Mass Transfer of Alkanes in Zeolite Packed-Bed Reactors Studied with Positron Emission Profiling (PEP). 1. Experiments

Abstract

Positron emission profiling (PEP) has been used to obtain in situ images of the pulses of 11 Clabeled alkanes passing through packed beds of acidic zeolites at temperatures typical of the hydroisomerization reaction. Used in this manner, PEP represents an in situ version of tracer pulse chromatography. The two-dimensional activity-position-time profiles measured were fit to an analytical solution. The method of moments was then applied to the subsequent fitted profiles to extract information regarding adsorption and diffusion of the hydrocarbons. Data concerning the mass transfer of alkanes are necessary to perform further modeling of profiles obtained during the hydroisomerization of n-alkanes on Pt/acidic zeolites.

See the unseen: applications of imaging techniques to study adsorption in microporous materials

“…A notable application of the imaging approach is that spatial heterogeneities in mass transport properties can be identified by the local adsorption behaviour in the packed bed, which can be caused by coke formation [76] or by intra-batch pellet variability [59]. PET represents an interesting alternative to MRI, because it enables real-time in-situ monitoring of liquid-and gas-phase processes, albeit at a lower spatial resolution (O(l) ∼ mm) [43]. However, because it detects spontaneous decay activity originating from the sample without the need for continuous excitation, PET can be used to investigate separation processes in three-dimensions, while retaining fast acquisition times (∼10 s, Figure 2f) [47].…”

11C,13Nand15OPositron (β+) Emitters in Catalysis Research

“…Such experiments allowed the determination of the surface coverage of CO on the Pt surface and the equilibrium constant for adsorption of CO 2 on ceria. The work was focused on the diffusion behavior of hydrocarbons in medium-pore zeolites [22][23][24][25][26][27][28][29][30][31][32][33], which is of relevance to hydroisomerization processes and also the oxidation of ammonia over Pt surfaces [13,[34][35][36][37]. In this direction, large concentration gradients exist during the catalytic reaction.…”

“…The model to describe the transport in the zeolite bed and in the zeolite crystals is based on a set of diffusion equations [25,26], describing the transport of molecules via convection and axial diffusion in the space between the crystals, adsorption and desorption at the zeolite crystal surface and diffusion inside the pores of the crystals. The model to describe the transport in the zeolite bed and in the zeolite crystals is based on a set of diffusion equations [25,26], describing the transport of molecules via convection and axial diffusion in the space between the crystals, adsorption and desorption at the zeolite crystal surface and diffusion inside the pores of the crystals.…”

Quantitative imaging of gas adsorption equilibrium and dynamics by X-ray computed tomography

“…Experimental approaches that enable in-situ imaging of concentration profiles within adsorbent columns have been proposed over the last few decades, although these have only been marginally applied. Positron emission tomography (PET) (Anderson et al 1998;Noordhoek et al 1998) and magnetic resonance imaging (MRI) (Bär et al 2002;Cheng et al 2005;Pavlovskaya et al 2015) have been successfully deployed, as both methods provide high temporal resolution and enable probing adsorption dynamics on the scale of a laboratory adsorption column. As recently reviewed in Pini and Joss (2019), the two approaches present notable features for the study of adsorption systems, including suitability to both gas and liquid systems and high molecule-specific sensitivity.…”