Hydrocarbon Processing - September 2021 - 59

Catalysts
B. SUNGNOEN, W. TANTHAPANICHAKOON
and K. LOURVANIJ, SCG Chemicals Co. Ltd.,
Rayong, Thailand
Avoid common pitfalls in upscaling
catalytic fixed-bed reactors
Driving innovation is an inescapable
strategic reality, not only for accelerating
new products development and technological
solutions but also for creating
new markets. Multidisciplinary collaborations-such
as research and development,
business and marketing, and engineering-are
indispensable to define
potential business and market share
targets. The development speed of new
products is very demanding because the
needs of customers have been influenced
by rapid disruptive changes.
In the early stages of so-called product
conceptualization, the purpose of a
new product or technology must match
the company's direction to compete in
the world market. Effective synergistic
collaboration between multidisciplinary
functions is a key success factor in this
stage of development. Development
must be based on numerous information
exchanges between specialists, researchers
and engineers to conceptualize
the commercial process, including
optimal operating conditions for largescale
production.
Challenges in dissimilarity of mass
throughput. A commercial
reactor is
usually designed to deliver high throughputs
to maximize profits while minimizing
total investment cost. Conversely, laboratory
and pilot reactors are commonly
used for experimentally investigating new
phenomena and producing the necessary
information that is applicable or adaptable
to the upscale design of new-or the
improvement of existing-commercial
processes and facilities. The utilization of
laboratory and pilot units with low mass
throughput is inevitable due to:
* Minimizing total investment
and economic risk
* Maintaining flexibility for frequent
reconfiguration
* Widening operating range
* Easing handling and waste disposal
* Decreased concern and
smaller risk of safety and
environmental impacts
* Increasing project speed, including
smooth startup and shutdown.
It is logical that the flow regimes inside
laboratory, pilot plant and commercial
reactors are significantly different.
Generally, the flow regime of fluid can be
classified into three types: laminar, transition
and turbulent flows. As expected,
this flow regime dissimilarity can significantly
impact the observed catalyst
performance in a heterogeneous (solidfluid)
catalytic reactor. The following
section will focus on the fixed-bed reactor,
as it is the most commonly used.
Rate-controlling mechanisms and
flow behavior. By focusing on a typical
porous catalyst pellet packed in a fixed
bed, several sequential and parallel mass
transfer and reaction steps can be seen,
as illustrated in FIG. 1.1
* Step 1: Reactants transfer from
the bulk fluid stream through a
stationary film to the external
surface of the pellet
* Step 2: Reactants next diffuse into
the pores to catalytic sites on the
internal walls
* Step 3: Reactants adsorb on
the active sites
* Step 4: Reactants are converted to
products via surface reaction
* Step 5: Products desorb from
the active sites
* Step 6: Products next diffuse
inside the pores to the pellet
external surface
* Step 7: Products transfer from the
pellet surface through the film
to the bulk fluid stream.
For most heterogeneous catalytic reactions,
it is reasonable to assume that the
first-order surface reaction, as well as very
fast adsorption and desorption steps, control
the overall reaction rate. Making use
FIG. 1. General steps of heterogeneous catalytic fluid-porous solid reaction, and an illustration of
concentration profile of Reactant A and Product B.
Hydrocarbon Processing | SEPTEMBER 2021 59

Hydrocarbon Processing - September 2021

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