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The CO 2 capture and separation performance is enhanced by the improved structural polarity and additional adsorption sites created by anchoring alkali metal Li/Na/K. And the increase shows a positive correlation with AM concentration. Specially, UPC-6Li presents the best CO 2 capture capacity of 221.64 cm3 cm−3, along with the CO 2 over N 2 /CH 4 selectivity of 308/206, among UPC-AMs. [Display omitted] • CO 2 capture and separation performance were evaluated in 2D-COFs anchored by different concentration alkali metal (Li, Na, and K). • UPC-6Li exhibited the best CO 2 capture capacity of 221.64 cm3 cm−3 and CO 2 over N 2 /CH 4 selectivity of 308/206. • Improved structural polarity and additional metal adsorption sites are the main reasons for optimized performance. The development of advanced adsorbents with high CO 2 capture and separation performances is essential for decreasing atmospheric CO 2 concentration. Herein, grand canonical Monte Carlo and density functional theory were employed to investigate the adsorption and separation properties of CO 2 , N 2 , and CH 4 in 2D covalent organic framework (COFs) anchored by alkali metal (AMs) Li, Na, and K (UPC-nAMs, n = 3 or 6) at 298 K and 0–1.0 bar. The anchoring of AMs formed favorable adsorption sites, endowing UPC-nAMs with better CO 2 capture and separation performances. This effect was more evident with an increase in Li/Na/K concentration. The CO 2 adsorption capacity of UPC-6Li/Na/K was ∼ 221.64, 188.28, and 140.50 cm3 cm−3. The smaller atomic size of Li occupied less adsorption space, resulting in the highest CO 2 capture capacity of 221.64 cm3 cm−3 with selectivity of 308/206 over N 2 /CH 4 in UPC-6Li at 298 K and 1.0 bar. Structural stability, pore characteristics, isothermal adsorption heat, van der Waals and Coulomb interactions, gas distribution density, adsorption configuration, and gas radial distribution function were analyzed to identify the intrinsic mechanism of anchoring Li/Na/K to improve CO 2 capture and separation performances. [ABSTRACT FROM AUTHOR]

Highlights • Heat-stable salts can reduce the absorption performance of MEA solution. • Heat-stable salts can promote the desorption performance of MEA solution. • Structure of acid have a significant effect on performance of MEA solution. • Countermeasures was proposed to maintain absorption/desorption performance. Abstract In order to study the effect of heat-stable salts (HSSs) on the CO 2 absorption performance of amine solution, the CO 2 absorption/desorption rates and cyclic CO 2 capacity of 30 wt% (monoethanolamine) MEA solutions in the presence of various acidic degradation products were comprehensively investigated systematically by an improved rate-based screening method. In addition, the initial pH values and CO 2 equilibrium solubility were also evaluated. These acidic degradation products considered were formic acid, acetic acid, propionic acid, butyric acid, glycolic acid, oxalic acid, lactic acid, malonic acid and bicine. The experimental results indicated that the carboxylic acids with different chemical structures can reduce the initial pH values, equilibrium solubility of CO 2 , absorption rate and cyclic CO 2 solubility, but promote the CO 2 desorption rate of aqueous MEA solution. Furthermore, a countermeasure was proposed to maintain absorption performance and reduce the energy requirement of solvent regeneration for an MEA amine-treating unit. The obtained results can provide a guidance for developing corresponding countermeasure for heat-stable salts control and removal in the CO 2 absorption-stripping process using amine solutions. [ABSTRACT FROM AUTHOR]

