C7- Polymerisation process

Question 1

What does LDPE stand for

Answer 1

Low density polyethylene

Question 2

Is LDPE highly branched?

Answer 2

yes

Question 3

What is HDPE

Answer 3

High density polyethylene

Question 4

Is HDPE highly branched?

Answer 4

no

Question 5

What is LLDPE

Answer 5

Linear Low-Density Polyethylene.
–>Copolymerization

Question 6

What is copolymerization?

Answer 6

1-alkene + ethene
short + uniform branches

Question 7

What are the process conditions for LDPE?

Answer 7

^P
^T (branching/side reactions)
low density

Question 8

What are the process conditions for LLDPE and HDPE?

Answer 8

low P
catalyst
density is proportional type and # of comonomere

Question 9

What is MFR?

Answer 9

mass flow rate

Question 10

What does high density do to polymers? (^)

Answer 10

^Properties: such as stifness and barrier properties

Question 11

What does high density do to polymers? (lowering)

Answer 11

lowers transparency
low T brittleness

Question 12

Is polymer density proportional to T for LDPE process at high P and high T? why

Answer 12

yes
at ^T = + side branching = + branching = lowers density

Question 13

How is polymer density affected in HDPE and LLDPE?

Answer 13

it is proportional to type and amount of comonomere added
side chains of different lenght = polymer as low density

Question 14

What are the 2 different types of polymerization reactions?

Answer 14

Polyaddition (chain growth)
and Polycondensation (step growth)

Question 15

Pros of polyaddition

Answer 15

No limit on molar mass
versatile

Question 16

Con’s of polyaddition

Answer 16

irreversible
hard to do depolymerization = waste

Question 17

Pros of Polycondensation

Answer 17

reversible or equilibrium
small molecule expelled

Question 18

Con’s of polycondensation

Answer 18

versatility losses
limits on equilibrium = limit on molar mass

Question 19

Process conditions (speed, equ?, endo vs exo) of polyaddition

Answer 19

fast
irreversible = easy to do depolym.
^^exo

Question 20

Process conditions (speed, equ?, endo vs exo) of polycondensation

Answer 20

slow
rev or equi
a little exo

Question 21

Polymerization mechanism is from chain growth or step growth?

Answer 21

chain growth

Question 22

what are the 2 type of polymerization mechanisms

Answer 22

radi or coodination

Question 23

Explain coordination polymerization mechanism

Answer 23

catalyst (uses transition metals)
more control on architecture: coordinate insertion of monom. at location of choice

Question 24

describe radiation mechanism

Answer 24

1. initiation
2. propagation
3. termination

Question 25

what is CON/ drawback in radiation mechanism?

Answer 25

back-bitting with radical = branches due to flexibilty/ folding = internal chain transfert = hard to control architecture

Question 26

PROS of coordination

Answer 26

no branching = no radicals control on architecture irreversible

Question 27

What are the 3 types of catalyst

Answer 27

Ziegler-Natta Phillips metallocenes

Question 28

PROS of Ziegler-Natta cat.

Answer 28

yields stereoregular polymers when ^alkene polym

Question 29

CON's of Ziegler-Natta cat.

Answer 29

contains a lot of active sites = different chain can grow

Question 30

Which cat is the most important

Answer 30

Phillip's

Question 31

PROS of phillips cat

Answer 31

most important good for ethylene production

Question 32

CONS of phillips cat

Answer 32

bad for homopolymerisation of propene or ^olefins

Question 33

PRO's of metallocenes

Answer 33

stereoselectivity

Question 34

What are 3 challenges when polymerising?

Answer 34

1. viscosity 2. highly exothermic 3. runaway

Question 35

why is viscosity a challenge ?

Answer 35

^visc = poor heat transfer

Question 36

why is high exothermicity a challenge?

Answer 36

if T to ^: ethene decomposes--> C, CH4, H2... limits conversion

Question 37

why is runaway a challenge?

Answer 37

decomposition of ethylene P,T rises uncontrallably = burst --> need P relief valves

Question 38

What are the 3 different processes for high pressure (LDPE)

Answer 38

1. autoclave process (CSTR) 2. tubular process (PFR) 3. master batch

Question 39

CON'S of autoclave process (X2)

Answer 39

- low conversion (20%) due to Tad(limit on T^) = recuperate ethylene - metal fatigue

Question 40

Ethylene acts as what in autoclave process?

Answer 40

solvent

Question 41

what is the P for autoclave process

Answer 41

1500-3000 bars

Question 42

PROS of tubular process (x2)

Answer 42

cooling with concentric tube syst (bc T =300°c = danger for ethylene decomposition) high velocity through reactor = low contamination on walls

Question 43

CON's of tubular process (x2)

Answer 43

^P ^T = fatigue

Question 44

what is the conversion for tubular process for one vs multiple initiators

Answer 44

20-35% (for multiple initiatior) 15-22% (for 1 initiator)

Question 45

What are the jackets for in the tubular process

Answer 45

heat transfert fluid and reactor

Question 46

What are the 2 pressures of the 2 step seperation of tubular process ?

