36 KB162 KB30 KB200020242012Benachour, DjaferMarghsi, Mohamedletnik:46številka:5str. 539-546ISSN:1580-2949COBISSID:945834URN:URN:NBN:SI:doc-S3TAZASYenInštitut za kovinske materiale in tehnologijeMateriali in tehnologijecevast reaktorchemical kineticskemijska kinetikamodelingmodeliranjepolietilenpolimerizacijapolyethylenepolymerizationpseudo-homogeneous two-dimensional modelpsevdohomogen dvodimenzionalni modelsimulacijasimulationtubular reactorUse of a two-dimensional pseudo-homogeneous model for the study of temperature and conversion profiles during a polymerization reaction in a tubular chemical reactor| Uporaba dvodimenzionalnega psevdohomogenega modela za študij temperature in profila pretvorbe med reakcijo polimerizacije v cevastem kemijskem reaktorju|A two-dimensional pseudo-homogeneous model is used to study temperature and conversion profiles during the polymerization reaction of low-density polyethylene (LDPE) in a tubular chemical reactor. This model is integrated with the Runge-Kutta 4th-order semi-implicit method, using orthogonal collocation to transform a system of complex equations into the ordinary differential ones, with respect to the heat and mass transfers involved. Ethylene polymerization has been simulated over a range of temperatures and pressures and according to the mechanisms of radical polymerization. The results of several tests, carried out under the conditions similar to those of an industrial-scale polymerization, are presented. The influences of the initial temperature Tsub0, the total pressure Psubt and the ratio L/D (the main dimensions of the reactor) on the profiles of the temperature and conversion rates are tested and analyzed to predict the behavior and performance of the tubular chemical reactor considered. The focus was on the effect of an increase in the initial temperature Tsub0 since such a rise results in a decrease in Tsubc (hot spot) appearing at the entrance of the reactor on the one hand, and in an improved conversion on the other hand. An opposite effect is observed for Psubt since a pressure increase will result in a rapid rise in Tsubc and a decrease in the conversion. The ranges of pressures and temperatures are thus limited by the system performance: excessive pressures must be avoided and working temperatures must be chosen in the range where the polymerization reaction is very fast; such conditions allow not only a good conversion, but also a resulting polymer with a low crystallinity and, thus, alow density. In the present work the effect of the L/D ratio was also studied in order to find the most suitable ratio that permits the best evacuation of the heat released during the polymerizationDvodimenzijski psevdohomogeni model je bil uporabljen za študij temperature in profila pretvorbe med reakcijo polimerizacije polietilena z nizko gostoto (LDPE) v cevastem kemijskem reaktorju. V model je bila vključena Runge-Kuttova semiimplicitna metoda 4. reda z uporabo ortogonalne kolokacije za pretvorbo sistema kompleksnih enačb v navadne diferencialne enačbe glede na vključen prenos toplote in mase. Simulirana je bila polimerizacija etilena v širšem področju temperature in tlaka skladno z mehanizmom radikalne polimerizacije. Predstavljenih je več preizkusov polimerizacije, izvedenih v razmerah, podobnih industrijskim. Preizkušen in analiziran je bil vpliv začetne temperature Tspodaj0, celotnega tlaka Pspodajt in razmerja L/D (glavne dimenzije reaktorja) na profil temperature in hitrost pretvorbe, da bi bilo mogoče napovedati ponašanje in zmogljivost uporabljenega cevastega reaktorja. Pozornost je bila usmerjena na učinek povišanja začetne temperature Tspodaj0, ker to po eni strani vpliva na znižanje Tspodajc (vroča točka) na vstopu v reaktor, po drugi pa na izboljšanje pretvorbe. Nasproten učinek je bil opažen za Pspodajt, ker se narastek tlaka izraža v hitrem povišanju Tspodajc in zmanjšanju konverzije. Območje tlaka in temperature je torej omejeno z zmogljivostmi sistema: treba se je izogibati prekomernemu tlaku, delovne temperature pa je treba izbrati v območju, kjer je reakcija polimerizacije zelo hitra; take razmere omogočajo dobro konverzijo, in nastali polimer ima majhno kristaliničnost in s tem nizko gostoto. V tem delu je bilo preučevano tudi razmerje L/D, da bi dobili najbolj primerno razmerje, ki omogoča najboljši odvod toplote, ki se sprošča med polimerizacijoTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaInštitut za kovinske materiale in tehnologije