petroleum naphtha
TRANSCRIPT
Petroleum naphthaPetroleum naphtha is an intermediate hydrocarbon liquid stream derived from the refining of crude oil.[1][2][3] 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 (or petrol).
There are quite literally 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. That means that it is virtually impossible to provide a definitive,
single definition of the word naphtha since each refinery produces its own naphthas with their
own unique initial and final boiling points and other physical and compositional characteristics.
In other words, naphtha is a generic term rather than a specific term.
In addition, naphthas may also be produced from coal tar, shale deposits, tar sands such as in
Canada, the destructive distillation of wood and coal gasification or biomass gasification to
produce a syngas[4][5] followed by the Fischer-Tropsch process to convert the syngas into liquid
hydrocarbon products. For that reason, this article is entitled Petroleum naphtha and deals
only with naphthas produced by the processing of crude oil in petroleum refineries.
Contents
[hide]
1 The major source of petroleum naphtha in a petroleum refinery
2 Types of virgin naphthas
3 Cracked naphthas
4 Removal of sulfur compounds from naphthas
5 Other uses
6 References
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 very many different
hydrocarbon compounds. It has an initial boiling point (IFP) of about 35 °C and a final boiling
point (FBP) of about 200 °C, and it contains paraffin, naphthene (cyclic paraffins) 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:[6]
a virgin light naphtha with an IFP of about 30 °C and a FBP of
about 145 °C containing most (but not all) of the hydrocarbons
with 6 or less carbon atoms
a virgin heavy naphtha containing most (but not all) of the
hydrocarbons with more than 6 carbon atoms. The heavy
naphtha has an IFP 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 (most particularly benzene) that gasoline may contain.[7][8][9]
Types of virgin naphthas
The table just below lists some fairly 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:
Typical Heavy Naphthas
Crude oil name Location
Barrow IslandAustralia[10]
Mutineer-ExeterAustralia[11]
CPC BlendKazakhstan[12]
DraugenNorth Sea[13]
Initial boiling point, °C 149 140 149 150
Final boiling point, °C 204 190 204 180
Paraffins, liquid volume % 46 62 57 38
Naphthenes, liquid volume %
42 32 27 45
Aromatics, liquid volume % 12 6 16 17
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 (but not all) petroleum refineries, the cracked naphthas are desulfurized and
catalytically reformed (as are the virgin naphthas) to produce additional high-octane gasoline
components.
Removal of sulfur compounds from naphthas
For more information, see: Hydrodesulfurization, Amine gas treating, and Merox
Most uses of petroleum refinery naphtha require the removal of sulfur compounds down to very
low levels (a few parts per million or less). That is usually accomplished in a catalytic chemical
process called hydrodesulfurization which converts the sulfur compounds into hydrogen sulfide
gas that is removed from the naphtha by distillation.
The hydrogen sulfide gas is then captured in amine gas treating units and subsequently
converted into byproduct elemental sulfur. In fact, the vast majority of the 64,000,000 metric
tons of sulfur produced worldwide in 2005 was byproduct sulfur from petroleum refining and
natural gas processing plants (which also use amine gas treating units to remove hydrogen
sulfide from the raw natural gas).[14][15]
In lieu of hydrodesulfurization, light naphthas may be treated in a Merox unit to remove any
hydrogen sulfide and, more particularly, to remove mercaptans.
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 (VM&P) . 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 (MSDS) 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 (which may be
and is converted into ammonia for fertilizers), ethylene and other olefins. Natural gas is also
used as feedstock to steam reformers and steam crackers.
Petroleum refining processesPetroleum refining processes are those chemical engineering processes and other facilities used in petroleum refineries (also referred to as oil refineries) to transform crude oil into useful products such as liquefied petroleum gas (LPG), gasoline or petrol, kerosene, jet fuel, diesel oil and fuel oils.[1][2][3]
Petroleum refineries are very large industrial complexes that involve a great many different
processing units and auxiliary facilities such as utility units and storage tanks. Each refinery has
its own unique arrangement and combination of refining processes largely determined by the
refinery location, desired products and economic considerations. There are most probably no
two refineries that are identical in every respect.
Some modern petroleum refineries process as much as 800,000 to 900,000 barrels (127,000 to
143,000 cubic meters) per day of crude oil.
