Effects of Hydrogen for Different Stereospecific Active Sites on Ultra Low TiCl₃ Loading Supported Catalyst

Abstract

The relationship between the stereospecificity of active sites and hydrogen effects on propylene polymerization was investigated for MgCl2‐supported TiCl3 catalysts at ultra‐low Ti contents. Hydrogen had no effect on the catalyst activities for isospecific sites and for aspecific sites. The efficiency of hydrogen as a chain‐transfer agent was found to depend on the stereospecificity of the active sites. Hydrogen was effective for isospecific sites but was not effective for aspecific sites. From the viewpoint of hydrogen dissociation, isospecific sites should have hydrogen dissociation sites in their surroundings. Therefore, isospecific sites may be in the island to be affected by hydrogen and isolated sites may be aspecific or have low isospecificity.

A Comparative Study of AlCl3and FeCl2-Modified TiCl4/MgCl2/THF Catalytic System in the Presence of Hydrogen for Ethylene Polymerization

“…Therefore, addition of Lewis acid causes the formation of more clustered active center leading to obtaining more chances to proceed chain transfer reaction by hydrogen. This result is in good agreement with article reported by Kouzai et al [29]. They revealed that chain transfer reactions by hydrogen will occur when hydrogen dissociation sites are located in the instant surrounding of polymerization sites.…”

“…Therefore, Fe-THF indicated the higher hydrogen response which showed rapidly dropped activity than Al-THF. However, a higher Ti content has a higher stereospecificity than a lower Ti content forming an isolated Ti site [29,33,34]. As a consequence, one of the possible reasons was the aggregation of Ti species which caused the reduction of active site concentration, resulting in remarkable depression of the monomer consumption [33] and finally decrease in activity.…”

Precise Active Site Analysis for TiCl3/MgCl2 Ziegler-Natta Model Catalyst Based on Fractionation and Statistical Methods

“…TiCl 3 /MgCl 2 model catalysts with a variety of Ti contents ranging from 0.011 to 1.3 wt% were prepared according to the previously reported procedure [5][6][7]. In brief, a specified amount of TiCl 3 ·3Py and milled MgCl 2 (donated by Toho Titanium Co., Ltd., a specific surface area of 65.1 m in n-heptane at r.t. for 3 h under N 2 , followed by repetitive washing with n-heptane.…”

“…Recently, we have reported the influences of the Ti dispersion state on propylene polymerization performances using TiCl 3 /MgCl 2 model catalysts with controlled Ti dispersion states [5][6][7]. In brief, the model catalysts were prepared by treating TiCl 3 ·3pyridine with diethylaluminum chloride (DEAC) in the presence of milled MgCl 2 .…”

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

“…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. [16] Accordingly, the distance between Ti species, i.e. the dispersion state of Ti species must highly influence the catalytic properties.…”