Analysis of the reduction of energy cost by using MEA-MDEA-PZ solvent for post-combustion carbon dioxide capture (PCC)

The blends of monoethanolamine (MEA), N-methyl-diethanolamine (MDEA) and piperazine (PZ) as a solvent for CO2 capture were investigated in terms of CO2 absorption-desorption performance. The total concentration of the blends was 6M mixed with different amine molar ratios, 3M MEA-2.5M MDEA-0.5M PZ (Blend-1), 3M MEA-2M MDEA-1M PZ (Blend-2) and 3M MEA-1.5M MDEA-1.5M PZ (Blend-3). The CO2 equilibrium solubility, absorption capacity, initial absorption rate, speciation, relative energy consumption and heat of absorption for each blend were investigated in this work. The results showed that Blend-3 had the best CO2 absorption performance in terms of the CO2 equilibrium solubility, initial CO2 absorption rate and CO2 absorption capacity compared to Blend-1 and Blend-2 and 5M MEA. 13C NMR spectroscopy was used to quantify species formed in the CO2-loaded MEA-MDEA-PZ solution and the results shows that Blend-1 system produced more bicarbonate and less carbamate compared to Blend-2 and Blend-3 systems. The heat of CO2 absorption was calculated using Gibbs-Helmholtz equation and the results showed that MEA-MDEA-PZ systems had lower absorption heat than that of MEA, DEA, AMP, PZ and trio-amine blends of MEA-AMP-PZ. For the CO2 desorption performance, three blends studied in this work had lower relative energy consumption for the solvent regeneration compared to 5M MEA and Blend-1 showed the best desorption performance. Among these blends, an increase in molar ratio of MDEA/PZ in the blends led to a decrease in energy consumption and an increase in cyclic capacity and the CO2 desorption rate. In addition, the blend of MEA-MDEA-PZ reduced the energy consumption by 15.22-49.92% compared to 5M MEA.