Jones D.S.J., Pujado P.R. Handbook of Petroleum Processing
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PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 59
Table 2.6. General specifications for gas oil finished products
Parameters Auto diesel Heating oil ASTM tests
Color 2.0 Max 1–1/2 D-155
Specific gravity,
◦
API 37.0–33.0 41.1–36.0 D-1298
Viscosity sus @ 100
◦
F 32.0–43.9 37.5 Max D-88
Flash point,
◦
F 150 Min 150 Min D-93
Pour point winter,
◦
F 5.0 Max 5.0 Max D-97
Pour point summer,
◦
F 15.0 Max 15.0 Max
Sulfur content, %wt 0.35 Max 0.5 Max D-129
Diesel index 54 Min 57 Min IP-21
Cetane number 45 Min 50 Min D-613
Distillation D-158
Recovered @ 446
◦
F %vol – 10 Min
Recovered @ 464
◦
F %vol 50 Max 50 Max
Recovered @ 482
◦
F %vol – 40 Min
Recovered @ 572
◦
F %vol – 70 Min
Recovered @ 619
◦
F %vol – 80 Min
Recovered @ 657
◦
F %vol 50 Min –
Recovered @ 675
◦
F %vol 90 Min 90 Max
FBP,
◦
F 725 Max 725 Max
be rich in olefins and these would be saturated by the hydro-desulfurization process to
meet heating oil specifications. Some traditional product specifications for the various
gas oil finished products are given in Table 2.6. With the advent of low-sulfur diesel,
these specifications are being modified considerably, with sulfur levels as low as 50
wt-ppm (0.005 wt%) and cetane numbers in excess of 50.
Products from the residues
The residues from the atmospheric and vacuum distillation of crude oil open a spec-
trum of saleable products which constitute a major source of revenue for many re-
fineries. These are listed in order of their importance as follows:
r
The fuel oils
r
Petroleum coke
r
The lube oil products
r
The asphalt products
The fuel oil products. There are two common fuel oil products in use today. The first
and perhaps the second most common product is the marine diesel. As the name
suggests it is the fuel used by heavy marine diesel engines. It is the least viscous
of the three grades and is usually a blend of a middle distillate (kerosene and/or
gas oil) with atmospheric residue. It has a general specification as shown in Ta-
ble 2.7.
60 CHAPTER 2
Table 2.7. General specifications for fuel oil products
Parameters Marine diesel No 6 fuel oil ASTM tests
Specific gravity,
◦
API 39–40 11.4 Max D1298
Viscosity redwood1@100
◦
F, sec 30–40 2,400 Max D445
Pour point summer,
◦
F 25 Max 65 Max D97
Winter,
◦
F 10 Max –
Flash point,
◦
F 150 Min 160 Min D93
Calorific value (Gross) Btu/lb 19,200 Min 18,300 Min D240
Sulfur content, %wt 1.0 Max 2.0 Max D129
Diesel index 45 Min – IP21
Ash, %wt 0.01 Max 0.1 Max D482
Sediment, %wt 0.01 Max 0.1 Max D473
Water, %wt 0.05 Max 1.0 Max D95
The most common fuel oil used in industry is the No 6 fuel oil which is either a
suitably cut atmospheric residue or a vacuum residue blended with a distillate cut
back. It may mean also that a cutback distillate has been desulfurized to meet the
product sulfur specification of the fuel oil. A general specification for No 6 fuel is
also shown in Table 2.7. Again, depending on use, sulfur specifications are being
lowered in many instances.
Several other fuel oil grades are often produced by blending one or other of the
distillation residues with suitable distillate streams. These however are customized
for clients specific needs. For example a No 5 fuel oil grade was once produced in
some quantity for the steel industry. This is a product less viscous and of a lower
gravity than No 6 fuel oil. It is now seldom produced.
Petroleum coke. This is not found in crude oil but is formed by the thermal cracking
of the residues from both atmospheric and vacuum distillation of the crude. The
coke is really the thermal conversion of these heavy products which contain the
resins and asphaltenes contained in the crude. The major purpose of the ‘Coking’
processes is to upgrade the residues by producing lighter marketable products in
the gasoline and middle distillate range. The coke becomes the by-product of these
thermal cracking mechanisms (see Chapter 12 for more details on these processes).
