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Generation of active site confined inside supercage of NaY zeolite on a nano-scale and its ethylene polymerization
European Polymer Journal 39 (2003) 1553–1557 www.elsevier.com/locate/europolj
Generation of active site confined inside supercage of NaY zeolite on a nano-scale and its ethylene polymerization Young Soo Ko *, Seong Ihl Woo Department of Chemical and Biomolecular Engineering & Center for Ultramicrochemical Process Systems (CUPS), Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea Received 30 January 2003; received in revised form 11 February 2003; accepted 24 February 2003
Abstract To generate an active site that consisted of one Cp2 ZrCl2 molecule and 1-2 MAO molecules inside supercage of NaY zeolite, two preparation ways for supported catalyst were estimated. First, higher concentration of MAO and Cp2 ZrCl2 , and long reaction time were introduced during the preparation of supported catalyst. It showed activity in ethylene polymerization without any additional MAO. It indicates that Cp2 ZrCl2 coordinated with only 1–2 MAO molecules could be an active site due to the fact that supercage has nano-scaled diameter of supercage, 1.2 nm, and it could contain only 1–2 MAO molecules inside it theoretically. In situ generation of active site between NaY/MAO and homogeneous Cp2 ZrCl2 also showed experimental evidence that an active site was generated inside the supercage of NaY zeolite. It showed low activity with long activation time, suggesting the presence of a diffusion effect of Cp2 ZrCl2 in the pore of NaY. However, NaY/Cp2 ZrCl2 and homogeneous MAO system showed the characteristic PE polymerization with homogeneous catalyst, indicating that active site was not generated inside the supercage of NaY. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Supported metallocene; Polyethylene; Polymerization; Nano-technology
1. Introduction There have been many studies on immobilization of metallocene catalyst for industrial and commercial purposes due to the fact that metallocene catalyst can only be applied to the several types of plant in heterogeneous form [1]. In previous articles, we have reported several studies on the application of zeolite and mesoporous material as a support for metallocene catalyst. According to our previous results, very peculiar effect of zeolite and
* Corresponding author. Present address: R & T, Research Location Porvoo, Borealis Polymers Oy. P.O. Box 330, FIN06101 Porvoo, Finland. Tel.: +358-9-3949-4569; fax: +358-93949-4620. E-mail address: [email protected] (Y.S. Ko).
mesoporous material on the polymerization and resulting polymer structures was observed, and it can be summarized as follow: NaY zeolite-entrapped metallocene catalyst can polymerize ethylene with small amount of additional MAO [2], and that Et(ind)2 ZrCl2 confined into the pores of MCM-41 and VPI-5 polymerizes propylene with a high activity [3]. MCM-41 supported Et(ind)2 ZrCl2 also showed the effect of steric hindrance of regular and small pore structure of MCM-41 on the copolymerization between ethylene and 1-octadecene [4]. Furthermore, it has been observed that the ethylenealpha olefin copolymerization with NaY/MAO/Cp2 ZrCl2 showed to be governed by shape and diffusion of monomer-controlled mechanism [5]. The copolymerization rate and the content of comonomer were affected by the shape and the diffusion of monomer through the pores of the zeolite. This provides a means of controlling the insertion rate and the amount of comonomer in copolymer chain by the shape selectivity of the zeolite
0014-3057/03/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0014-3057(03)00051-X
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during copolymerization. Silica and another inorganic supports generally possess a relatively broad pore size distribution due to their amorphous structure, reporting that pore structure cannot affect the polymerization mechanism in ethylene, propylene homopolymerization and ethylene-a-olefin copolymerization. Based on these results, nano-confinement of metallocene inside the supercage of NaY zeolite (pore diameter ¼ 0.7 nm, and supercage diameter ¼ 1.2 nm) can give the opportunity to control the copolymerization and molecular structure of copolymer by not only metallocene molecular structure, but also supporting carrier. In this article, it will be reported on the different supporting methods from previous one to generate active site inside the supercage of NaY, and on their results on ethylene polymerization. These can give more detailed explanation about active site confined inside the supercage of NaY.
