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On the differences between periodic domain and fluidized bed
No full textTo understand the effects of macroscale constraints on fluidization, we investigate the differences between the periodic domain and realistic bed by using fine-grid simulations. The differences in these two systems are highlighted by identifying three force-balance conditions with respect to the gas - phase, solid-phase and the mixture, respectively. Specifically, these three conditions are not satisfied at the microscale, but satisfied at the macroscale in both systems; Over the mesoscale, the gas-phase force balance is established in the periodic domain and in the fluidized bed at bubbling states, but not at tur- bulent states, whereas the solid-phase and the mixture force balance conditions are established only in the periodic domain, not in the realistic bed. The influence of the bounding wall can be implicitly included by introducing the gas-phase pressure gradient, turbulent kinetic energies (TKEs) of gas and solids phases, and drift velocity as the markers for the drag force.(c) 2022 Elsevier Ltd. All rights reserved
Rational construction of multiple hollow silicalite-1 zeolite with enhanced quasi acidity for robust vapor-phase Beckmann rearrangement
No full textDeveloping efficient and stable zeolites for vapor-phase Beckmann rearrangement of cyclohexanone oxime is still a great challenge to realize epsilon-caprolactam (CPL) green production. In this work, the hierarchical porous silicalite-1 zeolites with multiple hollow structure (S-1-M) are explored by in-situ desilication-recrystallization post-treatment of spongy highway-like zeolites (S-1-S), which are synthesized through silanization synthesis of conventional bulky silicalite-1 (S-1). Compared to S-1, S-1-M achieves superior catalytic performance, with improving the CPL selectivity from 85.7% to 94.1% and prolonging the catalyst lifetime from 74 to 126 h at a weight hourly space velocity (WHSV) of 6 h(-1). Comprehensive physiochemical studies demonstrate that the highly dispersed intracrystalline cavities within S-1-M endow greater mass diffusion and better quasi acidity inducing by the enhanced H-bonds among abundant H-bonded silanols, which is cooperatively responsible for its superior catalytic performance
