Transcript Slide 1

POLYMERIZATION PROCESS
HOMOGENEOUS
SYSTEM
BULK
POLYMERIZATION
SOLUTION
POLYMERIZATION
HETEROGENEOUS
SYSTEM
SUSPENSION POLYMERIZATION
EMULSION POLYMERIZATION
PRECIPITATION
POLYMERIZATION
INTERFACIAL AND SOLUTION
POLYCONDENSATIONS
In a homogeneous polymerization process, all
reactants, including monomers, initiators, and
solvents, are mutually soluble and compatible
with the resulting polymer.
initiator
monomer
• Monomer, initiator, and
polymer are miscible
• Generally exothermic
• The higher the
conversion, the higher
the viscosity
E-1
polymer
not very
exothermic
reactants are usually
of low activity
Step-growth
polymerization
high temperatures are required
• Low viscosity at the beginning
• high viscosities at later stages of the reaction
• problems with the removal of volatile
byproducts
• a possible change in the kinetics of the
reaction from a chemical-controlled regime
to a diffusion-controlled one.
• Low heat capacity
• Low thermal conductivity
• extremely viscous reaction media
• Low overall heat transfer coefficient
• Development of localized hot spots
• Runaway reactions
• Degradation of polymer product
• Broadened mole weight distribution
• Because of the above heat transfer problems,
bulk polymerization of vinyl monomers is
restricted to those with relatively low
reactivities and enthalpies of polymerization.
• This is exemplified by the homogeneous bulk
polymerization of methyl methacrylate and
styrene (see the following Table).
• Some polyurethanes and polyesters are
examples of step-reaction polymers that can be
produced by homogeneous bulk polymerizations.
• The products of these reactions might be a
solid, as in the case with acrylic polymers; a
melt, as produced by some continuous
polymerization of styrene; or a solution of
polymer in monomer, as with certain alkydtype polyesters.
To overcome the problems, the process is carried
out in two stages:
Stage I
Prepolymerization or polymerization
initiation stage, which is often carried
out in a short period (5 – 10 minutes)
resulting syrup (low degree of
polymerization and low viscosity)
Tahap II Polymerization stage, which is often
carried out in a mold resulting solid
polymer in a relatively long period.
• Another way of circumventing the heat transfer
problems is by continuous bulk polymerization.
• An example is the polymerization of
polystyrene, which is carried out in two stages.
• In the first stage, styrene is polymerized at 80°C
to 30 to 35% monomer conversion in a stirred
reactor known as a prepolymerizer.
• The resulting reaction mass — a viscous
solution or syrup of polymer in monomer —
subsequently passes down a tower with
increasing temperature.
• The increasing temperature helps to keep the
viscosity at manageable levels and also
enhances conversion, which reaches at least
95% at the exit of the tower.
• By removal of the heat of polymerization at the
top of the tower and proper temperature
control of the finished polymer at the bottom
of the tower, an optimum molecular weight
may be achieved and channeling of the polymer
may be minimized.
Vertical column reactor for the continuous bulk
polymerization of styrene
• Bulk polymerization is ideally suited for making
pure polymeric products, as in the manufacture
of optical grade poly(methyl methacrylate) or
impact-resistant polystyrene, because of
minimal contamination of the product.
• However, removal of the unreacted monomer
is usually necessary, and this can be a difficult
process.
• This may be achieved in vacuum extruders
where the molten polymer is extruded under
vacuum to suck off the residual monomer.
Bulk Polymerization is generally more suitable for
step-growth polymerization than chain-growth
polymerization because:
• The major problems in bulk polymerization are heat
removal and mixing.
• H condensation polymerization (2 – 6 kkal/kg) < H
addition polymerization (15 – 20 kkal/kg).
• Even at low conversion, viscosity of product of
addition polymerization > condensation
polymerization.
• All the problems leads to much lower heat transfer
coefficient in chain-growth polymerization than in
step-growth polymerization.
solvent
catalyst
monomer
initiator
• Monomer, initiator,
catalyst, and resulting
polymer are soluble in
the solvent
• Exothermic
E-1
Solution
• The higher the
conversion, the higher
the viscosity
• In solution polymerization, the monomer,
initiator, and resulting polymer are all soluble in
the solvent.
• Solution polymerization may involve a simple
process in which a monomer, catalyst, and
solvent are stirred together to form a solution
that reacts without the need for heating or
cooling or any special handling.
• On the other hand, elaborate equipment may
be required.
• For example, a synthetic rubber process using a
