CO2 Adsorption Kinetics Research Articles

Breakthrough analysis for parameter estimation of CO2 adsorption on pelletized flexible metal–organic framework

Pellets of elastic layer-structured metal–organic framework-11 (ELM-11), one of the flexible metal–organic frameworks (MOFs), were prepared by mixing ELM-11 powder with a cellulose binder, and the CO2 adsorption behavior of ELM-11 pellets in a fixed-bed adsorber was analyzed to estimate equilibrium and kinetic parameters. Adsorption breakthrough tests were performed under various conditions for the simulated flue gas (20 % CO2–80 % N2) of a blast furnace gas in addition to CO2 isotherm measurements. Experimental CO2 adsorption isotherms on ELM-11 followed a weighted dual-site Langmuir equilibrium model well. The breakthrough analysis results by numerical calculation using the equilibrium model suggested that the gate-opening pressure of ELM-11 shifted to a lower pressure through repeated breakthrough tests. The CO2 adsorption kinetics on ELM-11 pellets agreed well with the linear-driving-force model. Furthermore, CO2 adsorption behavior under various conditions was described well by a mathematical model using a constant value of the mass transfer coefficient under the condition of this study, which was validated against additional experimental data. In addition, it was found that the mass transfer becomes slow under certain conditions that the driving force of the phase transition of ELM-11 is smaller than a threshold, where the amount of CO2 adsorbed on the breakthrough tests did not reach the equilibrium capacity of CO2, which may because the rate-limiting step may be dependent on the CO2 partial pressure and temperature.

Influence of Supercritical CO2 Fluid on CH4 and CO2 Diffusion in Vitrinite-Rich Coals and Inertinite-Rich Coals

Coal maceral composition has a great effect on gas adsorption and diffusion. The interaction between maceral composition and supercritical CO2 (SCCO2) fluid will affect gas diffusion behavior in coals. Thus, the diffusivity derived from adsorption kinetics of CH4 and CO2 in vitrinite- and inertinite-rich coals with low-violate bituminous rank collected from the Hancheng mine of the Weibei coalfield pre- and post-SCCO2 fluid exposure (SFE) were tested at the conditions of 45 °C and 0.9 MPa. In combination with pore distribution and functional group content, the possible mechanism of the alterations in gas diffusion characteristics in coals with various maceral compositions was addressed. The results show that for vitrinite-rich coals, SFE increases the macropore apparent diffusion coefficient of CH4, while this treatment decreases the micropore apparent diffusion coefficient of CH4. However, the reverse trend is found for CO2 diffusion–adsorption rate. For inertinite-rich coals post-SFE, CH4 diffusion–adsorption rate increases, while an increase and a decrease in diffusivity CO2 occur for macropore and micropore, respectively. Generally, SFE shows a stronger impact on CO2 adsorption rate than CH4 in coals. The results suggest that the diffusion of CH4 and CO2 in coals with different maceral compositions show selectivity to SCCO2 fluid. The possible reason can be attributed to the changes in pore structure and surface functional group content. SFE causes an increase in macro/mesopore volume of all samples. However, SFE induces a reduction in oxygen-containing species content and micropore volume of inertinite-rich coals, while the opposite trend occurs in vitrinite-rich coals. Thus, the changes in pore volume and surface functional group account for the difference in gas diffusivity of coals with different maceral compositions. With regard to the micropore diffusion–adsorption behavior of CH4 and CO2, the impact of oxygen-containing species is superior to pore volume. The oxygen-containing species favor CO2 diffusion–adsorption but go against CH4 transport. This effect accounts for the reduction in the micropore diffusion–adsorption rate of CH4 and the increase in micropore diffusivity of CO2 in vitrinite-rich coals, respectively. However, the aforementioned effect is the opposite for inertinite-rich coals. Overall, the changes in gas diffusion in coals with different maceral composition during the CO2-ECBM process requires further attention.

Porous Structural Properties of K or Na-Co Hexacyanoferrates as Efficient Materials for CO2 Capture.