The carbon dioxide (CO 2 ) capture potential of amine blends, formed by mixing N,N-Diethylethanolamine (DEEA) and piperazine (PZ), were estimated using an improved rapid screening method. Absorption and desorption experiments were carried out at 313.15 K and 353.15 K to determine the absorption rate, cyclic CO 2 capacity and regeneration rate for 2 mol/L DEEA/PZ with molar ratios of 2.00:0.00, 1.50:0.50, 1.00:1.00, 0.75:1.25, 0.50:1.50, 0.25:1.75 and 0.00:2.00. Solvent screening experimental results showed that blended DEEA/PZ solution with molar ratio of 1.50:0.50 exhibited the higher CO 2 absorption rate and desorption rate, thereby yielding the highest cyclic CO 2 capacity of 0.8540 mol CO 2 /L. In addition, the experimental results also showed synergistic effects during CO 2 absorption into DEEA/PZ solution, resulting in increasing absorption and desorption rates. Also, the mass transfer performance of CO 2 absorption into the best 1.50 M DEEA+ 0.5 M PZ solution was investigated in a hollow fiber membrane contactor. The effects of liquid flow rate, feed temperature range, lean CO 2 loading, inert gas flow rate and CO 2 partial pressure on the mass transfer performance were evaluated in terms of CO 2 absorption flux and overall gas phase mass transfer coefficient (K G ). Furthermore, a correlation was developed for the prediction of mass transfer coefficient (K G ) for CO 2 absorption into DEEA/PZ solution in a hollow fiber membrane contactor. A comparison between the experimental data and the calculated values from the improved correlation demonstrated that this model is applicable to predict the CO 2 absorption performance in hollow fiber membrane contactors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Over 97 % of FGD gypsum was converted into CaS. • •The reduction is controlled by the phase boundary, which is a typical shrinking sphere reaction. • •The reduction process of S in the FGD gypsum is SO 4 2−-SO 3 2−-S 2 2−-S2−. • •The obtained CaS has a honeycomb structure, which is conducive to the reuse. • The mechanism of reduction roasting of FGD gypsum was proposed. Flue gas desulfurized (FGD) gypsum is produced during the removal of SO 2 from flue gas. The reductive decomposition of FGD gypsum to calcium sulfide (CaS) is a crucial method for resource utilization. This study investigated the reduction roasting behavior and mechanism to enrich and recycle the calcium and sulfur resources in FGD gypsum effectively. Firstly, thermodynamics calculation revealed that the complete reduction of CaSO 4 to CaS is feasible. Experimental results showed that more than 95 % of the FGD gypsum can be reduced to CaS. Subsequently, the kinetic parameters of the reduction process were calculated. The results indicate that the reaction is controlled by the phase boundary, which is a typical shrinking sphere reaction process. Based on the kinetic study, the micromorphological transformation during the reduction process were studied. The results show that the reduction reaction initially starts from the boundary and gradually occurs towards the core. Finally, the reduction roasting mechanism is proposed. The intermediate processes of calcium sulfate reduction behavior were studied through XRD and XPS. The phase conversion and behavior of the main elements S in the process were explored. The results indicate that the process is a step-by-step reduction, and the transformation of S is SO 4 2−-SO 3 2−-S 2 2−-S2−. The reduction product forms a hollowed-out spheroid structure that cannot only effectively enrich Ca and S resources, but also provide advantageous conditions for their subsequent reuse. [ABSTRACT FROM AUTHOR]

An improved fast screening method, i.e. the multiple fast screening method, was developed to quickly screen high efficiency solvents for post combustion CO 2 capture, especially for the existing amine-based CO 2 capture processes. The method was based on an integrated CO 2 absorption-desorption process, where the absorption process was performed at 40 °C with a certain initial lean loading, obtained by a pretreatment process, and desorption process is done at the temperature of 80 °C. The duration of each of the two processes was set to be 60 min. This screening method, taking into account the CO 2 absorption capacity as well as the absorption and desorption efficiency, was tested on five single alkanolamines in aqueous solutions with concentration of 30 wt%, and blended MEA/DEEA solutions with different ratio at a certain total molar concentration of 5 mole/L. The repeatable screening results of the single amines by this improved method show that the cyclic capacities of the amines are different from the experimental results obtained by using the equilibrium-based screening method, the experimental results of single amine solutions were finally further validated by a simulation process in Aspen Plus and show good agreement. For the blended amine systems screening, the molar ratio of MEA/DEEA of 2.5:2.5 presents the highest cyclic capacity, while no optimal ratio is found by using traditional equilibrium-based screening method. The absolute average difference (AAD) of mass balance between gas and liquid phases for both the single and blended amines screening experiments was calculated, and it turns out to be reliable with the value of 2.65% and 2.80%, respectively. [ABSTRACT FROM AUTHOR]

• Two types of sterically hindered primary/secondary alkanolamines were studied. • k 0 of eight primary/secondary alkanolamines with CO 2 were measured at 293–313 K. • Brønsted equations were fitted for tested amines with and without steric hindrance. • Mechanisms of steric hindrance effect on reaction kinetics was initially proposed. To figure out the steric hindrance and its magnitude effects on CO 2 absorption performance and Brønsted correlations of primary and secondary alkanolamines, the pKa values and kinetics data (second order reaction rate, k 2) were investigated for nine alkanolamines at 293–313 K using pH meter and stopped-flow technique. The tested amines include monoethanolamine (MEA), diethanolamine (DEA), 2-methyl-ethynolamine (MAE), 2-ethyl-ethynolamine (EAE), 1-amino-2-propanol (1-AP), 3-amino-1-propanol (3-AP), 2-amino-2-methyl-1-propanol (AMP), 2-amino-1-propanol (2-AP) and 3-Amino-1,2-propanediol (3-APD). In addition, the equilibrium solubility of MEA, MAE, EAE, 2-AP and AMP were tested for evaluation of steric hindrance effect on carbamate's stability. The comprehensive analysis of kinetics, solubility and Brønsted correlations indicated that the steric hindrance caused by alkyl group(s) attached to α-C atom has much significant effect on k 2 and solubility than that caused by alkyl group connected to amino group. Moreover, the k 2 and pK a values for sterically unhindered and hindered amines were separately fitted at 293–313 K, giving out an AARD of 5.2% and 16.5% between predicted and experimental k 2 , respectively. Finally, based on molecular structures and experimental results, mechanism of steric hindrance effect on reaction kinetics was proposed. [ABSTRACT FROM AUTHOR]