Brief history of the petroleum industry and petroleum refining
Prior to the 19th century, petroleum was known and utilized in various fashions in Babylon,
Egypt, China, Persia, Rome and Azerbaijan. However, the modern history of the petroleum
industry is said to have begun in 1846 when Abraham Gessner of Nova Scotia, Canada
discovered how to produce kerosene from coal. Shortly thereafter, in 1854, Ignacy Lukasiewicz
began producing kerosene from hand-dug oil wells near the town of Krosno, now in Poland. The
first large petroleum refinery was built in Ploesti, Romania in 1856 using the abundant oil
available in Romania.[4][5]
In North America, the first oil well was drilled in 1858 by James Miller Williams in Ontario,
Canada. In the United States, the petroleum industry began in 1859 when Edwin Drake found
oil near Titusville, Pennsylvania. The industry grew slowly in the 1800s, primarily producing
kerosene for oil lamps. In the early 1900's, the introduction of the internal combustion engine
and its use in automobiles created a market for gasoline that was the impetus for fairly rapid
growth of the petroleum industry. The early finds of petroleum like those in Ontario and
Pennsylvania were soon outstripped by large oil "booms" in Oklahoma, Texas and California.[6]
Prior to World War II in the early 1940s, most petroleum refineries in the United States
consisted simply of crude oil distillation units (often referred to as atmospheric crude oil
distillation units). Some refineries also had vacuum distillation units as well as thermal cracking
units such as visbreakers (viscosity breakers, units to lower the viscosity of the oil). All of the
many other refining processes discussed below were developed during the war or within a few
years after the war. They became commercially available within 5 to 10 years after the war
ended and the worldwide petroleum industry experienced very rapid growth. The driving force
for that growth in technology and in the number and size of refineries worldwide was the
growing demand for automotive gasoline and aircraft fuel.
In the United States, for various complex economic reasons, the construction of new refineries
came to a virtual stop in about the 1980's. However, many of the existing refineries in the United
States have revamped many of their units and/or constructed add-on units in order to: increase
their crude oil processing capacity, increase the octane rating of their product gasoline, lower
the sulfur content of their diesel fuel and home heating fuels to comply with environmental
regulations and comply with environmental air pollution and water pollution requirements.
Processing units used in refineries
Crude Oil Distillation unit: Distills the incoming crude oil into
various fractions for further processing in other units.
Vacuum Distillation unit: Further distills the residue oil from the
bottom of the crude oil distillation unit. The vacuum distillation
is performed at a pressure well below atmospheric pressure.
Naphtha Hydrotreater unit: Uses hydrogen to desulfurize the
naphtha fraction from the crude oil distillation or other units
within the refinery.
Catalytic Reforming unit: Converts the desulfurized naphtha
molecules into higher-octane molecules to produce reformate,
which is a component of the end-product gasoline or petrol.
Alkylation unit: Converts isobutane and butylenes into
alkylate, which is a very high-octane component of the end-
product gasoline or petrol.
Isomerization unit: Converts linear molecules such as normal
pentane into higher-octane branched molecules for blending
into the end-product gasoline. Also used to convert linear
normal butane into isobutane for use in the alkylation unit.
Distillate Hydrotreater unit: Uses hydrogen to desulfurize
some of the other distilled fractions from the crude oil
distillation unit (such as diesel oil).
Merox (mercaptan oxidizer) or similar units: Desulfurize LPG,
kerosene or jet fuel by oxidizing undesired mercaptans to
organic disulfides.
Amine gas treater, Claus unit, and tail gas treatment for
converting hydrogen sulfide gas from the hydrotreaters into
end-product elemental sulfur. The large majority of the
64,000,000 metric tons of sulfur produced worldwide in 2005
was byproduct sulfur from petroleum refining and natural gas
processing plants.[7][8]
Fluid Catalytic Cracking (FCC) unit: Upgrades the heavier,
higher-boiling fractions from the the crude oil distillation by
converting them into lighter and lower boiling, more valuable
products.
Hydrocracker unit: Uses hydrogen to upgrade heavier
fractions from the crude oil distillation and the vacuum
distillation units into lighter, more valuable products.
Visbreaker unit upgrades heavy residual oils from the vacuum
distillation unit by thermally cracking them into lighter, more
valuable reduced viscosity products.
Delayed coking and Fluid coker units: Convert very heavy
residual oils into end-product petroleum coke as well as
naphtha and diesel oil by-products.
Auxiliary facilities required in refineries
Steam reformer unit: Converts natural gas into hydrogen for
the hydrotreaters and/or the hydrocracker.
Sour water stripper unit: Uses steam to remove hydrogen
sulfide gas from various wastewater streams for subsequent
conversion into end-product sulfur in the Claus unit.[9]
Utility units such as cooling towers for furnishing circulating
cooling water, steam generators, instrument air systems for
pneumatically operated control valves and an electrical
substation.
