United Arab Emirates University

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United Arab Emirates University Faculty Of
Engineering Training Graduation Projects
Unit (Graduation Project II)
Design Optimization of a Polyethylene
Production UnitCHM1-5
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• Academic Advisor
• Dr. Eisa Al Matroushi
• Team Members
• Humaid Abdullah 980715054
• Rashid Abdullah 980715064
• Salem Al Aamry
  200005333

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Objectives

• Introduction
• Polyethylene
• PE production process
• Polymerization Process.
• Reactions
• Chain initiation
• Propagation
• Termination

• Designed Process
• Material balance
• Energy balance
• Sizing and design
• Economics and cost estimation
• Safety rules in chemical plants
• Environmental issue

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Introduction

• Polyethylene is a polymer known as plastic.
• Industrial production of polyethylene uses
  ethylene
• as a raw material.

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Introduction

• Ethylene is known as king of petrochemicals.
• The importance of ethylene can be summarized in
  the
• following points
• Simple structure with high reactivity.
• Relatively inexpensive compound.
• Easy to be produced from any hydrocarbon
  through steam cracking.
• Fewer by-products generated from ethylene
  reactions with other
• compounds than from other olefins.

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Polyethylene

• An example of the polymers.
• Made of ethylene which is a monomer.

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Why Polyethylene ?

• One of the largest petrochemical industries in
  the country.
• It is the most extensively used thermoplastic.
• Replaced or substituted many naturally derived
  products such as paper, wood and steel.

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General View

• The polyethylene production process goes through
  several steps in the industry.
• The process starts with Ethan which in turn
  reacts to form ethylene.
• The process of polymerization is then needed in
  order to transfer ethylene monomers into solid
  polyethylene particles.

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Ethane Cracking

• Cracking of ethane occurs at a high temperature
• presence.
• Usually done in a furnace.

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Ethylene

• Simplest alkenes.
• Also known as ethene
• Chemical formula C2H4.

• Properties
• Colorless
• Odorless
• Flammable gas.

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PE Process

• Low Pressure Polymerization
• Ethylene is dissolved in a solvent and activated
  with a catalyst.
• Elevated temperatures and pressures are not
  required.
• i.e. a high density PE (PE-HD), are obtained
  under well controlled conditions.

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Types of PE

• Polyethylene has different grades
• Low Density Polyethylene (LDPE).
• High Density Polyethylene (HDPE).

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LDPE

• It has an average molecules 19,000 of carbon
  long.
• Can be applied in many fields.
• Film (packaging, heavy duty sacks and bags).
• Extrusion ( coating of paper and board).
• Injection moldings for the production of toys,
  house wares, lids and caps.

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HDPE

• The molecules average is 200,000 of carbons atom
  long.
• Demand for the polymer consist of
• Milk bottles, drums, fuel tanks, house wares).
• Extruded pipe ( for water, gas, irrigation
  conduit and wire coating).

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Catalyst

• A substance that accelerates a reaction but
  undergoes no net chemical change.
• Function
• To lower the activation energy of the reaction.
• To achieve a higher reaction rate at the same
  temperature.

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Types

• Homogeneous Catalyst
• A catalyst that is in the same phase as the
  reaction mixture.
• Example an acid added to an aqueous solution.
• Heterogeneous Catalyst
• A catalyst that is in a different phase.
• Example a solid catalyst for a gas phase
  reaction.

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Metallocenes

• The advantages are obtained by
• Controlling of polymer molecular weight.
• Molecular weight distribution.
• Co-monomer distribution and content.

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Polymerization Process

• Polymerization is the process in which monomer
  units are linked together by a chemical reaction
  to form long chains.
• Process mainly based on chemical reaction.

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Polymerization Process
The polymer chains can be classified
into Linear branched Cross-linked (network)
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Polymerization Reactions

• Polymerization reactions can be divided into two
  groups
• Step-growth polymerization
• (also called condensation polymerization)
• Chain polymerization
• (also known as addition polymerization)

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Reaction's Steps

• Chain Initiation Step
• Chain initiation involves the reaction of a
  monomer molecule at a vacant active site to form
  a live polymer molecule of unit length at that
  site.
• This reaction converts a vacant active site to a
  propagation site.

