An experimental investigation of the impact of changes in temperature on the observed rate of polymerization of ethylene in the gas phase using a commercial Ziegler–Natta catalyst in the presence of induced condensing agents (ICAs) reveals some unexpected behavior. In the absence of ICA, the effect of temperature is as expected: raising the temperature of the gas phase from 70 to 90 °C causes the observed rate of polymerization to increase monotonically. It is demonstrated in the past that ICA can increase rate of polymerization of the ethylene in the gas phase due to a cosolubility effect. However, in the current study, it is shown that when ICA is present in the reactor, the same increase in temperature can actually lead to an observable decrease in the reaction rate under certain conditions of temperature and pressure. This is attributed to a lower impact of the ICA on the solubility of ethylene in the amorphous phase of the high‐density polyethylene in the reactor at higher temperatures. An order of magnitude analysis also reveals that the presence of ICA can have an impact on the particle temperature as well.
Gas phase copolymerizations of ethylene and an α-olefin comonomer are performed using a commercial Ziegler-Natta catalyst in the presence of different induced condensing agents (ICA). The impact of these factors on the yield and final polyethylene properties such as the melt flow index, crystallinity, and incorporation of comonomer is studied. It has been shown that the increase in the rate of polymerization is even more pronounced in the presence of ICA. It also appears that adding ICA to the copolymerizations changes the comonomer incorporation with respect to similar copolymerizations performed without ICA due to competing cosolubility effects.
The crystallization of high‐density polyethylene (HDPE) alone, and in the presence of n‐hexane (a common induced condensing agent [ICA]) is studied using differential scanning calorimetry. The presence of a noncrystallizable ICA which is partially soluble in the amorphous phase of HDPE reduces the rate of crystallization. This is reflected by a shifting of the crystallization and melting peaks of HDPE to lower temperatures when the ICA concentration in the medium increases. It is also observed that the rate of crystallization of HDPE can be very slow when the ratio of ICA to HDPE increases from zero. This behavior is useful to better understand the physical effects that can potentially occur at the beginning of the gas phase polymerization of ethylene, and suggests that the crystallization of the nascent polymer, and thus the properties of the polymer in the reactor will be quite different from those of the powder at later stages of the reaction when running in condensed mode.
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