ABSTRACT
In this study a comprehensive mathematical model for high pressure tubular ethylene/vinyl acetate copolymerization reactors is developed. A fairly general reaction mechanism is employed to describe the complex free radical kinetics of copolymerization. Using the method of moments, a system of differential equations is derived to describe the conservation of total mass, energy, momentum and the development of molecular weight and compositional changes in a two-zone jacketed tubular reactor. In addition, the model includes a number of correlations describing the variation of physical, thermodynamic and transport properties of the variation of physical, thermodynamic and transport properties of the reaction mixture as a function of temperature, pressure, composition and molecular weight distribution of polymer. Numerical solution of the reactor model equations permits a realistic calculation of monomer and initiator concentrations, temperature and pressure profiles, number and weight average molecular weights, copolymer composition as well as the number of short and long chain branches per 1000 carbon atoms under typical industrial operating conditions. Simulation results are presented showing the effects of ethylene, vinyl acetate, initiator and chain transfer agent on the polymer quality and reactor operation. The results of this investigation show that, in principle, we can obtain a copolymer product of desired molecular weight and composition by controlling the process variables. The procedure developed in this work is general and can lead to a more systematic design, optimization and control of industrial high pressure ethylene copolymerization reactors.
