Coking Resistance of Specialized Coil Materials during Steam Cracking of Sulfur-Free Naphtha

The reactor material strongly affects coke formation during steam cracking of hydrocarbons. Therefore, in the past decade several specialized reactor materials have been developed that have proven to be efficient in reducing coke formation for ethane steam cracking. However, their beneficial anticoking properties are questioned when heavier feedstocks such as naphtha are cracked. Therefore, the effect of the composition of the reactor material has been investigated for ethane and naphtha cracking in an electrobalance setup under industrially relevant conditions. A significant reduction of coke formation is obtained for specialized alloys compared to typical Fe-Cr-Ni heat resistant steels when a sulfur-free naphtha is cracked. A thin layer of alumina on the surface along with manganese chromite provides the highest resistance to coking, as was demonstrated by the SEM and EDX analyses. The decrease in coking rate translates in a run length increase of 50% for a typical naphtha furnace equipped with reactors made out of an Al-enhanced alloy instead of typically applied heat resistant steel.