Absorption - Introduction to Carbon Capture and Sequestration - page 217

leaving the stripper has a higher partial pressure of CO 2 and lower
water content.

3. Reactivity: The effi ciency of the absorber depends on the reactivity

of the amines.

4. Stability: The more stable the amines, the higher the temperature at

the bottom of stripper. This higher temperature translates to a higher
pressure at the top of the stripper.

5. Viscosity: A high viscosity makes the heat exchange less effi cient.

Rochelle and his co-workers evaluated different amines that are avail-
able commercially, and found that piperzine (diethylenediamine) performs
signifi cantly better than MEA on many of the points above. Changing from
MEA to piperzine reduced the energy requirements signifi cantly, as shown
in Figure 5.7.2 . The trouble with picking an amine, though, is that no sin-
gle selection seems to meet all of our ideal characteristics. Our perfect
solvent would have high capacity, high heat of absorption, and a high rate
of CO 2 absorption. We also want a higher stripper temperature. But the
amine with the best capacity is often not the same as the amine with the
best heat of absorption or the best absorption rate. So it's complicated,
and from a research point of view, it is interesting to see whether novel
amines will be developed that outperform piperzine.
As we will see in the next few chapters, alternative technologies such
as solid adsorption and membrane technologies do not have a preexist-
ing “cousin” technology upon which to base cost and designs.
Consequently, it will take us much longer to develop these methods
“from scratch,” so to speak. Due to these factors, it is likely that at least
the fi rst generation of carbon capture plants will be based on liquid
absorption. Some critics of carbon capture research say that because
liquid absorption has such a great lead time over alternative methods, it
will be very unlikely that competing technologies will ever be viable. On
the other hand, it is easy to point out many examples of new discoveries
that have been transformative within an industry, and our research is
aimed to achieve exactly this within the fi eld of carbon capture.
A different perspective has to do with the cost of carbon capture. A
liquid absorption carbon capture unit will account for something on the
order of 30% of the costs of a power plant. Compared to these numbers,
research is only a very tiny fraction of the costs of carbon capture adop-
tion. In this context, it is important that we explore all possibilities for