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

Cerium-MOF-Derived Composite Hierarchical Catalyst Enables Energy-Efficient and Green Amine Regeneration for CO2 Capture

The excessive energy consumed restricts the application of traditional postcombustion CO2 capture technology and limits the achievement of carbon-neutrality goals. Catalytic-rich CO2 amine regeneration has the potential to accelerate proton transfer and increase the energy efficiency in the CO2 separation process. Herein, we reported a Ce-metal-organic framework (MOF)-derived composite catalyst named HZ-Ni@UiO-66 with a hierarchical structure, which can increase the CO2 desorbed amount by 57.7% and decrease the relative heat duty by 36.5% in comparison with the noncatalytic monoethanolamine (MEA) regeneration process. The composite catalyst of the CeO2 coating from the UiO-66 precursor on the HZ-Ni carrier shows excellent stability with a long lifespan. The HZ-Ni@UiO-66 catalyst also shows a universal catalytic effect in typical blended amine systems with a large cyclic capacity. The HZ-Ni@UiO-66 catalyst effectively decreases the energy barrier of the CO2 desorption reaction to reduce the time required to reach thermodynamics, consequently saving the energy consumption generated by water evaporation. This research provides a new avenue for advancing amine regeneration with less heat duty at low temperatures.

Evaluating CO2 Capture Performance of Trisolvent MEA-BEA-AMP with Heterogeneous Catalysts in a Novel Bench-Scale Pilot Plant

To reduce the huge energy cost of CO2 capture technology applicable in industry, the CO2 absorption-desorption performance was conducted in a novel bench-scale pilot plant with hot water as a heat source. The trisolvent MEA(monoethanol amine)-BEA(butylethanol amine)-AMP(2-amino-2-methyl-1-propanol) was prepared at a specific concentration to analyze the CO2 capture performance and compared with 5 M MEA as the benchmark. Meanwhile, several solid acid catalysts, blended H-ZSM-5/γ-Al2O3(1/2), or HND-8, were packed in the desorber, and the solid base catalyst, CaCO3 or CaMg(CO3)2, was packed in the absorber with random packing. The CO2 absorption efficiency (AE), cyclic capacity (CC), and heat duty (HD) were tested onto MEA-BEA-AMP and MEA under various operating conditions. Experimental results indicated that the performance of 4.3 mol/L MEA-BEA-AMP was significantly better than 5 M MEA under both catalytic and noncatalytic operation. The most energy efficient combination of this study was discovered as 0.3 + 2 + 2 mol/L MEA-BEA-AMP, with 50 g (CaCO3/CaMg(CO3)2) in the absorber and 150 g H-ZSM-5/γ-Al2O3(1/2) in the desorber. The heat duty reached as low as 2.4 GJ/tCO2 at a FG of 7.0 L/min and a FL of 70 mL/min. These results were highly applicable in an industrial amine scrubbing pilot plant for CO2 capture.

Activated Carbon Produced from the Hydrothermal Treatment of Glucose with KOH Activation for Catalytic Absorption of CO2 in a BEA-AMP Bi-Solvent Blend

The amine-based postcombustion CO₂ capture (PCC) process involves absorption of CO₂ into a solvent and then regenerating the solvent to produce CO₂. In this study, the effect of an activated carbon (AC) catalyst, synthesized through hydrothermal treatment and furnace activation on CO₂ absorption in a 4M BEA/AMP amine blend, was evaluated and compared with that of a KMgO/CNTs (1:4) catalyst. The physical and chemical properties of AC were investigated with a scanning electron microscope (SEM), CO₂ temperature-programmed desorption (CO₂-TPD), Brunauer-Emmett-Teller (BET), powder X-ray diffraction (XRD), and thermogravimetric analyzer (TGA) and compared with the KMgO/CNTs (1:4) catalyst. The results showed that when compared against noncatalytic CO₂ absorption, AC enhanced the linear rate of CO₂ absorption by 33.3%, while for KMgO/CNTs, it was reported as 25.5%. The relatively higher surface area, combined with the higher number and strength of basic sites of AC relative to the KMgO/CNTs (1:4) catalyst, provided effective basic reaction sites for CO₂ absorption, thereby enhancing the rate of CO₂ absorption into the amine. AC was also relatively easier to synthesize which would provide a good replacement for the CNT-based catalyst which has carcinogenic tendencies.

