Physical diffusivity of CO2 in blended PZ-MPDL solvent – at different solvent concentrations and temperatures

https://doi.org/10.3390/en14206822

“In this study, the physical diffusivity of CO₂ in blended PZ-MPDL solvent was calculated based on the modified Stokes–Einstein equation as Eq. (9) [15] through the dynamic viscosity of the solvent (given in Table 4). The calculated results are presented in Fig. 3. It was found that the physical diffusivity of CO₂ in blended PZ-MPDL solvent increased as temperature increased. This dues to the fact that at elevated temperature, the CO₂ has higher kinetics energy to physically diffuse through the solvent [8]. Additionally, viscosity of the solvent was found to be lower as temperature increased (as shown in Table 4 and Fig. 2). As a result, CO₂ then easily diffused through the solvent. On another hand, as concentration of PZ in the blended solvent increased, the solvent viscosity was observed to be increased. Thus, the physical diffusivity of CO₂ became lower. Interestingly, among the three PZ/MPDL concentration ratios in this study, there was an insignificant difference of the physical CO₂ diffusivity as shown in Fig. 3. In comparison with conventional amines, the physical CO₂ diffusivity of blended PZ-MPDL was (i) lower than that of 30 %wt. AMP, 30 %wt. MDEA, and 30 %wt. MEA, respectively and (ii) in the same range with that of 12/18 %wt. PZ/AMP and 12/18 %wt. PZ/MDEA. The observed results are in good agreement with a prior discussion that the physical CO₂ diffusivity strongly depends on the solvent viscosity and decreases as solvent viscosity increased. Even though the physical CO₂ diffusivity of blended PZ-MPDL is lower than that of conventional single amines (i.e., AMP, MDEA, and MEA), it should be mentioned that the mass transfer and kinetics of CO₂ absorption of the amine solvent is controlled by chemical reactivity between CO₂ and amine; not by diffusion [19]. Hence, the mass transfer and kinetics performance of blended PZ-MPDL should be further investigated. Additionally, the physical CO₂ diffusivity data obtained from the present work will be very useful for those studies.(9)DCO2−solventμsolvent0.8=DCO2−waterμwater0.8where DCO2−solvent is physical diffusivity of CO₂ in blended PZ-MPDL solvent (m²/s), DCO2−water is physical diffusivity of CO₂ in water (m²/s), μsolvent is dynamic viscosity of blended PZ-MPDL solvent (mPa s), and μwater is dynamics viscosity of water (mPa s).”

“Fig. 3. Physical diffusivity of CO₂ in blended PZ-MPDL and conventional solvents.”