coordination catalyst requires rigorous
exclusion of air (to less than 10 ppm); moisture;
carbon dioxide; and other catalyst deactivators
from the monomer, solvent, and any other
ingredient with which the catalyst will come in
contact before the reaction.
• In addition, exclusion of air prevents the
tendency to form dangerous peroxides.
• To avoid product contamination and
discoloration, materials of construction also
need to be selected with the greatest care.
• Polymerization is performed in solution either
batchwise or continuously.
• The batch may be mixed and held at a constant
temperature while running for a given time, or
for a time dictated by tests made during the
progress of the run.
• A continuous reaction train, consists of a
number of reactors, usually up to about ten,
with the earlier ones overflowing into the next
and the later ones on level control, with
transfer from one to the next by pump.
• As the reaction progresses, solution polymerization
generally involves a pronounced increase in
viscosity and evolution of heat.
• The viscosity increase demands higher power and
stronger design for pumps and agitators.
• The reactor design depends largely on how the
heat evolved is dissipated.
• Reactors in solution polymerization service use
jackets; internal or external coils; evaporative
cooling with or without compression of the vapor
or simple reflux-cooling facilities, a pumped
recirculation loop through external heat exchanger;
and combinations of these.
ADVANTAGES OF SOLUTION POLYMERIZATION
• The catalyst is not coated by polymer so that its
efficiency is sustained and removal of catalyst
residues from the polymer, when required, is
simplified.
• Solution polymerization is one way of reducing the
heat transfer problems encountered in bulk
polymerization.
• The solvent acts as an inert diluent, increasing
overall heat capacity without contributing to heat
generation.
• By conducting the polymerization at the reflux
temperature of the reaction mass, the heat of
polymerization can be conveniently and efficiently
removed.
• Furthermore, relative to bulk polymerization,
mixing is facilitated because the presence of the
solvent reduces the rate of increase of reaction
medium viscosity as the reaction progresses.
DRAWBACKS OF SOLUTION POLYMERIZATION
• The solubility of polymers is generally limited,
particularly at higher molecular weights.
• Lower solubility requires that vessels be larger for a
given production capacity.
• The use of an inert solvent not only lowers the
yield per reactor volume but also reduces the
reaction rate and average chain length since these
quantities are proportional to monomer
concentration.
• The necessity of selecting an inert solvent to
eliminate the possibility of chain transfer to the
solvent.
• The solvent frequently presents hazards of toxicity,
fire, explosion, corrosion, and odor problems not
associated with the product itself.
• Solvent handling and recovery and separation of
the polymer involve additional costs, and removal
of unreacted monomer can be difficult. Complete
removal of the solvent is difficult in some cases.
• With certain monomers (e.g., acrylates) solution
polymerization leads to a relatively low reaction
rate and low-molecular-weight polymers as
compared with aqueous emulsion or suspension
polymerization.
• The problem of cleaning equipment and disposal of
dirty solvent constitutes another disadvantage of
solution polymerization.
COMMERCIAL USE
• Solution polymerization finds ready applications
when the end use of the polymer requires a
solution, as in certain adhesives and coating
processes [i.e., poly(vinyl acetate) to be converted
to poly(vinyl alcohol) and some acrylic ester
finishes].
• Solution polymerization is used widely in ionic and
coordination polymerization.
• High-density polyethylene, polybutadiene, and
butyl rubber are produced this way.
Typical Solution-Polymerization Processes
Notes:
a For example, 1,3-butadiene or isoprene
b Includes hexane, heptane, an olefin, benzene, or a
halogenated hydrocarbon. Must be free from moisture,
oxygen, and other catalyst deactivators.
c TiCl4, an aluminium, alkyl, and cobalt halide are reported to
be used to make meripol CB cis-polybutadiene.
d In the transesterification step, inorganic salts, alkali metals or
their alkoxides, or Cu, Cr, Pb, or Mn metal are used. In the
next step, the catalyst is not disclosed.
e Isotactic polymers are not usually formed completely in
solution but precipitate in the course of reaction.
f Amines, cyclic nitrogen compounds, arisine, stibine, or
phosphine.
initiator
monomer
• Monomer dan initiator
saling larut
• Polimer tidak larut dalam
sisa monomer,
• Biasanya eksotermis
E-1
monomer polymer
• Semakin besar konversi,