Evaluating CO2 Desorption Activity of Tri-Solvent MEA + EAE + AMP with Various Commercial Solid Acid Catalysts

The Paris Agreement and one of its goals, “carbon neutrality,” require intensive studies on CO2 absorption and desorption processes. When searching for ways of reducing the huge energy cost of CO2 desorption in the amine scrubbing process, the combination of blended amine with solid acid catalysts turned out to be a powerful solution in need of further investigation. In this study, the tri-solvent MEA (monoethanolamine) + EAE(2-(ethylamino)ethanol) + AMP(2-amino-2-methyl-1-propanol) was prepared at: 0.2 + 2 + 2, 0.5 + 2 + 2, 0.3 + 1.5 + 2.5 and 0.2 + 1 + 3 mol/L. The heterogeneous catalytic CO2 desorptions were tested with five commercial catalysts: blended γ-Al2O3/H-ZSM-5, H-beta, H-mordenite, HND-8 and HND-580. Desorption experiments were conducted via a recirculation process with direct heating at 363 K or using temperature programming method having a range of 303–363 K. Then, the average CO2 desorption rate, heat duty and desorption factors were studied. After comparison, the order of CO2 desorption performance was found to be HND-8 > HND-580 > H-mordenite > Hβ > blended γ-Al2O3/H-ZSM-5 > no catalyst. Among the other combinations, the 0.2 + 1 + 3 mol/L MEA + EAE + AMP with HND-8 had a minimized heat duty (HD) of 589.3 kJ/mol CO2 and the biggest desorption factor (DF) of 0.0277 × (10−3 mol CO2)3/L2 kJ min. This study provided a kind of tri-solvent with catalysts as an energy-efficient solution for CO2 absorption and desorption in industrial CO2 capture pilot plants.

One-Step Synthesized SO42-/ZrO2-HZSM-5 Solid Acid Catalyst for Carbamate Decomposition in CO2 Capture

Amine-based CO₂ capture technology requires high-energy consumption because the desorption temperature required for carbamate breakdown during absorbent regeneration is higher than 110 °C. In this study, we report a stable solid acid catalyst, namely, SO₄^2-/ZrO₂-HZSM-5 (SZ@H), which has improved Lewis acid sites (LASs) and Bronsted acid sites (BASs). The improved LASs and BASs enabled the CO₂ desorption temperature to be decreased to less than 98 °C. The BASs and LASs of SZ@H preferred to donate or accept protons; thus, the amount and rate of CO₂ desorption from spent monoethanolamine were more than 40 and 37% higher, respectively, when using SZ@H than when not using any catalyst. Consequently, the energy consumption was reduced by approximately 31%. A catalyzed proton-transfer mechanism is proposed for SZ@H-catalyzed CO₂ regeneration through experimental characterization and theoretical calculations. The results reveal the role of proton transfer during CO₂ desorption, which enables the feasibility of catalysts for CO₂ capture in industrial applications.

Eley-Rideal model of heterogeneous catalytic carbamate formation based on CO2-MEA absorptions with CaCO3, MgCO3 and BaCO3

The mechanism was proposed of heterogeneous catalytic CO₂ absorptions with primary/secondary amines involving 'catalytic carbamate formation'. Compared with the non-catalytic 'Zwitterion mechanism', this Eley-Rideal model was proposed for CO₂ + RR'NH with MCO₃ (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 CO₂-MEA absorptions with the existence of 0-25 g CaCO₃, MgCO₃ and BaCO₃. 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 CO₂ + primary/secondary amines over alkaline earth metal carbonate (MCO₃).

Study of Catalytic CO₂ Absorption and Desorption with Tertiary Amine DEEA and 1DMA-2P with the Aid of Solid Acid and Solid Alkaline Chemicals

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.