Vanadium Modification Effects on the (SiO₂/MgO/MgCl₂)•TiCl_xZiegler-Natta Polyethylene Catalyst

Abstract

MgCl 2 /TiCl 4 catalyst which was fi rst reported by Kashiwa [ 1 ] and Galli [ 2 ] independently in 1968. Anhydrous MgCl 2 was used as Mg-source, and excess amount of TiCl 4 removed the alcohol from MgCl 2 -alcoholate adduct and MgCl 2 was recrystallized simultaneously. This is a signifi cant innovation and greatly promotes the development of industrial polyolefi n processes. Another commercial MgCl 2 / TiCl 4 ZN catalyst was developed by Böhm, [ 3 ] and Mg(OEt) 2 as the Mg-source reacted with TiCl 4 directly to synthesize MgCl 2 support in situ. Later on, Union Carbide Corporation (UCC) also utilized anhydrous MgCl 2 as Mg-source and meanwhile introduced SiO 2 into the titanium-magnesium catalytic (TMC) system to develop a series of MgCl 2 /SiO 2 bi-supported ZN catalysts. The most famous MgCl 2 /SiO 2 ZN catalyst was M-1 catalyst and successfully applied in UNIPOL gas-phase polyethylene process. [ 4,5 ] Chamla [ 6 ] and Stevens [ 7 ] used alkyl magnesium (MgR 2 ) and Grignard reagents (RMgCl) as starting Mg-source, respectively, followed A novel vanadium-modifi ed (SiO 2 /MgO/MgCl 2 )·TiCl x Ziegler-Natta ethylene polymerization catalyst with much better catalytic performance is successfully developed. The catalyst is prepared by co-impregnation of aqueous solution of water-soluble magnesium and vanadium compounds on SiO 2 , and a supported thin layer of magnesium and vanadium oxides is formed over the surface of SiO 2 after high temperature calcination in dry air, followed by further reaction with titanium tetrachloride to synthesize the magnesium dichloride carrier in situ and to support the titanium species simultaneously. By characterization of the catalysts and the polymers and investigation of the polymerization behaviors, it is found that compared with the original (SiO 2 /MgO/MgCl 2 )·TiCl x ZN catalyst, the introduction of vanadium species induce improved catalytic performance with 27% higher activity, 48% higher hydrogen response, and 60% higher 1-hexene incorporation ability with better short chain branch distribution.

Ethylene Polymerization over MgCl2/SiO2 Bi‐Supported Ziegler–Natta Hybrid Titanium/Vanadium Catalysts

“…It is obvious that the introduction of vanadium species could adjust the average MW of the polymers more efficiently by adding hydrogen but with the sacrifice of the catalytic activity. The V‐modified Ziegler–Natta catalyst (including the MgTi‐V/Si and MgTiV/Si catalysts) showed higher hydrogen response in comparison with that of the MgTi/Si catalyst, which meant the V‐modified Ziegler–Natta catalysts exhibited much better hydrogen response than the V‐free Mg/Ti catalyst, which is also in agreement with the work of Wang et al Meanwhile, regarding the decrease in the average MW of the polymers in hydrogen response, the MgTi‐V/Si catalyst was 19.2% more effective with much more sacrifice of the activity than the MgTiV/Si catalyst, showing more characteristics of vanadium species in the MgTi‐V/Si catalyst. The MgV‐Ti/Si catalyst exhibited a similar hydrogen response to the MgTi/Si catalyst, showing more features of titanium species.…”

“…It can be seen that the actual loadings of magnesium in these catalysts were similar and largely less than the initial addition amounts, which might be due to the limitation of loading capacity on the surface of SiO 2 resulting in partial Mg‐losing during the catalyst preparation, or some supported species might be lost during the reaction process with the high concentration TiCl 4 or VOCl 3 . The titanium content as a significant factor could greatly affect the activity of the catalyst.…”

“…Their activities decreased when the 1‐hexene concentration in the feed increased. Besides, Wang et al investigated the vanadium modification effects on the (SiO 2 /MgO/MgCl 2 )·TiCl 4 Ziegler–Natta catalyst through co‐impregnation of water‐soluble magnesium and vanadium compounds on SiO 2 . On one hand, from T m values, the V/Ti/SiO 2 catalyst displayed the lowest sensitivity to 1‐hexene.…”

“…More recently, the introduction of vanadium into the Ziegler–Natta catalyst system has been conducted for improving catalytic activity and polymer branching in our lab. On the basis of (SiO 2 /MgO/MgCl 2 )·TiCl x Ziegler–Natta catalyst, Wang et al introduced the vanadium component to the catalyst system to synthesize vanadium‐modified (SiO 2 /MgO/MgCl 2 )·TiCl x Ziegler–Natta catalyst by co‐impregnation of water‐soluble magnesium and vanadium compounds . The catalyst showed improved ethylene polymerization activity and produced polymer with more branching.…”

The First Vanadium-Oxide-Based UHMWPE Catalyst Supported on Chemically Modified Silica Gel

“…Matta et al found that when hybridized with Phillips catalyst, VO x could enhance the in situ short chain branching ability of the chromium catalyst to a large extent . Wang et al found that when modified with vanadium oxide, the (SiO 2 /MgO/MgCl 2 )·TiCl x ZN catalyst got an improved hydrogen response . McDaniel found that the PE produced by vanadium‐oxide catalysts had very low melt index (MI), therefore, magnesium alkyls and titanium chlorides were introduced in order to attain higher activity and MI .…”