Design of Supported Ziegler-Natta Catalysts Using SiO2 as Carrier

DESIGN

OF

SUPPORTED

ZIEGLER-NATTA

CATALYSTS

USING

Si02 AS

CARRIER A. MUROZ-ESCALONA, J. G. HERNANDEZ and J . A .

GALLARDO

Laboratorio de Polimeros. Centro de Quimica. IVIC. Apartado 1872, Caracas 1010A. Venezuela. ABSTRACT The catalysts

systematic for

preparation

ethylene

of

supported

polymerization

was

Ziegler-Natta investigated.

Catalysts were synthesized by a series of reactions of Si02 with TiC14, A1R3-xClx, ZnEt2 and RMgI compounds. catalysts

used

Al(iso-Bu)3.

for

activation

were

The main co-

A1Et2C1,

A1Et3

and

Silicas Davison 951 and 952 having different sur-

face areas, porosities and mechanical properties were employed as carriers. It could be shown that, for the catalysts prepared by simple impregnation of Si02 with TiC14 and by coimpregnation with TiC14 and A1Et2C1, the carriers control the kinetic behavior of the catalysts. Thus, catalysts based on Davison 951 silica showed an acceleration type kinetic curve while those based on Davison 952 give a decay kinetic curve. Catalysts

obtained

by

re-impregnation

highest activities when A1 (iso-Bu) for activation.

methods

showed

the

was used for synthesis and

In this case, the

catalytical behavior

is

controlled by a layer of very active TiC13 crystallite formed as a consequence of the large amount of TiCl with activities as high as 18.000 g. atrn.

-1

and having a good control of

Catalysts -1 PE x g. Ti-’ x h. x 4

used.

the polymer morphology

could be obtained. INTRODUCTION In the past ten years great efforts have been made to synthesize highly active catalysts for olefin polymerization. Systems based on the support of TiC14 on carriers having high surface areas, such as: Si02, A1203 or SiO 2 - A1203, followed

1 23

124

A. Mudoz-Escalona, J.G. Hernandez and J . A .

Gallardo

by activation with alkyl aluminum compounds have been reported 1-4) . These cain the technical and scientific literature talysts exhibit higher activities than the conventional ones based

on

TiC13 and

also better

nascent polymer morphology 5 , 6 ) Highly

active

ability in

.

catalysts have

controlling

also been

prepared

the

using

Due to the low surface area of anhydrous MgC12 as support. MgC12, this and the TiC14, alone or together with other compounds, have to be ball-milled intensively in order to activate the MgC12 and to introduce sufficient amount of titanium in its crystal lattice7 ' 8 ) . talyst

for

The result is a very high active ca-

ethylene

and

propylene

polymerization,

however, the catalysts poor morphology.

showing,

This is a very impor-

tant factor, because as it has been reported')

the catalyst

imposes its shape and size to the polymers particle.

There-

fore, undesirable amounts of fine polymer particles could be obtained in the reactor, specially when insufficient activity is

present

and

consequently

factor

of the catalyst morphology can however, by treatment with high Al/Ti ratios1 0 )

be

to

size

replication

is

size

catalyst

the

relationship)

polymer

Improvement

.

very

(i.e. low.

achieved,

The ability of the catalyst to control the shape and size of the nascent polymer particles has been named replication phenomenum.

The catalyst particles are formed by more or less

loosely bounded aglomeration of subparticles, which at the same time consist of primary particles, leaving cracks and poros inside.

The monomer diffuses through the particles and poly-

merization takes place at the active centers located at the The poros and cracks are surface of the primary particles. filled by the growing polymer, leading to the fissuring, rupture and expansion of the aggregate and of the whole particle, exposing new active centers to polymerization. Therefore, the size, shape and texture (type of aggregation, porosity, etc.) of the catalyst particles control not only the resulting polymer

morphology'')

established

by

,

but

Natta's

also the polymerization kinetic, as finding12)

