Published in Engineering, a new study elaborates on the conceptual origins, theoretical advancements, engineering challenges, and industrial applications of the diameter-transformed fluidized bed (DTFB) reactor, a novel reactor design developed to address national demands for upgraded automotive gasoline quality and advanced heterogeneous catalytic reaction processes. The research, led by Youhao Xu and Bona Lu with collaborators from Sinopec and the Institute of Process Engineering of Chinese Academy of Sciences, traces the DTFB’s development from the dual reaction zone concept for the maximizing iso-paraffins (MIP) fluid catalytic cracking (FCC) process, and outlines a suite of catalytic reaction engineering (CRE) technologies built on the DTFB platform, alongside their successful industrial implementation.

The study begins by linking the DTFB’s invention to the thermodynamic and kinetic differences between olefin generation and conversion in FCC reactions. It identifies that endothermic cracking reactions favor high temperatures and short contact times (unimolecular mechanism), while exothermic isomerization and hydrogen transfer reactions require low temperatures and long contact times (bimolecular mechanism). The DTFB addresses this by varying reactor diameter to partition reaction sections, creating distinct flow regimes and reaction environments in a single reactor—eliminating the drawbacks of connecting multiple separate fluidized beds, such as prolonged intermediate residence time and increased catalyst wear.

A core challenge in DTFB development is achieving precise coupling between flow and reaction multimodalities, which requires accurate prediction of flow regime transitions. To this end, the research team proposed a two-way coupled energy minimization multi-scale (EMMS) drag model and corresponding multi-scale computational fluid dynamics (CFD) approach, which accounts for both macroscopic operating parameters and local hydrodynamics. This model, integrated into mainstream CFD software, enables grid-insensitive simulations and accurate prediction of choking behavior—a critical issue in diameter-expanded reaction zones—by establishing quantitative relationships between choking and key design parameters like diameter expansion ratio and bed height. The study also details a flow-reaction coupling simulation framework, combined with an EMMS-ANN drag supermodel, to realize full-loop reactive simulation of the FCC reaction-regeneration system, capturing unit interactions and facilitating instability diagnosis.

Engineering safeguards for DTFB industrialization include specialized distributor technologies (mushroom-headed and concave distributors) that enable stable flow regime transitions and reduce catalyst wear, alongside ancillary technologies for flexible control of temperature, density, and gas-solid contact time in each reaction zone. The study highlights eight fully industrialized DTFB-based processes, with one more set for industrialization by 2026, spanning petroleum hydrocarbon catalytic cracking, olefin-to-light olefin conversion, and methanol-to-light olefins (MTO). In FCC applications, DTFB retrofits have reduced dry gas and coke yields while increasing liquid yields and cutting energy consumption, and the technology has supported China’s gasoline quality upgrade from National I to National VI standards, holding over 70% of the domestic catalytic cracking gasoline market share with international patent licenses.

The research concludes by outlining future research directions for DTFB-based CRE technology, including exploring reaction-flow regime matching mechanisms, co-optimizing catalyst and reactor design via multi-scale kinetics, and developing AI-driven industrial large-scale models to accelerate technological innovation. The DTFB platform, the study notes, has achieved precise selectivity control for complex catalytic reactions in a single fluidized bed and resolved the historical trade-off between reaction selectivity and conversion in key industrial processes.

The paper “Diameter-Transformed Fluidized Bed-Based Catalytic Reaction Engineering and Industrial Application,” is authored by Youhao Xu, Bona Lu, Mingyuan He, Wei Wang. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.02.024. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.