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- Membrane can be classified in several ways, butalways there are arbitrary classifications.
• Structure: symmetric, asymmetric
• Configuration: flat, tubular, hollow fiber
• Material: organic, inorganic
• Surface charge: positive, negative, neutral
• ...and even other divisions and subdivisions
Membrane Separations
- Structure:
• Symmetric. Also called homogeneous. A crosssection shows a uniform porous structure.
• Asymmetric. In a cross section, one can see twodifferent structures, a thin dense layer and below aporous support layer.
- Integral: the layers are continuous.- Composites: the active layer (thickness0.1-0.5 �m) is supported over a highlyporous layer (50-150 �m), sometimesboth layers are of different materials.
Membrane Separations
Symmetric UF membrane of 0.45 µm made ofcellulose acetate (Millipore).
Membrane Separations
Symmetric ceramic membrane of 0.2 µm made ofalumina (Al2O3) (AnoporeTM).
Surface Cross section
Membrane Separations
Asymmetric ceramic membrane madeof γ-Al2O3 (Membralox).
Membrane Separations
UF integral asymmetric membrane made ofpolypropylene.
Membrane Separations
RO composite membranes.
Cellulose acetate
Polyamide
Membrane Separations
- Configuration and modules
• Configuration: geometric form given to thesynthetic membranes.
• Module: name of the devices supporting oneor several membranes (housing).
The module seals and isolates the different streams. Thegeometry and specific fluid movement through the confinedspace characterises each module. The type of f lux, thetransport mechanism and the membrane surface phenomenadepend on the module design.
Membrane Separations
- Configuration:
• Flat.
- The active layer is a flat.
- Synthesised as a continuous layer.
- Later, one can select a desired geometry(rectangle, circle,...) to be placed in the module.
- Used in two kind of modules: plate-and-frameand spiral wound.
- High surface area/volume ratio.
Membrane Separations
Plate-and-Frame Membrane System.
Membrane Separations
Consists of layers of membranes separated by corrugatedstructural sheets, alternating layers with feed materialflowing in and retentate flowing out in one direction,while permeate flows out in the other direction.
Spiral-wound module.
Membrane Separations
Membrane Separations
Spiral-wound module.
- Configuration:
• Tubular.
- It is like a tube.
- Usually the active layer is inside.
- The permeate crosses the membrane layer tothe outside (this is, the feed flows inside).
- Low surface are/volume ratio.
- Several lengths and diameter (>10 mm).
- Modules grouping one or various membranes.
Membrane Separations
Different types of tubular modules.
Membrane Separations
- Configuration:
• Capill ary (0.5-10 mm) and hollow fiber (<0.5 mm).- Active layer inside.
- Hollow fiber: usually ∅in from 40 to 120µm and ∅out from 85 to 250 µm.
Membrane Separations
• Capill ary, hollow fiber.
- Usually, the permeate goes from outside toinside, but the flux also can be reversed.
- Very high surface area/volume ratio.
Out-in
In-out
Membrane Separations
Capillary membranemodules.
Membrane Separations
Hollow fiber module.
Membrane Separations
Hollow fiber module.
Membrane Separations
Hollow fiber module.
Membrane Separations
Membrane Separations
Hank of polyamide hollow fiber for RO (DuPont).
Cross section of hollow fiber (Monsanto).Comparison with a clip.
Membrane Separations
Hollow fiber cross section of polyamidefor RO (DuPont).
Membrane Separations
Hollow fiber made of polysulfone(∅ ≈ 1 mm) for UF (detail ).
Membrane Separations
Hollow fiber cross section of ∅ ≈ 1 mm(Monsanto).
Membrane Separations
Hollow fiber surface of polypropylene (Celgard).
Membrane Separations
Hollow fiber ceramic membranes (CEPAration).
Membrane Separations
- Comparison between modular configurations.
Module
Parameter Tubular Spiral-wound Hollow fiber
Specific surface area (m2/m3) 300 1000 15000Inside diameter or spread (mm) 20-50 4-20 0.5-2Flux (L/m2 day) 300-1000 300-1000 30-100Production (m3/m3 per module & day) 100-1000 300-1000 450-1500Space velocity (cm/s) 100-500 25-50 0.5Pressure loss (bar) 2-3 1-2 0.3Pretreatment Simple Medium HighPlugging Small Medium ElevatedReplacement Easy Difficult ImpossibleCleaning:
MechanicalChemical
PossiblePossible
Not possiblePossible
Not possiblePossible
Membrane Separations
- Comparison between modular configurations.
Modular configurations and processes.
Module
Operation Tubular Spiral-wound Hollow fiber
Reverse Osmosis A VA VA
Ultrafiltration VA A NA
Microfil tration VA NA NA
Pervaporation A VA VA
Gas Permeation NA VA VA
VA = Very appropriate; A = Appropriate; NA = Not appropriate
Membrane Separations