The

acceleration

type

Design of Supported Ziegler-Natta Catalysts kinetic curves obtained d u r iny propylene polymerizatior: with ungrounded samples of o(- TiC13 have been understood on the basis of these explanations. In

regard

to

ethylene

polymerization

with

supported

Ziegler-Natta catalysts very little is shown in the literature on

how

carriers

stabilize the

influence

active

the

polymerization

dctivity

and

sites, and also how the catalyst mor-

phology influences the kinetic behavior and the morphology of the resulting polymers. EXPERIMENTAL General

outline

procedures

for the preparation

of

the

supported catalysts have been described elsewhere6) . Two grades of silica, Davison 951 and 952, both from Grace Davison USA, having very different characteristics were used as carriers. The

951 silica

shows a high surface area

(610 m2 x g.-'),

microporosity ( 0 . 9 0 ml x g.-' porous volume) and good mechani2 cal strength; while the 952 exhibits lower surface area (220 m x g. -1 ) , macroporosity (1.60 ml x g. -1 ) and breaks-up easily 6 ) . Before being used, the silicas were treated with diluted H2S04 and HC1 solutions, washed with plenty of distilled water and finally dried at 150°C under vacuum for 4 hours.

A group of catalysts were prepared by simple reaction of with both silicas, following procedures described in

TiC14

reference 6 and summarized later on in this paper. A second group of catalysts were obtained by reaction of Si02

simultaneously

with

each

of

the

following

pairs

of

reagents diluted in n-heptane: TiC14 and A1R3-xClx, TiC14 and ZnR2, and TiC14 and MgXR, as described in schemes 1-3. Similar procedures were employed for preparing a third group of catalysts identical to those prepared in the second group, excepting that they were heat treated at 450°C under vacuum for 4 hours followed by reagents

re-impregnation with

the

same mixture

of

125

126

A. Mufioz-Escalona, J.G, Hernandez and J.A. Gallarclo Careful precautions were taken to ensure anaerobic and anhydrous conditions in all steps of the catalysts preparation. The catalysts prepared were subsequently characterized by determining their surface area by BET method, surface acidity (Lewis and Breston acid centers) by Webb method based on the amount of chemisorbed NH3 gas, and metal content by colorimetric and atomic absorption methods

(see references 5 and 6

and also references therein for more details). Polymerization of ethylene was carried out at 50°C under a constant monomer pressure of 5 atm. in 1 liter stirred glass autoclave reactor using 0.5 liter of n-heptane as a solvent. The reactor was stirred at 1.200 rpm’s speed in order to minimize mass transfer control of polymerization rates.

Both

catalyst components, supported Ti and co-catalyst, were introduced

separately in the reactor, putting

first

in a glass

ampoule the Ti containing catalyst, and then the alkyl aluminium compound in the solvent, when it was saturated with ethylene at the selected polymerization pressure.

The Al/Ti

ratio was kept constant at 10 and the polymerization was timed just after breaking the ampoule containing the catalyst.

The

polymerization rate was determined from the rate of monomer consumption (volume of ethylene flow into the reactor) measured by a method similar to that described by Schnecko et. al. 1 3 ) This method has a very good reproducibility and the error in the rate measurements does not exceed

1%.

After

2-3

hours

polymerization time the reaction was quenched by introducing a solution of ethanol containing hydrochloric acid.

The polymers

obtained were washed several times with ethanol and dried in vacuum at 5 0 ° C . The intrinsic viscosity of the polyethylenes was measured at 1 3 5 + 0.05OC in decalin and molecular weight were calculated following procedures given in references 5 and 6. Finally, catalysts and resulting polymers were observed

Design o f Supported Z i e g l e r - N a t t a under t h e scanning e l e c t r o n microscope stubs

SEM

with

conductive-adhesive

distribution

size

then

were

Catalysts

( S E M ) by j o i n i n g them t o

silver

obtained

paint.

from

Particles

the

micrographs

t a k i n g a p o p u l a t i o n of 500 p a r t i c l e s . RESULTS AND DISCUSSION

C a t a l y s t s p r e p a r e d by s i m p l e r e a c t i o n of S i 0 2 w i t h T i C 1 4 The reaction

first at

n-heptane washed

room

for

with

catalysts were

g r o u p of

temperature

both

silicas

with

simple

TiC14

in

The s u p p o r t e d s o l i d s w e r e f i l t e r e d and

1 hour.

n-heptane,

detected i n the

of

s y n t h e s i z e d by

until

solutions.

no

trace

Finally,

of

metals

could

t h e y were d r i e d a t

be

50°C

u n d e r vacuum f o r more t h a n 1 h o u r t o o b t a i n c a t a l y s t s N o .

