Is the bulk density of polypropylene powder affected by hydrogen?
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The unit I work in utilizes a Unipol gas-phase polypropylene process. Due to the frequent switching between different grades, I have several questions during the production process that I’d like to discuss with everyone. For a long time, I have believed that the bulk density of polypropylene powder produced via this process depends on the shape, size, dispersion, and activity level of the catalyst. Naturally, a higher partial pressure of propylene leads to higher catalyst activity. Setting these factors aside for now, recent statistical analysis during grade transitions has shown that the bulk density of powder from products with a high melt flow index tends to be greater than that of products with a low melt flow index; this in turn directly affects production output. During such grade transitions, all we do is adjust the amount of hydrogen added; no other parameters are modified
We don’t have this kind of processing equipment; we’re not sure
Under the same equipment and processing conditions, the particle size of powder made from products with a high melt index is smaller than that of powder produced from products with a low melt index. I usually interpret this simply as follows: since the microstructure of materials with a high melt index features shorter molecular chains, this results in smaller powder particle sizes on a macroscopic level. Consequently, the bulk density increases. However, this explanation isn’t entirely accurate; it’s provided merely for reference
This is somewhat different from the liquid phase; it’s possible that when the molecular weight is low, gaseous propylene diffuses more easily. The factors affecting bulk density are quite complex and difficult to explain. Based on the density on the distribution plate and the temperature at each point, the flow rate can be appropriately increased a bit. For reference only.