Comprehensive Dynamic Model of the High-Pressure Polymerization of Ethylene in Tubular Reactors

MARIANO ASTEASUAIN; BRANDOLIN, A.

Lima, Perú

Congreso; XI Simposio Latinoamericano y IX Congreso Iberoamericano de Polímeros (SLAP 2008); 2008

Pontificia Universidad Católica del Perú, Universidad Nacional Mayor de San Marcos, Universidad Peruana Cayetano Heredia, Universidad Nacional de San Agustín

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:72.0pt 90.0pt 72.0pt 90.0pt; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> High-pressure polymerization of ethylene in tubular reactors is a very important industrial process. It allows obtaining branched low density polyethylene with characteristics that have not been reproduced by the more modern low or medium pressure polymerizations. Operating conditions of the high pressure polymerization are rigorous, involving very high pressures and axial velocities, and steep temperature profiles. Consequently, a mathematical model is an attractive tool to study safely and economically the influence of the different design and operative variables on production performance and product quality. Although different steady state models have been reported, less attention has been paid to the dynamic operation of this reactor. Except for few cases, most of the available dynamic models involve simplifications that weakens the validity of their results. Besides, focused has mainly been placed on average properties, but not on distributed properties such as the full molecular weight distribution (MWD). In previous works we developed a comprehensive steady state model of the process. This model was validated against experimental data from an actual industrial reactor. In this work, we present an extension of that model consisting in the incorporation of the dynamic operation. Rigorousness of the former model was kept. This involves a detailed calculation of physical and transport properties along the axial distance and time, as well as realistic reactor configurations. The resulting model is capable of computing the full MWD, as well as average branching indexes, monomer conversion and average molecular weights along time and reactor length. The probability generating function (pgf) technique was employed for calculating the full MWD, and the method of moments for the average molecular properties.