Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.
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Transcript of Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.
![Page 1: Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.](https://reader036.fdocuments.in/reader036/viewer/2022081508/56649d6e5503460f94a4eb90/html5/thumbnails/1.jpg)
Part (I)
Introduction to Membrane Technology in Drinking &
Industrial Water Production
![Page 2: Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.](https://reader036.fdocuments.in/reader036/viewer/2022081508/56649d6e5503460f94a4eb90/html5/thumbnails/2.jpg)
![Page 3: Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.](https://reader036.fdocuments.in/reader036/viewer/2022081508/56649d6e5503460f94a4eb90/html5/thumbnails/3.jpg)
![Page 4: Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.](https://reader036.fdocuments.in/reader036/viewer/2022081508/56649d6e5503460f94a4eb90/html5/thumbnails/4.jpg)
![Page 5: Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.](https://reader036.fdocuments.in/reader036/viewer/2022081508/56649d6e5503460f94a4eb90/html5/thumbnails/5.jpg)
What is a membrane?
A membrane is...
? ? ?
...a physical barrier (no necessarily solid) that gives, or at least helps, the separation of the components in a mixture.
Membrane Separations
![Page 6: Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.](https://reader036.fdocuments.in/reader036/viewer/2022081508/56649d6e5503460f94a4eb90/html5/thumbnails/6.jpg)
The sorting demon...
Membrane Separations
![Page 7: Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.](https://reader036.fdocuments.in/reader036/viewer/2022081508/56649d6e5503460f94a4eb90/html5/thumbnails/7.jpg)
- Membrane processes are not based in thermodynamic equilibrium but based in the different transport rate of each species through the membrane.
- The membrane market is still growing. In the 1986-96 decade, the sales related to membrane products and systems doubled.
- In 1998, these sales were over 5000 million €.
Membrane Separations
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Membrane Separations
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Advantages
Energy savings. The energy consumption is very low as there is no phase change.
Low temperature operation. Almost all processes proceed at room temperature, thus they can deal with compounds that are not resistant at high temperatures.
Water reuse. When applied to recover water, they avoid the transport of large water volumes and permit the reduction of the Chemical Oxygen Demand (COD) loading in sewage plants.
Recovery. Both the concentrate and the permeate could be recovered to use.
Membrane Separations
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Advantages
Compact operation. Which permits to save space .
Easy scale-up. Because usually they are designed in modules, which can be easily connected.
Automatic operation. The most of the membrane plants are managed by expert systems.
Tailored systems. In many cases, the membranes and systems can be specifically designed according the problem.
Membrane Separations
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Disadvantages
High cost. Membranes (and associated systems) are costly, but for low selective separations.
Lack of selectivity. In many cases, the separation factors are still insufficient.
Low fluxes. The permeat flowrate available are still too low for some applications.
Sensitive to chemical attack. Many materials can be damaged by acids, oxidants or organic solvents.
Lack of mechanical resistance. Many materials do not withstand abrasion, vibrations, high temperatures or pressures.
Membrane Separations
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- The membrane operations more widely used are those based in applying a pressure difference between both sides of the membrane.
• Microfiltration (MF).
• Ultrafiltration (UF).
• Nanofiltration (NF).
• Reverse osmosis (RO).
- Although similar in appearance, the involved mechanisms in the separation can be very very different.
Membrane Separations
Micro Filtration (MF)(10-0.1m)Bacteria, suspended particles
Ultrafiltration (UF)(0.05-0.005m) Colloids, macromolecules
Nanofiltration (NF)5e-3-5.e-4 mSugars, dyes, divalent salts
Reverse Osmosis (RO)(1.e-4-1e-5 m)Monovalent salts, ionic metals
Water
Micro Filtration (MF)(10-0.1m)Bacteria, suspended particles
Ultrafiltration (UF)(0.05-0.005m) Colloids, macromolecules
Nanofiltration (NF)5e-3-5.e-4 mSugars, dyes, divalent salts
Reverse Osmosis (RO)(1.e-4-1e-5 m)Monovalent salts, ionic metals
Water
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Hemoglobin(7 nm)
0.1 1 10 100 1000 10000
Pore diameter (nm)
Cells,bacteria
and polymers
Virus andproteinsVitamins
and sugars
Salts andlow molecular
weight compounds
H2O(0,2 nm)
Na+
(0,4 nm)
Glucose(1 nm)
Influenza Virus (100 nm)
PseudomonasDiminuta(280 nm)
Staphylococcus(1000 nm)
Starch(10000 nm)
Microfiltration
Ultrafiltration
Nanofiltration
Reverse Osmosis
Emulsionsand colloids
Name of the membrane process in function of the particle size.
