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Multiphasic continuous Reactors

Nima Yazdanpanah

What would be your choice of multiphasic continuous Reactors for handling gaseous reagents, and why?

 

There are different off-the-shelf modules in the market and some companies developed in-house creative equipment. In general, the categories are falling in Packed-bed, Structured reactors, Membrane reactors, Wall-coated, and Taylor flow. Some reaction limitations/requirements narrows the option to specific design;, such as catalytic hydrogenation that is mostly performed in packed bed reactor (with solid catalyst), or Diazo compound generators which are primarily membrane based.

 

Do you have experience with these applications? How did you develop your process? How was the scale-up performance?

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  • The reactor platforms in the continuous manufacturing in the pharmaceutical or fine chemical industries are typically Plug Flow Reactor (PFR) or Continuous Stirred Tank Reactors (CSTR). Both have their own advantages and disadvantages, applications, reason to avoid, or to love!

    I started a table here to kick-off the discussion. Could you add more characteristic aspects?

     

    Comparison of two Main Continuous Reactor Platforms (PFR and CSTR)

    Aspect

    PFR

    CSTR

    Slurry and Solid Handling

    Low capability, clogging issues

     

    Can handle high concentration of solid slurry

    RTD

    Narrow (depending on diameter and velocity)

    Broad

    Minimum residence time

    Seconds

    Minutes

    Minimum working volume

    Microliter

    Milliliter

    Heat transfer

    Great, large surface to volume ratio

    Average, can be increased by internal coils in addition to jacket

    Temperature limit

    Wide range from cryogenic to more than 1000°C

    Typically, -40 to 150°C

    Mixing

    Not good. Depends on flowrate or internal mixing elements or design of the reactor

    Great. Independent of flow rate

    Pressure limit

    High pressure, e.g. above 200 bar

    Usually up to 20 bar, due to safety concerns or sealing/leakage

    Concentration

    Spatial profile, constant at a specific location of the reactor

    Constant

    Sampling

    At the outlet, or alteration is required for sample point middle of the reactor

    Easy

    Multiphase reaction

    Limited solid involved reaction (as product or catalyst)

    Solid catalysts should be immobilized in a bed or structure

    All

    Cost

    Could be very low

    (it technically a coiled pipe in a heating bath)

    Considerably more expensive than PFR

    Stoichiometry of feed

    Critical, should avoid fluctuations

    Higher toleration, the CSTR could damp the fluctuations

    PAT implementation

    Mostly at the outlet. Placing PAT inside reactor required significant work/alteration.

    In-line, on-line (through a flow-cell). Easy implementation and sampling

    Process Control

    Could be slow for feedback control due to the time lag

    Could be fast

    Cleaning

    Easier, cheaper. Can be even disposable

    Costlier, harder

    ???

     

     

     

  • in reply to Nima Yazdanpanah

    Both tubular and CSTR's are great for specific reactions. I would also consider reactors such as the OFBR, the Autichem Dart reactor, the Nottingham university vortex photochemical reactor, the tube in tube reactor, the spinning disc reactor, the Stoli reactor, Scheibel Column, Spinid reactor to name a few. They all have their strengths and weaknesses, but they all need to be fed by pumps.

    What type of pump is required? what materials of construction? what flow rate range is required? and what pressure rating is required. Suddenly there are a lot of different options to apply to both the pumping system, reactor system, and heat exchanger systems. 

    Traditional bulk chemistry is performed in dedicated flow processing systems that have been refined over many years for the specific purpose of manufacturing a single product. 

    I truly believe that continuous reactor technology, when optimised, will result in higher yields, lower waste, lower cost processing, but the compromise is multi-purpose operation. When you optimise the engineering for a particular synthetic route to deliver a product, this engineered system will not be optimised for anything else. This is especially true for highly enabling steps such as photochemistry and electrochemistry.

    I think that there is a place for modularity, but only in the research domain. For full scale manufacturing a dedicated continuous process will be required in all cases to deliver an optimised solution. 

    While there will be opportunities to carry out problematic (low yielding) chemical transformations in large scale flow chemistry skids to deploy targeted improvements in existing processes, going forward, there will be greater gains to be had in the development of fully continuous systems for specific products.

    I feel there remains a significant amount of exciting flow development to explore!

     

     

  • in reply to Oliver Tames

    Thanks Oliver, great points. Thanks for mentioning some reactor examples. I think they are falling in either categories of CSTR/PFR or a combined characteristic, in terms of flow, mixing, RTD, …

    I was wondering if you could elaborate more on each of the Reactors you mentioned. Attached is an Excel spreadsheet, would you please fill that out and re-post?

    Also, anyone who is interested in contributing to the table content, you could post along or email me an offline version, so I’d consolidate all comments and post back (nima@procegence.com) .

Reply
  • in reply to Oliver Tames

    Thanks Oliver, great points. Thanks for mentioning some reactor examples. I think they are falling in either categories of CSTR/PFR or a combined characteristic, in terms of flow, mixing, RTD, …

    I was wondering if you could elaborate more on each of the Reactors you mentioned. Attached is an Excel spreadsheet, would you please fill that out and re-post?

    Also, anyone who is interested in contributing to the table content, you could post along or email me an offline version, so I’d consolidate all comments and post back (nima@procegence.com) .

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