Accurate Molecular Reconstruction of Cracking Feeds Improves the Predictions of Ethylene yields

摘要

Accurate characterization of petrochemical feeds plays a crucial role in describing the different reaction pathways and reactivity of the various isomer species. This knowledge becomes a need when it comes to develop comprehensive kinetic models of steam cracking process able to select the optimal design and operation of pyrolysis coils. For this reason, several efforts have been spent in the recent years to improve feedstock characterization and analytical separation techniques. The high potential of GC×GC combined with MS detection is a clear example of these efforts. Despite recent advancements of analytical techniques, a satisfactory molecular description cannot be obtained simply from these methods and the molecular reconstruction of the feedstocks needs to rely also on other bases. Isomers with almost identical physical properties, such as the isomers of branched alkanes and cycloalkanes, can exhibit very different cracking behaviors, and hence, a poor estimate of their internal distribution can significantly affect the ethylene yields. Thus, the horizontal lumping becomes more critical than the vertical one, and isomer distribution needs to be characterized with a different accuracy. This paper aims at emphasizing the role of the probability of methylation and alkylation inside the families of homologous hydrocarbons. For the first time, it is highlighted the importance of the internal distribution in the molecular feedstock reconstruction. To demonstrate the significance of the internal distributions, the SPYRO~R kinetic model has been extended to more than 500 species, covering a large detail of feed components. This kinetic extension, while giving the capability to evaluate the effect of both isomer distributions and thermal or catalytic treatments of refinery streams, further confirms the validity of the original lumping approach of SPYRO model.