Effect of ether on the phase composition of intermediate and final products in the synthesis of a propylene polymerization catalyst

Polymer Science U.S.S.R. Vol. 30, No. 3, pp. 621-627, 1988 Printed in Poland

0032-3950/88 Sl0.00+ .00 © 1989 Pergamon Press pie

EFFECT OF ETHER O N THE P H A S E COMPOSITION OF INTERMEDIATE AND FINAL P R O D U C T S IN THE SYNTHESIS OF A PROPYLENE POLYMERIZATION CATALYST* N. S. BUKHARKINA,V. P. K.ONOVALOV,L. L. YEZHENKOVA, 1. A. VOLOSHIN, O. M. ZVYAGIN, A. A. BAULIN, M. V. MAL'GINA, N. V. IVANOVAand R. KH. DENILOV Moscow Petroleum Processing Plant Okhtinsk Research and Production Unit "Plastpolimer" (Received 3 October 1986)

The effect of ether in the synthesis of a highly active propylene polymerization catalyst was studied; ether was used as an individual electron donating compound in TiCI3 treatment, and also in the form of complexes with TIC14 and EtzAIC1 in the process of TiCI3 synthesis. Application of ether in the form of complexes with diethylaluminium chloride leads to the formation of the highly defective ~'-form of TiCI3, with high activity and enhanced stereospecificity, directly during TiCI4 reduction, and of the highly defective b-form of TiCI3 with a high surface area and high activity. It was shown that the catalyst activity is determined by the size of its surface and the number of defects in it. IN recent years, catalysts for polypropylene (PP) synthesis based on titanium trichloride and characterized by a highly developed surface have been widely studied and introduced into industrial production [1-3]. In the synthesis of these catalysts, participation of electron donating compounds at a certain stage plays an important role [4, 5]. However, data on the effect of these electron donating compounds, usually ethers, on the process of catalyst synthesis, on the chemical and phase composition of the intermediate and final products detecmining the quality of the final catalyst, are practically missing in the literature. In the present work we have studied three variants of catalyst synthesis, differing in the sequence of component contacts: reduction of TiCI4 with diethylaluminium chloride and subsequent treatment of the product with dibutyl ether and final thermal treatment in TIC14 medium (multistage synthesis); reduction of TiCI4 with the diethylaluminittm chloride--dibutyl ether complex (single stage process); reduction of TiCI4 with an addition of dibutyl ether by means of diethylaluminivm chloride and diethylaiuminium chloride--dibutyl ether complex (single stage synthesis). The phase composition of the products and intermediates of the synthesis was determined with the X-ray diffractometer DRON-2 using monochromatized molybdenum radiation. Samples were measured in capillaries with wall thickness of 0.01-0.02 mm and diameter 1.05-1.1 ram. * Vysokomol. soyed. A30: No. 3, 623-628, 1988. 621

622

N.S. BUKHARKINAet al.

The activity of the prepared catalysts was determined by propylene polymerizationin liquid monomer medium under the following conditions: pressure 3 MPa, 70°, polymerizationtime 4 hr, weight ratio Et~A1CI: TiC13=10--15; hydrogen (for molecular mass control) 20-30 mmole/dm3. The contents of atactic fraction was determinedby extraction from the powder with cold heptune. Our study of the phase transitions during the synthesis of the highly active propylene polymerization catalyst in the presence of ether led to the elucidation of the effect of ether in the formation of various TiCI3 modifications, and enabled us to determine the connection b~tween the catalytic properties of the final product and the phase composition of the intermediates. In the multistage synthesis, ether treatment was applied to the product of the first stage, obtained by TiCI4 reduction with diethylaluminiumchloride [3, 6] (product I), consisting either of a mixture of ~(y) and//-forms of TiCI3 (Fig. 1, curve 1), or only of the//-form. The relative contents of these forms, as determined from the relative areas of the diffraction peaks $7°3o,/$6.s4,, characteristic of the//- and ~(y)-forms, depends on the purity of the applied reagents, their ratio and the rate of heating of the reaction mixture from 0 - - 5 to 40--45° [6]. Thus the presence of polar impurities in the solvent used as diluent for TIC14 and E%A1CI, results in the formation of practically only the

