[Discussion] In the production process of polypropylene, what effects will occur if too much DDS is added?

DDS has an inhibitory effect on the activity of the main catalyst; using too little results in low isotacticity, while using too much is also detrimental.

Reply to 1# hdj8899: The role of DDS is to match the externally added electron donor with the internal ester-based electron donor in the main catalyst, thereby facilitating coordination polymerization and enhancing the catalyst’s stereoselectivity. Therefore, increasing DDS within a certain range is beneficial for improving its isotropy. However, too high a level will affect another parameter of the product, namely ash content; moreover, an excessive amount increases production costs

Adding too little DDS results in insufficient product isotacticity, which leads to stickiness. On the other hand, adding too much of it suppresses the catalyst’s activity, poisons it, and this effect is irreversible. As for why, when introducing the catalyst during operation, TEAL should be added first, rather than DDS~~~

As an external electron donor, DDS functions to suppress the selectivity for atactic polypropylene. In fact, DDS inhibits the selectivity toward both isotactic and atactic polypropylene; however, the decrease in the reaction rate for isotactic polypropylene is much slower compared to that of atactic polypropylene. Consequently, the isotacticity is increased, but this somewhat affects the reaction rate. At the same time, an excessive amount of DDS not only fails to increase the isotacticity but actually leads to a decrease in it (as too high a dosage results in a low reaction rate; coupled with the effect of hydrogen adjustment, this leads to the production of too much polypropylene with low molecular weight, and according to the commonly used methods for measuring isotacticity, polypropylene with too low a molecular weight is considered random). Additionally, incomplete reactions also increase the ash content of polypropylene