersed particles
sink into the hydrocarbon while swelled microgels provide a guaranteed
retention of the liquid inside the gel-like stuff, as well as a loss of oil fluidity
under ambient conditions, whilst keeping its capacity to flow when some force is
applied. This set of properties provides opportunity for using materials of this
kind as sorbents and solidifiers, instead of the traditional means of clay, sand
etc., especially in cases where highly inflammable and toxic liquids are spilled.
References
[1]
August 1993
[2] Smolsky , B.M., Shulman, Z.P., Gorislavetz, V.M. Rheodynamics and Heat
Exchange in Non-linear Visco-plastic Materials, Science and Technology:
Minsk, pp. 191-197, 1970