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Accurate characterization of liquid feedstocks of steam cracking furnaces plays a crucial role in describing their pyrolysis mechanisms. This knowledge becomes a need when it comes to define comprehensive kinetic models of hydrocarbon pyrolysis for optimal design and operation of cracking coils. Despite recent improvements in analytical separation techniques, a satisfactory molecular reconstruction of liquid feedstock cannot be obtained simply from these methods. Isomers of branched alkanes, cyclo-alkanes, and aromatics, with almost identical physical properties, can exhibit very different cracking behaviors, due to different chemical structures. Their internal distribution significantly affects olefin yields. Thus, the horizontal lumping of different isomers becomes even more critical than the vertical lumping of homologous species with a different number of C atoms. This chapter emphasizes the role of methylation probability in hydrocarbon isomers, and also shows that a kinetic mechanism with a large detail of feed components, coupled with flexible lumping strategies, allows to estimate without difficulty the effect of refinery treatments and isomer distributions on product yields from pyrolysis process. |
