Environmental Impact of Industrial Processes and Products.

2023

Prof. Gabriella Garbarino

Gabriella.Garbarino@unige.it

Prof. Guido Busca

Guido.Busca@unige.it

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Reproduction and re-use of present material is forbidden. For study purpose only.
 3. Oil – related technologies.
Oil composition
Crude oil is composed of stable hydrocarbons, i.e. those are not very reactive, i.e.
linear paraffins
branched paraffins
cyclic paraffins or naphthenes: (alkyl)cyclopentanes and
(alkyl)cyclohexanes
bicyclic paraffins (alkyl)decalines
aromatics (alkyl)benzenes and (alkyl)tetralines
(alkyl)naphthalenes
polynuclear
Main impurities are sulphur compounds, nitrogen compounds and organometallic
compounds containing mainly Fe, Ni, V. Elemental composition by weight:
carbon 83 to 85%,
hydrogen 10 to 14 %
nitrogen 0.1 to 2% (mainly cyclic amines)
oxygen 0.05 to 1.5% (few oxygenated organics
sulfur 0.05 to 6.0% (mercaptans RSH, mainly cyclic organic sulphides)
metals < 0.1% (mainly Ni, V and Fe in metalloporphirines)
gasoline kerosene gasoils lubricants fraction

Composition of crude oil distillation fractions

Teb °C (1 Density Main compunds S H/C
atm) g/ml range % wt
Gas < 40 C1-C5 0,001
Naphtha/gasoline 40-180 0,70 C6-C10 0,011 2-2,2
Kerosene 180-230 0,79 C11, C12 0,20 1,9-2
Light gasoil 230-320 0,85 C13-C17 1,40
Heavy gasoil 320-400 0,90 C18-C25 2,0 1,8-1,9
“Lubricant” oil 400-520 0,91 C26-C38 3
Vacuum residue > 520 1,02 > C38 4-6 1,6

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Reproduction and re-use of present material is forbidden. For study purpose only.
 Properties of some crude oils.
light heavy
Gullfaks Alaska Texas Maya Athabasca
(Norway) (Mexico) (Canada)
Gravity °API 37 31 27 22 8
Density g/ml 0,84 0,87 0,89 0,92 1,01
Sulfur %w/w 0,3 1,0 2,2 3,5 >4
Nitrogen ppm wt 716 1600 1015 3600 > 4000
Naphtha % vol 23 23 13 17 1
Kerosene %vol 17 12 13 12 1
Gasoil %vol 18 16 17 9 8
VGO % vol 28 28 31 27 34
Residue % vol 12 19 26 33 56
API degree: (141.5/s) – 131.5 where s is density at 60 °F (288,6 K). Normally density
at 288 K (15 °C) is used.
Oil extraction technologies
A vertical well is drilled into the ground and into an oil-bearing reservoir with a
derrick. The crude is then pumped to the surface. While the underground pressure in
the oil reservoir is sufficient to force the oil to the surface, all that is necessary is to
place a complex arrangement of valves (the Christmas tree) on the well head to
connect the well to a pipeline network for storage and processing. Sometimes pumps,
such as beam pumps and electrical submersible pumps (ESPs), are used to bring the
oil to the surface; these are known as artificial lifting mechanisms. Secondary
recovery techniques increase the reservoir's pressure by water injection, natural gas
reinjection and gas lift, which injects air, carbon dioxide or some other gas into the
bottom of an active well. On average, the recovery factor after primary and secondary
oil recovery operations is between 35 and 45%. Tertiary recovery technologies, with
steam injection, allows another 5% to 15% of the reservoir's oil to be recovered.

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 Transport of oil and oil products: pipelines
Pipelines are a long-established, safe and efficient mode of transport for crude oil and
petroleum products. They are used both for short-distance transport (e.g. within a
refinery or depot, or between neighboring installations) and over long distances,e.g.
from inland production areas to refineries or to oil terminals, reversely, from oil ports
to refineries. Oil pipelines are made from steel or plastic tubes with inner diameter
typically from 4 to 48 inches (100 to 1,220 mm). Most pipelines are typically buried
at a depth of about 3 to 6 feet (0.91 to 1.83 m). To protect pipes from impact,
abrasion, and corrosion, a variety of methods are used. Intermediate reservoirs and
pumping systems are also needed.

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In Italy the following refineries are active today:
Eni Div. Refining & Marketing Sannazzaro (PV) 10,0 Mton/y
Sarpom, Trecate (NO) (Exxonmobil/IP) 9,0
Iplom , Busalla (GE) 1,9
Eni Div. Refining & Marketing, Livorno 4,2
Api Falconara M. (AN) 3,9
Eni Div. Refining & Marketing Taranto 5,2
Isab Priolo (SR), now Lukoil 19,4
Esso Augusta (SR), now Sonatrach 8,0
Raffineria di Milazzo, Milazzo (ME) 10,6
Saras Sarroch (CA) 15,0
A number of plants, among which refineries of Genova/Bolzaneto (ERG), La Spezia, Mantova,
Cremona, Porto Marghera (Venezia), Roma, Gela,.., have been closed or undergraded to deposits or
under modification to “biorefineries”.
Storage tanks
Refineries and petrochemical complexes are large plant where a number of plants are
located. A large number of liquid and gaseous flows and also solids are treated as raw
materials, intermediates and final products. Thus, a large number of tanks are needed
to store them before, after and in between the different process steps. These tanks can
have different sizes, ranging from 2 to 60 m diameter or more. They are generally
installed inside containment basins in order to contain spills in case of rupture of the
tank The minimum capacity of the basin volume should be equal to the capacity of
the largest tank plus 10% of the sum of the capacities of others. To prevent a spill or
other emergency the walls of the containment basin must be resistant to the product
and must be able to withstand considerable pressure. The drain Valve, which should
be incorporated into the outer side of the containment basin, must be closed to
prevent possible contamination to the environment.

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Basically there are eight types of tanks used to store fluids:
1. Fixed-roof tanks. They are the least expensive to construct and are generally
considered the minimum acceptable equipment for storing liquids. A typical fixed-
roof tank consists of a cylindrical steel shell with a cone- or dome-shaped roof that is
permanently affixed to the tank shell. Storage tanks are usually fully welded and
designed for both liquid and vapor tight.A Breather Valve (pressure-vacuum Valve),
which is commonly installed on many fixed-roof tanks, allows the tank to operate at a
slight internal pressure or vacuum.
2. External floating roof tanks. They consist of an open-topped cylindrical steel
shell equipped with a roof that floats on the surface of the stored liquid, rising and
falling with the liquid level. External floating roof tank is used for the storage of
volatile petroleum products, such as crude oil, fuel oil, kerosene, etc. There is an
annular space between the floating roof and storage tank wall, the annular space has a
sealing device, so that the liquid in the storage tank can be isolated from the
atmosphere when the floating roof floats up and down, greatly reducing the
evaporation loss of liquid during storage. Compared with fixed roof storage tank,
adopting an external floating roof tank to store oil products can reduce the
evaporation loss about 80%.
3. Internal floating roof tanks. They have both, a permanent fixed roof and a
floating roof inside. The function of the fixed roof is not to act as a vapor barrier, but
to block the wind.
4. Horizontal tanks are constructed for both above-ground and underground
service. Horizontal tanks are usually constructed of steel, steel with a fiberglass
overlay, or fiberglass-reinforced polyester. Horizontal tanks are generally small
storage tanks, constructed such that the length of the tank is not greater than six times
the diameter to ensure structural integrity. They are usually equipped with pressure-
vacuum vents, gauge hatches and sample wells, and manholes to provide accessibility
to these tanks. In addition, underground tanks may be cathodically protected to
prevent corrosion of the tank shell.
5. Spherical pressure tanks: this type of vessel is preferred for storage of high
pressure fluids. A sphere is a very strong structure. The even distribution of stresses
on the sphere's surfaces, both internally and externally, generally means that there are
no weak points. Spheres however, are much more costly to manufacture than
cylindrical vessels. Storage Spheres need ancillary equipment similar to tank storage
- e.g. Access manholes, Pressure / Vacuum vent that is set to prevent venting loss
from boiling and breathing loss from daily temperature or barometric pressure
changes, access ladders, earthing points, etc.An advantage of spherical storage
vessels is, that they have a smaller surface area per unit volume than any other shape
of vessel. This means, that the quantity of heat transferred from warmer surroundings

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to the liquid in the sphere, will be less than that for cylindrical or rectangular storage
vessels.
6. Cylindrical Pressure Vessel. Cylinders are widely used for storage due to their
being less expensive to produce than spheres. However, cylinders are not as strong as
spheres due to the weak point at each end. This weakness is reduced by hemispherical
or rounded ends being fitted. If the whole cylinder is manufactured from thicker
material than a comparable spherical vessel of similar capacity, storage pressure can
be similar to that of a sphere.

