Low-Temperature-Initiated Cracking of Hydrocarbons to Produce Olefins: Simulation and Comparison of Different Initiators

Abstract

Low-temperature-initiated cracking technology has significant potential to develop new hydrocarbon pyrolysis with better atomic economy and higher yields of light olefins. The impacts of three representative initiators, triethylamine (TEA), nitromethane (NM), and di-tert-butyl peroxide (DTBP), were compared. Sufficiently detailed co-cracking reaction networks of three initiators with n-hexane were obtained through an automatic reaction network generator RMG, and the corresponding steam cracking tubular reactor simulation was performed. The results showed that the initiator with a lower cracking temperature brought about a more noticeable decrease in the cracking temperature of n-hexane. Both TEA and NM increased the carbon atom conversion from n-hexane to ethylene and propylene, especially propylene. NM was more significant, while DTBP was almost ineffective. Through kinetic parameter analysis, it was found that the temperature dependence of the key reaction caused different initiator performance. NM completely cracked at an appropriate temperature where the rate constants of the hydrogen abstraction and ethylene generation had reached a high level, and the released free radicals were effective. Visual reaction network analysis revealed that NM had a strong ability to release free radicals, and these free radicals significantly adjusted the competitive reaction path to produce ethylene and propylene, resulting in the most obvious effect on improving the conversion of n-hexane and the yield of propylene. The action laws of NM described above under hydrocarbon pyrolysis conditions indicate that NM may be the most suitable initiator for low-temperature-initiated cracking of hydrocarbons among these three initiator types.