CHROMIUM OXIDE CATALYST FOR ETHYLENE POLYMERIZATION

Abstract

The invention relates to a solid catalyst system comprising a first chromium compound, a second chromium compound, a reaction product of an alkyl aluminium compound and a nitrogen containing compound and a silicon oxide support, wherein the first chromium compound is chromium trioxide or a compound convertible to chromium trioxide, the second chromium compound is a slilylchromate compound and the nitrogen containing compound is a cycloalkylamine compound having the general formula: R.sup.3—NH.sub.2, wherein R.sup.3 is selected from C3-C8 cycloalkyl groups.

Claims

1. A solid catalyst system comprising a first chromium compound, a second chromium compound, a reaction product of an alkyl aluminium compound and a nitrogen containing compound and a silicon oxide support, wherein the first chromium compound is chromium trioxide or a compound convertible to chromium trioxide, the second chromium compound is a silylchromate compound and the nitrogen containing compound is a cycloalkylamine compound having the general formula: R.sup.3—NH.sub.2, wherein R.sup.3 is selected from C3-C8 cycloalkyl groups.

2. The solid catalyst system according to claim 1, wherein the first chromium compound is selected from the group consisting of chromium trioxide, chromium acetyl acetone, chromium chloride, chromium nitrate, chromium acetate, chromium acetate hydroxide, chromium sulfate, ammonium chromate and ammonium dichromate.

3. The solid catalyst system according to claim 1, wherein the amount of Cr in the catalyst system is 0.10 to 2.0 wt %.

4. The solid catalyst system according to claim 1, wherein the amount of the first chromium compound with respect to the total of the first chromium compound and the second chromium compound is more than 35 wt % and at most 90 wt %.

5. The solid catalyst system according to claim 1, wherein the amount of the first chromium compound with respect to the total of the first chromium compound and the second chromium compound is at least 10 wt % and at most 35 wt %.

6. The solid catalyst system according to claim 1, wherein the alkyl aluminium compound is selected from the group consisting of trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, tri-n-hexyl aluminum and tri octyl aluminum.

7. The solid catalyst system according to claim 1, wherein the nitrogen containing compound is selected from the group consisting of cyclopropylamine, cyclobutylamine, cyclopentylamine, cyclohexylamine, cycloheptylamine and cyclooctylamine.

8. The solid catalyst system according to claim 1, wherein the molar ratio of the amount of Al in the solid catalyst system with respect to the amount of Cr in the solid catalyst system is 0.1 to 25.

9. The solid catalyst system according to claim 1, wherein the silicon oxide support has an average particle diameter of 20 to 50 μm, and/or a pore volume of at least 0.8 cm.sup.3 and/or a surface area of 150 to 800 m.sup.2/g.

10. The solid catalyst system according to claim 1, further comprising a non-chromium metal compound.

11. The solid catalyst system according to claim 10, wherein the non-chromium metal compound is a titanium alkoxy compound selected from the group consisting of tetraethoxy titanium, tetramethoxy titanium, tetrabutoxy titanium, tetrapropoxy titanium, tetraisobutoxy titanium, tetrapentoxy titanium, triethoxychloro titanium, diethoxydichloro titanium, trichloethoxy titanium, methoxy titanium trichloride, dimethoxy titanium dichloride, ethoxy titanium trichloride, diethoxy titanium dichloride, propoxy titanium trichloride, dipropoxy titanium dichloride, butoxy titanium trichloride, butoxy titanium dichloride and titanium tetrachloride.

12. A process for the preparation of the solid catalyst system according to claim 1, comprising i) mixing the silica support provided with the first chromium compound and the optional non-chromium compound with the second chromium compound and ii) treating the product obtained by step i) with the reaction product of the aluminium alkyl compound and the nitrogen-containing compound.

13. A process for the production of polyethylene by polymerisation of ethylene and an optional comonomer in the presence of the solid catalyst system according to claim 1.

14. The polyethylene obtained by or obtainable by the process according to claim 13.

15. An article comprising the polyethylene according to claim 14.

16. The solid catalyst system according to claim 1, wherein the amount of Cr in the catalyst system is 0.10 to 1.0 wt %.

17. The solid catalyst system according to claim 1, wherein the nitrogen containing compound is selected from the group consisting of cyclohexylamine and cyclooctylamine.

