Paper to the Mixing and Polymer Processing Conference of the European Federation of Chemical Engineering, Delft, Holland

S F Bush with E Jongen.

Introduction

A major problem in the manufacture of a number of important polymers such as polyethylene, polyester and nylon, is the occurrence of non uniformities which show up as streaks and blobs in film and cause breaks in filament. The major source of this problem lies in the fact that during manufacture a tiny fraction of the material is exposed to reaction conditions very significantly different from those applying to the bulk of the material, by virtue of the exceptional residence times developed at vessel walls. Such non uniformities are particularly likely to occur at cooling surfaces since the unavoidable tendency to stick there is enhanced by the increase in viscosity through the thermal boundary layer.

The present paper outlines a description of the reaction and flow of polyethylene and ethylene through tubes from which there is a substantial extraction of heat. The driving force is provided by pressure drop.

In the high pressure stirred autoclave process, the reaction in the tube is incidental to its main function of cooling the polymer and reducing pressure (by about 400 atmospheres) at the outlet from the autoclave. In the tubular process, the overall pressure drop through a tube is greater (around 2000 atmospheres), since the tube is itself the main reactor. The chemical kinetics and fluid mechanics equations have been set up to cover both cases, but the applications referred to in this paper arise from the autoclave process.

See also the section on Applications to Existing Products and Processes.