Process for the continuous gas-phase (co-)polymerisation of olefins in a fluidised bed reactor
The present invention relates to a process for the gas-phase (co-)polymerization of olefins in a fluidized bed reactor using a chromium oxide catalyst characterized in that the polymerization is performed in the presence of a polymer structure modifier.
1. A process for the continuous gas-phase (co-)polymerisation of olefins in a fluidised bed reactor, comprising contacting said olefins with an aluminium modified chromium oxide catalyst supported on silica and containing from 0.15 to 5% by weight of aluminium in the presence of a polymer structure modifier selected from the group consisting of CO, CO 2 , O 2 , H 2 O, NH 3 , N 2 O, H 2 O 2 and mixtures thereof.
2. The process according to claim 1 , wherein the polymer structure modifier is not added in admixture with the catalyst or a cocatalyst.
3. The process according to claim 1 or 2 , wherein the polymer structure modifier is water.
4. The process according to claim 1 , wherein a sole or main olefin is either ethylene or propylene, and an optional comonomer is selected from the group consisting of but-1-ene, pent-1-ene, hex-1-ene, 4-methylpent-1-ene and oct-1-ene.
5. The process according to claim 4 , wherein the main olefin is ethylene and the optional comonomer is selected from the group consisting of but-1-ene, hex-1-ene and 4-methylpent-1-ene.
6. The process according to claim 3 , wherein the water is added in an amount of between 0.001 and 4 ppm based on the weight of a main olefin introduced into the reactor.
7. The process according to claim 1 , wherein said catalyst contains from 0.05 to 5% by weight of chromium.
8. A process for producing an HDPE film having a dart impact as measured according to ASTM-D1709-01 Staircase method A on a 15 microns film which is higher than 150 g, the process comprising performing a continuous (co-)polymerisation of olefins in the gas phase in a single fluidised bed reactor with an aluminium modified chromium oxide catalyst supported on silica and containing from 0.15 to 5% by weight of aluminium, and during the process introducing a polymer structure modifier selected from the group consisting of CO, CO 2 , O 2 , H 2 O, NH 3 , N 2 O, H 2 O 2 and mixtures thereof.
9. The process of claim 6 , wherein the water is added in an amount of between 20 and 2000 ppb.
10. The process of claim 8 , wherein the dart impact is higher than 200 g.