(560ir) Modeling of Transport-Kinetic Interactions in Various Design Configurations of Egg-Shell Catalyst Particles

Catalyst design is one of
the most significant step in the development of a heterogeneous catalytic
reactor process (Sie and Krishna, 1998).  From a catalyst design perspective,
specification of size, shape, and internal pore structure are interlinked
parameters that have received notable attention by catalyst scientists and
engineers since these properties affect the catalyst effectiveness factor,
pressure drop, rate of catalyst attrition, catalyst mechanical integrity,
catalyst life, amongst other key measures of performance.  Determination of optimized
catalyst design parameters is often a tedious trial-and-error process since
tradeoffs exist in how the observed reaction rate and other measures of
performance may be affected by altering one or both of these parameters.

Technical catalysts
utilized to meet the economic norms of industrial processes are supplied as carrier-free,
supported, or coated configurations.  These catalysts are available in different
sizes and traditional shapes, such as powders for slurry or fluidized bed
reactors, and spheres, pellets, rings, extrudates, and honeycombs for fixed-bed
reactors (LePage et al., 2008).  Methods commonly employed for catalyst
preparation include deposition, precipitation and co-precipitation, gel
formation and selective removal (Haber et al., 1995).  In many catalysts,
the active metals may be distributed as a thin layer on a suitable support,
which is often referred to as an egg-shell catalyst type.

Particle-scale transport-kinetic
interactions, depending upon their magnitude, can affect the observed reaction
rates for products and reactants.  Significant transport effects are common in
fixed-bed catalytic processes that employ catalyst particles with diameters from
5 to 15 mm (Sie and Krishna, 1998).  Hence, it is important to utilize not only
the exterior catalyst surface for deposition of active metals, but also the interior
of the catalyst support to help reduce transport effects.  In an effort to
improve catalyst performance, non-traditional catalyst shapes with uniform
metal distribution have been developed, such as multi-lobes, wagon wheels, miniliths
and monoliths (Sie, 1993; Centi & Perathoner, 2003).  In addition, egg-shell
type catalysts with non-uniform metal distribution have been investigated (Lin and
Chou, 1994; Bukur et al., 2018).

The primary objective of
this work is to compare catalyst performance for different design configurations
of egg-shell catalyst particles using several oxidation and hydrogenation
reactions of commercial importance to quantify the proof of concept.  COMSOL
Multiphysics® is used as the numerical engine for modeling the particle-scale transport-kinetic
interactions.  An oxidation test case reaction was utilized for modeling
intraparticle diffusion and reaction for four different design configurations,
namely 1. Egg-shell; 2. Egg-shell with a central opening; 3. Egg white; and 4.
Egg yolk.  Figures 1(a) to 1(d) show the concentration profiles oxidation test
reaction reactant A for these configurations, respectively.  Figures 1(e) to
1(h) show the particle concentration profiles for reactants (A, B) and products
(C, D, and E) for these same catalyst design configurations.  Higher
conversions of reactant A were observed in egg-white and egg-yolk catalyst
design configurations.  Results for several test reaction cases provide
guidance on future catalyst synthesis for optimization.

Figure 1. Concentration profiles for different design
configuration of egg-shell catalyst particle.

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