515

( 9 5 1 s i l i c a ) a n d 548 (952 s i l i c a ) , r e s p e c t i v e l y .

Due t o t h e r e a c t i o n

of

TiC14

with

hydroxyl

s u r f a c e a r e a s of b o t h s i l i c a s d e c r e a s e d .

groups,

the

S i l i c a 951 u n d e r g o e s

g r e a t e r r e d u c t i o n i n i t s a v a i l a b l e s u r f a c e a r e a a s a r e s u l t of p l u g g i n g of i t s microporos.

T h i s d i d n o t happen t o t h a t e x t e n -

s i o n w i t h s i l i c a 952, b e c a u s e it h a s m a c r o p o r o s (see T a b l e 1 ) . I n r e g a r d t o t h e amount of T i s u p p o r t e d , s i l i c a 951 c a n l o a d a g r e a t e r amount

as compared t o s i l i c a 952

(6.7%)

(4.9%) due t o

t h e i r differences i n surface areas. The k i n e t i c b e h a v i o r of b o t h c a t a l y s t s w e r e v e r y d i f f e r e n t

as shown i n F i g u r e

1.

515 b a s e d on s i l i c a 951 pre-

Catalyst

s e n t s an a c c e l e r a t i o n t y p e c u r v e , decay curve.

A s a c o n s e q u e n c e of

a c t i v i t y than

catalyst

These

while

catalyst

548 shows a

t h a t , c a t a l y s t 515 h a s l o w e r

548 b a s e d on Si02 952

(see T a b l e

r e s u l t s may b e e x p l a i n e d c o n s i d e r i n g t h e d i f f e r e n c e s i n

mechanical

properties

and

porosities

of

the

two

E t h y l e n e monomer d i f f u s e more e a s i l y i n t o c a t a l y s t r e s u l t of i t s h i g h e r p o r o s i t y , 515.

2).

supports. 548,

t h a n i t does i n t o t h e

as a

catalyst

T h e r e f o r e , t.he polymer g r o w t h s i n s i d e o f t h e p a r t i c l e s of

catalyst

548 b r e a k i n g

its

lower mechanical

for

polymerization.

them up i n t o s m a l l e r strength,

fragments,

due t o

g e n e r a t i n g new a c t i v e c e n t e r s

This process

does

not take place

i n so

127

+ TiC14

a) t

=

=

450°C, 4 h

reaction time

Vacuum

Cat. 541, T

Si02(952) + TiC14-AlEt2C1 t=lha)

SiO (952) + TiC14-A1Et C1 2 t=3ha)

Si02(952)

Si02 (952)

Cat. 543,T = 450°C, 4h Vacuum

t-lha)

Si02(951)

+ TiC14 Si02 (951) + TiC14-AlEt2C1

Si02 (951)

Catalyst Preparation

TABLE 1.

542

541

(541)

150

150

150

190

240

-

548

260

7.1

9.5

3.5 9.4

0.40

7.8

12.3

280

545

8.7

350

0.35

543

610

Surface Surface Acidity 2 -1 -1 Area(m xg. ) ( m l . ~ ~ ~ cat. x g .)

515

-

NO.

Catalyst Al

Al/Ti

2.6

3.5

5.5

4.9

-

1.9

4.5

6.7

-

0.5

3.7

2.3

-

0.8 -

3.4

-

-

0.3

1.9

0.75

0.073

0.21

0.20

-

0.10

-

0.069

0.22

0.14

-

0.75

1.3

-

-

g. cat.-')

Total Amount of Metals

( w ~ ) (a)(mo1) (mls x 100

Ti

REACTION OF TiC14 AND CO-REACTION OF TiC14 AND AlEt2C1 ON Si02

PHYSICO-CHEMICAL CHARACTERIZATION OF CATALYSTS PREPARED BY

D e s i g n of S u p p o r t e d Z i e g l e r - N a t t a

Catalysts

1500

c

E

c

0

i 1000 .-

I-

m

\

\

w

n

CI,

e

*I-> !-

500

---

0

a

+*,*--*-+-+-

1I

L

3

2

TIME ( h )

Figure (0)

C a t a l y t i c a c t i v i t y VS. t i m e f o r t h e c a t a l y s t s : 1 ( 0 ) (541) ( A ) 541 and ( * ) 543. Polyrneri-

1.