Membrane Separations
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More examples.
Membrane Separations
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... and more.
Membrane Separations
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- There are other separation operations where a membrane is the responsible of the la selective separation of the compounds:
• Dialysis.• Electrodialysis (ED).• Pervaporation.
• Gas permeation (GP).
• Liquid membranes.
- In others, the membrane is not directly responsible for the separation but it actively participates:
• Membrane extraction.• Membrane distillation.• Osmotic distillation.
Membrane Separations
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Type of filtration.
Dead-end Cross-flow
Membrane Separations
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Simple scheme of a membrane module.
MembraneFeed Retentate(Concentrate)
Permeate(Filtrate)
CA,r, CB,r
CA,p, CB,p
CA,f, CB,f
Membrane Separations
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- Synthetic membranes are solid barriers that allow preferentially to pass specific compounds due to some driving force.
(Very) Simple scheme for some mechanisms of selective separation on a porous membrane.
+
+
+
+
+ ++
Membrane Separations
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- The separation ability of a synthetic material depends on its physical, chemical properties.
• Pore size and structure
• Design
• Chemical characteristics
• Electrical charge
Membrane Separations
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- The membranes can be roughly divided in two main groups: porous and non porous.
- Porous membranes give separation due to...
• size• shape• charge
...of the species.- Non porous membranes give separation due to...
• selective adsorption• diffusion
...of the species.
Membrane Separations
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Main parameters.
- Rejection, R, if there is just one component (RO)
f,A
p,A
f,A
p,Af,A
C
C1100
C
CC100 (%)R
- Separation factor - Enrichment factor
B
A
B,fA,f
B,pA,pA,B /CC
/CCα
A,f
A,pA C
C
Membrane Separations
for two or more component
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Main parameters.
- In RO, often we use the Recovery (Y)
Qp: Permeate flowrate (m3/s)
Qf: Feed flowrate (m3/s)
100Q
Q(%)Y
f
p
Membrane Separations
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Main parameters.
- Passive transport in membranes. The permeate flux is proportional to a given driving force (some difference in a property).
(X) ForcerivingD )A( onstantC (J)Flux
Driving forces:
Pressure (total o partial) Concentration Electric Potential
Membrane Separations
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Main parameters.Membrane processes and driving force.
ProcessFeedphase
Permeatephase
DrivingForce
Microfiltration L L ΔP
Ultrafiltration L L ΔP
Nanofiltration L L ΔP
Reverse Osmosis L L ΔP
Dialysis L L Δc
Electrodialysis L L ΔΕ
Pervaporation L G ΔP
Gas Permeation G G ΔP
Membrane Separations
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Main parameters.
- Permeate flux.
dP
8r
AQJ
2
mw
w
Jw: Solvent flux (m3/s·m2)
Qw: Solvent flowrate (m3/s)
Am: Membrane area (m2) r: Pore radius (m)
d: Membrane thickness (m)
: Viscosity (Pa ·s)
P: Hydraulic pressure difference (Pa)
: Tortuosity
In MF and UF, porous membrane model is assumed, where the a stream freely flows through the pore. Then, the transport law follows the Hagen-Poiseuille equation.
: Porosity
Membrane Separations
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Main parameters.
- The above model is good for cylindrical pores. However, if the membrane is rather formed by a aggregated particles, then the Kozeny-Carman relation works much better.
JW: Solvent flux (m3/s·m2)QW: Solvent flowrate (m3/s)S: Particle surface area (m2/m3)
K: Kozeny-Carman constant d: Membrane thickness (m): Viscosity (Pa ·s)
dP
1SK
AQJ
22
3
mw
w
Am: Membrane area (m2)
Membrane Separations
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- In the operations governed by the pressure, a phenomenon called concentration polarisation appears, which must be carefully controlled. This is due to the solute accumulation neighbouring the membrane surface.
FeedPolarisation layer
membrane
membrane
Permeate
Permeate
Formation of the polarisation layer.
Membrane Separations
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- Concentration polarisation.
(It is not fouling!!!)
Membrane Separations
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- Fouling: Irreversible reduction of the flux throughout the time.
