Petrochemical

Precursors

Ethylene & Propylene

Petrochemical Precursors

2

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.

.

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.

3

Ethylene (CH2=CH2 )

4

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

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.

3/15/2015Footer Text 5

Synthetic chemical intermediates and

products from ethylene

3/15/2015Footer Text 6

Propylene

3/15/2015Footer Text 7

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.

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

3/15/2015Footer Text 8

Synthetic chemical intermediates and

products from propylene

3/15/2015Footer Text 9

Processes in Refinery which gives Ethylene and Propylene

10

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

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.

11

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

Principle behind steam cracking

12

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.

Flow diagram of steam cracking unit

13

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

3/15/2015Footer Text 14

Cracking conditions

3/15/2015Footer Text 15

Process design considerations

3/15/2015Footer Text 16

Considerations for feedstock

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.

3/15/2015Footer Text 17

Global consumption of ethylene and

propylene

3/15/2015Footer Text 18

Thank You

3/15/2015Footer Text 19