Any Petrochemists here? Diesel, dyes and acids.

locum-motion

Does anyone here know anything about diesel, and how to tell if you're getting the real stuff?

My understanding is this; dyes are added to diesel that's to be used for farming or heating and it's sold at a lower tax rate. Certain unscrupulous characters then use some process involving acid to remove the dye and make a killing. The acidulated diesel then screws up your engine.

So how does it all work? Are the dyes involved similar to indicators such as Phenolphthalein, in that they turn colourless in acid? How the hell can diesel even be acidic; does it even have any disassociated Hydrogen ions? And is it possible to test your diesel at the pump with a piece of litmus paper to check if it's gonna **** up your engine?

Thanks in advance,
L-M.

locum-motion

Ach, I'm very disappointed, folks!

74 views so far, and none of you are petrochemists!

Do you think perhaps someone in 'Motoring' would know? Mods, is a move in order?

Xios

I'm quite curious too. Come on lads, tell us.

locum-motion

Maybe everyone who knows how is too busy taking the dyes out to tell us how to avoid being stung!

Conor_M1990

locum-motion wrote: »

Does anyone here know anything about diesel, and how to tell if you're getting the real stuff?

My understanding is this; dyes are added to diesel that's to be used for farming or heating and it's sold at a lower tax rate. Certain unscrupulous characters then use some process involving acid to remove the dye and make a killing. The acidulated diesel then screws up your engine.

So how does it all work? Are the dyes involved similar to indicators such as Phenolphthalein, in that they turn colourless in acid? How the hell can diesel even be acidic; does it even have any disassociated Hydrogen ions? And is it possible to test your diesel at the pump with a piece of litmus paper to check if it's gonna **** up your engine?

Thanks in advance,
L-M.

If it is acidic it should read lower then 7 when tested on a piece of litmus paper

Diesel normally has a chemical of structure of C12H13 diesal is normally washed with Sulfuric Acid which has a chemical structure H2SO4

So

C12H13 + H2SO4 -> C12H15 + SO4

since the reaction is one way the acid stays in the diesel. Id imagine diesel has a nuetral pH of 7 (Actually cant find an answer to this) a low pH means a high concentration of hydrogen ions and this is makes it acidic

Depending on how much acid is in the diesel will determine the acidity of the diesel

Hope this helps Im not a chemist btw

locum-motion

Conor_M1990 wrote: »

If it is acidic it should read lower then 7 when tested on a piece of litmus paper

Diesel normally has a chemical of structure of C12H13 diesal is normally washed with Sulfuric Acid which has a chemical structure H2SO4

So

C12H13 + H2SO4 -> C12H15 + SO4

since the reaction is one way the acid stays in the diesel. Id imagine diesel has a nuetral pH of 7 (Actually cant find an answer to this) a low pH means a high concentration of hydrogen ions and this is makes it acidic

Depending on how much acid is in the diesel will determine the acidity of the diesel

Hope this helps Im not a chemist btw

Thanks, but I don't think that that's the mechanism.
pH stands for 'power of Hydrogen'. It's a measure of the concentration of free H+ ions in a solution. In water, for example, a certain proportion of the H2O molecules are disassociated into H+ and OH- ions. The concentration of the H+ in water is in the order of 1.0 x 10 ^ -7, therefore the pH is 7. If there was more free H+, say 1.0 x 10 ^ -3, then the pH is 3, and so on.
If your equation above was what was happening, then there'd be less free H+, not more.
That of course is supposing there's any free H+ at all; in a non-aqueous mixture, is there any H+? (I'm not sure of the answer to that, BTW)

Anyway, diesel isn't C12H13. It's a mixture of different compunds containing between 8 and 21 Cs per molecule, and the number of Hs in any given one of those would be higher than just one higher. Even if the chain was 100% unsaturated (triple bonds), there'd have to be 2 more Hs than Cs.

I am a chemist, BTW, but of the Pharmaceutical variety, and Petrochemicals aren't really my forte.

Conor_M1990

locum-motion wrote: »

Thanks, but I don't think that that's the mechanism.
pH stands for 'power of Hydrogen'. It's a measure of the concentration of free H+ ions in a solution. In water, for example, a certain proportion of the H2O molecules are disassociated into H+ and OH- ions. The concentration of the H+ in water is in the order of 1.0 x 10 ^ -7, therefore the pH is 7. If there was more free H+, say 1.0 x 10 ^ -3, then the pH is 3, and so on.
If your equation above was what was happening, then there'd be less free H+, not more.
That of course is supposing there's any free H+ at all; in a non-aqueous mixture, is there any H+? (I'm not sure of the answer to that, BTW)

Anyway, diesel isn't C12H13. It's a mixture of different compunds containing between 8 and 21 Cs per molecule, and the number of Hs in any given one of those would be higher than just one higher. Even if the chain was 100% unsaturated (triple bonds), there'd have to be 2 more Hs than Cs.

I am a chemist, BTW, but of the Pharmaceutical variety, and Petrochemicals aren't really my forte.

Well Ive done chemistry in College alright just first year and my understanding is still fairly basic

I got the moleculer formula for the diesel off Wikipedia as it said it was the most common.

But id imagine if a compound is acidic and you pour it on a piece of litmus paper it should change colour

Failing that a GLC machine would tell you if its been messed with because I presume the diesel at the pumps only has hydrogen and carbon in it

From my understanding the acid is added to the diesel to bleach out the color but it has to be distilled aswell to remove the acid but this process removes the lubricant from the fuel.

