One step filtering

The glass filter dryer is changing the filtration and drying process in laboratories worldwide. Amanda Pitcher reports.

Since the 19th century chemists have used the commonly known method of Buchner filtration which would then be followed by the use of a tray dryer or other method to complete the drying phase. In 2010, glass filter dryer (GFD) technology was launched combining filtration, cake washing and drying all in one step.Working as a miniature agitated nustche filter dryer this technology allows laboratory development simulating the manufacturing process at a small scale.

The filtration area of the smallest size 'Mini Lab' GFD covers 0.002m2 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. Then the' Lab' GFD size includes a removable filtration basket of 0.01m2 for a cake volume around 0.5L for small scale synthesis, when the 'Maxi Lab' GFD is used within Kilo-Laboratory for a cake volume of 5L with 0.05m2 filtration area.

The 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 while the unique 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.

The glass vessel is of borosilicate 3.3 construction and is pressure rated to 0.5barg. 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.

The heated jacket is then used to heat the vessel for the drying phase. The vessel is rated to temperatures between -25°C and 150°C, and it is not uncommon for the GFD to be also used for the filtration of unstable products at low temperatures. The 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.

The filtration and drying times for calcium carbonate in water in a Maxi Lab GFD are highlighted in graph 1. Tests were performed under a 0.5barg pressure for 30min to assist filtration of the solvent (deionised water) layer in 3kg of calcium carbonate. Then loss on drying was performed on a wet cake sample.

Vacuum at -0.8barg and heating at 75°C was applied to the Maxi Lab GFD for eight hours with insulation jacket fitted to the vessel.

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Amanda Pitcher is Product Manager, Powder Systems Ltd (PSL), Liverpool, UK.

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