Spatiotemporal imaging analysis of mesoscale mass transfer performance of an FCC catalyst

Abstract

The mass transfer performance of fluid catalytic cracking (FCC) catalysts is a key factor affecting the reaction activity and selectivity of catalytic cracking. This study employs confocal laser scanning microscopy with rhodamine B as a macromolecular fluorescent probe to simulate and investigate the mesoscale mass transfer behavior of heavy oil molecules on an FCC catalyst, achieving spatiotemporal imaging analysis of mass transfer patterns within catalyst microspheres. Results revealed that after 10 min, the probe molecules penetrated only about one-tenth of the microsphere's depth below the surface layer. Moreover, significant variations in concentration distribution were observed at different locations. This phenomenon stemmed from the compositional and structural heterogeneity across distinct regions of FCC catalyst particles, resulting in differential diffusion rates for the probe molecules. Combined with Fick's law calculations, the effective diffusion coefficient was determined to be in the order of 10⁻¹⁴ m² s⁻¹, approximately 4 orders of magnitude lower than that of the intrinsic diffusion coefficient. This result fully confirmed that the surface composition and pore structure characteristics of the catalyst impose significant diffusion limitations on the mass transfer of large molecules within the FCC catalyst microspheres. A novel visualization methodology for studying the mass transfer in FCC catalysts was successfully developed based on super-resolution fluorescence imaging technology. This approach enables the mesoscale revelation of the mass transfer mechanisms for heavy oil macromolecules within FCC catalysts, thereby offering optimization strategies for enhancing catalyst mass transfer performance.