CHROMIUM OXIDE CATALYST FOR ETHYLENE POLYMERIZATION

Abstract

The invcntion relates to a solid catalyst system comprising a chromium compound, an aluminium alkoxide compound, a nitrogen containing compound and a silicon oxide support, wherein the aluminium alkoxidc compound has the formula (R.sup.1).sub.2—Al—OR.sup.2 wherein R.sup.1 is selected from C1-C8 alkyl groups and OR.sup.2 is selected from C1-C8 alkoxyl groups and wherein tlie nitrogen containing compound is a cycloalkvlaminc compound liavmg the general formula: R.sup.3—NH2, wherein R.sup.3 is selected from C3-C8 cycloalkyl groups.

Claims

1. A solid catalyst system comprising a chromium compound, an aluminium alkoxide compound, a nitrogen containing compound and a silicon oxide support, wherein the aluminium alkoxide compound has the formula
(R.sup.1).sub.2—Al—OR.sup.2 wherein R.sup.1 is selected from C1-C8 alkyl groups and OR.sup.2 is selected from C1-C8 alkoxyl groups and wherein the nitrogen containing compound is a cycloalkylamine compound having the general formula: R.sup.3—NH2, wherein R.sup.3 is selected from C3-C8 cycloalkyl groups.

2. The solid catalyst system according to claim 1, wherein the chromium compound is selected from 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 molar ratio of Al to Cr in the solid catalyst system is 1.0 to 10.0.

4. The solid catalyst system according to claim 1, wherein the aluminium alkoxide compound is selected from the group consisting of diethyl aluminium ethoxide, dihexyl aluminium ethoxide, dioctyl aluminium ethoxide and dihexyl aluminium propoxide.

5. 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.

6. The solid catalyst system according to claim 1, wherein the molar ratio of Cr to N in the solid catalyst system is 0.5 to 5.0.

7. The solid catalyst system according to claim 1, wherein the molar ratio of Al to N in the solid catalyst system is 3.0 to 20.

8. The solid catalyst system according to claim 1, wherein the silicon oxide support has an average particle diameter of 20 to 50 μm, a pore volume of 1.7 to 3.0 m.sup.3/kg and/or a surface area of 400 to 800 m.sup.2/g.

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

10. The solid catalyst system according to claim 9, 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.

11. The solid catalyst system according to claim 10, wherein the weight ratio of Ti:Cr is 2 to 4.

12. A process for the preparation of the solid catalyst system according to claims 1, comprising i) providing the chromium compound and the optional non-chromium compound on the silica support; and ii-1) treating the product obtained by step i) with the aluminium alkoxide compound and iii-1) treating the product obtained by step ii-1) with the nitrogen-containing compound, or ii-2) treating the product obtained by step i) with the nitrogen-containing compound and iii-2) treating the product obtained by step ii-2) with the aluminium alkoxide 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.

Description

EXAMPLE 1 (COMPARATIVE)

Catalyst A

[0080] To a three-necked round bottom flask equipped with a condenser and a mechanical stirrer, 200 g of dried silica support (surface area 550 m.sup.2/g, pore volume 1.85 ml/g and average particle diameter 33 μm) was placed at 200° C. 4.7 g of chromium acetate hydroxide was then added to the silica and then slurried in 250 cm.sup.3 of methanol (100%), which was stirred at 80° C. for 30 minutes. Subsequently, drying of the methanol solvent took place at 95° C. with nitrogen purge. The dried chromium on silica powder was cooled down to room temperature then slurried with 250 cm.sup.3 of iso-pentane, followed by the addition of 41 cm.sup.3 of tetraethoxy titanium Ti(OC.sub.2H.sub.5).sub.4 (100%). The contents were mixed at 65° C. for another 10 minutes and then the solvent was dried at 95° C. with nitrogen purge.

[0081] For chromium catalyst activation the dried catalyst powder was placed in a calciner and the following sequence was followed: [0082] Ramp from ambient to 400° C. in under N2 flow then hold for 20 minutes [0083] At 400° C. switch from N2 to Air flow [0084] Ramp from 400° C. to 800° C. under dry Air [0085] Hold at 800° C. for 4 hours under Dry Air [0086] Cool to room temperature then switch to N2 purge.

