The Performance of High Pressure Polyethylene Tubular Reactors with Multiple Injections of Initiator and Monomer

In the production of polyethylene under high pressure, yielding so called “low-density polyethylene”, control of the long-chain branching reaction is of paramount importance to product quality. This is because the long-chain branching level influences the rheological properties and processability of the polyethylene produced. The high pressure polyethylene tubular reactor is characterized by its large length-to-diameter ratio which ranges from 250 : 1 to as high as 1200 : 1. Since a significant portion of the production cost of polyethylene in a high-pressure tubular reactor is attributed to the power consumption needed to compress the ethylene, an increase in conversion should help reduce the production cost considerably. It has been suggested in the literature that the use of multiple injections of initiator and/or monomer can increase the conversion of ethylene considerably. We have recently investigated the performance (the conversion and product quality) of a high-pressure polyethylene tubular reactor with multiple injections of initiator and monomer. As part of the investigation, temperature profiles, monomer and initiator conversion, and the number-and weight-average molecular weights were calculated along the length of the reactor. In this paper, we shall present some of the highlights of the study.