• Pore size reduction by irreversible adsorption of compounds.
• Pore plugging.
• Formation of a gel layer over the membrane surface (cake).
Membrane Separations
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- Membrane can be classified in several ways, but always 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
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- Structure:
• Symmetric. Also called homogeneous. A cross section shows a uniform porous structure.
• Asymmetric. In a cross section, one can see two different structures, a thin dense layer and below a porous support layer.
- Integral: the layers are continuous. - Composites: the active layer (thickness 0.1-0.5 μm) is supported over a highly porous layer (50-150 μm), sometimes both layers are of different materials.
Membrane Separations
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Symmetric UF membrane of 0.45 m made of cellulose acetate (Millipore).
Membrane Separations
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Symmetric ceramic membrane of 0.2 m made of alumina (Al2O3) (AnoporeTM).
Surface Cross section
Membrane Separations
![Page 35: Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.](https://reader036.fdocuments.in/reader036/viewer/2022081508/56649d6e5503460f94a4eb90/html5/thumbnails/35.jpg)
Asymmetric ceramic membrane made of -Al2O3 (Membralox).
Membrane Separations
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UF integral asymmetric membrane made of polypropylene.
Membrane Separations
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RO composite membranes.
Cellulose acetate
Polyamide
Membrane Separations
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- Configuration and modules
• Configuration: geometric form given to the synthetic membranes.
• Module: name of the devices supporting one or several membranes (housing).
The module seals and isolates the different streams. The geometry and specific fluid movement through the confined space characterises each module. The type of flux, the transport mechanism and the membrane surface phenomena depend on the module design.
Membrane Separations
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- 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-frame and spiral wound.
- High surface area/volume ratio.
Membrane Separations
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Plate-and-Frame Membrane System.
Membrane Separations
Consists of layers of membranes separated by corrugated structural sheets, alternating layers with feed material flowing in and retentate flowing out in one direction, while permeate flows out in the other direction.
![Page 41: Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.](https://reader036.fdocuments.in/reader036/viewer/2022081508/56649d6e5503460f94a4eb90/html5/thumbnails/41.jpg)
Spiral-wound module.
Membrane Separations
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Membrane Separations
Spiral-wound module.
![Page 43: Part (I) Introduction to Membrane Technology in Drinking & Industrial Water Production.](https://reader036.fdocuments.in/reader036/viewer/2022081508/56649d6e5503460f94a4eb90/html5/thumbnails/43.jpg)
- Configuration:
• Tubular.
- It is like a tube.
- Usually the active layer is inside.
- The permeate crosses the membrane layer to the 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
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Different types of tubular modules.
Membrane Separations
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Hollow fiber module.
Membrane Separations
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Hank of polyamide hollow fiber for RO (DuPont).
Membrane Separations
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Cross section of hollow fiber (Monsanto). Comparison with a clip.
Membrane Separations
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Hollow fiber cross section of polyamide for RO (DuPont).
Membrane Separations
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Hollow fiber made of polysulfone ( 1 mm) for UF (detail).
Membrane Separations
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Hollow fiber cross section of 1 mm (Monsanto).
Membrane Separations
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Hollow fiber surface of polypropylene (Celgard).
Membrane Separations
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Hollow fiber ceramic membranes (CEPAration).
Membrane Separations
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- 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
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- Comparison between modular configurations.
Modular configurations and processes.
Module
Operation Tubular Spiral-wound Hollow fiber
Reverse Osmosis A VA VA
Ultrafiltration VA A NA
Microfiltration VA NA NA
Pervaporation A VA VA
Gas Permeation NA VA VA
VA = Very appropriate; A = Appropriate; NA = Not appropriate
Membrane Separations
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- Material:
• Organic.
- Made of polymers or polymer blends.
- Low cost.
- Problems with their mechanical, chemical resistance.
Temperature
pH, Solvents
Pressure
Membrane Separations
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Polypropylene with 0.2 m pores (Accurel).
Membrane Separations
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Polytetrafluoroetylene with 0.2 m pores.
Membrane Separations
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Polytetrafluoroetylene with 0.2 m pores.
Membrane Separations
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Membrane Technology
• Dialysis
- Applied since the 70’s.
- Low industrial interest.
- Ions & species of low MW (<100 Da).
- Ionic Membranes (just like ED).
- Driving Force: concentration gradient.
- Slow and low selective.
