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213
ISSN 2070-0504, Catalysis in Industry, 2016, Vol. 8, No. 3, pp. 213–216. © Pleiades Publishing, Ltd., 2016.
Ori gin al R ussi an T ext © I.I . Sal akh ov, A .Z. Bat yrsh in, S.A. Ser geev , G. D. Bu kat ov, A.A. Bar aban ov, M.A. Mat s’ko , A. G. S akha but dinov, V.A. Zakharov, 2016, published in Kataliz
v Promyshlennosti.
Effect of Titanium–Magnesium Catalyst Morphology
on the Properties of Polypropylene upon Propylene Polymerization
in a Liquid Monomer
I. I. Salakhova, *, A. Z. Batyrshina, **, S. A. Sergeevb, ***, G. D. Bukatovb, ****,
A. A. Barabanovb, *****, M. A. Mats’kob, ******, A. G. Sakhabutdinova, *******,
and V. A. Zakharovb, ********
aPAO Nizhnekamskneftekhim, Nizhnekamsk, 423574 Russia
bBoreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
*e-mail: SalahovII@nknh.ru
**e-mail: ajr-b@yandex.ru, BatyrshinAZ@nknh.ru
***e-mail: Sergeev@catalysis.ru
****e-mail: Bukatov@catalysis.ru
*****e-mail: Barabanov@catalysis.ru
******e-mail: Matsko@catalysis.ru
*******e-mail: SahabutdinovAG@nknh.ru
********e-mail: ZVA@catalysis.ru
Received January 26, 2016
Abstract—The effect of the particle size of an IK-8-21 domestic titanium-magnesium catalyst on the properties of
polypropylene (PP) produced during the polymerization of propylene in a liquid monomer is studied. Catalysts
with particle sizes of 20 to 64 μm are shown to have high activity and identical sensitivity to hydrogen and allow PP
to be obtained with a narrow distribution of particles over size, high isotacticity, and close values of crystallinity,
melting temperature, and physicomechanical properties. A slight decrease in the activity and bulk density of PP
powder is observed when the average size of catalyst particles is increased from 20 to 43 μm. A more notable reduc-
tion in the activity and bulk density of PP powder is observed for catalyst with particle sizes of 62 to 64 μm. IK-8-21
catalyst is not inferior to its foreign analogues with respect to the properties of the resulting PP.
Keywords: Ziegler–Natta catalyst, titanium-magnesium catalyst, polymerization, propylene, polypropylene
properties
DOI: 10.1134/S2070050416030107
INTRODUCTION
The production of polypropylene (PP) requires
high-activity catalysts that ensure PP with high stereo-
regularity and improved powder morphology (low
content of a small fraction less than 200 μm in the poly-
mer) and have a high sensitivity to molecular weight reg-
ulators, particularly hydrogen. Stable production
requires powder with high yield strength and bulk density
(i.e., particles close to spherical in shape) with no dust
fraction and a narrow particle size distribution.
It is known that the morphology of PP particles is
determined by that of catalyst particles [1, 2], due to
replication. The size of the catalyst particles used in
the production of PP depends on the PP production
technology and product requirements. A catalyst
larger than those employed in obtaining a homopoly-
mer is thus used at PAO Nizhnekamskneftekhim to
obtain shockproof propylene/ethylene block copoly-
mers. Russian companies currently use imported cat-
alysts to produce PP. The aim of using domestic cata-
lysts for olefin polymerization is part of an import sub-
stitution program. IK-8-21 magnesium–titanium
catalyst (MTC) was developed at the Boreskov Insti-
tute of Catalysis for the PP polymerization process [4, 5].
A number of tests were performed with catalysts for the
polymerization process in a liquid monomer and they
showed that IK-8-21 catalyst is not inferior to its for-
eign analogues in terms of activity and the quality of
the resulting PP [6].
The aim of this work was to determine how the
properties of IK-8-21 catalyst can change during
polymerization in a liquid monomer, and how some
characteristics of the obtained PP depend on the size
of catalyst particles in the range of 20 to 64 μm.
EXPERIMENTAL
IK-8-21 MTC samples with the composition
TiCl4/D1/MgCl2 (D1 is an internal donor, dibutyl
CATALYSIS IN CHEMICAL
AND PETROCHEMICAL INDUSTRY
214
CATALYSIS IN INDUSTRY Vol. 8 No. 3 2016
SALAKHOV et al.
phthalate) were prepared following the procedure
described in [7]. Five samples with average particle
sizes of 20 to 64 μm were synthesized.
The distribution of the catalyst’s particle size was
determined by means of laser diffraction on a Master-
sizer 2000 unit. The contents of titanium and magne-
sium in the samples was determined via atomic emis-
sion spectrometry with inductively coupled plasma on
an Optima 4300 DV spectrometer, while the mass
fraction of dibutyl phthalate was measured through
liquid chromatography on a LC-20 Prominence chro-
matograph.
