Higher Institute of Engineering and Technology in Tanta

Chemical engineering Department

Petrochemical Industries (CHE361)
Lecture (9)

Lecture (9)

conversion processes for selected petrochemicals

➢ Conversion processes for selected petrochemicals are crucial steps in transforming raw
hydrocarbons (such as crude oil and natural gas) into valuable chemical products.

Examples of Conversion processes :

1. Steam Cracking:

➢ Feedstocks: Ethane, propane, naphtha, gas oil.

➢ Products: Ethylene, propylene, butadiene, benzene, toluene.
➢ Process Description:

➢ Hydrocarbons are heated to high temperatures (750–850°C) in the presence of

steam.
➢ The molecules undergo thermal cracking, breaking down into smaller olefins and
aromatics.

2. Catalytic Reforming:

➢ Feedstocks: Naphtha (light and heavy).

➢ Products: Benzene, toluene, xylenes (BTX aromatics), hydrogen.
➢ Process Description:

➢ Naphtha is heated in the presence of a catalyst (e.g., platinum) and hydrogen.

➢ The process increases the octane number and yields aromatic compounds.

3. Alkylation:

➢ Feedstocks: Isobutane and olefins (e.g., propylene, butylenes).

➢ Products: Alkylate (a high-octane gasoline blending component).
➢ Process Description:

➢ Olefins react with isobutane in the presence of a strong acid catalyst (HF or
H2SO4).
➢ Produces a highly branched alkane.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

4. Polymerization:

➢ Feedstocks: Ethylene, propylene, butadiene, styrene.

➢ Products: Polyethylene, polypropylene, synthetic rubbers, polystyrene.
➢ Process Description:

➢ Olefins are linked together into long chains under specific conditions (heat,
pressure, and catalysts).
➢ Forms thermoplastics and elastomers.

5. Aromatization:

➢ Feedstocks: Paraffins and naphthenes.

➢ Products: Benzene, toluene, xylenes.
➢ Process Description:

➢ Converts paraffinic hydrocarbons into aromatic hydrocarbons using a

catalyst at elevated temperatures.
➢ Byproduct: Hydrogen.

6. Hydrocracking:

➢ Feedstocks: Gas oils, residual oils.

➢ Products: Jet fuel, diesel, naphtha, LPG.
➢ Process Description:

➢ Heavy hydrocarbons are broken into lighter fractions in the presence of

hydrogen and a bifunctional catalyst.
➢ Reduces sulfur and nitrogen impurities.

7. Dehydrogenation:

➢ Feedstocks: Alkanes (e.g., propane, butane).

➢ Products: Olefins (e.g., propylene, butadiene).
➢ Process Description:

➢ Alkanes are heated in the presence of a catalyst to remove hydrogen.

➢ Produces alkenes used in polymer and rubber production.

8. Methanol-to-Olefins (MTO)

➢ Feedstocks: Methanol derived from natural gas or coal.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

➢ Products: Ethylene, propylene.

➢ Process Description:

➢ Methanol is converted to olefins via zeolite catalysts in a two-step

reaction.
➢ Useful for regions without direct olefin sources.

9. Fischer-Tropsch Synthesis

➢ Feedstocks: Syngas (CO + H2 from coal, natural gas, or biomass).

➢ Products: Synthetic hydrocarbons, alcohols, waxes.
➢ Process Description:

➢ Catalytic conversion of syngas at moderate temperatures and pressures.

➢ Used to produce fuels and petrochemical intermediates.

Each process is tailored for specific products, balancing economic feasibility, feedstock
availability, and market demand for petrochemical products.

Polyethylene (PE):

➢ Polyethylene is one of the most widely used thermoplastics globally due to its versatility,
ease of processing, and affordability. It is produced through the polymerization of ethylene
monomers.
➢ Polyethylene is a thermoplastic polymer composed of repeating units of ethylene (C₂H₄).
➢ It is created through the polymerization of ethylene monomers.
➢ It is characterized by its lightweight, durable, and flexible properties.
➢ Polyethylene is one of the most commonly used plastics worldwide, with applications
ranging from packaging materials to industrial and medical uses.
➢ Its properties vary based on its density and molecular structure, leading to types such as
LDPE, HDPE, LLDPE, and UHMWPE.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

Advantages:

• Lightweight yet durable.

• Chemical and moisture resistance.
• Easy to mold and recycle.

Disadvantages:

• Poor heat resistance.

• Environmental concerns due to non-biodegradability (though recycling mitigates this).

Types of Polyethylene:

Polyethylene is classified based on density and molecular structure:

1. Low-Density Polyethylene (LDPE):

➢ Structure: Highly branched, resulting in a low density.

➢ Properties:

▪ Flexible and tough.

▪ High impact resistance.
▪ Low melting point (about 110°C).

➢ Applications:

▪ Plastic bags, films, and packaging materials.

