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Concentration of valuables from aqueous product solutions


The concentration of product solutions in the food industry, chemical industry
and pharmaceutical industry is often performed using thermal processes.
The solvent, water, is typically evaporated in a multi-stage evaporation
process at temperatures of up to 130°C until the desired residual content is
achieved. In spite of improvements, the technology remains highly energyintensive and linked to high thermal loads on product materials.


The aim of the research conducted by the work group led by Professor
Harasek in the area of „Thermal Process Engineering & Simulation“ at TU
Wien was to develop alternatives to the conventional evaporation process
with significantly lower energy requirements. The procedure must be able to
be used for a wide range of concentrations and should be based on industrially
available components, in order not to be tied to one or a few component

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The use of the membrane separation process of reverse osmosis or nanofiltration
for the concentration of product solutions, such as sugar solutions,
fruit juices, lactic acid and amino acid solutions is well known. However, due
to the high osmotic pressure and high viscosities, limits are quickly reached
for these processes. The idea of the research team was to develop a multistage
membrane process – from a combination of reverse osmosis and at
least two nanofiltration stages.


In this process, membranes with lower retention capacities are deliberately
used, so that the osmotic pressure difference can be controlled very precisely
at every stage and lower process operating pressures of as low as 40 bar are
sufficient. With intelligent recovery of the separated flows of recyclable
materials into the upstream process steps, loss of valuable material is minimised.
Water is only discharged in the reverse osmosis stage. As a result of
the low process temperature – in comparison to the evaporation method –
product quality increases. The number of stages can be adapted depending
on the requirements for the concentration.



The team of researchers has already demonstrated it developement in a three-stage reverse osmosis/
nanofiltration system. The pilot system is fully automated and can be used at operating pressures of
up to 60 bar and temperatures of up to 80°C. Comprehensive test results are already available for
the concentration of diluted sugar syrup with a wide range of different membrane combinations. The
prototype successfully confirmed energy savings of over 50% compared to the conventional multi-stage evaporation process.


There are no particular restrictions on the selection of the product material
to be separated in the process designed by TU Wien. Here, sugar solutions
or fruit juice, or solutions of lactic acid or a salt thereof, amino acid solutions
or other aqueous, non-aqueous or mixed aqueous/nonaqueous solutions
can be used, as for example occur in the chemical, pharmaceutical and biotechnology
This technology is particularly suitable as a pre-concentration step in conventional
evaporation processes – for example in the sugar industry – or anywhere
conventional pressure-driven membrane separation processes are used.

  • Reduction of more than 50% in the thermal energy requirement for the evaporation
  • Operation also possible with high concentrations of product materials and viscous media
  • Multi-stage reverse osmosis/nanofiltration process instead of conventional evaporation
  • Higher energy efficiency and lower operating pressures than conventional membrane methods thanks to intelligent process circuit
  • Integrability/Debottlenecking of existing systems
  • Simple scale-up based on data
  • Fully automated demonstration system with approx. 50 m² of installed membrane surface area ready for use in the technical centre for customer tests
  • Several months of operational experience already shown with the demonstration system
  • Design model for estimation of energy savings

DI Dr. Tanja Sovic
+43 1 58801 41537
Karlsplatz 13
1040 Wien




energy saving, environmental friendly nanofiltration, reverse osmosis

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