CO2 Adsorption Separation Research Articles

Preparation and characterization of UiO-66-(OH)2/MWCNTs composites for CO2/N2 adsorption separation

The increasing CO2 concentration in the atmosphere can lead to climate change, and CO2 capture technology is one of the most direct and effective means of reducing carbon emissions. In this study, a new composite was prepared in situ by loading multi-walled carbon nanotubes (MWCNTs) onto metal–organic frameworks (MOFs) to efficiently capture CO2 in flue gas. The morphological states and pore structures of the composites were analyzed using characterization methods. The CO2 adsorption properties of the composites were tested at 273 K and 298 K with different MWCNTs loadings. The optimal CO2 adsorption quantities of the composite material were measured to be 4.4 and 5.75 mmol/g, respectively, which increased the adsorption capacity by 66.7 % and 55 %, respectively, compared with the parent material at a pressure of 1 bar. The CO2/N2 separation performance of the composites was examined using ideal adsorption solution theory calculations and dynamic adsorption breakthrough experiments. The stability of the composites was investigated by thermogravimetric analysis, acidification experiments, and cyclical adsorption–desorption experimentation. The UiO-66-(OH)2/MWCNTs composites exhibited superior CO2 adsorption–separation performance, thermal stability, acid resistance, and cycling stability. Therefore, the composite has potential applications in CO2 capture separation technology.

Molecular Simulation of Adsorption Separation of CO2 from Combustion Exhaust Mixture of Commercial Zeolites

The adsorption thermodynamics and kinetics of CO2 and six combustion products (H2O, SO2, N2, O2, NO and NO2) of two most commonly used commercial zeolites (13X and 5A) were studied based on validated molecular simulations. Adsorption isotherms at wide range of temperatures (253–333 K) were fitted by a Langmuir model, obtaining equilibrium parameters including the adsorption capacity, strength, heterogeneity and CO2 selectivity from the mixture. The diffusion coefficients, isosteric adsorption heats and distributions of potential energy were simulated for further explanation. The comprehensive evaluation results suggest that, in actual combustion product mixtures, the presence of H2O in combustion products has a significant impact on CO2 capture efficiency. Under the influence of water, the adsorption capacity of CO2 was reduced by over 80%.

Porphyrinic Porous Aromatic Frameworks for Carbon Dioxide Adsorption and Separation.

The capture of carbon dioxide (CO2) from industrial process emissions is increasingly important for the mitigation and prevention of the disruptive effects of global warming. In this study, PAF (porous aromatic frameworks)-TPB(1,3,5-triphenylbenzene) and three-dimensional PAF-TPM (tetraphenylmethane) porphyrin-based aromatic porous materials were synthesized through the Scholl reaction. The CO2 and N2 adsorption isotherms at 273 K and 298 K were studied to determine the performance in carbon dioxide capture at flue gas conditions. There is a significant difference in the adsorption capacity of the two materials for CO2 and N2, so they can be used for CO2/N2 adsorption separation. PAF-TPM has better CO2/N2 separation at low pressure (150 mbar), while PAF-TPB has the advantage of greater CO2/N2 separation at high pressure (1 bar). It can be applied to CO2 adsorption separation at low and high pressure, respectively. In particular, PAF-TPB has a CO2/N2 separation efficiency of up to 100.9 at 1 bar and 273 K. This work provides ideas for the design and synthesis of organic porous materials for the adsorption separation of CO2 and N2.

A Novel Strategy to Enhance the Performance of CO2 Adsorption Separation: Grafting Hyper-cross-linked Polyimide onto Composites of UiO-66-NH2 and GO.

