The influence of the valence state of titanium in MgCl₂‐supported titanium catalysts on olefin polymerization

Abstract

The relationships between the valence state of titanium in MgCI,-supported titanium catalysts and polymerization performances for ethylene and propylene were studied. When the titanium species of the supported titanium catalyst 1 was preliminarily reduced by treating it with AlEt3, the resulting catalyst system 2 had lost the activity for propylene polymerization completely. The catalyst activity for ethylene polymerization was found to be reduced to 20% of that of the original catalyst 1. In the AlEt3-pretreated catalyst 2 no Ti4+ is found and 80% of the total titanium is present as Ti2+. The catalyst system 2 plus AlEt3, however, does exhibit activity towards ethylene-propylene copolymerization, propylene insertion being possible if the end of the growing polymer chain is an ethylene unit. The titanium in the AlEt3-reduced catalyst 2 could be oxidized again by treatment with various agents. The oxidized catalysts 3, in conjunction with freshly added AIEt, as cocatalyst, are active for propylene polymerization and show increased activity for ethylene polymerization in relation to the extent of oxidation. 0025-116X/84/$03.00Polymerization of propylene: The same procedure was adopted. Ethylene-propylene copolymerization: The same procedure was adopted. The mole ratio of the ethylene/propylene feed was 9/1. Analysis of thepolymers:The stereoregularity (1.1.: Isotacticity index) of polypropylene was obtained from the weight percent of polymers insoluble in boiling heptane. This composition of the ethylene-propylene copolymers was obtained from the IR spectra of the film (deformation vibration of -CH3: 1380 cm-'). Results and discussion Reduction of the supported catalystThe valence state of titanium in the original MgC1,-supported titanium catalyst 1 was confirmed to be four by polarographic measurements. After AlEt,-treatment of the solid catalyst 1, all the Ti4+ was found to be reduced to Ti2+ or Ti3 + (it is known that the reduction of T i c 4 by AlEt, results in the formation of Ti2+ and Ti3+ as shown

Gas‐phase polymerization of ethylene using MgCl2/ethyl benzoate/TiCl4 + triethylaluminum catalyst: Effects of triethylaluminum and temperature

“…The limiting factor appeared to be the transfer processes across the external film boundary layer, where again initial particle size was critical. For high-activity catalyst with a diameter of 30 pm and a particle moving at a speed of 20 cm -s-l a temperature difference across the layer was estimated at 10 K. A particle of 10 pm had a A T < 1 K. Floyd et al" investigated differing particle velocities and found that a greater velocity lowered AT. The particle velocity of this reactor system, if evaluated at the edge of the stir blades, is about 163 cm -s-', eight times the largest velocity considered by Floyd et al, so A T in this system should be further reduced ( < 1 K ) .…”

The discovery and progress of MgCl2‐supported TiCl4 catalysts

“…We reported direct evidence of EB transforming the aspecific sites into highly stereospecific sites. 14 We invested enormous effort to reveal the roles and behavior of EB, [15][16][17][18] enabling us to discover more effective electron donors (as described subsequently). For example, Figure 5 demonstrates the relation of the amount of EB and the activities.…”

Surface science of single-site heterogeneous olefin polymerization catalysts

“…Industrial catalysts produce Ϸ100-500 g polypropylene per g catalyst per hr⅐atm and Ϸ2,000-10,000 g polyethylene per g catalyst per hr⅐atm (9). The fact that the model catalysts exhibit activities similar to the industrial catalysts suggests that the surface properties of the model catalysts prepared in UHV are relevant to those of industrial catalysts (25,26). Single-site propylene polymerization.…”