• The models of H e C O 2 - M E A / 1 D M A 2 P and α e q were constructed. • Mass transfer performance of MEA/1DMA2P solution was comprehensively investigated. • An integrative K G a v was established by embedding and α e q model. • The effect of y A ⁎ on K G a v was considered based on the H e C O 2 - M E A / 1 D M A 2 P data. • y CO 2 , o u t were correlated by using new K G a v models. In order to establish an integrative mass transfer coefficient (K G a V) model for CO 2 absorption into blended monoethanolamine (MEA)/1-dimethylamino-2-propanol (1DMA2P) solution in packed column, the models of CO 2 Henry's law constants (He CO₂-MEA/1DMA2P) and the equilibrium CO 2 solubility (α eq) were constructed. The experimental produced data can be reasonably analyzed. In this work, the Arrhenius equation was employed to fit the values of He CO₂-MEA/1DMA2P at different temperature with AARD of 4.06%; the Kent-Eisenberg prediction model and empirical polynomial prediction model were used to predict the data of α eq under different CO 2 partial pressures and temperatures with AARDs of 2.64% and 0.83%, respectively; the empirical K G a V model proposed by Li, the empirical K G a V model proposed by Aroonwilas and new K G a V model were used to correlate the average values of K G a V with AARDs of 14.36%, 12.44% and 9.03%, respectively; the model for outlet CO 2 concentration (y CO₂,out) in packed column was developed with AARD of 15.97%. Moreover, the heat of CO 2 absorption in 6 kmol/m3 MEA/1DMA2P solution was estimated by Gibbs-Helmholtz equation which gave a value of −39.8 kJ/mol. The results show that the blended MEA/1DMA2P solution has advantages that make it a potential absorbent for CO 2 capture. [ABSTRACT FROM AUTHOR]

Two-dimensional conjugated aromatic polymer with S/P substitutions demonstrated significant balance of H 2 permeance and selectivities over CO 2 /CO/N 2 /CH 4 via the effects of pore size and gas-membrane interaction. [Display omitted] • High cohesive energies confirm high structural stabilities of CAP-1S/CAP-1P. • CAP-1P exhibits almost complete H 2 selectivity with high H 2 permeance. • S/P substitution creates large pore sizes and strong gas-membrane interactions. • The interaction and pore size render efficient H 2 purification jointly. Based on two-dimensional conjugated aromatic polymer (2D-CAP), CAP-1S/CAP-1P monolayers were designed by substituting N with S/P atoms for H 2 purification. By using MD and DFT approaches, the H 2 purification performance and separation mechanisms of CAP-1S/CAP-1P membranes were investigated. Results showed that ultrahigh H 2 permeances of 3.546 × 10−5 and 2.593 × 10−4 mol m−2 s−1 Pa−1 were obtained in CAP-1S/CAP-1P, which were almost 104–105 times larger than the industrially acceptable standard. The selectivities of H 2 over CO 2 /CO/CH 4 /N 2 ranged from 5.719 × 1018 to 3.683 × 1039 in CAP-1S and 4.554 × 1013 to 2.153 × 1033 in CAP-1P. From a statistic viewpoint, the CAP-1S/CAP-1P membranes exhibited complete selectivities of H 2 over CO 2 /CO/CH 4 /N 2. The cohesive energies confirmed the high stabilities of CAP-1S/CAP-1P membranes. The minimum energy pathways, energy profiles, electron density, and charge density difference were analyzed to illustrate the significant impact of precise pore size on the H 2 separation performance. From a statistic mechanics view, the interaction between gases and CAP-1S/CAP-1P membranes indicated that the long-range Coulomb interactions dominated the gas diffusion processes. Results of this work highlighted CAP-1P as a promising H 2 separation membrane and elucidated the promotion mechanism by fine-tunning pore size and interaction between gases and membranes to balance the H 2 permeance and selectivity jointly. [ABSTRACT FROM AUTHOR]