Oil tankers and oil terminals

Modern oil tankers fall into two categories—crude tankers and product tankers.
Crude tankers transport the unrefined oil to refineries and product tankers move the
petroleum products to markets where they can be sold. The product tankers are
smaller than crude tankers.
There are more than 600 very large crude carriers (VLCC) class tankers today
carrying over 1 million gallons of oil each. They carry around one-third of the
world’s tanker volume. A modern ultra-large crude carrier (ULCC) can be 1,300 feet
long and have a capacity of 500,000 DWT (DeadWeight Tonnage). Deadweight
tonnage measures the maximum total cargo, provisions, fuel, ballast and crew weight
that a ship can safely carry. The larger size vessels mean the price of shipping the oil
has fallen to roughly 5-10 percent of the price per barrel.

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The main reason for the expansion in size of oil tankers is economical. The bigger a
tanker is, the more oil it can move, and the more efficient the journey will be. The
introduction of larger oil tankers has also brought with it a bigger danger of massive
oil spills. In recent years, double hulls are required. The double hulls are exactly as
they sound: one hull inside the other as an extra layer of protection if the ship runs
into trouble.

The Multedo/Pegli Oil Terminal is one of the biggest over Italy and Mediterranean
together with the Terminals of Trieste and Marseille. Other important terminals are at
Augusta, Melilli and Sarroch. Multedo Oil Terminal is able to handle 30 millions of
Tons of products per year;a 2000 kms long pipe line connects the terminal to the most
important european and northern italy refineries, including the ENI refinery at
Sannazzaro de’Burgundi and the IPLOM plant in Busalla. The total surface on which
the terminal stands is 345000 sqm ,13400 of which are land areas. Since 1960,when it
was on the beginning,this terminal has been continuosly modernized; actually it is
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based on an inner port with 4 main piers able to gather up to 8 tankers and 1 long
westerly wharf for special chemical products and able to gather up to 4 small
tankers.This wharf is equipped with special gears according to the products treated.

The Vado Ligure buoy field. In the the vado Ligure harbour, Sarpom (Exxonmobil-
TotalErg) operates a buoy field located around 0.7 miles from the coast, where oil
tankers upo to 316000 tons DWT can moor. Two underwater pipelines convey the oil
to 7 on-shore tanks (overall capacity 360000 m3) from where it reaches the Trecate
refinery through a 146 km 20” oil pipeline.
In the Vado Ligure harbour, IP operates an unloading plant for oil products,
consisting in a mooring platform (450 m offshore), connected via underwater pipeline
to a coastal depot for fuel and lubricants.

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 The refinery for the production of fuels
Automotive Fuels
Gasolines.
Motor gasoline and diesel fuel are the most common liquid fuels for automotive,
produced in oil refineries. They are “middle distillates” intermediate between the gas
fractions, which represent refinery by-products and are used to produce LPG
(Liquefied Petroleum Gas, C3+C4) and burned as refinery fuels, and heavy gas oils,
the use of which is now decreasing. For this, the refinery tends to increase the
volumes of these middle distillates fractions, with processes that crack heavier
fractions (cracking processes) and "combine" lighter molecules. Indeed, the gasoline
fraction is about 20% of the main oils, but gasoline fuel for cars is more than 40% of
the products of the refinery, in average.
Commercial gasolines (Teb 30-200 °C) and Diesel fuels for motor vehicles (T eb 170-
360 °C) are mixtures of various fractions derived from various treatments of the
refinery, and only in part obtained by simple distillation.
The "technical" quality of gasoline is mainly associated with its anti-knocking
properties, i.e. the ability to not burn before the spark produced by candles acts as
ignition agent. The best gasoline burns slowly, until a certain limit. The rate of the
combustion reaction depends on the speed of the slowest step (the "rate determining
step") which is the abstraction of a hydrogen atom from the hydrocarbon molecule
by an oxygen molecule. For this, the aromatics have a very high anti-knock
properties, and branched paraffins (whose reactivity is dominated by methyls) have
an antiknock property better than that of linear paraffins.
The octane number (ON) is the measure of the antiknocking properties of a fuel
useful to evaluate its performance in “Otto cycle engines” (i.e. gasoline fueled
engines): it is the % of isooctane (2,2,4-trimethylpentane) in a mixture of isooctane /
n-heptane that has the same anti-knocking properties of the mixture considered.

ON is measured in two different conditions, RON (research octane number) and

MON (motor octane number) that correspond to two different operating conditions of
the engine. RON simulates the fuel performance under low severity engine operation
and is determined by running the fuel in a test engine with a variable compression
ratio at 600 rpm. MON simulates the fuel performance under more severe engine
operation using the same test engine but with a preheated fuel mixture, at 900 rpm
and with variable ignition timing. In Italy the RON is given, in the US the average
(RON + MON / 2) is given.
The current engines for cars require motor gasolines (mogas) with RON ~ 95-98
(R+M/2 ~ 88-95). For some Avio gasoline (for aircrafts, Avgas 100) a minimum of
MON 100 is required. These values of ON were obtained with so-called "super"

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gasolines (no longer used for cars), and are obtained for Avio gasolines (avgas)
mixing small amounts of tetraethyl-lead (Pb(CH2CH3)4), a powerful anti-knock
additive. After the introduction of catalytic converters for cars, with the so-called
"three-way catalysts" (based on Pt or Pd), used in order to reduce the amount of CO,
NO, and unburned hydrocarbons in the exhaust gases, the use of tetraethyl-lead in
gasoline for cars was no more possible, because Pb deactivates noble metal catalysts
forming inactive alloys. Thus, green gasoline (unleaded) is now used. In some
nations organo- manganese anti-knock additives are used today.
To obtain the required ON, mixing in the pool of gasoline fractions with highly anti-
knocking components is necessary. Aromatics have excellent anti-knocking
properties but are the most responsible for the formation of unburned polycyclic
aromatic hydrocarbons, of significant toxicity. Additionally, benzene is one of the
most active known carcinogens. For this reason, the amount of benzene in gasoline
must be kept under the limit of 1% by law, and that of aromatics is also limited.
Olefins may have good octane but are also slightly toxic and limited by law. The best
gasoline components, combining good octane and non-toxicity, are certainly
branched paraffins. Thus, several processes are performed in refineries producing
branched alkanes (such as catalytic reforming, isomerization, alkylation,
oligomerization, etc.). In any case, further high ON components are needed to obtain
> 95 RON.
Oxygenates have high ON too. Methanol has good anti-knocking properties but
demixes from gasoline in the presence of moisture. The mixture MAS (methanol-
higher alcohols) seems usable but is expensive. The branched ethers MTBE (methyl
tert-butyl ether), ETBE (ethyl tert-butyl ether), TAME (tert-amyl methyl ether) and
TAEE (tert-amyl ethyl ether) have excellent properties. MTBE has been used since
30 years in unleaded petrol.
The bio-ethanol is used as a neat fuel (E100, ON 129) in Brazil and Argentina, or
mixed with gasolines at 85 % (E85, ON 105) in the USA. In the EU at least 1% of
biofuel, usually bioethanol, must be present in the commercial gasoline, while no
more than 10 % can be used (E10) to fulfill the oxygen limit of 3.7 % w/w.

