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1 1 Membrane Processes CE 370 2 Membrane Processes -Overview ?? What is a Membrane? • The membrane can be defined essentially as a barrier, which separates two phases and restricts transport of various chemicals in a selective manner. ?? Membrane Separation Technology • A membrane separation system separates an influent stream into two effluent streams known as the permeate and the concentrate. • The permeate is the portion of the fluid that has passed through the semi-permeable membrane. • The concentrate stream contains the constituents that have been rejected by the membrane.
2 3 Membrane Processes -Overview Qin Permeate Concentrate Membrane Dissolved Solids (ions) Water 4 Membrane Processes -Overview ??The main membrane processes are -Dialysis -Electro-dialysis -Reverse osmosis ??Driving forces that cause mass transfer of solutes are: -Difference in concentration (dialysis) -Difference in electric potential (electro-dialysis) -Difference in pressure (reverse osmosis)
3 5 Dialysis ??Theory • Dialysis depends on separating solutes of different ionic or molecular size in a solution by means of a selectively permeable membrane. • The driving force for dialysis is the difference in the solute concentration across the membrane ??The mass transfer of solute through the membrane is given by – M = mass transferred per unit time (gram/hour) – K = mass transfer coefficient [gram/(hr-cm2)(gram/cm3)] – A = membrane area (cm2) – ?C = difference in concentration of solute passing through the membrane (gram/cm3) M = KA?C 6 Dialysis Membrane
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5 9 Applications of Dialysis ??In environmental engineering, Dialysis is not used to an appreciable extent. ??In industrial applications, Dialysis can be used to recover Sodium Hydroxide from textile wastewater. ??Dialysis is limited to small flows due to small mass transfer coefficient (K) 10 Electro-Dialysis ??Theory • This process depends on the presence of an electrical filed across the selectively permeable membrane. • The…