T

2"/~ t

~ ~

20

/ ~ .-.-----

t0

gO*

I

FI~. I. X-ray diagrams of products of multistagesynthesis:/-product I (after reduction of TIC14with diethylaluminiumchloride);2 - product II (after ether treatment)- r-form of TiCIa; 3-product III (after treatment in TIC14medium)-~-form of TiCla. r-form of TiCl3, containing A1+3 mostly only in the form of A1CI3, while the formation of the ~(~,)-form is connected with reduction mainly to EtA1CI2. The aim of the second stage of ether treatment is the enhancement of the porosity and surface of the catalyst by extraction of A1+3 from the crystal lattice of TiCI3, by way of ether-A1Cl3 complex formation and transformation of EtAICI2 into soluble compounds [7]. As the Lewis acids TiCI3, A1C13 and EtAICI2 differ in strength [8, 9], the results of the ether treatment depend not only on the parameters of the treatment process, but also on the chemical and phase composition of product I. As a result of the treatment, in product II obtained at this stage, A1+3 contents is decreased from 4.8-5.2 to 0.5-0.7 wt. Yo; at the same time, the ~-, y-forms of TiCI3 are destroyed and transfocmed into a

Synthesis of propylene polymerization catalyst

623

state amorphous by X-ray criteria, as indicated by the increase of the structureless background in the X-ray diagram and gradual decrease of the diffraction peak intensity at 20=6054 ' (Fig. 2). Practically only the highly defective if-form is left, characterized by the broad diffraction peak at 20= 7030' (Fig. 1, curve 2). At this stage, the phase z

c

b

1 9

I

I

I

5

9

I

d

I 5

g

5

1 9

I "e:~i ,Y Z$*

FIG. 2. Dynamics of phase composition of product II during ether treatment. Molar ratio ROR : TIC13=0"3 (a), 0"5 (b), 0"7 (c) and 0"9 (d).

structure changes more readily, the smaller the relative contents of the fl-form in product I. Extraction of AICI3 from the TiCI3 crystal lattice is much more difficult, and therefore the fl-form is much more slowly destroyed; nevertheless, even this process can be controlled by an increase in the molar ratio ROR : TiCI3 or in the ROR concentration. Transformation of product I into an X-ray-amorphous state is accompanied by the destruction of the macrostructure of the spherical catalyst particles. A large increase in the ratio ROR : TiCI3 leads to complete destruction of TiCI3 crystal lattice and dissolution of the catalyst. Thus in dependence on the ratio ROR : TiCI s and ROR concentration, product I can undergo the following transformations: ROR : a'ia~=0.6-1 ~-fl-form-product II product I

ROR : lrio~= 1.2-1-5 X.ray amorphous product

(~-, ~,- and fl-forms of TiCIs) [t~oR: TiCi,~2.5 ~dissolution of product I As a result of the extraction of AI +3 compounds from the TiCla lattice, the porous structure of the catalyst is formed. Development of the porous structure, final shaping of the pha~e structure, decomposition of TIC13 ether complexes and dissolution of A1CI3 complexes sorbed at TiCI3 surface occurs during thermal treatment of product H in TIC14 medium-yielding product III. At this stage, the highly defective ~-form of TiCI3 is formed (Fig. 1, curve 3), of enhanced activity. The rate of phase transitions and the final result of the synthesis depend on the phase structure of product II: when product II has the character of a highly defective fl-form of TiCla, with a high X-ray-amorphous background, then the phase transition is completed at temperatures <50-55 ° with highly defective 6-form formation; these conditions

624

N.S. BUKHARKINAet

al.

favour the synthesis of highly effective catalysts with developed surface and high stereospecificity. With a low X-ray-amorphous background, c¢- or y-forms of TiCI3 are formed, or a mixture of the two. During thermal treatment of product II, consisting mainly of the defect-free fl-form of TiC13, a mixture of 0¢-, 7- and fl-forms of TiCIs is produced. TABLE 1.