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• Dialysis
- NaOH recovery in textile effluents, alcohol removal from beer, salts removal (pharmaceutical industry).
- Artificial kidney.
Membrane Technology
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GS
MF
UFRO
HD
EDPV
• Dialysis
Membrane and module markets
Looks not very important...?.
Membrane Technology
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• Electrodialysis (ED)
- Ion Separations.
- Ionic Membranes (non porous).
- Driving Force: gradient in electrical potential.
- Flat configuration.
- Hundreds of anionic and cationic membranes placed alternatively.
- Orthogonal electrical field.
- First applications back at 30’s.
- Potential: 1-2 V.
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• Electrodialysis (ED)
Membrane Technology
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• Electrodialysis (ED)
Membrane Technology
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• Electrodialysis (ED)
- Ionic Membranes (non porous).
- Based on polystyrene or polypropylene with sulfonic and quaternary amine groups.
- ED with reverse polarization (EDR).
- ED at high temperature (60ºC).
- Thickness: 0.15-0.6 mm.
- ED with electrolysis.
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• Electrodialysis (ED)
- Required membrane area
j+
VC c+
in
VC c+
out
0dczVdAj Cm Mass balance (in equivalents)
Charge flow
mdAdI
iFj
combining
i
FzccVi
FzccVNANA outinoutinC
mT
η: global electrical efficiency (~0.5 commercial equipment)
F: Faraday constant (96500 C/eq) N: number cells in the equipment
i: electric current density (A/m2)Am: membrane surface (m2)
j: cation flow (eq/m2 s)
z: cation charge (eq/mol)
Membrane Technology
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• Electrodialysis (ED)
- Then the required energy, E (J), is
tRINtIUN E C2
C
as
then
FzccV
AiI outinCm
UC: potential gradient in a cell (V)
RC: total resistance in a cell ()
tRFzcV
N E C
2C
C
2C R
FzcVN P ó
P: required Power (J/s)
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• Electrodialysis (ED)
Where, the required specific energy, (J/m3), is
C
2
CC
RFzc
VtVN
E E
La cell resistance can be estimated from a model based on series of resistances where the resistances to transport are considered through two membranes and the compartments concentrate and diluted.
Membrane Technology
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• Electrodialysis (ED)- How to determine operational i?
t
Ficcz
DtFi DMD
M
Cation Transport
tt
cczFDi
M
DMD
If cDM+ = 0
tt
czFDi
M
Dlim
Usually: i = 0.8ilim t: transport numberD: diffusion coefficient
Cationic Membrane
Limit boundary
cCM+
cC+
cDM+
cD+
- +
concentrate diluted
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• Electrodialysis (ED)- Intensity Evolution versus applied potential
i (A/m2)
ilim
Ohmic zone
U (V)
Resistance rise
Ionic water splitting
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• Electrodialysis (ED)
- Fields of application: Water desalination.
- Competing to RO.
- Economically more interesting at very high or very salt concentrations.
- Other fields of application: Food Industry.
Treatment of heavy metal polluted water.
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• Electrodialysis (ED)
- Examples:
Production of drinking water from salty water.
Water softening. Nitrate removal. Lactose demineralization. Acid removal in fruit juice. Tartrate removal from wines. Heavy metal recovery. Production of chlorine and sodium hydroxide.
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• Electrodialysis (ED)
electrolytic Cell for the production of chlorine and sodium hydroxide with cationic membrane.
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• Electrodialysis (ED)
Electrolytic cell for the production of sulfuric acid and sodium hydroxide with bipolar membrane.
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Membrane Technology
• Electrodialysis (ED)
Hydrogen fuel cell with a cationic membrane.
Cathode
Anode
Global
H2 2H++ 2e-
O2 + 4e- + 4H+ 2H2O
2H2 + O2 2H2O
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• Pervaporation
- Discovered 1917.
- Only operation with phase change.
- Non-Porous Membranes.
- Mechanism solution-diffusion.
- Driving force: difference in partial pressure.
-Vacuum (<40 mm Hg), dilution (inert gas, N2) or temperature difference.
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• Pervaporation
Condenser
Pervaporat. module
Feed
Retentate
Vacuum pump
Permeate condensate
Heater
General Pervaporation system.
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• Pervaporation
- Industrial applications.
- Alternative to distillation when thermodynamic limitations.
