In the Name of God Four ur Pr Pressure essure Driven riven Mem Membrane brane Pr Processes cesses 1
Four pressure driven membrane processes MF UF NF RO P = <0.2 MPa 0.1-1 MPa 0.5-2.5 MPa >1.5 MPa 2
- Microfiltration (MF) - Ultrafiltration (UF) - Nanofiltration (NF) - Reverse osmosis (RO) 3
Introduction 4
Introduction Schematic drawing of water flow as a function of applied pressure ( ∆ P):
Introduction 6
Introduction RT = − π Ln( γ X ) w w V w ◼ Van ΄ t Hoff equation (for dilute solutions) non-ionisable materials: = c RT( ) Ionisable salts: M = c iRT( ) M ▪ Virial equation: = + + 2 3 Ac Bc Dc 7
Microfiltration (MF) ◼ Membranes: (a)symmetric porous ◼ Thickness: 10-150 µm ◼ Pore sizes: 0.05-10 µm ◼ Driving force: pressure difference (< 2 bar) ◼ Separation principle: sieving mechanism
Microfiltration (MF) : Membrane materials for MF applications Hydrophobic polymeric membranes Polytetrafluoroethylene (PTFE, teflon) Poly(vinylidene fluoride) (PVDF) Polypropylene (PP) Polyethylene (PE) Hydrophilic polymeric membranes Cellulose esters Polycarbonate (PC) Polysulfone/poly(ethersulfone)(PSf/PES) Polyimide/poly(ether imide) (PI/PEI) Polyamide (PA) Polyetheretherketone (PEEK) Ceramic membranes Alumina (Al 2 O 3 ) Zirconia (ZrO 2 ) Titania (TiO 2 ) Silicium carbide (SiC)
Microfiltration (MF) Some applications: ✓ Juice, wine or beer clarification ✓ Sterilization ✓ Separation of oil-water emulsions ✓ Water and wastewater treatment ✓ Membrane bioreactor 10
Ultrafiltration (UF) ◼ Membranes: asymmetric porous ◼ Thickness: 150 µm ◼ Pore sizes: 1-100 nm ◼ Driving force: pressure difference (1-10bar) ◼ Separation principle: sieving mechanism
Ultrafiltration (UF) - Characteristic parameter: Molecular Weight Cut-Off MWCO is defined as the molecular weight which is 90% rejected by the membrane. Relation between MWCO and the pore size for UF Membranes . 1 Dalton (Da) represents the mass of a hydrogen atom 12
Ultrafiltration (UF) Membrane materials for UF applications: ◼ Polysulfone/ poly (ether sulfone) / sulfonated polysulfone ◼ Poly(vinylidene fluoride) ◼ Polyacrylonitrile ◼ Cellulosics (e.g. cellulose acetate) ◼ Polyimide / poly (ether imide) ◼ Polyamide ◼ Polyetheretherketone ◼ In addition to such polymeric materials, inorganic (ceramic) materials have also been used for ultrafiltration membranes, especially alumina and zirconia.
Ultrafiltration (UF) Some applications: ✓ Concentration of milk ✓ Treatment of oil-water emulsion ✓ Water and wastewater treatment ✓ Recovery of whey proteins 14
Nanofiltration (NF) ◼ Membranes: composite ◼ Thickness: sublayer: about 150 µm; toplayer: about 1 µm ◼ Pore sizes: < 10 nm ◼ Driving force: pressure difference (5-25 bar) ◼ Separation principle: solution-diffusion ◼ Membrane material: polyamide
Nanofiltration (NF) Some applications: ✓ Water softening ✓ Desalination of brackish water (amount of salt: 1000- 5000 ppm) ✓ Wastewater treatment ✓ Removal of micropollutants ✓ Retention of dyes (textile industry) Still looking for applications. Potentially when UF does not give sufficient rejection and RO is not economical. 16
Reverse osmosis (RO) ◼ Membranes: asymmetric ◼ Thickness: sublayer: about 150 µm; toplayer: about 1 µm ◼ Pore sizes: < 2 nm ◼ Driving force: pressure difference (brackish water: 15-25 bar and sea water: 40-80 bar) ◼ Separation principle: solution-diffusion ◼ Membrane material: cellulose triacetate, polyamide and poly(ether urea)
Reverse osmosis (RO) Some applications: ✓ Production of ultra pure water for electronic industry ✓ Desalination of brackish or sea water (amount of salt: 35000 ppm) ✓ Wastewater treatment ✓ Concentration of juices, milk or sugar solutions 18
Reverse osmosis (RO) Comparison of retention characteristics between nanofiltration and reverse osmosis:
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In the Name of God Dialysis and Electrodialysis Processes 21
Dialysis ◼ Membranes: homogeneous ◼ Thickness: 10-100 µm ◼ Driving force: concentration difference ◼ Separation principle: difference in diffusion rate, solution-diffusion
Dialysis Membrane materials for dialysis applications: ❖ CA (cellulose acetate) ❖ Regenerated cellulose such as cellophane and cuprophane ❖ PVA (poly vinyl alcohol) ❖ PAA (polyacrylic acid) ❖ PMMA (polymethylmethacrylate) ❖ PC (polycarbonates)
Dialysis Applications: ◼ Hemodialysis (removal of toxic substances from blood) ◼ Alcohol reduction in beer ◼ salt removal in pharmaceutical industry ◼ Alkali recovery in pulp and paper industry 24
Hemodialysis (HD) Artificial kidney 25
Electrodialysis (ED) ◼ Membranes: anion-exchange and cation-exchange membranes ◼ Thickness: 100-500 µm ◼ Driving force: electrical potential difference ◼ Separation principle: Donnan exclusion mechanism ◼ Membrane material: crosslinked copolymers based on divinylbenzene (DVB) with polystyrene or polyvinylpyridine, copolymers of polytetrafluoroethylene (PTFE) and poly (sulfonyl fluoride-vinyl ether)
Electrodialysis (ED) The basic parameters for a good membrane: • High selectivity • High electrical conductivity • Moderate degree of swelling • High mechanical strength 27
Electrodialysis (ED) 28
Electrodialysis (ED) 29
Electrodialysis (ED) - ED with reverse polarization (EDR) - ED at high temperature - ED with electrolysis 30
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Intensity evolution versus applied potential 35
Electrodialysis (ED) Applications: ◼ Desalination of water ◼ Production of salt ◼ Demineralisation of whey ◼ Deacidification of fruit juices ◼ Production of boiler feed water ◼ Removal of organic acids from a fermentation broth ◼ Separation of amino acids from each other 36
Electrolytic cell for the production of Cl2 and NaOH with cationic membrane 37
In the Name of God Pervaporation, gas separation and liquid membrane 38
Pervaporation - Operation with phase change - Composite membranes (0.1 to few µm for top layer) - Nonporous membranes - Solution-diffusion mechanism - Driving force: difference in partial pressure - Vacuum (<40 mm Hg) and dilution (inert gas, N2) ➢ Overall the vacuum mode is more popular. ➢ The inert gas plays the same role as vacuum in creating a driving force for transport through the membrane. 39
Pervaporation 40
Pervaporation 41
Pervaporation - Three-step mechanism: • Selective sorption on the upstream side of the membrane • Selective diffusion through the membrane • Desorption on the permeate side 42
Pervaporation Pervaporation has the following advantages: ◼ Low capital and operating cost. ◼ Azeotropes can be readily broken by using an appropriate membrane. ◼ Easy operation and space saving ◼ Clean operation ◼ Compact and scalable units 43
Pervaporation - Simplified transport equation: Pi: permeability coefficient of component i 44
Pervaporation - Main membrane parameters: - Separation factor: - Enrichment factors: 45
Pervaporation of methanol/MTBE mixtures BP of Methanol=65 ° C BP of C 5 H 12 O=55 ° C ◼ 46
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Pervaporation (applications) ◼ Aqueous mixtures Two main classes can be distinguished here; either a small amount of water has to be removed from an organic solvent (dehydration) or a small amount of organic solvent has to be removed from water: Dehydration ◼ Removal of water from organic solvents. Even traces of water can be removed (e.g., from chlorinated hydrocarbons and alcohol)
Pervaporation (applications) Removal of volatile organic compounds from water ◼ Alcohol from fermentation broths (ethanol, butanol and acetone-butanol-ethanol (ABE)) ◼ Volatile organic contaminants from wastewater (aromatics, chlorinated hydrocarbons) ◼ Removal of flavour and aroma compounds ◼ Removal of phenolics
Pervaporation (applications) ◼ Non-aqueous mixtures: Polar/non-polar ◼ Alcohols/aromatics (methanol/toluene) ◼ Alcohols/ethers (methanol/ methyl-t- butylether (MTBE)) Saturated/unsaturated ◼ Butane/butene Separation of isomers ◼ C-8 isomers
Pervaporation (applications) ◼ Although dehydration has widespread application, the other applications are not as commercially successful as dehydration. ◼ The process is currently best identified with dehydration of ethanol, isopropyl alcohol, and ethylene glycol. ◼ The membrane polymer to be selected for a given separation should have high sorption affinity for the solute to be removed preferentially. 51
Pervaporation Hydrophilic Polymers Available for Selective Water Removal Poly(vinyl alcohol) (different cross-linkers) Poly(acryclic acid) (different cross-linkers) Various poly(amide)s Various poly(imide)s Cellulose acetate Other cellulose derivatives/forms 52
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