This work presents an exhaustive mathematical model for the high pressure polymerization of ethylene in tubular reactors of configuration sim1lar to that encountered in the industry. Multiple injection of monomer, mixtures of initiators and chain transfer agents are considered together with realistic flux configurations. Typical heat transfer coefficients are estimated from industrial plant data. The effects of pressure pulse on the reactor behavior are also analyzed. Instantaneous temperature profiles produced by such pressure pulse were recovered from stationary simulations showing a very good agreement with the corresponding experimental data . The model features are demonstrated by predictions of temperature, concentrations of reactants and products and molecular properties as a function of reactor length. Also, appropriate predictive capabilities are d1sclosed by comparison of model simulation results and experimental data. The generation of a high temperature initiator, derived from oxygen, is assessed by comparison of temperature profiles corresponding to runs with and without oxygen.

We propose a generalized kinetic model for the peroxide initiated modification of polyethylene. It takes into account not only combination reactions but also transfer to polymer and scission. The model describes the length of the polymer chain and the concentration of vinyl groups simultaneously. Any number of vinyl groups per molecule is allowed. The resulting infinite system of mass balance equations is solved using a double moment technique. The model calculates number, weight and z‐average molecular weights and the average concentration of vinyl groups as functions of time. The kinetic constants and the initiation efficiency were estimated through a nonlinear regression using experimental data. The relevance of each one of the reactions included in the mechanism was assessed. By means of the model we studied the influence of temperature and initial peroxide concentration on the modified polymer properties. It follows well the observed experimental trends and gives good estimates of both average molecular weights and average vinyl content, within experimental error.

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We present a method for the adjustment of parameters in the mathematical modeling of industrial tubular reactors for high pressure polymerization of ethylene. We propose a reduced mathematical model for these reactors that aids in the task of model parameter update commonly done periodically in industrial plants. This reduced model was built from a detailed model for multiple peroxide and oxygen initiator systems we had developed before. Some of the assumptions in that rigorous model were reviewed in order to minimize computational effort. Good and faster predictions were obtained by assuming different constant jacket temperatures and pressures at each zone. Pressure pulse equations had to be included in the model. A simplification of the adjustment procedure is also proposed here. It consists in using only the reactions considered crucial for the description of this polymerization. The peroxide initiator and solvent mixtures were treated as fictitious unique initiator and solvent respectively. A procedure was established for the quick estimation of the kinetic parameters that represent initiator and solvent mixtures of different compositions. This resulted in a model that can be adjusted rapidly to predict the behavior of a specific industrial reactor. The reduced model was validated using experimental runs initiated by oxygen either alone or together with peroxide mixtures.

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