Low energy costs. Low investment costs. Better selectivity, without thermodynamic limitations. Clean and closed operation. No process wastes. Compact and scalable units.
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• Pervaporation
- Drawbacks:
- Organic substances dehydratation.
Scarce Membrane market. Low permeate flows. Limited applications:
- Recovery of volatile compounds at low concentrations.
- Separation of azeotropic mixtures.
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• Pervaporation.
- Do not mistake with a distillation where a membrane is just separating phases.
- Three steps mechanisms:
Selective absorption on the membrane. Dissolution at the membrane. Diffusion through the membrane.
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• Pervaporation
- The membrane is active in this process.
- The permeability coefficient (P) of a compound depends on the solubility (S) and the diffusivity (D), in the polymeric phase, of the crossing compound
Pi = Si (ci, cj)· Di (ci, cj)
- Simplificated transport equation:
pioiii
ii pypx
dP
J
Ji: flux of component i d: membrane thickness xi: molarfraction in liquid i: activity coefficientpi
o: vapour pressure yi: molar fraction at permeate pp: pressure at permeate side
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• Pervaporation
- Main membrane parameters:
- Separation factors - Enrichment factors
B
A
B,fA,f
B,pA,pA,B /CC
/CCα
A,f
A,pA C
C
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• Pervaporation
Pervaporation process of an ethanol/water mixture with a PVA membrane.
0.00.2 0.4 0.6 0.8 1.0
0.2
0.4
0.6
0.8
1.0
azeotrope
pseudoazeotropeEh
tan
ol a
t p
erm
eate
(v
apou
r)
Ethanol at feed (liquid)
Phase equilibria
pervaporation
0.0
Membrane Technology
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Intermediat tank
Condenser
Pervap. unit
Feed
Ethanol >90% w/w
Permeate
Boiler
Water
Distillation column
Ethanol >99.95% w/w
Ethanol 20-80% w/w
Ethanol 15% w/w
• Pervaporation
Combination of distillation and pervaporation for the production of pure ethanol.
Plant for production of ethanol from sugar (Bethéniville, France).
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• Pervaporation
Methanol Alil alcohol Ethyl Acetate Tricloretilene Ethanol Furfurol Buthyl acetate Tetrachloretane n-Propanol Methylfurfurol Diethyl ether Tretrahydrofurane Isopropanol Diethilenglicol Diisopropyl ether Aniline n-Buthanol Acetone Dipropyl ether Benzene t-Buthanol Buthanone Ethyl propyl ether Toluene 2-Penthanol Cyclohexanone Chloroform Xylene Hexanol Methyl ethyl Ketone Methyl Chloride Ethylen diamine Cyclohexanol Metil isobuthyl Ketone Chlorethylene Ethanol amine Isoamilic Alcohol Caprolactame Dichloro ethylene Diethyl amine
Organic solvents to apply pervaporation.
Dehydration of organic solvents.
Hydrophilic membranes: PVA, PAN...
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• Pervaporation
- Organic compounds recovery.
For volatile compounds. Economically competitive. Hydrophobic membranes: PDMS and derivatives.
- Azeotrope breaking of organic compounds.
Studied at lab scale. Low selectivity.
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• Pervaporation
Lab scale separations reported.
Mixture Membrane Selectivity Ethylbenzene/xylene Polyethylene Not available
p-xilene/o-xilene Polyethylene Not available m-xilene/p-xilene Polypropilene m-Xylene
Dichlor ethane/trichlor ethane
Poliamide/polyeth Dichlorethane
Benzene/cyclohexane Polyimide Benzene Acetone/cyclohexane Polyimide Acetone
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• Pervaporation
Hybrid process: extractive distillation and pervaporation for the production of pure benzene and cyclohexane .
Pure cyclohexane
Pervaporation unit
Pure benzene
Feed
Solvent
Column
1
Column
2
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• Gas permeation
- Since 50’s.
- Membranes: porous and no porous.
- Several possible mechanisms for gas transport:
Knudsen Flow.
- The last two are selective.
Solution-diffusion.
X Viscous Flow.
