Lessons learned in commercial scale-up of
new chemical processes (1)
Commercializing a new chemical process can be as simple as installing
one or more homogenous batch reactor(s), or as complex as designing a fully
integrated chemical complex requiring one or more heterogeneous reaction steps
processing gas, liquid and/or solids, with other units required to prepare
feeds, recover products/byproducts and recycle streams.
Commercializing
a new chemical process can be as simple as installing one or more homogenous
batch reactor(s), or as complex as designing a fully integrated chemical
complex requiring one or more heterogeneous reaction steps processing
gas, liquid and/or
solids, with other units required to prepare feeds, recover products/byproducts
and recycle streams. The latter is focused on here, with further clarification
that there are always exceptions to the rules.
Typically,
process scale-up evolves from lab scale to pilot, demo and commercial. The lab
scale is usually limited to studying the reactor and catalyst performance. The
pilot plant should be a scaled-down version of the commercial process
configuration to the greatest extent feasible. The pilot is used to
confirm/expand reactor and catalyst performance data and to test the balance of
plant concepts. The demo stage is usually used when large quantities of product
are needed for performance testing by end users.
Know the reaction chemistry
The
reaction chemistry must be well-advanced at the lab scale. However, having a
developed idea of the range of selectivity, yield and potential byproducts may
be sufficient to proceed to the next step, such as piloting, where these items
can be further solidified.
Often,
the right group of people with varied backgrounds can brainstorm and produce
engineering solutions to mitigate this risk. Every effort should be made to
obtain data under
conditions anticipated for the commercial unit—e.g., pressure, temperature and
gas/solid residence time.
A common
mistake is to use low-pressure units to study the chemistry of a high-pressure
process. This decision may transpire either because the reactor cost is lower,
or because the low-pressure unit already exists. Note that tests in a lab
require personnel and a host of equipment and instruments, of which the reactor
is only one cost component. Therefore, the lifecycle savings from using a
low-pressure reactor is a small fraction of the total cost of the program.
What is
the drawback of using a low-pressure unit? In one example, a partial oxidation
reaction converts a hydrocarbon to an oxygenated main product containing
carbon, oxygen and hydrogen, and byproducts consisting of water and carbon
oxides. Extensive tests were conducted in a ready-to-use low-pressure unit. Concerns
about catalyst deactivation in the presence of high partial pressure of the
hydrocarbon feed were addressed by raising the concentration of the hydrocarbon
in the feed, effectively reducing the partial pressure of other species. No
deactivation was noticed, and very high yields were obtained. A larger unit was
built and operated at actual conditions, with significantly lower yields and
measurable catalyst deactivation. These results were due to several factors:
- Yield
of this partial oxidation reaction decreased as pressure was raised.
- Reducing
the partial pressure of the other reaction species resulted in easier
desorption of these species in the lab unit, making catalyst sites more
readily available for the main reaction path. Under actual pressure, it
was more difficult for these other species to desorb, resulting in both
reduced yield and more rapid catalyst deactivation.
Such
oversights are far more common than published, occurring even within R&D at
major corporations.
CONTINUES
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