2. Experimental 2.1. Materials Cp2 ZrCl2 (from Aldrich Co.) was used without purification. NaY zeolite (NaY) (from Strem Co., Ltd.) was dehydrated at 450 °C for 24 h in vacuo. MMAO-3A was purchased from Akzo Chemical Inc. Ethylene (donated from Daelim Ind. Co., Korea) and nitrogen were purified with two columns of Fisher RIDOX and molecular sieve 5A/13X. Toluene (from J.T. Baker Chem. Co., Ltd.) was purified by refluxing over sodium metal. Trimethylaluminium (TMA), triethylaluminium (TEAL), and triisobutylaluminium (TIBAL) (from Aldrich Co.) were used without further purification. 2.2. Preparation of the supported catalyst NaY/MAO/Cp2 ZrCl2 , 9.0 g of dehydrated NaY zeolite and 100 mmol-Al of MAO solution (1.98 M-Al solution in toluene) were suspended in 50 cm3 of toluene and stirred for 120 h at 60 °C. The resulting solid was washed more than five times with 150 cm3 of toluene and dried at 25 °C in vacuo. MAO-pretreated NaY zeolite wase impregnated into 10.0 mmol of Cp2 ZrCl2 100 cm3 of toluene, followed by vigorous stirring at 60 °C for 148 h. Then solid part was washed more than five times with 150 cm3 of toluene to remove Cp2 ZrCl2 physisorbed on the exterior surface of zeolite and dried in vacuo. All manipulation was performed in N2 atmosphere. Preparation of NaY/MAO and NaY/Cp2 ZrCl2 : 4.5 g of dehydrated NaY zeolite and 140 mmol of MAO (1.98 M solution in toluene), or 2.5 mmol of Cp2 ZrCl2 were suspended in 70 cm3 of toluene and stirred for 190 h at 60 °C. Washing and drying procedures to prepare this
catalyst were the same as those to prepare 1:1 model catalyst. 2.3. Polymerization Slurry polymerization was carried out in a 1 l autoclave filled with 350 cm3 toluene at 8 atm and 70 °C. Three hundred milligrams of supported catalyst in glass ampoule and additional MAO was introduced to the reactor. The detailed procedures for the polymerization were described elsewhere [6]. 2.4. Analysis of catalyst and polymer The contents of metal in supported catalysts were measured by inductively coupled plasma spectroscopy for zirconium. Al contents on NaY zeolite after pretreatment of NaY with MAO were analyzed by measuring CH4 evolved and quenching method which measured Al content of solid resulting from the quenching the MAO solution with acidic alcohol after immobilization of MAO on NaY zeolite. Number and weight-averaged molecular weight (Mn and Mw ) and molecular weight distribution (MWD) were measured at 145 °C by GPC (Waters Associates; model ALC-GPC-150C) using o-dichlorobenzene as a solvent. The melting point (Tm ) was measured by DSC (Dupont Analyst 2000) at a heating rate of 5 °C/min after removing thermal history of sample of first heating (20 °C/min). 3. Results and discussion 3.1. Generation of active site inside the supercage of NaY zeolite and its ethylene polymerization In previous report, the contents of aluminium and zirconium in NaY zeolite supported catalyst were lower in comparison with the number of supercage inside NaY zeolite (Al ¼ 1.06 mmol/g-MAO treated NaY, Zr ¼ 35.7 lmol/g-catalyst) [2]. This meant that the mathematical probability for a generation of active site between MAO and metallocene catalyst would be quite low during the preparation step, resulting that small amount of additional MAO (Al/Zr ¼ above 186) was needed to perform ethylene polymerization with this supported catalyst. In order to generate an active site with MAO and Cp2 ZrCl2 inside the supercage of NaY during supporting step, the loading amount of MAO was increased up to 30 times compared to previous reported catalyst, and the content of Al was 29.0 mmol-Al/g-MAO-pretreated NaY. The content of Zr in the catalyst was increased up to 61.7 lmol/g-cat. This implies that most of supercages are filled up with MAO molecules, Cp2 ZrCl2 molecule could react with MAO, and generate active sites inside
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Table 1 Results of polymerizations using NaY-supported Cp2 ZrCl2 prepared by various supporting methodsa Catalyst
Al/Zrb
Co-catalyst
Al/Zrc
