Petrol Composition

Section V: Petrol Composition.=


The stuff they pull out of the ground in any oil field, is one of the biggest organic soups of all time. Mixed all together are short chain and long chain molecules, straight chains, rings, alcohols, sulphurated compounds, blah, blah, blah. The chart above represents all of the liquid compounds in that mixture. Those of you who have been reading up to this point should be able to cipher this chart pretty completely, but it does deserve a little bit of an explanation.

First, you notice four distinct and slightly overlapping color zones. There’s a green, blue, pink and purple zone. The blue zone along the left side is the “paraffin” zone, using the stricter sense of the term. The green zone is the Naphtha zone. The pink is somewhat unfairly labeled the gasoline zone, and finally the largest zone is kerosene. Anything above the color is a gas at room temp, like propane, and anything below the chart is a gel, like vaseline.
The green Naphtha zone has a chunk out if it because you need 6 atoms to form a benzene ring. These atoms have the fewest number of carbons, ranging from 5 to 8 carbons total, and may include the full spectrum of forms. White gas has the ring types and sulphurated compounds stripped out for a very sweet light mixture that is essentially a short chain paraffin mix.
All of the Naphthas have a very low flash point and are often mixed with longer chain molecules to yield a more responsive mix. For example, Zippo fuel uses ring naphthas to make the mix easier to ignite with a single spark. Also, these aromatic rings are particularly good at dissolving organic compounds and form the backbone of the paint stripping industry.
Along the left side are the blue paraffin molecules. The term “paraffin” has a lot of definitions, unfortunately, but this is the legal one in the US. A substance must have at least 50% of these molecules to be considered a paraffin. Not terribly helpful, but to call your substance “pure” paraffin, or 99% paraffin, it must be stripped of all but these molecules.
If you remember the last chapter, these molecules are the least reactive, biologically, and amongst the cleanest burning molecules. These are the molecules that the NAFAA regs refer to when they suggest the most purified fuels. The shorter chains are white gas, the longer chains are lamp oil. Only alcohols burn cleaner (but they don’t burn nearly as bright).
The art of blending gasoline today is a very specific science. Not only do you need a large bulk of very specific burn products, but you need detergents, emissions reduction, safety colorants and aromatics. As we stated at the beginning, the pink gasoline section is a bit of a misnomer. This area represents the general range from which the very specific ingredients for gasoline are selected. The true picture might resemble a patchwork quilt.
What isn’t used in this section is distributed as something else. Some of it overlaps the legal Naphtha definition and might be distributed under that name, the rest can be legally sold as Kerosene components.
More than any other fuel, Kerosene has the broadest legal definitions. Functionally, kero and naphtha cover the entire spectrum of liquid petrol chemicals. This makes it very difficult to know exactly what it is that you have when you get a bottle of “kerosene”. Also, kero is often mixed with other petrol products that are left over from primary fuel productions making it, generally speaking, the dirtiest fuel available and the least consistent.
However, modern chemical processing can allow refineries to “crack” the kerosene molecule into two or more shorter chain molecules making it a legal naphtha mix. Longer chain molecules that would normally become grease can also be cracked down to workable kerosene molecules with surprising results.

Artificial kerosenes are made precisely this way. They are either cracked from very long molecules or “hydrogenated” aromatics. The results are aliphatic mixes without the need to strip out the undesirable molecules. Some of these are refined into “paraffins” but most are sold as aviation blends.
Fuels : colored fuels

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