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Reaction's Steps

• Chain Initiation Step
• is vacant catalyst sites of type k.
• Mi is monomer.
• is a live polymer chain of unit length
• attached to an active site of type k.

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Reaction's Steps
Initiation reaction only depends on the initiator
concentration. The initiator decomposes
according to equation The rate equation
becomes
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Reaction's Steps

• Propagation Step
• The live polymer at each active site type grows
  or propagates through the addition of monomer
  molecules.
• Long polymer chains are formed.

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Reaction's Steps

• Propagation Step
• is live polymer chain of length n having an
  active
• segment of type i attached to a active site
  of type k.
• Mj is monomer.
• is a growing polymer

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Reaction's Steps
The reaction is a second order. It is
unimolecular in RMn and M The rate law
becomes
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Reaction's Steps

• Termination Step
• The formation of the dead polymer occurs
  primarily by addition mechanisms.
• P is the complete polymer

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Reaction's Steps
The termination reaction is The rate law
becomes
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Designed Process

• Production rate 210,000 ton/year
• Raw Materials (in fresh feeds)
• Ethylene 38,300 kg/hr
• Propane 20,300 kg/hr
• Hydrogen 34.6 kg/hr
• Co-catalyst 10.5 kg/hr
• Catalyst 1 kg/hr

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Designed Process

• Reactors
• 2 loop reactors
• 1 Conversion reactor.
• Two separation vessels.
• Three pumps.
• Compressor.
• Heater.
• Two Mixers.

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Designed Process

• Polyethylene Production Rate
• Pre-loop reactor 2.4 (0.1646 kg/hr)
• Loop reactor 34 (2.3193 kg/hr)
• Conversion reactor 63.6 (4.3415 kg/hr)

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Material Balance

• It is done for every stream in the process.
• The general mass balance equation applies
• Input output generation consumption
  accumulation
• The process is steady state.

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Energy Balance

• Utilities
• The pre-loop reactor 17.64 m3/hr
• The loop reactor 199.5 m3/hr.
• The conversion reactor 403.2 m3/hr

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Energy Balance

• Heat Duties

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Energy Balance

• Pre-loop reactor temperature profile

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Energy Balance

• Loop reactor temperature profile

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Sizing and Design

• Pumps
• Pump-1
• Volumetric flow rate 1.22 m3/hr
• Type single stage centrifugal pump.
• Pump-2
• Volumetric flow rate 14.72 m3/hr
• Type single stage centrifugal pump.
• Pump-3
• Volumetric flow rate 11.62 m3/hr
• Type single stage centrifugal pump.

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Sizing and Design

• Heater
• Shell tube heat exchanger.
• Heat transfer area 15 m2.

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Sizing and Design

• Compressor
• Volumetric flow rate 700 m3/hr.
• Discharge pressure 50 bars.
• Type reciprocating compressor.

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Sizing and Design

• Separation Vessels
• Vessel-1
• Diameter 3.62 m
• Height 6.21 m
• Vessel-2
• Diameter 1.52 m
• Height 6.50 m

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Sizing and Design

• Reactors
• Pre-loop reactor
• Volume 5.6 m3
• No. of Tubes 10
• Diameter of tube 0.3 m
• Length of tube 8 m
• Loop reactor
• Volume 154 m3
• No. of Tubes 20
• Diameter of tube 0.7 m
• Length of tube 20 m

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Economics Cost Estimation

• Variable cost 30,006,241.96
• Total Fixed Cost 728,425.2
• Direct production cost 30,734,667.2
• Total investment required for the project
  1,038,297.6
• Annual revenue 186,417,000 /year
• Capital cost 195,073,468.3

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Safety Rules in chemical Handling

• The potential for hazardous situation is
  associated with many
• chemicals.
• Risk can be minimized or even totally removed
  with the correct
• Knowledge
• Personal protection
• Storage conditions
• Handling

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Equipment Related Issues

• Hot Surfaces
• Electricity
• Temporary Equipment

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Hot Surfaces

• Several equipment and piping are hot in loop
  reactor area.
• Normally, these surfaces are insulated to
  decrease the surface temperature.
• Surfaces located where personnel may be exposed
  to surface temperatures
• above 65 C are designed to be insulated.
• However, in some cases, the insulation is
  removed for a period of time.