Graphene oxide (GO) is widely used to improve the pore structure, dispersion capacity, adsorption selectivity, resistance to acids and bases, and thermal stability of metal-organic frameworks (MOFs). However, it remains a daunting challenge to enhance selectivity simply by modifying the pore surface polarity and producing a suitable pore structure for CO2 molecules through a combination of GO with MOFs. Herein, we demonstrate a novel porous hyper-cross-linked polyimide-UiO-graphene composite adsorbent for CO2 capture via in situ chemical knitting and condensation reactions. Specifically, a network of polyimides rich in carbonyl and nitrogen atoms with amino terminations was synthesized via the reaction of 4,4'-oxydiphthalic anhydride (ODPA) and 2,4,6-trimethyl-1,3-phenylenediamine (DAM). The product plays a crucial role in the separation of CO2 from N2. As expected, the resulting composite (PI-UiO/GO-1) exhibited a 3-fold higher CO2 capacity (8.24 vs 2.8 mmol·g-1 at 298 K and 30 bar), 4.2 times higher CO2/N2 selectivity (64.71 vs 15.43), and significantly improved acid-base resistance stability compared with those values of pristine UiO-66-NH2. Furthermore, breakthrough experiments verified that the porous composites can effectively separate CO2 from simulated fuel gas (CO2/N2 = 15/85 vol %) with great potential in industrial applications. More importantly, this strategy can be extended to prepare other MOF-based composites. This clearly advances the development of MOF-polymer materials for gas capture.

In-situ SIFSIX-3-Cu growth into melamine formaldehyde sponge monolith for CO2 efficient capture

CO2 adsorption separation by metal-organic frameworks (MOFs) is an efficient carbon capture and storage method. We proposed a strategy of two-step in-situ MOFs growth in porous carrier to prepare high efficient CO2 adsorbent for low concentration CO2 adsorption. At first, metal ions were introduced into the pores of melamine formaldehyde sponge (MFS) monolith carriers onto which inner walls a thin layer of PVA was adhered in advance, then organic ligands were introduced into the pores of MFS. The thin PVA layer greatly strengthened the anchoring of MOFs in the carriers. The in-situ MOFs growth in MFS effectively avoided crystals stack together, presented a multi-level pore structure in fixed bed, which is beneficial for gas diffusion with rapid adsorption kinetics. The CO2 adsorption was carried out in a fixed bed by conducting breakthrough experiments. The MOFs crystals uniformly grown in pores of MFS. The monolith composite adsorbent prepared at 6% organic ligand, with MOFs loading ratio of 5 g·g−1(carrier), showed good CO2 uptake value of 1.02 mmol·g−1(adsorbent) in the CO2/N2 atmosphere with CO2 concentration of 5000 PPM at 20 °C. By secondary growth, higher MOFs loading ratio and desired morphology crystals were achieved. The effects of CO2 concentration and gas flow rate on adsorption properties of the secondary-growth adsorbent were investigated. The working CO2 capacity was better than that of 13X zeolite. The presence of 21 vol% O2 did not influence the CO2 adsorption. After 10 cycles adsorption-desorption in 15 days, the as-prepared adsorbent still showed a very stable adsorption separation performance.

Synthesis of CO[formula omitted]-adsorbing ZSM-5 zeolite from rice husk ash via the colloidal pretreatment method

The novel ZSM-5 zeolite was successfully prepared by the colloidal pretreatment method and using rice husk ash (RHA) and pseudo-boehmite as raw materials of silicon and aluminum. A series of samples (ZSM-5-X) with various colloidal silica usage quantity were characterized by XRD, FTIR, SEM and nitrogen adsorption–desorption methods, and the results indicated that the method can reduce the formation of impurity crystals and increase the micropore volume. The CO2 adsorption measurement showed that the maximum adsorption amount of the samples was 55.01 cm3/g (ZSM-5-25) at 0 °C and 23.08 cm3/g (ZSM-5-75) at 90 °C. The Langmuir, Freundlich and Sips isotherm models were used to fit gas adsorption experimental data and analyze adsorption mechanisms. The three-parameter Sips model with a heterogeneous coefficient was suitable for simulating CO2 adsorption, and the correlation coefficient of the Langmuir model was close to 1 for fitting N2 and O2 adsorption. Higher CO2/N2 and CO2/O2 adsorption selectivity and stable adsorption–desorption regeneration performance have been demonstrated, and it indicated that the adsorbent had a promising application in the adsorption separation of CO2 from industrial flue gas.