Time evolution of EU legislation (summertime type gasoline, private cars).

1990 1995 1998 Euro 3 Euro 4 Euro 5 Euro 6
2000 2005 2009 9/2014
S ppm wt max 1000 500 500 150 50 10 10
benzene % v/v max 5 5 1 1 1 1 1
olefins % v/v max 18 18 18 18
aromatics % v/v max 42 42 35 35 35
oxygen % w/w max 2.7 2.7 2.7 3.7
3
density kg/m 720-775 720-775
Vap. press. kPa* max 80 60 60 60 60
RON min 95
MON min 85
Pb mg/l max 5

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 Octane number of hydrocarbons

Diesel fuels
The "technical" quality of Diesel fuels is mainly associated with its knocking power,
that is, the ability to give rise to explosion in the working conditions of the Diesel
engine. The detonating power is maximum for linear paraffins, lower for branched
and cyclic paraffins and even lower for aromatics. The cetane number (CN) is the
measure of the detonating power of a Diesel fuel: is the % of cetane (n-hexadecane,
CN = 100) in a mixture cetane / 1-methyl-naphthalene (CN = 0) that has the same
properties of the detonating mixture considered. More recently, 2,2,4,4,6,8,8- hepta-
methyl-nonane (Isocetane), has been
substituted for 1-methyl-naphthalene as a
reference, with CN = 15.
Diesel fuels on the market today have a
CN = 51. They must also have a
solidification point sufficiently low to
allow the engine ignition at very low T.
“Cetane-improvers” additives are
commercially available as
2-ethyl-hexyl-nitrate
CH3
CH2 O
H3C CH2 CH2 CH2 CH CH2 O N
O

and diethoxyethane
CH3CH(OCH2CH3)2
and ignition improvers (e.g. diethylether).
Evolution of the specifications for Diesel fuel for private cars in Europe.
1990 1994 1995 Euro 3 Euro 4 Euro 5 Euro 6
2000 2005 2009 9/2014
cetane n. min 49 49 49 51 51 51 51
S ppm max 3000 2000 500 350 50 10 10
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Density Kg/m 860 max 820-845 820-845 820-845 820- 845
T95 °C 370 360 360 360 360
HPA.% wt max 35 11 11 11 8
Biodiesel % vol 5 max 5 max 7 max 7 max

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 Aviation Fuels
density Distillation°C flash S max Freezin MON
15 °C point°C ppm g Lean/rich
g/ml point°C
AvGas 100 0.72 T10 75 Pb 500 - 58 100/130
TMAX170 g/l max 1.12
JetA 0.775 T10 205 38 aromatics 3000 - 40 ON/CN not
kerosene 0.840 TMAX 300 25 % max relevant

Other liquid fuels from refineries

Gasoline for agriculture RON 95 S 50 ppm
Heating gasoil S 20000 ppm
Bunker oils: Marine Gasoil (MGO) to be used in ECA zones: 0.1% S
Marine Fuel Oil can be used in high sea: 0.5 % S
For ships with SO2 scrubbing system: High Sulphur Marine Fuel Oil, 3.5 % S.

Liquified Petroleum Gas (LPG)

Household : 25 % C3, 75 % C4, olefins max 10%, S < 0.01 % wt, d15°C 0.550-0.565
Commercial : 95 % C3, propylene max 10%, S < 0.01 % wt, d15°C 0.505-0.51

The refinery

The Sarpom refinery (Exxonmobil/API) in Trecate (Novara)

The refinery is a very complex structures where a number of processes are eprormed
to purify oil fractions mainly from sulphur and to increase the amount of more
valuable products (gasoline and Diesel oils) from the less useful ones (heavy
fractions and gases)

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 5.3 THE REFINERY
Refinery Flowsheet

sulfur recovery
sulfur
light ends GPL
gas plant

light naphtha oligom

lt naphtha HT or sweetening isomerization gasoline pool

naphtha reforming gasoline post treat

atm still
hvy naphta hvy naphtha HT
arom extraction
desalter BTX
crude light distillate
sweetening lt dist. HT
kerosene Jet fuel Diesel heat
heavy distillateheavy distillate HT Diesel post treat
atm GO

Mild HT
alkylation
atm resid FCC

light VGO tail gas treating

hydrogen generation heavy VGO
hydrocracking
vac MTBE
stillDAOdelayed coking
pet-coke
solvent DA
heavy
visbreaking fuel oil
lube treating
lube oils

asphalts
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 Desalting
Crude oil, despite having already undergone a process of desalination at the
extraction fields, must be further desalted, to avoid problems of precipitation of solids
and corrosion. The process consists in a washing with water (3-10 vol% at 100-150 °
C), in the presence of an electric field which breaks the salted water / oil emulsions.
Distillation Trains
Atmospheric distillation (topping)
It operates at 1,5-2,5 atm in a continuous distillation column, 5-6 meters radius and
30-50 m high, 30-60 trays (20-30 theoretical trays), 0.4-1 m away. The temperature at
the base is 380-450 °C, obtained by preheating in heat exchangers cooling the
different product fractions as well as with the fumes of a burner.

Atmospheric distillation tower

vacuu

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 Cogeneration plants in refineries
Refineries are usually autonomous in the generation of electrical energy, to not
depend from possible blackouts in the national electricity network. Refineries have
their own power plant and sell in normal conditions energy to the national network.
In case of need, they can instead buy energy from the network. The burner of the
atmospheric distillation column can be coupled with the power generation plant in the
refinery, in cogeneration systems. The furnace can be heated by the combustion gas
of a gas-turbine based generation system. Steam to strip the column is generated in
the same furnace.

Cogeneration associated to crude preheating. Preheating burner

Vacuum distillation
The atmospheric residue is preheated to 380-450 °C. The distillation occurs at a
pressure of 10 – 30 Torr, produced by flows of high pressure steam in suitable
ejectors. The vacuum column is quite stubby and low, with around 25-30 trays, or,
more commonly today, with different packed sections between the trays needed to
extract fractions.

Vacuum distillation in a lubricants bases producing refinery.

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 Vacuum generation system.

Treatment of light fractions – refinery gas plants

The light fractions from atmospheric distillation are separated at the head of the
topping tower, by cooling to room temperature. The liquid fraction (stright run light
naphtha) is further treated in a stabilizer, where lighter compounds (mainly butane)
are distilled off. Gases from atmospheric distillation are light alkanes that are
separated by cryogenic distillation in the Saturated (Sat) Gas Plant, similar to that
seen for separating NGL. In general, ethane and methane are not separated, being
used to feed burners in the refinery. Propane and butanes are separated to prepare
LPG. Isobutane can be separated, to feed the alkylation process.
Unsaturated (unsat) gas plants recover light ends from a number of refinery off-gas
sources such as from FCC and delayed coker overhead accumulators or fractionation
receivers. Unsaturated hydrocarbons are separated and used for alkylation,
oligometization, etc.