High loading NaY/ MAO/Cp2 ZrCl2
470 470 470
TMA TEAL TiBAL
500 500 500
120 120 120
3.7 2.1 1.7
NaY/MAO-homogeneous Cp2 ZrCl2
4370
TMA
500
240
NaY/Cp2 ZrCl2 NaY/Cp2 ZrCl2
– –
MAO TMA
1500 1500
60 120
Time (min)
Tm (°C)
Mn e
MWDe
12.4 7.1 5.9
139.1 138.5 140.1
–f –f –f
–f –f –f
4.6
35.8
139.7
–f
–f
15.4 0.6
1180.5 21.9
138.7 136.2
420,000 –f
2.3 –f
Yield (g)
Activityd
a
Polymerization condition: temperature ¼ 50 °C, Pt ¼ 8 atm, solvent ¼ 350 cc of toluene. Al/Zr molar ratio in the supported catalyst after preparation of catalyst. c Al/Zr molar ratio in the reaction medium during polymerization. d Unit ¼ kg-PE/(mol-Zr atm h). e Measured by GPC. f Cannot measure because sample do not be dissolved in solvent. b
the supercage of NaY during preparation step of catalyst. Table 1 and Fig. 1 show the polymerization results and kinetic behavior of resulting supported catalyst in the presence of additional aluminum alkyls, TMA, TEAL, or TIBAL as scavenger. Ethylene could not be polymerized with lower loading-NaY/MAO/Cp2 ZrCl2 without additional MAO as reported in previous paper [2]. However, higher MAO and Cp2 ZrCl2 -loading NaY supported catalyst could polymerize ethylene with relatively lower activity. This indicates that active site is generated during preparation step, and has activity in ethylene polymer-
30
Rp (kg-PE/mol-Zr atm hr)
25 20 (A)
15 (B)
10
3.2. In situ generation of active site inside the pore and supercage of NaY zeolite during the ethylene polymerization
(C)
5 0 0
20
40
ization without additional MAO. It has been hard to examine how many MAO molecules are needed to generate one active site, and there was little clear and concrete work concerning this issue. This result could show an indirect evidence that 1–2 MAOs are necessary to make active site that has activity in ethylene polymerization due to nano-space inside the supercage (diameter ¼ 1.2 nm). However, the total number of active sites in NaY zeolite in this result was low, resulting in low activity. In addition, the kinds of aluminium alkyls influenced on the activity and kinetic behavior during polymerization as shown in Fig. 1. Polymerization rate increased rapidly at the initial stage of polymerization in case of TMA, and then decay of activity was shown. In case of TEAL, the kinetic behavior was similar to that of TMA, but it showed lower activity than that of TMA. In case of TIBAL, no rapid activation was shown, but activity was maintained during polymerization. This difference in kinetic profile suggests that aluminium alkyl influence on the polymerization performance of active site, resulting in change in activity.
60
80
100
120
time (min) Fig. 1. Profiles of monomer consumption rate in ethylene polymerization catalyzed with high loaded Cp2 ZrCl2 and MAO inside the supercage of NaY, and with additional cocatalyst: (A) TMA, (B) TEAL and (C) TIBAL. Polymerization condition: See Table 1.
In situ generation of active site inside the supercage of NaY was performed in two different ways in order to see generation mechanism of active site including a diffusion effect inside the pore and supercage of NaY on generation of active site during polymerization. One method was the catalytic system that was combined between NaY/MAO and homogeneous Cp2 ZrCl2 , and the other was between NaY/Cp2 ZrCl2 and homogeneous MAO. Fig. 2 reveals the polymerization rate when polymerization of ethylene was conducted with homogeneous
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200 40
Rp (kg-PE/mol-Zr atm hr)
Rp (kg-PE/molZr atm hr)
4000
150
30 20 10
100 0 0
20
40
60
50
3000
2000
1000
0
0 0
60
120
180
240
time (min)
0
10
20
30
40
50
60
time (min)
Fig. 2. Profiles of monomer consumption rate in ethylene polymerization catalyzed with homogeneous Cp2 ZrCl2 and MAO confined inside the supercage of NaY. Polymerization condition: See Table 1.
Fig. 3. Profiles of monomer consumption rate in ethylene polymerization catalyzed with Cp2 ZrCl2 confined inside the supercage of NaY, and homogeneous MAO. Polymerization condition: See Table 1.
