DYNAMIC MODELING OF PRODUCT GRADE TRANSITIONS FOR OLEFIN POLYMERIZATION PROCESSES

Most olefin polymerization processes produce a wide range of resin grades to suit market demand. Determining the transition policy between these grades is an important consideration that can affect process economics and safety. In this article, we compare several grade transition strategies and the relative performance of solution, slurry, bulk and gas-phase processes for the production of polypropylene, linear low-density polyethylene, high-density polyethylene and ethylene-propylene rubber. It is shown that the most important parameters that determine the grade transition performance of a process are reactor design, residence time, runtime per grade and residence time distribution of the polymer, gas and/or solution phases. Slow hydrogen dynamics severely retard grade changes involving increases in product molecular weight. The simulation results are obtained by using the dynamic simulation package ''POLYRED'' developed at the University of Wisconsin-Madison.