Emulsion separation through fibrous media is a popular and complex process, and certain factors significantly affect the separation performance. This research investigates the influence of inlet droplet size distribution and redispersion on quantitative separation efficiency. The gravity settling method was developed to analyze the water droplet size distribution, and a novel grade efficiency curve was used to demonstrate the impact of redispersion. In addition, other critical factors, including specific surface area, bed permeability, degree of saturation, superficial velocity and bed depth were investigated. The results are useful for elucidating emulsion transport in fibrous media and identifying the optimum media and operating conditions. [ABSTRACT FROM AUTHOR]

By regulating the doping number of Li atoms in graphdiyne (GDY), the adsorption site of the structure is increased and the interaction between gas and skeleton is enhanced, thus creating a favorable environment for CO 2 adsorption. Li-GDYs have ultra-high CO 2 adsorption capacity and CO 2 /N 2 selectivity. [Display omitted] • Three structures with different Li doping types are screened. • Li-GDYs exhibit an ultra-high CO 2 adsorption capacity and CO 2 /N 2 selectivity. • Li doping has a more pronounced effect on enhancing the CO 2 − Li-GDYs interaction. • Gas distribution analyses demonstrate Li doping provides more adsorption sites. The development of CO 2 adsorbents with high adsorption and separation performances is important to solve severe environmental problems. Herein, two-dimensional graphdiyne acetylene rings doped with different concentrations of lithium atoms (1/2/6Li-GDYs) were introduced as potential adsorbents for CO 2 capture and separation by using Grand Canonical Monte Carlo and Density Functional Theory methods. According to the structure analysis, Li atoms could stably bind to GDY with a binding energy of 1.04 – 2.77 eV/atom; 1/2/6Li-GDYs had high cohesive energy of 7.02 – 7.54 eV/atom. Electronic structure analysis confirmed the large charge transfer and strong interaction between Li atoms and GDY. The pore physical properties of Li-GDYs indicated that the pore volume, porosity, and pore size provided a favorable environment for CO 2 adsorption. Among Li-GDYs, 2/6Li-GDYs exhibited an ultra-high CO 2 adsorption capacity of 11.91 mmol/g at 298 K and 100 kPa, and was superior to other metal-modified adsorbents. The CO 2 /N 2 selectivity in 1/2/6Li-GDYs reached ∼ 168, ∼311, and ∼ 1021 at 298 K and 100 kPa. Gas distribution analysis revealed a broad CO 2 distribution consisting of multilayer adsorption peaks around Li and adjacent C atoms, illustrating the significant effect of Li and Li-connected C atoms on CO 2 adsorption. Interaction analysis showed that Li doping enhanced the CO 2 -framework interaction more significantly than the N 2 -framework interaction, resulting in ultra-high CO 2 adsorption capacity and CO 2 /N 2 selectivity. The results of this work highlight 1/2/6Li-GDYs as ultrahigh-performance adsorbent materials for CO 2 adsorption and separation over N 2. [ABSTRACT FROM AUTHOR]

• Reaction kinetics between CO 2 and loaded MEDA solution was studied. • Contribution of hydroxyl is a crucial to overall reaction rate constant for loaded system. • Kinetics of unloaded system is approximately twice as that of literature and loaded system. The stopped-flow technique was applied for the investigation of kinetics of CO 2 absorption into loaded MDEA solution over the range of MDEA concentration of 0.4 to 1.0 kmol/m3, CO 2 loading of 0.14 to 0.17 mol CO 2 /mol amine and the temperature of 293 to 308 K. The kinetics of unloaded MDEA was also investigated for the comparison and a huge difference of results which should be equal theoretically was indicated between loaded and unloaded systems. Then, the effect of CO 2 loading on the kinetics was studied. As the loading increases, there is a turning point around loading of 0.10, below which the overall reaction constant decreases strongly. It was found that contribution of hydroxyl is a crucial to overall reaction rate constant and cannot be ignored and the influence of reverse reaction of MDEA and CO 2 can be ignored. The kinetics of loaded system obtained in this work was modified and interpreted well by the base-catalyzed mechanism with AARD of 6.29% and compares favorably with literature using gas-liquid apparatus. The kinetics of unloaded system in this work is approximately twice as that of literature and loaded system. This work provided literature review and interpretation of MDEA-CO 2 -H 2 O and is hopeful to shed light on kinetic study of CO 2 absorption in tertiary amine using stopped-flow apparatus. [ABSTRACT FROM AUTHOR]