Cp2 ZrCl2 , NaY-supported MAO and TMA as scavenger. NaY/MAO and homogeneous Cp2 ZrCl2 catalyst system was active in ethylene polymerization. This catalyst system did not show any activity for 40 min after start of polymerization. After 40 min of polymerization time passed, polymerization rate increased slowly, and then maintained steadily. This can be explained as follows: Cp2 ZrCl2 was diffused into the pore and supercage of NaY, and made an active site with MAO molecule. However, the diffusion rate of Cp2 ZrCl2 was low due to small and regular-shaped pore of NaY zeolite. Another method for in situ generation of active site was tested with NaY-supported Cp2 ZrCl2 catalyst with homogeneous MAO as a co-catalyst. For this catalyst system, MAO molecule had to diffuse into the pore of NaY to make an active site inside the pore and supercage of NaY. The content of Zr was 10.0 mol-Zr/g-cat in NaY/Cp2 ZrCl2 catalyst. The polymerization behavior was shown in Fig. 3. Polymerization rate increased rapidly during 5 min after start of polymerization, then decreased slowly. The resulting polymer was flake-type and was similar to that of homogeneous Cp2 ZrCl2 MAO system. Judging from these observations, it could be concluded that some of Cp2 ZrCl2 molecules were leached out to the polymerization medium, following the generation of active sites with MAO in homogeneous form, but not inside the pore and supercage of NaY in heterogeneous form. The MWD of polymer was 2.3, similar to that of homogeneous catalyst, and was also an evidence for leaching. It could be explained that NaY zeolite, which was not treated with MAO or other
chemicals, could not hold Cp2 ZrCl2 tightly in chemical manner inside the pore of it. The polymerization behavior of ethylene with NaY/ Cp2 ZrCl2 catalyst and additional TMA was shown in Fig. 4. Although deactivation of polymerization rate was shown, the polymerization rate was maintained for about 40 min. The molecular weight of resulting PE could not be measured because it was not dissolved conveniently in DCB at 145 °C. This could be coming from that Cp2 ZrCl2 confined inside the supercage of NaY could produce very higher molecular weight during ethylene polymerization compared to homogeneous Cp2 ZrCl2 as reported in previous report [2], and that the residue of NaY zeolite was relatively higher due to lower activity. The generation of active site can be explained by that TMA was diffused into the pore of NaY, and made an active site with Cp2 ZrCl2 that was confined inside the supercage of NaY, and affected by the environment of it. Furthermore, taking this result with that from NaY/Cp2 ZrCl2 –MAO system into consideration, MAO could play a role in leaching out Cp2 ZrCl2 molecule from pore of NaY. In conclusion, the active site consisting of one Cp2 ZrCl2 and 1–2 MAO molecules inside the nanoscaled space, supercage of NaY zeolite was active in ethylene polymerization with low activity without any additional MAO. Furthermore, the activity was dependent on the kind of aluminium alkyl. In situ generation of active site between NaY/MAO and homogeneous Cp2 ZrCl2 showed low activity with long activation time, and it could be regarded as the diffusion effect of
Rp (kg-PE/mol-Zr atm hr)
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Acknowledgement
150
This research was funded by Center for Ultramicrochemical Process Systems (CUPS) sponsored by KOSEF. References
100
50
0 0
20
40
60
80
100
120
time (min) Fig. 4. Profiles of monomer consumption rate in ethylene polymerization catalyzed with Cp2 ZrCl2 confined inside the supercage of NaY, and homogeneous TMA. Polymerization condition: See Table 1.
Cp2 ZrCl2 inside the supercage of NaY. NaY/Cp2 ZrCl2 and homogeneous MAO system showed the characteristic PE polymerization with homogeneous catalyst, indicating that active site was not generated inside the supercage of NaY.
[1] Hlatky GG. Heterogeneous single-site catalysts for olefin polymerization. Chem Rev 2000;100:1347–76; Gladysz JA. Frontiers in metal-catalyzed polymerization: Designer metallocenes, designs on new monomers, demystifying MAO, Metathesis Deshabille. Chem Rev 2000;100: 1167–8. [2] Woo SI, Ko YS, Han TK. Polymerization of ethylene over metallocenes confined inside the supercage of NaY. Macromol Rapid Commun 1995;16:489. [3] Ko YS, Han TK, Park JW, Woo SI. Propylene polymerization catalyzed over MCM-41 and VPI-5-supported Et(ind)2 ZrCl2 catalysts. Macromol Chem Rapid Commun 1996;17:749. [4] Ko YS, Woo SI. Copolymerization of olefins inside pore of MCM-41 with Et(ind)2 ZrCl2 . Macromol Chem Phys 2001; 202:739. [5] Ko YS, Seo TS, Hong DS, Woo SI. In: Kaminsky W, editor. Preparation of novel supported metallocene and their olefin polymerization capabilities. Berlin: Springer-Verlag; 1999. p. 368–80. [6] Han TK, Choi HK, Jeung DW, Ko YS, Woo SI. Control of molecular weight and molecular weight distribution in ethylene polymerization catalyzed over metallocene catalysts. Macromol Chem Phys 1995;196:2637.