The stoichiometry of the components of hexacyanoferrate materials affecting their final porosity properties and applications in CO2 capture is an issue that is rarely studied. In this work, the effect that stoichiometry of all element components and oxidation states of transition metals has on the structures of mesoporous K or Na-cobalt hexacyanoferrates (CoHCFs) and CO2 removal is reported. A series of CoHCFs model systems are synthesized using the co-precipitation method with varying amounts of Co ions. CoHCFs are characterized by N2 adsorption, TGA, FTIR-ATR, XRD, and XPS. N2 adsorption results reveal a more developed external surface area (72.69-172.18 m2/g) generated in samples containing mixtures of K+/Fe2+/Fe3+ ions (system III) compared to samples with Na+/Fe2+ ions (systems I, II). TGA results show that the porous structure of CoHCFs is affected by Fe and Co ions oxidation states, the number of water molecules, and alkali ions. The formation of two crystalline cells (FCC and triclinic) is confirmed by XRD results. Fe and Co oxidation states are authenticated by XPS and allow for the confirmation of charges involved in the stabilization of CoCHFs. CO2 removal capacities (3.04 mmol/g) are comparable with other materials reported. CO2 adsorption kinetics is fast (3-6 s), making CoHCFs attractive for continuous operations. Qst (24.3 kJ/mol) reveals a physical adsorption process. Regeneration effectiveness for adsorption/desorption cycles indicates ~1.6% loss and selectivity (~47) for gas mixtures (CO2:N2 = 15:85). The results of this study demonstrate that the CoHCFs have practical implications in the potential use of CO2 capture and flue gas separations.

CO2 Emission Control Using Selective Oxidation of Catalytic Zeolite13x

Abstract: For this research, Zeolite 13 x was prepared under high pressure with a mixture of activated charcoal and Natural coconut residue. The isotherms of adsorption and Kinetic curves of the Co2 on the prepared adsorbent materials are measured at 328k, 318 k, 308 k, and 298 K and using the gravimetric adsorption method, and with a pressure range of 0–30 bar[1]. Separately, the mass transfer constants and adsorption activation energy Ea of CO2 on the adsorbents were calculated. The results showed that the amount of CO2 adsorbed on the zeolite 13X was greater. The linear driving force (LDF) model can accurately describe CO2 adsorption kinetics. The mass transfer constants of CO2 adsorption on both samples increased as the temperature increased. The adsorption activation energy Ea for CO2 on the two adsorbents decreased as the concentration increased[2] .

Intensified bio-oil steam reforming for high-purity hydrogen production: Numerical simulation and sorption kinetics

This work proposes the production of high-purity hydrogen by an intensified non-isothermal sorption-enhanced bio-oil steam reforming (SEBOSR) process, by combining the bio-oil steam reforming over a Ni/La2O3-αAl2O3 catalyst and in-situ CO2 adsorption over Li2CuO2. The kinetics of CO2 adsorption on Li2CuO2 was studied experimentally and applied to assess the performance of SEBOSR in a fixed bed reactor via a non-isothermal mathematical model. Model simulations show that the prebreakthrough stage of the SEBOSR process, which corresponds to high purity H2 production, can be extended by increasing the adsorbent loading and the S/C ratio, as well as by decreasing the inlet gas velocity. Increasing inlet temperature generates longer prebreakthrough step times but leads to a reduction in hydrogen purity. This intensified process allows to diminish the catalyst deactivation, which ultimately only occurs in the inlet region of the packed bed to some extent. In addition, SEBOSR indirectly uses sustainable CO2-neutral biomass as a source of hydrogen; highly pure and renewable H2 can be produced in one step (without the need of additional gas purification), via a process with enhanced thermal efficiency.

CO2 capture from dilute sources using triamine functionalized MCF silica at ambient temperature

