We have examined the rejection properties of nanofiltration (NF) membranes
for alkyl phthalates and other solutes such as mono-substituted benzenes, a
lcohols, and saccharides. In this study, four kinds of NF membranes were us
ed, each with nominal desalting degree (NaCl rejection) of 91, 60, 51, and
15%, respectively. The membrane separation experiments were carried out wit
h a bench scale batch type cell at room temperature.
The rejection of alcohols and saccharides was mainly controlled by steric h
indrance. We have found that molecular width is a useful descriptor to repr
esent this effect. On the other hand, the rejection of aromatic compounds,
alkyl phthalates and mono-substituted benzenes, was strongly affected by th
eir hydrophobic properties (log P).
Higher hydrophobic alkyl phthalates (log P > 4.7) were rejected at more tha
n 99% even by the lowest desalting membrane. The highest desalting membrane
rejected almost all alkyl phthalates at more than 96%. However, p-dimethyl
phthalate and p-diethyl phthalate showed significantly lower rejection, fr
om which it can be concluded that their molecular widths are close to those
of mono-substituted benzenes, i.e. smaller than those of the other alkyl p
hthalates. (C) 2001 Elsevier Science B.V. All rights reserved.