CHROMIUM OXIDE CATALYST FOR ETHYLENE POLYMERIZATION

Abstract

The invention relates to a solid catalyst system comprising a chromium compound, a metal compound, an aluminium compound and a silicon oxide support, wherein the silicon oxide support has an average particle diameter in the range between ≥20 and ≤50 μm, a pore volume in the range between ≥1.7 ml/g and ≤3 ml/g, and a surface area in the range between ≥400 m.sup.2/g and ≤800 m.sup.2/g, and wherein the aluminium alkoxide compound has the formula

R.sub.1—Al—OR.sub.2

wherein R.sub.1 is selected from (C.sub.1-C.sub.8) alkyl groups and OR.sub.2 is selected from (C.sub.1-C.sub.8) alkoxyl groups.

Claims

1. Solid catalyst system comprising a chromium compound, a metal compound, an aluminum compound and a silicon oxide support, wherein the silicon oxide support has an average particle diameter in the range between ≥20 and ≤50 μm, a pore volume in the range between ≥1.7 ml/g and ≤3 ml/g, and a surface area in the range between ≥400 m.sup.2/g and ≤800 m.sup.2/g and wherein the aluminum alkoxide compound has the formula
R.sub.1—Al—OR.sub.2 wherein R.sub.1 is selected from (C.sub.1-C.sub.8) alkyl groups and OR.sub.2 is selected from (C.sub.1-C.sub.8) alkoxyl groups.

2. Catalyst system according to claim 1 wherein the silicon oxide support has an average particle diameter in the range between ≥30 and ≤40 μm, a pore volume in the range between ≥1.7 ml/g and ≤1.9 ml/g, and a surface area in the range between ≥500 m.sup.2/g and ≤600 m.sup.2/g.

3. Catalyst system according to claim 1 wherein the chromium compound is selected from chromium trioxide, chromium acetonyl acetonate, chromium acetate and/or chromium acetate hydroxide.

4. Catalyst system according to claim 1, wherein the metal compound is represented by formulas T.sub.m(OR.sup.1).sub.nX.sub.4-n and T.sub.m(R.sup.2).sub.nX.sub.4-n, wherein T.sub.m represents a transition metal of Group IVB, VB, or VIB, R.sup.1 and R.sup.2 represent an (C.sub.1-C.sub.20) alkyl group, (C.sub.1-C.sub.20) aryl group or (C.sub.1-C.sub.20) cycloalkyl group, X represents a halogen atom, preferably chlorine and n represents a number satisfying 0≤n≤4.

5. Catalyst system according to claim 1 wherein the metal is selected from titanium, vanadium, hafnium and zirconium.

6. Catalyst system according to claim 5 wherein the metal is titanium.

7. Catalyst system according to claim 6 wherein the titanium compound is a compound according to the formulas Ti (OR.sup.1).sub.nX.sub.4-n and Ti (R.sup.2).sub.nX.sub.4-n, wherein R.sup.1 and R.sup.2 represent an (C.sub.1-C.sub.20) alkyl group, (C.sub.1-C.sub.20) aryl group or (C.sub.1-C.sub.20) cycloalkyl group, X represents a halogen atom, preferably chlorine, and n represents a number satisfying 0≤n≤4.

8. Catalyst system according to claim 1 wherein R.sub.1 and the R.sub.2 of the aluminium alkoxide compound according to the formula
R.sub.1-A1-0R.sub.2 can be the same or different.

9. Catalyst system according to claim 1, wherein the aluminum compound is selected from diethyl aluminum ethoxide, dihexyl ethoxide, dioctyl aluminum ethoxide and/or dihexyl propoxide.

10. Catalyst system according to claim 9, wherein the aluminum compound is diethyl aluminium ethoxide.

11. Polyethylene produced with a catalyst system according to claim 1 in a gas phase polymerisation process wherein the obtained polyethylene has high-load melt index (HLMI 21.6 kg)≥0.1 g/10 min and ≤30 g/10 min (according to ISO 1133) M.sub.w/M.sub.n≥10 and ≤18 (according to size exclusion chromatography (SEC) measurement) density ≥930 kg/m.sup.3 and ≤970 kg/m.sup.3 (according to ISO1183) and resin bulk density ≥450 and ≤530 kg/m.sup.3 (according to ASTM D-1895)

12. An ethylene gas phase polymerisation process wherein the catalyst is a catalyst according to claim 1.

13. An article prepared using the product obtained with the process according to claim 12.

14. Fuel tank prepared using the product obtained with the process according to claim 12.

Description

EXAMPLES

[0061] The properties of the polymers produced in the Examples were determined as follows:

[0062] The high load melt index (HLMI) is determined using the procedures of ASTM D-1238 10 Condition F using a load of 21.6 kg at a temperature of 190° C.

