NAMS 2002 Workshop - ICOM 2008

Nanofiltration and Reverse Osmosis II - Imaging and Characterization – 6
Tuesday July 15, 11:30 AM-12:00 PM, Maui
Evidence of Change in the Top Surface Layer Structure of Nanofiltration
Membranes Due to Operating Temperature Variation
H. Saidani, Ecole Nationale des Ingénieurs de Tunis, France
B. Nihel, Ecole Nationale des Ingénieurs de Tunis, France
P. John, Université Paul Sabatier, France
D. Andre (Speaker), Université Montpellier 2, France, Andre.Deratani@iemm.univ-montp2.fr
The applications of nanofiltration (NF) in the treatment of water and wastewater
is developing very quickly. Of special concern for this application is the influence
of temperature on the performances of NF membranes, because water to be
treated can be at temperatures higher than 40°C. The temperature effect is not
yet well understood [1] and is usually described through a simple correction
factor applied to the water permeability. The present report shows the influence
of operating temperature variation on the permeability and the rejection of neutral
and charged solutes. Two commercial NF membranes were used in the course
of this study, the DESAL DK (GE Water Technologies -USA) and NF90 (Dow /
Filmtec - USA).
The results obtained show an important variation of membrane performances
with temperature change both in terms of flux and rejection. Interestingly, while
the DESAL DK exhibits the expected flux increase (due to a decrease in solution
viscosity) and rejection decrease with increasing temperature, the NF90 shows
the opposite trend. Moreover, it was observed that this variation becomes
irreversible if the operating temperature exceeds a critical temperature (Tc),
which depends on the membrane type.
To understand these phenomena, the thermal behavior of the top surface layer
for each NF membrane was investigated. It was found that Tc corresponds to the
glass transition temperature Tg of the polymer constituting the membrane top
active layer. The pore size and effective layer thickness were estimated using the
Nanoflux® NF modeling software [2].
The NF data are interpreted in terms of structural changes occurring during
temperature cycles that are intimately related to the intrinsic thermal properties of
the polymeric materials.
[1] Nihel Ben Amar, Hafedh Saidani, André Deratani, John Palmeri, Effect Of Temperature On
The Transport Of Water And Neutral Solutes Across Nanofiltration Membranes, Langmuir 23,
2937 (2007).