Answer 46

2000 --> 1 bar

Question 47

Describe the big steps of the tubular process

Answer 47

ethene --> mix with monom --> compressor1 --> mix with monom. --> compressor 2 --> initiator --> reactor --> shockwave valve --> HP sep --> LP sep (1. recycle) --> 2 extension --> dryer --> LD polymer

Question 48

What is the goal of the master batch process?

Answer 48

additive + other batch of polymers to dilute to get good ppm level (1000)

Question 49

What is the ppm of additives? What is its impact on recycling

Answer 49

1000

Question 50

is it easier to blend 2 polymers with each other or to add an additive?

Answer 50

with each other

Question 51

What is the function of functional additives

Answer 51

avoid polymer to break down / stabilize

Question 52

What are 4 types of additives

Answer 52

1. functionnal additives 2. pigments 3. fillers 4. reinforcement

Question 53

What affects runaway?

Answer 53

^Tin = faster runaway Steam cracking difference in ethyne in feed (biger = faster)

Question 54

What are the process conditions for low pressure polym (HDPE, LLDPE)?

Answer 54

low P Cat

Question 55

Describe the gas phase reactor (for low P)

Answer 55

fluidized bed reactor monomer as the fluidizing agent (gas) polymer + cat = solid

Question 56

PRO's of gas phase reactor (for low P)

Answer 56

good heat transfer mixing

Question 57

CON's of gas phase reactor (for low P)

Answer 57

conductivity of gas is lower than fluid gas is a bad conductor

Question 58

what is the solution to gas being a bad conductor for of gas phase reactor (for low P)?

Answer 58

low residance time = ^gas velocity, particle + , condensing comonomer = abs + heat = ^conversion control of cat = control of T

Question 59

What happens if there is runaway in the gas phase reactor (for low P)?

Answer 59

+ CO2 = poisons the cat = no runaway

Question 60

Describe the slurry/suspension polymerization technique.

Answer 60

liquid = better heat transfer: monomere is dissolved in diluent polymer particles formed slurry circulating double wall = control T recupurate solvant

Question 61

What happens if T < Tmelt in slurry/suspension techniques(for low P)

Answer 61

solid particles in monomere-HC mixture

Question 62

Does the catalyst dissolves in slurry/suspension techniques(for low P)

Answer 62

no : in suspension w/ HC-ethylene mix --. HDPE

Question 63

Is the liquid ethylene the solvent in in slurry/suspension techniques(for low P)

Answer 63

yes doesn't dissolve polymer, doesn't evaporate

Question 64

What are 2 modes of operation for slurry polym?

Answer 64

bulk vs diluent

Question 65

What type of reactor is used for slurry in bulk?

Answer 65

CSTR (stirred autoclave) :) easily build, uniform rxn

Question 66

What is max T in bulk slurry, why?

Answer 66

120°C to avoid melting PE

Question 67

what is the feed for bulk slurry?

Answer 67

liquid monomere

Question 68

What is the heat transfer limited to in bulk slurry?

Answer 68

surface:volume ration

Question 69

how to have extra T control for bulk slurry?

Answer 69

using heat of evap of monomere to remove heat of polymere (good for PP polym)

Question 70

is the diluent slurry process most used, what reactor is used?

Answer 70

yes, loop reactor

Question 71

what is the diluent medium for diluent slurry process

Answer 71

non-solvent for polyolefins (isobutane, hexane)

Question 72

what is the goal of diluent slurry process

Answer 72

diluent used to dissipate heat + heat removal through double wall

Question 73

does diluent slurry process need a recovery step

Answer 73

yes

Question 74

is the polymer slurry continuously circulated?

Answer 74

yes

Question 75

Is solvent / solution polymerization used for high or low Pressure

Answer 75

low p

Question 76

Describe dilution polymerization

Answer 76

monomere and catalyst are dissolved in non-reactive solvent (halogenated) the solvent-liq absorbs heat gen by chemical reaction = control rate rxn

Question 77

The dilution polymerization is suitable only for what? why

Answer 77

only for creation of wet polymer types --> removal of excess solvent is difficult (not $$)

Question 78

Advantages of dilution polymerization

Answer 78

precise control of chem rxn control of heat and viscosity control over acceleration of process

Question 79

disadvantages of dilution polymerization

Answer 79

difficulty of removal of excess solvent from finished polymer = must be chose carefully need non-reactive solvent w/ monomere if not could result in auto acceleration, side products

Question 80

why is auto acceleration bad, what is it

Answer 80

hest of product doesn't dissipate quickly enough by solvent