High-Pressure Polymerization of Ethylene in Tubular Reactors: Prediction of the Bivariate Distributions of Molecular Weight-Branches with a Rigorous Reactor Model

Abstract

Abstract Low-density polyethylene (LDPE) is a branched polymer whose processing and end-use properties are mainly determined by the molecular weight distribution (MWD), the long chain branching distribution (LCBD) and short chain branching distribution (SCBD). In general, a suitable characterization of LDPE needs a simultaneous knowledge of these three distributions. This work presents a rigorous model of the high-pressure ethylene polymerization in tubular reactors, capable of predicting the joint bivariate distributions MWD-LCBD and MWD-SCBD, as well as monomer conversion and average molecular properties. The bivariate distributions are modeled using the 2D probability-generating function (2D pgf) technique. This deterministic technique allows a simple and efficient calculation of the distributions, in spite of the complex mathematical description of the process. The reactor model is used to analyze the effect of different process and design variables on the above mentioned joint distributions and on other properties of the product.