what is this polymer?

in a ziegler natter process to make polybutadiene, we use a cobalt catalyst and diethylaluminium chloride (DEAC) with water as co catalyst. This is a common commercial system. Prior to adding the cobalt compound to the reactor the DEAC and water are allowed to react in an ageing vessel. At this point the solution contains butadiene, C6 solvent and mixed butenes mostly but 1 ene. This drum is fouling up with a substance that is 97% organic. The 3% residue, i am sure is aluminium hydroxide. The organic component is white and powdery on drying and has a H:C ratio of almost exactly 2:1. I assumed it was some sort of polybutadiene but this should have a H:C ratio of 3:2. Any ideas what this polymer is and the mechanism of formation? free radical? cationic? And better still , any ideas on preventing its formation? ( main problem is the pipes clog up forcing us to shut down every other month to clean)

any suggestions appreciated. Terry

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Hi Terry,

I hesitated somewhat to answer because it is difficult to comment without hands-on investigations.

One of the possible explanations could be ( as you suggested) a cationic polymerisation of the small amount of isobutylene. Alumina alkyls with water are a good catalyst for that and low temperatures ( is your pre-reactor cooled ?) give reasonable long chains. poly-isobutylene fits well C/H ratio 1:2. A radical mechanism would probably also start polymerisation of the butadiene ...

Unfortunately there is afaik no easy way to inhibit a cationic polymerisation, so maybe you can try to reduce the content of isobutylene in your butadiene feed? Is it the full butadiene stream in this vessel or only small sidestream ? In this case you could try to use "better" butadiene here ?



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Matthias Bertram

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