The hydraulic permeability of the membrane for
water, methanol, ethanol, n-propanol and n-octanol
74 A. Dafinov et al. / Journal of Membrane Science 196 (2002) 69–77
were determined in order to highlight the hydrophilic
characteristics of the membrane. After each solvent
test, the membrane was regenerated as described in
the experimental section in order to remove any possible
chemisorbed compound. The water permeability
obtained after each regeneration was progressively
increasing from 3.6×10−17 to 7.0×10−17 m2, which
indicates that the thermal treatment damages the
membrane structure to some extent. Assuming that,
the interaction between water and the pore surface
was not changed by the regeneration procedure, the
pore size estimated from Eq. (2) goes from the original
6.3 to 8.8 nm after the last regeneration. Therefore,
the test-to-test change in pore size could invalidate
the comparison of solvent permeabilities if this is just
done in terms of permeability constants. To overcome
this drawback, the comparison will be done in terms
of normalised permeability constants as defined by
Eq. (3), which only accounts for interactions between
the solvent and the membrane material. Thus, as can
be seen in Table 2, the normalised permeability constant
for water is 0.91 whereas this parameter ranges
from 0.39 to 0.53 for normal alcohol. Hence, as expected,
the alumina membrane shows hydrophilic
characteristics that facilitates the pass of water across
the membrane. The similar values obtained for the alcohol,
regardless of their molecular size, suggest that
the permeation could be strongly influenced by the
interactions between the alcohol functional groups
and the hydroxylated surface of alumina. Only, the
larger n-octanol shows a significantly lower permeability.
This higher difficulty to permeate could be