Diffusion of pyrolysis vapors and their upgraded products within zeolite pores is one of the most important catalytic properties of zeolite catalysts. Diffusion of the molecules to the active site in zeolites can be a rate-limiting step and can affect substrate separation. Characterizing the diffusion behaviors of representative biofuel model compounds and their competition for active sites in zeolites at pyrolysis temperatures is important to interpret shape selectivity and product distribution during vapor phase upgrading. Yet, experimentally such measurements are extremely difficult. Molecular dynamics (MD) simulations are able to simulate the dynamical behaviors of molecules within zeolite pores, and can make a major contribution to understand the factors that control shape selectivity. In this work, we have conducted MD simulations to investigate the diffusivity of few chosen substrates, such as water, methanol, glycolaldehyde, toluene, guaiacol, and 2-phenylether phenol in zeolite H-ZSM5 to compare with available NMR results. The effects of zeolite acidity, molecular loading, and temperatures on the diffusivities of various oxygenates in H-ZSM5 will be discussed. Our results show the diffusivity depends largely on molecular loading and temperature. The diffusion coefficients characterized by NMR measurements at room temperature may not represent the true diffusivity of oxygenates in zeolites at pyrolysis temperature. Deeper understanding of the effects of pore size, shape, and topology on the diffusivity will enable designing new zeolites with optimized pore topology for a given molecular distribution to enhance the selectivity and separation.<br/> <br/><br/>

Diffusion of pyrolysis oxygenates in H-ZSM5

252nd National Meeting (2016)

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