Wednesday, November 25, 2015

Process Wednesday: gotta wait until the dryers are done

From Francis X. McConville's "The Pilot Plant Real Book" and its short section on dryers, a comment about dryer characteristics:
The properties of product from pilot drying equipment may be significantly different from that of product dried in laboratory vacuum tray dryers. This is particularly true of units that agitate the cake mechanically such as orbiting screw conical dryers. Particle attrition or agglomeration can result in major differences in particle size distribution, bulk density, compaction and flowability. These things in turn affect solubility, bioavailability, formulation, processing, packing and shipping. Therefore, it is not valid to base projected product properties on the results of tray-dried samples when different equipment will be used on scale-up. 
The behavior of a given product in different dryer types cannot be easily predicted. Bench or small pilot-sized test units are available for tumble or paddle dryers, but the dynamic similarity to large-scale equipment is poor. 
The best way to determine what the product will look like is by performing pilot studies in representative drying equipment. Sometimes the actual product characteristics will not be known until the first production batch comes out in the dryer. 
Just in case you thought you could predict the future in this sense, you cannot. Gosh, it is remarkable to me how much is not known in this business. 

1 comment:

  1. if you have with you a chemist who worked on the scale up methodology optimization, there is a good chance he can anticipate some of the problems with drying the material in the plant floor, once he understands the difference (and shortcomings) of the plant equipment. By working with the stuff in bulk before, he should have a "feel" how sticky the material could become, what is the chance it could decompose or turn into mean hard turd-dumplings on prolonged heating with the residual solvent in the cake.


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