Ethylene gas phase polymerisation process

Abstract

The invention relates to a gas phase polymerisation process for the production of ethylene polymers in the presence of a catalyst composition based on a chromium compound, a titanium compound and a silica support material. The silica support material has a surface area (SA) between 685 m.sup.2/g and 800 m.sup.2/g, a pore volume (PV) between 1.65 and 1.85 cm.sup.3/g and an average particle size in the range between 25 and 35 micrometres. The catalyst composition is injected by a dry catalyst feeder into the polymerization reactor.

Claims

1. A gas phase polymerisation process for the production of ethylene polymers, comprising: polymerizing ethylene in the presence of a catalyst composition based on a chromium compound, a titanium compound and a silica support material characterized in that the silica support material has a surface area (SA) 685 m.sup.2/g and 800 m.sup.2/g, a pore volume (PV) 1.65 and 1.85 cm.sup.3/g and an average particle size in the range 25 and 35 micrometres, wherein the catalyst composition does not comprise a magnesium compound.

2. The process according to claim 1, wherein the surface area (SA) 700 m.sup.2/g.

3. The process according to claim 1, wherein the pore volume (PV) is 1.7 cm.sup.2/g.

4. The process according to claim 1, wherein the average particle size is 33 micrometres.

5. The process according to claim 1, wherein the catalyst composition is injected by a dry catalyst feeder into the polymerization reactor.

6. The process according to claim 1, wherein the catalyst composition is a dry catalyst composition.

7. The process according to claim 1, wherein the polymerization of ethylene takes place in a gas phase polymerization in the presence of a comonomer.

8. The process according to claim 7, wherein the comonomer is 1-hexene.

9. The process according to claim 1, wherein the ethylene polymer has high load melt index (HLMI) 2 g/10 min and 10 g/10 min (HLMI determined using the procedures of ASTM D-1238 Condition F using a load of 21.6 kg at a temperature of 190 C.)

10. The process according to claim 1, wherein the ethylene polymer has M.sub.w/M.sub.n between 8 and 15 (according to size exclusion chromatography (SEC) measurement), density between 939 kg/m.sup.3 and 955 kg/m.sup.3 (according to ISO1183), Izod impact strength (30 C.) between 10 KJ/m.sup.2 and 50 KJ/m.sup.2 (according to ISO 180/A) and resin bulk density between 450 kg/m.sup.3 and 520 kg/m.sup.3 (according to ASTM D-1895).

11. A gas phase polymerisation process for the production of ethylene polymers, comprising: injecting a catalyst composition with a dry catalyst feeder into a gas phase polymerization reactor; and polymerizing ethylene in the gas phase polymerization reactor in the presence of the catalyst composition; wherein the catalyst composition is based on a chromium compound, a titanium compound, and a silica support material, wherein the silica support material has a surface area (SA) 685 m.sup.2/g and 800 m.sup.2/g, a pore volume (PV) 1.65 and 1.85 cm.sup.3/g and an average particle size in the range 25 and 35 micrometres; and wherein the catalyst composition does not comprise a magnesium compound.

12. The process according to claim 11, wherein the polymerizing is in the presence of 1-hexene.

13. The process according to claim 11, wherein the ethylene polymer has M.sub.w/M.sub.n between 8 and 15 (according to size exclusion chromatography (SEC) measurement); density between 939 kg/m.sup.3 and 955 kg/m.sup.3 (according to ISO1183); Izod impact strength (30 C.) between 10 KJ/m.sup.2 and 50 KJ/m.sup.2 (according to ISO 180/A); and resin bulk density between 450 kg/m.sup.3 and 520 kg/m.sup.3 (according to ASTM D-1895).

Description

EXAMPLES

(1) The properties of the polymers produced in the Examples were determined as follows:

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

(3) The bulk density was measured according to ASTM D-1895.

(4) 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 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.

(5) M.sub.w/M.sub.n is determined according to size exclusion chromatography (SEC) measurement).

(6) The density is determined according to ISO1183.

(7) The Izod impact strength (30 C.) is determined according to ISO 180/A.

