Dispersant

Source: Wikipedia, the free encyclopedia.

A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid (such as a colloid or emulsion) to improve the separation of the particles and to prevent their settling or clumping.[1]

Dispersants are widely used to stabilize various industrial and artisanal products, such as

emulsifier, used to create homogeneous mixtures of immiscible liquids like water and oil. Natural suspensions like milk and latex
contain substances that act as dispersants.

Applications

Automotive

Automotive engine oils contain both detergents and dispersants. Metallic-based detergents prevent the accumulation of varnish like deposits on the cylinder walls. They also neutralize acids. Dispersants maintain contaminants in suspension.

Dispersants added to gasoline prevent the buildup of gummy residues.

Bio-dispersing

Dispersants are used to prevent formation of

biocides
.

Concrete and stucco

Dispersants are used as plasticizers or superplasticizers in concrete formulations to lower the use of water while retaining the needed slump (flow) property. A lower water content makes the concrete stronger and more impervious to water penetration.[2]

Similarly, dispersants are used as plasticizers in the

wallboard manufacture, to reduce the amount of water used. The lower water usage allows lower energy use to dry the wallboard.[3]

Detergents

Dispersing is the principal goal in the use of

emulsifiers
in some applications). Laundry detergents encase dirt and grime in miscelles, which naturally disperse.

Oil drilling

Dispersants in

deflocculants. Clay dispersants prevent formation of "fish-eye" globules. For dispersing (emulsification) of oil into water (or water into oils), surfactants selected on the basis of hydrophilic-lipophilic balance (HLB) number can be used. For foam drilling fluids, synthetic detergents and soaps are used, along with polymers
, to disperse foam bubbles into the air or gas.

Oil spill

Main article:
Oil dispersants

Dispersants can be used to dissipate

oil-in-water emulsions. However, laboratory experiments showed that dispersants increased toxic hydrocarbon levels in fish by a factor of up to 100 and may kill fish eggs.[5]

Dispersant Corexit 9527 was for example used to disperse an oil slick in the Gulf of Mexico in 1979 (

Ixtoc)[6] over one thousand square miles of sea. The same dispersant was also used in an attempt to clean up the Exxon Valdez oil spill[4] in 1989, though its use was discontinued as there was not enough wave action to mix the dispersant with the oil in the water. During the Deepwater Horizon oil spill in 2010, unprecedented amounts of the dispersants Corexit 9500 and 9527 were used (approximately 7 million liters).[7]

Process industry

In the

process industry dispersing agents are added to process liquids to prevent unwanted deposits
by keeping them finely dispersed. They function in both aqueous and nonaqueous media.

Surface coating

In order to provide optimal performance, pigment particles must act independently of each other in the coating film and thus must remain well dispersed throughout manufacture, storage, application, and film formation. Unfortunately, colloidal dispersions such as the pigment dispersions in liquid coatings are inherently unstable, and they must be stabilized against the flocculation that might occur.

See also

References

  1. doi:10.2533/000942902777680496
    .
  2. ^ Superplasticizers Archived June 12, 2010, at the Wayback Machine. Fhwa.dot.gov. Retrieved on 2010-10-27.
  3. ^ Gypsum wallboard, and method of making same - Patent 5879446. Freepatentsonline.com. Retrieved on 2010-10-27.
  4. ^ a b "Spill Response - Dispersants". International Tanker Operators Pollution Federation Limited. Archived from the original on 2013-11-14. Retrieved 2010-05-03.
  5. ^ "Spill Response - Dispersants Kill Fish Eggs". Journal Environmental Toxicology and Chemistry. 10 April 2009. Retrieved 2010-05-21.
  6. JSTOR 4312725
    .
  7. ^ The use of surface and subsea dispersants during the BP Deepwater Horizon oil spill (Working Paper). Washington, DC, USA: National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling. Published 2011. Available from: https://purl.fdlp.gov/GPO/gpo184
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