Desulphurization and Hydrotreatments

Impurities in oil fractions.
Crude oil contains heteroatoms such as S and N in the form of sulfides (mercaptans,
thioethers, and heterocyclic compounds such as thiophene and benzothiophenes,
dibenzothiophenes), amines and nitriles, which, besides giving a heavy smell to
vapors, may poison catalysts and produce SOx and NOx during combustion. These
compounds are present in the medium fractions and especially in the heavier ones.
In the heavier fractions, metals (up to 1000 ppm in the residue from the vacuum
distillation) are also present, in particular vanadium and nickel, as solubilized metal-
porphyrin complexes. During the combustion of heavy fractions, they give rise to
dust emitted in the atmosphere as particulates and, also, they poison
hydrodesulfurization catalysts. Moreover, to improve the technical (cetane number)
and environmental quality of Diesel fuels today also the concentration of aromatics,
especially the polynuclear ones (naphthalenes), in gas oils should be reduced.

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 RSH RSR N
S
S S H
mercaptans sulfides thiophene benzothiophene dibenzothiophene carbazole

RNH2 R2NH R3N R C N

N N
N
amines nitriles pyiridine quinoline acridine

N pyrene

N Ni N naphthalene anthracene
N
phenantrene

Nickel porphyrin

Caustic washing process for Jet Fuel sweetening

Caustic soda washing processes are used since decades with the main purpose of
deodorization (sweetening) petroleum fractions, malodorous because of the presence
of mercaptans, very smelly. The process based on the conversion of mercaptans into
disulfides, not smelly, in the presence of alkali, oxygen and catalysts (cobalt
complexes):
RSH + NaOH  RS-Na+ + H2O
2 RS-Na+ + ½ O2 + H2O  RSSR + 2 NaOH

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 Hydrotreatments (HT)
The purification of the various oil fractions is obtained today mostly through a family
of processes called Hydrotreatments (HT). These reactions consume much hydrogen
which, in refinery, is essentially produced during the catalytic reforming process.
However, given the enormous development of hydrotreating processes, the balance of
hydrogen in the refinery is going negative. Many refineries are equipping themselves
with the processes of production of hydrogen via synthesis gas (e.g. by steam
reforming of methane) to meet the deficit of hydrogen.
The typical reactions which can occur during the hydrotreating processes, depending
on the operating conditions, are:
hydrodesulphurization (HDS) of organic sulphides: H  - 60
kJ/molH2 es.
3 H2 +
+ H2S
S
At higher temperature and pressures, hydrocracking (HCR) occurs i.e. large
molecules brack uinto smaller ones hydrogenolitically:
hydrodealkylation of alkylaromatics: H  - 20-50 kJ/molH2

+ H2 +

es.

NHT: Naphtha hydrotreatment (pretreatment to catalytic reforming); ULSK: Ultralow sulphur kerosene;
FCC-PT: FCC pretreatment; MHC: mild hydrocracking; E-bd: ebullated bed; WABT: weighted averaged
bed temperature.

UDHDS = Ultra Deep Hydro-De-Sulphurization of Diesel gasoils. LHSV 0.7-

1.5, H2/HC ratio 250 Nm3/m3, 355 °C, 57 bar.

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 Trickle bed hydrocracking
Different kinds of hydrotreatments of heavy fractions have been developed. VGOs
and/or DAOs can be converted into low sulphur middle distillates by mild
hydrocracking or high conversion hydrocracking where hydrodesulphurization is
combined with hydrogenolytic cracking. Due to the medium-low volatility of the
feed, trickle fixed bed reactors are used. They are multiple fixed bed reactors where
the feed is a gas/liquid mixture. Several reactors or beds are frequently used, with
hydrogen quenching. In the first stage, sacrificial hydrodemetallation catalysts
(HDM, mostly based on low value clays) are loaded. Later, hydrodesulphurization
(HDS) catalysts are loaded, followed by catalysts with high hydrodenitrogenation
(HDN, usually of the NiMo type) activity. After, catalysts with high
hydrodearomatization (HDA) activity are loaded and finally catalysts with high
hydrocracking (HCR) activity are used such as combinations of Ni-USY faujasite
mixed with NiMo or CoMo sulphides supported on alumina.

Configuration for trickle bed

hydrocracking of DAO

Trickle bed hydroctrackers Delaware City refinery.

LCD Unionfining
UOP Process for the
hydrotreatment of
heavy residues for
the production of
fuels or feeds for
HCR, FCC or
Cokers. The first
reactor (guard
reactor) contains a
catalyst for the
sacrifical
hydrodemetallation.
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 Fluid Catalitic Cracking (FCC)
The FCC process is the most modern version of cracking of heavy gas oils in the
refinery, which have the purpose of producing light fractions (naphtha and gasoline)
from atmospheric residues (AR), vacuum gas oil (VGO) or deasphalted oil (DAO). It
is to pass heavy oils on solid acid catalysts at temperatures of 700-500 ° C. The
catalytically active phase (originally montmorillonites, then synthetic silica-aluminas,
now synthetic acidic zeolites, usually Faujasites Y exchanged with rare earths, REY)
is dispersed (eg. 40%) in a matrix consisting of binders (kaolin, silicas, aluminas) and
additives. The reactions primarily involved in cracking processes are the following:
1. Cracking of paraffins: paraffin  paraffin + olefin
C15H32  C7H16 + C8H16
2. Cracking of alkyl-napthenes: alkyl-naphthene  naphthene + olefin

C8H17  + C8H16

3. Cracking of alkyl-aromatics: alkyl-aromatic  aromatic + olefine

C8H17  + C8H16

These are two reactor-systems, one for the cracking reaction and the other for the
continuous catalyst regeneration, between which the fluidized powder moves
cyclically. The reagent mixture is fed along with steam at the base of the "raiser" a
vertical tube where it comes into contact with the freshly regenerated and very hot (>
700 ° C) catalyst. The reaction takes place essentially here, where reagents and the
catalyst raise at a speed of 10-20 m/s up to the reactor, now mostly called
“disengager”. The reaction is completed at 480-550 ° C and a slight overpressure of 2
atm,   3-10 sec. The partially coked catalyst is separated from the reaction
products by means of cyclones, is "stripped" with steam and is conveyed to the
regeneration reactor. This is a fluid bed burner. Here the coke burns generating
temperatures of 650-750 ° C, at  2 atm,   15 min, and the catalyst, cleaned, is
again pushed up in the raiser by the flow of the feed. The heat for the endothermic
cracking reaction is generated by the combustion of the coke formed on the catalyst.
Thus the overall process is autothermic or even exothermic because the generator flue
gas may contain big amount of CO that can be burner later in a steam generator to
recover energy. However, part of the hydrocarbon mass is lost. The gasoline yield is
usually in the range 50-60 %, with near 20 % of gasoils (LCO+HCO) and near 20 %
of olefin-rich gases. Thus the “liquid yield” is generally lower than 80%. The FCC
processes may be carried out on hydrotreated or non-hydrotreated gasoils. The main
product of the process is a "gasoline FCC", with good NO (90-94 RON) but rather
rich in benzene and aromatic and especially in sulfur (200-40 ppm using feeds
previously “mildly hydrotreated”).