18. The solid catalyst system according to claim 1, wherein the molar ratio of the amount of Al in the solid catalyst system with respect to the amount of Cr in the solid catalyst system is 0.5 to 10.

19. The solid catalyst system according to claim 1, further comprising a non-chromium metal compound represented by Tm(OR.sup.5).sub.nX.sub.4-n and Tm(R.sup.6).sub.nX.sub.4-n wherein Tm represents a transition metal of Group IVB, VB, or VIB, R.sup.5 and R.sup.6 is independently selected from C1-C20 alkyl groups, C1-C20 aryl groups and C1-C20 cycloalkyl groups, X represents a halogen atom, and n represents a number satisfying 0≤n≤4. wherein 1≤n≤4.

Description

EXAMPLES A TO E

Catalyst Preparation

[0077] 150 g of a silica-supported chromium oxide catalyst with surface area of 300 m.sup.2/g, pore volume of 1.5 ml/g and average particle size of 48 μm (activated at 825° C.) was placed in a flask. Then 7.5 g of silyl chromate (SC) was added into the flask such that the CrOx/SC weight ratio was 53/47, and both solids were mixed.

[0078] Dried and degassed isopentane was introduced into the flask equipped with a magnetic stirrer and the mixture was stirred for 2 hours at room temperature. Then a reaction product of triisobutyl aluminum (TIBAL) and cyclohexylamine (CHA) was added via syringe into the flask in amounts as shown in Table 1. Subsequently, the catalyst system was dried under vacuum at 60° C. The amount of Cr in the final catalyst system was 0.87 wt % with respect to the catalyst system.

EXAMPLES F, G

[0079] Example B was repeated except that the amount of silyl chromate was selected such that the CrOx/SC weight ratio was as shown in Table 2.

EXAMPLE H (COMPARATIVE)

[0080] Example B was repeated except that diethylaluminum ethoxide (DEALE) was added instead of the reaction product of TIBAL and CHA.

Ethylene Polymerization

[0081] The polymerization reaction was carried out in a two liters stirred autoclave reactor in deoxygenated isopentane using the respective catalyst system A-H. The polymerization reaction was conducted at 100° C. and 20 bars (290 psi) of total pressure. Ethylene polymerization was carried out for 1 hour, with ethylene supplied on demand to maintain the total reactor pressure at 20 bar. Upon completion of the polymerization, the reactor was vented and cooled to ambient temperature to recover the polymer.

[0082] Polymer molecular weight and its distribution (MWD) were determined by Polymer Labs 220 gel permeation chromatograph. The chromatograms were run at 150° C. using 1,2,4-trichlorobenzene as the solvent with a flow rate of 0.9 ml/min. A refractive index detector is used to collect the signal for molecular weights. The software used is Cirrus from PolyLab for molecular weights from GPC. The calibration of the HT-GPC uses a Hamielec type calibration with broad standard and fresh calibration with each sample set.

[0083] Results are shown in Table 1.

TABLE-US-00001 TABLE 1 Al/Cr Al/N Cat. CrOx/SC molar molar Activity g Density Example ratio (%) ratio ratio PE/g.cat.hr (g/cc) Mw MWD A 53/47 1.2 2.8 553 B 53/47 1.6 2.8 777 0.949 595274 40 C 53/47 1.8 2.8 617 D 53/47 2.0 2.8 497 E 53/47 2.7 2.8 447 F 70/30 1.6 2.8 1193 0.946 446274 35 G 30/70 1.6 2.8 577 677493 37 H 53/47 1.6 — 711 0.961 316205 28

[0084] The comparison of Example B and H shows that the use of the reaction product of TIBAL/CHA results in a higher Mw and broader MWD of the produced polyethylene.

[0085] The comparison of Examples A-E shows that the catalyst exhibits the highest activity at Al/Cr=1.6 molar ratio.

[0086] The comparison of Examples B, F and G shows that Mw and MWD can be adjusted by adjusting the ratio between CrOx and SC. The MWD was the highest at CrOx/SC ratio of 53/47.