W. Richard Bowen and Nidal Hilal 4

126 4. INvEsTIgATINg MEMbRANEs ANd MEMbRANE PROCEssEs
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gave very good separation with little fouling. By quantification of the
fraction of humic acids deposited during filtration, it was possible to
show that both planar (S5-20) and tubular (T5-20) versions of the membranes
showed high critical flux values, whereas membranes already in
commercial use for such separations (CA202 and ES404, PCI Membranes)
did not show such a favourable property, Figure 4.22 [11].
To allow for the different membrane geometries, the data in Figure 4.22
is expressed as critical Peclet numbers (J/k, where J is the flux and k is
the mass transfer coefficient). The critical Peclet numbers were 4.6 and
6.4 for the planar and tubular membranes respectively. Further details of
the development of PSU/SPEEK membranes are given in Chapter 5.
4.8 ChARACTERISATIOn OF METAL SURFACES
The surface properties and morphology of process equipment surfaces
are of fundamental importance in the fulfilment of their purpose and
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FIgURE 4.21 High-resolution images of unmodified membrane (left) and membrane
modified with 5% SPEEK (right, S5-20).
TAbLE 4.5 Normalised Adhesion Forces for a Range of Colloid Probes at a PsU/
sPEEK Membrane (s5-20).
Materials Mean F/R (mN m �1 )
SPEEK/PSU PSU
Silica 0.84�0.35 6.5�0.8
Cellulose 0.51�0.23 2.2�0.32
Latex 2.1�0.52 14.3�0.8
BSA 1.4�0.64 12.3�1.4
Yeast 3.2�0.85 9.5�1.5
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