semakin tinggi viskositasnya
CONTOH The high pressure free radical process for the
manufacture of Low Density Polyethylene
initiator
ethylene
T = 200 – 280C
P = 1000 – 3000 atm
E-1
ethylene
polyethylene
Supercritical
• Polyethylene membentuk cabang karena proses selfbranching.
• Cabang yang lebih panjang dari metil tidak dapat
masuk ke kisi kristal polyethylene, sehingga polimer
padat yang dihasilkan kurang bersifat kristal (tidak
transparan) dan lebih kaku daripada HDPE (0.9350.96 g cm-3) yang dibuat dengan reaksi coordination
polymerization
solven
katalis
monomer
inisiator
• Monomer, initiator, dan
katalis larut dalam solven,
• Polimer tidak larut dalam
larutan
• Ekotermis
• Semakin besar konversi,
semakin tinggi viskositasnya
E-1
Larutan
polimer
Langkah-langkah proses polimerisasi slurry:
1. Langkah penyiapan katalis.
Katalis yang pada umumnya berupa padatan,
diproduksi sedemikian rupa sehingga tidak ada air dan
oksigen pada katalis.
2. Langkah polimerisasi
Reaksi polimerisasi dilakukan pada P < 50 atm dan T <
110C (untuk menghidari larutnya polimer) sehingga
terbentuk slurry dengan konsentrasi polimer 20%
dalam diluen cairan alifatik (misal propylene, dalam
pembuatan polypropylene).
3. Recovery polimer:
Langkah ini dilakukan dengan cara stripping terhadap
diluen, pencucian untuk menghilangkan sisa katalis,
dan ekstraksi komponen polimer yang tak dikehendaki
(jika perlu).
4. Langkah “compounding”:
Langkah ini bertujuan untuk mencampur berbagai
macam stabilizer dan bahan aditif dengan lelehan
polimer, yang kemudian diikuti dengan pendinginan
dan pembentukan pellet.
• Jika konsentrasi katalis sangat kecil, maka
langkah penghilangan katalis dapat diabaikan.
• Konversi biasanya lebih tinggi dibandingkan
dengan free-radical, high-pressure
polymerization process, sehingga lebih sedikit
monomer yang harus direcycle.
• Temperatur reaksi pada proses slurry dapat
dikontrol dengan me-reflux solven.
Dispersing agent
inisiator
monomer
air
• Monomer dan initiator
tidak larut dalam solven,
• Polimer tidak larut dalam
larutan
• Ekotermis
E-1
Polimer tersuspensi
• Semakin besar konversi,
viskositas relatif tidak
berubah.
Peran air:
1. Media transfer panas.
2. Menjaga viskositas media reaksi tetap rendah.
Dalam polimerisasi vinyl chloride :
(CP)monomer = (CP)polimer = ¼ (CP)air
Rasio air/monomer : 1,5/1 – 1,75/1
Inisiator
Senyawa
peroxide
Benzoyl peroxide
Diacetyl peroxide
Lauryl peroxide
t-butyl-peroxides
Senyawa
azo
Senyawa
ionik
Azo-bisisobutyronitrile
(AIBN)
aluminum alkyl
antimony alkyl
titanium chloride
chromium oxides
Jumlah katalis : 0.1 – 0.5% dari berat monomer
Apa yang terjadi dalam tetesan monomer?
0%
10 – 20%
75 – 80%
Encer
Kental
Lengket
Padatan
Tidak lengket
Masalah utama
Aglomerasi
(terutama pada tahap dimana tetesan menjadi kental dan lengket)
Pengadukan
Stabilizing agent
Stabilizing agent
Surface-active agents
(surfactants)
Garam dari asam lemak,
MgCO3 , CaCO3
Ca3(PO4)2
TiO, Al2O3
Polimer yang
larut dalam air
gelatin, methyl cellulose,
poly(vinyl alcohol),
starches, gums, dan
poly(acrylic acids) beserta
garamnya
Jumlah stabilizing agent: 0,01 – 0,5% dari berat monomer
Diagram alir polimerisasi suspensi untuk pembuatan PPMA
• Dalam polimerisasi suspensi, monomer +
inisiator yang terlarut didispersikan dalam
bentuk tetesan kecil ke dalam air yang
mengandung sedikit suspension agent.
• Begitu polimerisasi berlangsung, tetesan
monomer berubah menjadi kental dan lengket.
• Hasil akhir reaksi mengandung polimer 25-50%
yang terdispersi dalam air.
• Koagulasi dari dispersi dikontrol dengan
pengadukan dan bantuan stabilizing agent.
• Jika polimerisasi sudah selesai, suspensi polimer
dialirkan ke blowdown tank atau stripper untuk
memisahkan sisa monomer.
• Slurry dipompa ke centrifuge atau filter untuk
menyaring, mencuci, dan mengeringkan polimer.
• Polimer basah (30% air) dikeringkan dengan udara
hangat (66 to 149°C) dalam dryer.
• Polimer kering dikirim ke storage.
REAKTOR
• Bentuk reaktor umumnya tangki vertikal
berpengaduk yang terbuat dari stainless steel
atau glass-lined carbon steel.
• Reaktor dilengkapi dengan pengaduk (tipe
paddle atau anchor) dengan 20 – 60 rpm.
• Yang perlu diperhatikan adalah kontrol
temperatur.
REAKTOR
STAINLESS STEEL
• Perpindahan panas bagus
• Masalah fouling
GLASS-LINED
CARBON STEEL
• Perpindahan panas kurang
• Tidak ada fouling
Reaksi eksotermis
Kontrol temperatur
sangat penting
Reaktor
dengan jaket
Reaktor
dengan baffle
Hati-hati! Dead volume
Sistem
refrijerasi
• Jika ukuran reaktor berjaket diperbesar, timbul
masalah luas perpindahan panas.
• Luas perpindahan panas tidak berbanding lurus
dengan volume reaktor.
• Untuk tangki silinder, pertambahan luas
perpindahan panas jaket sebanding dengan
kenaikan volume dipangkatkan 0,67.
Untuk L = D:
D12L1 D13
V1 

