Impact of Process Poisons on the Performance of Post-Phthalate Supported Ziegler–Natta Catalysts in Gas Phase Propylene Polymerization

Abstract

The impact of common process catalyst poisons on the performance of a 6th generation Ziegler–Natta catalysts during the gas phase polymerization of propylene are examined using two approaches: introducing propylene without purification, or with one or two sets of purification columns, and by introducing carbon dioxide (CO₂), oxygen (O₂), water (H₂O), methanol (CH₃OH), ethyl acetate (C₄H₈O₂) and dimethyl sulfoxide (C₂H₆SO) during the polymerization. As expected, purification columns increases the catalyst activity significantly, slightly reduce catalyst decay. Injecting TiBA during the reaction leads to an activity increase. The addition of two full sets of columns substantially increased the repeatability of polymerization reactions. The power of deactivation of poisons injected during the polymerization reaction is: O₂ > CO₂ > CH₃OH > C₂H₆SO > C₄H₈O₂ > H₂O. Adding CO₂, O₂, and CH₃OH resulted in a progressive decrease in molecular weight while almost no effect is observed with H₂O. However, C₄H₈O₂, and C₂H₆SO resulted in a mild increase in molecular weight. Additionally, the effects on crystallinity and stereoregularity are similar where CO₂, O₂, H₂O and CH₃OH caused a progressive decrease while C₄H₈O₂ and C₂H₆SO resulted in a mild increase, indicating some isotacticity control by these two poisons.