Comparative Kinetic Studies of Solid Absorber Catalyst (K/MgO) and Solid Desorber Catalyst (HZSM-5)-Aided CO2 Absorption and Desorption from Aqueous Solutions of MEA and Blended Solutions of BEA-AMP and MEA-MDEA
Abstract:The kinetic performance of a novel amine solvent blend BEA-AMP was compared with MEA and blended MEA-MDEA in the presence and absence of a solid acid catalyst (HZSM-5) in the desorber column of a bench-scale pilot plant. In addition, a total of seven solid base catalysts were screened using a semibatch reactor to select the one that is most suitable as catalyst for amine-based CO 2 absorption. The selected solid base catalyst, K/MgO, was placed in the absorber of the pilot plant. Overall, three absorber-desorb… Show more
“…These surface areas were much larger than gas–liquid interfacial area (55.4 cm 2 ) of the reactor [23]. The pore diameters were 31.3 nm (CaCO 3 ), 4.31 nm (MgCO 3 ) from this study and 6.46 nm (BaCO 3 ) from other work [29], which facilitated the external mass transfer of MEA molecules onto solid surface. Figure 2.SEM and BET of CaCO 3 , MgCO 3 .Figure 3.SEM of BaCO 3 .…”
Section: Resultsmentioning
confidence: 59%
“…From BET, the surface areas were 0.428 m 2 g −1 for CaCO 3 and 9.498 m 2 g −1 for MgCO 3 from this work. BaCO 3 is reported by others as 4.66 m 2 g −1 for surface area, pore volume of 0.008 cm 3 g −1 and pore size of 6.46 nm [29]. These surface areas were much larger than gas–liquid interfacial area (55.4 cm 2 ) of the reactor [23].…”
The mechanism was proposed of heterogeneous catalytic CO
2
absorptions with primary/secondary amines involving ‘catalytic carbamate formation’. Compared with the non-catalytic ‘Zwitterion mechanism’, this Eley–Rideal model was proposed for CO
2
+ RR′NH with MCO
3
(M = Ca, Mg, and Ba) with four elementary reaction steps: (B1) amine adsorption, (B2) Zwitterion formation, (B3) carbamate formation, and (B4) carbamate desorption. The rate law if determining step of each elementary step was generated based on ‘steady-state approximation’. Furthermore, the solid chemicals were characterized by SEM and BET, and this rate model was verified with 39 sets of experimental datasets of catalytic CO
2
–MEA absorptions with the existence of 0–25 g CaCO
3
, MgCO
3
and BaCO
3
. The results indicated that the rate-determining step was B1 as amine adsorption onto solid surface, which was pseudo-first-order for MEA. This was the first time that the Eley–Rideal model had been adopted onto the reactions of CO
2
+ primary/secondary amines over alkaline earth metal carbonate (MCO
3
).
“…These surface areas were much larger than gas–liquid interfacial area (55.4 cm 2 ) of the reactor [23]. The pore diameters were 31.3 nm (CaCO 3 ), 4.31 nm (MgCO 3 ) from this study and 6.46 nm (BaCO 3 ) from other work [29], which facilitated the external mass transfer of MEA molecules onto solid surface. Figure 2.SEM and BET of CaCO 3 , MgCO 3 .Figure 3.SEM of BaCO 3 .…”
Section: Resultsmentioning
confidence: 59%
“…From BET, the surface areas were 0.428 m 2 g −1 for CaCO 3 and 9.498 m 2 g −1 for MgCO 3 from this work. BaCO 3 is reported by others as 4.66 m 2 g −1 for surface area, pore volume of 0.008 cm 3 g −1 and pore size of 6.46 nm [29]. These surface areas were much larger than gas–liquid interfacial area (55.4 cm 2 ) of the reactor [23].…”
The mechanism was proposed of heterogeneous catalytic CO
2
absorptions with primary/secondary amines involving ‘catalytic carbamate formation’. Compared with the non-catalytic ‘Zwitterion mechanism’, this Eley–Rideal model was proposed for CO
2
+ RR′NH with MCO
3
(M = Ca, Mg, and Ba) with four elementary reaction steps: (B1) amine adsorption, (B2) Zwitterion formation, (B3) carbamate formation, and (B4) carbamate desorption. The rate law if determining step of each elementary step was generated based on ‘steady-state approximation’. Furthermore, the solid chemicals were characterized by SEM and BET, and this rate model was verified with 39 sets of experimental datasets of catalytic CO
2
–MEA absorptions with the existence of 0–25 g CaCO
3
, MgCO
3
and BaCO
3
. The results indicated that the rate-determining step was B1 as amine adsorption onto solid surface, which was pseudo-first-order for MEA. This was the first time that the Eley–Rideal model had been adopted onto the reactions of CO
2
+ primary/secondary amines over alkaline earth metal carbonate (MCO
3
).