548,

zation

515,

( A )

conditions:

P=5atm.

T=50°C,

Al/Ti=lO.

Co-catalyst

AlEt C1

great

extension

in

case

of

catalyst

515,

where t h e

catalyst

p a r t i c l e s become e n c a p s u l a t e d w i t h polymer and a s a r e s u l t i t s a c t i v i t y tends t o be lower. Figures different

and

2

co-catalysts

both c a t a l y s t s . all

types

of

based

based

Si02

the

(A1Et3,

kinetic

curves

A1Et2C1

on 952,

i.e.

used,

using

A1 (iso-Bu) 3 )

S i 0 2 9 5 1 and resulting

acceleration curves

decay

the

for

Kg. PE x g . Ti-'

for

curves

for

catalysts

Al(iso-Bu)3

the

best

c a t a l y s t , p r o d u c i n g 22.8 Kg. PE x g . T i - ' 5.4

and

obtained

The same c a t a l y s t i c b e h a v i o r c a n b e s e e n w i t h

co-catalysts

catalysts on

3 show

co-

w i t h c a t a l y s t 548 and

w i t h c a t a l y s t 515 (see T a b l e 2 ) .

129

130

Hernandez and J . A .

A. Mufioz-Escalona, J . G . Table

2.

Influence

of

activity

catalysts

co-impregnation of

SiO

of

co-catalysts

obtained 2

Gallardo

by

Davison 951 and

Polymerization time TiCl -AlEt C1. 4 2 ~ O O C ,A ~ / T L = 10.

=

the

on

simple

catalytic

impregnation

and

952 with TiC14 and

2h.,

P

=

5 atni., T

=

Catalytic Activity (Kg. PExg.Ti-’) Catalyst Preparationa)

Catalyst No. AlEt2C1

AlEt3

Al (is-Bu)

Si02(951)+TiC14

515

4.9

3.5

5.4

Si02 (952)+TiC14

548

11.2

11.7

22.8

SiO (951)+TiC14-AlEt2C1 2

543

0.04

-

-

SiO (952)+TiC14-AlEt2C1

541

0.81

-

2

t=lhb) SiO (952)+TiC14-A.lEt2C1 2

(541)

3.2

t=3hb)

a)

See schemes 1 and 2 for details

b,

t = reaction time Catalysts prepared by co-impregnation of Si02 with TiC14

and AIEtZCl As it has been published many years ago by Tornqvist et. a d 4 ) , the reduction of TiC14 with A1Et2Cl leads to the formation o f a solid solution of A1C13 in the crystal lattice of the TiC13 formed. aluminium

may

The isomorphous substitution of the Ti atoms f o r produce

the

activation

of

the

titanium

by

disrupting its crystal lattice and due to the electronic inBearing in fluence of the A 1 through chlorine atom bridges.

0

2

TIME (h)

3

A1 (iso-Bu) 3 , (0)

AIEtZCl

Polymerization conditions:

(0)

t i m e using the following

P=Satm. T=50°C, A l / T i = l O

A1Et3.

co-catalysts:

(0)

I

C a t a l y t i c a c t i v i t y of t h e

c a t a l y s t 515 vs.

Figure 2.

a

H

200

= !>

>

300

0,

>1000

I

2

3

TIME ( h ) C a t a l y t i c a c t i v i t y vs.

t i m e of

h

0

t

(0)

T=50°C, A l / T i

=

10

P=5atm.

A 1 E t 3 ( o ) A 1 E t 2 C 1 and

Polymerization conditions:

Al(iso-Bu)3,

ZnEt2.

(*)

(A)

c a t a l y s t 548 u s i n g t h e following c o - c a t a l y s t s :

F i g u r e 3.