The coke as produced in the refinery process is called Green Coke and this may be
subclassified as Sponge coke from a delayed coking process and Needle Coke from
a Fluid coking process. Approximately one half of the green coke (both Needle and
Sponge) is further calcined to make the calcined coke product.
Uncalcined coke has a heating value of around 14,000 Btu/lb and is primarily used
as a fuel. High sulfur uncalcined sponge coke is particularly popular in the cement
industry since the sulfur reacts to form sulfates. Low sulfur low metals sponge coke
may be calcined to remove volatiles and is used mostly as anodes in the aluminum
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 61
Table 2.8. Typical sponge coke specification
Parameter Green coke Calcined coke
Fixed carbon, %wt 86–92 99.5
Moisture, %wt 6–14 0.1
Volatile matter, %wt 8–14 0.5
Sulfur, %wt <2.5 <2.5
Ash, %wt 0.25 0.4
Silicon, %wt 0.02 0.02
Nickel, %wt 0.02 0.03
Vanadium, %wt 0.02 0.03
Iron, %wt 0.01 0.02
industry while needle coke is calcined for anodes in the steel industry. Table 2.8
defines the general specification for green coke and calcined coke.
Lube oil production. The second most important products from the residue of crude
oil is the lube oil products. Details of the lube oil production processes are given in
Chapter 12. A brief description of this aspect of refinery products with a short history
of its growth in the industrial countries. The development of the industrial revolution
gave a big incentive for the production of high quality lubricants from the processing
of crude oil. A further boost to these processes followed the rapid development of the
automotive industry, particularly in the Western world. More and more sophisticated
processes were developed for the purpose of this growing demand and an increasing
quality requirement. This has culminated in the use of the hydro-processes used
extensively in today’s modern refineries.
Through the years the lubricant market has developed its own lexicon of terms. Some
of these are:
A Lube Oil Base Stock—This refers to a base lube oil product from a lube oil process
which meets all the requirement for blending to make a spectrum of lube oil finished
product.
A Lube Oil Slate—is a set of lube oil base stocks that makes up a particular finished
product. Usually these are between 3 and 5 such stocks.
Neutral Lubes—are lube oil streams obtained as side cuts from the vacuum distillation
of the crude oil atmospheric residue.
Bright Stock Lubes—These are processed as de-asphalted oil from vacuum residues.
(Note: de-asphalted oils are also used as feedstock to fluid catalytic crackers and
more commonly to heavy oil hydro-crackes).
Paraffinic Lubes—Are all grades, both neutral and bright stock with a finished vis-
cosity index of more than 75.
Naphthenic Lubes—Are all grades with finished viscosity index of less than 75.
62 CHAPTER 2
Table 2.9. SAE viscosity specification for single-grade motor oil grades
Max viscosity Max viscosity Min viscosity
Grade (SUS) @ 0
◦
F (SUS) @ 210
◦
F (SUS) @ 210
◦
F
5 W 6,000 – –
10 W 12,000 – –
20 W 48,000 – –
20 – 58 45
30 – 70 58
40 – 86 70
50 – 110 85
The important properties of lube oils are:
Kinetic Viscosity (Centistokes)
r
Kinetic viscosity (Centistokes)
r
Color
r
Pour point
r
Flash point
r
Volatility
r
Oxidation stability
r
Thermal stability
Although Kinematic Viscosity is measured in centistokes it is usually specified in
Saybolt Seconds (SSU). Specifications for lube oils are established by the Society
of Automotive Engineers who also perform research on a wide range of automotive
topics. One very well known motor oil specification is the SAE viscosity. This is given
in Table 2.9. Multi-grade oils (10–20, 10–30, 10–50, etc.) prevail in today’s markets.
There are a great many specifications covering all grades and uses for the lube oil
products. Many of these, particularly for the motor lube oils, are customized within
certain basic maximum, and minimum constraints (such as viscosity), for the local
climate, motor type, and legislative requirements.
The asphalt products. Asphalt is the heaviest boiling point product that can be pro-
duced in the processing of crude oil. Contrary to common beliefs asphalts can only
be made from crude oils that contain asphalt. That is they contain the right amount
of the carbon and the resin that allows the formation of asphalts. A full description of
the types and the production of asphalt is given in Chapter 12. Briefly most grades of
asphalt are produced from the deep cut vacuum residue of suitable crudes. The asphalt
extract from the lube oil de-asphalting process may also be included with the residue
for the production of certain asphalt grades. The finished product is often treated by
air blowing to achieve the required hardness and ductility of the product. Asphalt
becomes an important product because of its wide use in road and other building
industries.
