A Study of the Gas Phase Polymerization of Propylene: The Impact of Catalyst Treatment, Injection Conditions and the Presence of Alkanes on Polymerization and Polymer Properties
A Study of the Gas Phase Polymerization of Propylene: The Impact of Catalyst Treatment, Injection Conditions and the Presence of Alkanes on Polymerization and Polymer Properties
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DOI：
10.1002/mren.201600011
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发表时间：
2017-02
影响因子：
1.5
通讯作者：
A. Martins;A. Cancelas;T. McKenna
中科院分区：
文献类型：
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作者：
A. Martins;A. Cancelas;T. McKenna
丙烯在2.5L半间歇式反应器中使用市售的负载型齐格勒-纳塔（ZN）催化剂在气相中聚合。的注射方式（湿与干），包括预聚合步骤的影响，并改变气相的组成进行了系统的研究，在它们的瞬时聚合速率和聚合物性能的影响。观察到预聚合提高聚合活性。这至少部分归因于预聚合步骤在反应的初始时刻减少局部颗粒过热的效果。此外，与在装入反应器之前首先用石蜡油润湿时相比，当催化剂干燥注入时观察到催化剂活性的显著降低。向催化剂中加入烃类最终可以降低聚合的关键初始时刻过热的风险，因为它增加了单体扩散到活性位点的阻力，起到"原位"预聚合的作用。提高生产率的方法也会改善粉末形态。最后，发现向气相中添加汽化的异己烷引起瞬时聚合速率的增加，并且增加了氢气对速率和分子量的影响。
Propylene is polymerized in the gas phase in a 2.5 L semibatch reactor using a commercially available supported Ziegler–Natta (ZN) catalyst. The mode of injection (wet vs dry), the impact of including a prepolymerization step, and of changing the composition of the gas phase are systematically investigated in terms of their influence on the instantaneous polymerization rate and polymer properties. Prepolymerization is observed to enhance the polymerization activity. This is attributed, at least in part, to the effect of prepolymerization step in decreasing local particle overheating in the initial instants of reaction. Furthermore, a noticeable decrease of the catalyst activity is observed when the catalyst is injected dry as compared to when is first wetted with paraffinic oil before being charged to the reactor. Adding a hydrocarbon to the catalyst can eventually reduce the risk of overheating during the critical initial instants of polymerization since it increases resistance of the diffusion of monomer to the active sites, acting as an “in situ” prepolymerization. Methods that increased the productivity also lead to an improvement of the powder morphology. Finally, it is found that adding vaporized iso-hexane to the gas phase provokes an increase in the instantaneous polymerization rate, and increases the impact of hydrogen on the rate and molecular weight.