petrochemical precursor ethylene and propylene

1. Petrochemical
Precursors
Ethylene & Propylene

2. Petrochemical Precursors
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Petrochemical is a chemical compound or element recovered
or derived partially or entirely from petroleum or natural gas
and are intended for Chemical markets. Primary
petrochemicals are divided into three groups depending on
their chemical structure.
 Olefins include ethylene ,propylene and butadiene.
 Aromatics include benzene, toluene and xylenes.
 Synthesis gas is a mixture of carbon monoxide and
hydrogen used to make ammonia and methanol.
.

3. Olefins
Olefins are a class of hydrocarbons with a single double bond
and a chemical formula CnH2n. The two most important olefins
are ethylene and propylene,as they form the backbone of
petrochemicals market.The highly reactive double bond
makes the olefin molecule ideal for conversion to many useful
end products.
Oil refineries produce olefins by fluid catalytic
cracking of petroleum fractions.Chemical plants produce
Olefins by steam cracking of natural gas liquids like ethane
and propane.Olefins and aromatics are the building blocks for
a wide range of materials such as solvents, detergents and
adhesives.
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4. Ethylene (CH2=CH2 )
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Ethylene (ethene), the first member of the alkenes,
is a colorless gas with a sweet odor. It is slightly
soluble in water and alcohol. It is a highly active
compound that reacts easily by addition to many
chemical reagents.
Ethylene is obtained from ,Fermentation alcohol,
Refinery off-gases ,Hydrocarbon steam cracking
Physical properties-
 Mol. Wt. 28.03
 M.P. -169.4 0 C
 B.P. -103.8 0 C

5. Properties of Ethylene
• Unsaturated
• Non – polar molecule
• A flammable gas
• Participates in Addition reactions
(test of unsaturation)
• Polymerises to form Polyethene
• Very low BP (–104°C)
• Double bond makes it very reactive
• Catalytic oxidation of ethylene produces ethylene oxide, which
is hydrolyzed to ethylene glycol. Ethylene glycol is a
monomer for the production of synthetic fibers.
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6. Synthetic chemical intermediates and
products from ethylene
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7. Propylene
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Propylene(propene) is a colourless
unsaturated gas with a weak but
unpleasant smell having the chemical
formula C3H6
Propene is a byproduct of oil refining and natural gas
processing. During oil refining ethylene, propylene and other
compounds are produced ass a result of cracking larger
hydrocarbon molecules to produce hydrocarbons more in
demand. Propene can be separated by fractional distillation
from hydrocarbon mixtures obtained from cracking and other
refining processes.

8. Properties of Propylene
• Propylene can be polymerized alone or copolymerized with
other monomers
• Many important chemicals are based on propylene such as
isopropanol, allyl alcohol, glycerol, and acrylonitrile
• Highly flammable
• Has higher density and B.P. than ethylene due to its greater
mass
• Lacks strongly polar bonds ,yet the molecule has a small
dipole moment (0.366D) due to its reduced symmetry
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9. Synthetic chemical intermediates and
products from propylene
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10. Processes in Refinery which gives Ethylene and Propylene
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 Steam cracking of petroleum from LPG and
naphtha feedstock
 Thermal pyrolysis of ethane and propane
 Refinery off-gases
The main route for producing ethylene and
propylene ,is the steam cracking of
Hydrocarbons

11. Steam cracking of petroleum hydrocarbons
Steam cracking is a pyrolysis process.The cracking reactions are
principally bond breaking and a substantial amount of energy is
needed to drive the reaction towards olefin production. Cracking can
be visualized as a free radical dehydrogenation reaction, where
hydrogen is a coproduct.
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A hydrocarbon mixture is heated in a metal tubes inside a furnace
in the presence of steam to a temperature at which hydrocarbon
molecules thermally decompose.
These reactions have a residence time of less than one second and
are endothermic

12. Principle behind steam cracking
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Chemical Reaction
CxH2x+2 + H2O + O2  C2H4(4-15 %) + C3H6 + C2H6 + C2H2(7-13%) + H2(25-
30%) + CO + CO2 + CH4 + C3H8 + C4H10 + C4H8 + C4H6 +C +Heavy oil fraction
Co-products formed include acetylene, butylene, butadiene,
aromatics such as benzene ,toluene, xylene heavy oil residues.

13. Flow diagram of steam cracking unit
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14. Process description of a steam cracking unit
The process is a high temperature thermal reforming using ethane,
propane, butane and liquid naphtha. Superheated steam is mixed with the
hydrocarbon and fed through the heated coils of a pyrolysis furnace. The C2-
C4 feed is pyrolyzed in a separate furnace because different residence time-
temperature conditions are required. The pyrolyzed gases are quenched in a
tower and then scrubbed with gas oil to remove solids and heavy
hydrocarbons before sending to compressors to boost pressure to 35atms.
The compression station may also handle refinery off-gases which can
be separated in the same system. Flash vaporization removes C1-C2 fractions
which are caustic-scrubbed to remove carbon dioxide, dried with activated
alumina, and then separated into acetylene and ethylene by a combination of
absorption, extraction and fractionation steps. Ethane is recycled for pyrolysis
and methane ,hydrogen , carbon monoxide can be further processed to obtain
synthesis gas or used as a fuel.
The liquid fraction from the flash chamber is split by fractionation
into ethylene , propylene and a few byproducts
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15. Cracking conditions
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16. Process design considerations
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Considerations for feedstock

17. Major engineering problems
• Choice of process: Numerous process modifications are
possible in the pyrolysis of hydrocarbons. These can be done in
the Feed type ,choice of pyrolysis agent and in the choice of
pyrolysis equipment.
• Product ratio control: The product effluent composition is
controlled by steam-hydrocarbon mole ratio and residence time.
If no acetylene is desired, the light ends gas is split at the C2
level and acetylene is mildly hydrogenated to ethylene.
• Steam economy : Heat added in pyrolysis section can be
recovered in part by incorporating stack and quench boiler ,the
latter recovering heat that would otherwise be wasted in water
or oil quenching.
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18. Global consumption of ethylene and
propylene
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19. Thank You
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