A Catalytic, Coke-Preventing Coating For Ethylene Steam Crackers

General Electric Company, Global Research Center, One Research Circle, Niskayuna NY

 Kevin Van Geem,* Guy Marin and Carl Schietekat

Laboratory for Chemical Technology, Department of Chemical Engineering, Ghent University, Technologiepark 918, B-9052 Zwijnaarde, Belgium

Ethylene is a globally-significant commodity feedstock that is produced by steam cracking of hydrocarbons at 800-1000 ^oC.  In this process, a hydrocarbon (naphtha or ethane) and steam are conducted through a nickel alloy tube positioned in a furnace that is maintained at the desired cracking temperature.  During the cracking run, an unavoidable side reaction occurs that results in the deposition of coke on the inner surface of the tube.  The coke deposit is thermally insulating and when the maximum tube metal temperature is exceeded the run must be interrupted to allow for a decoking operation to be carried out. 

In this paper we describe our four-year research effort that has discovered a robust, novel coating technology for the inner wall of the furnace tube that prevents this deposition of coke. This coating is based upon a family of ceramic catalysts having a doped perovskite structure that are capable of converting coke to carbon oxides on contact.  Thus, when coke forms during cracking it is instantaneously gasified on contact with the wall.  We will describe the experiments that led to the discovery of this family of catalysts with tuneable activities, as well as methods of applying this catalyst as a coating to the IDs furnace tubes. We have established that the coating is robust to thermal shocks, exposure to a range of common impurities, to multiple, severe decoking cycles and to a 50% decrease in steam dilution.

The performance of these coatings has been demonstrated in a series of pilot experiments at the University of Ghent with both ethane and naptha feeds.  These pilot experiments showed that the catalyst is robust and maintains anti-coking activity for the equivalent of 10+ years in accelerated life testing.