“…With the aid of MgCO 3 , the time was reduced to 24 min (21 min less) for 1.0 mol/L and 45 min for 1.5 mol/L at optimized conditions. The effect of MgCO 3 was similar to that of CaCO 3 at 1.0 mol/L, but not very helpful at 1.5 mol/L with 5 g. If bigger than 5 g MgCO 3 , the absorption curves were worse than the non-catalytic curves due to “agglomeration” [40]. Therefore, CaCO 3 was a better solid for DEEA than MgCO 3 .…”
Section: Resultsmentioning
confidence: 99%
“…This poorer effect of CaCO 3 and MgCO 3 at large amount to 1.5 mol/L DEEA was probably due to the “agglomeration” [40] of solid chemicals, where the liquid covered the solid surface area and inhibited the catalysis. Such phenomena were also reported by other researchers with 0 g > 50 g CaCO 3 to 4.0 mol/L BEA + AMP amine blend [40]. For 1DMA-2P, it was 7.5 g > 5 g > 10 g > 0 g for 1.0 mol/L and 10 g > 7.5 g ≈ 5 g > 0 g for 1.5 mol/L for CaCO 3 .…”
Section: Resultsmentioning
confidence: 99%
“…For MgCO 3 , it was 10 g > 5 g > 7.5 g > 0 g for 1.0 mol/L and 5 g > 7.5 g ≈ 10 g ≈ 0 g for 1.5 mol/L. The larger amount of MgCO 3 at 1.5 mol/L also resulted in agglomeration and made the catalysis comparable to non-catalytic absorption [40]. The removal of agglomeration awaits further investigation.…”
Studies of catalytic CO2 absorption and desorption were completed in two well-performed tertiary amines: diethylmonoethanolamine (DEEA) and 1-dimethylamino-2-propanol (1DMA-2P), with the aid of CaCO3 and MgCO3 in the absorption process, and with the aid of γ-Al2O3 and H-ZSM-5 in the desorption process. The batch process was used for CO2 absorption with solid alkalis, and the recirculation process was used for CO2 desorption with solid acid catalysts. The CO2 equilibrium solubility and pKa were also measured at 293 K with results comparable to the literature. The catalytic tests discovered that the heterogeneous catalysis of tertiary amines on both absorption and desorption sides were quite different from monoethanolamine (MEA) and diethanolamine (DEA). These results were illustrative as a start-up to further study of the kinetics of heterogeneous catalysis of CO2 to tertiary amines based on their special reaction schemes and base-catalyzed hydration mechanism.
The “coordinative effect” was discovered in MEA + DEA bi‐solvents already, and it enhances both CO2 absorption and desorption within MEA + RR'NH simultaneously. A recent study verified strong coordinative effects within MEA + BEA (RR'NH) + AMP tri‐solvents, but whether the coordination was 100% attributed to interaction of MEA + BEA needs to be confirmed. This study investigated the “coordinative effect” separately within MEA + AMP (hindered amine) and MEA + BEA (RR'NH). The CO2 absorption and desorption processes were performed onto MEA + AMP and MEA + BEA (0.1 + 2–0.5 + 2 mol/L) separately. The CO2 absorption–desorption parameters were calculated to evaluate the coordinative effects on a consistent level. Results indicated negligible “coordinative effect” within MEA + AMP but strong coordination within MEA + BEA. Both CO2 absorption and desorption performance of MEA + BEA (0.2 + 2 mol/L) was better than 2.0 mol/L BEA simultaneously. The coordinative effect was optimum within MEA + BEA bi‐solvents at 0.2 + 2 mol/L close to 0.3 + 2 + 2 mol/L of MEA + BEA + AMP tri‐solvents. Based on analysis, carbamate stability and pKa were two main factors that determine negligible–strong coordinative effects between AMP and BEA; different pKa reflected the optimized blending ratios of MEA + DEA (3/7) and MEA + BEA (2/20).
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