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 63
2.3 A discussion on the motive fuels of gasoline and diesel
Of all the petroleum products that are marketable, motive fuels are the ones that are
most common to the general public. Because of this they are continually in the public
focus for change with respect to their performance, their availability and cost, and
their effect on the environment. This section of Chapter 2 continues with a closer look
at the make up, manufacture and the environmental impact of these two motive fuels.
It begins with the gasolines.
The parameters of gasoline
Parameters affecting engine performance
The following parameters are the major criteria in the production of finished gasoline
with respect to its performance: These are:
r
Octane number
r
Thermal efficiency
r
Volatility of the gasoline
r
Engine deposits
Octane number. Among the most important parameters in the manufacture of gasoline
is its resistance to ‘Knocking’. This resistance is expressed as an ‘Octane Number’.
A definition of octane number and its measurement has already been given in Cha-
pter 1.
Knocking limits the power that can be developed by the engine/fuel combination.
Detonation is the spontaneous explosion of the residual fuel (after almost complete
combustion) and the air in the combustion chamber as the normal mechanism of
combustion nears its end. It’s a very fast oxidation reaction which sets up its own
flame front. The knocking occurs when this front and that of the normal combustion
collide creating a pressure wave.
Another, and perhaps, a more destructive form of engine knock is ‘Pre-ignition’.
This is the spontaneous ignition of the fuel/air mixture before the ignition spark.
This in turn is caused when the unburned gases are compressed in the cylinder and
the resulting temperature reaches the auto ignition point before the ignition spark
occurs. This pre-ignition usually causes major engine damage in just a few seconds
or minutes.
Increasing humidity, cooler ambient air temperatures, and altitude reduce require-
ments for antiknock.
64 CHAPTER 2
Thermal efficiency. As may be expected fuel economy is a factor in determining the
thermal efficiency of the auto engine. The engines efficiency increases with the in-
crease in compression ratio. However with the increase in compression ratio there is an
increasing need for fuels that do not knock. Since around 1980s engine manufacturers
have been incorporating knock sensors to the engine electronic management system
to continuously adjust the ignition timing. This development allows the timing of the
spark to occur in advance of the piston reaching the top of its travel. The maximum
engine efficiency is produced with this timing control measured and adjusted by the
computer control of fuel to air ratio. Further development and testing of individual
engine design sets an optimum criteria for fuel octane number of the fuel and air ratio
for lean mixture combustion.
Volatility of the gasoline. Another important property of gasoline is its volatility. The
gasoline must be volatile enough to provide the engine capable of starting at the
lowest temperature expected in its service. At too low a volatility the engine would
have difficulty starting and would be prone to stalling in service. On the other hand
too high a volatility would cause excessive vapor which in turn would cause vapor
lock in pipes and pumps, etc.
Engine deposits. Engine deposits affect fuel efficiency and emissions. Deposits are
of particular concern in the carburetor, fuel injectors, inlet valves, and combustion
chamber. These deposit are essentially fine carbon granules which are formed by
high inlet valve temperatures, airflow inconsistencies, and minor oil contaminat-
ion.
Parameters affecting pollution by emission
Air pollution is an important factor in motive fuel design and manufacture. There are
two main types of air pollutants that affect the manufacture of motive fuels. These
are:
r
Hazardous air pollutants (HAPs)
r
Criteria air pollutants
Hazardous air pollutants
These are air pollutants that have been shown statistically to cause major health
disorders such as cancer, neurological damage, respiratory irritation, and reproductive
disorders. In general these pollutants are believed to have no threshold, and are harmful
even in small doses or concentrations. The Environmental Protection Agency (EPA)
has been regulating these pollutants since the 1977 Clean Air Act. There are 189
hazardous air pollutants among which Benzene, formaldehyde, and 1,3-butadiene
which are formed by combustion of motive fuel such as gasoline.
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 65
Criteria air pollutants
These are pollutants that can injure health, harm the environment, and cause property
damage. These pollutants do have a threshold level however, below which they are
relatively harmless. The EPA labels these pollutants as Criteria Air Pollutants because
the basis for setting standards are developed from health based criteria. There are six
criteria of are pollutants that affect the design and manufacture of gasoline. These
are:
r
Lead
r
Carbon monoxide (CO)
r
Sulfur dioxide (SO
2
)
r
Nitrogen dioxide (NO
2
)
r
Particulate matter
r
Ozone (O
3
).
