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Membrane separation processes: Introduction : 

Membrane separation processes: Introduction Definition: A membrane is a thin barrier which allows selective passage of different species through it. This selectivity is utilized for separation. The selectivity is due to: Size Shape Electrostatic charge Diffusivity Physicochemical interactions Volatility Polarity/solubility

Membrane separation processes: Applications : 

Membrane separation processes: Applications Product concentration, i.e. removal of solvent from solute/s Clarification, i.e. removal of particles from fluids, a special case being sterilization which refers to removal of microorganisms from fluids Removal of solute from solvent, e.g. desalting, desalination, demineralization, dialysis Fractionation, i.e. separation of one solute from another Gas separation, i.e. separation of one gas from another Pervaporation, i.e. removal of volatiles from non volatiles (usually solvents)

Membrane material : 

Membrane material Organic polymers Polysulfone (PS) Polyethersulfone (PES) Cellulose acetate (CA) Regenerated cellulose Polyamides (PA) Polyvinylidedefluoride (PVDF) Polyacrylonitrile (PAN) Inorganics -alumina -alumina Borosilicate glass Pyrolyzed carbon Zirconia/stainless steel Zirconia carbon

Membrane structure and morphology : 

Membrane structure and morphology Symmetrical Asymmetrical

Membrane preparation : 

Membrane preparation Polymer casting Precipitation from vapour phase Precipitation by evaporation Immersion precipitation Thermal precipitation Other methods Stretching Sintering Slip casting Leaching Track etching

Driving force in membrane processes : 

Driving force in membrane processes Transmembrane pressure (TMP) Concentration gradient Chemical potential Osmotic pressure Electric field Magnetic field Partial pressure pH gradient

Classification of membrane processes based on pore size : 

Classification of membrane processes based on pore size

Membrane processes primarily based on species size : 

Membrane processes primarily based on species size Microfiltration (MF) Micron sized pores Mainly used for particle-fluid separation TMP: 1 to 50 psig Ultrafiltration (UF) Pores: 10 – 1000 angstroms Used for: Concentration, desalting, clarification and fractionation TMP: 10 – 100 psig Nanofiltration (NF) TMP: 40 – 200 psig Reverse osmosis (RO) TMP: 200 – 300 psig Dialysis Concentration gradient driven Selectivity based indirectly on size

Membrane processes based on principles other than species size : 

Membrane processes based on principles other than species size Pervaporation (PV) Driven by partial pressure Selectivity depends on volatility and solubility of species in membrane Gas separation Driven by partial pressure Selectivity depends on solubility of species in membrane Electrodialysis (ED) Driven by electric field Selectivity depends of charge exclusion