Commercial Membrane Separation Processes

The current status of membrane separation technology is summarized in Table 1. There are seven commercial membrane separation processes. Of these, the first five - microfiltration, ultrafiltration, reverse osmosis, electrodialysis and dialysis - are all well-established technologies with a market served by several experienced companies. Although incremental improvements in membranes and membrane systems for these technologies are expected, no major breakthroughs appear imminent. The remaining two technologies - gas separation and pervaporation - are developing technologies for which the market size, application area, and process design are still changing. Finally, several processes not shown in Table 1, including coupled and facilitated transport, membrane contactors and membrane reactors, are still in

Table 1 Summary of the established membrane separation technologies

Process Type of Material Material Driving Status - typical application membrane passed retained force

Microfiltration

Ultrafiltration

Reverse osmosis

Electrodialysis

Dialysis

Gas separation

Pervaporation

Finely microporous 0.1-10 |im

Finely microporous 1-100 nm

Dense solution-

diffusion

Electrically charged films

Finely microporous 10-100 nm

Dense, solution-

diffusion

Dense, solution-

diffusion

Water, dissolved solutes

Suspended solids, bacteria

Water, dissolved Macromolecules, salts colloids

Water

Water

Dissolved salts

Ions

Dissolved salts, Blood dissolved gases

Permeable gases Impermeable and vapours gases and vapors

Permeable Impermeable micro-solutes micro-solutes and solvents and solvents

Pressure Developed (& US$700 million per difference year). Removal of suspended solids,

5-50 psi bacteria in pharmaceutical, electronics industries

Pressure Developed (& US$150 million per difference year). Removal of colloidal material

20-100 psi from wastewater, food process streams

Pressure Developed (& US$200 million per difference year). Drinking water from sea, brack-100-1000 psi ish or groundwater; production of ultrapure water for electronics and pharmaceutical industries

Voltage Developed (& US$200 million per difference year). Drinking water from brackish 1 -2 V water; some industrial applications too

Concentration Developed (&US$1.3 billion per year differences for artificial kidney; US$500 million per year for artificial lung)

Pressure Developing (&US$150 million per difference year). Nitrogen from air, hydrogen from 100-1000 psi petrochemical/refinery vents, carbon dioxide from natural gas, propylene and VOCs from petrochemical vents

Vapour Developing (& US$10 million per year).

pressure Dehydration of solvents (especially

1-10 psi ethanol)

the laboratory or early commercial stage. In the following sections each of these membrane technology areas is described briefly. More detailed descriptions of the more important processes are given elsewhere in the encyclopedia.

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