5
Flexycracking Process (Exxomobil)

5
 Treatments of the Bottom of the Barrel
The recent utilization of oil shales and bituminous sands as well as the treatment of
oils of lesser quality, implies the conversion of big amounts of solid or semisolid
residues.
Processes that can transform all or almost all of these masses into useful compounds
were then recently developed, producing light distillates and / or hydrogen from
them. Among these we have:
Visbreaking (Viscosity breaking)
Visbreaking is moderate thermal cracking process. The vacuum residue is heated at
460-480 ° C and 5-20 atm in a tubular furnace, with relatively short contact times.
The product is cooled and then fractionated. The heavier products are distilled under
vacuum. The main product is a more fluid heavy gasoil but about 30% of distilled
liquids are usable in the Diesel pool.
Solvent deasphalting (SDA).
Is a solvent extraction process: liquid propane or butane or pentane extract the non-
aromatic components (lubricating oils or fuels) from asphaltene rich heavy oil. The
DAO (de-asphalted oil) is an excellent feed for catalytic cracking and for the
hydrocracking. The residues are used as bitumen and asphalt.
Coking.
Coking is a deep thermal cracking with high contact times at 480-550 ° C, obtaining
the production of coke and recycling the vapors to the distillation tower. It operates
with one or more pairs of reactors, working alternately with cycles of 24 hours.
Gasification of residues from refining and semi-solid components.
The gasification processes originally developed for coal conversion (see pp. 88-92)
can be easily extended to solid or semisolid refinery residues, ultra-heavy crude oils,
tar sands, biomasses and mixtures thereof. It produces a syngas used to make
methanol, hydrocarbons via the Fischer-Tropsch reaction, hydrogen, energy.
Deep hydrocracking.
Various deep hydrocracking technologies in the presence of catalysts in slurry phase
at 450-480 ° C and 150-250 bar of hydrogen have been recently developed. Among
these, the ENI Slurry Technology (EST) is a deep hydrocracking in the slurry phase
in the presence of catalysts based on unsupported molybdenum sulfide filaments
(MoS2) at 450 ° C and 150 bar.

Catalytic Reforming and synthesis of aromatics

The original purpose of the Catalytic reforming process was to increase the octane
number of gasoline, by increasing the content of aromatics (BTX, benzene, toluene
and xylene) at the expense of linear paraffins. Today, given the need to limit the
content of benzene and aromatics (for environmental reasons) in gasoline, this
process has partially changed its face. In fact, in the refinery process (Octanizing
Catalytic Reforming), it is the process that produces hydrogen to be used in
hydrotreatments, and, together, a high octane gasoline fraction (the reformate), trying
to limit benzene production. Thus it is mostly carried out on dehexanized gasoline
(75 ° C <Teb <200 ° C). In the petrochemical version of the process (Aromizing

5
Catalytic Reforming), aimed at the production of BTX aromatics as chemical
intermediates, it is carried out using depentanized (45 ° C <Teb <200 ° C) gasoline, to
allow the production of benzene too. BTX are extracted, later, from the “reformate”.
Catalytic reforming is carried out at 480-530 °C. The bifunctional catalysts consist of
about <1% wt / wt of Pt-Re-Sn alloy particles supported on chlorinated -Al2O3 (175-
300 m2/g), extruded into particles of 1-3 mm diameter. Recently, new catalysts were
developed based on Pt- KLzeolite, which are highly selective towards the production
of benzene (RZ platforming from UOP, Aromax from Chevron). The reactions are:
1. dehydrogenation of naphthenes. H = + 221 kJ/mol,
R R endothermic equilibrium reaction, favored at
low P and high T, metallic catalysis, fast
+ 3 H2 mostly occurs on naphthenes already present in
the feed in the first reactor that cools very
much
2. naphthenes isomerization
H = - 16 kJ/mol
R R'
slightly hexothermic, acid catalysis, slow, is
followed by reaction 1

3.n-paraffins skeletal isomerization (cyclization)

R'
R' + H = + 40 kJ/mol
H2 endothermic, bifunctional
catalysis, slow, is followed by
reaction 1 producing paraffin
4.n-paraffin skeletal isomerization (branching) aromatization of dehydrocylization

R' R' H = - 5.9 kJ/mol

slightly hexothermic, favored for
5. hydrogenolysis or hydrocracking paraffins with more than 7 atoms
acid catalysis
R' R' H ~ - 45 kJ/mol
+ H2 +
metallic catalysis
slow
6.catalyst coking and deactivation

The overall reaction is endothermic, with co-fed hydrogen (to limit the coking of the
catalyst), with more reactors at P = 15-35 atm with intermediate heating. The space
velocity LHSV (liquid hourly space velocity) is 1-3 h-1. The reactors are usually
radial downflow with intermediate heating. The catalyst needs more or less frequent
regeneration, depending on the process configurations. The catalysts regenerated by
coke burning, chlorinated and re-reduced are too reactive. They should be slightly
poisoned (by sulfidation) before operating.

5
There are three process families:
1. Semiregenerative processes:
They operate with three, four or five reactors in series with intermediate heating in a
furnace to provide the heat of reaction. The reactors have increasing size to contrast
the progressive lowering of the reaction rate. The temperature decreases very much in
the first reactor where aromatization of naphthenes occurs. In the other reactors
skeletal isomerization and cyclization of paraffins (slightly exothermic) occur too,
producing further naphthenes and aromatics. After the last reactor, gases (mainly
hydrogen) separate from the liquids and are recirculated to the first reactor. These
systems are shut down about every six months for the catalyst regeneration procedure
performed in situ with appropriated devices.
2. Cyclic processes.
The scheme is identical to the previous one but it has an additional reactor. One of
the reactors in turn, by means of valve systems, is in reactivation phase (in different
streams to burn coke, chlorinate, reduce and slightly sulphide the catalyst) while the
others are in operation. Thus, shut down of the entire plant for regeneration is not
needed. To allow rotation, the reactors have the same size, thus not working in
optimal conditions. Coking is faster in last reactor where the average temperature is
higher. Thus the last reactor is regenerated more frequently. It can operate in
conditions that cause rapid coking of the catalysts (low pressure and high
temperature) but produce mixtures with a higher octane number and higher aromatics
content.
3. Moving bed processes.
Also in the case of moving bed processes, the pattern is identical, with three or four
reactors in series, normally with growing volumes, with intermediate heating.
However, the reactors are constructed in a manner that the moving catalyst passes
from the first reactor to the following and, finally, in a regeneration reactor where
reactivation procedure is performed. After, the catalyst is recirculated to the first
reactor at the top. In the case of the UOP process the first three reactors are one under
the other and the catalyst falls by gravity from the first to the second and third, and, in
a parallel path, along the fourth reactor. Through a system of carrier gas, the catalyst
is pushed into a regeneration reactor and then sent back into the head of the first and
fourth reactor. In the IFP process the reactors are three or four side by side and in
series. A carrier gas (nitrogen) transports the catalyst on top of the reactors, one after
the other, and then to the regenerator.

5
UOP RZ platforming, a semiregenerative process

Most of catalytic reforming processes use radial

flow reactors that produce far less pressure drop
across the bed than axial flow reactors. Not only
does this produce a higher yield, it’s more energy
efficient as well.
Radial flow systems increase contact efficiency
between the process stream and catalyst bed.
Because of this, vessel size can be reduced.
The outer screen may either be a basket or an
arrangement of scallops (see above,right) or a
perforated sheet

A cyclic catalytic reforming process

58
Moving bed Catalitic Reforming process Axens-IFPEN.

5
 Production of other gasoline flows.
A number of processes allow the further production of high-quality gasoline flows
either by improvement of low-value gasoline flow or by converting gases into
gasolines. These processes are:
Light gasoline isomerization. This process consists in the low temperature skeletal
isomerization of medium paraffins (in particular pentanes and hexanes) enriching
them into their branched isomers isopentane e dimethylbutanes, having much higher
ON. This is done on acid catalysts at 200-350 °C.
Separation or conversion of benzene. Due to the strong toxicity of benzene, it must
be separated from gasoline or reduced down to the limit of 1%. This can be
accomplished by simple distillation, when a fraction (T eb  80°C) rich in benzene (
50 %) can be distilled from a light gasoline and an heavy gasoline, both with benzene
< 1%. Alternatively, benzene separation from a C6 cut can be obtained by extraction
or extractive distillation. Finally, benzene can be hydrogenated to cyclohexane or
alkylated to alkylbenzenes.
Alkylation. A fraction rich in isooctane (2,2,4-trimethylpentane, ON = 100) can be
synthesized by alkylation, the reaction of isobutene with isobutene:

+
H
The reaction is done in liquid phase (really a gas-liquid-liquid three-phasic system) at
0-50°C at 3-10 atm using concentrated sulphuric acid or hydrofluoric acid.
Light olefin oligomerization. The acid-catalyzed oligomerization of propylene and
isobutene to their dimers and trimers produces highly branched olefins, with high
H3C H2C CH3
H3C H3C H2C CH3 H3C H3C H2C CH2
2 HC CH2 H3C C CH 3 HC CH2 H3C C CH

H3C H3C H3C

H3C H3C C CH3 H3 C CH3 H3 CH CH3
C C
2 C CH H3C C CH H3C C CH + H2 H3C C CH2
H3C 2
H3C H3C H3C

6
ON. The reaction is performed either on gas phase over zeolite or other acid solid
catalysts at 170-220 °C, 40-60 bar or in liquid phase over polymeric acid solids
(sulphonated polystyrene) at 70-130 °C, ca 20-50 bar. The limit of this process is that
this fraction is olefinic, whose amount in commercial gasolines is limited. However, a
further hydrogenation step can be performed finally producing a high octane paraffin
flow. In thei case the overall process is denoted as “indirect alkylation”.
Synthesis of ethers. The ethers MTBE (methyl-tert-butyl-ether, produced from
isobutene + methanol), ETBE (ethyl-tert-butyl ether, produced from isobutene +
ethanol), TAME (TerAmyl-Methyl Ether, from isopentene + methanol) and TAEE
(TerAmyl-Ethyl Ether, from isopentene and ethanol) have excellent antiknocking
properties and moderate oxygen content. They are produced in liquid phase in the
presence of sulphonated polybenzene catalysts at 50-85 °C and 7-15 atm.
CH3
H3C CH3
O H H3C CH2CH3 H3 CH3
HC C O C O H3CC C O
H3C C CH2
3 MTBE
H3H
C H 3C ETBE TAME
C3
H3C CH3CH2

Formulation of gasolines and Diesel fuels

Automotive fuels are produced by blending different refinery flows to optimize the
properties of the final products and fulfill regulations.

Properties of gasoline fractions

pool comp RON R+M/2 RVPa psi % b % arom % olefins % S pool
butanes 91-95 93 59 0-10 0 <3 0
straight run 55-75 68 11 10-20 10 2 1
gasoline
reformate 94-104 93 3 20-60 50-80 1 0
FCC gas. C5- 89 83 19 25-50 30 98c
FCC gas. C6+ 105 100 2 23-33
d
HC gasoline 86-87 83 16 0-3 2-6 0 0
coker gasoline 70 0-3 4-8 35 1
alkylate 93-100 94 5 0-15 0 0,5 0
polymerate 95 90 9 0-5 0 96 0
isomerate 82-90 84 14 0-20 0-4 0 0
ethanol 118 105 11 1-10 0 0 0
MTBE 115 110 9 0-10 0 0 0
e
MTG 92 87 12-13 26 12 0
a b c d
Reid Vapor Pressure % in the pool FCC gasoline without previous HT
hydrocracker gasoline e Methanol to Gasoline process.

6
 Typical properties of middle distillates usable in the pool of Diesel fuels.
taglio CN Aromatics Olefins Plugging
% v/v % v/v point °C *
straight run gasoil (SRGO) 40-45 25-40 0-2 - 10
light cycle oil (LCO, from FCC) 18-25 60-90 1-5 -5
hydrocracker gasoil 58 - 14
light coker gasoil (LCGO) 30-40 30-50 25-35 -8
visbreaker gasoil (VBGO) 40 -4
Biodiesel (FAMEs) 48-60 0 0 -13
biodiesel ECOFINING 70-90 0 -20- +10
Fischer Tropsch LTFT gasoil 80 0 10 -5
hydrocracked LTFT waxes 75 1.4 0 -5
COD from FT olefins 54 <2 40 -50
gasification gasoils 38 -7

Oil industry: safety and environmental issues

Flammability and explodibility. As already seen for natural gas, hydrocarbons are
instable in air and can burn or give rise to explosions. The danger of an hydrocarbon
mixture in this respect is associated to its volatility as well as to the density of the
vapors.
Light gases such as hydrogen and methane are much lighter than air and this limits
the danger of explosions in open air, while they are very dangerous in closed
environments. Highly volatile liquids as well as heavy gases, like gasolines and
GPL, are very dangerous because they raise the explosion limits easily at ambient
temperature and they vapors are denser than air thus concentrating at ground level.
Heavier liquids such as kerosene, jet fuel, Diesel fuel oils and gasoils are less
dangerous, because they usually do not produce flammable mixtures with air in
ambient conditions.
Emission of toxic hydrocarbon vapours. Benzene is an extremely toxic substance and
is also highly volatile. For this reason it is a very dangerous compound. All other
liquid hydrocarbons have limited toxicity or virtually no toxicity.
Pollution of waters and soils. The solubility of hydrocarbons in water is very small,
like for aromatics, or almost zero. However, most liquid hydrocarbons float over
water limiting the access of oxygen. Hydrocarbon leaks are a typical accident that
causes pollution of water and soil.
Pollution of soils by heavy hydrocarbons. Heavy hydrocarbons, such a refinery
residues, are nearly solid. They contain polycyclic aromatic hydrocarbons that may
be very toxic and persistent in the environment.
Refinery wastes. The refinery industry produces gas emissions, which are generally
treated by appropriate abatement techniques, spent waters that are usually treated
biologically before readmission to the environment, and solid wastes such as e.g.
spent catalysts, that must be treated correctly before landfilling, but in several cases
find recycling.

6
 Environmental protection related to the use of fuels.
European regulations
IMMATRICOLATION EMISSIONS g/km
OF THE CAR CO HC NOx HC+NOx PM10 PN #/km
EURO 4 '05-'09 1.00 0.10 0.08 -
Gasoline EURO 5 > 09/ 2009 1.00 0.10 0.06 0.005
Cars (light duty) EURO 6 > 2014 * 1.00 0.10 0.06 0.005 6 1011
Diesel engine EURO 4 '05-'09 0.50 0.05 0.25 0.30 0.025
Cars (light duty) EURO 5 > 09/ 2009 0.50 0.18 0.23 0.005 6 1011
EURO 6 > 2014 * 0.50 0.08 0.17 0.003 6 1011
Because different measuring methods give different results, in Euro 6 legislation a
progressive revision of the measuring methods has been introduced (6b, 6c, 6dTEMP,
6d), tending to those which give larger results. The full Euro 6d (or Euro 6.3) is
mandatory for vehicles omologated starting from 1.1.2020 and registered from
1.1.2021: RDE (Real Driving Emissions), a test carried out on public roads to make
sure 'reality' matches 'controlled environment', is mandatory.

Automotive aftertreatment systems

The three-way catalytic converters for gasoline cars aftertreatment.

