The effect of different prepared TiCl4-MgCl2 catalysts on the behavior of gas-phase ethylene/1-hexene copolymerization

Abstract

The effect of different prepared magnesium sources including MgCl2 (ZN-THF), metallic magnesium powder (ZN-O), and MGE (ZN-MGE) as the support of titanium-based Ziegler-Natta catalysts on behaviors of gas-phase ethylene/1-hexene copolymerization was investigated. These catalysts reacted with TEA presented higher catalytic activity than using TnOA. This is due to TEA had higher reducing power. Moreover, it revealed that ZN-MGE exhibited the highest activity among other catalysts because ZN-MGE had the highest distribution of titanium contents measured by EDX, and then generated more active sites. The average particle sizes of these catalysts were around 35 µm, which was suitable for commercial application. Considering copolymer size, the size of EH-ZN-O-TEA and EH-ZN-MGE-TnOA (ca. 420 µm) displayed the largest particle size. The large size of EH-ZN-MGE-TnOA was expected due to the agglomeration and steric hindrance of the catalyst reacted with TnOA. For the particle size distribution, only EH-ZN-O-TEA showed the bimodal distribution meaning that both fragmentation and no fragmentation occurred. Other copolymers showed positive-skewed distribution. Typically, the morphologies of copolymer were spheroidal lump without fine particles. The roles of comonomer content on thermal behaviors were presented by melting temperature, C7-soluble content, and crystallinity. It was found that although all catalysts with TEA exhibited higher activity than TnOA, the use of TnOA perhaps tended to facilitate the comonomer insertion. It revealed that steric hindrance of TnOA cocatalyst may retard the copolymer chain attachment. As the result, the comonomer insertion of EH-ZN-MGE was the highest among other catalysts.

Keywords

• Gas-phase polymerization
• Magnesium sources
• Ziegler-Natta catalyst
• Triethylaluminum
• Trioctylaluminum
• Copolymerization