Björn Hobus outlines the advantages of carrying out filtration using pre-folded paper filters. Here he describes what to look for in a suitable filter paper.In almost every analytical laboratory for example in quality assurance in the food industry or in environmental institutes filtration processes are performed using paper filters.
However much the investigations may differ from one another, the aim of the filtration process is always the same in the end: particles must be separated from a medium in as large a quantity and as quickly as possible.
Efficient filtration
A suitable filter paper must be carefully selected to ensure an efficient filtration process. The composition, thickness and density of the paper used will depend on the type, quantity and size of the particles to be separated, as well as the properties of the filtered medium.
The combination of these factors will in the end determine the degree of separation and the speed of the filtration process.
During filtration particles are retained and are continually deposited in the filter matrix, thus causing a significant reduction in the flow rate.
In the case of larger quantities of liquid that are heavily loaded with particles or contain clogging substances, such as, for example, mucilaginous substances, sugar and dextrin, this can lead to undesirably long filtration times.
The use of folded filters is the obvious solution here, particularly when the filtrate is needed, as they make efficient filtration possible. Folded filters have a number of advantages that help save time and money.
Advantages of folded filters
1. Time is saved even when placing the filter into the cone, as, unlike with a round filter, it is not necessary to fold it into four. All you have to do with a folded filter after taking it out of the packet is open it and then place it directly in the conical funnel.
2. With a round filter folded into four only half of the surface of the paper can in effect be used for the filtration process (and half of this again is in three layers on top of each other), whereas with a folded filter the entire surface of the filter paper is available for the filtration process.
As a result the total filtration time is reduced by as much as 50 per cent in comparison with round filters folded in four.
3. In contrast to the round filter, where the entire surface is in contact with the side of the funnel, only individual lines of folded filters are in contact with the filter, corresponding to the number of folds.
This creates channels enabling the filtrate to drain away freely while at the same time producing a suction effect together with the base of the funnel. The overall result is an improved filtration effect with an increased flow rate.
4. Because a folded filter has a larger useful area it has a significantly higher total capacity for absorbing particles than a round filter. Greater volumes can therefore be filtered without the usual falling off in the filtration speed.
The example of a medium-sized German brewery should make clear the advantages of using folded filters.
Approximately 20 000 filters are required annually in quality assurance, for example, for the filtration of the mash (analysis of malt and wort) and for decarbonating the beer.
As fig. 1 shows, there are admittedly somewhat higher material costs involved with the use of folded filters, but, on the other hand, considerable savings can be achieved in personnel costs due to easier handling and shorter filtration times.
In the brewery described here the total filtration costs are lower by around 10 000E, corresponding to a cost reduction of about
30 per cent. u
ENQUIRY No 72
Björn Hobus is product manager with Schleicher & Schuell GmbH,
Dassel, Germany. www.s-and-s.com