4
4
D22L2 D23
V2 

4
4
A1  D1L1  D12
A2  D2L2  D22
A2  D2   D2 
     
A1  D1   D1 
2
V2

V1
D23
D13
A2

A1
D22
D12
3 23



 V2 
 
 V1 
4  D2 
 
4  D1 
 D2 
 
 D1 
23
2
3
Dispersi monomer
1 m – 0,5 cm
Reaktor mini
Keuntungan polimerisasi suspensi:
1. Penggunaan air sebagai media pertukaran panas
lebih ekonomis daripada solven organik.
2. Dengan nilai CP yang besar, pengambilan panas
reaksi lebih efektif dan kontrol terhadap
temperatur menjadi lebih mudah.
3. Pemisahan dan penanganan polimer lebih mudah
daripada polimerisasi emulsi dan larutan.
4. Produk lebih mudah dimurnikan.
Polimerisasi suspensi paling banyak digunakan untuk
memprodukasi resin plastik:
• Semua jenis resin termoplastik
• Polystyrene,
• Polymethyl methacrylate,
• Polyvinyl chloride,
• Polyvinylidene chloride,
• Polyvinyl acetate,
• Polyethylene,
• Polypropylene
Komposisi dan kondisi reaksi beberapa sistem polimerisasi suspensi
CONTOH SOAL
Mengapa penggunaan coil pendingin dalam reaktor
untuk polimerisasi suspensi tidak dianjurkan?
PENYESAIAN:
Masalah utama dalam reaktor untuk polmerisasi
suspensi adalah terbentuknya kerak polimer. Jika kerak
terbentuk di antara coil-coil pendingin, maka
pembersihannya akan sangat sulit.
• Polimerisasi emulsi saat ini banyak dimanfaatkan secara komersial untuk memproduksi berbagai jenis polimer.
• Polimer yang dibuat dengan proses ini addition
polymer dan memerlukan inisiator radikal
bebas.
Pada umumnya, sistem polimerisasi emulsi terdiri
atas :
• monomer,
• dispersing medium,
• emulsifying agent,
• Inisiator yang larut dalam air,
• transfer agent.
Distribusi Komponen
Contoh resep polimerisasi emulsi:
• 180 bagian (b) air,
• 100 bagian (b) monomer,
• 5 bagian (b) sabun (emulsifying agent),
• 0.5 bagian (b) of potassium persulfate (inisiator
yang larut dalam air).
Bagaimana komponen-komponen ini terdistribusi
dalam sistem?
Sabun adalah garam Na atau K dari asam organik,
seperti sodium stearate:
O
[CH3 (CH2)16  C  O–] Na+
R
Jika sejumlah kecil sabun dimasukkan ke air, maka
akan terionisasi:
O
[CH3 (CH2)16  C  O–] Na+
O
[CH3 (CH2)16  C  O–] + Na+
Anion sabun terdiri dari bagian yang tak larut dalam
air (R) yang berupa rantai panjang, dan diakhiri oleh
bagian yang larut dalam air.
O
[CH3 (CH2)16  C  O–]
Hydrophobic
group
Hydrophilic
group
First addition
of surfactant
More addition
of surfactant
More addition
of surfactant
Surfactant dissolves
in the bulk and form
an adsorption film at
the air/water
interface
colloidal particles
The micelles remain
in dynamic
equilibrium with the
soap molecules
dissolved in water
Micelle bentuk
batang
2  panjang molekul sabun
50 – 100 molekul sabun
Micelle bentuk bola
Jika monomer yang tidak larut/sedikit larut
dalam air diemulsikan dalam air dengan bantuan
sabun dan pengadukan, maka akan terbentuk
tiga fasa:
• Fasa air dengan sedikit sabun dan monomer
