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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dispersant action, thus enhancing the biodegradation processes. At the same time, oil that
is dispersed is no longer subject to the action of wind which makes it drift towards the coast
or other sensitive areas. Moreover, dispersants prevent coalescence of oil droplets and
reforming of the oil slick.
3.2 History of dispersants
The idea of applying the well known principle of removing a greasy substance by mixing it
with a dispersing agent (soap, detergent) and washing it with water was first proposed in the
early sixties.
The first extensive use of mixtures of industrial detergents and hydrocarbon aromatics
solvents used as dispersants (first generation), in response to the "Torrey Canyon" oil spill in
March 1967, unfortunately demonstrated that their toxicity was much too high and that
devastating impact on marine life outweighed their efficiency as pollution clean-up agents.
Very soon after, new formulations environmentally acceptable made of less toxic surfactants
much less toxic low-aromatic or non-aromatic hydrocarbons (e.g. low aromatic kerosene or
high boiling solvents containing branched saturated hydrocarbons) appeared on the market.
These new products became known as "second generation" dispersants or referred to as
“conventionals” and are less and less in use nowadays.
Dispersants of "the third generation" often referred to as "concentrates" appeared by the mid
seventies. These mixtures of emulsifiers, wetting agents and oxygenated solvents which
have an higher content of active components (surfactants) and less solvents are more
efficient than "the second generation" dispersants and therefore can be used at lower
dispersant
–
oil dosage than the conventionals.They can be applied from boat neat or pre-
diluted into seawater, or by aircrafts (always neat). Most of the products marketed today
belong to this category.
Since their appearance, dispersants have been used during numerous oil spills of various
sizes all over the world and they became an important tool in responding to oil spills. The
development of application techniques and significant scientific research in the field of
environmental effects of dispersants and dispersed oil was followed by the development of
new products.
Figure 2: Slicks being dispersed by a helicopter
3.3 Nomenclature of dispersants
The following table summarizes the nomenclature of current dispersants. Dispersants are
classified basically into 2 classes: second and third “generations”, commonly called
conventionals and concentrates. Aside this classification, the UK authorities classified
dispersants according to the generation and to the application method for which the product
has been approved: type 1, conventional dispersants; type 2 concentrates approved to be
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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applied pre-diluted into sea water (from boats); type 3, concentrates approved to be applied
neat (from boats or aircrafts).
The table below gives a comparative presentation of these systems:
Table 2: Dispersants classification
GENERATION
STANDARD
NAME
DISPERSANT-OIL
DOSAGE
TYPE OF
SOLVENT
TYPE
APPROVED TO
BE APPLIED
(U.K.)
2
nd
Conventional
dispersants
High dispersant
dosage: 30
–
50%
of the oil quantity
Non-aromatic
hydrocarbons
1
Undiluted (neat),
from vessels
3
rd
Concentrate
dispersants
Low dispersant
dosage: 5
–
10%
of the oil quantity
Oxygenates
(e.g. glycol
ethers) and
non-aromatic
hydrocarbons
2
Diluted,
from vessels
3
Undiluted (neat),
from vessels
and/or aircraft
Figure 3: Plume of dispersed oil at sea
3.4 Composition of dispersants
Oil spill dispersants are composed of two main groups of components:
surface active agents (surfactants),
solvents
Surfactants (or surface active agents) are chemical compounds with molecules composed
of two dissimilar parts:
a “water
-
loving” (hydrophilic) part and an “oil
-
loving” (oleophilic) part.
Surfactant
s act as a ‟chemical bridge‟ between oily materials and water and enable these
two phases to mix with each other more easily (in other words the surfactant molecules
when migrating to the oil
–
water interface, contribute to reduce the interfacial tension
between oil and water). Therefore, the natural agitation (e.g. waves) can break the oil into
myriads of tiny droplets which disseminate as a plume into the top layers of the water
column.
In order to improve the performance of the dispersant, several surfactants are often
combined but only nonionic and anionic surfactants are used in modern formulations: