Continuous ethylene oligomerization with in-situ catalyst preparation

Abstract

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 1×10grams 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.