Raising the filtration standard

Michael Sidebottom, from Carlson Filtration, highlights the latest developments in depth filtration

Two years ago,¹ depth filtration techniques, traditionally best known for filtering foods and beverages, were being developed to suit the demands for increasing filtration performance by fine chemicals and pharmaceuticals manufacturers.

Industry reports suggest that since then depth filter manufacturers have continued to invest in developing higher and higher filtration performance. So what has actually been happening in the last couple of years?

Tony Duffy, technical development centre manager at UK depth filtration sheet manufacturer Carlson Filtration, has been concentrating his team's efforts on two areas:

• Developing depth filters containing various grades of activated carbon. Activated carbon is incorporated into depth filter sheets, in order to improve the sheet's selective adsorptive ability and hence remove colour bodies, colour precursors and other impurities from intermediates and finished products alike;

• Lenticular filter module design. These modules are used in a simple housing and present an excellent alternative to depth filter sheets in a press.

'Our main challenge has been to optimise selective adsorption for individual customers, as well as focusing on their use in lenticular module format,' Duffy explained.

As far as selective adsorption is concerned, in Carlson's case, this has included examination of the adsorptive performance characteristics of activated carbons derived from different original base structures. As a result the company has introduced a new range of carbon-containing sheets, called CarlCarb (figure 1)

A typical three to five-fold increase in adsorptive capacity, resulting in higher filtration capacity and higher filtrate purity levels is the sort of performance enhancement achieved. This in turn has led to:

• an increasing range of applications in which CarlCarb can be used;

• incorporation of lower cost carbon bases which opens up the range of applications for which CarlCarb presents an economic solution;

• increased manufacturing process flexibility, which allows Carlson to offer a bespoke individual CarlCarb product development service.

greater tolerance

As far as lenticular module design is concerned, Carlson looked for ways of achieving tolerance to ever-greater pressure differentials across the module, thereby allowing increased secure filtration capacity; enhanced resistance to pressure 'shock' on the module, for example at start up; and ease of installation in the housing thereby minimising changeover time.

The work programme was based on building a new test rig, which includes instrumentation for monitoring operating conditions pre-filtration, inside the module and post filtration. This allows simulation of extreme operating process conditions and hence secure operating and performance limits. Carlson's new CarLent lenticular module has been launched as a result of this work.

module design

The development concentrated on three main aspects of module design:

• a new inter-cellular sealing mechanism and end cap design, allowing manufacture using much greater assembly pressure, giving increased resistance to pressure shock and differentials across the module

• a new centre core support mechanism and separator ring design that maintains zero fibre release. This allows the new CarLent series to be used for high purity applications, where alternative filtration methods have had to be used in the past.

• an inter-modular flat gasket design, which eliminates the need for a costly and inconvenient double o-ring bayonet sealing system.

The field of solid/liquid separation has a wide variety of applications including pharmaceuticals, beers and lagers, distilled spirits, fruit juices, chemicals, gelatine and other food products.

Carlson's range of sheet filter presses, filter sheets, lenticular housings and modules are produced to the manufacturing systems detailed in its drug master file, number 14255 - assigned by the US Food and Drug Administration - and these latest developments have ensured that depth filtration is attaining the higher and higher performance standards needed by the industry.