SEPARATION OF NANO PARTICLES USING BOKELA’s DYNO FILTER
The dynamic Cross Flow Filtration — the solution for a highly topical challenge
Dr. Thomas Langeloh, Dr. Reinhard Bott, Egon Ehrfeld
BOKELA GmbH, 76131 Karlsruhe, Tullastr. 64, Tel.: +49 (0)721/96 456-0
Suspensions and dispersions containing nanoscale particles are becoming an increasing challenge inthe field of separation technology. As a part of the process technology, the separation techniques aretherefore confronted with a completely new and unusual task profile. The filtration of these kinds ofsuspensions is consequently an especially ambitious and a highly relevant mission.
The traditional separation procedures, such as cake forming filtration and centrifugation, operate
mainly within the micron spectrum whereby forces of gravity determine primarily the prevailingseparation physics. In the sub-micron spectrum, however, the micro filtration and ultra-filtration
procedures are applied in great variety besides some adapted traditional separation technologies.
For these sub-micron suspensions the separation physics are more determined by phenomena
arising from surface forces. Dipole behavior and other influences deriving from chemical processes
such as zeta potential, isoelectric point, etc. are dominating and the traditional separation theories
are only partially valid. Not only the separation behavior of nanoscale suspensions is changed but
also the aim of the separation procedures is a different one in the sub-micron spectrum. In thiscontext, excessive dewatering or even total de-liquoring is not permissible. Therefore, these tasks
require separation procedures with innovative and unusual profiles.
The BOKELA DYNO Filter, however, provides new opportunities. Both, the process and apparatus ofthe DYNO Filter fit almost perfectly to the requirements of nano-scale suspensions. The DynamicCross Flow Filtration has been known and been applied for rather a long time. BOKELA, however,developed this filtration process into the new DYNO Filter and thus, discovered completely newsolutions by an innovative process design. Thanks to the filtration of nano-scale suspensions, theDYNO Filter is now entering an especially challenging and promising area of applications.

The dynamic Cross Flow Filtration, obtained excellent results. In order to solve the given task, a DYNO
Filter with a 6 m2 filter area and equipped with a polymer membrane is required. With an initial
particle concentration of 7% of the total weight, the nano particles are thickened up to aconcentration of 23% in the DYNO Filter and undergo a washing procedure afterwards. During thisstage, a 1.000 fold reduction of the ion concentration is obtained. As a consequence, the pH value isreduced from 14 to the targeted value of 11. At the same time, an entire separation of particles isachieved whereas the filtrate is turned into a solids free liquid. At slightly lower throughput rates, aconcentration up to 40% can be obtained.
Further nano-scale suspensions used in the chemical, pharmaceutical and pigment sector as well as
in the area of environmental protection, were examined on their processing characteristics in
BOKELA's large-scale tests. The results have proved not only the feasibility but also the superiority of
the Dynamic Cross Flow Filtration with the DYNO Filter compared to other separation processes: anentire separation of particles, high filtrate flows, high thickening concentration, and excellent
washing results.

SEPARATION OF NANO PARTICLES USING BOKELA’s DYNO FILTER
The dynamic Cross Flow Filtration — the solution for a highly topical challenge
Dr. Thomas Langeloh, Dr. Reinhard Bott, Egon Ehrfeld
BOKELA GmbH, 76131 Karlsruhe, Tullastr. 64, Tel.: +49 (0)721/96 456-0
Extensive Field testing with the BOKELA DYNO filter for different nano-scale suspensions used in thechemical, pharmaceutical and pigment sector as well as in the area of environmental protection, wasconducted. The results have proved not only the feasibility but also the superiority of the Dynamic
Cross Flow Filtration with the DYNO Filter compared to other separation processes: an entire
separation of particles, high filtrate flows, high thickening concentration, and excellent washing
results.