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Separation Techniques

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•         There’s much more in the world than distillation.

•         New techniques and improvements are under constant development.

•         Usually begun in the laboratory, and later adopted (and adapted) by industry for scale-up and lower cost.

•         No one knows them all, must less is expert in all.

•         Classification by separation mechanism

–        Chemical equilibria

–        Kinetics

–        Mechanical

–        Combinations

•         Examples follow.  Google for more information.

Examples of separation by equilibria

 

•         Vapor-liquid equilibria:  distillation, absorption, stripping, extractive distillation, vacuum distillation

•         Liquid-liquid equilibria: extraction (types of equipment)

•         Solid-liquid equilibria: crystallization (search “crystallization”), precipitation,  zone melting (search “Wilcox”) (zone melting organic compounds), ion exchange, supercritical extraction, adsorption, polysaccharides, antiobiotics and Pirkle phases (for chiral molecules)

•         Solid-vapor equilibria: sublimation, freeze drying, adsorption

•         Chemical equilibria:  hydrometallurgy, calcining, roasting, smelting

•         Electrochemical equilibria: Electrolysis, electrorefining

Examples of separation by kinetics

 

•         Membrane methods: dialysis, reverse osmosis, ultrafiltration, gas permeation, electrodialysis

•         Molecular distillation (short-path evaporation), centrifugal molecular distillation (evaporation)

•         Gaseous diffusion

•         Thermal diffusion (Soret effect)

•         Single-phase sedimentation, e.g. in the atmosphere or in a centrifuge.  Ultracentrifuge

•         Gel-permeation and ion-exclusion (see chromatography)

Examples of mechanical separations

 

•         Particle removal from gases

•         Filtration (batch & continuous)

•         Difference in density (particles & drops): sedimentation, decanter, demister, centrifuge, cyclone

•         Electric field: electrostatic precipitation, electrophoresis

•         Temperature field: thermophoretic particle separation (gases, microfluidics, nanoparticles, DNA)

•         Magnetic field and magnetic field gradient

•         Field Flow Fractionation

Examples of combination methods

 

•         Phase equilibria + kinetics: Crystallization to separate stereo-isomers

•         Chemical reaction + other: absorption with chemical reaction, isotope separation by laser excitation, extraction from solids, reactive distillation

•         Phase equilibria + mechanical: flotation

•         Multiple methods: aluminum production

Chromatography

 

•         http://en.wikipedia.org/wiki/Chromatography

•         May utilize differences in equilibrium between the fixed phase and the fluid, e.g. in ion exchange, adsorption, gas-liquid

•         May utilize differences in ability to diffuse into the fixed phase, e.g. gel-permeation and ion exclusion

•         Fixed column (small scale, e.g. HPLC – high-performance or high-pressure liquid chromatography)

–        breakthrough simulation

–        chromatography simulation

•         Simulated moving bed (large scale for manufacturing)

•         Pressure swing adsorption, e.g., hydrogen, oxygen

 

W.R. Wilcox, Clarkson University.  Last modified July 7, 2009.

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