CHARACTERISTICS OF PRODUCT

III,

PREPARED BY MULTISTAGE SYNTHESIS, AS PROPYLENE

POLYMERIZATION CATALYST

Thermal treatment

T°

time, hr

0"5 55 05 60 1 65 65 2 70 1 70 3 80 3 100 2 TiCI3 •0"33 AICIs

Physical characteristics, of the product

phase composition

6 8

pore volume, cm3/g

[12] 0"138

8

8 8

0" 120

~+y+P 0"032

Chemical composition

Catalytic properties

ratio mole/mole surface,

Ti, wt.~o

m2/g

140 130 120 120 98 76 60 22 25

iso° ×

29"1 29"0 28'9 29'0 28"8 27"8 27"9 26"5 24"5

(A1 : ROR: : Ti) x 103 : Ti T12 18 13 12 20 44 44 130 330

0"03 0"04 0' 035 0'003 0"01 0"05 0"06 0"041

atactic fraction,

tacticity,

wt. %

%

0"8 0"9 0"9 1"0 1"2 2'0 2"8 4"0 5"5

97'5 97"8 97"5 97"2 97"2 96"0 95"0 89"0 90"0

1"68 1"6 1"48 1"48 1"3 1"2 1"01 0'4 0'5

In Table 1, the chemical and phase composition, physical characteristics and catalytic properties of product III are summarized in dependence on the conditions of thermal treatment. The highest activity and stereospecificity is exhibited by the c~-form obtained under mild conditions of thermal treatment. It exhibits the largest surface. D a t a on the traditional catalyst, TiCI3"0"33AICI3 (aluminothermic reduction), activated by grinding, are included for comparison. The phase transitions in the above described multistage synthesis can be schematically described as follows: product I---,product II--*product I I I 0¢+ y-forms--,fl (highly defective)) . + X - r a y - a m o r p h o u s p r o d u c t ; - ~ o - i o r m or ~¢+ y fl (highly crystalline)-~fl (highly crystalline)-~fl (highly crystalline) Although the ~-form consists of ~- and y-form components, the above scheme indicates that in the course of the synthetic process, the highly crystalline fl-form remains unchanged at all stages; from the X-ray-amorphous stage, the 0¢- and y-focms are transformed back into the same, but with a more defective structure. Therefore for the direct preparation of the 8-form of TiCI3, evidently all three stages can be unified.

Synthesis of propylene polymerization catalyst

625

With this aim, the single-stage syntheses (second and third variant0 were performed, i.e. with the participation of ether in TiCI, reduction. It was found that with the ratio ROR : Et2A1CI=2 and TiCI, excess, a solid product crystallizes from the liquid TiCIa" •nROR complex (n>0.5) at 27-30 °. The X-ray diagram of this product is shown in Fig. 3 (curve 1). The high defectiveness of the structure is indicated by two broad halos at 20=7054 ' and 15024' where peaks of the d-from normally appear. The "disorder"

1

I

I

....

gO

l

10

I ~0 °

Fro. 3. X-ray diagrams of products of single stage synthesis: 1-tV-form of TiCla (ratio R O R : Et2A1CI = 2); 2 - p r e p a r e d with TiCI, ether complexes and Et2AICI. TABLE 2.

CHARACYrERISTICS OF CATALYSTS PREPARED WITH THE ETHER COMPLEX OF

Et2AIC1

As

REDUCING AGENT

Synthesis parameters

Catalytic properties

AI +a I R O R

A x 10 -a, ~R

g of poly-

Et2AICI, hole, mole

mer

wt.

T°

O

g of catae~

t 3 5

2"0 1'8

6a 6b 60 7a 7b 10 11 12 13

1"3

25

27a 27b 27c 38 31a 3 9 ....

