Process Development Case Studies

Session Chair:

• Stacie Santhany, The Dow Chemical Company

Session Description:

As engineers and scientists, we have been taught to realize problems, do in-depth research to gain understanding, and come up with simple, scalable, innovative solution that help the world while generating money for our companies.  During this session, presenters will tell a story from beginning to end about a process development or technical problem.  The presenters will teach the audience about what went well and what could have gone better, and we can all stand to learn a lot about both.  The outcome from these presentations may help the audience have a different way of thinking about their engineering and process development projects. 

Schedule:

Abstracts:

Chemical Processes

Chemical engineers are well equipped to analyze an existing or proposed manufacturing process to solve problems and to make sound decisions. Developing a new process uses these analysis skills as well as some new ones. This talk is about the process of process development, how it works, and what we achieve along the way. We don’t make chemicals; we only control conditions that chemicals experience. Then what we want to happen occurs spontaneously. To do this, we need to know and exploit the behavior of the materials.  We will also discuss the underlying drivers and realities of large processes and how these impact our work. Process development is especially fun and rewarding role for chemical engineers.

The Nub of Successful Mixing Process Research and Scale-up

Mixing has recently been described by Dr. Suzanne Kresta of the University of Alberta, Canada as the “Forgotten Unit Operation”.  This is in spite of the fact that effective fluid mixing undergirds successful process research, development and scale-up to plant operations in all chemical and allied process industries.  In this presentation the nub or what is central for defining effective mixing for successful process research and scale-up will be discussed.  Three case studies will be employed to illuminate key aspects.

Fixed Bed Reactor Fouling

Fixed bed reactors are a workhorse in the chemical and petroleum refining industry. A reactor is often expected to run uninterrupted for multiple years between planned shutdowns.  Chemical engineers are expected to skillfully monitor and manage the forecasted remaining catalyst life, as unplanned outages are significantly more costly than scheduled maintenance shutdowns.

Catalyst poisoning may occur when a hydrocarbon reactor receives feed material contaminated with non-hydrocarbon materials, such as metal ions. In addition to poisoning, the catalyst bed is subject to mechanical obstruction from solids in the feed.  Catalyst extrudates are often very small to reduce mass transfer resistance, and a deep bed of fine catalyst extrudates is an efficient particulate capture system. Particulate fouling will be evidenced by increasing reactor differential pressure.  Examples of undesired feed particles include carbonaceous materials, polymeric material, pipe scale, and inorganic suspended matter.

Either loss of catalyst activity or rising differential pressure may necessitate reactor throughput reduction or an expensive unplanned shutdown to replace the catalyst.  In the event of a shutdown it is the job of the chemical engineer to adjust the catalyst loading plan to maximize the cycle life of the unit. Removing a portion of the catalyst and replacing it with grading material will increase tolerance to feed particulates but at the expense of fewer active catalyst sites and a higher deactivation rate. Increasing the amount of catalyst loaded either by dense-loading or by removing a portion of the grading layer volume may increase tolerance to poisons and reduce deactivation rates, but at the expense of reduced tolerance to feed particulate contamination. 

In this engineer’s experience, there is a third reactor fouling mode that is unusual and unexpected by most: particulate plugging of the bottom bed of a multi-bed reactor while  the upper bed stays clean and free of particulate contamination, despite both beds containing the same size, type, and density catalyst. This failure mode will be discussed along with potential root causes.