How the Aviation turbine fuel colour is colourless or straw/Yellow?
How the Aviation turbine fuel colour is colourless or straw/Yellow?
As given in last blog article normally colour of Jet A-1 is either colourless, straw/yellow or a very little shade of blue, pink or red. Reason for each colour is explained in this article.
Colour
of Aviation turbine fuel depends upon a) composition of crude oil & 2) Refinery
processes used in refining the crude.
Composition of Crude:
Any
given crude oil consists of besides hydrocarbons, varying amount of Sulphur,
nitrogen and oxygen attached hydrocarbons like:
Sulphur
compounds: Dimethyl sulphide, Phenyl mercaptan,
Cyclohexylthiol, Thiophene, Benzothiophene etc.
Nitrogen
compounds: Carbazoles,
indoles, benzcarbazoles, pyrroles, pyridines, quionlines, phenazines,
dibenzofuran etc
Oxygen
compounds: Phenols, Amides, Ketones, Benzofuran, Cresylic
acid, Aromatics acids etc
The
hydrocarbons having Sulphur, Nitrogen, Oxygen from crude are usually brown to
red colour. Any of such coloured hydrocarbon
when comes out of crude along with streams which go into blend formulation for
Aviation turbine fuel will carry this dark colour. Though the ultimate percentage of such
coloured hydrocarbon is very less but give a yellowish tinge to whole product.
Refining Processes for Jet A-1 production
Aviation turbine fuel streams in any refinery
may be mainly a) straight run from atmospheric distillation units, b) Secondary
units streams which are further hydro-processed / hydrofinished etc.
Thus,
colour of Jet A-1 will be straw / yellow when the crude oil used has
some of Sulphur, Nitrogen, Oxygen compound in sufficient quantity and the only
straight run streams from atmospheric distillation unit is used for Jet A-1
blending.
Colour of Jet A-1 will be colourless or water-white when the hydrocarbons are hydro-processed. In hydrotreatment plant, hydrogen at very high pressure (above 3000 psi ) and temperature ( 450 C) breaks Sulphur and Nitrogen compounds and further remove them after combining with hydrogen, as hydrogen disulphide and ammonia gases. This way when coloured compounds are taken out from hydrocarbons, the product become colourless.
Red
or blue tinge in Jet A-1 is usually due to trace contamination
picked up by Jet A-1 if common carrier like pipeline, marine tanker where other
dyed product like coloured diesel or kerosene which are coloured using some
dyes are also transported. Any such Jet A-1 batch having tinge of red or blue
or any abnormal colour must be further investigated before the product is
cleared as Jet A-1.
Further
interesting topic is which one is better – Colourless or straw / Yellowcoloured Jet A-1? read the next article.
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