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Electricity

• The main risk associated with electricity are
  burns and electrical shock.
• Both are life threatening.
• The open junction electrical boxes will act as
  an ignition source.
• The electricity can be generated inside the
  unit. (Static Electricity)
• It is characterized as a high voltage and low
  current.
• The energy may be high enough to ignite a
  combustible mixture.

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Electricity

• Avoidance of Static Electricity build-up is
  accomplished in the design through
• earth connections.
• They keep the electrical potential of various
  equipment and parts at the
• same level.
• The earth connections should be checked that
• They are in place
• Functioning especially after maintenance
  activities

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Temporary Equipment

• For various reasons, temporary equipment will
  be used in the plant for
• Maintenance
• Operation
• Examples are
• Movable compressors and pumps
• Cranes and fork-lift trucks

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Temporary Equipment

• The risks associated with the use of temporary
  equipment in the plant are
• many and varied depending on the equipment.
• Examples are
• Blockage of access and escape routes.
• Hitting nearby process equipment.
• Acting as ignition sources.
• Risk of personal injury caused by the handling
  of the temporary equipment.

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Environmental Issues

• Environmental impact assessment
• Should be made for designing the high density
  polyethylene as a new
• project.
• Represents a summary of the environmental
  inventory.
• Noise
• One of the most pervasive environmental
  problems.
• Should be accounted for in the design and
  selecting equipment.

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Environmental Issues

• Air Pollution
• HDPE generally
• Is considered one of the least problematic
  plastics,
• Has no indications of toxicity associated with
  the polymer have been
• identified from authorities and industry. .
• During the process operation
• Some times needed to release some gases to
  atmosphere to reduce the
• pressure from the safety valve.
• Some vapors emissions during the process contain
  high concentrations
• of some gases.

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Ethylene

• Its respiration has a slightly narcotic effect.
• In high concentrations, it presents a risk of
  suffocation by replacing
• oxygen in air.
• Liquefied ethylene can cause cold burns in
  contact with skin.
• It is not to be handled near an open flame or
  source of heat or ignition.
• When handling ethylene, sufficient ventilation
  and good personal
• protection should be provided.

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Propane

• Exposure of propane at high concentration is
  narcotic.
• In high concentrations, it presents a risk of
  suffocation by replacing oxygen in
• air.
• Liquefied propane can cause cold burns in
  contact with skin.
• It is not to be handled near an open flame or
  source of heat or ignition.
• When handling, sufficient ventilation and good
  personal protection should be
• provided.

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Hydrogen

• Hydrogen ignites easily and forms together with
  oxygen an explosive gas.
• The explosive limits of hydrogen/air mixtures
  are 4 to 75 v/v.
• Although hydrogen is non-toxic, absorption of
  large quantities of the gas may
• cause headache and nausea.
• Hydrogen gas is not to be handled near an open
  flame or source of heat or
• ignition.

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Tri-ethyl aluminum (TEAL)

• It is essential to ensure that all pipes and
  equipment are thoroughly dried and
• free from oxygen before initially introducing
  TEAL.
• During maintenance, full body protective
  clothing made of aluminized material
• is recommended.
• Water must not be used to extinguish fires in
  which TEAL is or may be
• involved.
• Dry powder is a suitable extinguishing agent to
  be used against TEAL fires.

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Catalyst

• All Ziegler-Natta catalysts form irritating
  gases containing hydrogen chloride
• when they react with
• Oxygen in air
• Moisture or water
• The catalyst powder is irritant and corrosive
  to skin and eyes.
• The catalyst should always be kept under a
  small nitrogen pressure to avoid
• air, water, or moisture contact.
• Powder or CO2 can be used to extinguish
  catalyst fires, water must not be used.

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Thank you
Questions are welcomed !