Fig. 1
XRD diffraction pattern of the nano-CaO adsorbent.
Note: XRD, X-ray diffraction
Fig. 2
SEM micrograph of Cao adsorbent at 5000× and EDS analysis.
Notes: EDS, electron diffraction scattering; SEM, scanning electron microscopy
Fig. 3
Determination of pore-size distribution by the BJH method.
Notes: BJH, Barrett-Joyner-Halenda
Table 1
Kinetic parameters evaluated for the process of CO2 adsorption onto the nano-CaO adsorbent at different temperatures
| 25°C | 50°C | 75°C | ||
|---|---|---|---|---|
| Pseudo-first-order model | k1 (/min) | 0.24 | 0.58 | 0.13 |
| qmax (mmol/g) | 4.59 | 3.81 | 5.27 | |
| R2 | 0.78 | 0.58 | 0.74 | |
| Pseudo-second-order model | k2 (/min) | 3.41 | 1.4 | 0.20 |
| qmax (mmol/g) | 9.02 | 10.08 | 11.02 | |
| R2 | 0.9999 | 0.9996 | 0.9998 | |
| Elovich | α (mmol/g) | 176.8 | 122.1 | 41.2 |
| β (mmol/g) | 1.00 | 1.16 | 1.40 | |
| R2 | 0.48 | 0.50 | 0.59 | |
Intraparticle diffusion
| qe (mmol/g) | 7.56 | 8.33 | 8.53 |
| kip1 (mmol/g min1/2) | 4.36 | 4.81 | 4.92 | |
| R2 | 0.87 | 0.85 | 0.90 | |
| qe (mmol/g) | 3.38 | 3.51 | 4.64 | |
| kip2 (mmol/g min1/2) | 0.87 | 0.90 | 1.19 | |
| R2 | 0.995 | 0.94 | 0.94 |
Fig. 4
Kinetic data of CaO adsorption onto nano-CaO adsorbent, at different temperatures and 1 atm pressure.
Notes: Linear plots of the pseudo-second-order model: t/qt = 0.11t + 0.004 (25°C); t/qt = 0.099t + 0.02 (50°C); t/qt = 0.089t + 0.05 (75°C); R2 = 0.9. qt = the amount of CO2 adsorbed at time t; R2, correlation coefficient
Fig. 5
Kinetic data of CaO adsorption onto nano-CaO adsorbent, at different temperatures under 1 atm pressure.
Notes: Linear plots correspond to the intraparticle diffusion kinetic model. (1) qt = 7.1√t, qt = 0.73√t+6.2 (R2 = 0.94), and qe = 9.2 (25°C). (2) qt = 7.7√t, qt = 0.86√t+6.7 (R2 = 0.96), and qe = 10.3 (50°C). (3) qt = 7.72√t, qt = 0.86√t+6.7 (R2 = 0.97), and qe = 10.9 (75°C). qe, the amount of CO2 adsorbed at equilibrium; qt = the amount of CO2 adsorbed at time t; R2, correlation coefficient
Table 2
Summarized linear isotherm parameters for CO2 adsorption on nano-CaO adsorbent at the temperatures of 25°C, 50°C, and 75°C and at pressures of 1 atm, 5 atm, 10 atm, and 15 atm for each temperature
| Temperature (°C) | Langmuir constants | Freundlich constants | ||||
|---|---|---|---|---|---|---|
| qmax (mmol/g) | KL (/atm) | R2 | KF (mmol/g [atm]1/n) | 1/n | R2 | |
| 25 | 10.74 | 0.48 | 0.996 | 0.111 | 0.049 | 0.78 |
| 50 | 11.31 | 0.35 | 0.998 | 0.099 | 0.022 | 0.75 |
| 75 | 12.55 | 0.31 | 0.998 | 0.091 | 0.009 | 0.88 |
Fig. 6
Isotherm data of CaO adsorption onto nano-CaO adsorbent, at different temperatures.
Notes: Linear equations of the Langmuir model: (1) PCO2/qe = 0.093 PCO2 +0.045 (R2 = 0.996) (25°C). (2) PCO2/qe = 0.088 PCO2 +0.031 (R2 = 0.998) (50°C). (3) PCO2/qe = 0.080 PCO2 +0.024 (R2 = 0.998) (75°C). PCO2, pressure of the adsorbed gas CO2; qe is the maximum adsorption capacity of CO2 at equilibrium; R2, correlation coefficient
Fig. 7
Thermodynamic data of CaO adsorption onto nano-CaO adsorbent, at different temperatures under 1 atm pressure.
Notes: Linear plot of the van’t Hoff modified equation: ln KL = −3917 (1/T) + 12.2 (R2 = 0.9). KL, the Langmuir isotherm constant; R2, correlation coefficient
Fig. 8
Thermodynamic data of CaO adsorption onto nano-CaO adsorbent, at different temperatures under 1 atm pressure.
Notes: Linear plot of the Arrhenius equation: ln kV = 8830 (1/T) – 26.9 (R2 = 0.93). kv, the velocity constant; R2, correlation coefficient