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: