Wednesday, November 16, 2016

TECH SPECIAL.... Lessons learned in commercial scale-up of new chemical processes (1)

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.
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