An efficient temperature swing adsorption (TSA) process for separating CO2 from CO2/N2 mixture using Mg-MOF-74

Carbon dioxide emitted from fossil fuel burning processes is quantitatively the most contributor to global warming. It is believed that climate change could be mitigated by means of Carbon Capture and Storage (CCS). CO2 physical adsorption separation has the potential of capture carbon dioxide with minimum energy costs. A special type of metal organic frameworks named Mg-MOF-74 is an exceptional adsorbent amongst other porous materials with high CO2 uptake at flue gas conditions. Temperature swing adsorption (TSA) composed of 4 steps (feed, rinse, heating, and cooling), for separating CO2 from CO2/N2 mixture using Mg-MOF-74; has been mathematically modeled. A computer model implementation was developed employing User-Defined-Functions linked to Ansys-Fluent software. The CFD two- and three-dimensional models have been validated against adsorption breakthrough experimental data obtained by the authors, at ambient temperature, and against published experimental data for high temperature conditions.The regeneration (heating and cooling) time has been tuned to explore the performance improvement for the TSA process. The TSA optimal key performance indices in terms of CO2 purity, recovery, productivity, and process power consumption have been found to be 96.22%, 86.5%, 0.279 kg of CO2 per hour per kg of Mg-MOF-74, and 663.8 kWh per ton of CO2 captured, respectively. These productivity and power consumption values showed a substantial enhancement in the CO2 adsorption separation compared to those reported in the literature, especially when the heating process is used for the desorption part of the process.

Simulation of CO2 adsorption-separation from an N2/CO2 gas mixture in a Fixed MgMOF-74 Column

A computational study of adsorption-separation of CO2 from an N2/CO2 gas mixture is presented in this paper. A detailed one-dimensional, transient mathematical model has been formulated to include the heat and mass transfer, the pressure drop and multi-component mass diffusion. The model has been implemented on a MATLAB program using second order discretisation. Validation of the model was performed using a complete experimental data set for carbon dioxide separation using activated carbon. Simulation of the adsorption breakthrough experiment on fixed bed has been carried out to evaluate the capacity of Mg-MOF-74 for CO2 capture with varying feed gas temperature of 301 K, 323 K, 373 K and 423 K. The results show the superiority of MOF adsorbent in comparison to activated carbon. The simulated breakthrough time for CO2 on Mg-MOF-74 with feed temperature and pressure of 301 K and 1.02 bar respectively is about 500 min as compared to 50 min for activated carbon. The amount of CO2 adsorbed on Mg-MOF-74 under this condition is 6.43 mole per kilogram of adsorbent. The maximum temperature exhibited in the system is at the bed exit with a value of about 356 K after about 500 min of simulation.

(Invited) Elevated Temperature CO2 Adsorption Separation and Electrochemical Conversion：Reaction Mechanism and Technology Development

