Process for the production of ultra high molecular weight polyethylene

Abstract

The invention relates to a process for the production of ultra high molecular weight polyethylene in the presence of a catalyst system that comprises (I) the solid reaction product obtained from the reaction of a) a hydrocarbon solution containing 1) an organic oxygen containing magnesium compound or a halogen containing magnesium compound and 2) an organic oxygen containing titanium compound and b) an aluminium compound of the formula AlR.sub.aX.sub.(3-a) where R is a hydrocarbylgroup containing (3-10) carbon atoms, X is an halogenide and 0<a<3 and (I!) an aluminium compound having the formula AlR.sub.3 in which R is a wherein the molar ratio of aluminium from (b): titanium from (a) is higher than 3:1 and the average particle size of the catalyst ranges between 0.1 m and 1.0 m and The obtained polymer is in the form of spheroidal particles with an average particle size of less than 50 m or is in the form of loosely bound agglomerates consisting of spheroidal sub-particles with an average particle size of less than 50 m.

Claims

1. A process for the production of ultra high molecular weight polyethylene, the process comprising polymerizing ethylene in the presence of a catalyst system that comprises: (I) a catalyst which is a solid reaction product obtained from the reaction of: a) a hydrocarbon solution containing 1) an organic oxygen containing magnesium compound or a halogen containing magnesium compound, and 2) an organic oxygen containing titanium compound and b) an aluminium compound of the formula AlR.sub.aX.sub.(3-a) where R is a hydrocarbyl group containing 3-10 carbon atoms, X is an halogenide, and 0<a<3 , and (II) aluminium compound having the formula AlR.sub.3 in which R is a hydrocarbon radical containing 1-10 carbon atom, wherein the molar ratio of aluminium from (b): titanium from (a) is higher than 3:1, and the average particle size of the catalyst ranges between 0.01 m and 1.0 m.

2. The process according to claim 1, characterised in that the obtained polymer is in the form of spheroidal particles with an average particle size of less than 50 m or is in the form of loosely bound agglomerates consisting of spheroidal sub-particles with an average particle size of less than 50 m.

3. The process according to claim 1, characterised in that in the aluminium compound of formula AlR.sub.aX.sub.(3-a) X is chlorine and R is a branched (C.sub.3-C.sub.10) alkyl group.

4. The process according to claim 1, characterised in that the aluminium compound of formula AlR.sub.aX(.sub.3-a) is selected from di-isobutyl aluminium chloride (DIBAC), isobutyl-aluminium-dichloride (IBADIC) and mixtures thereof.

5. The process according to claim 1, characterised in that in the aluminium compound of the formula AlR.sub.aX.sub.(3-a) 1.5a2.5.

6. The process according to claim 4, characterised in that the aluminium compound of formula AlR.sub.aX.sub.(3-a) is di-isobutyl aluminium chloride (DIBAC).

7. The process according to claim 1, characterised in that the organic oxygen containing magnesium compound is magnesium alkoxide.

8. The process according to claim 1, characterised in that the organic oxygen containing titanium compound is titanium alkoxide.

9. The process according to claim 8 characterised in that the titanium alkoxide is Ti(OC.sub.4H.sub.9).sub.4 or Ti(OC.sub.8H.sub.15).sub.4.

10. The process according to claim 1, characterised in that the the aluminium compound having the formula AlR.sub.3 is triethylaluminium or triisobutyl aluminium.

11. The process according to claim 1, characterised in that the molar ratio of magnesium: titanium is lower than 3:1.

12. The process according to claim 1, characterised in that the average particle size of the catalyst ranges between 0.05 m and 0.45 m.

13. The process according to claim 1, characterised in that in the aluminium compound of formula AlR.sub.aX.sub.(3-a) X is chlorine and hydrocarbylgroup R is a branched (C.sub.3-C.sub.10)alkyl group, that in the aluminium compound of the formula AlR.sub.aX.sub.(3-a) 1.5a2.5, and that the organic oxygen containing titanium compound is Ti(OC.sub.4H.sub.9).sub.4 or Ti(OC.sub.8H.sub.15).sub.4, and that the average particle size of the catalyst ranges between 0.05 m and 0.45 m.