[0063] Density was measured according to ASTM D-792 08.

[0064] Bulk density was measured according to ASTM D-1895.

[0065] Polymer molecular weight and its distribution (MWD) were determined by Polymer Labs 220 gel permeation chromatograph (GPC). 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 Polyab 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. [0066] M.sub.z and M.sub.z+1 are higher average molecular weights (according to ASTM D-6474 12) [0067] M.sub.w: weight-average molecular weight (according to ASTM D-6474 12) [0068] M.sub.n: number-average molecular weight (according to ASTM D-6474 12) [0069] MWD (molecular weight distribution) is the ratio of weight-average molecular weight (M.sub.w) to number-average molecular weight (M.sub.n), (according to ASTM D-6474 12)

Catalyst Synthesis

[0070] To a three-necked round bottom flask, equipped with a condenser and a mechanical stirrer 200 g of dried silicon oxide support at 200° C. is placed into the flask then 4.7 g of chromium acetate hydroxide were added to the silica then slurried in 250 cm.sup.3 of methanol (100%), which was stirred at 80° C. for 30 minutes. After which, drying 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 then drying the solvent at 95° C. with nitrogen purge.

[0071] For chromium catalyst activation the dried catalyst powder was placed in a calciner and the following sequence was followed:

[0072] Ramp from ambient to 400° C. in under N2 flow then hold for 20 minutes

[0073] At 400° C. switch from N2 to Air flow

[0074] Ramp from 400° C. to 800° C. under dry Air

[0075] Hold at 777° C. for 4 hours under Dry Air

[0076] Cool to room temperature then switch to N2 purge.

[0077] The dried chrome-titanium on silica powder was cooled down to room temperature then slurried with 250 cm.sup.3 of Iso-pentane, followed by the addition of 17 cm.sup.3 of diethyl aluminium ethoxide (C.sub.2H.sub.5).sub.2Al—OC.sub.2H.sub.5 (98%). The contents were mixed at 45° C. for another 10 minutes then drying the solvent at 85° C. with nitrogen purge.

TABLE-US-00001 TABLE 1 Overview of prepared catalyst systems. Cat Cat Cat Cat Cat Cat Inv. Comp. Comp. Comp. Comp. Comp. Ex I Ex. A Ex. B* Ex. C Ex. D Ex. E Silicon oxide support (silica) surface m.sup.2/g 550 310 555 525 525 625 area pore ml/g 1.8 1.50 1.8 1.55 3 3 volume average μm 33 48 33 49 75 75 particle diameter Elemental analysis of catalyst system Cr wt % 0.6 0.6 0.57% 0.55% 0.57% 0.57% Ti wt % 3.8 3.9 3%   2.7%  2.5%  2.5%  Al wt % 1.55 1.51 1.47% 1.48% 1.5%  1.5%  *Instead of diethyl aluminium ethoxide (C.sub.2H.sub.5).sub.2Al—OC.sub.2H.sub.5 (98%) TEAL was used in the preparation of the catalyst Inv. Ex. = Inventive examples, Comp. Ex. = Comparative examples

[0078] Instead of diethyl aluminium ethoxide (C.sub.2H.sub.5).sub.2Al—OC.sub.2H.sub.5 (98%), TEAL was used in the preparation of the sample Cat Comp. Ex. B.

Ethylene Copolymerization

[0079] An autoclave with a volume of 2 liters was purged with nitrogen at 130° C. for 30 minutes. After cooling the autoclave to 70° C., one liter of iso-pentane was introduced to the reactor+10 ml of 1-hexene, then the reactor was pressurized with 15 bar ethylene. Then 0.1 mmol of TEAL was injected into the reactor by the averages of a catalyst injection pump.

[0080] This was followed by injection of 0.2 g of catalyst according to Table 1 after being slurried in 20 cm.sup.3 of Iso-pentane solvent. The reactor temperature was raised to 101° C. Ethylene polymerization was carried out for 60 minutes; with ethylene supplied on demand to maintain the total reactor pressure at 20 bar.