A series of mesocellular siliceous foams (MCFs) with three-dimensional (3D) interconnected porous structure and tunable porosity were synthesized as supports to prepare triamine grafted sorbents using N’-[2-(3-trimethoxysilylpropylamino)ethyl]ethane-1,2-diamine for CO2 capture, particularly focusing upon the impact of pore structure of support on the adsorptive properties of final sorbents. The results indicate that both pore volume and diameter of MCF played a critical role in both CO2 adsorption capacity and kinetics at ambient temperature. Tested at 25 °C, the sorbent prepared by MCF with a large pore size of 33.7 nm and pore volume of 3.24 cm3/g exhibited remarkable CO2 adsorption capacity at low CO2 concentrations, which could achieve 2.14 mmol/g at 0.15 bar CO2 and 1.34 mmol/g under simulated air of 500 ppm CO2. Advanced characterization demonstrated that the increasing pore volume and diameter led to an increase of amine density on the MCF surface, which could enhance the steric hindrance and reduce the amine efficiency for CO2 adsorption at ambient temperature. It was also found that large pore size benefits the CO2 adsorption kinetics as the t80 and t90 of sorbents decreased with an increasing pore size of support. Moreover, the MCF-based sorbents exhibited superior thermo-stability with no adsorption loss during 50 cyclic adsorption-desorption tests. These results highlighted that the 3D MCF is a promising material for preparing amine grafted sorbents for flue gas CO2 capture and air purification applications.

A Cluster Based Cooperative Kinetic Model for CO2 Adsorption on Amine Functionalized Metal–Organic Frameworks

A new model for the adsorption kinetics of CO2 on amine functionalized metal–organic frameworks Mg2 (dobpdc) and Mn2 (dobpdc) is proposed. The equilibrium adsorption is evaluated using the cooperative lattice theory of Kundu et al. The lattice theory provides a microscopic interpretation of adsorption behavior on the basis of the state of adsorbed CO2: singly adsorbed, chain ends, and chain interiors. On this basis, the proposed kinetic model accounts for the kinetics of singly adsorbed CO2, as well as the kinetics of adsorption into chains. These two kinetic paths have separate yet coupled rate laws. This allows for the accurate description of complex kinetic phenomena observed in low partial pressure CO2 breakthrough curves on mmen-Mg2 (dobpdc). In addition to good numerical agreement with measured data, the approach developed in this work provides a needed microscopic interpretation of measured kinetic data in these systems. This microscopic picture may allow for more targeted material design and a pathway to include additional factors such as the effect of humidity on CO2 adsorption and kinetics.

Effects of supercritical CO2 exposure on diffusion and adsorption kinetics of CH4, CO2 and water vapor in various rank coals

The physico-chemical effects caused by supercritical CO2 (ScCO2) exposure is one of the leading problems for CO2 storage in deep coal seams as it will significantly alter the flow behaviors of gases. The main objective of this study was to investigate the effects of ScCO2 injection on diffusion and adsorption kinetics of CH4, CO2 and water vapor in various rank coals. The powdered coal samples were immersed in ScCO2 for 30 days using a high-pressure sealed reactor. Then, the diffusion and adsorption kinetics of CH4, CO2 and water vapor in the coals both before and after exposure were examined. Results indicate that the diffusivities of CH4 and CO2 are significantly increased due to the combined matrix swelling and solvent effect caused by ScCO2 exposure, which may induce secondary faults and remove some volatile matters that block the pore throats. On the other hand, the diffusivities of water vapor are reduced due to the elimination of surface functional groups with ScCO2 exposure. It is concluded that density of the surface function groups is the controlling factor for water vapor diffusion rather than the pore properties. The unipore model and pseudo-first-order equation can simulate the diffusion and adsorption kinetics of CH4 and CO2 very well, but the unipore model is not capable of well describing water vapor diffusion. The effective diffusivity (De), diffusion coefficient (D) and adsorption rates (k1) of CH4 and CO2 are significantly increased after ScCO2 exposure, while the values of water vapor are decreased notably. Thus, the injection of ScCO2 will efficiently improve the transport properties of CH4 and CO2 but hinder the movement of water molecules in coal seams.

