210
L. F. Vega et al.
step) → 10 kPa (desorption step) for VSA. For instance, for zeolite 13X, as H 2 O
molecules are pre-adsorbed in the pores, available adsorption sites on the porous
surface decrease, consequently resulting in a decreased CO 2 working capacity.
Conversely, water content affects the M-MOF-74 in less extend.
Moreover, M-MOF-74 structures offer better results, demonstrating that this type
of material can be appropriate for this technology. It should be mentioned that ACs
at the selected VSA conditions possess low working capacities, nonetheless, as a
consequence higher adsorption pressures lead to a much higher amount of recovered
CO 2 using these materials, even higher than obtained with Mg-MOF-74.
Swing adsorption cycles can be controlled to meet an array of testing requirements. For example, same working capacities, higher purities, etc., are attainable by
adjusting the conditions for adsorption/desorption. However, the best selection for
the CO 2 capture process is dictated by the most cost-effective material [181]. The
growth of the energy consumption index (i.e. the amount of energy required per mass
of CO 2 captured and separated [198]) with the increase in the amount of impurities
present in the mixture is also depicted in Fig. 22, in order to assess its effect in
different materials performance. A higher required adiabatic work is associated with
a lower desorption pressure in VSA. However, reducing the regeneration pressure
from 10 to 5 kPa decreases the energetic index due to a higher proportional increase
in the amount of carbon dioxide recovered per cycle. It can also be seen that the
specific energy consumption index in VSA processes has the tendency to increase
as impurities are included in the mixture. However, it is remarkable that in some
cases, the value decreases with including impurity traces in the feed stream, up to
an inflection point of a very low H 2 O content, where the index will exponentially
increase by having a higher water content in the mixture, as observed in [181]. Subsequently, a trade-off between increased working capacities and energy costs exists. By
comparing with absorption technology [199], some structures achieve values close
to 2–2.5 GJ tCO 2
−1 , similar values to the ones obtained in the previous section for
aqueous amines.
In summary, in this section, we have illustrated how accurate force fields empower
molecular simulations as a tool to assess the best materials for CO 2 separation by
adsorption at the needed operating conditions, even in the absence of experimental
data for mixtures. After evaluating the different parameters, Mg-MOF-74 is recognised as a promising material utilised in V/PSA processes due to its excellent performance and “buffer” behaviour with the inclusion of lower amounts of impurities. Its
future applicability will depend on its stability, price and availability.
5 Summary and Conclusions
Throughout this chapter, we have illustrated some examples of how the theory of
complex fluids and molecular simulations can help to mitigate climate change by
applying them to specific cases where molecular information is needed to better
L. F. Vega et al.
step) → 10 kPa (desorption step) for VSA. For instance, for zeolite 13X, as H 2 O
molecules are pre-adsorbed in the pores, available adsorption sites on the porous
surface decrease, consequently resulting in a decreased CO 2 working capacity.
Conversely, water content affects the M-MOF-74 in less extend.
Moreover, M-MOF-74 structures offer better results, demonstrating that this type
of material can be appropriate for this technology. It should be mentioned that ACs
at the selected VSA conditions possess low working capacities, nonetheless, as a
consequence higher adsorption pressures lead to a much higher amount of recovered
CO 2 using these materials, even higher than obtained with Mg-MOF-74.
Swing adsorption cycles can be controlled to meet an array of testing requirements. For example, same working capacities, higher purities, etc., are attainable by
adjusting the conditions for adsorption/desorption. However, the best selection for
the CO 2 capture process is dictated by the most cost-effective material [181]. The
growth of the energy consumption index (i.e. the amount of energy required per mass
of CO 2 captured and separated [198]) with the increase in the amount of impurities
present in the mixture is also depicted in Fig. 22, in order to assess its effect in
different materials performance. A higher required adiabatic work is associated with
a lower desorption pressure in VSA. However, reducing the regeneration pressure
from 10 to 5 kPa decreases the energetic index due to a higher proportional increase
in the amount of carbon dioxide recovered per cycle. It can also be seen that the
specific energy consumption index in VSA processes has the tendency to increase
as impurities are included in the mixture. However, it is remarkable that in some
cases, the value decreases with including impurity traces in the feed stream, up to
an inflection point of a very low H 2 O content, where the index will exponentially
increase by having a higher water content in the mixture, as observed in [181]. Subsequently, a trade-off between increased working capacities and energy costs exists. By
comparing with absorption technology [199], some structures achieve values close
to 2–2.5 GJ tCO 2
−1 , similar values to the ones obtained in the previous section for
aqueous amines.
In summary, in this section, we have illustrated how accurate force fields empower
molecular simulations as a tool to assess the best materials for CO 2 separation by
adsorption at the needed operating conditions, even in the absence of experimental
data for mixtures. After evaluating the different parameters, Mg-MOF-74 is recognised as a promising material utilised in V/PSA processes due to its excellent performance and “buffer” behaviour with the inclusion of lower amounts of impurities. Its
future applicability will depend on its stability, price and availability.
5 Summary and Conclusions
Throughout this chapter, we have illustrated some examples of how the theory of
complex fluids and molecular simulations can help to mitigate climate change by
applying them to specific cases where molecular information is needed to better