NAMS 2002 Workshop - ICOM 2008

Composite Polymeric Membrane Formation – 4
Monday July 14, 4:00 PM-4:30 PM, Waialua
Preparation of Poly(vinyl alcohol) Composite Reverse Osmosis and
Nanofiltration Membranes
G. Ramos (Speaker), Federal University of Rio de Janeiro, PEQ, Chemical Engineering, Brazil,
gaby@peq.coppe.ufrj.br
B. Cristiano, Federal University of Rio de Janeiro, PEQ, Chemical Engineering, Brazil
Nowadays, in reverse osmosis (RO) and nanofiltration (NF) processes, the thinlayer
composite polyamide (PA) membrane is accepted as a reference system.
These PA membranes are widely commercialized for these processes due to
their excellent saline rejection and hydraulic permeability. However, one of the
major factors reducing the overall performance of the RO and NF processes is
fouling. Membrane fouling can cause irreversible loss of system productivity.
Among the types of fouling, biofouling is the one of the most serious fouling
problems and polyamide membranes are particularly susceptible to it.
In addiction, the major concern with PA membranes is their lost of performance
when exposed to oxidizing agents, such as aqueous chlorine, commonly used in
water disinfection. It is known that after an exposition to chorine of 500 to 2,000
ppm.h membranes salt rejection decreases and the water flux increase. In order
to protect the membrane, the chlorine should be completely removed in the pretreatment
stage, increasing costs and allowing the growth of microorganisms
throughout the system and, especially, the formation of biofilm on the surface of
the membrane. Also, sodium bi-sulfite, added to remove chlorine, attacks the PA
membrane under presence of heavy metals, such as Cu, Co, etc.
New polymer material with enhanced resistance to fouling and oxidation is
subject of many research works. By far, the simplest technique to prepare a
composite membrane is the dip-coating using a diluted polymer solution, which
allows the use of several polymers to prepare the top layer. Poly(vinyl alcohol)
(PVA) is an attractive material because it is an hydrophilic polymer with low
fouling potential, has chemical stability, low cost and it can be easily deposit on
top of many existing porous supports. Furthermore, the hollow fibers have
advantages in relation to the flat membranes: they are self supported and
appropriated for compact modules with large area of membrane.
The aim of this work is to investigate the synthesis of reverse osmosis and
nanofiltration composite membranes by using PVA as top layer, prepared by dip
coating technique. The molecular packing density of PVA dense layer was varied
by choosing the parameters that affect the crosslinking reaction of PVA
molecules. The PVA 80 and 99% hydrolyzed was crosslinked by using different