ANALYTICAL AND LABORATORY EQUIPMENT 23
Pressured lab-scale filtration and drying
Camille Flores-Kilfoyle discusses how advanced filter dryer technology is enabling new product development.
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Fig. 1. PSL’s new metallic lab nutsche filter dryer, part of the GFD range.
ab-scale filter dryer technology has not always been available for accurate scaling up. During laboratory studies and R&D product development, chemists need to work on similar technology to evaluate and determine the appropriate process parameters.
Traditional filtration and drying methods usually found in laboratories are Buchner filtration, centrifuge and oven dryer. Tese technologies cannot be transferred successfully onto commercial production scale.
Terefore, smaller agitated nutsche filter dryers have been developed to provide the same
technology for 10 to 500 grams batch of final product. Tey can be found in glass for complete process visibility and now also in stainless steel for higher pressure requirements (Fig. 1).
Tese lab filter dryers perform the same filtration under vacuum and pressure, washing and re- slurry capabilities and thermal drying through a heating jacket.
Te GFD design allows a total recovery of the final dried powder thanks to a filtration basket that can be removed for efficient product harvesting.
Te new lab filter dryer is pressure rated at 4 bar(g) for a typical pressured filtration at 2 bar(g). Te glass version still allows up to 0.5 bar(g), ideal when applying low pressure during the filtration process.
Te GFD products range from the smallest size Mini Lab GFD with 0.002m² filtration basket for a total volume of 0.3L and can filter a cake volume up to 0.1L; this is a suitable piece of equipment for lab-scale trials.
Ten the Lab GFD size includes a removable filtration basket of 0.01m² for a cake volume around 0.5L for small scale synthesis. Tis is the most popular size of the range thanks to its polyvalent use.
Te Maxi Lab GFD is used within Kilo-Laboratory for a cake volume of 5L with 0.05m² filtration area.
Te full range uses the same accessories, including control box and drive system for the agitator, allowing true flexibility between the different vessels in glass
borosilicate 3.3 or stainless steel (see Fig. 2).
How does it work? Te slurry enters the vessel through one of the nozzles located on the vessel lid. During the filtration phase, vacuum is pulled at the bottom of the vessel whilst the filter basket collects the product. It is then possible to wash the cake, again using a nozzle of choice on the lid to introduce the solvent and the heated vessel jacket if required.
It is common practice to apply pressure to the top of the filter cake during filtration whilst the bi-directional motor is running in a clockwise direction to smooth the cake. Optimal filtration is achieved in this way as you can pressure filter with no cracks in the cake.
Te heated jacket is then used to heat the vessel for the drying phase. Te vessel is rated to temperatures between 25°C and 150°C, and it is not uncommon for the GFD to also be used for the filtration of unstable products at low temperatures. Te bi- directional motor is lowered into the cake during this phase and is now used in the anti-clockwise direction to dig into the cake thus resulting in the homogeneous drying of the product.
Technology transfer When scaling up the processes, the following key parameters must be taken into consideration for a positive technological transfer on a filter dryer: the heat transfer area; the agitator type; and the product cake depth.
Te heat transfer area efficiency must be determined for both size agitated nutsche filter dryers.
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