▪ Electrical insulation.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

2. High-Density Polyethylene (HDPE):

➢ Structure: Linear structure with minimal branching, resulting in higher density.

➢ Properties:

▪ High tensile strength.

▪ Chemical resistance.
▪ Melting point around 130°C.

➢ Applications:

▪ Containers, pipes, and household products.

▪ Fuel tanks and detergent bottles.

3. Linear Low-Density Polyethylene (LLDPE):

➢ Structure: Similar to LDPE but with short, controlled branching.

➢ Properties:

▪ Higher tensile strength than LDPE.

▪ Good puncture resistance.

➢ Applications:

▪ Stretch films and industrial packaging.

4. Ultra-High Molecular Weight Polyethylene (UHMWPE):

➢ Structure: Extremely long molecular chains.

➢ Properties:

▪ High impact strength.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

▪ Excellent wear resistance.

➢ Applications:

▪ Bulletproof vests, medical implants, and conveyor belts.

Manufacturing Processes:

1. Ziegler-Natta Polymerization (for HDPE and LLDPE):

o Uses transition metal catalysts at moderate temperatures and pressures.
o Produces linear polymers with controlled branching.
2. Free Radical Polymerization (for LDPE):
o Conducted under high pressure (1000–3000 atm) and high temperature (200–
300°C).
o Produces highly branched structures.
3. Metallocene Catalysts:
o Advanced catalysts that allow precise control over polymer structure.
o Used to produce specialty PE grades.

Applications:

Polyethylene is extensively used across industries due to its adaptability. Common applications
include:

1. Packaging:
a. Films, wraps, and bottles.
2. Construction:
a. Pipes, geomembranes, and tanks.
3. Consumer Goods:
a. Toys, household items, and storage containers.
4. Medical:
a. Prosthetics and tubing (UHMWPE).
5. Industrial:
a. Wire and cable insulation.

Polymerization of Ethylene :

➢ Polymerization of ethylene molecules into heavy molecular weight PE is a reaction in

which a chain of macromolecule, is produced by the combination of ethylene molecules.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

➢ Ethylene is a highly reactive monomer that starts combining with other molecules of
ethylene in the presence of a catalyst (Ziegler Nutta catalyst) under a certain pressure and
temperature.
➢ The reaction is exothermic and hence it is essential to control temperature by a proper heat
removal system.
➢ The properties of a polymer vary with the operating pressure, temperature, and time of
reaction.
➢ The reaction steps are in three stages , namely, initiation, propagation, and termination .

Initiations :

A radical molecule is formed in the presence of the catalyst .

Propagation:

The radical then starts combining with the monomers repeatedly in this stage, which continues
indefinitely as long as the monomer molecules are available during reaction .

termination :

stopping the reaction of polymerization with the quenching step .

production of low density polyethylene (LDPE)

➢ the reaction happened in the tubular reactor because tubular reactors are prone to plugging
and poor heat transfer problems, a thick walled,
➢ stirred tank vessel reactor is used.
➢ In a tubular reactor, pure liquid ethylene ( 99.99 %) is mixed with hydrogen peroxide and
forced through the tubular reactor at very high pressure ( 3500 atm), surrounded by a
cooling medium to extract heat of polymerization reaction.
➢ Oxygen is used with hydrogen peroxide as the initiator.
➢ The reaction takes place in solution. The heat of the reaction is given as 3650 kj /Kg
➢ The temperature in the reactor is controlled above 200°C to avoid crystallization of LDPE,
which will otherwise damage the reactor tube.
➢ High speed agitation helps in good heat transfer.
➢ If the agitator stops, the temperature will rise to such an extent that explosion may takes
place because of the presence of oxygen in the reaction mixture.
➢ Effluent from the reactor , consisting of the product and the unconverted monomer, is
separated by high and low pressure separator vessels.
➢ The overall conversion achieved by recycling is about 95 97 %.
➢ Finally, the molten LDPE is withdrawn from the low pressure separator and extruded,
followed by cooling, drying, and pilling.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

A high pressure low density polyethylene (LDPE) plant

production of High density polyethylene (HDPE):

➢ HDPE is manufactured by the suspension polymerization method. And also produced by a

fluidized method in modern plants.
➢ In this method, high purity ethylene is introduced into the reactor vessel in which a catalyst
(Ziegler Nutta catalyst, TiCl 4 in alkyl aluminium ) is suspended in benzene at a pressure
of 20 -35 atm and at a temperature of 60°C 80°C.
➢ The main economic advantage of HDPE production method is that it can be manufactured
at much lower pressure as compared to LDPE.
➢ The ratio of alkyl aluminium and titanium chloride determines the size of the polymer.
➢ The greater the ratio, the greater the molecular weight of the polymer.
➢ Catalyst consumption is about 1 g of titanium ( Ti ) per 1500 kg of polymer. This is due to
the high residual presence of the catalyst within the polymer.
➢ After the reaction, the polymer mixture is separated from ethylene and inserts in a flash
➢ drum.
➢ The polymer is water washed and filtered to recover the catalyst (water soluble) and reused.
However, recovery of the catalyst from the polymer is not complete.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

Low pressure Ziegler process for high density polyethylene manufacture

production of 1,3 linear low density polyethylene (LLDPE):

➢ LLDPE is a copolymer of ethylene and 1 butene having linear structure.