Q

0

t-

t I

2000

3 000

Q, v

0

w n

\

I-

o, 400

w

I-

.-

i \

500

E

0

L

.-

s

0

c

E

1

600

-

3500

132

A. Mufioz-Escalona, J.G. Hernandez and J.A. Gallardo mind these i d e a s , we tricd to produce a birrietallic corriplex by co-impregnation of both silicas with dilute solutions of TiCl and

AlEt2Cl

4 n-heptane, following procedures described in

in

schemes 1 and 2.

Catalysts 541 and (541)l based on silica 952

and catalyst 543 based on silica 951 were prepared.

Catalysts

541 and (541)' differ by the co-impregnation time, been lh. for the 541 and 3h. for the (541)1 . Under these conditions both metals compete for the hydroxyl groups of the silicas and could be supported.

The supported amounts are shown in Table 1.

a result, the

surface areas of both

silicas undergo

reduction compared to the simple impregnation with TiC14. surface

acidities,

however,

increase.

The

kinetic

As

higher The

curves

follow the same pattern, i.e. those catalysts obtained with silica 951 give rise to acceleration curves, while those based It is noteworthy, that

on silica 952 decay one (See Fig. 1).

the catalytic activity of catalysts obtained by co-impregnation are much lower than the ones prepared by simple reaction with TiC14

(Fig. 1 and Table 2).

umbrella

effect

of

the

This could be explained by

aluminium

and

its

chlorine

the

atoms

On the other

attached to it, which cover the titanium atoms.

hand, catalysts based on silica 952 (541 and (541)')

are more

active than the ones based on silica 951, although the latter have

higher

surface

areas.

The result may be explained by

admitting that the mechanical properties and porosities of the carriers still influence the catalytic behavior at this step of the preparation. Catalysts prepared by re-impreqnation of modified Si02 with TiC14 and alkyl aluminium compounds The catalysts prepared by co-impregnation of silicas 951 and 952 with TiC14 and A1Et2Cl were calcinated at 450°C under vacuum for 4h. to obtain catalysts 545 and 542 respectively (see schemes 1 and 2). By this treatment, part of the supported metals

are

removed

from

the

silica,

leaving

its surface metal oxide partially chlorinated

behind

on

(see Table 1) ,

having, as a consequence, a high population of chloride vacancies.

Furthermore, these

catalysts

were

re-impregnated

by

D e s i g n of S u p p o r t e d Z i e g l e r - N a t t a

1

S i O a (951) n - heptone

Catalysts

I

t=lh. T = 2 0 ° C F i 1 ter W a s h & Dry

t=4h

T=450°C i

Catalyst

545

A

e n - heptane

1

I

n- hap t a n r T n - hop tan e t= 3 h.

Filter

W a s h 8 Dry

1 T= 5OoC

Filter

W a s h 8 Dry t=lh T=50°C

Catalyst

Scheme 1.

Catalyst

Catalyst

C a t a l y s t p r e p a r a t i o n by s u p p o r t i n g T F C 1 4 a n d

a l k y l a l u m i n i u m compounds o v e r S i 0 2 9 5 1 .

133

134

A. Mufioz-Escalona, J.G. Hernandez and J.A. Gallardo

S i 02 (952) n -heptane

t=3hl Filter

I

(541)'

VA CC .

tn- h r p t a n r

Filter

n

n- h r p t a n r

Filter

Wash 8 Dry

Scheme 2.

- heptone.

Filter

Catalyst preparation by supporting TiC14 and 952.

a l k y l aluminium compounds o v e r SiO

2

Design of Supported Ziegler-Natta Catalysts reacting them with diluted solutions of TiC14 in n-heptane together with solutions of AIEtZCl, A1Et3 and Al(iso-Bu)

3' respectively, in order to obtain catalysts 546, 555 and 554 based

on silica 951 and the series 565, 567 and 566 based on silica

952.

The physico-chemical characterization of these catalysts

i s presented in Table 3.

The surface areas were further re2 -1 duced due to the re-impregnation, falling down to 150 m xg. 2 -1 for the two series of catalysts. The surface and 110 rn xg. acidities

and

amount

of supported T i ,

on the contrary, in-

Catalytic activities as a function of polymerization

crease.

time are given in Figs. talysts.

4 and 5 for the two series of ca-

The polymerization rates decay rapidly with time for

catalysts based on silica 952 and 951.

