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Some Aspects of Modeling in Petroleum Processing
Published in E. Robert Becker, Carmo J. Pereira, Computer-Aided Design of Catalysts, 2020
Ajit V. Sapre, James R. Katzer
Modern analytical chemistry provides the ability to characterize feedstocks at essentially the molecular level of detail. Thus a wealth of new information is now available for inclusion in kinetic modeling. Molecular-level feedstock characterization is now possible due to advances in analytical techniques, such as high-performance liquid chromatography (HPLC), gas chromatography (GC), mass spectrometry (MS), field ionization mass spectrometry (FIMS), nuclear magnetic resonance (NMR), and so on. Such detailed feedstock description allows deeper understanding of reaction networks for each characterized molecular lump. For each reaction type, such as cracking, isomerization, and so on, elementary reaction steps and single event kinetics can be incorporated into kinetic models. For example, in catalytic cracking, carbenium ion theory, stability and reactivity of primary, secondary, and tertiary carbenium ions, beta-scission rules, and so on, are applied at the pseudomolecular level.
Particle Characterization and Dynamics
Published in Wen-Ching Yang, Handbook of Fluidization and Fluid-Particle Systems, 2003
The actual cracking step of the catalytic reaction is the beta scission of the carbenium ions. The cracking step occurs at the beta position because the carbon-to-carbon bond beta to the charged carbon on the carbenium ions is the weakest bond of the entire hydrocarbon chain and the easiest to break. The beta scission of a carbenium ion produces an olefin and a new carbenium ion. The new carbenium ion produced by the beta scission can repeat the beta scission or undergo first isomerization and then beta scission. The combination of beta scission and the fact that the primary carbenium ion is the least stable means that the hydrocarbon molecule formed by catalytic cracking contains at least three carbon atoms. This results in high production of C3 and C4 in LPG from the catalytic cracking reactions. As the hydrocarbon chain length of the carbenium ion becomes shorter, the reaction rate of the beta scission becomes lower. Thus the rate of catalytic cracking decreases as conversion gets higher in the upper riser.
Analytical Pyrolysis: An Overview
Published in Karen D. Sam, Thomas P. Wampler, Analytical Pyrolysis Handbook, 2021
This new secondary free radical will either undergo beta scission or another 1–5 H shift. Beta scission produces a molecule of hexene, the trimer of ethylene, while a second 1–5 shift moves the unpaired electron to carbon number 9. Beta scission of this new free radical would generate a molecule of decene, the pentamer. This stabilization by 1–5 hydrogen shifting explains the increased abundance of products in the pyrolysate of poly(ethylene) containing 6, 10, and 14 carbons. These products are the result of performing a 1–5 hydrogen shift one, two, and three times, respectively (see again Figure 1.1 in which 10 and 14 carbon species are marked).
Improvement of heavy crude oil via catalytic cracking process for refining into valuable blending stocks
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2018
Based on these results, it can be said that the carbenium ions forming by breaking of the bonds of C–C, C–H, etc. were cracked into valuable hydrocarbon molecules via beta-scission, hydride transfer, protonation, isomerization, cyclization, etc. (Jensen and Chunrning 1999; Lee et al. 2011; Silva et al. 2017) during catalytic cracking of pre-upgraded heavy oil.