Example I

(8) Synthesis of Catalyst Composition

(9) To a 3 L three-necked round bottom flask, equipped with a condenser and a mechanical stirrer 200 g of silica average particle size of 33 micrometers, a pore volume (PV) of 1.73 ml/g and a surface area (SA) of 705 m.sup.2/g dried at 150 C. for 3 hours under nitrogen purge (85 L/h). 4.5 g of chromium acetate hydroxide were added to the silica then slurried in 250 cm.sup.3 of methanol (99.9%), which was stirred at 70 C. for 30 minutes. Afterwards drying methanol solvent took place at 95 C. with nitrogen purge. The dried chromium salt on silica powder was cooled down to room temperature then slurried with 900 cm.sup.3 of iso-pentane, to be followed by the addition of 41 cm.sup.3 of 98.8% Ti(OC.sub.4H.sub.5).sub.4 (tetra n-Butoxy titanium) which was allowed to mix for 30 minutes at 45 C. then drying the solvent at 95 C. with nitrogen purge. For the chromium catalyst activation the dried catalyst powder was placed in the calciner and the following sequence was followed: Ramp from ambient to 150 C. in 3 hours under N.sub.2 flow then hold for 10 minutes Ramp from 150 C. to 450 C. in 3 hours At 450 C. switch from N.sub.2 to O.sub.2 flow Ramp from 450 C. to 755 C. in 3 hours under O.sub.2 Hold at 755 C. for 2 hours Cool to 250 C. then switch to N.sub.2 purge. Elemental analysis: 0.55 wt % Cr and 2.1 wt % Ti [Ti]:[Cr] Molar ratio=4.1

Example II

(10) Ethylene Polymerization

(11) 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, then the reactor was pressurized with 15 bar ethylene.

(12) Then 0.1 mmol of TEAL was injected into the reactor by the means of a catalyst injection pump. This was followed by injection of 0.2 g of catalyst composition according to Example I after being slurried in 20 cm.sup.3 of Iso-pentane solvent. The reactor temperature was raised to 103 C. Ethylene polymerization was carried out for 60 minutes; with ethylene supplied on demand to maintain the total reactor pressure at 20 bar.

(13) 498 liters of ethylene were consumed and 451 grams of polyethylene were recovered giving a catalyst productivity of 2,275 g PE/g cat h at 20 bar.

(14) The characteristics of the obtained polyethylene: weight average molecular weight: 300430, number average molecular weight: 19005 molecular weight distribution: 15 HLMI=3.2 Density=954 kg/m.sup.3 Bulk density=405 kg/m.sup.3. Fines level was measured at 1.5%. NeoHookean fit Modulus: 33.5 MPa Izod 30 C: 23.4 MPa Charpy Impact: 8.1 kJ/m2 FNTC: 103 hrs

Example III

(15) Synthesis of Catalyst Composition

(16) To a 3 L three-necked round bottom flask, equipped with a condenser and a mechanical stirrer 200 g of silica average particle size of 32 micrometers, a pore volume (PV) of 1.7 ml/g and a surface area (SA) of 705 m.sup.2/g dried at 200 C. for 3 hours. 4.3 g of chromium acetate hydroxide were added to the silica then slurried in 250 cm.sup.3 of methanol (100%), which was stirred at 70 C. for 30 minutes. Afterwards drying ethanol solvent took place at 85 C. with nitrogen purge. The dried chromium salt on silica powder was cooled down to room temperature then slurried with 250 cm.sup.3 of iso-pentane, to be followed by the addition of 39 cm.sup.3 of 100% Ti(OC.sub.2H.sub.5).sub.4 (tetra ethoxy titanium) which was allowed to mix for 30 minutes at 45 C. then drying the solvent at 75 C. with nitrogen purge. For the chromium catalyst activation the dried catalyst powder was placed in the calciner and the following sequence was followed: Ramp from ambient to 150 C. in 3 hours under N.sub.2 flow then hold for 10 minutes Ramp from 150 C. to 450 C. in 3 hours At 450 C. switch from N.sub.2 to O.sub.2 flow Ramp from 450 C. to 759 C. in 3 hours under O.sub.2 Hold at 759 C. for 3 hours Cool to room temperature then switch to N.sub.2 purge. Elemental analysis: 0.35 wt % Cr and 2.9 wt % Ti

Comparative Example A

(17) Synthesis of Catalyst Composition

(18) To a 3 L three-necked round bottom flask, equipped with a condenser and a mechanical stirrer 200 g of dried silica average particle size of 45 micrometers, a pore volume (PV) of 1.5 m.sup.3/kg and a surface area (SA) of 310 m.sup.2/g with 0.5% Cr at 200 C. slurried with 250 cm.sup.3 of iso-pentane, to be followed by the addition of 65 cm.sup.3 of tetraethoxy titanium Ti(OC.sub.2H.sub.5).sub.4 (100%). The contents were mixed at 35 C. for another 60 minutes followed by drying the solvent at 85 C. with nitrogen purge. For the chrome catalyst activation the dried catalyst powder was placed in the calciner and was activated in air at 825 C. for 4 hours. Elemental analysis: 0.5 wt % Cr and 3.8 wt % Ti

