Olefin polymerisation process
A process for producing an olefin polymer in a slurry polymerisation process is disclosed, in which the process is operating at a temperature of 90° C. to 107° C. and utilising a chromium catalyst having an activity of at least 1,000 g polymer/g catalyst/hour on a support having a pore volume of at least 1.3 cm 3 /g, comprising adding to the polymerisation mixture from 0.1 to 100 ppm by weight of an anti-static agent, wherein the resulting polymer has a particle size distribution such that less than 8 vol %, preferably less than 5 Vol % of the polymer particles have an average diameter of 125 μm or less.
1 . Process for producing an olefin polymer in a slurry polymerisation process operating at a temperature of 90° C. to 107° C. and utilising a chromium catalyst having an activity of at least 1,000 g polymer/g catalyst/hour on a support having a pore volume of at least 1.3 cm 3 /g, comprising adding to the polymerisation mixture an anti-static agent in an amount of from 0.1 to 100 ppm by weight based on the diluent in the slurry, wherein the resulting polymer has a particle size distribution such that less than 8 vol %, preferably less than 5 vol % of the polymer particles have an average diameter of 125 μm or less.
2 . Process according to claim 1 , wherein from 0.2 to 30 ppm weight, preferably from 0.4 to 10 ppm weight of the anti-static agent is added to the polymerisation mixture.
3 . Process according to claim 1 or 2 , wherein the anti-static agent is a quaternary ammonium compound or oil soluble sulfonic acid or sulfonate.
4 . Process according to claim 3 , wherein the anti-static agent is a dialkyl dimethyl ammonium chloride.
5 . Process according to claim 4 , wherein the alkyl chains of the dialkyl dimethyl ammonium chloride are both between C8 to C22.
6 . Process according to claim 5 , wherein the dialkyl dimethyl ammonium chloride is dicocoyl dimethyl ammonium chloride.
7 . Process according to any preceding claim, wherein the chromium catalyst support has a pore volume of at least 1.3 cm 3 /g, and more preferably at least 1.6 cm 3 /g.
8 . Process according to any preceding claim, wherein the chromium catalyst support has a specific surface area no higher than 800 m 2 /g, and preferably no higher than 650 m 2 /g.
9 . Process according to any preceding claim, wherein the chromium catalyst support is in the form of a powder comprising particles of from 20 to 200 μm in diameter.
10 . Use of 0.1 to 100 ppm by weight of an anti-static agent in a slurry polymerisation process operating at a temperature of 90° C. to 107° C. and utilising a chromium catalyst having an activity of at least 1,000 g polymer/g catalyst/hour on a support having a pore volume of at least 1.3 cm 3 /g, to control the particle size distribution of polymer produced in said process such that less than 8 vol %, preferably less than 5 vol % of the polymer particles have an average diameter of 125 μm or less.
11 . Process or use according to any preceding claim, wherein the quantity of particles having an average diameter of 125 μm or less is reduced by at least 30 vol %, preferably at least 50 vol %, compared with the level in an identical process in which no anti-static agent has been added.