Membrane Separation

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 痠 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