heating oil

[wilster99]

why does heating oil change colour from yellow to red

[buildersmate]

Since when does it do that?

[theprof]

I think I may be able to offer further clarification to EDDIE51's answer.

To start with, the petroleum product known as heating oil in the USA, has been called red diesel in the rest of world for many years. Therefore, it would have been a bit easier if we knew for certain where you lived wilster99.

Anyhow, since 2002 in the EU, all countries have had to add what is termed a "Euromarker" dye called Solvent Yellow 124 to what is popularly known as red diesel in the UK. Red Diesel is coloured with a dye called Solvent Red 24.

The important thing to realise here is that regardless of whether the low-tax diesel is dyed red (as in the UK) or not (as in certain other EU Countries), it must have Solvent Yellow 124 added. Furthermore, whatever the colour of the visible dye permitted by local Customs and Excise, it must not interfere with the detection of Solvent Yellow 124 in the fuel.

Solvent Yellow 124 turns a bright scarlet colour at an acidic pH, allowing relatively simple detection when the origin of the fuel is in question. The preferred method is solvent extraction using hydrochloric acid and there are portable automated detection systems available for use in the field.

In cases where red diesel has been mixed with legitimate diesel, it's possible to perform a quantatative analysis on the amount of Solvent Yellow 124 in the mixed fuel to give a ratio of one to the other as the quantity of Solvent Yellow 124 per litre of red diesel is standardised throughout the EU. The higher the proportion of red diesel in the fuel mixture, the stiffer the penalty.

So wilster99, we're left with the question of under what circumstances is your heating oil changing from yellow to red? What are you doing to it?

[wilster99]

I forgot to add that the containers i am storing the oil in have been left outside. I am unsure whether water has got into the containers and have turned the oil red or whether it is the sun doing this????

[theprof]

Sunlight is to blame here.

Heating oil also contains another dyestuff commonly known as Quinizarine. This partially toxic chemical is also known as Red 1,4-Dihydroxy anthroquinone and in it's almost pure state (>95%), it's a bright orange-red powder. Quinizarine is another Euromarker used in fuel - I didn't mention it in my previous answer as I didn't want to complicate matters needlessly.

What's happening here is that the Solvent Yellow 124 is breaking down chemically to simpler compounds when the fuel is exposed to sunlight - Solvent Yellow 124 is not very stable in these circumstances. These analogues are colourless, so the yellow dyestuff colour fades.

Quinizarine on the other hand has properties which are almost the opposite of Solvent Yellow 124 in sunlight. Exposure can lead to an intensifying of the colour in the fuel and this combined with the removal of the yellow dyestuff results in an overall redddish colour developing.

That's about it in simple terms: to understand from a chemical viewpoint exactly what's going on in the fuel requires a fair understanding of some obscure aspects of organic chemistry. It took me a while to get my head around them and I'm a university professor!

Incidentally as far as Customs and Excise are concerned, if they fail to detect Solvent Yellow 124 in a dubious fuel sample, they check for these other more stable dyestuffs. Either way, if they find it being used as DERV, it still means an appearance in the BIg House.

[ukjoe90]

Hi can i ask if this happen to the oil dus it affect the use of the oil i am running in a Chinese diesel heater