14. The process according to claim 1, characterised in that the aluminium compound of formula AlR.sub.aX.sub.(3-a) is selected from di-isobutyl aluminium chloride (DIBAC), isobutyl-aluminium-dichloride (IBADIC) and mixtures thereof, that in the aluminium compound of the formula AlR.sub.aX.sub.(3-a) 1.5a2.5, that the organic oxygen containing titanium compound is Ti(OC.sub.4H.sub.9).sub.4 or Ti(OC.sub.8H.sub.15).sub.4, and that the average particle size of the catalyst ranges between 0.05 m and 0.45 m.

Description

EXAMPLES

(1) The poured bulk density of the ultra-high molecular weight polyethylene polymer powder is determined by measuring the bulk density of the polymer powder according to the procedure outlined in ASTM D1895/A. The average particle size (D.sub.50) of the catalyst was determined by the so called laser light scattering method in hexanes diluent using a Malvern Mastersizer equipment. The average particle size and particle size distribution (span) of the polymer powders were determined by laser light scattering method using a Beckman Coulter equipment. The intrinsic viscosity is determined according to ISO1628-3. The polymer powders are treated with a Hosokawa 100 AFG jet-mill during 30 minutes. In such a jet-mill, the loosely bound agglomerates are broken down to the individual sub-particles. By adjusting the rotation-speed of the classifier wheel, the polymer particles are screened according to their average particle size. Increasing the rotation speed of the classifier wheel results in a smaller average particle size of particles that can pass this classifier wheel. Polymer particles that are too large to pass the classifier wheel or are in the form of not loosely bound agglomerates, remain in the jet-mill.

Example I

Preparation of a hydrocarbon Solution Comprising Mg(OC.SUB.2.H.SUB.5.).SUB.2 .and Ti(OC.SUB.4.H.SUB.9.).SUB.4

(2) 92 grams of granular Mg(OC.sub.2H.sub.5).sub.2 and 138 millilitres of Ti(OC.sub.4H.sub.9).sub.4 were brought in a 2 litre round bottomed flask equipped with a reflux condensor and stirrer. While gently stirring, the mixture was heated to 180 C. and subsequently stirred for 1.5 hours. During this, a clear liquid was obtained. The mixture was cooled down to 120 C. and subsequently diluted with 518 ml of hexane. Upon addition of the hexane, the mixture cooled further down to 67 C. The mixture was kept at this temperature for 2 hours and subsequently cooled down to room temperature. The resulting clear solution was stored under nitrogen atmosphere and was used as obtained. Analyses on the solution showed a titanium concentration of 0.55 mol/l.

Example II

Preparation of a Hydrocarbon Solution Comprising Mg(OC.SUB.2.H.SUB.5.).SUB.2 .and Ti(OC.SUB.8.H.SUB.17.).SUB.4

(3) 112 grams of granular Mg(OC.sub.2H.sub.5).sub.2 and 200 millilitres of Ti(OC.sub.8H.sub.17).sub.4 were transferred to a 2 litre round bottomed flask equipped with a reflux condenser and stirrer. While gently stirring, the mixture was heated to 180 C. and subsequently stirred for 2 hours. During this, a clear liquid was obtained. The mixture was cooled down to 120 C. and subsequently diluted with 1186 grams of hexanes. Upon addition of the hexane, the mixture cooled further down to 67 C. The mixture was kept at this temperature for 2 hours and subsequently cooled down to room temperature. The resulting clear solution was stored under nitrogen atmosphere and was used as obtained. Analyses on the solution showed a titanium concentration of 0.34 mol/I.