40

15 4 7

1.9

10

1.8 2.0 2"0 1"2 1-7 O.8

25 28 30 30 .... 28 28

I'0 1"7 1"I 1"7 1"6

•

0-- I O

30

atactic fraction, wt. %

lyst

bulk Treatment den- temperasity, ture, °C g/din a

5"5 5"0

6, I 146 t~' 100

1"6 1.32

0"9 1.4

260 370

0.21 -

fll J I

0-7 1-3

7.0 1-5

300

90 4-0 2.4 -

JJ'l J'] 100 6' I 150 ~'1 -

1.2 1-36 1"89 1.82

2"3 1"5 2'8 3"0

300 420 350 366

~

/~1

0.720

7.5

28

J' [ 120

1-43

2"5

360

28 -

30

4.0

~

-

1.32

1'5

370

6.5

~/

lS61

1.98

1.0

186

o5

4"5 "3.s

# r - J

-

-

fl- I ~165 1..9.2 1"3 ~ ' [ 1 8 6 / .......i:98"[ ......... 1"..].....

4013 4ic

55 45 40 50 70 40 55 48 43 45 55 '46

45 70 70 7O ...... 70 ....

626

N . S . BUKHARKINAe t

at.

in Ti atom positions can be judged from the hardly discernible peak in the range of 20= 6054' . However, with increasing temperature of the subsequent thermal treatment the disorder is reduced, and at 50 ° the X-ray diagram of the product assumes a normal appearance characteristic of the J-form of TiCl3 (Fig. I, curve 3). This intermediate modification of TiCla we named J'-form. The contents of AI + 3 in this product usually does not exceed 0.5 wt. ~o (Table 2). As the specific surface and activity of the familiar J-form prepared by multistage synthesis, and of the J'-form are practically identical (Table 1 and 2), it may be concluded that the catalytic activity is predominantly determined by the size of the surface and the number of defects. At the same time the contents of the atactic fraction in the polymer prepared with the J'-form is higher than when prepared with the &form of TiCIa (Table 2). Evidently in this case the distribution of Ti atoms has a major effect on the coordination of monomer and yield of the atactic fraction. The solid product formed at the ratio 1.4 < (ROR : Et2A1CI)< 1.8 has the character of a highly defective fl-form; its X-ray diagram is similar to that of product II obtained by ether treatment in multistage synthesis (Fig. 1, curve 5). The contents of A1 + 3 in this product usually also does not exceed 0.5 wt. ~o. The specific surface, activity and stereospecificity of this highly defective fl-form are high and comparable to those of the J- and J'-forms of TiCla (Table 2, experiments 39 and 40). This confirms our conclusion on the predominant importance of the size and defect structure of the surface on the activity of the catalyst and the minor role of the phase composition. At the ratio ROR : Et2AICI < 1.3, the fl-form of TIC13 is formed; this is transformed into the J-form either by thermal treatment at 65-70 ° (Table 2, experiment 6), as in the multistage synthesis, or with repeated additions of R O R up to the ratio ROR • Et2A1CI = 1 . 8 - 2 and thermal treatment at 40-45 ° (Table 2, experiment 27). With TIC14 containing some ether as the substrate to be reduced, and the Et2AICI.xROR complex with the ratio R O R : Et2A1CI= 1.0-1.6 as the reducing agent, a product is formed the X-ray diagram of which differs from those of the known modifications, o~, ~,, J and fl of TiCI3 TABLE 3. CHEMICAL COMPOSITION OF PRODUCTS PREPARED BY REDUCTION OF TiCl4 ETHER COMPLEXES

WITH Et2AIC1 Chemical composition, wt. ~o

Parameters of s y n t h e s i s Experiment

% 30 (1)

30 (2) 32 (1) 32 (2) 33 (1) 33 (2) 37

ROR

ROR

TiCI, Et2A1C1 mole/mole 0.33 1-9

reduction temp., °C 22

0.25

1"80

45

0.5

1.64

36

0"8

--

0

TIC14 Et2A1CI, mole/mole 1.8 1 2 2"3 2 2"1 2 2.5

Ti

A1

23"8 26" 1 19"2 29"4 18"9 29"0 28" 5

1"4 0.8 7"2 0"2 7"7 0"3 0"4

ROR

1"2~8 8"3 18"1 2"5 18"6 3"5 2"5

NoW. Samples taken at 40 ° (1) and after addition of fresh TiCI4 and heating to 65 ° (2). Fresh TiCI4 added dutias heating.

