Pilot-scale enhancement of vacuum residue conversion via dual-stage catalytic cracking coupled with hydrogen regulation: Toward optimal product selectivity

Efficient conversion of vacuum residue (VR) into high-value light olefins and aromatics is critical for the sustainable utilization of heavy carbon resources. In this study, we propose a dual-stage gas-phase catalytic cracking process using a modified dual-stage self-mixing downer circulating fluidized bed (DS-DCFB) reactor tailored for intermediate-naphthenic VR. In the primary stage (530 °C, calcium aluminate catalyst (CaAl)), a 69.21 wt% liquid yield and 70.24 % heavy oil conversion were achieved with only 11.05 wt% coke formation. The dual-stage system (Stage I: 530 °C, CaAl catalyst; Stage II: 610 °C, acid-base composite catalyst (Z-CA)) significantly enhanced light olefin selectivity, yielding 30.13 wt% light olefins (C₂–C₄) and 40.64 wt% liquid products, while maintaining coke yield at 14.61 wt%. Notably, introducing 1.00 wt% H₂ co-feeding suppressed methane and coke formation by 22.29 % and 11.02 % and simultaneously increased the yields of benzene, toluene, and xylene (BTX) by 2.87 wt%. The DS-DCFB reactor exhibited robust stability during 12-hour continuous pilot-scale operation, confirming its efficiency for VR-to-chemicals conversion. These findings demonstrate the synergistic role of hierarchical catalysis and hydrogen regulation in suppressing coke formation, enhancing light olefin yield, and achieving stable pilot-scale performance. This work provides key experimental insights for industrial VR valorization and offers a promising pathway for heavy oil upgrading toward chemical feedstock production.