Example III

Preparation of the Catalyst

(4) In a 0.8 liters glass reactor, equipped with baffles, reflux condenser and stirrer, 180 ml hexanes and 136 ml of the complex from Example I (80 mmol Ti) was dosed. The stirrer was set at 1400 RPM. Via a peristaltic pump, 250 ml of a diisobutyl aluminium chloride (DiBAC) solution (150 ml DIBAC+100 ml hexanes) were dosed in 2 hours time. The aluminium to titanium molar ratio was 10.7. Subsequently, the mixture was refluxed for 2 hours. After cooling down to ambient temperature, the obtained red/brown suspension was washed 5 times with 500 ml hexanes via decantation. Finally, the solids were taken up in 500 ml of hexanes and the resulting slurry was stored under nitrogen. The average particle size of the catalyst is 0.18 m

Example IV

Preparation of the Catalyst

(5) In a 0.8 liters glass reactor, equipped with baffles, reflux condenser and stirrer, 271 ml hexanes and 99 ml of the complex from Example II (17 mmol Ti) was dosed. The stirrer was set to 1200 RPM. Via a peristaltic pump, 200 ml of a diisobutyl aluminium chloride (DiBAC) solution (160 ml DiBAC+40 ml hexanes) were dosed in 1 hour. The aluminium to titanium molar ratio was 14. Subsequently, the mixture was refluxed for 2 hours. After cooling down to ambient temperature, the obtained black suspension was washed 5 times with 500 ml hexanes via decantation. Finally, the solids were taken up in 500 ml of hexanes and the resulting slurry was stored under nitrogen. The average particle size of the catalyst is 0.12 m

Example V

Polymerization

(6) The polymerization was carried out in a 10 litres autoclave using 5 litres purified hexanes as a diluent. 4 mmols of tri-isobutylaluminum were added to the 5 litres purified hexanes. The mixture was heated to 60 C. and pressurized with 1 bars ethylene. Subsequently a slurry containing 20 mg of the catalyst obtained in Example III was dosed. The temperature was maintained at 60 C. and the pressure was kept constant by feeding ethylene. The reaction was stopped after 120 minutes. Stopping was performed by de-pressurizing and cooling down the reactor. The reactor contents were passed through a filter; the wet polymer powder was collected and subsequently dried. An amount of 366 grams of UHMWPE powder was produced. The powder was treated with a Hosokawa 100 AFG jet mill during 30 minutes, setting the rotation-speed of classifier wheel at 4000 RPM. After this treatment the polymer powder that passed the classifier wheel had an average particle size of 23.3 m. The yield of polymer passing the classifier wheel at 4000 RPM was 85% by weight.

Examples VI-XIII

(7) Example V was repeated by adjusting the conditions as indicated in the overview of polymerization results as listed in Table 1. The results of jet mill treatments are summarised in Table 2.

Comparative Example A

Preparation of the Catalyst.

(8) In a 0.8 liters glass reactor, equipped with baffles, reflux condenser and stirrer, 200 ml hexanes and 140 ml of the complex from Example I (80 mmol Ti) was dosed. The stirrer was set at 1400 RPM. Via a peristaltic pump, 206 ml of diethyl aluminium chloride (DEAC) solution (106 ml DEAC+100 ml hexanes) were dosed in 2 hours' time. Aluminium to titanium ratio is 10.7. Subsequently, the mixture was refluxed for 2 hours. After cooling down to ambient temperature, the obtained red/brown suspension was transferred to a glass filter and the solids were separated. The solids were washed 3 times with 500 ml hexanes. Finally, the solids were taken up in 500 ml of hexanes and the resulting slurry was stored under nitrogen. The average particle size is 5.2 m.

Comparative Example B

Preparation of the Catalyst

(9) In a 0.8 liters glass reactor, equipped with baffles, reflux condenser and stirrer, 200 ml hexanes and 140 ml of the complex from Example I (80 mmol Ti) was dosed. The stirrer was set at 1400 RPM. Via a peristaltic pump, 200 ml of ethyl aluminium dichloride (EADC) solution (126 ml 50 wt % EADC+74 ml hexanes) were dosed in 2 hours' time. Aluminium to titanium ratio of 5.4. Subsequently, the mixture was refluxed for 2 hours. After cooling down to ambient temperature, the obtained red/brown suspension was transferred to a glass filter and the solids were separated. The solids were washed 3 times with 500 ml hexanes. Finally, the solids were taken up in 500 ml of hexanes and the resulting slurry was stored under nitrogen. The average particle size is 8.1 m.