Example IV

(19) Ethylene Polymerization:

(20) Ethylene was polymerized in the presence of the catalyst according to Example III and Comparative Example A as described in Table 1 via a gas phase polymerisation system with reactor pressure: 20.7 bar, bed temperature up to 104 C., bed weight average of 50 kg; C.sub.2 partial pressure: 15 bar; C.sub.6/O.sub.2 ratio 0.0008; H.sub.2/C.sub.2 ratio 0.16 and super gas velocity (S.G.V) 0.44 m/sec. The production rate was 12 kg/h and the catalyst productivity 12,500 kg/kg. The main characteristics of the obtained polyethylene: Upper fluidized Bulk Density: 303 kg/m.sup.3 Resin Bulk Density: 453 kg/m.sup.3 HLMI: 3 Polymer Density: 951 kg/m.sup.3

(21) Table 1 shows the HDPE from Example III and Comparative Example A.

(22) TABLE-US-00001 TABLE 1 Catalyst from Catalyst from Comparative Example A Example (III) Ethylene Partial Pressure 15 bar 15 bar C.sub.6/C.sub.2 Molar Ratio (1-Hexene) 0.00125 0.0008 H.sub.2/C.sub.2 0.16 0.16 Bed Temperature 90 C. 104 C. Bed Weight 49 52 Upper Fluidized Bulk Density 252 303 Production Rate 10.2 12.3 Catalyst Productivity 10,000 12,500 Superficial Gas Velocity 0.44 m/sec 0.44 m/sec HLMI (21.6 kg) 3.34 3.15 Density 953 kg/m.sup.3 951 kg/m.sup.3 Ash 99 ppm 81 ppm Resin Bulk Density 401 kg/m.sup.3 453 kg/m.sup.3 Fines % 0.59% 0.21%

(23) The catalyst according to the invention results in enhanced 1-hexene co-monomer incorporation by no less 33%. The catalyst results in increased resin bulk density, which caused an increase in bed weight and hence increased the drop size which caused an increase in the production rate.

(24) The catalyst results in increase in the upper fluidized bulk density in gas phase reactor which gave room to increase the superficial gas velocity and hence increasing production rate and reducing carry over.

(25) Another advantage is the superior spherical morphology resin with minimum amount of fines improving fluidization in gas phase reactors and reducing fouling effects.

Example V

(26) Ethylene Polymerization

(27) The catalyst as produced in Example 1 was used to produce high density polyethylene in a fluidized bed gas phase polymerization reactor. The fluidized bed gas phase polymerization reactor had an internal diameter of 45 cm and was operated with a 140 cm zone height. The catalyst was fed to the reactor using a dry solid catalyst feeder to maintain a production rate of 12 kg per hour. Ethylene, 1-hexene, hydrogen and nitrogen were introduced to the reactor to yield polymer with the required specifications. The reactor bed temperature was maintained at 105 C., ethylene partial pressure at 15 bar, total reactor pressure at 20.7 bar and superficial gas velocity at 0.43 m/s. Further process conditions are listed in table 2

(28) TABLE-US-00002 TABLE 2 Process parameter Value Total reactor pressure 20.7 bar Reactor bed temperature 105 C. Ethylene partial pressure 15 bar Ethylene fraction in feed gas 75.6 vol % Hydrogen fraction in feed gas 73.66 vol % 1-Hexene fraction in feed gas 0.03 vol % Bed weight 50 Kg Bed level 34 mbar FBD 370 mbar Superficial gas velocity 0.43 m/s Static 0.007 kv

(29) The catalyst is added with a dry catalyst feeder had a speed of 21%, a nitrogen flow of 1.80 kg/hr, diff pressure 25 mbar and 6 metering disk holes. The material properties of the HDPE obtained from above Example were determined. The values are presented in table 3.

(30) TABLE-US-00003 TABLE 3 Property Test method Example 1 Density (kg/km.sup.3) ASTM D-792 08 954 High-load Melt Index (HLMI) ASTM D-1238 10 2.6 21.6 kg/190 C. (g/10 min) Melt Flow Rate (MFR) ASTM D-1238 10 18.6 Mn (g/mole) ASTM D-6474 12 40,483 Mw (g/mole) ASTM D-6474 12 325,000 MWD (g/mole) ASTM D-6474 12 8.1 Mz (g/mole) ASTM D-6474 12 1.91 106 Mz/Mw ASTM D-6474 12 5.877 Bulk Density (kg/m.sup.3) ASTM D-6683 08 541 Average particle size (mm) ASTM D-1921 12 0.45 Fines (%) ASTM D-1921 12 0.2