Polymerization Reactors

Polymerization Reactors

General aspects

Traditional stirred tank reactor is probably still the most common

reactor type used in polymerizations. This is due to its wide

application area and modification possibilities. The reactor can be

arranged in a cascade and may include various mixing and

cooling systems. Stirred tank reactor is used for mass, suspension

as well as emulsion polymerizations.

Stirred tank reactor

Advantages of stirred tank reactor:

Suitabily for both continuous and batch use

Applicability for different scales from laboratory to industrial

production

Flexibility in terms of operation method, conditions and

build-up

Standardized structure and many applications

Possiblity to use various materials and their combinations

Easy to maintain and clean

Relatively easy to modify for other products

Stirred tank reactor

Disadvantages of stirred tank reactor:

Large decrease in cooling surface area in relation to volume

when reactor size increases

Mass and heat transfer as well as mixing becomes more difficult

when the viscosity of the reaction mixture increses

Difficulty to obtain narrow residence time distribution in

continuous operation

Stirred tank reactor

Factors influencing stirred tank reactor operation:

Kinetics

Residence time distribution

Homogenicity and rate of mixing

Stirred tank reactor

In recent decades the volume of polymer production hasincreased significantly. Consequently this trend has resultedin ever larger reactors. The size of the largest reactors hasincreased from 40 m3 to 500 m3. Pressure/volume area ofstirred tank reactor:

Stirred tank reactor

Examples of the use of stirred tank reactors in polymerizations (1/2):

Polymerization

type

Reactor

type

Mass Solution- Precipitation Suspension - Gas phase

Batch

reactor

Polyesters Adhesive

resins

PolyHEMA

PVC

PS

HIPS

PFTE

PVC

SB-latex

PS

PVAcStirred

tankSemi-

batch

reactor

PS

Continuous

reactor

PE-LD EPR

PE-HD

PE-LLD

EPR PVC PE-HD

PE-LLD

PP

CSTR

cascade

PS

PET

PE

PP

reactor

Emulsion

polymeriza-

tion

polymeriza-

tion

polymeriza-

tion

polymeriza-

tion

polymeriza-

tion

polymeriza-

tion

… (2/2):

Polymerization type

Reactor type

Mass polymerization

Tubular reactorPE-LD

Polyester

Mould reactor

PMMA

Melamine

PUR

Epoxides

UF resins

Polyester resins

Line reactor

PUR

Varnish resins

Polyester resin

Stirred tank reactor

Observations for the use of stirred tank reactor:

Material choice of the inner surface of the reactor is an

important factor …adhesion properties vs. mechanical

durability

Cooling …jacket cooling up until reactor size of about 30 m3

Mixing and heat transfer become more difficult as viscosity

increases …need for mixing power vs. amount of heat

requires optimation

In the case of continuous stirred tank reactors (CSTR) usually

two or three step CSTR cascade is sufficient …residence time

distribution

Stirred tank reactor

10. Comparision between Batch

and Continuous Reactors

Batch vs. continuos operation

Batch:

Scale: small…large

Inexpensive investment

Cleanable

Optimation of conditions

Semi-batch principle

Fast grade changes

Yield/time …low

Non-steady state

• shutdown

• start-up

Continuous:

Large scale

Large investment

Polymerization must not stain

Grade changes have to be planned

Yield/time…low

Steady state achieved after 3-4 residence times

Batch reactor types

Reactor vs. reaction

Suitability of reactor types for different reaction types:

Reactor vs. reaction

Batch reactor …precipitation polymerizations such as

polymerization of acrylonitrile in water phase, azeotropic

copolymerization of styrene with acrylonitrile and various

aqueous dispersion polymerizations.

Discontinuous stirred tank reactor …production of beadlike

polymer products in large scale…PVC, EPS, ion-exchange resins

as styrene-vinylbenzenecopolymer, polymethyl methacrylate and

polyvinyl acetate.

Reactor vs. reaction

Continuous stirred tank reactor (CSTR) …chainpolymerizations such as solution polymerization of butadiene,polymerization of ethylene and propylene and theircopolymerization and terpolymerization with a diene (e.g.,EPM or EPDM) using different types of Ziegler catalysts.

Continuous precipitation polymerization …polymersuspension …production of polyethylene, polypropylene,EPM and EPDM.

Reactor vs. reaction

Batch stirred tank reactor …melt or solution polymerization type polycondensation reactions, during which the melt is mixed often only by the forming water vapour…for example condensation resins made of formaldehyde and urea, melamine or phenol …also interfacial polymerization is possible

Reactive injection moulding (RIM) …two components are intermixed and injected instantly into a mould. The reaction occurs only in the mould. For example the production of polyuretane in which a diol and di-isocyanate are mixed and foamed in a mould. Therefore the mould fuctions as a batch reactor. Another similar process is the anionic polymerization of e-caprolactams in a mould.

Reactor Cascades

Kaskadit

Sekoitusreaktorikaskadi on panostoimisen sekoitusreaktorin jälkeen ehkä monipuolisin kaikista polymerointeihin käytetyistä reaktorityypeistä.

Sitä käytetään mm. styreeni/butadieenikumin, nitriilikumin, akryylinitriili/butadieenin ja polykloropreenin emulsio-polymeroinneissa, sekä stereosäännöllisen butadieenin ja isopreenin eri katalyyteillä initioiduissa liuospolymeroinneissa.

Jatkuvatoimisissa sekoitusreaktorikaskadeissa voidaan tehdä myös eteenin ja propeenin homo- tai kopolymerointeja liuoksessa tai niiden terpolymerointeja siirtymämetallikatalyyttien avulla.

Kaskadit

Kaskadi- ja sekoitusreaktorityyppejä:

Special Cases of Continuous

Stirred Reactors

Loop-reaktori

Phillips-Petroleum-yhtiö kehitti niin sanotun loop-reaktorin alun

perin polyeteenin polymerointiin. Nykyisin tätä reaktorityyppiä

käytetään yleisesti myös propeenin saostusperiaatteella

toimivassa massapolymeroinnissa.

Loop-reaktori lähestyy viipymäaikajakaumansa puolesta

jatkuvatoimista sekoitusreaktoria, kun kiertonopeus loopissa on

hyvin paljon suurempi kuin syöttönopeus. Loop-reaktoria

käytetään ennen kaikkea eteenin slurry-polymerointiin. Suuri

virtausnopeus takaa hyvän lämmönsiirron ja sen, ettei reaktori

likaannu.

Leijupetireaktori

Kaasufaasireaktioita voidaan suorittaa leijukerrosreaktoreissa. Niissä polymerointipulveri polymeroituu kaasumaisessa monomeerissä, ei siis oikeastaan kaasufaasissa. Initiaattori sijaitsee polymeeripartikkelin sisällä, ja monomeeri itse asiassa liukenee polymeeripartikkeliin.

Union Carbide Company (UCC) että BASF ovat kehittäneet suurimittakaavaisia kaasufaasipolymerointiprosesseja eteenin ja propenin matalapainepolymerointiin.

Reaktoreita

”Erityistapauksia”:

13. Tubular reactors

Tubular reactors

Tubular reactors are used alongside with autoclave for

continuous polymerization of high density polyethylene. Also for

example polyamide 66 can be polycondensated in tubular

reactors.

Stirred tower reactors reside between tubular reactors and CSTR

in terms of their residence time distribution. Partial feedback may

occur in stirred tower reactors.

Tubular reactors

Some tubular reactor types used for polymerizations: