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Membrane Separations

Membrane Separations

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Membrane Separations

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  1. Membrane Separations Blake Brown Lynsey Turgeon Allison Horst Blythe Miron

  2. Membrane Separation • separate parts of a flow by passing it through a membrane barrier • Four common types: • Reverse osmosis • Nanofiltration • Microfiltration • Ultrafiltration

  3. Membrane Separation RO NF UF MF Pressure 400-100 120-600 5-220 5 (psi) Cross Flow 6-9 6-9 9-12 9-24 (ft/sec) Process Flux 5-40 20-80 3-200 50-500 (1tr/m2/hr)

  4. Reverse Osmosis • The finest method of membrane separation • Utilizes semi-permeable membrane • Water purification • Capable of filtering ions from solution • The larger the charge on an ion, the more likely it will be rejected by the membrane

  5. Requires a lot of energy, more expensive, but is the most precise method • Membrane can reject molecules with molecular weight greater than 150 daltons • A dalton is one twelfth the weight of a Carbon-12 atom • Solution driven through liquid by pressure source

  6. Nanofiltration • Slightly less precise than reverse osmosis, but requires less energy (more cost efficient) • Larger membrane pores • Can concentrate desired products (ex. corn syrup) • Rejects constituents with molecular weight greater than 1000 daltons

  7. Microfiltration • Highest molecular level filtration • Two methods: dead-end & cross-flow

  8. Liquid filtered directly Buildup on membrane Increases hydraulic resistance Filtrate flux Jopen=ΔP/(μRm) Jblocked=ΔP/(μ(Rm + Rpo + R’mp)) Rm is the membrane resistance, Rpo is the initial resistance, R’mp is the specific resistance of the deposit Dead-end

  9. Cross-flow • Designed to prevent the cover layer • Flow across membrane 3 to 8m/s • Blackflushing used to break up the cover layer

  10. Ultrafiltration • Second highest molecular level filtration • Separates particles larger than 2nm • Permate Flux: • J=k ln((Cm-Cp)/(Cb-Cp)) • k is the mass transfer • C is the solute concentration for membrane surface, in the permeate and in the bulk retentate

  11. Applications of Reverse Osmosis • Water filtration • Removal of charged ions • Pharmaceutical industry • Food and beverage production • Paper • Semiconductor

  12. Advantages of Reverse Osmosis • Operation at low temperatures • Capability to filter out oils, pyrogens, bacteria, viruses, sulfate ions,salt, other charged particles • Filters beverages without compromising taste or color (beer/wine)

  13. Applications of Nanofiltration • Water purification for soft drink production • Concentrating fruit juices, sugar, coffee • Removal of pesticides and nitrates from ground water • Removal of heavy metals from wastewater • Laundry water recycle streams • Dairy Industry

  14. Applications of Microfiltration • Production of : fruit juice, beer, wine • Treating wastewater- remove salts, sediments, detergents

  15. Applications of Ultrafiltration • Separation of oil and water (removal of oil from waste streams) • Milk production- filters out whey products, butterfat, bacteria

  16. Competing methods • Alternatives • Spray Evaporation • Partial demineralization • Anaerobic biodegradation • GAC (Granular Activated Carbon) • Ion Exchange • Chlorination • Distillation (less time and energy efficient)

  17. Conclusion • Valuable to industry • Water purification, concentration process, filtering out toxins, separating products • All methods follow same basic principles • Pressure driven • Porous/semi-permeable membrane rejects some components of a mixture while letting others through in order to separate them • Method of separation determined by size of constituents • Simple in theory, but can be rather complicated • Difficult to separate constituents of similar size