Loeb-Sourirajan phase inversion

Loeb-Sourirajan phase inversion Composite asymmetric membranes ... 

Phase inversion is a process in which a polymer is transformed from a liquid to a solid state. There are a number of methods to achieve phase inversion. Among others, the dry-wet phase inversion technique and the temperature induced phase separation (TIPS) are most commonly used in the industrial membrane manufacturing. The dry-wet phase inversion technique was applied by Loeb and Sourirajan in their development... 

Cellulose acetate is the material for the first-generation reverse osmosis (RO) membranes. The announcement of cellulose acetate membranes for seawater desalination by Loeb and Sourirajan in 1960 triggered the applications of membrane separation processes in many industrial sectors. Cellulose acetate membranes are prepared by the dry-wet phase inversion technique. 

Hyperfiltration, particularly RO, was the first membrane process to be run on an industrial scale, as early as the 1960s [1,3]. The great breakthroughs here were the invention in the early sixties by Loeb and Sourirajan [4] of asymmetric membranes prepared via phase inversion and the development of membranes prepared via interfacial polymerization [5]. The membranes appHed are densified even more than those for UF and a Hmit is reached membranes may get so dense that the... 

Based on the pioneering work of Loeb and Sourirajan [4], membranes prepared according to the phase-inversion technique form the most important group of NF/RO-membranes, together with those prepared via interfacial polymerization... 

The membrane is the heart of any membrane-based separation processes. Initial breakthrough in membrane technology came from the phase inversion technique developed by Loeb and Sourirajan. The membrane prepared by adopting... 

An RO membrane acts as a barrier to flow, allowing selective passage of a particular species (solvent) while other species (solutes) are retained partially or completely. Solute separation and permeate solvent (water in most cases) flux depend on the material selection, the preparation procedures, and the structure of the membrane barrier layer [5,15]. Cellulose acetate (CA) is the material for the first generation reverse osmosis membrane. The announcement of CA membranes for sea water desalination by Loeb and Sourirajan in 1960 triggered the applications of membrane separation processes in many industrial sectors. CA membranes are prepared by the dry-wet phase inversion technique. Another polymeric material for RO is aromatic polyamide [16]. 

The first breakthrough came in 1959 when Sourirajan and Loeb discovered a method to make a very thin cellulose acetate (CA) membrane using the phase inversion method [4]. This technique produces homogenous membranes with an asymmetric (or anisotropic) structure. The membranes were subsequently found to be skinned when examined under an electron microscope by Riley in 1964 [3]. The membranes consisted of a very thin, porous salt-rejecting barrier of CA, integrally supported by a fine CA porous substrate. Pictures of asymmetric membranes are shown in Figures 1.2 and 1.3. These early Loeb-Sourirajan (L-S) membranes exhibited water fluxes that were lOtimes higher than those observed by Reid, and with comparable salt rejection [5]. The membrane flux was 8—18 1/m /h (knh) with 0.05% NaCl product water from a 5.25% NaCl feedwater... 

The importance of the thickness of the membrane is evident from Equation (1.1) since flux is inversely proportional to thickness. The Loeb—Sourirajan RO membranes produced by the phase-inversion technique have an effective skin thickness of 0.1-0.2 pm that makes it possible to achieve acceptable fluxes (2—20 l/m" /h) at reasonable feed pressures (30—60 bar g) for water desalination. UF membranes with a similar but less tight skin structure (pore size 1-50 nm vs. 0.6 nm for RO membranes) have fluxes on the order of 15—1501/m /h (hnh) at feed pressures of 1—5 bar g. The ability to minimise thickness without introducing defects relies upon controlling the membrane morphology during fabrication. 

Loeb and Sourirajan invented the first integrally-skinned membrane in 1960 for desalination by phase inversion of cellulose acetate sols (1). In the interrally-skinned membrane, the skin and substructure are composed of the same material. The skin layer determines both the permeability and selectivity of the bilayer, whereas the porous substructure functions primarily as a physical support for the skin. Differences in density between the two layers are the result of interfacial forces and the fact that solvent loss occurs more rapidly from the air-solution and solution-nonsolvent bath interfaces than from the solution interior (2). 

The majority of the commereial gas separation membranes are made by wet phase inversion method whieh results in an integrally skinned asymmetrie membrane. This method was first used by Loeb and Sourirajan to produee cellulose acetate membranes for desalination of sea water. An alternative method for making gas separation membranes uses an ultra-porous skinned asymmetric membrane over which a thin polymer film is deposited by either coating or by interfacial polymerization. This method was developed by Cadotte for the creation of in situ dense skin thin film composite membranes for water desalination. These membrane fabrication techniques were made commercially successful for gas separation membranes by a brilliant empirical discovery for in situ sealing of the tiny pinhole defects on the skin of the membrane. 

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