(73d) Initiation Steam Cracking of Hydrocarbons By Hyperbranched Poly(amidoamine) (PAMAM) Initiator

The addition of initiators, possessing bonds with low bond dissociation energy, has been widely recognized as an effective method to promote the hydrocarbon cracking reactions. We synthesize the amidoamine-structured hyperbranched polymer (PAMAM) with the molecular weight of 12,500 as a novel macroinitiator, using ethylenediamine and methyl acrylate as raw materials. The experimental results show that 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 •NH₂ and •CH₃ radicals, which significantly increase the rate of hydrogen abstraction. To further investigate its initiation effect on hydrocarbons with different molecule structures, the steam cracking of three C6 hydrocarbons, namely n-hexane, iso-hexane and methyl-cyclopentane (MCP) were investigated experimentally in a stainless-steel tubular reactor, and the detailed kinetic reaction models and reaction process simulations are conducted by Reaction Mechanism Generator and Chemkin-pro software packages. The results confirm that 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 will provide a direction for efficient production of light olefins from steam cracking of naphtha.