Generation of active site confined inside supercage of NaY zeolite on a nano-scale and its ethylene polymerization Young Soo Ko *, Seong Ihl Woo Department of Chemical and Biomolecular Engineering & Center for Ultramicrochemical Process Systems (CUPS), Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea Received 30 January 2003; received in revised form 11 February 2003; accepted 24 February 2003
Abstract To generate an active site that consisted of one Cp2 ZrCl2 molecule and 1-2 MAO molecules inside supercage of NaY zeolite, two preparation ways for supported catalyst were estimated. First, higher concentration of MAO and Cp2 ZrCl2 , and long reaction time were introduced during the preparation of supported catalyst. It showed activity in ethylene polymerization without any additional MAO. It indicates that Cp2 ZrCl2 coordinated with only 1–2 MAO molecules could be an active site due to the fact that supercage has nano-scaled diameter of supercage, 1.2 nm, and it could contain only 1–2 MAO molecules inside it theoretically. In situ generation of active site between NaY/MAO and homogeneous Cp2 ZrCl2 also showed experimental evidence that an active site was generated inside the supercage of NaY zeolite. It showed low activity with long activation time, suggesting the presence of a diffusion effect of Cp2 ZrCl2 in the pore of NaY. However, NaY/Cp2 ZrCl2 and homogeneous MAO system showed the characteristic PE polymerization with homogeneous catalyst, indicating that active site was not generated inside the supercage of NaY. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Supported metallocene; Polyethylene; Polymerization; Nano-technology
1. Introduction There have been many studies on immobilization of metallocene catalyst for industrial and commercial purposes due to the fact that metallocene catalyst can only be applied to the several types of plant in heterogeneous form [1]. In previous articles, we have reported several studies on the application of zeolite and mesoporous material as a support for metallocene catalyst. According to our previous results, very peculiar effect of zeolite and
* Corresponding author. Present address: R & T, Research Location Porvoo, Borealis Polymers Oy. P.O. Box 330, FIN06101 Porvoo, Finland. Tel.: +358-9-3949-4569; fax: +358-93949-4620. E-mail address: [email protected] (Y.S. Ko).
mesoporous material on the polymerization and resulting polymer structures was observed, and it can be summarized as follow: NaY zeolite-entrapped metallocene catalyst can polymerize ethylene with small amount of additional MAO [2], and that Et(ind)2 ZrCl2 confined into the pores of MCM-41 and VPI-5 polymerizes propylene with a high activity [3]. MCM-41 supported Et(ind)2 ZrCl2 also showed the effect of steric hindrance of regular and small pore structure of MCM-41 on the copolymerization between ethylene and 1-octadecene [4]. Furthermore, it has been observed that the ethylenealpha olefin copolymerization with NaY/MAO/Cp2 ZrCl2 showed to be governed by shape and diffusion of monomer-controlled mechanism [5]. The copolymerization rate and the content of comonomer were affected by the shape and the diffusion of monomer through the pores of the zeolite. This provides a means of controlling the insertion rate and the amount of comonomer in copolymer chain by the shape selectivity of the zeolite
0014-3057/03/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0014-3057(03)00051-X
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during copolymerization. Silica and another inorganic supports generally possess a relatively broad pore size distribution due to their amorphous structure, reporting that pore structure cannot affect the polymerization mechanism in ethylene, propylene homopolymerization and ethylene-a-olefin copolymerization. Based on these results, nano-confinement of metallocene inside the supercage of NaY zeolite (pore diameter ¼ 0.7 nm, and supercage diameter ¼ 1.2 nm) can give the opportunity to control the copolymerization and molecular structure of copolymer by not only metallocene molecular structure, but also supporting carrier. In this article, it will be reported on the different supporting methods from previous one to generate active site inside the supercage of NaY, and on their results on ethylene polymerization. These can give more detailed explanation about active site confined inside the supercage of NaY.
