Study of the state of titanium ions and the composition of the active component in titanium‐magnesium catalysts for ethylene polymerization

Abstract

The state of Ti3+ ions formed at various steps of preparation and activation of highly active titanium-magnesium catalysts of various composition (dry milling of TiC13 with MgCl,; reduction of T i c 4 by nonsolvated magnesium dialkyl; interaction of the TiC14/MgCl s stem with an organoaluminium compound) was studied by the ESR method. It was found that In all systems studied the same three types of Ti3+ ions in the chlorine environment are formed, differing in coordination and localization sites in MgCI,. The content of these ions depends on the composition and preparation conditions of the catalysts, and does not exceed 20% of the total content of titanium. Most of the Ti3+ ions formed in all systems enter the composition of particles or surface aggregates of TiC13 and appear in the ESR spectra only after dissolution of the sample in pyridine. The active centers of titanium-magnesium catalysts are supposed to be constituents of these particles or of surface aggregates. Y

Propylene Polymerization Performance of Isolated and Aggregated Ti Species Studied Using a Well‐Designed TiCl3/MgCl2 Ziegler‐Natta Model Catalyst

“…[16] In TiCl 4 -based ZN catalysts, a series of ESR studies proved that Ti species formed aggregates in the course of reduction with alkylaluminum. [13][14][15] Our recent computational study showed that reduced Ti species can aggregate with each other also on the MgCl 2 (110) surface to form isospecific and ESR-silent active sites, [10] although it had been conventionally believed that Ti species could form multi-nuclear species only on the (100) surface to be the sole isospecific origin. [8] That is, the broad peak at ca.…”

“…The stereoregularity (mmmm) was determined by 13 C NMR (Varian Gemini-300 spectrometer) at 120 8C using hexachloro-1,3-butadiene as a diluent and 1,1,2,2-tetrachloroethane-d 2 was added as an internal lock and reference. Temperature-rising elution fractionation (TREF) was performed with an online system (Senshu SSC-7300) using ODCB.…”

“…In other words, polymerization properties of Ti species are assumed to be affected by another Ti species nearby even if they do not have direct Ti-Cl-Ti bridges. For example, TiCl 4 mononuclear species can form multinuclear species as a result of reduction during polymerization, [13][14][15] and the probability of the aggregation should strongly depend on the original Ti-Ti distance. In addition, it was previously suggested that the chain transfer reaction with hydrogen occurred through the migration of atomic hydrogen from a hydrogen dissociation site to a polymerization site close to each other.…”

Polymerization of olefins through heterogeneous catalysis. XVII. Experimental study and model interpretation of some aspects of olefin polymerization over a TiCl4/MgCl2 catalyst

“…These studies indicate that the is the effective Al/Ti ratio present, the reactions are believed to be quite complicated. 4,38 Although it appears that besides present initially in the system. Because of the acting as a reducing agent, TEA also participates complex side reactions involved in supported catain the active site formation through the formation lysts, the experimental Al/Ti ratio is often much of bimetallic active centers, 18,39 the true nature of greater than the stoichiometric ratio.…”

“…[1][2][3] In spite of ical measurements. Using techniques such as electron spin resonance spectrometry (ESR), 4 their successful applications in industrial practice, a complete knowledge of these catalyst systems is photometry, 5 chemical ionization-mass spectrometry (CI-MS), 6 X-ray absorption spectrosstill lacking. Some of the unresolved issues relate to the active site structure and its formation, as well copy, 7 and chemical titration methods, 5,8 the occurrence of oxidation state reduction upon the as the role of components such as the cocatalyst and electron donor and their influence on the catalyst mixing of catalyst and cocatalyst has been confirmed.…”