N2 72 %
CO2 13.5 %
H2O 12,5 %
CO 0,68 %
O2 0,51 %
H2 0,23 %
NOx 1050 ppm
HC 750 ppm

The exhaust gas of a gasoline engine car has an average composition indicated in the
table. Thus it contains significant amounts of poisonous molecules (in particular CO)
and / or pollutants (NOx and hydrocarbons, HC). The amount of these molecules
depends in reality on various factors and in particular on the so-called "A/F ratio" (air
to fuel) by weight. For A/F (air/gasoline weight ratio) = 14.7, the equivalence ratio
() is 1, that is, the mixture is stoichiometric (oxygen is exactly that necessary for the
combustion). For  > 1 (i.e. A /F> 14.7) combustion is "lean", on the contrary for 
<1 is "rich". In rich conditions, CO and HC are more concentrated, whereas NO has a

6
maximum for A/F = 1.6 because it is the condition at which the temperature of the
engine is higher.
Gasoline engines most typically work in rich conditions. The exhaust gas of a
gasoline engine has an average composition indicated in the table on the left. To
comply with the current legal limits (Euro 6) it is necessary to break down these
pollutants. The "three ways" catalytic converters (Three Way Catalysts, TWC) allow
to obtain together the three following reactions:
CO + O2  CO2 H°298 = - 283 kJ/mol
-CH2- + O2  CO2 + H2O H°298 = - 600 kJ/molC
CO + NO  CO2 + ½ N2 H°298 = - 373 kJ/mol
then purifying the discharge of NO, CO and hydrocarbons. This must be done
without causing significant pressure losses. It is a catalyst deposited most frequently
onto a ceramic "monolith" filter consisting of cordierite (a Mg silico-aluminate,
which has a minimum coefficient of thermal expansion) in whose channels has been
deposited a "washcoat" of ceria-alumina (Al2O3-CeO2) or alumina-ceria-zirconia
(Al2O3-CeO2-ZrO2), sometimes containing also La2O3, over which the catalyst is
supported. The catalyst consists of nanoparticles of Platinum Group Metals (PGM),
i.e. Pt or Pd or Pt-Rh or Pd-Rh. Alternatively, the monolith is built with stainless steel
sheets riddled coils, on which the washcoat and the catalyst are deposited.
Pt and Pd are the most active for the oxidation reactions of CO and hydrocarbons,
(reactions 1 and 2) while Rh is the most active in the reduction of NO (reaction 3).
The composition in terms of Pt and Pd mainly depends on their relative price, which
is very variable. In recent years the content of the noble metal (or PGM) has been
greatly diminished down to less than 1 g total per muffler, which of course allows to
decrease the cost of the system.
The reactions 1 and 3 are almost complete already slightly above 300 ° C while
reaction 2 is slower and is completed above 500 ° C. The efficiency of the catalyst is
maximum, with conversion of the three pollutants (CO, HC and NOx) well over 95%,
only for A/F very close to 14.7.

6
Scheme of the regulation system associated with the use of the catalytic converter
(above) and representation of a catalytic converter with ceramic filter (in the middle)
or metal-coated substrate (below).

6
 The lambda sensor is an electrochemical
oxygen sensor. In fact, it is a
concentration battery, based on a solid
electrolyte, zirconia ZrO2, pure or doped
with Yttria, who works on different
oxygen pressure on the "reference side "
(air P°O2) and on the analysis side (the
waste gas, PO2)
½ O2 + 2 e-  O2-
O2-  ½ O2 + 2
e-
(mV)= 0.0496 T log10 P°O2 / PO2

Gasoline Particulate Filter (GPF)

The particulate filter technology was developed to limit particle emissions from
Diesel engines. The recent Euro 6 revisions however suggest the use of similar
devices also for GDI (Gasoline direct ingnition) vehicles. Diesel and petrol particle
morphology are similar, with 80-100 nm (median) aggregate of primary particles of <
10 nm diameter. However, gasoline engines emit lower masses of soot than diesel
engines under typical driving conditions. Therefore less frequent regenerations are
required and this allows lower thermal mass wall-flow filters than DPFs. Also GPF
systems operate at higher temperatures than DPFs which entails that passive soot
regeneration occurs more readily; this improves the scope for three-way catalyst
conversion activity. Particulate Matter (PM) will accumulate less on the filter under
gasoline exhaust conditions than in diesel; low pressure loss and high filtration
efficiency are thus required already without PM. Higher porosity filters allow higher
washcoat loadings for three-way catalyst coated GPF. The coating also contributes to
increase filtration efficiency. The smaller and bigger particles are all trapped; the
lower filtration efficiency is observed for particles of around 200 nm in diameter.

The GPF can be combined with the three way catalyst (TWC) into a single catalyzed GPF (cGPF).

6
 Purfication of exhaust gases of Diesel engines.
In contrast to most gasoline engines, the typical operating conditions of a Diesel
cycle engine are "lean", i.e. with a considerable excess of oxygen
(remaining 10-15%). For this reason, three-
Typical composition of
way catalytic converters do not work for diesel
untreated Diesel engine
exhaust engines to abate NOx. In the case of diesel
O2 9-17 % % engines, however, the problem of the
CO2 < 12 % formation (and thus of the abatement) of the
H 2O < 12 % particulate ("soot"), i.e. of dust produced in the
CO < 450 ppm engine, is very relevant and adds to the need to
NOx < 1500 ppm
HC < 300 ppm
abate CO, hydrocarbons and NOx. This is
PM 50000-1000 mainly due to the pressure that is generated,
g/Nm3 that is very high (up to 2000 bar), and which
SO2 < 300 ppm causes the formation of "drops" of fuel where
N2 balance (60-70 %) combustion is realized in "rich" conditions.
The soot particles, once formed, burn very slowly and partially into the "lean"
combustion zone. Particulate matter is made up of particles with a core of almost
pure carbon with adsorbed hydrocarbons and sulphate particles outside.

DOC: Diesel Oxidation Catalysts

Oxidizing mufflers, similar to three way catalysts, are applicable to Diesel engines.
They are denoted as DOC, Diesel Oxidation Catalysts, and contain an oxidation
catalyst (a PGM, Pt or Pd, or also systems based on transition metals such as LSM,
lanthanum strontium manganite, Lal-xSrxMnO3), that allow to realize the reactions of
oxidation of CO and hydrocarbons,
CO + ½ O2  CO2
HC + n O2  CO2 + H2O
but not the reduction of nitrogen oxides. These catalysts have little effect also on the
particulate. In recent years the DOC may be designed also to catalize the reaction:
NO + ½ O2 D NO2
to favor the next particulate combustion and NOx abatement (see below).
Diesel Particulate Filters, DPF

6
 (FAP: Filtri AntiParticolato)
To remove particulate (soot), car manufacturers (the first were Peugeot and Citroen in
2000) have introduced the DPF (Diesel Particulate Filter). It is a monolithic ceramic
filter made of porous cordierite or silicon carbide, containing small channels. The
channels are closed at the end. The channel walls are permeable to gas but not to the
particles of soot that are retained in the front of the wall. Particles whose size is > 100
nm are removed, which do mean the vast majority of PM 1O and also of the PM2.5
(particles with size less than 10 and 2.5 , respectively that get over the bronchial
tissue). The DPF is required for a new car with the regulations Euro5 and 6.

CSF, Catalyzed Soot Filter, or CDPF, Catalyzed Diesel Particulate Filter

In the more recent technologies, in the internal surface of the channels an oxidation
catalyst is deposited. Thus, the filter can be regenerated by burning the powders
trapped at ca 600 °C if O 2 present in the exhaust is the oxidant, at ca 250 °C if NO 2 is
the oxidant. There are different regeneration systems, passive and active.
In the case of Continuously Regenerating Trap ((C)CRT) systems, the oxidation
catalyst removes CO and HC and oxidises some of the NO in the exhaust gases to
NO2. This NO2 then reacts with the PM trapped in the filter, producing NO and CO 2.
Some of the NO is then reoxidised to NO2 in the filter, which then reacts with more
trapped PM. This enables the system to regenerate in applications with very low
exhaust gas temperatures or low NOx:PM ratios in the exhaust gases.
In the case of Fuel Borne Catalyst system, regeneration of the filter is performed by
means of the additives (e.g. cerium and copper based additives in 60 to 100 ppm
concentration) mixed with the diesel fuel, which lower the ignition temperature of the

6
soot to approximately 380°C, thereby allowing for continuous regeneration of the
filter system even at the relatively low exhaust temperatures of diesel engines.
All active filter regeneration techniques operate discontinuously by raising the
temperature of the filter to around 600 °C. This is the temperature at which the
particulate (PM) collected in the filter will combust rapidly in oxygen. This can be
accomplished by an electrical heater, or with fuel injection systems, where fuel is
injected by a electric heated fuel vapouriser and will be oxidised over the installed
catalyst to reach 600 °C to burn and remove the collected carbon. These systems use
diesel fuel from the tank and on-board voltage.