It is very interesting

to point out the change in the kinetic behavior of the catalysts based on silica 951, changing from acceleration curves to decay ones.

These results suggest that the catalytic be-

havior is now controlled by the solid layer formed on the surface of the silica, rather than by

the silica itself.

The

physical and chemical nature of this layer has to be very complicated, but it may be speculated here that it could be very porous

allowing

monomer

diffusion

inwards.

In addition

to

that, it may be formed by very active T i C 1 3 cystallites produced

by

the

transformation of

existing o( -TiC13 under the

action of TiC14, which behaves as a catalyst. Catalytic activities as high as 18.000 g. PE x g.Ti-lxh.

-1

xatm-I could be obtained with catalyst 554 using Al(iso-Bu13 as co-catalyst (see Fig. 4).

This catalyst system has, therefore,

potential as a high mileage if the over-reduction of the titanium

is depressed by adequate formulation of the co-catalyst

system15).

In Fig. 5 the kinetic curves €or the catalysts pre-

pared with silica 952 are presented.

The productivities of

these catalysts activated with different co-catalysts are given in Table 4.

The best catalysts are those synthesized using

Al(iso-Bu)3 both for re-impregnation and also as co-catalyst.

135

+ TiC14-Al (iso-Bu)

Cat. 545

565 567 566

+ TiC14-AlEt2C1

+ TiCl4-AlEt3

+ TiCl4-Al(iso-Bd3

Cat. 542

Cat. 542

542

Cat. 542

Si02 (952) + TiC14-AlEt2C1 T = 450°C, t=3h vacc.

554

555

+

Cat. 545

TiC14-AlEt3

546

+ TiC14-AlEt2C1

Cat. 545

545

NO.

Catalyst

115

103

117

150

150

146

150

260

10.2

8.8

9.3

7.1

10.9

7.7

15.3

7.8

Surf ace Acidity 2 -1 Area(m xg. ) (rnl.~~~xg.cat.-') Surf ace

2.7

9.1

9.4

2.6

7.8

7.3

8.8

2.7

5.5

0.5

0.5

0.5

3.9

3.1

0.8

0.50

1.10

0.10

0.30

0.11

0.95

0.63

0.75

0.31

0.39

0.22

0.073

0.18

0.30

0.30

0.069

(ml) (rmls x 100 g- cat.-')

(w%)

(w%)

1.9

Al/Ti

Al

Ti

Total Amount of Metals

PHYSICO-CHEMICAL CHARACTERIZATION OF CATALYSTS PREPARED BY REIMPREGNATION

OF MODIFIED Si02 WITH TiC14 AND ALKYL ALUMINIUM COMPOUNDS

SiO (951) + TiC14AlEt2C1 2 T=45OoC, t=3h vacc.

Catalyst Preparation

TABLE 3 .

137

0

0

0

0

2!

0

0

0

8 0 10

0

0 10

N

c

aJ

E

0 h

aJa c

a,r:

h u m

138

A. Mufioz-Escalona, J.G. Hernandez and J . A . Table

4.

Influence of

the

Gallardo

co-catalyst on the catalytic

activity of the catalysts obtained by re-impregnation of silica Davison 951 and 952 with TiC14 and alkyl aluminium compounds Polymerization conditions:

T=5O0C, P=5atm., Al/Ti=10, Time=2h. 1 Catalytic Activity (Kg. PEXg.Ti- )

Catalyst Preparationa)

Catalyst No. AlEt2Cl AlEt3

A 1 (iso-Bu)

ZnEX2

Catalyst 545+ TiCL4-AlEt2C1

546

6.6

20.8

15.4

10.5

555

8.2

10.1

34.8

2.2

554

14.6

11.0

16.8

15.2

565

2.1

18.1

14.1

-

567

1.2

13.1

7.1

-

566

4.1

14.5

25.0

-

Catalyst 545+ TiCl -AlEt3 4 Catalyst 545-t TiC14-Al (iso-Bu) Catalyst 542+ TiC14-AlEt2C1 Catalyst 542-t TiC14-AlEt3 Catalyst 542+ TiCl -Al (iso-Bu)3 4

a)

See schemes 1 and 2 for details.

