A pharmaceutical suspension is synthesized such that a significant amount of salt is formed during neutralization. This micro-fine suspension is washed out of salt by diafiltration and further concentrated. Initial salt concentration is about 10% and the active ingredient is around 3.5%. The desired final concentration is almost no salt (< 0.1%) and 7.5% active ingredient.

The fineness of the suspension requires microfiltration. With conventional crossflow technology a further concentration of the suspension is impossible due to the high viscosity. Therefore, dynamic crossflow filtration is required. Systems with rotating ceramic discs have too low throughput and require 100 m² filter area. Hence the BoCross Dynamic Filter is the only available technology for this challenging separation task.

Three 8 m² BoCross Dynamic Filters are applied for thickening and washing of this viscous suspension achieving the target values of 7.8% active ingredient and 0.1% salt.

BoCross Dynamic Filter L8 – Hygenic Design

Units installed

[ - ]


Filter area per unit




[ - ]

1.4435 (316 L)

Filter drive power



Foot print per unit



Year of commissioning

[ - ]

2 units in 2008 / 1 unit in 2016


Process and Operation Data

Solids content in feed

[wt -%]


Solids content in retentate

[wt -%]


Solids content in filtrate


Free of particles

Washing out of salt

[ - ]

1 : 100

Operation pressure

[bar, g]

1.5 – 3.0


Product Data

Product   Iron hydroxide (pharmaceutical product)
Range of particle sizes [µm] 1 – 50
Flow behaviour ­ thixotropic


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