2. Experimental 2.1. Materials Cp2 ZrCl2 (from Aldrich Co.) was used without purification. NaY zeolite (NaY) (from Strem Co., Ltd.) was dehydrated at 450 °C for 24 h in vacuo. MMAO-3A was purchased from Akzo Chemical Inc. Ethylene (donated from Daelim Ind. Co., Korea) and nitrogen were purified with two columns of Fisher RIDOX and molecular sieve 5A/13X. Toluene (from J.T. Baker Chem. Co., Ltd.) was purified by refluxing over sodium metal. Trimethylaluminium (TMA), triethylaluminium (TEAL), and triisobutylaluminium (TIBAL) (from Aldrich Co.) were used without further purification. 2.2. Preparation of the supported catalyst NaY/MAO/Cp2 ZrCl2 , 9.0 g of dehydrated NaY zeolite and 100 mmol-Al of MAO solution (1.98 M-Al solution in toluene) were suspended in 50 cm3 of toluene and stirred for 120 h at 60 °C. The resulting solid was washed more than five times with 150 cm3 of toluene and dried at 25 °C in vacuo. MAO-pretreated NaY zeolite wase impregnated into 10.0 mmol of Cp2 ZrCl2 100 cm3 of toluene, followed by vigorous stirring at 60 °C for 148 h. Then solid part was washed more than five times with 150 cm3 of toluene to remove Cp2 ZrCl2 physisorbed on the exterior surface of zeolite and dried in vacuo. All manipulation was performed in N2 atmosphere. Preparation of NaY/MAO and NaY/Cp2 ZrCl2 : 4.5 g of dehydrated NaY zeolite and 140 mmol of MAO (1.98 M solution in toluene), or 2.5 mmol of Cp2 ZrCl2 were suspended in 70 cm3 of toluene and stirred for 190 h at 60 °C. Washing and drying procedures to prepare this
catalyst were the same as those to prepare 1:1 model catalyst. 2.3. Polymerization Slurry polymerization was carried out in a 1 l autoclave filled with 350 cm3 toluene at 8 atm and 70 °C. Three hundred milligrams of supported catalyst in glass ampoule and additional MAO was introduced to the reactor. The detailed procedures for the polymerization were described elsewhere [6]. 2.4. Analysis of catalyst and polymer The contents of metal in supported catalysts were measured by inductively coupled plasma spectroscopy for zirconium. Al contents on NaY zeolite after pretreatment of NaY with MAO were analyzed by measuring CH4 evolved and quenching method which measured Al content of solid resulting from the quenching the MAO solution with acidic alcohol after immobilization of MAO on NaY zeolite. Number and weight-averaged molecular weight (Mn and Mw ) and molecular weight distribution (MWD) were measured at 145 °C by GPC (Waters Associates; model ALC-GPC-150C) using o-dichlorobenzene as a solvent. The melting point (Tm ) was measured by DSC (Dupont Analyst 2000) at a heating rate of 5 °C/min after removing thermal history of sample of first heating (20 °C/min). 3. Results and discussion 3.1. Generation of active site inside the supercage of NaY zeolite and its ethylene polymerization In previous report, the contents of aluminium and zirconium in NaY zeolite supported catalyst were lower in comparison with the number of supercage inside NaY zeolite (Al ¼ 1.06 mmol/g-MAO treated NaY, Zr ¼ 35.7 lmol/g-catalyst) [2]. This meant that the mathematical probability for a generation of active site between MAO and metallocene catalyst would be quite low during the preparation step, resulting that small amount of additional MAO (Al/Zr ¼ above 186) was needed to perform ethylene polymerization with this supported catalyst. In order to generate an active site with MAO and Cp2 ZrCl2 inside the supercage of NaY during supporting step, the loading amount of MAO was increased up to 30 times compared to previous reported catalyst, and the content of Al was 29.0 mmol-Al/g-MAO-pretreated NaY. The content of Zr in the catalyst was increased up to 61.7 lmol/g-cat. This implies that most of supercages are filled up with MAO molecules, Cp2 ZrCl2 molecule could react with MAO, and generate active sites inside
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Table 1 Results of polymerizations using NaY-supported Cp2 ZrCl2 prepared by various supporting methodsa Catalyst
Al/Zrb
Co-catalyst
Al/Zrc
