Petroleum naphtha is an intermediate hydrocarbon liquid stream derived from
the refining of crude oil. It is most usually desulfurized and then
catalytically reformed, which re-arranges or re-structures the
hydrocarbon molecules in the naphtha as well as breaking some of the molecules
into smaller molecules to produce a high-octane component of gasoline.
There are hundreds of different petroleum crude oil sources worldwide
and each crude oil has its own unique composition or assay. There are also
hundreds of petroleum refineries worldwide and each of them is designed
to process either a specific crude oil or specific types of crude oils. Naphtha
is a general term as each refinery produces its own naphthas with their own
unique initial and final boiling points and other physical and compositional
characteristics. Naphthas may also be produced from other
material such as coal tar, shale deposits, tar sands and the destructive
distillation of wood. The major source of petroleum naphtha in
a petroleum refinery The first unit process in a petroleum
refinery is the crude oil distillation unit. The overhead liquid distillate
from that unit is called virgin or straight-run naphtha and that distillate
is the largest source of naphtha in most petroleum refineries. The naphtha is a
mixture of many different hydrocarbon compounds. It has an initial boiling
point of about 35 °C and a final boiling point of about 200 °C, and it contains
paraffin, naphthene and aromatic hydrocarbons ranging from those
containing 4 carbon atoms to those containing about 10 or 11 carbon atoms.
The virgin naphtha is often further distilled into two streams:
a virgin light naphtha with an IBP of about 30 °C and a FBP of about 145 °C
containing most of the hydrocarbons with 6 or less carbon atoms
a virgin heavy naphtha containing most of the hydrocarbons with more than 6
carbon atoms. The heavy naphtha has an IBP of about 140 °C and a FBP of about
205 °C. It is the virgin heavy naphtha that is
usually processed in a catalytic reformer because the light naphtha has
molecules with 6 or less carbon atoms which, when reformed, tend to crack into
butane and lower molecular weight hydrocarbons which are not useful as
high-octane gasoline blending components. Also, the molecules with 6
carbon atoms tend to form aromatics which is undesirable because
governmental environmental regulations in a number of countries limit the
amount of aromatics that gasoline may contain.
Types of virgin naphthas The table below lists some typical
virgin heavy naphthas, available for catalytic reforming, derived from
various crude oils. It can be seen that they differ significantly in their
content of paraffins, naphthenes and aromatics:
Cracked naphthas Some refinery naphthas also contain some
olefinic hydrocarbons, such as naphthas derived from the fluid catalytic
cracking, visbreakers and coking processes used in many refineries. Those
olefin-containing naphthas are often referred to as cracked naphthas.
In some petroleum refineries, the cracked naphthas are desulfurized and
catalytically reformed to produce additional high-octane gasoline
components. Other uses
Some petroleum refineries also produce small amounts of specialty naphthas for
use as solvents, cleaning fluids, paint and varnish diluents, asphalt diluents,
rubber industry solvents, dry-cleaning, cigarette lighters, and portable camping
stove and lantern fuels. Those specialty naphthas are subjected to various
purification processes. Sometimes the specialty naphthas are
called petroleum ether, petroleum spirits, mineral spirits, paraffin,
benzine, hexanes, ligroin, white oil or white gas, painters naphtha, refined
solvent naphtha and Varnish makers' & painters' naphtha . The best way to
determine the boiling range and other compositional characteristics of any of
the specialty naphthas is to read the Material Safety Data Sheet for the
specific naphtha of interest. On a much larger scale, petroleum
naphtha is also used in the petrochemicals industry as feedstock to
steam reformers and steam crackers for the production of hydrogen, ethylene and
other olefins. Natural gas is also used as feedstock to steam reformers and
steam crackers. Safety
People can be exposed to petroleum naphtha in the workplace by breathing it
in, swallowing it, skin contact, and eye contact. The Occupational Safety and
Health Administration has set the legal limit for petroleum naphtha exposure in
the workplace as 500 ppm over an 8-hour workday. The National Institute for
Occupational Safety and Health has set a recommended exposure limit of 350 mg/m3
over an 8-hour workday and 1800 mg/m3 over 15 minutes. At levels of 1100 ppm,
10% of the lower explosive limit, petroleum naphtha is immediately
dangerous to life and health. References
This article incorporates material from the Citizendium article "Petroleum
naphtha", which is licensed under the Creative Commons Attribution-ShareAlike
3.0 Unported License but not under the GFDL.
External links CDC - NIOSH Pocket Guide to Chemical
Hazards - Petroleum distillates