The propylene was polymerized in a steel autoclave
with a capacity of 5 dm3 using a liquid monomer at
70°C and a pressure of 30 kgf/cm2 for 2 h. Propyl-
ene of polymerization purity (PAO Nizhnekamsk-
neftekhim) with a 99.8% volume fraction of the main
substance was used for polymerization. The standard
conditions were propylene weight (1300 g); the weight
of the catalyst sample mcat (0.015 g); the Al/Ti mole
ratio (1500); and the Al/D2 mole ratio (2), where D2
was cyclohexylmethyldimethoxysilane as the external
donor. To control the molecular weight of the synthe-
sized polymer, equal amounts of hydrogen (3.5 L)
were introduced into the reactor in all our experi-
ments. A catalytic complex was prepared in a glass
flask by mixing a calculated amount of triethylalumi-
num (TEA), cyclohexylmethyldimethoxysilane, and
MTC in n-hexane. After the reactants were introduced
into the flask and stirred for 5 min, the catalyst com-
plex was loaded into the reactor. To preserve the cata-
lyst’s morphology, a preliminary polymerization step
was conducted at 20°C for 5 min, and the temperature
was then raised to 70°C.
The isotacticity of PP (XI) was determined by dis-
solving a PP sample in o-xylene, with subsequent slow
cooling of the solution down to 25°C, separation of the
solid phase via filtration, evaporating o-xylene from the
solution, and determining the content of the atactic PP
fraction to be soluble in xylene (XS, wt %). The isotactic-
ity of PP was calculated as XI = 100 − XS (wt %).
The particle size of the PP powder was determined
from the particle size distribution using an Octagon
Digital sieve machine according to ASTM D 1921,
while the bulk density of the PP powder was measured
according to GOST (State Standard) 11035.1-93. The
melting temperature and crystallinity were measured
Table 1. Properties of our IK-8-21 MTC samples
Property Catalyst sample
MTC-1 MTC-2 MTC-3 MTC-4 MTC-5
Average size of catalyst particles, μm20 34 47 62 64
Amount of (in wt %):
titanium 2.5 2.2 2.5 2.4 2.5
magnesium 19.2 18.3 17.7 18.5 18.0
internal donor, DBP 11.8 9.7 10.2 9.2 10.5
SPAN = (d90 − d10)/d50 0.5 0.3 0.5 0.4 0.4
Table 2. Properties of PP powders obtained using MTC with different particle sizes
Property
Catalyst sample
MTC-1 MTC-2 MTC-3 MTC-4 MTC-5
Average size of MTC
particles, μm
20 34 47 62 64
Catalyst activity, kg of PP per
1 g of catalyst
63 60 57 52 48
Bulk density of PP powder, g/cm30.470 0.460 0.450 0.440 0.430
Average PP particle size, μm 800 1270 1720 2100 2280
SPAN = (d90 − d10)/d50 0.40.30.40.40.4
Content of small fraction
(less than 200 μm), %
0.1 No
Isotacticity (XI), wt % 98.2 98.3 98.0 97.9 98.1
Melting temperature, °C 166 164 165 166 165
Crystallinity, % 32 30 29 31 30
CATALYSIS IN INDUSTRY Vol. 8 No. 3 2016
EFFECT OF TITANIUM–MAGNESIUM CATALYST MORPHOLOGY 215
by means of differential scanning calorimetry (DSC)
on a DSC 204F1 Phoenix unit (Netzsch), in accor-
dance with ASTM E 794-85.
The melt flow index (MFI) of the polymer was
measured on a Ray-Ran extrusion rheometer according
to ASTM 1238 at 230°C and a constant load of 2.16 kg.
The Izod impact strength test was performed accord-
ing to ASTM D 256. The bending elasticity modulus
was measured according to ASTM D 790 and yield
strength under tension was determined according to
ASTM D 638.
RESULTS AND DISCUSSION
Table 1 contains data on the composition and par-
ticle sizes of IK-8-21 MTC samples studied during the
polymerization of propylene in liqud monomer. The
amounts of titanium, magnesium, and dibuthyl
phthalate were 2.2–2.5, 17.7–19.2, and 9.2–11.8 wt %,
respectively.
As was mentioned above, the polymerization pro-
cess is stable in liquid monomer along with MTC sam-
ples having sizes of 20 to 64 μm. The data on propylene
polymerization on MTC samples are given in the fig-
ure and in Table 2. They indicate that all the samples
would allow us to obtain high yields of PP–more than
45 kg per one gram of catalyst. In addition, the smaller
the size of the catalyst’s particles, the greater its activ-
ity in PP synthesis. The samples with, e.g., particle
sizes of 20 and 34 μm yielded 60 kg of PP per one gram
of catalyst. The drop in activity when the particle size
was 62–64 μm was probably due to diffusion limita-
tions.
