Chromatography analysis of various fuels

[JHZR2]

This is an analysis of my own make (mods, move it somewhere else if you desire), which hopefully will find some interest on BITOG. Im doing gas chromatography analysis of various fuels for projects that Im working on, and so am quantifying various fuels and additives via flame ionization detection and pulsed flame photometric detection. The FID is a hydrocarbon specific destructive detector - it separates the hydrocarbons through the power of chromatography, then burns them to classify. FID results will be my first set of posts.

Some might be interested by this, I hope.

First, gasoline:

Next, gasoline doped with a few drops of n-octane. Note that due to all the light boilers, there are a lot of peaks on the far left that dont separate; it is very difficult to resolve all the hydrocarbons in gasoline, plus, given the overwhelming presence of C8 species, its tough to see a difference:

Next, a little heavier - JP-5 fuel, which is a high flashpoint Navy jet fuel:

Next, JP-5 fuel doped with some n-c8. Since chromatography is a comparative technique at heart, the addition of the notable c8 spike lets you recognize the rest of the hydrocarbons:

Next, road diesel fuel. Since all of these fuels were tested by the same chromatography method, it is valid to compare the times it takes on the scale for the various compounds to elude on these chromatograms versus those of the other fuels:

Next, road diesel fuel doped with some n-c8 for numbering purposes. Fortunately this method doesnt separate the isomers of the various hydrocarbons, so we get real nice distinct peaks where each one is:

And, once again, since it is a comparative technique and the same method was always used... here is the general location where your C8 molecules come through:

Enjoy!



[ July 18, 2006, 04:59 PM: Message edited by: JHZR2 ]

 

[mechtech]

Any chance tht you could test gas with FP 60 , acetone, or Lucas UCL?

 

[JHZR2]

Ive been trying to run Lucas UCL.. its boiling point seems a bit too high to get any good results in my setup. Ive tried cutting it and using different temperature profiles. Id venture to guess that FP and LC would be similar, even when cut with octane or gasoline. Ill probably try something along thoe lines somewhere down the line though... Im doing 2-stroke oil in c8 right now, as well as lucas, and thatll give insight on testing the heavier stuff.

Ive done redline SI-1, and currently are running MMO, gumout regaine, cheapo octane booster, mobil1 MX2T cut in C8, and different ways to resolve Lucas UCL.

Acetone would be quite boring... it will look like the C8 chromatogram I posted (bottom) only the peak will be more to the left, as it should elude faster through the column.

GC analysis really isnt for reverse engineering or anything like that. You certainly could verify that this compound or that compound is in this or that, provided you can get a sample of said compound in more or less pure form. As I mentioned before, it is a comparative technique, so what do I have to compare? I ran C8 and we can see what hydrocarbon sizes are in various fuels compared to C8... this is easily seen in the JP-5 and diesel chromatograms that I posted, where each HC setof isomers one carbon heavier has its own nice clean peak. From my initial results, its similar with SI-1 and MMO, with some interesting results! more to come...

Ill likely be running all of these in PFPD mode, which will let me gauge sulfur content of each. My system is set up to measure sulfur and hydrocarbons, and thats what I need to do, so its what I do. I also have a total sulfur and total nitrogen analyzer, and it would probably be interesting to get the total content of both of them as a pure ppm number for these things too. Sooner or later Ill do that, as I need to do it for my work research.

More chromatograms tomorrow, so long as nothing scrwed up overnight!

 

[JHZR2]

OK, here are some more that people might find interesting. The same method was used, so the relative locations of hydrocarbons can be matched up 1:1. on some of these tests, I had to cut the fluid with c8 due to viscosity issues (my syringe would register an error otherwise, on stuff with the viscosity of lucal, MX2T, etc.).

Here is redline SI-1 fuel injector cleaner:

Gumout regaine cleaner:

Marvel Mystery Oil:

O'Reilly brand octane booster:

M1 MX2T 2-cycle engine oil in C8 (note that there are low quantities of high boilers, 280-320C range at the tail end... but all in very small quantities, so the line goes up as time increases, but you dont get good resolution of peaks):

Im still working on things thelike of Lucas. I dont have any LC/FO with me now, so those tests will have to be done doen the road.

Enjoy!

 

[JHZR2]

Notice that all of the chromatograms, fuels, and additives, straight and undiluted, all have a peak at 1 minute 48 seconds. This is regardless of how heavy the stuff is otherwise (e.g. undiluted diesel, octane additive, MMO, etc. have it too). It must be some sort of HC marker for one purpose or another. I dont know what it really is - at some point Ill try to un benzene or toluene through, and other similar size compounds to see if I can get a positive match.

Its just strange that everything has this peak - unless its some constant impurity in the system like remnants of IPA used to wash the syringe... I guess I should test that too! Thing is, if it was a systematic impurity, the peak height should be about constant for all injections - and it does not appear to be so!

