Catalytic fast pyrolysis (CFP) is a promising thermal-chemical technology to convert lignocellulosic biomass to produce aromatic hydrocarbons in the near term. Diffusion of pyrolysis vapors and their upgraded products in zeolites plays a critical role during CFP, since diffusion can affect coke formation, catalyst lifetime, and product selectivity. Unfortunately, experimental determinations on diffusion coefficients of biomass relevant compounds in zeolites are scarce in the literature and the results differ significantly. Alternatively, molecular dynamics (MD) simulations can make a major contribution to characterize the diffusivities of molecules in zeolites at various temperatures relevant to CFP. In this work, we have studied the diffusivities of few biomass relevant species in H-ZSM-5 using MD simulations. The effects of molecular weight, size, and molecular orientation on the diffusivity will be discussed. Additionally, the diffusivity in mesoporous H-ZSM-5 nanosheets will also be investigated to understand their enhanced catalysis ability relative to the microporous H-ZSM-5. Furthermore, the diffusion in a particle model of H-ZSM-5 catalyst at 2-mm length scale will be examined to understand the intercrystalline and intracrystalline mass transfer. This work will provide deeper understanding of diffusion in H-ZSM-5 from nanometer scale to micrometer scale, which could facilitate the design of new zeolites to enhance the product selectivity and benefit the optimization of reaction conditions in a reactor.

Understanding diffusion during catalytic fast pyrolysis of biomass over H-ZSM-5 by multiscale modeling

253rd National Meeting (2017)

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