Lead. This emission from gasoline engines have been known to be toxic for several
decades. It adversely affects kidneys, liver, and other organs, and leads to neurolog-
ical impairment, learning deficits, and behavioral disorders. The reduction of lead
programs conducted in the 1970s and 1980s have made leaded gasoline (TEL added)
unavailable for on-road vehicles in the 1990s.
Carbon monoxide (CO). This is a colorless odorless and poisonous gas produced
from the incomplete combustion of carbon in fuels. Elevated exposures are serious
for those suffering from cardiovascular disease and leads to visual impairment, loss
of manual dexterity, and the ability to perform complex tasks. At high enough levels
it depresses cardiac activity and respiration, causes convulsions and ultimately death.
Over half the carbon monoxide emissions are from motor vehicles.
Sulfur dioxide. This is formed during burning of sulfur containing fuels. Motor
vehicles are a minor source of SO
2
due to the de-sulfurizing processes used in the
production of motive fuel components. Short-term exposure to high concentration
leads to reduced lung function, while longer exposures are associated with respira-
tory problems. Sulfur dioxide mixed with nitrogen oxide is a major contributor to the
formation of Acid Rain. This in turn causes acidification of lakes, rivers, and water-
ways. It damages crops and trees, and accelerates the corrosion of building materials
and coatings.
Nitrogen dioxide. Also known as nitrogen peroxide is a brown gas formed by high
temperature combustion of fuels. It is one of a family of nitrogen oxides which are
often treated as one species under the term NO
x
. Nitrogen dioxide is a severe irritant
to the lungs and can cause respiratory infections, pneumonia and bronchitis. Nitrogen
dioxide coupled with volatile organic compound (VOC) and ozone are the main
components of smog.
66 CHAPTER 2
Particulate matter. Dust, dirt, smoke, and liquid droplets form the particulate matter
in motor emission and pollutants. Some of the liquid droplets are formed in the
atmosphere by the condensation of sulfates, nitrates, and hydrocarbons. Fine particles
with diameter less than 2.5 µm are emitted by motor vehicles. Gasoline driven vehicles
however do not emit significant levels of particulate matter compared with diesel
driven engines. Particulate matter aggravates existing respiratory and cardiovascular
disease, damages lung tissue and may cause cancer. Fine particles of 2.5 µm or less
are considered more serious since they can penetrate easily into the respiratory tract
and are retained longer. Particulate matter also contributes to haze.
Ozone. This photochemical oxidant is found in the atmosphere from ground level
to 6 miles above the ground and again in the Stratosphere 6–30 miles above the
earth. At ground level Ozone together with the Nitrogen oxides, the volatile organic
compounds and sunlight are the major constituents of ‘Smog’. Ozone is a strong
oxidant and damages lung tissue, and reduces lung function.
More details of gas emission are given in Chapter 5.
Meeting the gasoline parameters
Prior to 1990 the performance and emission characteristics were mainly the responsi-
bility of the engine manufacturers with some notable changes imposed on the gasoline
manufactures. Notable among the restrictions imposed on the refineries in the gaso-
line manufacture was the restriction on the use of TEL (tetra ethyl lead) as an octane
enhancer. The EPA (environmental protection agency) had, as early as 1970 enforced
a program to reduce the addition of lead so that even before 1990 there was available
only ‘no lead’ gasoline for road vehicles. The ‘Clean Air Act’ of 1990 however put the
onus on the gasoline manufacturer for meeting the act’s requirements. In the USA and
indeed the North American Continent a program to introduce reformulated gasoline
was launched. This RFG allows the performance of the gasoline to be retained whilst
reducing the harmful emission caused by the traditional octane enhancers such as
aromatics (from reformates) and olefines (from cracked naphtha).
Reducing aromatics in gasoline. The most stringent environmental restriction im-
posed on aromatics in gasoline is on benzene in gasoline. This component in benzene
has now been reduced to levels below 1.0 %vol in the product. Refining processing
philosophy has undergone some extensive changes to meet this single requirement.