Wastewater collection and treating systems consisting of API
separators, dissolved air flotation (DAF) units and some type
of further treatment (such as an activated sludge biotreater) to
make the wastewaters suitable for reuse or for disposal.[9]
Liquified gas (LPG) storage vessels for propane and similar
gaseous fuels at a pressure sufficient to maintain them in
liquid form. These are usually spherical vessels or bullets
(horizontal vessels with rounded ends).
Storage tanks for crude oil and finished products, usually
vertical, cylindrical vessels with some sort of vapor emission
control and surrounded by an earthen berm to contain liquid
spills.
The crude oil distillation unit
The crude oil distillation unit (CDU) is the first processing unit in virtually all petroleum refineries.
The CDU distills the incoming crude oil into various fractions of different boiling ranges, each of
which are then processed further in the other refinery processing units. The CDU is often
referred to as the atmospheric distillation unit because it operates at slightly above atmospheric
pressure.[1][2][10]
Below is a schematic flow diagram of a typical crude oil distillation unit. The incoming crude oil
is preheated by exchanging heat with some of the hot, distilled fractions and other streams. It is
then desalted to remove inorganic salts (primarily sodium chloride).
Following the desalter, the crude oil is further heated by exchanging heat with some of the hot,
distilled fractions and other streams. It is then heated in a fuel-fired furnace (fired heater) to a
temperature of about 398 °C and routed into the bottom of the distillation unit.
The cooling and condensing of the distillation tower overhead is provided partially by
exchanging heat with the incoming crude oil and partially by either an air-cooled or water-cooled
condenser. Additional heat is removed from the distillation column by a pumparound system as
shown in the diagram below.
As shown in the flow diagram, the overhead distillate fraction from the distillation column is
naphtha. The fractions removed from the side of the distillation column at various points
between the column top and bottom are called sidecuts. Each of the sidecuts (i.e., the
kerosene, light gas oil and heavy gas oil) is cooled by exchanging heat with the incoming crude
oil. All of the fractions (i.e., the overhead naphtha, the sidecuts and the bottom residue) are sent
to intermediate storage tanks before being processed further.
(PD) Drawing: Milton BeychokSchematic flow diagram of a typical crude oil distillation unit.
Flow diagram of a typical petroleum refinery
The image below is a schematic flow diagram of a typical petroleum refinery that depicts the
various refining processes and the flow of intermediate product streams that occurs between the
inlet crude oil feedstock and the final end-products.
The diagram depicts only one of the literally hundreds of different oil refinery configurations. The
diagram also does not include any of the usual refinery facilities providing utilities such as
steam, cooling water, and electric power as well as storage tanks for crude oil feedstock and for
intermediate products and end products.[1][2][11]
(GNU) Image: Milton BeychokA schematic flow diagram of a typical petroleum refinery.
Refining end-products
The primary end-products produced in petroleum refining may be grouped into four categories:
light distillates, middle distillates, heavy distillates and others.
Light distillates
Liquid petroleum gas (LPG)
Gasoline (also known as petrol)
Kerosene
Jet fuel and other aircraft fuel
Middle distillates
Automotive and railroad diesel fuels
Residential heating fuel
Other light fuel oils
Heavy distillates
Heavy fuel oils
Bunker fuel oil and other residual fuel oils
Others
Many of these are not produced in all petroleum refineries.
Specialty petroleum naphthas
Specialty solvents
Elemental sulfur (and sometimes sulfuric acid)
Petrochemical feedstocks
Asphalt and tar
Petroleum coke
Lubricating oils
Waxes and greases
Transformer and cable oils
Carbon black
Sulfuric acid
sulfuric acidIUPAC name: sulfuric acid
Synonyms:sulphuric acid and others
Formula: H2SO4
Uses:acid, dehydration, reduction
Properties: strong acid
Hazards:Toxic, Corrosive
Mass (g/mol): CAS #:98.08 7664-93-9
Sulfuric acid, also spelled sulphuric acid, is a strong, corrosive acid and
oxidizing agent having the chemical formula H2SO4. It is the diprotic acid of the
sulfate anion SO4-2. At room temperature and pressure, it is a clear, colorless,
rather viscous liquid. Sulfuric acid is one of the most important chemicals in the
chemical industry. Personal protective gear should be worn when using
sulfuric acid.
Contents
[hide]
1 Synonyms
2 Properties and uses of sulfuric acid
3 Synthesis of sulfuric acid
4 Soluble and insoluble sulfate salts
Synonyms
Sulfuric acid is also called oil of vitriol, mattling acid, vitriol, battery acid, dipping
acid, electrolyte acid, vitriol brown oil, sulphuric acid, Babcock acid and sulphuric
acid.