Coal gasification is a clean way to utilize coal. Carbon dioxide is a significant emission in coal chemical plants. Before the fuel gas produced from coal chemical plants is utilized, CO2 mixed in the fuel gas has to be separated. A technical route combining elevated temperature CO2 adsorption separation, high temperature CO2 electrolysis and curtailed renewable energy can achieve high-efficiency carbon dioxide separation and utilization in a coal chemical plant. Elevated temperature CO2 adsorption separation (250-350oC) greatly match the temperature of the produced gas from coal chemical plants and thereby purifies the fuel gas in an efficient way. Further, high temperature CO2 electrolysis by solid oxide electrolysis cell (SOEC, operated at 600-1000oC) can fully utilize the curtailed renewable energy, like solar power, wind power and hydropower, to convert CO2/H2O into syngas again. In this study, the effort on these two key technologies, the elevated temperature CO2 adsorption separation and CO2 electrolysis by SOEC, were focused from the perspective of micro scale to macro scale. In the micro scale, the heterogeneous reaction mechanism of CO2 adsorption and electrolysis at an elevated temperature was discussed. In the unit level, the reactor was developed coupling the reaction mechanism and multi-physics (including fluid flow, diffusion, heat transfer and charge transfer). Facing with unstable renewable energy, the dynamic behavior of CO2 electrolysis become a new study focus. In the macro scale, system integration and technology development in the future were analyzed. This technical route is a potential way to simultaneously relieve such a great amount of renewable energy curtailment and carbon dioxide emission.

Adsorption separation of CO2 and N2 on MIL-101 metal-organic framework and activated carbon

In this work, the CO2 and N2 adsorption properties of MIL-101 metal-organic framework (MOF) and activated carbon (AC) were investigated using a standard gravimetric method within the pressure range of 0–30 bar and at four different temperatures (298, 308, 318 and 328 K). The dual-site Langmuir–Freundlich (DSLF) model was used to describe the CO2 adsorption behaviors on these two adsorbents. The diffusion coefficients and activation energy Ea for diffusion of CO2 in the MIL-101 and AC samples were estimated separately. Results showed that the isosteric heat of CO2 adsorption on the MIL-101 at zero loading was much higher than that on the AC due to a much stronger interaction between CO2 molecule and the unsaturated metal sites Cr3+ on MIL-101. Meanwhile, the dramatically decreased isosteric heats of CO2 adsorption on MIL-101 indicated a more heterogeneous surface of MIL-101. Furthermore, the adsorption kinetic behaviors of CO2 on the two samples can be well described by the micropore diffusion model. With the increase of temperature, the diffusion coefficients of CO2 in the two samples both increased. The activation energy Ea for diffusion of CO2 in MIL-101 was slightly lower than that in AC, suggesting that MIL-101 was much favorable for the CO2 adsorption. The CO2/N2 selectivities on MIL-101 and AC were separately estimated to be 13.7 and 9.2 using Henry law constant, which were much higher than those on other MOFs.

Adsorption separation of CO2, CH4, and N2 on microwave activated carbon

In this study, the adsorption equilibrium isotherms of carbon dioxide, methane and nitrogen on microwave activated carbon (MAC) at three temperatures (298, 308 and 323K) have been obtained by a static volume instrument. The adsorption equilibrium data of CO2, CH4 and N2 at various temperatures were fitted to Langmuir and Toth isotherm models. It was found that the fitting results of Toth model were fine. The capacities of pure gas CO2, CH4 and N2 were 2.13, 0.98 and 0.33mmolg−1 at 298K and the partial pressure of 100kPa. The competition adsorption behavior of multi component was predicted by the extend Langmuir and Toth model. The results indicated that CO2 still dominate the adsorption system in the ternary mixtures. Additionally, the separation factors of the binary mixtures CO2/CH4, CO2/N2 and CH4/N2 were calculated from the isotherms data. The results showed that the separation factors (S) of different binary mixtures at 298K and the total pressure of 100kPa were as follows: CO2/N2 (14.6)>CO2/CH4 (4.37)>CH4/N2 (3.33). Finally, thermodynamic functions integral Gibbs’ free energy (ΔG), integral molar enthalpy change (ΔH) and entropy change (ΔS) were calculated to characterize adsorption behavior.