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• Gas Permeation
- Knudsen Flow (porous membranes). When the porous diameter is on the range of the average free space of the molecule (kinetic theory for gases).
ik
i PTR
Dd
J
MTR8
r32
Dk
i
j
j
i
M
M
JJ
Transport equation
Knudsen diffusivity
: porosity d: membrane thickness: tortuosity R: gas constant
T: temperature P: transmembrane P
r: porus radi
M: MW
Enrichment
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• Gas permeation
-Solution-diffusion (non-porous membranes).
j
i
j
i
j
iij S
SDD
PP
The selectivity is referred to the separation factors of the compounds to be separated
Pi = Si· Di
There are “slow” and “fast gases” for a determined membrane.
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• Gas permeation
- Driving force: partial pressure gradient.
- Working pressure: up to 100 bar.
- Non-porous polymeric membranes:
PDMS, CA, PS, PES i PI
- Ceramic Membranes (small pores for Knudsen).
- Metallic membranes (Pd and Ag alloys).
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• Gas permeation
- Asymmetric membranes.
- Thin polymer on a structural porous material.
- Preferred configuration Hollow Fiber or Spiral, others like flat or tubular also possible.
- Applied in petrochemistry.
Purification of H2, CO2, CH4 and gaseous hydrocarbons of difficult distillation.
Nitrogen purification.
Membrane Technology
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• Gas permeation
- Some examples:
Enrichment, recovery and dehydration of N2.
H2 recovery in residual flows of proceses, purge o natural gas.
Adjust of the ratio H2/CO synthesis gas.
Acid gas removal (CO2, H2S) from natural gas.
Helium recovery from natural gas and other sources.
VOC removal from process flow.
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Residuals gases
Gas permeation
to fuel-gas
Hydrogen
Recycle of n-C4
Unitat de isomerització
n-Butane
Isobutane
Recycle
H2 (96%)
• Gas permeation
Hydrogen recovery in a butane isomeration plant.
A typical PRISM® Separator (Airproducts)
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• Liquid Membranes
- A liquid barrier between to phases.
- Not yet industrial uses.
- Driving force: chemical potential, concentration.
Emulsion (ELM).
- Two configurations:
Supported Liquid Membranes (SLM).
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• Liquid Membranes
Possible configuration for LM.
Emulsion liquid Mem.
Organic liquid + surfactant (membrane)
Receiving phase
Aqueous phase
Porous Support
Organic liquid impregnated into the pores
SLM
Membrane Technology
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• Liquid Membranes
- Advantages:
High flows due to the transport velocity in liquids.
- Drawbacks:
Selective separations due to the presence of specific reagents.
Pumping effect (against the gradient) due to the carrier equilibrium.
Small quantities of solvent lets to the application of expensive solvents.
Low stability of emulsions in ELM.
Leaching out of organic phase from the pores of a SLM .
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• Liquid Membranes
Facilitated Transport in Liquid Membrane.
Liquid Membrane
M + B MB
B: selective carrierM: selectively separated
M M
B
MBN
P
O
Ag+
O
O
O
O
O
O diphenyl-18-crown-6
O
O
O
O
O
O
Ag+
Membrane Technology
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• Liquid Membranes- ELM: low practical interest
- SLM: lab scale and few applications restricted high added value compounds.- Hydrophobic Membranes (PE, PP ...).- Hollow fibers.
- Potential applications:
Selective removal and concentration of cations in solution.
Selective separation of gases.
Recovery of acid or basic compounds.
Organic compound separation in complex mixtures.
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• Other Techniques
- Membrane distillation.
A hydrophobic membrane separates two aqueous phases.
The volatile compounds cross the membrane and condensate.
The hydrophobic membrane avoids the aqueous phases to get into the membrane. The driving force in the temperature gradient.
Membrane Technology
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• Other techniques
- Membrane distillation.
Driven by the phase equilibrium in both sides of the membrane.
The membrane acts just like a physical barrier.
Some applications:
Water demineralization. Inorganic acid or salt concentration.
Ethanol extraction at the fermentation.
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• Other techniques- Osmotic distillation.
Similar to membrane distillation. Both phases at the same temperature.
The osmotic pressure is risen by adding appropriate compounds to the receiving phase.
The partial pressure gradient due to the osmotic pressure is the driving force.
Attractive to the food industry provided it maintains the temperature.
Alcohol removal from wine and beer. Fruit juice enrichment.
Membrane Technology
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• Other techniques
- Membrane extraction.
The membrane acts as a barrier to separate immiscible phases.
It has to assure immiscibility between phases.
Hollow Fiber membranes have high area.
It makes possible to avoid the separation at decanting of the phases at the end.
Lab scale research.
Membrane Technology