Synthesis of propylene polymerization catalyst

627

(Fig. 3, curve 2): all diffraction peaks characteristic of these modifications (20=6054 ' , 7°30 ', 7054 ') are absent, but new peaks appear at 2 0 = 5°32 ', 6 ° and 8048 '. As these products contain up to 18 Yo o f ether (Table 3), it may be assumed that solid ether-TiC13 complexes are formed which are destroyed by subsequent heating with TiCI4. The X-ray diagrams then become typical of 8-TiCIs (Fig. 1, curve 3). By reduction of TiCI4 containing ether in the ratio ROR : TiCI4=0.8-1"I with diethylaluminium chloride (Table 3, experiment 37), a highly defective fl-form of TIC13 is formed; this is transformed to the 8-form by addition o f TiC]4 and heating to 50--70° [I0]. At the ratio (ROR : Et2A1CI) >2.5-3, as mentioned earlier, the obtained TiCIs is dissolved in R O R with complex formation. Solid phase formation has not been observed in this case. The obtained results indicate that highly effective propylene polymerization catalysts can consist of both ,8- and ~'-forms o f TiCI3 prepared under mild conditions with the addition of electron donating compounds, and exhibiting enhanced specific surface areas and high contents of defects. Translated by D. DOSKO~ILOVA REFERENCES

1. 2. 3. 4.

Chem. and Engng. News 61: 6, 1983 Chem. Ind. 107: 27, 1984 R. Kit. DENILOV, I. A. VOLOSHIN and Yu. M. NIKIFOROV, Plast. massy, 6, 55, 1983 A. SATO, K. KIKUTA, T. UWAI and T. HANARI, U.S.A. Pat. 4420593 (Izobreteniya v SSSR i za rubezhom 58, No. 16, 49, 1984) 5. N. GOKO and Y. UEHARA, Pat. 0099026 EP (Izobreteniya v SSSR i za rubezhom 58, No. 1, 4, 1984) 6. N. S. BUKHARKINA, V. P. KONOVALOV, B. V. YEROFEYEV, A. Ya. VALENDO and M. A. KUSHEL', Izv. AN BSSR, Set. khim. nauk, 2, 20, 1981 7. L BOOR, Jr., Ziegler-Natta Catalysts and Polymerization, p. 670, N.Y., 1979 8. F. BASOLLO and R. PEARSON, Mekhanizmy neorganicheskikh reaktsii (Mechanisms of Inorganic Reactions). p. 592, Moscow, 1971 9. K. TANABE, Solid Acids and Bases. Their Catalytic Properties. Tokyo, Kodanshan, N.Y.-L., 1970 10. L.L. YEZHENKOVA, N. S. BUKHARKINA, T. V. TRAPEZNIKOVA and V. F. VASILENKO, Sintez, svoistva, pererabotka poliolefinov (Synthesis, Properties and Processing of Polyolefins). p. 41, Leningrad, 1984 11. G. NATTA, P. CORRADINI and G. ALLEGRA, J. Polymer Sci. 51: 399, 1961 12. Yu. A. GAVRILOV, A. M. ALADYSHEV, N. Yu. KOVALEVA, L. A. NOVOKSHONOVA, N. S. BUKHARKINA and V. P. KONOVALOV, Vysokomol. soyed. A27: 2300, !985 (Translated in Polymer Sci. U.S.S.R. 27: 11, 2583, 1985)