Synthesis and CO2 adsorption kinetics of Aluminum Fumarate MOFs pellet with high recovery

As a promising CO2 adsorbent, Aluminum Fumarate (AlFu) metal organic frameworks (MOFs) were explored for pelletizing technology and CO2 adsorption characteristics. The effects of binder type (sodium carboxymethylcellulose (CMC), aluminum sol (AS)) and content (2.5 wt%-20 wt%), CO2 partial pressure (0.3 bar–1 bar) and temperature (35 °C–65 °C) on the mechanical performance and adsorption process were investigated. The results revealed that with the increase of binder mass, the pellet mechanical strength rose while the CO2 adsorption amount decreased. The AlFu pellet with 2.5 wt% CMC could retain the powder porosity and adsorption capacity. The mechanical strength of AlFu@CMC-2.5 wt% achieved 1.486 MPa, and the maximum adsorption capacity was 1.26 mmol/g at 35 °C and 1.0 bar. The CO2 adsorption capacity was increased with lower adsorption temperature and higher CO2 partial pressure. Compared with pseudo second order model and pseudo first order kinetic model, Avrami kinetic model could better describe the CO2 adsorption behavior of AlFu pellet. It indicated that the adsorption process was not a single physical or chemical adsorption. The rate-limiting kinetic analysis showed that the CO2 adsorption rate was determined by film diffusion and intraparticle diffusion rather than inter-particle diffusion.

Adsorption of CO2 by surface modified coal-based activated carbons: kinetic and thermodynamic analysis

Abstract The effects of different surface modifiers on the CO2 adsorption capacity of coal-based activated carbons were studied, and the diffusion behavior, adsorption kinetics and thermodynamic parameters of CO2 in activated carbons were analyzed. The results show that compared with ethylene glycol, 1,2-propylenediamine and zinc chloride, potassium hydroxide and sodium hydroxide can greatly improve CO2 adsorption capacity. The adsorption rate is faster, and the adsorption capacity is larger, with the maximum CO2 adsorption capacity being 33.54 mL/g. Fick's law can well describe the diffusion behavior of CO2 in activated carbon. The addition of a surface modifier can increase the diffusion coefficient. The diffusion of CO2 in activated carbon falls into the category of crystal diffusion. The adsorption kinetics of CO2 before and after surface modification follow the Bangham equation. During the adsorption process, δ H < 0, δ G < 0, δ S < 0. Surface modification can reduce adsorption heat and promote adsorption, and the adsorption process is dominated by physisorption.

Enhancing the CO2 adsorption kinetics on Na-RHO and Cs-MER zeolites by NH4F/H2O2 etching induced mesoporosity

The Na+-form (Na-RHO) of zeolite rho has emerged as a potential CO2 adsorbent with excellent selectivities toward CH4 and N2, but the very slow CO2 adsorption kinetics hinders its practical use. Here we report that mesoporous Na-RHO, prepared by NH4F/H2O2 etching, shows remarkably enhanced CO2 adsorption kinetics (ca. 7 min vs > 2 h) compared to the Na-RHO, which was also observed for the NH4F/H2O2-etched, Cs+-form (Cs-MER) of merlinoite. A combination of SEM, TEM, and N2 adsorption measurements demonstrates that such kinetics enhancement originated from the mesopore creation by fluoride medium etching, while minimizing the loss of zeolite crystallinity. The observed differences in the zeolite crystal morphology of Na-RHO and Cs-MER and in the characteristics of their intrinsic defect sites appear to be responsible for those in the shape and average size of the secondary mesopores created. The overall results of this study suggest that NH4F/H2O2 etching can be also applied to other small-pore zeolites to improve CO2 adsorption kinetics.

Unprecedented improvement of the hydrothermal stability of amine-grafted MCM-41 silica for CO2 capture via aluminum incorporation

The hydrothermal stability of amine-containing CO2 adsorbents is of paramount importance as steam stripping is often practiced for regenerating CO2-loaded materials. The impact of aluminum incorporation into the structure of MCM-41 silica on its adsorptive properties and hydrothermal stability during CO2 capture was studied. Large-pore MCM-41 silica and MCM-41 aluminosilicate (Si/Al = 15) supports with similar average pore sizes of 64 and 66 Å, respectively, were synthesized using a novel method. Amine functionalization of the supports was conducted using grafting of triamine under dry and wet conditions. Amine-tethered MCM-41 aluminosilicate adsorbents exhibited higher CO2 uptakes (up to 63% higher after 60 min of adsorption at 25 °C) and faster CO2 adsorption kinetics (up to 71% faster after two minutes of adsorption at 25 °C) relative to their MCM-41 silica counterparts. Following a three-hour exposure to steam, extensive deterioration of adsorptive properties was observed for the triamine-grafted MCM-41 silica materials, particularly at low adsorption temperatures of 25 and 50 °C, showing CO2 uptake losses as high as 73 and 56%, respectively. The triamine-grafted MCM-41 aluminosilicate materials, however, showed unprecedented hydrothermal stability with no significant drop in CO2 uptake (respective losses as high as 27 and 17%) and adsorption kinetics. After steam stripping, N2 adsorption-desorption measurements at 77 K showed significantly higher reductions in the Brunauer-Emmett-Teller surface area of the triamine-grafted MCM-41 silica materials (losses of 36–49%) compared to their MCM-41 aluminosilicate counterparts (losses of 31 to 35%). It is inferred that aluminum incorporation into the support increases the hydrothermal stability of the resulting grafted materials in the presence of steam.

