surface filtration in oscillatory shear


Removal of fines (undersize) from a particulate product
(i.e. Diafiltration of fine particles from a suspension)
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Equipment for washing fines from a particulate product

When operating at high shear a deposit, or secondary membrane, can be completely eliminated. Thus, it is possible to pass the finer particles in a distribution through a membrane whilst retaining the coarser ones. If fresh liquid is added to the system the fine particles can be washed out in a type of Diafiltration process. Hence, it is possible to remove the fines from a suspension of particles.

The economics of a diafiltration process are improved if the solvent forming the permeate can be recycled to wash more particles from the system. In this case, a second VibraFilter with a finer membrane is used to recover the solvent which is then recycled back to the diafiltration stage to wash more fines out.


Removal of fines by washing, also known as Diafiltration In this example the removal of material below 4 microns was required in a very high value product. The vessel size for the diafiltration was 0.5 litres and solvent was recycled according to the above schematic diagram.

The initial distribution shows a large number of particles less than 4 microns - the distribution is almost linear on the concentration scale. After one litre had passed through the VibraFilter, using a 5 micron slotted membrane, the distribution is developing a prominent mode between 5 and 6 microns. After three litres have passed only a small residual amount of sub-4 microns material is left.



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