 

[kanling]

Could you give us the quick tutorial on the chromatogrophy process and explain what is really represented by the horizontal and vertical axes? I always thought that horizontal was like an atomic size or weight... I don't understand what it means to be time.

 

[JHZR2]

The detector used here is a Flame Ionization Detector. Per Paul Sadek's "Illustrated Pocket Dictionary of Chromatography", a FID is a destructive mass flow detector used in GC analyses. The sample is burned in the detector, in hydrogen and air, and the current generated by the sample combustion (actually the conductivity of a flame is greatly different from that of pure combusted hydrogen gas that carries the hydrocarbons through) generates the signal. For hydrocarbon compounds, the FID signal is approximately proportional to the number of carbons in the sample"

So, a compound, such as fuel, fuel mixed with octane, fuel aditive, etc is injected into the machine, where it is immediately evaporated in full and a portion of the evaporated sample goes into a long column, where it immediately recondenses.

The columns have very long, tortuous paths, which are useful for separation of compounds. The column sits in an oven, and the oven temperature is ramped up so that individual components of the sample vaporize and slowly elude through the column at different rates. The vaporized compounds are carried through the column in hydrogen carrier gas.

As the compounds reach the end, they hit the FID. when no compounds are coming out, there is still hydrogen gas being constanty combusted in air, however the detector is designed to have a zero signal when pure hydrogen is being combusted. As a hydrocarbon comes through, it is combusted in the hydrogen and air, and as the conductivity of the flame changes, the detector registers a voltage. The voltage is related to the number of carbons - either due to higher amounts of a hydrocarbon sample coming through, or else due to the size of the hydrocarbon molecule.

The samples I have posted all use the same method. The injector is set at 320C, the column oven starts at 50C and ramps up to 320C at 20C/minute. The detector is maintained at 300C.

As a result, you get the compounds of the sample seperated by boiling point/vaporization, and then also by elution time through the tortuous path in the column - related to size/weight of the molecules.

Obviously, octane wil evaporate faster than C16. This is why you get varous peaks for various hydrocarbon isomers. Then, there are additional peaks for all sorts of other compounds with different characteristics - so stuff like polyaromatics will come through at different times than chains that have the same numbr of carbons.

Take this example:

I doped jet fuel with octane. Octane is the large peak atthe front, at about 3 minutes 12 seconds. Since we know some background information about the fuel, we can then see the identical (though smaller) evenly spaced peaks, corresponding to each higher hydrocarbon... So, the peak afterthe large C8 peak is c9, then c10, then c11, then c12, etc. The rest of the stuff inbetween are other sorts of compounds, like rings, aromatics, rings with chains, etc.

As a result, elution time is directly related to the characteritics of the compounds. Chromatography is comparative in nature, this is why we can figure out what range of hydrocarbons are in these fuels and additives. Comparison only is valid for the same method, occurring the same way, as it is for all of these samples.

Now, since it is a comparative technique, we only know what things are by prior analysis of what the elution time is for this or that compound for the same conditions. So, say that we wanted to test if additve ABC contans active ingredient DEF. We can take a chromatogram of the ABC additive, and get peaks. If we can take a chromatogram of pure additvie DEF, and see what time it comes through at the same method - then we can quantify the relative amount of additive DEF based upon the size of the peak that comes through at the specific time, compared to the size of the peak of the pure or straight diluted sample.

I hope to run similar tests with a PFPD to find sulfur content of a lot of this stuff, the results will be different, but so long as we can do relative comparisons, we get insight as to what is in this or that.

I hope this helps, it is a complex technique, with a lot of things to consider. How much information it provides to anyone is questionable, but at the minimum, you can see what kind of hydrocarbon ranges are in the various things.

Sorry if this isnt the best explanation, but ask any other questions if you like.

 

[mechtech]

At this point, let me digest all this for a while.
But, thank you !

 

[bunnspecial]

Would you mind to post the full method that you're using? I see some details but would like to see the full thing and possibly replicate it.

I'm also interested in your 1.8min ghost peak that, in my skimming, you didn't ID. Again, I'd be interested to see if I can replicate that and find out what it is.

Thanks for posting this.

 

[dlayman]

Just a couple of comments on the methodology. You might gain more info and better separation by slowing down your temperature gradient, unless you are pressed for time or something. 20 degrees per minute is too fast for getting good separation of relatively low boilers. Also in general it's not good to have your final column temp higher than your detector temp as eventually you will get condensation of high boilers or column stationary phase bleed on your flame jet. A GC/MS analysis would of course give you much more info. I doubt the 1.8 peak is a ghost from your syringe rinse. It's too big in many of your chromatograms to be a ghost. It would be much smaller if it were a ghost. I also might suggest isopropyl alcohol is not a good choice for rinse, a lower boiling hydrocarbon, such as hexane would be better, or even methanol.