A green synthesis strategy for low-cost multi-porous solid CO2 adsorbent using blast furnace slag

The low-cost of CO2 adsorbent is crucial for realistic CO2 adsorption application. In this paper, a series of green CO2 adsorbents were prepared using tetraethylenepentamine (TEPA) functionalized blast furnace slag (BFS) as raw materials, which not only implemented the recycling of blast furnace slag solid waste, but also realized the low cost of amine adsorbents. A series of characterization analyses were performed on the synthesized hydrotalcite-like and hydrated calcium silicate green support materials. The effects of structures, TEPA loadings and adsorption temperatures on the material properties were investigated. The result shows that BFS10.5-50TEPA with more pores is an ideal adsorbent, its optimum adsorption capacity for CO2 is 5.64 mmol/g at 80 ℃, and the amine efficiency is as high as 38.42 %. According to CO2-TPD analysis, the dominant CO2 adsorption mechanism of BFS10.5-50TEPA were physisorption and weak chemisorption. Moreover, the adsorption kinetics and regeneration performances also studied. The results indicate that pseudo-first-order model and pseudo-second-order model are both not accurately at predicting experimental results, while the Avrami model can accurately predict the adsorption kinetics of CO2 at both low adsorption temperature and high adsorption temperature. After 10 adsorption-desorption recycles, the CO2 adsorption capacity of BFS10.5-50TEPA still maintain 5.02 mmol/g. This study provides a novel method for the preparation of solid amine adsorbents with high adsorption performance from low-cost solid waste.

Unravelling the pore templating effect on CO2 adsorption performance of alkali metal nitrates promoted MgO pellets

Alkali metal salts (AMS) promoted MgO with high CO2 uptakes represents a promising adsorbent candidate for CO2 capture. The AMS-MgO composite adsorbents are facing the challenges of increased pressure drop or elutriation when employed in dual fixed-bed reactor or twin circulating fluidized-bed configurations. Granulation by the extrusion-spheronization technique represents an effective problem-solving strategy. However, textural properties and CO2 uptakes of MgO-based adsorbent pellets might be adversely affected by the granulation process. In this work, AMS-MgO composite adsorbent pellets were prepared by the extrusion-spheronization method. Citric acid (CA), ammonium bicarbonate (AB), urea (UA) and microcrystalline cellulose (MC) were employed as pore-forming templates to improve the porous structures and CO2 uptakes of the AMS-MgO pellets. CO2 uptakes and adsorption kinetics of the adsorbent pellets were studied using a fixed-bed reactor. Effects of granulation and pore templating on the structure-performance relationships of the AMS-MgO pellets were unraveled. Granulation had resulted in the remarkable decrease in CO2 uptake from 10.87 to 4.24 mmol CO2/g due to the impaired textural parameters. The employed sacrificial templates endowed the AMS-MgO pellets with enhanced CO2 uptakes and improved carbonation kinetics. This was associated with extended surface area and expanded pore structures due to gas liberation in the pyrolysis of templates, which had facilitated the kinetics of CO2 bulk diffusion. The desired AMS-MgO-MC pellet modified with MC template showed a high CO2 uptake of 7.54 mmol CO2/g in 50%CO2 at 340 °C, and its CO2 uptake was stabilized around 5.0 mmol CO2/g within 20 cycles. Besides, the AMS-MgO-MC pellet also exhibited good mechanical properties. The results will guide the rational design of highly efficient and robust MgO-based adsorbent pellets for CO2 capture applications.

