A COMPREHENSIVE MATHEMATICAL-MODEL FOR A MULTIZONE TUBULAR HIGH-PRESSURE LDPE REACTOR

In this study a comprehensive mathematical model of high pressure tubu lar ethylene polymerization reactors is presented. A fairly general re action mechanism is employed to describe the complex kinetics of ethyl ene polymerization. To determine the variation of molecular properties along the reactor length the method of moments is applied to the infi nite set of species balance equations to transform it into a low order system of differential equations in terms of the leading moments of t he number chain length distribution. Detailed algebraic equations are given describing the variation of kinetic rate constants, thermodynami c and transport properties of the reaction mixture with temperature, p ressure and composition. A new correlation is derived to describe the change of reaction viscosity with reactor operating conditions. The mo del permits a realistic calculation of temperature and pressure profil es, monomer and initiator concentrations, molecular properties of LDPE (i.e. M(n), M(w), LCB and SCB) as well as the variation of inside fil m heat transfer coefficient with respect to the reactor length. Simula tion results are presented illustrating the effects of initiator conce ntration, inlet pressure, chain transfer concentration and wall foulin g on the polymer quality and reactor operation. The present model pred ictions are in good agreement with experimental observations in indust rial high pressure tubular LDPE reactors.