Ethylene Polymerization via Metallocenes: An Experimental Study

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Ethylene Polymerization via Metallocenes: An Experimental Study. Ramiro Infante-Martínez*, Enrique Saldívar-Guerra, Odilia Pérez-Camacho, Maricela García-Zamora Centro de Investigación en Química Aplicada, Saltillo, Coahuila. México * To whom correspondence should be addressed: ramiro.infante @ciqa.edu.mx Keywords sensor, kinetics, calorimetry, polymerization. ABSTRACT An experimental study oriented to gather kinetic modelling data in the ethylene polymerization via metallocenes is reported. Also is illustrated the employment of two methods for determination of kinetic behavior and the instantaneous activity of ZieglerNatta catalysts in the slurry polymerization of ethylene. The theoretical basis for both methods is described as well as the required instrumentation for its implantation at a laboratory level. An experimental program of polymerization with two different metallocenic systems was executed, showing that the direct (measurement of ethylene flow) as well as the calorimetric method (based on energy balances) give equivalent high quality information on the kinetic performance of the catalyst. INTRODUCTION The evaluation of a Ziegler-Natta catalyst is performed in reactors of complete mixing with an exchange heat jacket at an operation scale of 200 mL to 2 L. The operation is realized in a semicontinuos form, at constant pressure and controlled temperature (in the reactor or jacket) in an ethylene atmosphere. The addition of ethylene is carried out in a continuous way by means of a deposit of higher pressure that the reactor pressure. Since the pressure of the reactor is constant, the flow of ethylene is controlled by the polymerization rate. The measurement of this flow gives directly the polymerization rate. Additionally, the liberated heat by reaction can be used to estimate the reaction extent. This method (calorimetric) has been employed successfully in a variety of polymerization reactions.[4-9] Rincón et. Al.[4] and Esposito et. al.[5] studied the batch and semi-batch emulsion polymerization of vinylacetate in a 5 liters calorimetric type reactor. They used a Kalman type filter to estimate the heat transfer coefficient as well as the conversion evolution. Korber et. Al.,[6,7] working with a commercial calorimeter (RC1 from MettlerToledo) in the propylene polymerization via metallocenes, report comparable results between on-line calorimetry and propylene consumption measurement with a mass flowmeter. Altarawneh et. Al.[8] investigated the emulsion polymerization of Styrene via RAFT. They were able to monitor the conversion as well as the molecular weight using only calorimetric techniques. However, the reports of the use of calorimetry for monitoring the ethylene polymerization are scarce. In a recent report,[9] the calorimetric method has been used for the monitoring of ethylene polymerization via metallocenes in a laboratory reactor. The authors refer successful results when they develop a calorimetric observer and

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compare it with an estimation of ethylene consumption based on the pressure of an