Friday, June 18, 2010

Secret Gulf Oil Dispersant Finally Revealled - Corexit Composition Published

BP has been using Corexit 9500 and 9527 ever since the beginning -- even though the government told them to switch. The composition has been the subject of speculation on my blog (31May) (23May) and elsewhere, but the EPA has finally published the composition. The difference  between the two was supposed to be the solvent butoxy ethanol or EB, but it seems the actual difference is the ratio of ingredients.

CAS Registry NumberChemical Name
Ethanol, 2-butoxy-*
Butanedioic acid, 2-sulfo-, 1,4-bis(2-ethylhexyl) ester, sodium salt (1:1)
Sorbitan, mono-(9Z)-9-octadecenoate
Sorbitan, mono-(9Z)-9-octadecenoate, poly(oxy-1,2-ethanediyl) derivs.
Sorbitan, tri-(9Z)-9-octadecenoate, poly(oxy-1,2-ethanediyl) derivs
2-Propanol, 1-(2-butoxy-1-methylethoxy)-
Distillates (petroleum), hydrotreated light
*Note: This chemical component (Ethanol, 2-butoxy-) is not included in the composition of COREXIT 9500.
Learn more about CAS Registry Numbers from the American Chemical Society  
The highlights are that there are three deterents, and there are three solvents including one petroleum distillate, a ethylene glycol derivative and a propylene glycol derivative.

My previous post is here. My original oil field dispersant post is here.

A good site for the BP spill chemistry is the Facebook group Project Tantalus.
Span 80 = Sorbitan Oleate = 1338-43-8

||MSDS for Span 80.||
It is also called sorbitan monooleate. It is used in foods including ice cream and pickles.

Span 80 is a weak non-ionic surfactant with an HLB of 4.3 (low), and would be useful in emulsifying water into oil.

Polysorbitan 80 = 9005-65-6
                      ||An MSDS for Polysorbitan 80|| Polysorbate 80 is routinely used in foods especially ice cream, and in medicine including flu vaccine.

Polysorbate or Polysorbitan 80 has an HLB of 14, which is relatively high for a non-ionic surfactant.

Tween 85 = polyethyleneoxide sorbitan trioleate = 9005-70-3
||Tween 85 MSDS here.||
It is also called polyethylene glycol sorbitan trioleate, or polysorbate 85. 
This has an HLB of 11, which is intermediate. This is a large surfactant, which means it gives long term stability, but may not be as fast acting.