TABLE-US-00002 TABLE 2 Properties of PE—Results from Slurry bench scale reactor. For polymerisation the corresponding catalyst systems of Table 1 were used. Sample Inv. Comp. Comp. Comp. Comp. Comp. Ex I Ex. A Ex. B Ex. C Ex. D Ex. E Catalyst system Cat Cat Cat Cat Cat Cat Inv. Comp. Comp. Comp. Comp. Comp. Ex I Ex. A Ex. B Ex. C Ex. D Ex. E catalyst 4,560 2,135 933 3,870 3,760 4,100 productivity g PE/g cat h at 200 psig M.sub.w 411,194 455,355 266,554 320,355 412,656 393,357 M.sub.z 2,688,431 2,631,020 2,121,323 1,878,326 1,967,723 2,221,456 M.sub.n 14,277 17,145 17,876 18,279 15,878 16,899 MWD 28 26.5 14 17.5 25 23 Density kg/m.sup.3 950 951 949 949 947 946 Resin Bulk 431 301 465 398 342 351 density kg/m.sup.3 Fines level % 0.2 1.6 0.4 1.5 0.5 0.53

[0081] As one can see from Table 2. The Inventive example Inv. Ex I yields in an excellent resin bulk density while at the same time the catalyst productivity is high in comparison to the comparative examples Comp. Ex. A to E.

TABLE-US-00003 TABLE 3 Mechanical properties of the PE resins. Inv. Comp. Comp. Ex I Ex. A Ex. B Izod Impact ISO 20 17 18 (@ −30° C.) kJ/m.sup.2 180/A Charpy Impact ISO 179 17 13 13 (@ −40° C.) kJ/m.sup.2 ESCR (Hours) ASTM 700 487 510 bent strip D 1693 FNCT (Hours) ISO 50 41 53 16770

[0082] The inventive Ex. I resulted in a resin well suited as fuel tank grade. The resin properties are much better compared to the samples Comp. Ex. A and Comp. Ex. B.

[0083] The data with reference to the catalyst according to the comparative example A and the example according to the invention I applied in the Fluidized Bed gas phase polymerizations are summarized in Table 4.

TABLE-US-00004 TABLE 4 Gas phase polymerization—conditions and resin properties. Sample Inv. Ex I-G Comp. Ex. A-G Catalyst Cat Inv. Ex I Cat Comp. Ex. A Bed Temp 106° C. 103° C. ΔT  4.9° C.  4.3° C. Total reactor 20.6 20.7 pressure Ethylene partial 15.4 bar  15.4 bar  pressure C.sub.6/C.sub.2 molar 0.0037 0.004 ratio H.sub.2/C.sub.2 0.015 0.014 Fluidized bulk 380 kg/m.sup.3 220 kg/m.sup.3 density Superficial gas 0.44 m/sec  0.42 m/sec  velocity Resin Bulk 477 kg/m.sup.3 318 kg/m.sup.3 Density Ash <100 ppm   110 ppm  Density 945 kg/m.sup.3 945 kg/m.sup.3 HLMI 6.8 6.7 Average 0.53 mm   0.55 mm   particle size Fines    0.2%    1.8%

[0084] Space Time Yield Calculations:

[0085] Defined as production per unit volume: STY=Production Rate (lb/h)/Volume (ft).sup.3

[0086] The residence time according to the comparative example:

Residence time=Bed Weight/Production Rate

Residence Time=93 kg/(40 kg/h)=2.35 hour

[0087] With the present invention the bed weight increased to 118 kg

[0088] To maintain the same residence time of 2.35, production rate was increased to 51 kg/h

Residence time with the present invention: 118 kg/51 kg/h=2.32

Space-Time Yield with the comparative catalyst=40 kg (88 lb)/6.8 ft.sup.3=12.9

Space-Time Yield with the catalyst according to the invention=51 kg (112.2 lb)/6.8 ft.sup.3=16.5

[0089] This results in an increase of the Space-Time Yield of 27.9%

[0090] As one can see from Table 4, the Inv. Ex I-G shows a much higher resin bulk density than Comp. Ex. A-G. In addition, the Inv. Ex I-G shows a much higher yield compared to Comp. Ex. A-G.