Membranes - Introduction to Carbon Capture and Sequestration - page 284

Reverse Reverse

Osmosis

Utrafiltration Particle filtration

Separation
Process

Osmosis

Microfiltration

Nanofiltration

Aqueous
Salt

Whole
Broth Cells

E-Coat Pigment

Milk Proteins

Red Blood Cells

Relative
Size of
Common
Materials

Gelatin

Fat Micelles

Bacteria

Metal Ion

Endotoxin Pyrogen Activated

Carbon

Oil Emulsions

Synthetic
Dyes
Lactose
(Sugars)

Virus

Blue
Indigo Dye

Cryptosporidium

Colloidal
Silica

Giardia
Cyst

Human Hair

Microns 0.001 0.01 0.1 1.0 10 100 1000

Approx Molecular
Weight

100 200 1,000 20,000 100,000 500,000 1 MM 5 MM

Figure 7.1.2 Filtration using membranes
Figure adapted from Koch Membrane Company.

Figure 7.1.2 illustrates the types of separations that are carried out by
fi ltration. We see that through microfi ltration we can remove bacteria
from water. However, if we would like to use this sieving mechanism for
gas separation, we will need to make materials with very narrow pores.
In fact, if we were to plot the molecular weights of the gasses we are
interested in separating on Figure 7.1.2 , we would see they are outside
the scale of “common” materials as defi ned in this graphic.
Membranes are often made of materials that are common and not
too expensive, such as rubber, polycarbonate, or polyimide. While not
exactly cheap either, they are common and accessible and can be made
in large quantities. A signifi cant number of applied technologies presently
use membrane processes for large volumes of fl uids. It is not too much
of a stretch of the imagination to think that membrane separation could
become part of CCS.