Catalysts prepared by co- and re-impregnation of SiO 2951 with TiCln-ZnEt? and TiC14-RYgI mixtures Owing to the fact that silica 951 with the highest surface area

produces

a

very

active

catalytic

system

by

the

re-

impregnation method, catalysts based on this silica were syn-

Design of Supported Ziegler-Natta Catalysts mixtures, following

thesized using TiCl4-LnEt2 dnd T i C 1 4 - R M j I procedures already described.

In Scheme 3, the steps to obtain

catalysts No. 556, 557 and 558 are presented.

Replacing ZnEt

2 by RMgI the corresponding catalysts No. 562, 563 and 568 were also synthesized

(see Table 5).

For the co-impregnation step

the mixture Tic1 -MeMgI was used, while for re-impregnation the 4 mixture TiCl -HexMgI was preferred. Table 5 shows the physico4 It can be seen chemical characterization of all catalysts. that catalysts prepared by TiCl -RMgI have higher surface areas 4 and acidities than those based on TiCl 4-ZnEt 2. It is also noteworthy, that the surface area of catalyst No. 563 obtained by calcination of catalyst 562 increases due to the heat treatment. The

kinetic

curves

obtained

with

the

re-impregnation

catalysts (No. 558 and 568) are shown in Figs. 6 and 7.

Both

catalysts present a decay curve, and the best co-catalyst for activation is now the A1Et3.

The productivities are given in 1 Table 6 reaching values as high as 61,2 Kg.PE x g.Ti- , with the catalyst containing Mg, after 2h, 5 0 ° C and 5 atm. polymerization sensitive

pressure. to

the

Furthermore,

type

of

this

co-catalyst

catalyst

used

for

is

very

activation.

Thus, very low activities could be obtained when A1Et2Cl and A l ( i s 0 - B ~ )were ~ used for activation,

wnile A1Et3 give very

good

co-catalyst.

results,

emerging

as

the

best

Similar

results, have been found with catalysts based on TiC14 supported over M g C 1 2 . Viscosity average molecular weights Very high molecular weights were obtained with all catalysts, when no H 2 was used as chain transfer agent for molecular weight control, as shown in Table 7. Morphology of catalysts and polymer particles A good catalyst must have very high activity in order to produce high

purity

polymer, it

must also

have an excellent

139

140

A.

Mufioz-Escalona,

J.G. Hernandez and J . A .

+

Gallardo

n - heptane

n- heptane

Filter

WJ Catalyst

t = 4 h. T = 4 5 0 ' C

+n-

h eptane

_- n - h e p t a n e n-heptane T i CI4

Z n Et2

-1

Scheme 3 .

C a t a l y s t s p r e p a r a t i o n by s u p p o r t i n g T i C 1 4 and

ZnEt2 o v e r Si02 9 5 1 .

141

d N

0 d

0

0

9 N

m

I

c n 0

r0

0

m

I

W

m

W

W

Tr

N

m

W

0

0

N

Tr

Tr

W

m m

!ir r: N

lTr rl

U E+

Ti

+

N

“

4 0

0

m W

m

Y w; “II 9

o E

rn W

i

i II

m c , +J

id

U

8000

2500

0 2 3

Catalytic activity vs. time €or

TIME(h)

I

(0)

A1Et3.

0

TIME ( h )

2

3

Catalytic activity vs. time f o r

I

(*)

A l ( i ~ o - B u ) ~ (,0 ) A1Et2C1 and

( 0 )A1Et3.

and Al/Ti=lO

AIEtZCl and

2000

500C

catalyst 568 using the following co-catalysts:

Figure 7.

a

0

I-

L

t

>

v

0

a

W

\

0

I-

.-

and Al/Ti=lO

(0)

O

r

IOOOC

Polymerization conditions: P=5atm., T=50°C,

Al(iso-Bu)3,

E

c

-

12ooc

Polymerization conditions: P=5atm., T=50°C

(*)

catalyst 558 using the following co-catalysts:

Figure 6 .

a

V

k

l-

->

>. 5 0 0 0

Y

0, 0

W

\

m

I-

.-

r

9

c

E

-

I0500

Design of Supported Ziegler-Natta Catalysts Table 6.

