Influence of solvent on CO2 absorption with different liquid to gas ratios

“The figure (Fig. 7) illustrates the effect of the L/G ratio on CO2 recovery for three selected amine solutions: 30 wt%
MEA—the standard reference solution, the amine most commonly used in the industry for removing acidic components;
AMP/PZ solution, a system of an amine with steric hindrance with the addition of a polyamine; and multicomponent
solution 2, which is a novel mixture of an amine with an organic compound [25]. As predicted, the novel solvents gave
a higher CO2 recovery than the standard MEA solution. Differences in CO2 recovery between the solutions analyzed are
dictated by the various sorption capacities, reaction kinetics (absorption rate) and some physicochemical properties (density, viscosity, surface tension, etc.) that were described in previous publications where new absorption solutions were
found [25,31].”


“Multicomponent CO2 recovery exhibits higher CO2 recovery than MEA solution, mainly because of the higher sorption capacity and comparable absorption rate [25]. Thus, the solvent can absorb more carbon dioxide molecules at a similar liquid flow. CO2 recovery for the multicomponent did not significantly change CO2 recovery with a liquid-to-gas ratio compared to other solutions, so the multicomponent can be used over a wider L/G range, giving a more constant CO2 separation efficiency (6.5−8.4 kg/kg). Among the others, the highest CO2 efficiency at the conducted liquid flow is shown by AMP/PZ (93.4–97.0%). This result can be explained by
the higher sorption capacity of AMP/PZ with faster reaction kinetics. Therefore, the sorbent can absorb additional CO2
particles faster [31]. The optimal CO2 recovery for AMP/PZ solution was obtained for an L/G ratio of approximately 7.6 kg/kg, which was higher than MEA (ca. 6.5) and higher than multicomponent (ca. 7.2 kg/kg).
Figure 8 illustrates the effects of the L/G ratio on the reboiler heat duty for selected solvents. For MEA at an
L/G ratio equal to approximately 6.5, we see the lowest reboiler heat duty. With the L/G ratio increasing, the optimal reboiler heat duty for both AMP/PZ and multicomponent decreases [32]. The reboiler heat duty in the solvent regeneration process for both AMP/PZ and multicomponent is lower than with the MEA solution. Therefore, the strong influence on the studied system arises from the relationship between the separated CO2 from the gas stream and the reboiler heat duty as well as the kinetics of the absorption [31].

From Figs. 7 and 8, we can simply read that MEA requires a higher heater power setting to attain satisfactory efficiency (>85%). Thus, the reboiler heat duty will increase. Lowering the heater power setting for AMP/PZ solution can lower heat requirements in addition, so AMP/PZ solution will have the lowest reboiler heat duty among the solvents investigated and will give a perspective for investigating the CO2 absorption process on a larger scale.”

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