The formation of butadiene polymer is a common problem in butadiene extraction units, as well as ethylene plant purification columns processing high levels of butadiene. Butadiene polymer may manifest itself in several different forms, commonly described as sheet, rubber, crystalline, or popcorn polymer. An important issue is the nature of this fouling material and its identification, especially if it is popcorn polymer because this is its most dangerous form. Popcorn polymer expands at a tremendously rapid rate, thus it is a safety issue that has led to metal rupture.
Based upon appearance, two Dow plants discovered popcorn-like polymer in the top of purification columns containing levels of butadiene (43-50 %) thought to be unable to form popcorn. Not all crystalline butadiene polymer is popcorn, and in the past popcorn has been reported to not form in streams containing < 70 % butadiene. While the sample of crystalline, white polymer looked like popcorn, the only way to identify it is through testing.
One method to identify popcorn polymer is to place the recovered polymer as a seed in styrene, heat this to 60 ºC, and note the rate of polymerization over time. This is compared to a styrene solution containing a known popcorn seed that has been stored under inert atmosphere for use as a reference in this test. If the rate of polymer formation with the test seed is equal to or greater than the reference, then the polymer is indeed popcorn. For both samples tested from these low-concentration butadiene containing columns, these were identified as popcorn.
In this presentation findings from these plants and the results of laboratory experiments will be shown. Also, the implications of forming popcorn polymer at lower levels of butadiene will be discussed.
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