Activation and Deactivation of Phillips Catalyst for Ethylene Polymerization Using Various Activators

Abstract

The present article reveals important roles of metal alkyl activators in tuning the performance of the Phillips catalyst in ethylene polymerization. The addition of aluminum alkyl aids the activation of the catalyst, while excess addition leads to the loss of the activity. The balance between the activation and deactivation depends on the type of employed aluminum alkyl, and tri‐n‐octylaluminum offers the most efficient catalyst usage by preferentially suppressing the deactivation. The passivation of aluminum trialkyl with a hindered phenol mildens not only the deactivation but also chain transfer reactions, leading to an increment of high molecular weight fractions.

Remarkable Promotion Effect of Sulfation over the SiO2‐Supported Vanadium‐Oxide‐Based Catalysts for UHMWPE

“…Figure ). It is obvious that all the catalysts show an optimum Al/V at which the maximum activity is reached, as the cocatalysts act as alkylation reagent for active centers and scavenger for reaction system, but overdose of cocatalyst would result in deactivation through overreduction of the active centers . The optimum Al/V for VO x /SiO 2 –Al 2 O 3 –SO 4 2− , VO x /SiO 2 –ZrO 2 –SO 4 2− and VO x /SiO 2 –TiO 2 –SO 4 2− are 60, 60, and 70, respectively, and the maximum activity is similar for each catalyst at 2200 kg PE mol −1 V, which is equal to or lower than the activity of some supported V‐based Ziegler‐Natta catalysts, but is definitely higher than that of VO x /SiO 2 –MO y (M = Al, Zr, or Ti) at 1200 kg PE mol −1 V .…”

“…It is obvious that all the catalysts show an optimum Al/V at which the maximum activity is reached, as the cocatalysts act as alkylation reagent for active centers and scavenger for reaction system, but overdose of cocatalyst would result in deactivation through overreduction of the active centers. [36] The optimum Al 4 2− and VO x /SiO 2 -TiO 2 -SO 4 2− are 60, 60, and 70, respectively, and the maximum activity is similar for each catalyst at 2200 kg PE mol −1 V, which is equal to or lower than the activity of some supported V-based Ziegler-Natta catalysts, but is definitely higher than that of VO x /SiO 2 -MO y (M = Al, Zr, or Ti) at 1200 kg PE mol −1 V. [22,37,38] This confirms that the sulfation indeed helps to improve the activity of the vanadium-oxide-based catalysts for ethylene polymerization. The PEs synthesized under the given conditions have M v about 3 × 10 6 g mol −1 , which is definitely above the critical value for UHMWPE (see Table 2).…”

Effects of Alkyl Aluminum on SiO2‐Supported Silyl‐Chromate(Cr)/Imido‐Vanadium(V) Bimetallic Catalysts for Producing Bimodal Polyethylene

“…[6,7] The added alkyl aluminum can also improve the hydrogen response of Phillips Cr-based catalyst in the ethylene polymerization, while the original catalyst is not sensitive to hydrogen as a chain transfer agent. [8] S-2 catalyst used in the UNIPOL gas phase process is pretreated with alkyl aluminum, which is called the prereduction process. [9,10] There are several patent literature about the prereduction step of alkyl aluminum in the preparation of catalyst.…”

“…It was reported that with the addition of alkyl aluminum, a chain growth initiator of chromium‐alkyl species could be formed during polymerization and the frequency of long chain branches in polyethylene was improved as a result of enhanced active site densities . The added alkyl aluminum can also improve the hydrogen response of Phillips Cr‐based catalyst in the ethylene polymerization, while the original catalyst is not sensitive to hydrogen as a chain transfer agent …”

“…Barzan et al studied the prereduction of Phillips catalyst by cyclohexene and found that cyclohexene can efficiently reduce the surface chromates sites at room temperature to give mainly divalent chromium sites and aldehyde by‐products . Zeng et al reported that the polymer yield of Phillips catalyst was dependent on the type and concentration of alkyl aluminum and large alkyl groups could enhance the polymerization performance . A prereduction step can not only shorten the induction time but also has a great influence on the polyethylene properties (characterized by high melting points, high densities, and good stiffness) .…”