Molecular simulation of separation of CO2 from flue gases in CU‐BTC metal‐organic framework

AbstractIn this work, a computational study was performed on the adsorption separation of CO2 from flue gases (mixtures of CO2/N2/O2) in Cu‐BTC metal‐organic framework (MOF) to investigate the applicability of MOFs to this important industrial system. The computational results showed that Cu‐BTC is a promising material for separation of CO2 from flue gases, and the macroscopic separation behaviors of the MOF were elucidated at a molecular level to give insight into the underlying mechanisms. The present work not only provided useful information for understanding the separation characteristics of MOFs, but also showed their potential applications in chemical industry. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Influence of Moisture on CO2 Separation from Gas Mixture by a Nanoporous Adsorbent Based on Polyethylenimine-Modified Molecular Sieve MCM-41

Adsorption separation of CO2 from simulated flue gas containing CO2, O2, and N2 with and without moisture was investigated using a novel nanoporous adsorbent based on polyethylenimine (PEI)-modified mesoporous molecular sieve MCM-41 in a flow system. The CO2 adsorption capacity and CO2 separation selectivity of MCM-41 were greatly improved by loading PEI into its nanosized pore channels, which made the resulting adsorbent operating like a “molecular basket” for CO2. CO2 adsorption capacity of the MCM-41-PEI adsorbent for the simulated moist flue gas was higher than that for the simulated dry flue gas. CO2 separation selectivity of the MCM-41-PEI adsorbent was also improved in the presence of moisture when compared with those in the dry gas condition. The influence of moisture concentrations in the simulated flue gas on the CO2 adsorption separation performance was also examined. The results of adsorption/desorption separation cycles showed that the MCM-41-PEI adsorbent was stable over 10 cycles of adsorption/desorption operations. The hydrothermal stability of the “molecular basket” adsorbent was better than that of the MCM-41 support alone.

Adsorption separation of CO<SUB align=right>2 from simulated flue gas mixtures by novel CO<SUB align=right>2 "molecular basket" adsorbents

Adsorption separation of CO2 from simulated flue gas mixtures containing CO2, O2, and N2 by using a novel CO2 "molecular basket" adsorbent was investigated in a flow adsorption separation system. The novel CO2 "molecular basket" adsorbents were developed by synthesising mesoporous molecular sieve MCM-41 and modifying it with polyethylenimine (PEI). The influence of operation conditions, including feed flow rate, temperature, feed CO2 concentration, and sweep gas flow rate, on the CO2 adsorption/desorption separation performance and CO2 breakthrough were examined. The CO2 adsorption capacity was 91.0 ml (STP)/g-PEI, which was 27 times higher than that of the MCM-41 alone. Further, the adsorbent showed separation selectivity of greater than 1000 for CO2/N2 ratio and approximately 180 for CO2/O2, which are significantly higher than those of the MCM-41, zeolites, and activated carbons. Cyclic adsorption/desorption measurements showed that the CO2 "molecular basket" adsorbent was stable at 75°C. However, the CO2 "molecular basket" adsorbent was not stable when the operation temperature was higher than 100°C.

Adsorption Separation of Low Concentrations of CO2 and NO2 by Synthetic Zeolites

The CO2 equilibrium adsorption and breakthrough activity of CO2−NO2 mixtures on A- and faujasite-type zeolites and Na- and proton-type (HM) mordenites were studied to determine the appropriate zeolite for separation of low-concentration mixtures of CO2 and NO2. Adsorption of CO2 correlated with the polarity of the zeolites as a result of dominant adsorption via interaction of the quadrupole moment and polar surface sites. Competitive adsorption of NO2 and CO2 gives nearly zero breakthrough times for CO2 on 5A- and faujasite-type zeolites and HM. Adsorption separation of CO2 and NO2 by zeolites depends on the NO2 adsorptivity, which is determined not only by surface polar sites but also by pore geometry and dimension. 13X had the greatest NO2 adsorptivity, but the thermal instability in NO2 adsorptive sites is the main obstacle for its use as a substrate for the separation of CO2 and NO2. Sufficient protonation of NaM leads to zero CO2 adsorption and still keeps a great NO2 adsorption. Because of the therm...