https://doi.org/10.1016/j.petlm.2016.11.002
“The potential of tri–solvent blends has indicated quad–solvent blends can also prove to be a viable alternative aqueous amine solution, though their study is still very scarce. This combination can further guarantee a high equilibrium CO2 loading and cyclic loading and cyclic capacity with no precipitation and reduced energy of regeneration. Aqueous quad–solvent blends containing MEA, TETA, 2-amino–2–methyl–1–propanediol (AMPD), and (piperazinyl1-1)-2-ethylamine (PZEA) has been studied [115]. Based on the pilot plant studies, they confirmed that their novel quad–solvent blends showed less energy of regeneration (25%) and reduced liquid/gas flow rate ratio (27%) compared to 5 kmol/m3 MEA.
An in–house experimental analysis was carried out on the equilibrium CO2 solubility and absorption capacity (40 °C, atmospheric pressure and 99.99% CO2) of a novel quad–solvent blend consisting of AMP, PZ, MEA and DETA [112]. The concentration of each solvent in this novel quad–solvent blend was varied while the total aqueous solution concentration being kept constantly at 5 kmol/m3. The quad–solvent blend concentration was 2 kmol/m3 AMP–0.5 kmol/m3 PZ–1 kmol/m3 DETA–1.5 kmol/m3 MEA and 1.5 kmol/m3 AMP–0.5 kmol/m3 PZ–1.5 kmol/m3 DETA–1.5 kmol/m3 MEA. It was confirmed that the quad–solvent blends showed much higher equilibrium CO2 loading (39.8–45.7%) and absorption capacity (37–43%) compared to those of 5 kmol/m3 MEA. In addition, no precipitation was observed when the CO2 rich solutions of the quad–solvent blends were cooled at 20 °C for 400 h.
It is clear from Fig. 9 that that the absorption capacity of these quad–solvent blends (AMP–PZ–DETA–MEA) is similar to that the AMP–PZ–MEA tri–solvent blends but higher than single solvent MEA and AMP–PZ bi–solvent blend [112], [113].
Fig. 9. Comparison between MEA, bi–solvent, tri–solvent and quad–solvent blends in terms of αCO2 (mol CO2/mol amine) and absorption capacity (AC, mol CO2/l-amine soln.) at 99.99% CO2, 101.3 kPa and 40 °C.
Based on the results of the quad–solvent experimental study, it can be proposed that the application of quad–solvent blends will out–perform both single solvent MEA and bi–solvent blends but are competitive with tri–solvent blends for CO2 capture application. The studied quad–solvent blend developed by our research group comprised of one bicarbonate forming solvent (AMP) and three rate promoters (i.e. PZ, DETA and MEA). This combination can be further modified to improve the blend performance such as;
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blending two bicarbonate forming solvents (sterically hindered and/or tertiary monoamines) and two rate promoters (primary or secondary amines or polyamines).
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blending three bicarbonate forming solvents (sterically hindered and/or tertiary monoamines) and one rate promoter (polyamines).
Further studies will prove the viability of various solvent blend combinations.
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