The basic
products from fractional distillation are:
Liquid petroleum gas
(LPG) has carbon numbers of 1-5 and a boiling point
up to 20 °C. Most of the LPGs are propane and butane, with carbon number 3 and
4 and boiling points -42 °C and -1 °C, respectively. Typical usage is domestic
and camping gas, LPG vehicles and petrochemical feedstock.
Naphtha, or full range naphtha, is the fraction with
boiling points between 30 °C and 200 °C and molecules generally having carbon
numbers 5 to 12. The fraction is typically 15–30% of crude oil by weight. It is
used mainly as a feedstock for other processes:
• In the refinery for producing
additives for high octane gasoline
• A diluent for transporting
very heavy crude
• Feedstock to the
petrochemical olefins chain
• Feedstock for many other
chemicals
• As a solvent in cleaning
Gasoline has carbon numbers mainly between 4 and 12 and boiling points up
to 120 °C. Its main use is as fuel for internal combustion engines. Early on,
this fraction could be sold directly as gasoline for cars, but today’s engines
require more precisely formulated fuel, so less than 20% of gasoline at the
pump is the raw gasoline fraction. Additional sources are needed to meet the
demand, and additives are required to control such parameters as octane rating
and volatility. Also, other sources such as bioethanol may be added, up to
about 5%.
Kerosene has main carbon numbers 10 to 16 (range 6 to 16) boiling between
150 °C and 275 °C. Its main use is as aviation fuel, where the best known blend
is Jet A-1. Kerosene is also used for lighting (paraffin lamps) and heating.
Diesel oil, or petrodiesel, is used for diesel engines in
cars, trucks, ships, trains and utility machinery. It has a carbon number range
of 8 to 21 (mainly 16-20) and is the fraction that boils between 200 °C and 350
°C.
White and black oils: The above products are often called white oils, and
the fractions are generally available from the atmospheric distillation column.
The remaining fraction below are the black oils, which must be
further separated by vacuum distillation due to the temperature restriction of
heating raw crude to no more than 370-380 °C. This allows the lighter fractions
to boil off at a lower temperatures than with atmospheric distillation,
avoiding overheating.
Lubricating oils, or mineral base lubricating oil (as opposed to
synthetic lubricants), form the basis for lubricating waxes and polishes. These
typically contain 90% raw material with carbon numbers from 20 to 50 and a
fraction boiling at 300-600 °C. 10% additives are used to control lubricant
properties, such as viscosity.
Fuel oils is a common term encompassing a wide range of fuels that also
includes forms of kerosene and diesel, as well as the heavy fuel
oil and bunker that is produced at the low end of the
column before bitumen and coke residues. Fuel oil is graded on a scale of 1 to
6 where grade 1 and 2 is similar to kerosene and diesel, 3 is rarely used
anymore. 4-6 are the heavy
fuels, also called Bunker A, B
and C, where B and C are very high viscosity at normal ambient temperatures and
requires preheating to about 100 °C and 120 °C respectively, before it flows
enough to be used in an engine or burner. Fuel oil grade 4 does not require
preheating and is sometimes mixed with off spec products, such as tank residue
and interface liquid from multiphase pipelines or with grade 2 fuel oil to
achieve low-enough viscosity at ambient temperatures. Fuel oil 6 is the lowest
grade, its specification also allows 2% water and 0.5% mineral soil and is
consumed almost exclusively by large ships in international waters, where
pollutants such as sulfur is less regulated.
Bitumen and other residues like coke and tar has carbon numbers above 70
and boiling points above 525 °C. Low sulfur coke can be used for anodes in the
metals industry (aluminum and steel) after processing (calcining). The
remainder is a problem fuel, because of high sulfur content and even higher CO2
emissions than coal (typically 15% higher). Bitumen in the form of asphalt
boiling above 525 °C is used for roofing and road paving. Asphalt concrete pavement
material is commonly composed of 5% asphalt/bitumen and 95% stone, sand, and
gravel (aggregates).
