CO2 absorption capacity of blended PZ-MPDL solvent

“The CO2 absorption of blended PZ-MPDL solvent was experimentally measured in terms of CO2 loading (mol CO2/mol amine). This CO2 absorption performance indicator is widely used in the literature and can be interpreted that the larger the CO2 loading, the higher the absorption capacity. In this study, the experiment was done at 313 K and 10% v/v CO2 at atmospheric pressure, which is a typical operating condition of gas absorption column for fossil fired power generation plant. The CO2 absorption capacity of novel blended PZ-MPDL and conventional benchmarking MEA are presented in Table 6. The results showed that the absorption capacity of 30 %wt. blended PZ-MPDL (at 5/25, 10/20, and 15/15 %wt.) were much higher than that of 30 %wt. MEA at 30, 45, and 49%, respectively. Additionally, it was observed that the absorption capacity increased as concentration of PZ increased. This is because PZ has higher absorption capacity than MPDL and much higher than MEA [6]. As a result, 15/15 %wt. PZ/MPDL possessed the highest absorption capacity among the three studied ratios (at 0.741 mol CO2/mol amine). It is worthwhile to mention that the CO2 absorption capacity is one of important parameters affecting an operation of absorption column. The solvent with high absorption capacity is favorable and leads to a larger amount of absorbed CO2 in the absorption column. Based on the results obtained from the current study in that the blended PZ-MPDL solvent has much higher absorption capacity than the conventional benchmarking MEA, it can be pointed out that several advantages of using blended PZ-MPDL can be proposed. For the same level of CO2 removal, in comparison with conventional MEA, a utilization of blended PZ-MPDL can (i) reduce the total amine concentration in lean solvent stream, (ii) lower the lean solvent flow rate, (iii) elevate the rich gas flow rate, and (iv) decrease the liquid-gas mass ratio. As a result, energy requirement for fluid transportation and operating cost of CO2 capture can be reduced.

Based on the results presented in this work, it can be summarized that the novel blended PZ-MPDL showed a great potential as an alternative solvent for capturing CO2. Its density was found to be very close to that of water and conventional solvents. The viscosity of blended PZ-MPDL was slightly higher than that of conventional single solvent (i.e., AMP) and close to that of conventional blended solvents (i.e., PZ-MDEA and PZ-AMP). In terms of physical diffusivity of CO2, it was found that there was an insignificant difference among the three concentrations of blended PZ-MPDL. Additionally, their physical diffusivities of CO2 were lower than that of AMP, MDEA, and MEA solvents, respectively and in the same range with that of conventional blended PZ-MEDEA and PZ-MEA solvents. These physical properties are essential for (i) further investigation on mass transfer and absorption kinetics, (ii) fluid dynamics simulation, and (iii) design of gas and liquid flow rates in the absorption operation. In addition to the physical properties, the CO2 absorption capacity, which is a very efficient indicating parameter representing the CO2 capture performance, was evaluated. The novel blended PZ-MPDL showed much higher CO2 absorption capacity than that of 30 %wt. MEA. Especially, at PZ/MPDL blended ratio of 15/15 %wt., 49% increment of CO2 absorption capacity was observed. In comparison with MEA solvent, PZ-MPDL solvent can lead to a reduction of lean amine concentration and lean amine flow rate as well as an augmentation of gas flow rate to achieve the same CO2 removal in the absorption column. Even though, the physical properties and the CO2 absorption capacity of novel blended PZ-MPDL solvent preliminary showed its great potential as an alternative solvent for carbon capture applications, its comprehensive investigation on mass transfer performance, absorption kinetics, energy requirement for solvent regeneration, and solvent stability should be further studied for an effectively utilization of this novel solvent.

Table 6. Absorption capacity of CO2 into PZ-MPDL and MEA at 313 K and 10% v/v CO2.

Temperature (K) Absorption capacity (mol CO2/mol amine)
Empty Cell 30 %wt. MEA 5/25 %wt. PZ/MPDL 10/20 %wt. PZ/MPDL 15/15 %wt. PZ/MPDL
313 0.496 0.647 0.719 0.741

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