Agitated Nutsche Filter Dryers vs Büchner Funnels

June 8, 2022

The Nutsche agitated filter dryer and Büchner funnel are designed to perform the same fundamental task: solid-liquid separation. There are, however, significant differences between the two in terms of features and applications.

How does a Büchner funnel work?

The Büchner funnel is a common piece of chemical laboratory equipment designed for filtration. The mechanism is relatively simple: the funnel contains either a perforated plate (on which a paper filter is placed) or a sintered glass plate which can be used without a paper filter. The narrow part of the funnel is usually sealed to a side-arm flask (also known as a Büchner flask), with the flask arm connected via a tube to a vacuum pump. The liquid to be filtered is poured into the top of the funnel and is drawn through the paper/sintered glass filter by a combination of gravity and suction provided by the vacuum pump. Suspended solids are filtered out and the filtrate collects at the bottom of the side arm flask.

Typically made of porcelain, glass, or plastic, Büchner funnels are inexpensive pieces of equipment that provide much faster filtration than simply allowing gravity to draw liquid through a filter. Büchner funnels support a relatively wide range of applications. For example, funnels about an inch in diameter are common on chemistry lab benches. In contrast, large models up to around one meter in diameter can support pilot plant scale applications (often using ‘trowels’ to manually smooth out cracks in the compacted solid material) . Troweling the cake in this manner introduces the problem of operator variability and human error.

However, for industrial applications – especially pharmaceuticals or fine chemicals – Büchner funnels are generally avoided in favor of Nutsche agitated filter driers.

How Nutsche Agitated Filter Dryers Work

A Nutsche agitated filter dryer is specialized equipment designed to provide a more sophisticated method of filtration than Büchner funnels.

Nutsche agitated filter dryers use a blade drive assembly to provide low speed, high torque agitation/mixing of the sludge, ensuring that the height of the “cake” (i.e. the filtered solids ) has no impact on the filtration rate. One of the main differences between an agitated Nutsche filter dryer and a Büchner funnel is that, while Büchner funnels only provide bottom suction, agitated Nutsche filter dryers provide both bottom suction and pressure from above. The result is faster filtration and a much lower moisture content in the filtered solid.

As the filtration progresses, the blades inside the Nutsche agitated filter dryer move up the cake to automatically smooth out cracks and/or preferential channels. Therefore, operator variability is not an issue as with the smoothing process in the Büchner funnel.

Once the solids have been completely separated, an agitated Nutsche filter dryer will remove any remaining filtrate and impurities. Büchner funnels take care of washing, but Nutsche agitated filter-driers offer superior washing either by traditional methods (in which a solvent percolates through the product cake) or by resuspension washing (similar conventional washing but using the agitator to force the solvent into the cake before pressing – this reduces the amount of solvent needed and optimizes the removal of impurities).

The similarities between the two different filter types diverge here, with Nutsche agitated filter dryers gaining additional benefits. Products discharged from a Büchner funnel should be dried in secondary equipment, such as a tray dryer or desiccator. Both drying methods are small-scale, which makes them understandably unsuitable for many industrial applications.

By comparison, the filtered and washed solids are dried in an agitated Nutsche filter drier. This can be done either by pressurized gas heating or by vacuum assisted heating. The agitator plays an essential role in ensuring the homogeneity of drying and in breaking up difficult products.

Finally, the product is discharged from the agitated Nutsche filter dryer. The agitator again plays a primary role by gradually pushing the cake towards the discharge valve.

For all applications that require high performance filtration, Nutsche agitated filter dryers allow fast and efficient batch processing of up to 1000L.

It should also be noted that stirred Nutsche filters provide a fully enclosed environment that allows for certain processes that may be difficult or impossible with a Büchner filter. Many very potent toxicants and a range of volatile solvents should be handled with care using a Büchner filter, possibly requiring external ventilation. This is not the case with a stirred Nutsche filter.

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Powder Systems Ltd. offers a complete line of high performance Nutsche agitated filter dryers suitable for all applications from R&D to commercial manufacturing. Contact PSL today to learn more.

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