SiYProTM Case StudyEthylene dichloride – light ends program

SituationAn Asian PVC producer was carrying out a standard prac-tice of sending some product to waste in their ethylene dichloride (EDC) unit. The light ends tower removes low boiling impurities from the crude EDC by distillation. In-cluded in these low boilers is the reactive monomer chlo-roprene, which is present in a recycle stream from the EDC cracking furnace. In the overhead section of the tower, this can reach a high enough concentration and temperature to undergo radical polymerisation. This in turn can lead to fouling and blockage of the overhead con-denser. A common practice is to dilute the chloroprene by operating the tower in such a way that more EDC product goes overhead. This dilution effect can stop the polymeri-sation but results in a yield loss of EDC. Additionally, the tower needs to operate at a higher temperature to allow this higher amount of EDC to pass overhead.

ApproachThere are several potential solutions here, one option is to chlorinate the furnace recycle stream which contains the chloroprene, but this requires capital investment, and creates a stream rich in heavy molecules with a high foul-ing tendency. The Evonik approach is to apply an inhibi-tor to prevent the chloroprene undergoing radical po-lymerisation in the light ends tower. However, at the top of the tower, hydrogen chloride is present, it was im- portant to select an inhibitor which is compatible with this difficult environment.

ResultsSiYPro™ S275 was applied via injection nozzle to the overhead section of the light ends tower; a dosage of 500ppm based on chloroprene monomer concentration was selected. Polychloroprene concentration was moni-tored in the condenser, and an upper limit of 300ppm was agreed with the customer.

Over a period of one month, the reboiler temperature was reduced to allow less EDC to distil. At the beginning of the trial, the overhead stream contained 73% EDC, by the end of the trial this had been reduced to 55%.

On an annual basis the customer was able to reclaim 3,000 tonnes of EDC by using SiYPro™ S275.

SiYProSimplify Your Process

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CrudeEDC

Light ends

EDC to heavyends tower

EDC Light Ends Tow

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Evonik Performance Materials GmbHDr. Phillip R. James, Global Technology Marketing Manager Phone +44 7802 720232, phillip.james@evonik.com www.evonik.com/siypro

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August 2014