The morphology of the obtained PP powder is of
great significance, since it determines the operational
stability of industrial machines. It is important that the
Table 3. Physicomechanical properties of the PP samples obtained using MTCs with different particle sizes
Property
Catalyst sample
MTC-1 MTC-2 MTC-3 MTC-4 MTC-5
MFI, g/10 min 3.8 4.1 3.9 4.2 4.0
Bending elasticity modulus, МPа 1145 1140 1145 1120 1160
Notched Izod impact strength at 23°С, J/m6668696667
Ultimate tensile yield strength, МPа 33.3 33.6 33.8 33.6 33.5
Activity of the IK-8-21 catalyst samples and average particle size of the PP powders obtained upon polymerization in liquid pro-
pylene on MTCs with different particle sizes.
80 3000
2500
2000
1500
1000
500
0
30
40
50
10
20
0
60
70
20
(MTC-1)
34
(MTC-2)
47
(MTC-3)
62
(MTC-4)
64
(MTC-5)
Catalyst activity, kg of PP
per 1 g of catalyst
Average particle size of PP
powder, µm
Catalyst activity
Average particle size of PP powder
Average size of catalyst particles, µm
63
800
60
1270
57
1720
52 2100
48
2280
216
CATALYSIS IN INDUSTRY Vol. 8 No. 3 2016
SALAKHOV et al.
catalyst has the optimum average size of PP particles
and minimal amounts of the small polymer fraction.
The granulometric composition of powders formed on
the MTC samples showed that when the average size
of the catalyst particles is raised, the average size of the
PP particles grows as well (figure). The data from
Table 2 indicate that there was no fraction of small
particles (<200 μm) in our PP powders (0.1 wt % for
MTC-1 with a particle size of 20 μm), while the distri-
bution of PP particles over size was narrow (SPAN =
0.3–0.4). When the average size of catalyst particles
was raised from 20 to 64 μm, a slight reduction in the
bulk density of our PP powder was observed: from 0.47
to 0.43 g/cm3.
Table 2 clearly shows that the content of the atactic
fraction of our PP samples dissolved in o-xylene,
obtained on IK-8-21 catalyst with different particle
sizes, did not change significantly and was within 1.8–
2.1 wt %, indicating that the catalyst’s morphology did
not influence the stereoregularity of the PP. Neither
did the catalyst’s morphology have any effect on the
viscosity characteristics of the PP samples synthesized
on MTC samples with particle sizes of 20 to 64 μm
under comparable propylene polymerization condi-
tions; the MFI values are within 3.8–4.2 g per 10 min
(Table 3). This indicates that the IK-8-21 catalyst
samples with different particle sizes had a similar sen-
sitivity to hydrogen. The PP samples obtained with our
MTC samples had similar melting temperatures and
crystallinities (see Table 2).
Our study of the physicomechanical properties of
PP samples obtained on IK-8-21 catalyst samples with
different particle sizes showed that when the MFIs are
close, PP samples have similar bending elasticity moduli
upon bending, Izod impact strength at 23°C, and ulti-
mate tensile yield strengths under tension (see Table 3).
Particle size thus had a weak impact on the physicome-
chanical properties of the obtained polymers.
CONCLUSIONS
The effect of the particle size of IK-8-21 catalyst on
its properties during propylene polymerization in a
liquid monomer, and the characteristics of the
obtained polypropylene, were studied. Catalyst sam-
ples with particle sizes of 2 to 64 μm were shown to
have high activity and similar sensitivity to hydrogen,
and allow us to obtain polypropylene with high isotac-
ticity, bending elasticity moduli, and Izod impact
strengths.
When the particle size of the catalyst was raised
from 20 to 64 μm, the size of the resulting polypropyl-
ene’s particles was found to grow from 800 to 2280 μm,
and a powder with a narrow particle distribution over
size and no pulverulent fraction (less than 200 μm)
formed.
A slight drop in activity and bulk density were
observed upon raising the average particle size of the
catalyst from 20 to 43 μm. A more notable drop in cat-
alyst activity and the bulk density of our polypropylene
powder was observed upon raising the average size of
the catalyst particles from 62 to 64 μm.
This way of synthesizing domestic IK-8-21 magne-
sium–titanium catalyst enables us to obtain highly
active catalysts with particle sizes of 20 to 64 μm, and
to use them in the production of homo- and static
polypropylene, and shockproof propylene/ethylene
block copolymers. Our results from studying catalysts
with different morphologies offer the possibility of
choosing the optimum particle size of polypropylene
powder to prevent the formation of agglomerates and
deposits in reactors during propylene polymerization
and the extraction of polypropylene powder.
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Translated by A. Tulyabaev