Properties and uses of sulfuric acid
Sulfuric acid is a strong acid, an oxidizing agent and a dehydrating agent. Two
hydrogen ions can dissociate from H2SO4. In an aqueous (water) solution, the first
hydrogen dissociates completely (100%) to form the bisulfate anion HSO4-. Since
this dissociation is complete, sulfuric acid is considered a strong acid. HSO4- is a
medium strength acid from which the second hydrogen dissociates to form the
sulfate anion SO4-2.
H2SO4 + H2O → H3O+ + HSO4− K1 = 2.4 x 106 (strong acid)
HSO4− + H20 → H3O+ + SO4
2− K2 = 1.0 x 10-2 [1]
K1 and K2 are the acid dissociation constants.
Sulfuric acid is used to make many soluble phophates for fertilizers, ammonium
sulfate and many other chemicals, including drugs. Newly made steel is cleaned
with sulfuric acid to remove rust before the steel is coated with a protective layer of
zinc, tin or enamel. It is also used in lead sulfate batteries. Many explosives are
manufactured using sulfuric acid.
Because it has a high boiling point (33°C), it can be used to make other more
volatile acids using the appropriate acid salt. Nitric acid can be made by reacting
sulfuric acid with sodium nitrate, NaNO3. Distilling the resultant nitric acid
(BP=86°C) drives the reaction towards completion.
NaNO3 + H2SO4 → HNO3 + NaHSO4
Contact of water and sulfuric acid is exothermic. When handling them, always add
acid to water, not the reverse or the resulting boiling can spray hot acid.
The explosive nitroglycerin (glyceryl trinitrate), is made by reacting glycerine and
nitric acid in the presence of sulfuric acid. This reaction is very dangerous, do
not attempt.
C3H5(OH)3 + 3HNO3 + (H2SO4 catalyst)→ C3H5(NO3)3 + 3H2O.
Sulfuric acid can be used as a drying agent for gases that do not react with sulfuric
acid by bubbling the gas through sulfuric acid.
Synthesis of sulfuric acid
Sulfuric acid is made be reacting sulfur trioxide with water in an exothermic
reaction.
SO3(g) + H2O(l) → H2SO4(l) + 130 kJ mole-1
In the commercial production of sulfuric acid, the contact process or the lead-
chamber process is used. In the contact method, sulfur dioxide is catalytically
converted to sulfur trioxide by surface chemistry with fine platinum powder or,
more recently, vanadium pentoxide (V2O5). The resulting sulfur trioxide gas is
bubbled through sulfuric acid and the addition of water at the correct rate yields
98% acid pulled out.
The lead-chamber process uses sulfur dioxide, oxygen, nitric acid and water vapor
are introduced into a lead-lined chamber. White crystals of nitrosulfuric acid
(nitronium sulfate), NOHSO4, are formed. The introduction of steam then converts
the nitrosulfuric acid to sulfuric acid liberates nitrogen oxides, which can be reused
in the first step of the reaction.
1) 2SO2 + NO + NO2 + O2 + H2O → 2NOHSO4
2) 2NOHSO4 + H2O → 2H2SO4 + NO + NO2
Soluble and insoluble sulfate salts
The soluble salts of sulfate include sodium sulfate (Na2SO4)•10H2O, ammonium
sulfate (NH4)2SO4, magnesium sulfate (Epsom salt, MgSO4•7H2O, copper sulfate
(blue vitriol, CuSO4•5H2O), iron sulfate (FeSO4•7H2O), zinc sulfate (ZnSO4•7H2O),
potassium aluminum sulfate (alum, KAl(SO4)2•12H2O), ammonium aluminum
sulfate (ammonium alum, NH4Al(SO4)2•12H2O), and chrome alum
(KCr(SO4)2•12H2O).
Barium sulfate (barite) is the least soluble sulfate salt and its white precitate is
used as a test for sulfate anions. Other sulfates with diminished solubility include
lead sulfate (PbSO4), strontium sulfate (SrSO4) and calcium sulfate (gypsum,
CaSO4•2H2O.
PetrochemicalsPetrochemicals are chemical products made from the hydrocarbons present in
raw natural gas and petroleum crude oil. The largest petrochemical manufacturing
industries are to be found in the United States, Western Europe, Asia and the
Middle East.
