Claims
- 1. A process for preparing a propylene-ethylene copolymer which is conducted in three distinct polymerization steps in the gas phase in an agitated fixed bed by means of a Ziegler-Natta catalyst system which, in addition to a titanium-containing solid component based on a finely divided silicia as a carrier, also contains, as cocatalyst, an aluminum compound, which process comprisesin a first polymerization step, polymerizing propylene at from 60 to 90° C. and at from 20 to 40 bar and at a mean residence time of the reaction mixture of from 0.5 to 5 hours, then, in a second polymerization step, polymerizing a mixture of propylene and ethylene onto the polymer obtained from the first polymerization step at from 40 to 110° C. and from 5 to 30 bar, this pressure being at least 7 bar below the pressure in the first polymerization step, and at a mean residence time of the reaction mixture of from 0.2 hours to 4 hours, and then, in a third polymerization step, polymerizing ethylene and a mixture of ethylene a propylene onto the polymer obtained from the second polymerization step at from 50 to 110° C. and from 5 to 30 bar and at a mean residence time of the reaction mixture of from 0.1 to 5 hours, the weight ratio between the monomers reacted in the first and second polymerization steps being from 1:1 to 20:1 and the weight ratio between the monomers reacted in the first two polymerization steps and those reacted in the third polymerization step being from 1:2 to 20:1.
- 2. A process as defined in claim 1, in which the weight ratio between the monomers reacted in the first and second polymerization steps is from 1.5:1 to 10:1.
- 3. A process as defined in claim 1, in which the weight ratio between the monomers reacted in the first two polymerization steps and those reacted in the third polymerization step is from 1:1.5 to 10:1.
- 4. A process as defined in claim 1, wherein the three polymerization steps are carried out in successive reactors, the polymer being formed in the first and second steps being transferred to the next reactor.
- 5. A process as defined in claim 1, wherein the titanium-containing solid component comprises an electron-donor compound of the formula 1where X and Y are independently C1-C8-alkoxy.
- 6. A process as defined in claim 1, wherein the atomic ratio between aluminum from the aluminum compound and titanium-containing solid component is from 20:1 to 200:1.
- 7. A process as defined in claim 1, wherein the pressure in the second polymerization step is at least 10 bar below that in the first polymerization step.
- 8. A process as defined in claim 1, wherein the ratio between the partial pressures of propylene and ethylene in the second polymerization step is from 1:8 to 5:1.
Priority Claims (1)
Number |
Date |
Country |
Kind |
41 17 842 |
May 1991 |
DE |
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Parent Case Info
This application is a continuation of application Ser. No. 08/304,820, filed on Sep. 13, 1994, abandoned. which is a divisional of application Ser. No. 08/121,462, filed on Sep. 16, 1993, abandoned. which is a continuation-in-part of application Ser. No. 07/888,720, filed on May 27, 1992 abandoned.
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Number |
Name |
Date |
Kind |
4547552 |
Toyota et al. |
Oct 1985 |
|
4977210 |
Kerth et al. |
Dec 1990 |
|
5006600 |
Buechner et al. |
Apr 1991 |
|
5162465 |
Kerth et al. |
Nov 1992 |
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Foreign Referenced Citations (1)
Number |
Date |
Country |
566 021 |
Jul 1984 |
AU |
Continuations (1)
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Number |
Date |
Country |
Parent |
08/304820 |
Sep 1994 |
US |
Child |
08/524024 |
|
US |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
07/888720 |
May 1992 |
US |
Child |
08/121462 |
|
US |