Supercritical carbon dioxide enhanced natural gas recovery from kerogen micropores

As the global energy demand increases, a sustainable and environmentally friendly methane (CH4) extraction technique must be developed to assist in the transition off of fossil fuels. In recent years, supercritical carbon dioxide (CO2) has been poised as a candidate for enhanced gas recovery (EGR) from CH4-rich source rocks, potentially with the reservoir serving as a carbon sink for CO2. However, the underlying molecular-scale mechanisms of CO2-EGR processes are still poorly understood. Using constant chemical potential molecular dynamics (CμMD), this study investigates the CH4 recovery process via supercritical CO2 injection into immature (Type I-A) and overmature (Type II-D) kerogens in real-time and at reservoir conditions (365 K and 275 bar). A pseudo-second order (PSO) rate law was used to quantify the adsorption and desorption kinetics of CO2 and CH4. The kinetics of simultaneous adsorption/desorption are rapid in immature kerogen due to better connected pore volume facilitating fluid diffusion, whereas in overmature kerogen, the structural heterogeneity hinders fluid diffusion. Estimated second order kinetic rate coefficients reveal that CO2 adsorption and CH4 desorption in Type I-A are about two times and an order of magnitude faster, respectively, compared to those of in Type II-D. Furthermore, overmature Type II-D kerogen contains inaccessible micropores which prevent full recovery of CH4. For every CH4 molecule replaced, at least two and six CO2 molecules are adsorbed in Type-II-D and Type I-A kerogens, respectively. Overall, this study shows that CO2 injection can achieve 90 % and 65 % CH4 recovery in Type I-A and Type II-D kerogens, respectively.

Development of in situ polymerized amines into mesoporous silica for direct air CO2 capture

Direct air CO2 capture (DAC) is inevitable to achieve negative emissions and lower CO2 concentration in the atmosphere. The use of class III supported amine materials has shown great potential as effective materials for CO2 capture from both flue gas and low concentrations of CO2. In this work, a linear polyethylene amine tethered to mesoporous silica foam was synthesized by controlled in situ cationic ring opening polymerization of 2-methyl-2-oxazoline. The sorbent was characterized based on porosity, FTIR, elemental analysis, and surface morphology. The CO2 capture performance at different temperatures was measured using a volumetric method, whereas the dynamic breakthrough analysis (DBA) technique was evaluated using simulated air of 400 ppm CO2 at different temperatures and relative humidities. The CO2 adsorption isotherms were studied in the temperature range from 5 to 80 °C and were fitted using different isotherm models. To evaluate the effects of moisture on the CO2 capture performance, breakthrough experiments were performed using 400 ppm CO2 at various relative humidities (0–65%). It was found that the CO2 uptake calculated from the breakthrough experiment is enhanced at higher moisture contents and decreases at higher temperatures. The maximum CO2 uptake was 1.50 mmol/g at 25 °C and 65% RH. The CO2 adsorption kinetics of the sorbent was found to follow the Avrami model, whereas the dual site Langmuir model was found to be the best fit for the adsorption isotherms. The developed sorbent exhibited a stable cyclic performance and retained its initial CO2 uptake during 10 consecutive cycles. This study demonstrates that in situ polymerization of amines into porous supports is a viable route for designing sorbents with high CO2 adsorption performance for DAC applications.

Amine-grafted mesoporous silica materials for single-stage biogas upgrading to biomethane

The potential of amine-grafted silica materials (i.e., aminosilicas) was investigated for single-stage biogas purification via simultaneous removal of CO2, H2S, and water vapor. Custom aminosilicas were synthesized by covalent tethering of primary amines onto commercially available mesoporous silica. Screening adsorption experiments were completed at 40 °C in the presence of dry 30 vol% CO2 in N2, and performance was measured using thermogravimetric analysis. Selected materials with equilibrium CO2 uptakes greater than 6 wt% were chosen for additional assessments in terms of CO2 adsorption kinetics. The highest-performing aminosilica achieved fast CO2 uptake by reaching 82% of its equilibrium CO2 uptake in one minute. This material was subjected to rigorous 100-cycle testing and retained stable performance as evidenced by maintaining 99% of its initial CO2 uptake throughout cycling, regardless of using air or N2 as desorption purge gas. The final candidate also underwent column-breakthrough tests in the presence of humid 24% CO2, 200 ppmv H2S, balance N2, at 40 °C, and achieved concurrent and complete (100%) removal of all target impurities, namely CO2, H2S, and water vapor, prior to their respective breakthrough times. The results suggest promising potential of aminosilicas as a viable method of biogas purification, particularly in remote areas where access to other purge gases such as steam or N2 is not practical.