High loading NaY/ MAO/Cp2 ZrCl2
470 470 470
TMA TEAL TiBAL
500 500 500
120 120 120
3.7 2.1 1.7
NaY/MAO-homogeneous Cp2 ZrCl2
4370
TMA
500
240
NaY/Cp2 ZrCl2 NaY/Cp2 ZrCl2
– –
MAO TMA
1500 1500
60 120
Time (min)
Tm (°C)
Mn e
MWDe
12.4 7.1 5.9
139.1 138.5 140.1
–f –f –f
–f –f –f
4.6
35.8
139.7
–f
–f
15.4 0.6
1180.5 21.9
138.7 136.2
420,000 –f
2.3 –f
Yield (g)
Activityd
a
Polymerization condition: temperature ¼ 50 °C, Pt ¼ 8 atm, solvent ¼ 350 cc of toluene. Al/Zr molar ratio in the supported catalyst after preparation of catalyst. c Al/Zr molar ratio in the reaction medium during polymerization. d Unit ¼ kg-PE/(mol-Zr atm h). e Measured by GPC. f Cannot measure because sample do not be dissolved in solvent. b
the supercage of NaY during preparation step of catalyst. Table 1 and Fig. 1 show the polymerization results and kinetic behavior of resulting supported catalyst in the presence of additional aluminum alkyls, TMA, TEAL, or TIBAL as scavenger. Ethylene could not be polymerized with lower loading-NaY/MAO/Cp2 ZrCl2 without additional MAO as reported in previous paper [2]. However, higher MAO and Cp2 ZrCl2 -loading NaY supported catalyst could polymerize ethylene with relatively lower activity. This indicates that active site is generated during preparation step, and has activity in ethylene polymer-
30
Rp (kg-PE/mol-Zr atm hr)
25 20 (A)
15 (B)
10
3.2. In situ generation of active site inside the pore and supercage of NaY zeolite during the ethylene polymerization
(C)
5 0 0
20
40
ization without additional MAO. It has been hard to examine how many MAO molecules are needed to generate one active site, and there was little clear and concrete work concerning this issue. This result could show an indirect evidence that 1–2 MAOs are necessary to make active site that has activity in ethylene polymerization due to nano-space inside the supercage (diameter ¼ 1.2 nm). However, the total number of active sites in NaY zeolite in this result was low, resulting in low activity. In addition, the kinds of aluminium alkyls influenced on the activity and kinetic behavior during polymerization as shown in Fig. 1. Polymerization rate increased rapidly at the initial stage of polymerization in case of TMA, and then decay of activity was shown. In case of TEAL, the kinetic behavior was similar to that of TMA, but it showed lower activity than that of TMA. In case of TIBAL, no rapid activation was shown, but activity was maintained during polymerization. This difference in kinetic profile suggests that aluminium alkyl influence on the polymerization performance of active site, resulting in change in activity.
60
80
100
120
time (min) Fig. 1. Profiles of monomer consumption rate in ethylene polymerization catalyzed with high loaded Cp2 ZrCl2 and MAO inside the supercage of NaY, and with additional cocatalyst: (A) TMA, (B) TEAL and (C) TIBAL. Polymerization condition: See Table 1.
In situ generation of active site inside the supercage of NaY was performed in two different ways in order to see generation mechanism of active site including a diffusion effect inside the pore and supercage of NaY on generation of active site during polymerization. One method was the catalytic system that was combined between NaY/MAO and homogeneous Cp2 ZrCl2 , and the other was between NaY/Cp2 ZrCl2 and homogeneous MAO. Fig. 2 reveals the polymerization rate when polymerization of ethylene was conducted with homogeneous
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200 40
Rp (kg-PE/mol-Zr atm hr)
Rp (kg-PE/molZr atm hr)
4000
150
30 20 10
100 0 0
20
40
60
50
3000
2000
1000
0
0 0
60
120
180
240
time (min)
0
10
20
30
40
50
60
time (min)
Fig. 2. Profiles of monomer consumption rate in ethylene polymerization catalyzed with homogeneous Cp2 ZrCl2 and MAO confined inside the supercage of NaY. Polymerization condition: See Table 1.
Fig. 3. Profiles of monomer consumption rate in ethylene polymerization catalyzed with Cp2 ZrCl2 confined inside the supercage of NaY, and homogeneous MAO. Polymerization condition: See Table 1.