Comparative Example C

Preparation of the Catalyst

(10) In a 0.8 liters glass reactor, equipped with baffles, reflux condenser and stirrer, 100 ml hexanes and 70 ml of the complex from Example I (40 mmol Ti) was dosed. The stirrer was set at 1400 RPM. Via a peristaltic pump, 166 ml of ethyl aluminium dichloride (EADC) solution (126 ml 50 wt % EADC+40 ml hexanes) were dosed in 2 hours' time. Aluminium to titanium ratio was 10.8. Subsequently, the mixture was refluxed for 2 hours. After cooling down to ambient temperature, the obtained red/brown suspension was transferred to a glass filter and the solids were separated. The solids were washed 3 times with 500 ml hexanes. Finally, the solids were taken up in 500 ml of hexanes and the resulting slurry was stored under nitrogen. The average particle size is 7.3 m.

Comparative Example D

Preparation of the Catalyst

(11) In a 0.8 liters glass reactor, equipped with baffles, reflux condenser and stirrer, 271 ml hexanes and 99 ml of the complex from Example II (17 mmol Ti) was dosed. The stirrer was set at 1600 RPM. Via a peristaltic pump, 200 ml of ethyl aluminium dichloride (EADC) solution (37 ml 50 wt % EADC+163 ml hexanes) were dosed in 1 hours' time. Aluminium to titanium ratio was 8.5. Subsequently, the mixture was refluxed for 2 hours. After cooling down to ambient temperature, the obtained red/brown suspension was transferred to a glass filter and the solids were separated. The solids were washed 3 times with 500 ml hexanes. Finally, the solids were taken up in 500 ml of hexanes and the resulting slurry was stored under nitrogen. The average particle size is 8.8 m. The comparative examples A-D result in average particle sizes of the catalysts of 5.2, 8.1, 7.3 and 8.8 m respectively, which is far above the average particle size of the catalyst according to the invention ranging between 0.01 m and 1.0 m

(12) TABLE-US-00001 TABLE 1 Partial Catalyst ethylene Polymer Catalyst Intrinsic according to Cat amount Temp pressure time Yield Yield viscosity Example mg C. bar (min) g Kg/g dl/g Example V Example III 20 60 1 120 366 18.3 21.0 Example VI Example III 30 60 1 126 1025 34.2 20.4 Example VII Example III 100 60 0.34 247 1000 10.0 17.9 Example VIII Example III 30 60 0.5 475 1048 34.9 19.8 Example IX Example III 0.5 60 10 135 261 522.0 17.7 Example X Example III 200 60 0.34 177 1014 5.1 16.1 Example XI Example IV 100 60 0.34 492 1002 10.0 20.4 Example XII Example III 200 75 0.34 210 1074 5.4 13.5 Example XIII Example IV 200 60 0.34 351 1002 5.0 13.1

(13) TABLE-US-00002 TABLE 2 Yield of D.sub.50 of the Rotation polymer polymer that speed of passing the passed the classifier classifier classifier Polymer from wheel wheel wheel example: RPM % m Example V 4000 85 23.3 Example VI 4000 85 24.9 Example VII 4000 85 20.8 Example VII 6000 86 14.6 Example VIII 4000 93 24.4 Example X 4000 99 26.3 Example X 6000 95 15.1 Example X 8000 80 11.2 Example XI 4000 99 20.6 Example XI 6000 80 13.4 Example XII 4000 80 26.5 Example XII 8000 65 11.4 Example XIII 4000 99 16.8 Example XIII 6000 99 15.5 FIG. 1 illustrates the spheroidal shape of the obtained polymer particles from Example VII at a rotation speed of the classifier wheel of 6000 rpm.