➢ Today, it is produced by a low pressure fluidized bed process where the temperature and
pressure are 100°C and 7-20 atm 0.7- 2 MPa), respectively.
➢ A long residence time in the range of 3- 5 h is required for a reaction.
➢ Unreacted monomers are separated from the effluent and recycled to the reactor.

A fluidized bed LLDPE manufacturing unit.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

Polypropylene :

➢ Polypropylene (PP) is a thermoplastic polymer widely used in various industries due to its
versatile properties. It is made by polymerizing propylene, a hydrocarbon monomer.
➢ After PE, polypropylene is a valuable polymer .

Advantages:

➢ Economical and widely available.

➢ Recyclable (resin identification code #5).
➢ Durable and chemically inert.
➢ Versatile with excellent processability.

Limitations:

➢ Susceptible to UV degradation; requires stabilization for outdoor use.

➢ Poor resistance to low temperatures.
➢ Flammable without flame retardant additives.

Applications:

1. Packaging:
➢ Used in food packaging, containers, and bottles due to its safety and durability.
➢ Flexible and rigid packaging films.

2. Textiles:
➢ Nonwoven fabrics for hygiene products (diapers, sanitary napkins).
➢ Rugs, upholstery, and outdoor furniture fabrics.

3. Automotive:
➢ Components like bumpers, dashboards, and battery cases.
➢ Interior and exterior trims.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

4. Healthcare:
➢ Medical devices and packaging (e.g., syringes, IV bottles).
➢ Sterilizable containers.

5. Consumer Goods:
➢ Household items like storage bins, furniture, and toys.
➢ Stationery, ropes, and luggage.

6. Industrial Uses:
➢ Pipes, sheets, and insulation materials.
➢ Electrical insulation components.

Polymerization Methods used in production :

a) Gas-Phase Polymerization:

• Process: Propylene gas is polymerized in a fluidized bed or a stirred reactor.

• Steps:
1. Propylene gas is introduced into a reactor containing a catalyst (usually Ziegler-
Natta or metallocene catalysts).
2. Polymerization occurs as the propylene molecules bond to form long polymer
chains.
3. The reaction generates heat, which is removed via cooling systems.
4. Polypropylene powder (polymer) is collected and further processed.

b) Bulk-Phase Polymerization:

• Process: Polymerization occurs in liquid propylene, eliminating the need for an inert
solvent.
• Steps:
1. Liquid propylene is fed into a reactor.
2. Catalysts are added to initiate the polymerization.
3. The polymer grows in the liquid phase, with unreacted propylene separated and
recycled.
4. The polymer slurry is removed, dried, and processed.

c) Slurry-Phase Polymerization:

• Process: Polymerization occurs in a hydrocarbon diluent (e.g., hexane or heptane).

• Steps:
1. Propylene, catalyst, and a diluent are fed into the reactor.

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

2. Polymerization occurs at controlled temperatures and pressures.

3. The polymer is recovered from the diluent through separation and drying.
4. The diluent is recycled back into the system.

➢ It is manufactured by catalytic reaction in a stirred tank reactor, where Ti and aluminium

halides are used as catalysts at a temperature of 60°C 70°C and a pressure of 1- 2 MPa.

Chemical reaction :

➢ An unreacted monomer is recycled after it is separated from the catalyst and polymer
mixture in a flash chamber under vigorous stirring conditions.
➢ The mixture of polymer and catalyst is then passed to a centrifugal separator where a
catalyst and polypropylene polymer is recovered.
➢ Further processing of the spent catalyst in the presence of alcohol is carried out to recover
the active components of the catalyst for its reuse.

A polypropylene manufacturing unit

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 Higher Institute of Engineering and Technology in Tanta
Chemical engineering Department
Petrochemical Industries (CHE361)
Lecture (9)

Questions on lecture (9)

Answer the following questions:
1. write on the examples of Conversion processes.
2. write short notes on the advantages and disadvantages of polyethylene.
3. write short notes on the types of polyethylene.
4. Draw the flow sheet of A high pressure low density polyethylene (LDPE) plant
5. Draw the flow sheet of Low pressure Ziegler process for high density
polyethylene manufacture
6. Draw the flow sheet of A fluidized bed LLDPE manufacturing unit.
7. Draw the flow sheet of A polypropylene manufacturing unit
Best wishes
Asso.Prof :Wafaa Ahmed

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