Chromium catalysts are used throughout the world for the polymerization of polyethylene. Catalyst manufacturers prepare the catalysts, often by placing the chromium on a solid support, such as alumina or silica. The support helps to stabilize the activity of the chromium and allows the catalyst to be shipped in an inactive form to the purchaser. Once the catalyst arrives at a polymer manufacturing site, it must be activated for use in the polymerization process. Typical commercial activation processes consist of activating chromium catalysts by calcining or heating large quantities of the catalyst in dry air. Activation is performed in some type of activation apparatus or vessel such as a fluidized bed activator. This procedure may involve large and expensive equipment in which the catalyst is heated over a period of time or “ramped up” to an activation temperature of 600-900° C. The ramp up is conducted slowly over a period of many hours and then the temperature is maintained typically for another 12 hours. The catalyst is then cooled down and discharged from the activator equipment. The entire procedure generally requires 36 hours to complete one cycle. Decreasing the amount of time required to activate the catalyst would shorten the process cycle time and increase the productivity of the catalyst activating equipment.
USPTO Backgrounds
USPTO Backgrounds