Cp2 ZrCl2 , NaY-supported MAO and TMA as scavenger. NaY/MAO and homogeneous Cp2 ZrCl2 catalyst system was active in ethylene polymerization. This catalyst system did not show any activity for 40 min after start of polymerization. After 40 min of polymerization time passed, polymerization rate increased slowly, and then maintained steadily. This can be explained as follows: Cp2 ZrCl2 was diffused into the pore and supercage of NaY, and made an active site with MAO molecule. However, the diffusion rate of Cp2 ZrCl2 was low due to small and regular-shaped pore of NaY zeolite. Another method for in situ generation of active site was tested with NaY-supported Cp2 ZrCl2 catalyst with homogeneous MAO as a co-catalyst. For this catalyst system, MAO molecule had to diffuse into the pore of NaY to make an active site inside the pore and supercage of NaY. The content of Zr was 10.0 mol-Zr/g-cat in NaY/Cp2 ZrCl2 catalyst. The polymerization behavior was shown in Fig. 3. Polymerization rate increased rapidly during 5 min after start of polymerization, then decreased slowly. The resulting polymer was flake-type and was similar to that of homogeneous Cp2 ZrCl2 MAO system. Judging from these observations, it could be concluded that some of Cp2 ZrCl2 molecules were leached out to the polymerization medium, following the generation of active sites with MAO in homogeneous form, but not inside the pore and supercage of NaY in heterogeneous form. The MWD of polymer was 2.3, similar to that of homogeneous catalyst, and was also an evidence for leaching. It could be explained that NaY zeolite, which was not treated with MAO or other
chemicals, could not hold Cp2 ZrCl2 tightly in chemical manner inside the pore of it. The polymerization behavior of ethylene with NaY/ Cp2 ZrCl2 catalyst and additional TMA was shown in Fig. 4. Although deactivation of polymerization rate was shown, the polymerization rate was maintained for about 40 min. The molecular weight of resulting PE could not be measured because it was not dissolved conveniently in DCB at 145 °C. This could be coming from that Cp2 ZrCl2 confined inside the supercage of NaY could produce very higher molecular weight during ethylene polymerization compared to homogeneous Cp2 ZrCl2 as reported in previous report [2], and that the residue of NaY zeolite was relatively higher due to lower activity. The generation of active site can be explained by that TMA was diffused into the pore of NaY, and made an active site with Cp2 ZrCl2 that was confined inside the supercage of NaY, and affected by the environment of it. Furthermore, taking this result with that from NaY/Cp2 ZrCl2 –MAO system into consideration, MAO could play a role in leaching out Cp2 ZrCl2 molecule from pore of NaY. In conclusion, the active site consisting of one Cp2 ZrCl2 and 1–2 MAO molecules inside the nanoscaled space, supercage of NaY zeolite was active in ethylene polymerization with low activity without any additional MAO. Furthermore, the activity was dependent on the kind of aluminium alkyl. In situ generation of active site between NaY/MAO and homogeneous Cp2 ZrCl2 showed low activity with long activation time, and it could be regarded as the diffusion effect of
Rp (kg-PE/mol-Zr atm hr)
Y.S. Ko, S.I. Woo / European Polymer Journal 39 (2003) 1553–1557
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Acknowledgement
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This research was funded by Center for Ultramicrochemical Process Systems (CUPS) sponsored by KOSEF. References
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time (min) Fig. 4. Profiles of monomer consumption rate in ethylene polymerization catalyzed with Cp2 ZrCl2 confined inside the supercage of NaY, and homogeneous TMA. Polymerization condition: See Table 1.
Cp2 ZrCl2 inside the supercage of NaY. NaY/Cp2 ZrCl2 and homogeneous MAO system showed the characteristic PE polymerization with homogeneous catalyst, indicating that active site was not generated inside the supercage of NaY.
[1] Hlatky GG. Heterogeneous single-site catalysts for olefin polymerization. Chem Rev 2000;100:1347–76; Gladysz JA. Frontiers in metal-catalyzed polymerization: Designer metallocenes, designs on new monomers, demystifying MAO, Metathesis Deshabille. Chem Rev 2000;100: 1167–8. [2] Woo SI, Ko YS, Han TK. Polymerization of ethylene over metallocenes confined inside the supercage of NaY. Macromol Rapid Commun 1995;16:489. [3] Ko YS, Han TK, Park JW, Woo SI. Propylene polymerization catalyzed over MCM-41 and VPI-5-supported Et(ind)2 ZrCl2 catalysts. Macromol Chem Rapid Commun 1996;17:749. [4] Ko YS, Woo SI. Copolymerization of olefins inside pore of MCM-41 with Et(ind)2 ZrCl2 . Macromol Chem Phys 2001; 202:739. [5] Ko YS, Seo TS, Hong DS, Woo SI. In: Kaminsky W, editor. Preparation of novel supported metallocene and their olefin polymerization capabilities. Berlin: Springer-Verlag; 1999. p. 368–80. [6] Han TK, Choi HK, Jeung DW, Ko YS, Woo SI. Control of molecular weight and molecular weight distribution in ethylene polymerization catalyzed over metallocene catalysts. Macromol Chem Phys 1995;196:2637.