Fabrication of Alkaline Earth Oxide-Containing Glass Adsorbents for Capturing Carbon Dioxide under Mild Conditions

With growing global concern on radiological hazards, there has been strong interest in the adsorbents for the treatment of radioactive carbon dioxide (CO2) containing C-14, which should be removed under mild operating conditions. In this study, we fabricated a new class of alkaline earth oxide-containing glass adsorbents with high CO2 adsorption capacity and good adsorption rate under mild aqueous conditions, which is not feasible with alkaline earth oxide-containing natural minerals. The glass adsorbents were fabricated by incorporating alkaline earth oxides (SrO or CaO) into an amorphous glass framework using network modifiers (Na2O or K2O). The comprehensive characterization of the structure and adsorption and dissolution properties of the fabricated glass adsorbents revealed that CO2 was adsorbed via the dissolution of alkaline earth metal ions and their subsequent carbonation through heterogeneous surface nucleation. Variation in the type of alkaline earth metals and network modifiers significantly affected the CO2 adsorption performance and kinetics of the glass adsorbents by altering the dissolution behavior of the alkaline earth metal ions. The best fabricated glass adsorbent exhibited a high maximum CO2 capacity of 5.56 mmol g−1 and a fast carbonation rate of 5.31 mmol g−1 h−1 in deionized water under ambient conditions, demonstrating its potential application in treating radioactive CO2.

Adsorption of CO2 onto zeolite ZSM-5: Kinetic, equilibrium and thermodynamic studies

The aim of this research is to evaluate the adsorption isotherms and the adsorption kinetics of CO2 on the zeolite ZSM-5. The sample was identified by FTIR, SEM, DRX, and N2 adsorption–desorption. The O2 adsorption isotherms of the adsorbent were evaluated at three temperature 318, 308 and 298 K with a volumetric method. Langmuir and Freundlich models were employed to fit the CO2 adsorption. The Langmuir model represented the best fit against the experimental data with a correlation coefficient (R2) of 0.99. The calculated thermodynamics parameters like Entropy, Enthalpy and Gibbs Free Energy showed that CO2 adsorption is a spontaneous and exothermic process. The CO2 adsorption kinetics curves on the adsorbent were calculated and then correlated with the linear driving force (LDF) model. The results showed that the mass transfer constants of CO2 adsorption on the adsorbent increased with rising of temperature. Moreover, the activation energy of CO2 adsorption on the adsorbent decreases with rising of pressure. Through adsorption technology, the obtained results can be applied to the CO2 separation and to evaluate the performance of CO2 adsorption systems.

CuAl2O4 nanoplates as a nanocatalyst for carbon dioxide adsorption at high temperatures

Since industrial processes cause uncontrolled CO2 emissions, resulting in global warming and acidification of the oceans, different strategies have been used to directly absorb CO2 from different sources of effluent. The most common method of solving this problem is carbon sequestration (CCS); however, due to the problems arising from this approach, researchers are trying to produce dual-function materials (DFMs) that effectively absorb CO2 and turn it into valuable products. In this regard, nanostructured alkaline-earth metal oxide adsorbents were employed for dynamic and static adsorption of CO2. Here, CuAl2O4 nanoplates showed high CO2 uptake capacity with extremely fast kinetics. Owing to the CuAl2O4 nanoplate morphology, they produce a satisfactory outer layer for CO2 uptake at every metal-site. The CuAl2O4 nanoplate morphology resulted in systematic CO2 emission to guarantee reaction with the whole sheet and prepare rapid CO2 adsorption kinetics.