So even if its not acidic it can damage an Engine

locum-motion

Conor_M1990 wrote: »

Well Ive done chemistry in College alright just first year and my understanding is still fairly basic

I got the moleculer formula for the diesel off Wikipedia as it said it was the most common.

Wikipedia doesn't say that. It says: "The average chemical formula for common diesel fuel is C12H23, ranging approximately from C10H20 to C15H28." I wasn't questioning the number of C's you quoted, but the number of H's. However, that may just have been a typo, so not to worry.

Conor_M1990 wrote: »

But id imagine if a compound is acidic and you pour it on a piece of litmus paper it should change colour

Failing that a GLC machine would tell you if its been messed with because I presume the diesel at the pumps only has hydrogen and carbon in it

From my understanding the acid is added to the diesel to bleach out the color but it has to be distilled aswell to remove the acid but this process removes the lubricant from the fuel.

So even if its not acidic it can damage an Engine

We could be getting somewhere now, I suppose. That said, neither of the two of us is an expert in this particular field of chemistry. I was hoping that there might be a Petrochemist here who'd know definitively.

Jokesetal

The quick answer: The colour is due to a mixture of azo dyes.
There are several older publications on this (eg. Timkovich, Analysis of regulatory dye in diesel petroleum, Dyes and Pigments 46 (2000) 69-79).
The colour is due to azo chemistry (nitrogen double bonds), and can be tuned to be red, green, etc. depending on the level of conjugation (no. of double bonds) and the side groups.

The OP mentioned acid/base chemistry as a suggestion, which although a good starting point, was incorrect.

From a corrosion point of view, using any hydrocarbon fuel with water present will reduce the efficiency of the combustion process while also accelerating oxidative damage to the engine components.

locum-motion

Close off on silly question

Everything's a silly question to an expert in that particular field, but not to persons who aren't. I get asked 'silly questions' in my field every single day, but I'd never say to the asker "That's a silly question!", as, to them, it isn't.

Thanks for your input and for pointing us in the right direction (and I'll see if I can find the publication you referenced), but you haven't "closed off" the question either, since you didn't answer it fully.

It's quite arrogant, IMO, to caption your comment thus "Close off on silly question"

Jokesetal

Apologies,
Didn't intend to insult OP, but obviously did. I can supply the reference as a peace offering by PM.
The "silly" related to replies discussing the possibility of water in diesel fuel. Having just changed diesel and oil filters last weekend, the adverse effect of water in a fuel line is very easy to see (sludge).

Another Newer paper is:
The structure and purity of a reference dye standard used for quantification of C.I. Solvent Red 164 in fuels
Dyes and Pigments, Volume 82, Issue 3, September 2009, Pages 307-315
Scott D. Harvey

Actual Question: How do you tell the real stuff from the fake?
Probably a paper TLC will work with the dyes, but won't distinguish between diesels (blends vary between suppliers and geographical origin). That leaves you with a straight forward but expensive GC experiment (which most TLI's (Uni's or IOT's) have available if you have a friendly word with their Chemistry Dept.). If it's a supply issue (leading to litigation) then you'd have to get an accredited lab to analyse it (http://www.inab.ie/directoryofaccreditedbodies/laboratoryaccreditationtesting/).

Techie answer: The easiest method would be headspace detection (running at ambient temperature) onto a standard C18 column, with a gradient temperature up to about 250C with a MS detector. Varian supply such a method as part of their standard in-built methods on newer models.

locum-motion

So, there's no way to check at the pump, then, is there?

napapa

If you want to check that the diesel you are buying at the pump is washed with water (even if it contains excess H2SO4), why not check its polarity. A simple solvatochromic dye (such as reichardt's dye) would tell you if your diesel has traces of water, but you will need to reference this to a completely water free diesel sample.
As it is a simple colour change I believe this could be a simple qualitative solution to your answer. If you want quantitative data, get yourself a spectrometer (or even a camera, RGB values can be used) and do up a nice calibration curve.....you get the gist.

hope this helps

p.s. discussing pH in non-aqueous systems is a bad idea.

locum-motion

napapa wrote: »

...
hope this helps

p.s. discussing pH in non-aqueous systems is a bad idea.

Thanks for that. BSc or not, I have to confess some of that was over my head.

So was I right about the lack of disassociated H+ ions?

craggles

locum-motion wrote: »

So was I right about the lack of disassociated H+ ions?

There would be some but hardly any at all whatsoever.

chem

I dont think H2SO4 is used to remove the Dye anymore. I was told cat litter is used now :eek:

So I dont think a pH test would show up anything.

So keep a close eye on anyone who has large bags of cat litter around and no cats :D

ianobrien

I would imagine that you would get a higher throughput of diesel with an acid wash. The people that do it are not worried about the disposal of the acidic sludge. Using cat litter is fine for small amounts of fuel, but for the scale that the illegal fuel operators use, you would be needing cat litter by the 100kg bag.

I think Solvent Blue 79 is used here to mark road diesel.

Road diesel sold here is Ultra Low Sulphur Diesel, with a Sulphur level of less than 50ppm. The fuel goes through a complicated and expensive process in the refinery. Ordinary diesel has a typical Sulphur level of 350 to 500ppm (depending on where the crude came from). "Green" diesel comes from ordinary diesel, and it's the Sulphur level that is the way to tell them apart properly. X-ray fluorescence is used to measure Sulphur levels in organics.

The problem with laundered diesel is the improperly neutralised acid wash. It's the acid that causes havoc with the injector pumps.....