action of metal components on the surface metal components such as nickel and iron may catalyze a hydrocarbon to reduce or eliminate hydrogen from the olefin termed u201c dehydrogenation u201d metal components presenting catalytic activities are generally in the order of ni gt gt gt gt fe gt gt cr nio gt ni feo gt fe gt fe2o3 these metals and oxides catalyze reaction to form filament and coil type coke by successive dehydrogenation as shown in fig1 catalytic coke tends to be very mechanically hard u201c hard coke u201d and normally difficult to remove hard coke must often be removed from surfaces by mechanical means the formation of catalytic coke is believed to be most often involved in beginning the coking process of the tle and is believed to act as trap for pyrolytic coke pyrolytic coke is divided into gaseous and condensation coke pyrolytic coke is softer and generally easier to remove than catalytic coke gaseous coke is typically formed by dehydrogenation of such light olefinic hydrocarbon as acetylene condensation coke is formed by condensation polymerization and dehydrogenation of heavy aromatic compounds pyroltyic coke can be classified as globular black mirror fluffy or amorphous types according to morphology it is believed that the coking process of the tle begins with the hydrocarbon reacting by catalyst action of metal components on metal surfaces and forms filamentous coke which grows and provides deposit sites for various types of coke free radical coking causes coke filaments to thicken and as catalytic coke filaments grow carbon starts to block metal surfaces tar is.