Natural Gas is a mixture of very low boiling hydrocarbons.
Natural gas can only be liquefied under extremely high pressures and very low
temperatures. It is called "dry" when methane (CH4) is the primary
component, and "wet" if it contains higher boiling hydrocarbons. If it
smells bad, because of sulfur compounds, it is called "sour".
Otherwise, it is called "sweet".
Liquefied Petroleum Gas (LPG) is a very light fraction of
petroleum. It is also a fairly simple fraction containing mainly
propane and butane. First, it should be noted that under normal pressures
LPG is actually a gas, unlike gasoline (often just called "gas") which is
really a liquid (ugh). However, under modestly high pressures these
compounds can be converted to a liquid (hence their name). Being able to
store them as a liquid reduces the container size by a factor of a
hundred. This is no doubt why propane stoves are so popular. As
cracking methods have evolved more and more LPG has been produced by
refineries.
Gasoline is a light fraction of petroleum which is quite volatile
and burns rapidly. Straight run gasoline refers to gasoline produced by
distillation instead of cracking, although it really doesn't make a difference.
Gasoline is often just called "gas", however it is a liquid at typical
pressures. This confusing state of affairs developed because the first
internal combustion engines ran on town gas (a mixture of carbon monoxide,
CO, and hydrogen, H2, both actual gases). These engines were therefore called "gas
engines". When gasoline replaced town gas people still called the motors
"gas engines" and also started calling gasoline "gas". Today, the average
American uses 450 gallons of gasoline a year.
Octane Number rates a fuel's ability to avoid premature ignition
called knock. Premature ignition reduces an engine's power and
quickly wares it out. The octane scale arbitrarily defines n-heptane
a value of 0, and isooctane (2,2,4-trimethyl pentane) an octane number of
100. Isooctane is then added to heptane until the mixture has the same knock
characteristics as the fuel being tested, and the percent isooctane is taken as
the unknown fuels octane number. Tetraethyl lead used to be a common
anti-knock additive which would raise a fuels octane number. High octane fuel
can be used in engines with high compression ratios which in turn produce
much more power. However, the additive is no longer used because of
concerns over lead pollution.
Naphtha is a light fraction of petroleum used to make gasoline.
Naphtha also produces solvents and feedstocks for the
petrochemical industry.
Kerosene was the first important petroleum fraction, replacing
whale oils in lamps over a hundred years ago. Some unscrupulous
refiners failed to distill off all the naphtha from the kerosene fraction
thereby increasing the volume of their final product. This lead to many lamp
explosions and fires.
Diesel fuels find use in the fleet of trucks which transport
the nations goods. Diesel engines power these larger engines, and use
higher compression ratios (and temperatures) than their gasoline cousins.
They are therefore more efficient. It is also interesting to note that
diesel engines have no spark plugs, instead the fuel-air mixture is
ignited by the rising temperatures and pressures during the compression
stroke.
Gas Oil (or fuel oils) are used for domestic heating. In the
winter refineries produce more gas oil, whereas during the summer
driving months they produce more gasoline.
Heavy Fuel Oil is often blended with gas oils for easier use in
industry. Ships burn heavy fuel oils but they call it bunker oil.
Atmospheric Residual is everything that cannot be vaporized under
normal pressures. Atmospheric residual is fed into another distillation
column, operating at lower pressures, which can separate out some of the lighter
compounds. Lubricants and waxes reside in this fraction.
Vacuum Residual is the bottom of the barrel. It includes
asphalt and some coke.
Pitch is a thick, black, sticky material. It is left behind when the
lighter components of coal tar or petroleum are distilled off. Pitch is a
"natural" form of asphalt.
Asphalt is a high boiling component of crude oil. It is
therefore found at the "bottom of the barrel" when petroleum is
distilled.
Tars are byproducts formed when coke is made from coal
or charcoal is made from wood. It is a thick, complex, oily black mixture
of heavy organic compounds very similar to pitch or asphalt, though from a
different source.
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