A relatively small number of hydrocarbon feedstocks form the basis of the
petrochemical industries, namely methane, ethylene, propylene, butanes,
butadiene, benzene, toluene and xylenes.[1][2]
As of 2007, there were 2,980 operating petrochemical plants in 4,320 locations
worldwide.[3] The petrochemical end products from those plants include plastics,
soaps, detergents, solvents, paints, drugs, fertilizer, pesticides, explosives,
synthetic textile fibers and rubbers, flooring and insulating materials and much
more.
Petrochemicals are found in such common consumer products as aspirin, cars,
clothing, compact discs, video tapes, electronic equipment, furniture, and a great
many others.[4]
Feedstocks sources
(PD) Image: Milton Beychok Figure 2: Petrochemical feedstock sources.
Figure 2 schematically depicts the major hydrocarbon sources used in producing
petrochemicals are:[1][2][5][6]
Methane, ethane, propane and butanes:
Obtained primarily from natural gas
processing plants.
Naphtha obtained from petroleum
refineries.
Benzene, toluene and xylenes, as a
whole referred to as BTX and primarily
obtained from petroleum refineries by
extraction from the reformate produced in
catalytic reformers.
Gas oil obtained from petroleum
refineries.
Methane and BTX are used directly as feedstocks for producing petrochemicals.
However, the ethane, propane, butanes, naphtha and gas oil serve as optional
feedstocks for steam-assisted thermal cracking plants referred to as steam
crackers that produce these intermediate petrochemical feedstocks:
Ethylene
Propylene
Butenes and butadiene
Benzene
In 2007, the amounts of ethylene and propylene produced in steam crackers were
about 115 Mt (megatonnes) and 70 Mt, respectively.[7] The output ethylene capacity
of large steam crackers ranged up to as much as 1.0 – 1.5 Mt per year.[8][9]
Steam crackers are not to be confused with steam reforming plants used to
produce hydrogen and ammonia.
Worldwide usage of optional steam cracking feedstock sources
As of 2004, the percentage of the worldwide steam cracking plants using each of
the optional steam cracking feed sources was:[10]
Ethane: 35%
Propane: 9%
Butanes: 3%
Naphtha: 45%
Gas oil: 5%
Other: 3 %
The effect of feedstock on the steam cracking yields of intermediate petrochemical products
The effect of feedstock selection upon the yields of steam cracking products is
summarized in the table below:
Steam cracking feedstocks versus yields of intermediate petrochemical products
Product Yields
Feedstocksource
Ethyleneweight %
Propyleneweight %
Butadieneweight %
Aromatics (a)
weight%
Ethane 84.0 1.4 1.4 0.4
Propane 45.0 14.0 2.0 3.5
Butane 44.0 17.3 3.0 3.4
Naphtha (c) 34.4 14.4 4.9 14.0
Gas oil (d) 25.5 13.5 4.9 12.8
(a) Includes benzene, toluene, xylenes and any other aromatics.
(b) Includes hydrogen, methane, butenes, non-aromatic portion of pyrolysis gasoline
oil.
(c) Full-range naphtha (as differentiated from light or heavy naphtha).
(d) The portion of petroleum crude oil that has a boiling range of about 250 to 550 °C (480 to
1020 °F).
That encompasses the boiling range of atmospheric gas oil (AGO) produced by the
distillation
of petroleum crude oil and the boiling range of vacuum gas oil (VGO) produced by the
distillation
of petroleum crude oil.
Feedstocks and example petrochemical products
The table below includes some representative examples of the petrochemical end
products produced from the eight hydrocarbon feedstocks – methane, ethylene,
propylene, butenes, butadiene, benzene, toluene and xylenes:
Feedstocks and example petrochemical products
methane ethylene propylenebutenes
and Bhutanese
benzene toluene xylenes
hydrogen polyethylenepolypropyle
ne
styrene-butadiene
rubber (SBR)
styrenebenzoic
acidphthalic
anhydride
ammonia ethanol isopropanolmethyl tert-butyl ether
(MTBE)
polystyrene
toluene diisocyanat
epolyesters
methanol ethylene glycolpropylene
glycolpolybutadie
nephenol
polyurethanes
dimethyl terephthal
ate
methyl chloride
vinyl acetate allyl chloride
acrylonitrile-butadiene-
styrene
cumene caprolactam
terephthalate acid
(ABS)
carbon black
perchloroethylene
acrylonitrilepolybutene
saniline nylons
polyethylene
terephthalate
acetylenepolyvinyl acetate
acrylic acid
methyl ethyl
ketone (MEK)
adipic acid
polyureasdioctyl
phthalate
formaldehyde
glycol ethersepoxy resins
tert-butanol nylons