Abstract
In this paper we report the results of an extensive experimental kinetic study carried out on the novel ethylene trimerization catalyst system, comprising the chromium source [CrCl3(thf)(3)] (thf = tetrahydrofuran), a Ph2P-N(iPr)-P(Ph)-N(iPr)H (PNPNH) ligand (Ph = phenyl, iPr = isopropyl), and triethylaluminum (AlEt3) as activator. It could be shown that the initial activity shows a first-order dependency first-order dependency was found for the catalyst concentration. The initial activity follows a typical Arrhenius behavior with an experimentally determined activation energy of 52.6 kJ mol. At elevated temperatures (ca. 80 degrees C), a significant deactivation was observed, which can be tentatively traced back to a ligand rearrangement in the presence of AlEt3. After a fast initial phase, a pronounced 'kink' in the ethylene-uptake curve is observed, followed by a slow, almost linear, further increase of the total ethylene consumption. The catalyst composition, in particular the ligand/chromium and the cocatalyst/chromium molar ratio, has a strong impact on the catalytic performance of the trimerization of ethylene.