Membrane Separation Processes - An Overview

Dateline: 12/01/97

The following tables give an overview and a classification of membrane separation processes.

Table 1 shows size of materials retained, driving force, and type of membrane for various membrane separation processes. Additionally, links to pages with more information on external Web sites are provided.

Table 2 shows examples of applications and separation processes which compete with the respective membrane separation process.

Sources: Perry's Chemical Engineers' Handbook, 7th edition, pages 22-37 to 22-69. The IUPAC Commission on Functional Polymers has published an article on 'Terminology for membranes and membrane processes' in Pure & Applied Chemistry Vol. 68, pages 1479-1489 (1996) .

Table 1: Size of Materials Retained, Driving Force, and Type of Membrane
Process
Size of materials retained
Driving force
Type of membrane
Microfiltration
0.1 - 10 Ám
microparticles
Pressure difference
(0.5 - 2 bar)
Porous
Ultrafiltration
1 - 100 nm
macromolecules
Pressure difference
(1 - 10 bar)
Microporous
Nanofiltration
0.5 - 5 nm
molecules
Pressure difference
(10 - 70 bar)
Microporous
Reverse Osmosis
< 1 nm
molecules
Pressure difference
(10 - 100 bar)
Nonporous
Dialysis
< 1 nm
molecules
Concentration difference
Nonporous or microporous
Electrodialysis
< 1 nm
molecules
Electrical potential difference
Nonporous or microporous
Pervaporation
< 1 nm
molecules
Concentration difference
Nonporous
Gas Permeation
< 1 nm
molecules
Partial pressure difference
(1 - 100 bar)
Nonporous
Membrane Distillation
< 1 nm
molecules
Partial pressure difference
Microporous


Table 2: Examples of Applications and Alternative Separation Processes
Process
Applications
Alternative Processes
Microfiltration
Separation of bacteria and cells from solutions
Sedimentation,
Centrifugation
Ultrafiltration
Separation of proteins and virus,
concentration of oil-in-water emulsions
Centrifugation
Nanofiltration
Separation of dye and sugar,
water softening
Distillation,
Evaporation
Reverse Osmosis
Desalination of sea and brackish water,
process water purification
Distillation,
Evaporation,
Dialysis
Dialysis
Purification of blood (artificial kidney)
Reverse osmosis
Electrodialysis
Separation of electrolytes from nonelectrolytes
Crystallization,
Precipitation
Pervaporation
Dehydration of ethanol and organic solvents
Distillation
Gas Permeation
Hydrogen recovery from process gas streams,
dehydration and separation of air
Absorption,
Adsorption,
Condensation
Membrane Distillation
Water purification and desalination
Distillation