Four-Carbon Segmented Discrete Hydrocracking of Long-Chain Paraffins in MTT Channels Following a Pore-Mouth Mechanism

Hydrocracking of long-chain paraffins is a key process in petroleum refining. A fundamental understanding of the reaction on the bifunctional catalyst is of great importance for controllable cracking. In this work, a mechanism study on the hydrocracking of long-chain paraffins catalyzed by Pt/ZSM-23 has been carried out. The distribution and accessibility of acid sites on MTT channels are purposefully adjusted. Based on reasonable simplification, the reaction data are analyzed to reveal the shape selectivity, reaction path, and catalytic mechanism. The applicability of the pore-mouth mechanism in this system has been carefully verified by experiments. Both protonated cyclopropane (PCP) and beta-scission paths occurred simultaneously at the pore mouths, accounting for 60 and 40%, respectively. The proportions of PCP and beta-scission paths with different chain lengths inserted in the pore are quantitatively calculated, which are multimodal. Shape selectivity of the teardrop-shaped MTT skeletal structure is investigated by the joint experimental-theoretical method. The insertion of the paraffin chain in the MTT channel is discretely segmented by integral multiples of four sequential carbon atoms starting at one end of the chain, which is followed by cracking through the mixed PCP and fi-scission paths at pore mouths.

Automated summary

This study investigates the mechanism of hydrocracking of long-chain paraffins catalyzed by Pt/ZSM-23. By adjusting the distribution and accessibility of acid sites, the selectivity, pathway, and mechanism of the reaction are revealed. The applicability of the pore-mouth mechanism is confirmed through experiments, and the shape selectivity of the MTT skeletal structure is studied using a combined experimental-theoretical approach.