EXAMPLE 2 (COMPARATIVE)

Catalyst B

[0087] 120 gram of catalyst A was placed in a 1000 cm.sup.3 flask. 800 cm.sup.3 of isopentane was added to slurry the activated catalyst, then diethylaluminum ethoxide (DEALE) was added to the flask and the resultant mixture was agitated for 5 minutes at 45° C. The slurry was dried under vacuum or using a nitrogen purge at a temperature of 60° C. The modified catalyst was stored under nitrogen until use. The mole ratio of Cr/Al was 1:6.

EXAMPLE 3 (INVENTIVE)

Catalyst C

[0088] 120 gram of catalyst A was placed in a 1000 cm.sup.3 flask. 800 cm.sup.3 of isopentane was added to slurry the activated catalyst, then cyclohexylamine (CHA) was added to the flask and the resultant mixture agitated for 5 minutes at 45° C. then followed by the addition of diethylaluminum ethoxide (DEALE). The slurry was dried under vacuum or using a nitrogen purge at a temperature of 60° C. The modified catalyst was stored under nitrogen until use. The mole ratio of Cr/Al/N was 1:6:1.

EXAMPLE 4 (INVENTIVE)

Catalyst D

[0089] 120 gram of catalyst A was placed in a 1000 cm.sup.3 flask. 800 cm.sup.3 of isopentane was added to slurry the activated catalyst, then diethylaluminum ethoxide (DEALE) was added to the flask and the resultant mixture agitated for 5 minutes at 45° C. then followed by the addition of cyclohexylamine. The slurry was dried under vacuum or using a nitrogen purge at a temperature of 60° C. The modified catalyst was stored under nitrogen until use. The mole ratio of Cr/Al/N was 1:6:1.

EXAMPLE 5 (INVENTIVE)

Catalyst E

[0090] 120 gram of catalyst A was placed in a 1000 cm.sup.3 flask. 800 cm.sup.3 of isopentane was added to slurry the activated catalyst, then diethylaluminum ethoxide (DEALE) was added to the flask and the resultant mixture agitated for 5 minutes at 45° C. then followed by the addition of cyclohexylamine. The slurry was dried under vacuum or using a nitrogen purge at a temperature of 60° C. The modified catalyst was stored under nitrogen until use. The mole ratio of Cr/Al/N was 1:6:0.5.

[0091] Polymerization

[0092] The polymerization reaction was carried out in a two liters stirred autoclave reactor in deoxygenated isopentane using catalysts A-E. The polymerisation reaction was conducted at 100° C. and 20 bars (290 psi) of total pressure. Ethylene polymerisation was carried out for 1 hour, with ethylene supplied on demand to maintain the total reactor pressure at 20 bar. Upon completion of the polymerisation, the reactor was vented and cooled to ambient temperature to recover the polymer.

[0093] 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 Ham ielec type calibration with broad standard and fresh calibration with each sample set.

[0094] The results are shown in Table 1 and Table 2.

TABLE-US-00001 TABLE 1 Catalyst activity Density Catalyst Example Catalyst gPE/gcat .Math. r (g/cm.sup.3) Flowability 1 A 1240 0.39 Excellent 2 B  970 0.38 Poor 3 C  505 0.38 Excellent 4 D  580 0.38 Excellent 5 E 1010 0.37 Good

TABLE-US-00002 TABLE 2 Example Catalyst Mw Mn MWD Mz Mz + 1 1 A 165090 11766 14.0 1229396 3658589 2 B 234678 12909 17.2 1655289 3368837 3 C 348746 16497 21.1 2207647 4562116 4 D 339284 15543 21.8 2326247 4954030 5 E 294786 15343 20.1 2169620 4518563

[0095] It can be understood by the comparison of catalysts A and B that the addition of DEALE leads to a decrease in the catalyst flowability although the MWD is increased.

[0096] The comparison of catalysts C-E with B shows that the addition of the amine compound leads to an increase in the catalyst flowability and an increase in the MWD.

[0097] The comparison of catalyst C and catalyst D shows that the the order of the addition of the aluminium alkoxide compound and the amine compound does not have a large influence in the catalyst properties.

[0098] Catalyst E has a substantially higher catalyst activity than catalyst D and thus the best balance of the catalyst activity, catalyst flowability and MWD. The comparison of catalyst D and catalyst E shows that the higher amount of Cr and Al with respect to N.