The following steps have needed to be taken in part or as a whole to meet this change:
r
Reducing reformer severity. This also reduces the quantity of the heavier aromatics.
r
Reducing the final boiling point of the gasoline. This essentially reduces the amount
of the heavier aromatics in the gasoline.
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 67
r
Increasing the quantity of isoparaffin. This is accomplished by saturating the ben-
zene ring and isomerization of the naphthenes to isoparaffins.
r
Reducing the aromatics in the cracked naphtha stock. Catalytic cracker naphtha is
high in olefins in the front end but high in aromatics in the back end. The reduction
of aromatics from this source is accomplished by lowering the cut’s final boiling
point.
r
Aromatic extraction using an extraction process similar to that used in produc-
ing the petrochemical aromatic complex feed (e.g., the sulfolane process). Only
about 20 of the largest refineries in North America has this extraction facility how-
ever.
Reducing the olefin in gasoline. Almost all the olefins and sulfur in the gasoline pool
come from the Catalytic Cracker naphtha with a relatively small amount from thermal
crackers. The following methods again in part or as a whole are used to reduce this
olefin content:
r
Alkylation and Etherification. The light olefins of C
5
can be fractionated out
and following a simple sulfur removal is feed to an alkylation process to pro-
duce good high octane C
9
alkylate. Alternatively the light fraction from the
cracked naphtha can be processed to the oxygenate TAME (Tertiary Amyl Methyl
Ether).
r
Isomerization of the C
6
and C
7
fractions. These two olefin components of cracked
naphtha may be hydrogenated and isomerized to provide a good octane rating. The
two olefin components are only small in quantity in gasoline they are however
highly reactive and their removal and conversion is necessary to meet the present
restrictions in gasoline manufacture.
Meeting the gasoline sulfur content. Almost all of the sulfur in gasoline comes from
the catalytic cracker and other thermal crackers. The current phase 2 of the RFG
program is expected to reduce sulfur in gasoline to around 30 ppm by weight; European
specifications are being lowered to 10 wt-ppm. To meet this new criteria refiners are
looking at the following approaches:
r
Route the heavy end about 20 %vol of the catalytic naphtha into the middle distillate
pool. This does not reduce the sulfur but it moves a large portion of it and the heavy
aromatics into other parts of the product slate. Thus reducing the sulfur and aromatic
content of the gasoline.
r
Either hydrogenate or treat with a caustic type wash the lighter portion of the cracked
naphtha. This is rich in olefins and sulfur. Treating by hydrogenation does reduce
the octane value of the naphtha in that it saturates the olefins to lower octane paraffin
or naphthene. Treating with sulfur extraction wash (e.g., UOP’s Merox process) is
the often preferred route.
68 CHAPTER 2
Table 2.10. A gasoline recipe prior to 1990
Component %vol Aromatics %vol Olefins %vol ON res clear ON ratio
Butane 3.75 0 0 92 3
LSR 12.5 10 2 69 8
Reformate 24.39 89 0 91 18
Lt crack naphthas 12.5 35 89 18
Hy crack naphthas 21.19 53 90 19
Alkylate 25.67 0 0 95 24
Total 100.00 31.0 12.0 90
SG@60
◦
F 0.7749
RVP 7.0 psig
r
The back end of cracked naphtha is high in sulfur, aromatics, and olefins. This
may be hydrogenated using a catalyst selective in removing sulfur, and leaving the
aromatics essentially as they were.
r
Hydro-treating of the catalytic cracker gas oil feed is becoming quite common. This
significantly reduces the sulfur content of all the cracked products from the catalytic
cracker unit.
Manufacturing gasoline
The requirements of the clean air act of 1990 and additions to it since has changed
refining requirements to meet this product’s need quite significantly. Prior to this
date much of the gasoline finished product recipe consisted of normal light naphtha,
a reformate, usually some cracked naphtha, and possibly an alkalate some butane
may be included if required to meet volatility. The Clean Air requirement and its
subsequent additions forces a reduction of both the reformate and the cracked stock
(see Tables 2.10 and 2.11).
Table 2.11. A gasoline recipe post 1996
Component %vol Aromatics %vol Olefins %vol ON res clear ON ratio
Butane 1 0 0 92 0.9
LSR 15 0 0 69 10.0
Reformate 30 60 0 80 24.0
Cat naphthas 32 25 35 82 26.0
Alkylate 20 0 0 95 27.0
MTBE 2 0 0 110 2.1
Total 100 26 11.2 90.0