TECH SPECIAL..... Lessons learned in commercial scale-up of new chemical processes (2)

Lessons learned in commercial scale-up of new chemical processes (2)

Knowing the catalyst

By the time the process is commercialized, the catalyst formulation, shape, size distribution, porosity, attrition properties, deactivation rate, and (if required) reactivation method and rate, must be known. But what about the mid-step involving pilot or demo units? Does everything about the catalyst need to be known to design these units? The answer is: sometimes, no. Pilot and demo plants can be designed to test catalyst formulations that are vastly different with respect to activity and size.

For example, a new process used catalyst circulation between a reaction zone and a regeneration zone, similar to that practiced in refinery fluid catalytic cracking units (FCCUs). Several formulations of catalyst were being developed with a wide range of reactivity and attrition properties. It was estimated that the time span needed to develop a final catalyst formulation was approximately the same as that needed to design and build a larger unit.

Rather than waiting for the catalyst formulation to be finalized, the project to design a larger unit was undertaken. The challenge was posed to design a flexible unit to handle a range of catalyst formulations with low to high activities, resulting in the approximate concurrent operating ranges:

• 2:1 turndown in operating pressure
• 3:1 turndown in reactor gas residence
• 4:1 turndown in solid circulation
• 2:1 turndown in auxiliary vessel solid holdup
• 2:1 turndown in regenerator solid holdup.

Readers familiar with FCCU design and operation know that these are challenging requirements; however, they were successfully met. The solutions increased the pilot plant’s cost somewhat, but they also measurably reduced time to market.

A different pilot plant project was designed to operate with both fine and coarse catalysts, while research proceeded in parallel to determine which option to follow. Readers familiar with fluidization know that this is not an easy design.

One of the key mistakes made in the early stages of development is that the rapid replacement of catalyst can mask potential long-term catalyst deactivation. Another is limited run length (i.e., not operating continuously). Run length is especially critical when chain reactions can result in molecular growth that causes vaporizable products to turn into non-vaporizing high-boiling-point compounds, or when material deposition can result in size growth.

CONTINUES

Jazayeri, B., Reacxion http://www.hydrocarbonprocessing.com/magazine/2016/october-2016/process-control-and-instrumentation/lessons-learned-in-commercial-scale-up-of-new-chemical-processes