Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region
Part II: Basic information on dispersants and their application
–
Page 5
nonionic surfactants: sorbitan esters of oleic or lauric acid, ethoxylated sorbitan
esters of oleic or lauric acid, polyethylene
glycol esters of oleic acid, ethoxylated
and propoxylated fatty alcohols, ethoxylated octylphenol.
anionic surfactants: sodium dioctyl sulfosuccinate, sodium ditridecanoyl
sulfosuccinate.
Solvents are simple or mixed added to dispersants in order to dissolve solid surfactants, to
reduce the viscosity of the product thus enabling uniform application, to enhance the
solubility of the surfactant in the oil and/or to depress the freezing point of the dispersant.
Solvents may be divided in 3 main groups: (a) water, (b) water miscible hydroxy compounds
and (c) hydrocarbons. Hydroxy compounds used in dispersant formulations include ethylene
glycol monobutyl ether, diethylene glycol monomethyl ether and diethylene glycol monobutyl
ether. Hydrocarbon solvents used in modern dispersants include odourless, low aromatic
kerosene and high boiling solvents containing branched saturated hydrocarbons.
The two groups of modern dispersants have approximately the following composition:
Table 3: Composition of conventional and concentrate dispersants
Conventional (2nd generation) dispersants
Concentrate (3rd generation) dispersants
10 to 25% surfactant
25 to 60% surfactant
Hydrocarbon solvent
Polar organic solvent or mixed with
hydrocarbon
solvent
Figure 4: Dispersant stockpile in drums
Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region
Part II: Basic information on dispersants and their application
–
Page 6
Table 4: Typical compounds used in dispersant formulations
Generation
Description
UK Type
Surfactants
Solvents
Second
Hydrocarbon-
base,
Conventional
Type 1
(i)
Fatty acid esters
(ii)
Ethoxylated fatty acid esters
Light petroleum distillates:
Odourless or de-aromatised kerosene
Low aromatics (less than 3% wt.)
kerosene
CAS No. 64742-47-8
EC No. 265-149-8
Third
Water-
dilutable
concentrate
Type 2
(i)
Fatty acid esters
or sorbitan esters such as Span
series
CAS No.1338-43-8
(ii)
Ethoxylated fatty acid esters (PEG
esters) or ethoxylated sorbitan esters
such as Tween
series
CAS No. 103991-30-6
(iii)
Sodium di-iso-octyl sulphosuccinate
EC No. 209-406-4
CAS No. 577-11-7
Glycol ethers such as:
Ethylene glycol
Dipropylene glycol
2-butoxyethanol (Butyl Cellosolve
)
CAS No. 111-76-2
Di-propylene glycol monomethyl ether
CAS No. 34590-94-8
EC No. 252-104-2
Light petroleum distillates:
Hydrotreated light distillates
CAS No 64742-47-8
EC No. 265-149-8
Concentrate
Type 3
Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region
Part II: Basic information on dispersants and their application
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Page 7
4.
USE OF DISPERSANTS IN THE OIL SPILL RESPONSE STRATEGY
Chemical dispersion is one of the response options at
sea, with “mechanical recovery
associated with containment”,
“do nothing and monitor the spill”, and (for general reference) “in
situ burning”.
The use of dispersants in oil spill response has a number of advantages:
By removing the oil from the surface
it helps to stop the wind effect on the oil slick‟s
movement that may otherwise push the surface slick towards sensitive areas (often
the shoreline).
In contrast to containment and recovery, dispersants can be used in stronger
currents and greater sea states.
It is often the quickest response option.
It reduces the possibility of contamination of some resources sensitive to the
floating oil (surface slick) such as sea birds and mammals.
It inhibits the formation of "chocolate mousse".
It enhances the natural degradation of oil.
Dispersion does not produce wastes to be disposed.
The use of dispersants has also its disadvantages:
By dislocating the floating oil into the water column, it may adversely affect certain
parts of biota which otherwise would not be reached by surface oil .
If oil dispersion is not achieved, effectiveness of other response methods on oil
treated by dispersants decreases.
Dispersant are not efficient towards all oil pollutants, especially those which present
a high viscosity.
When initially efficient, chemical dispersion is applicable only for the first hours/days
of the operation, before the oil becomes non dispersible.
On significant pollution, chemical dispersion is not applicable in a too calm sea state
(sea state 0, 1 possibly 2 according to the situation).
If used near the shore and in shallow waters, it may increase the penetration of oil
into the sediments; similarly, if suspended sediments are present, dispersants
facilitate the adhesion of oil to the particles.
It introduces an additional quantity of extraneous substances into the marine
environment.