NO oxidation catalyst
A noble metal based catalyst can be also used to catalyse NO oxidation to NO 2. This
ca help soot oxidation (NO2 oxidizes soot) as well as the Selective Catalytic
Reduction by ammonia (see below).

Denitrification of exhaust gases of diesel engines

Exhaust Gas Recirculation (EGR)
A fraction of the exhaust gas is recirculated to the combustion chamber to lower
reaction temperature allowing lower NOx production. This can be coupled with other
DeNOx treatments.
Automotive SCR
The so-called “automotive SCR” is a solution for NOx analogous to the SCR
(Selective Catalytic Reduction) process, used for the denitrification of exhaust gases
from thermal power stations, nitric acid plants and other stationary sources of NOx.
The "classic" SCR process involves the injection of ammonia (vaporized pure liquid
or most commonly aqueous solution) and conduct the reaction:
4 NO + 4 NH3 + O2  4 N2 + 6 H2O.
at about 350 °C over SCR catalysts. To avoid storage of liquid or aqueous ammonia
in vehicles, more commonly, SCR process is realized with urea (H 2N-CO-NH2),
which produces ammonia decomposing in a Decomposition Reactor Tube (DRT) or
Urea Decomposition Catalyst with water vapor,
H2N-CO-NH2+ 2H2O  2 NH3 + CO2
and then produces the SCR reaction as above. Urea can be stored as a water solution
(AdBlue, ie the 32.5% solution in water from BASF), denoted as DEF (Diesel
Exhaust Fluid), or solid and injected molten (180-200 °C). The SCR reaction is
accelerated, and it can therefore be achieved at lower temperature, oxidizing before
NO to NO2 with another oxidation catalyst, or using the activity of the same SCR
catalyst in NO oxidation:
NO + ½ O2  NO2
then operating the so-called "fast SCR" reaction:
2 NO + 2 NO2 + 4 NH3  4 N2 + 6 H2O.
The SCR catalyst can be very similar to the DeNOx-SCR catalysts for stationary
applications, that is, based on V2O5-WO3-TiO2 (anatase) in the form of ceramic

6
monolith. More recently, catalysts have been developed based on Fe-ZSM-5 or Cu-
ZSM-5 zeolites deposited on ceramic monolith. They have a larger working
"window" (total conversion of NOx from 300 to 500 ° C).

SCR-Catalysed Diesel Particulate Filter (SDPF or SCRF)

Besides the application on a conventional flow-through substrate, SCR technology
can also be coated on a wall-flow filter substrate. The corresponding technology is
called SDPF and controls both nitrous oxides (NOx) and particulate matter (PM). It
additionally offers also the opportunity for a close coupled application, whereas
SCR catalysts are typically used in an underfloor position.

Ammonia Slip Oxidation (ASO)

To allow the total abatement of NOx is possible to operate SCR with an excess of
urea and ammonia, which causes, however, the leakage of ammonia ("ammonia
slip"). To avoid this you another catalyst called ASO (Ammonia Slip Oxidation) or
ASC (Ammonia Slip Catalyst) based on Pt-Cu/A 2O3, for the selective catalytic
oxidation of ammonia to nitrogen (SCO) using the residual oxygen: 2 NH 3 + 3/2
O2  N2 + 3 H2O.

NSR, NOx Storage and Reduction or LNT, Lean NOx Trap

Toyota has first developed this system, originally called "NOx storage and reduction"
(NSR). It uses an adsorbent catalyst consisting of oxides of aluminum containing
BaO or K2O and also a bit of platinum or platinum and rhodium. The solid adsorbs
NOx to form barium nitrate when working in "lean" conditions. When saturated,
intermittently, however, it receives a "rich" flow (an injection of the diesel fuel, e.g.
one each min) and at this moment hydrocarbons reduce NOx to nitrogen.
2 NO + 3/2 O2 + BaO  Ba (NO3)2 catalyzed by Pt
Ba (NO3)2 + 2 -CH2- + ½ O2  BaO + N2 + 2 CO2 + 2 H2O catalyzed by Rh or Pt
• NOx storage during lean engine operation
• NOx reduction during rich operation phases
• LNT desulfurization under rich conditions and high temperatures, at least 650°C.
This system is more effective for lght duty vehicles than for heavy duty vehicles
becuase of the low gas temperature in the former that increases adsorption.

Diesel particulate and NOx Reduction (DPNR)

The Toyota Avensis features the catalyst 4-way DPNR (Diesel Particulate NOx
Reduction), which is a catalytic filter that has both the functionality NSR (based on
Pt-BaO/Al2O3 or Pt-K2O/Al2O3) and that of the particulate filter. NOx adsorb in the
form of nitrates and oxygen burns the particulate in "lean" conditions while NOx are
reduced to N2 in a "rich" step. The complete system is a sequence NSR-DPNR-DOC.

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 Passive NOx adsorbers
Passive NOx adsorbers (PNA) or Low Temperature NOx Adsorbers (LTNA) store
NOx during a cold start and release it at higher temperatures when the SCR system is
operational. They are based on Pd/zeolite powder.

Passive SCR
Short periods of rich engine operation generate ammonia by reduction of NOx on a
TWC or on a LNT which is stored on the next SCR device. During subsequent lean
operations, the NOx that breaks through the TWC converters is converted by the
NH3 stored on the SCR catalysts.
All these devices can be used in series, leading to a number of different solutions.
Here below the most common actual solutions for light-duty and heavy duty diesel
vehicles are summarized

Common aftertreatment systems for light duty Diesel vehicles.

Configurations of the aftertreatment system of heavy duty Diesel vehicles.

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 Naval aftertreatment systems
Three types of marine fuels (also denoted as bunker oils) are used. Ships that do not
have the scrubbing system for removing SO 2 from waste gases, must use Marine
GasOil (MGO, or Distillate Marine Fuel, DMA, which is a distillate similar to car
Diesel fuel, but with < 0.1% sulphur, pour point -6 °C, 40 CN) near the coast and in
the Emission Control Areas (ECA), while Marine Fuel Oil (or Residual Marine Fuel,
which is a blend of gasoil and heavy fuel oil, with  0.5% sulphur, pour point 
30°C) can be used in the high sea. However, ships with SO 2 abatement systems, can
use Residual Marine Fuel with up to 3.5 % sulphur, pour point 30°C. The latter is,
today, the most economic solution. The global shipping fleet now consumes about 4
million barrels per day (bpd) of fuel oil.

To use high S fuel, exhaust gas cleaning systems to limit SOx emissions to ≤ 6
g/kWh (as SO2) must be applied. The open loop scrubbing systems operate utilising
the natural alkalinity of seawater (pH usually between 7.5 and 8.4) to remove SO 2
from the exhaust as sulphite ion. Exhaust gas enters the scrubber and is sprayed with
seawater in three different stages. Wash water from the scrubber is treated and
monitored at the inlet and outlet to ensure that it conforms with the discharge criteria.
It can then be discharged into the sea with no risk of harm to the environment. The
closed loop systems operate using soda solutions.

Open loop system Closed loop system

Depending on the engine maximum operating speed, as well as in the position

(ECA/non ECA) a limit for NOx emission also exists from 2 to 14.4 gNOx/kWh.
Liquefied natural gas will probably become the most used fuel for ships in the future.
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