On the mechanism of initiation steam cracking of C6 hydrocarbons by hyperbranched poly(amidoamine) (PAMAM) initiator

Initiators with low bond dissociation energy can initiate the cracking of hydrocarbons, but the initiation effect on hydrocarbons with different molecule structures remains ambiguous. In this study, the steam cracking of three C6 hydrocarbons, namely n-hexane, iso-hexane and methyl-cyclopentane (MCP), initiated by hyperbranched poly (amidoamine) (PAMAM) were investigated experimentally in a stainless-steel tubular reactor, and the detailed kinetic reaction models and reaction process simulations were conducted by Reaction Mechanism Generator and Chemkin-pro software packages. The results confirm that the addition of PAMAM can significantly promote the cracking conversion and reduce the initial cracking temperature of hydrocarbons because the decomposition of PAMAM at relatively low temperature produces high concentration of active center dot NH2 and center dot CH3 radicals, which significantly increases the rate of hydrogen abstraction. Importantly, the promotion efficiency of the initiator can be highly dependent on the cracking behaviour of hydrocarbons. The initiator will show higher promotion efficiency for hydrocarbon that is more prone to undergo sustained hydrogen abstraction after initiation. Therefore, the promotion efficiency of PAMAM follows the order of n-hexane > iso-hexane > MCP. This study is helpful for a better understanding of the initiation mechanism and will guide the design and screening of effective initiators for naphtha with different compositions.

Automated summary

This study investigates the effect of hyperbranched poly (amidoamine) (PAMAM) on the steam cracking of three C6 hydrocarbons. The results show that PAMAM can significantly promote the cracking conversion of hydrocarbons and reduce the initial cracking temperature. The study also reveals that the efficiency of the initiator depends on the cracking behavior of hydrocarbons.