Newsgroups: sci.chem
From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Subject: Re: Age dating gasoline??
Date: Fri, 02 Aug 1996 17:53:07 GMT

"Paul E. Herr" <peherr@midplains.net> wrote:

>I am a former exploration geologist for Shell Oil.  I am currently
>working in the environmental consulting field.  I am trying to
>determine the age of a gasoline spill.  

This topic is technically described as "weathering" of gasoline or crude oil.
Almost all the important characterics of gasoline will change with time.
There has been plenty of research into chararterising spills, and contacting
your local EPA, the API, and oil companies should  point you in the right 
direction.   

>I have some rough ideas regarding how to proceed, but I am not sure how
>practical they are.  Please look these ideas over and comment on the
>ones you think might succeed.  Any references, case studies or
>information would be appreciated.

Frankly, I think you need to get in contact with some of the above groups,
or read some of the revelent journals like Environmental Science &
Technology, Journal of Chromatographic Science, Marine Pollution
Bulletin, but regardless - your main assumptions are invalid. The
gasoline " weathers " several ways - the more volatile fractions are
lost through the soil, the more water-soluble fractions ( low molecular
aromatics and oxygenates are ) dissolved out. The less stable 
hydrocarbons ( olefins and aromatics ) also degrade faster.  

>FAR FETCHED???

>1.	Molecular fossils are present in crude oil and reflect the
>types of plant and animal life from which the oil was derived (Tissot
>and Welte, 1978).  I believe that some of these molecular fossils
>survive the refining process and can be found in gasoline.  

Not in gasoline, you are thinking of pristane and phytane and other isoprenoids
- they are in heavier distillate fractions.

>The same brand of gasoline could vary in composition through time, and
>from station to station, based upon the source of the gasoline (the
>particular oil field with its unique combination of molecular
>fossils).  This phenomenon, if true, would likely be too complex to
>sort out.

Exactly - without representative reference samples it's very difficult,
and when weathering is added in....

>2.	Isotopic composition of gasoline might vary depending upon the
>refining process used to refine it.  If refining processes have changed
>dramatically as a function of time, maybe isotopic composition could be
>used to estimate the age of the gasoline (look at carbon, nitrogen,
>sulfur or oxygen isotope ratios).  Oxygen isotopic composition is often
>used to date groundwater.  For example, glacial ice became enriched in
>oxygen 18 during the last ice age (oxygen 16 and oxygen 18 have
>different responses to evaporation and condensation resulting in more
>oxygen 18 in the ice). Groundwater from this period is therefore
>enriched in the heavy isotope of oxygen. An analogous type of
>enrichment may occur in gasoline due to isotopic responses to
>variations in the refining process, catalysts, etc as a function of
>time.

Not relevant with reference samples. You would have to select which
components you wanted to monitor - expensive and fruitless, IMO.

>3.	Leaded gasoline produced prior to the 1970s contained antiknock
>compounds containing tetraethyl lead.  Groundwater contamination
>containing tetraethyl lead must have originated during this period.
>The oil companies continue to use a variety of antiknock compounds and
>detergent additives.  These compounds have start and end dates
>associated with their use that can be used to determine the approximate
>age of a given gasoline spill. 

Not true. The basic leaded gasoline formulations were constant over decades,
using TEL, TML, and a few mixed alkyl lead compounds. The selection was
based on the refinery configuration and crude feeds, to ensure octane
distribution over the boiling range was appropriate.

> The problem here is that many of these compounds are probably
>proprietary and perhaps difficult to analyze for (i.e., they are not
>evaluated in a normal gas-chromatograph/mass-spectrometer VOC scan). 

No, The alkyl lead formulations also included large amounts of halogenated
lead scavengers ( ethylene dibromide, ethylene dichloride ) which are
easily detected. Lead is easily analysed by AAS.

>4.	I believe that gasoline contains distinctive chemical markers
>that are added by the oil companies to allow them to identify their
>gasoline. I believe these compounds are used to prevent theft and track
>gasoline supplies.  Does anybody know of a reference that discusses
>these additives and the tests used to detect them??

May be true, not the practice in international shipments, can't see why they
would bother routinely wasting money. It is true that some additives may
be unique, but in many cases the additives come for speciality additive
firms like AMOCO chemicals and Lubrizol and are used by several compoanies.

Talk to the professionals.

                 Bruce Hamilton

From: glenns4250@aol.com (GlennS4250)
Newsgroups: sci.chem
Subject: Re: Age dating gasoline??
Date: 1 Aug 1996 08:42:52 -0400

Just a thought from an old refiner:

Since gasolines are relatively light materials boiling from butane to 400
Deg F, it would seem that the gasoline would produce a distinctive GC
trace. (GC=gas chromatography)  Then by weathering the
gasoline....essentially letting the light ends evaporate...you could
observe the pattern of change in the GC trace.  Maybe this could be
calibrated against time.

Now  I imagine that the lighter materials will evaporate rather quickly,
so long term dating would have to be confined to the heavier end of the GC
trace and disappearance of the some of the heavier components.  One might
wish to mix the gasoline with the local dirt, just on the chance that the
dirt has some catalytic or reactive affect on the gasoline.  If you are
looking at dating the spill in terms of months or years, I doubt if this
would work.  Maybe you could date spills in terms of hours and days this
way.  It really needs to be developed.

The so called "tagging" of the gasoline that you described really doesn't
happen with gasoline.  Gasoline is so heavily controlled by federal law
for collection of taxes that it is almost impossible to steal
gasoline....unless it is "drip gasoline" at an oil field, or something
upstream of a  refinery.  Crude oils are often "tagged" by mixing the oil
with microfilm dots which contain the name of the oil company.  Under a
microscope, the microdots can be used to verify the owner.  Evidently, it
is easier to steal a barrel of whole crude than it is a barrel of
gasoline.

Some of the current gasolines are more than hydrocarbons.  They contain
methanols, ethers and other oxygenated additives by law.  Furthermore, the
gasolines are blends of different refinery components depending upon the
season that you are going to sell the gasoline.  Winter gasoline differs
from summer gasolines, etc.

Tough problem!  I am not too hopeful for some your suggestions.  Some of
the "secrets" that you think the oil companies are using really don't
exist.  The fact is that gasoline is a commodity product and oil companies
trade and use each other's gasolines across the country.   You might be
able to identify additive packages in lubricating oils and tie these to
particular oil companies, but this is not the case in gasolines.

Regards,

Oil Fellow