fluXXion’s technology should be categorised as cross flow micro filtration technology. Contrary to existing micro filtration products, the fluXXion micro sieves are made from a 150 mm diameter silicon wafer (standard in the semiconductor industry). The wafer is coated with a one-micron thick layer of silicon nitride which is the basis for the micro sieves. Using a specialized semiconductor technology, pockets are etched into one side of the wafer, forming a supporting frame for the covering silicon nitride layer that forms the micro sieve. In the next step, millions of (sub) micron-sized holes are etched through the separation layer with advanced semiconductor processes.

The ultimate goal in micro filtration is to achieve a micro sieve with a low flow resistance, a high chemical and temperature resistance and a well-controlled pore size distribution. No better way of achieving these goals than using semiconductor technologies for micro sieve production. This industry has a very long experience in high volume, high quality production of products with extremely small dimensions with ongoing research towards even smaller sizes. The result: fluXXion micro sieves made out of silicon nitride, one of the most inert materials. Thanks to the lithographic technologies employed, the pore size distribution is much more narrow than can be achieved with conventional membrane fabrication methods. The absolute pore size is also very well controlled, leading to very good separation characteristics. The main advantage of a filter characterized by a thin separation layer and having uniformly sized pores with very short lengths (~ 1 µm) is the very low flow resistance. The fluxes achievable with these micro sieves and the durability against chemical attack proved invaluable in several areas. However, due to their low flow resistance, process settings are much different from conventional membranes and developmental work had to be done to optimise the product and the filtration process.

Generally, liquid products that need to be filtered have a high fouling nature. This limits the permeate flux of most filter types. In the micro filtration installations, typical permeate fluxes in cross flow filtration are in the range of 20 to 400 litres of filtrate per hour per square meter of membrane as opposed to the fluxes of fluXXion which could be up to 100 to 200 times higher. Although there are many new technologies, they still don’t match the obtained fluxes of the fluXXion micro sieves. The main strengths of micro sieves are the low-pressure operation and the extremely high fluxes. The smooth surface and the chemical inertness of the micro sieves makes them rather insensitive to fouling, leading to long intervals between cleaning. Apart from these favourable characteristics fluXXion also developed the unique D(ynamic) C(ross flow) P(ulsing) technology followed by a much improved version the I(ntensified) C(am) A(ctivated) P(ulsing) technology. A highly frequent backpulse of up to 20 Hz keeps the micro sieve continuously clean during filtration by breaking up the fouling deposit layer on the micro sieve. The effect is an even longer filtration cycle without the use of cleaning chemicals at very low power consumption. In effect not only very long filtration runs are possible before cleaning is finally needed but also the cleaning time itself is very short.