CONTINUOUS ETHYLENE OLIGOMERIZATION WITH IN-SITU CATALYST PREPARATION

The oligomerization of ethylene using a chromium (Cr) catalyst having a phosphorus-nitrogen-phosphorus (P-N-P) ligand is known. Reactor fouling with by-product polyethylene can be severe at operating temperatures of greater than 60°C. However, the activation of such catalysts in a continuous flow reactor at low temperatures can be difficult and activity can be low. We have now discovered that highly active Cr/P-N-P catalysts may be prepared and activated in-situ (i.e. directly in the polymerization reactor) at low temperatures (from about 30 to about 45°C) by combining the Cr; the P-N-P ligand and an aluminoxane in the process solvent in the presence of hydrogen. The use of hydrogen allows very high productivity (greater than 1 x 10 6 grams of ethylene conversion per gram of Cr) at low temperature. We have also observed reactor fouling rates as low as 2 to 10 parts per million of polyethylene per hour (based on total ethylene conversion) using this process.