Influence of the co-catalysts on the activity of

catalysts prepared by

co- and re-impregnation of silica 951

with TiC14-ZnEt2 and Tic14-RMgI mixtures. Polymerization temperature = 50°C, P = 5 atm., Al/Ti =

=

10, Time

2h.

Catalyst

Table 7.

Catalytic activity (Kg.PE x g. . T i - L )

No.

AlEt2C1

A1Et3

A1 (iso-Bu)

558

4.3

27.5

24.8

568

0.31

61.2

0.13

Viscosity average molecular weights.

515 548

0.5 0.6

541

1.9

543

1.8

555

1.5

control of polymer morphology.

These characteristics should be

of main concern in the catalyst synthesis. By controlling the average size and size distribution of the polymer particles, as well as the bulk density, the reactor productivity can be enhanced and many problems in plant operations can be eliminated. This can be done by synthesizing catalysts with good morphological characteristics.

The

ability of the catalysts syn-

thesized to control the size of the nascent polymer particles

143

50

30

0

10

of s i l i c a 9 5 1

Particle s i z e d i s t r i b u t i o n

DIAMETER ( p m )

0-10 10-20 20-30 30-40 4050 50-60 60-70 ?080 80-90

c

F i g u r e 8.a

n

0

L z 20

W 0

$

(3

w 40

'4 ( p m)

A l E t C1 c a l c i n a t i o n a t 4 5 0 ° C a n d r e - i m p r e g n a 2 tion with T i C l -AlEt 3 4

c a t a l y s t 555 p r e p a r e d w i t h C i 0 2 ( 9 5 1 )+ T i C 1 4 -

P a r t i c l e s i z e d i s t r i b u t i o n of

DIAMETER

0 0-10 10-20 20-30 30-4040-50 5 0 6 0 60-70 70-80 80-90

10

20

30

40

Figure 8.b

n

0

[L

V

W

a Iz

W

W

4 4

P

Design of Supported Ziegler-Natta Catalysts Figure 8 shows the particle s i z e distribution of

were tested.

silica 951 and of the resulting catalyst 545. By reacting silica 951 with TiClq and A1Et2C1 its size increases slightly, and its surface becomes more rough1’)

The Figure 9 polymer particle size distribution of the resulting polymer is shown.

It can be seen that most polymer particles

are bigger than 500 considered as fine.

r-m and that only a small percentage can be

80 W

c3 Q I-

z

64 48

W V

cc 32

2

16

0

<38

38-45

45-75 75-150 150-250 250-500

,500

DIAMETER ( p m )

Particle size distribution of the polyethylene

Figure 9. obtained

with

the

catalyst

555

using

Al(iso-Bu)3

as

co-catalyst. ACKNOWLEDGMENT The

authors

C.A.-INDESCA

wish

to thank

Investigaci6n y Desarrollo,

(Maracaibo, Venezuela) for secretarial assistance

in the preparation of the manuscript and particularly to its General Manager, Dr. I. Rodon for reading it and correcting the English text. REFERENCES Chien, J. Catal.,

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J.C.W.

2.

J. Murray, J.J. Sharp and J.A. Hockey, J. Catal

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18,52

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A. Mufioz-Escalona, J.G. Hernandez and J.A. Gallardo 3.

K. Soga, T. Sano and R. Onishi, Polyrn.

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A. Mufioz-Escalona, A. Martin and J. Hidalgo, Eur. Polym. J.,

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A. Mufioz-Escalona in "Transition Metal Catalyzed Polymeri-

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A Mufioz-Escalona, J.G. Hernsndez and J.A. Gallardo, J. Appl. Polym. SCl.,

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Alkenes and Dienes", Edited by R.P. Quirk. Harwood Academic Publishers, London, 1983, p. 355. 9.

J. Boor, Jr.,

"Ziegler-Natta Catalysts and Polymeriza-

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A. Mufioz-Escalona, P. Frias and A. Sierraalta. Org. Coat. Plast. Chem (ACS) 44, 170 (1981).

11.

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12.

T. Keii, "Kinetics of Ziegler-Natta Polymerization", Chapman and Hall, Londor,, 1972.

13.

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69, 105

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presented in next ACS meeting in Chicago, September 1985.