527 Q6 Ch4 Adsorption 1&2

Adsorbents are porous solids, while absorbents are liquid solutions.

• True

• False

Answer explanation

Which of the following statements is true?

• CC by adsorption always selectively adsorbs the CO₂ only.

• CC by adsorption always selectively adsorbs the other gases that are mixed with the CO₂.

• Either option is doable.

To capture CO₂ from a dilute mixture (i.e., with low CO₂ concentration),

• absorption techniques are more effective.

• adsorption techniques are more effective.

• both absorption and adsorption techniques are equally effective.

"Chemisorption offers greater binding strength between a gas molecule and the adsorbent surface, compared to physisorption. So, chemisorption is the primary mechanism in terms of material design, in order to minimize the energy required for regeneration."

Which part of this paragraph is TRUE?

• Chemisorption offers greater binding strength between a gas molecule and the adsorbent surface, compared to physisorption.

• Chemisorption is the primary mechanism in terms of material design, in order to minimize the energy required for regeneration.

• The entire paragraph is true.

Which of the following statements is TRUE?

(check all that applies; no partial credit)

• Sorbents with larger pore size are saturated with CO₂ more slowly.

• Sorbents with larger pore size have limited uptake capacities.

• CO₂ travels more easily in sorbent particles with larger pores.

• None of them is true.

To increase CO₂ uptake, we need highly porous solid particles with interconnected pores.

• True

• False

To separate a gas selectively from a given mixture, the sorbent could be designed to target differences in molecular weight or kinetic diameters of the mixture components, which lead to different rates of diffusion through the sorbent.

• True

• False

For a flue-gas mixture containing CO₂, O₂, and N₂, which of the following statements is TRUE?

(check all that applies; no partial credit)

• It is difficult to separate CO₂ from O₂ and N₂ based on kinetic diameter (i.e., molecule size).

• The higher reactivity of CO₂, compared to O₂ and N₂, makes a zeolite sorbent more selective for CO₂.

• It is not possible to capture CO₂ from flue-gas mixtures using adsorption systems.

• MOFs with polar functional groups (like −NO₂ and −CN) can be used because they have higher CO₂/CH₄, CO₂/N₂, and CO₂/O₂ selectivities.

To increase the CO₂ selectivity of zeolites and MOFs, a flue-gas mixture of CO₂, H₂O, O₂, and N₂ must be pre-treated to remove the H₂O prior to CC.

• True

• False

Metal Organic Frameworks (MOFs) are materials containing a framework of metal vertices and organic-based linkers. The CO₂ selectivity can be tuned through the choice of metal and the length/chemical composition of the linkers.

• True

• False