State-of-the-art of Coke Formation during Steam Cracking: Anti-Coking Surface Technologies

Although steam cracking is a mature technology, mitigation of coke formation remains one of the main challenges in the petrochemical industry. To increase the olefin output of existing plants, coil materials that can withstand higher temperatures are desired. This work reviews material technologies that were developed and tested in the past three decades to minimize the rate of coke deposition and extend the furnace run length. The material not only determines the mechanical properties of the coil but also affects the coking rate substantially. In some cases, differences in coking rates by more than a factor 10 have been observed. SiC materials could be operated at significantly higher temperatures, and this leads to higher olefin selectivity if one includes acetylene hydrogenation; however, the mechanical joints make it currently impossible to take advantage of their superior temperature resistance. On the industrial scale, operational improvements have been reported with advanced reactor surface technologies such as high-performance alloys and coatings during the past decade. Catalytic coatings go a step further than barrier coatings by actively removing coke that is deposited on the coils. Another trend is to add aluminum to the coil material, which forms a protective aluminum oxide layer on the reactor wall during operation and results in reduced carburization. To optimize the coking mitigation capabilities of the coils, the state-of-the-art materials and/or coatings should be combined with 3D reactor technologies, which is not always possible for all materials because of the advanced machining that is needed.