yang terlarut.
• Tetesan monomer yang teremulsikan.
• Micelle (monomer-swollen micelles).
• Diameter tetesan monomer : 1 μm.
• Ukuran butiran sangat dipengaruhi oleh
kecepatan pengadukan.
• Konsentrasi micelle: 1018 micelle per ml
• Konsentrasi tetesan monomer: 1010 – 1011 per
ml.
Contoh diagram alir polimerisasi emulsi
Pembentukan agregat dalam air sangat tergantung pada beberapa faktor:
• Konsentrasi surfactant
• Temperatur
• Kekuatan ion
• Keberadaaan molekul lain
LOKASI POLIMERISASI
Jika inisiator yang larut dalam air, seperti
potassium persulfate, ditambahkan ke sistem
polimerisasi emulsi, maka senyawa tersebut
akan mengalami dekomposisi termal menjadi
anion radikal sulfat:
S2O8–
panas
 2 SO4–
Anion radikal yang larut dalam air akan bereaksi
dengan monomer terlarut dalam fasa air membentuk radikal bebas tipe sabun:
SO4–
50 – 60C
+ (n + 1) M 
– S2O4– (CH2 – CX2)n – CH2 – CX2
Lokasi polimerisasi
Alasan mengapa reaksi polimerisasi terjadi dalam
micelle:
(1) Dimensi micelle 50 – 100 Å sementara tetesan
monomer > 1 μm (10,000 Å). Karena rasio luas
permukaan/volume bola adalah 3/R, maka
micelle memiliki luas pemukaan yang lebih
besar.
(2) Konsentrasi micelles lebih tinggi daripada
tetesan monomer (1018 vs. 1011 per cm3).
Tiga tahap polimerisasi
Sebelum inisiasi:
• Dispersing medium, biasanya air, yang
mengandung sedikit sabun (emulsifier) dan
monomer.
• Tetesan monomer dengan ukuran 10.000 Å
terpisah akibat stabilisasi oleh molekul emulsifier.
• Konsentrasi tetesan monomer 1010–1011 per ml.
• Jika CMC terlampaui, 50 –100 molekul
emulsifier akan membentuk micelle yang
berbentuk bola dengan ukuran 40 – 50 Å;
• Beberapa micelles terisi oleh lebih banyak
monomer dan memiliki ukuran 50 – 100 Å;
• Konsentrasi micelle  1018 per ml.
• Tegangan permukaan rendah karena adanya
sufactant.
TAHAP I (konversi 12–20%):
STAGE II (25 – 50% conversion):
• Konsentrasi molekul monomer terlarut menjadi
kecil.
• Tidak ada emulsifier terlarut.
• Polimerisasi hanya terjadi dalam partikel
monomer-swollen polymer (latex) melalui difusi
monomer dari tetesan monomer.
• Partikel polimer tumbuh, sementara ukuran
tetesan monomer berkurang.
• Tidak ada inti partikel baru (jumlah partikel
latex konstan), dan karena konsentrasi
monomer konstan, maka kecepatan
polimerisasi juga konstan.
• Akhir dari tahap ini ditandai dengan hilangnya
tetesan monomer.
STAGE III (50 – 80% conversion):
• Tidak ada monomer dan emulsifier terlarut,
emulsifier micelles, tetesan monomer atau
monomer-swollen micelles.
• Karena tetesan monomer tidak ada, maka
kecepatan polimerisasi berhenti, yang ditandai
dengan habisnya monomer dalam partikel latex.
• Di akhir polimerisasi (konversi 100%), sistem
mengandung partikel polimer (400–800 Å) yang
terdispersi dalam fasa air.
Tahapan dalam polimerisasi emulsi