The Büchner funnel and the agitated Nutsche filter dryer are built to perform the same basic task – solid-liquid separation. However, there are important distinctions between the two when it comes to functionality and applications.
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This article will outline the advantages of the agitated Nutsche filter dryer compared to the simpler Büchner funnel.
How Does a Büchner Funnel Work?
The Büchner funnel is a well-known piece of chemical lab equipment built for filtration. The mechanism is quite simple: the funnel has either a perforated plate fitted with a paper filter or a fritted glass plate without a paper filter.
The narrow part of the funnel is usually sealed to a side-arm flask, or Büchner flask, with the flask arm connected to a vacuum pump via a tube.
The liquid that is to be filtered out is then poured into the top of the funnel and pulled through the paper filter or fritted glass via a combination of gravity and suction generated by the vacuum pump. Suspended solids are trapped by the filter, while the filtrate accumulates in the bottom of the side-arm flask.
Usually made out of glass, porcelain, or plastic, Büchner funnels are affordable pieces of equipment that offer quicker filtration than simply waiting on gravity to draw liquid through a filter.
Büchner funnels are able to support a respectably varied number of applications. For example, funnels with a diameter of around one inch are commonly found on chemistry lab benchtops.
In contrast, large models of up to around a meter in diameter can support pilot plant scale applications (often with the aid of“trowels” to manually smooth over fissures in the compacted solid material). Troweling the cake in this manner, however, introduces the problem of operator variability and human error.
However, for industrial applications – especially pharmaceuticals or fine chemicals –agitated Nutsche filter dryers are often chosen over Büchner funnels.
How Agitated Nutsche Filter Dryers Work
An agitated Nutsche filter dryer is a specialist piece of equipment built to offer a more sophisticated filtration method than Büchner funnels.
Agitated Nutsche filter dryers make use of a bladed drive assembly for low-speed, high-torque agitation/mixing of the slurry, which ensures that the height of the “cake” (i.e., filtered solids) has no effect on the filtration rate.
One important distinction between the agitated Nutsche filter dryer and the Büchner funnel is that Büchner funnels provide suction from underneath, while agitated Nutsche filter dryers can offer suction from below and pressure from above. This means quicker filtration and significantly lower moisture content in the filtered solid.
The blades in the agitated Nutsche filter dryer rise to the top of the cake as filtration advances, automatically smoothing out cracks and/or preferential channels. Operator interference is not an issue using this method, as it can be with the Büchner funnel.
Following full separation of the solids, an agitated Nutsche filter dryer washes out any remaining impurities and filtrate.
Büchner funnels are able to support washing, but agitated Nutsche filter dryers offer better washing whether using traditional methods (where solvent seeps through the product cake) or by re-slurry washing (where the agitator plows the solvent into the cake before pressing). Re-slurry washing limits the amount of solvent needed and optimizes impurity removal.
This is where the similarities between the different types of filters split, as the agitated Nutsche filter dryers offer additional advantages.
Once discharged from a Büchner funnel, products require drying in a secondary piece of equipment, like a desiccator or tray dryer. These methods are both small-scale, making them unworkable for many industrial applications.
By comparison, filtered and washed solids are dried within an agitated Nutsche filter dryer. This can be carried out by either pressurized gas heating or vacuum-assisted heating.
The agitator plays a vital role by providing drying homogeneity and breaking down difficult products. Finally, the product is discharged from the agitated Nutsche filter dryer. The agitator once again plays a vital role by gradually pushing the cake to the discharge valve.
For all high-performance filtration applications, agitated Nutsche filter dryers enable quick and effective processing in batches of up to 1000 L.
It is also important to note that agitated Nutsche filters offer a completely enclosed environment, which allows for the completion of processes that can be difficult or even impossible with a Büchner filter.
This can include toxic, highly potent products and an array of volatile solvents, which must be handled carefully using a Büchner filter and may require external ventilation. This is not necessary with an agitated Nutsche filter.
This information has been sourced, reviewed and adapted from materials provided by Powder Systems.
For more information on this source, please visit Powder Systems.