Dual-site Langmuir – Freundlich Research Articles

Enhancing the CO2, CH4, and N2 adsorption and kinetic performance on FAU zeolites for CO2 capture from flue gas by metal incorporation technique

Various metals including alkali (Na+, K+), alkaline earth (Mg2+ and Ca2+), and transition metals (Cu2+ and Fe3+) were successfully incorporated into the structure of faujasite zeolites (X and Y) by novel post-synthesis modification method. The effect of metal-doping on the CO2, CH4, and N2 adsorption and kinetic performance in the context of flue gas carbon capture and natural gas purification was examined by four approaches; (i) the impact on structural properties was examined by XRD, FTIR, UV–visible, H2-TPR, FESEM, EDX Dot-Mapping, and BET analysis; (ii) the influence on the CO2, CH4, and N2 adsorption capacity was acquired by volumetric method up to 100 kPa at 25 °C (iii) the effect on binary CO2/CH4 and CO2/N2 selectivity was determined by the Henry constant and IAST selectivity; (iv) the micropore - macropore kinetic model was utilized to study the influence on diffusion coefficients. The dual-site Langmuir-Freundlich (DSLF) isotherm was found to be the best adaptability to the experimental isotherms data. The results showed an extraordinary increase in CO2 absorption capacity to 4.9 and 7 for KX and KY, respectively. Faujasite zeolite with a lower Si/Al ratio (zeolite X) outperforms CO2/CH4 and CO2/N2 separation performance than higher ones (zeolite Y). Among all samples, KX showed the highest CO2/CH4 and CO2/N2 IAST selectivity with values of 61 and 152 at 100 kPa, respectively, in addition to the highest diffusion coefficients for CH4 and N2. The incorporated potassium metal into the faujasite zeolites showed promising sorbents for the separation of CO2 from flue gas and natural gas streams.

Ideal adsorbed solution theory, two-dimensional equation of state, and molecular simulation for separation of H2/N2/O2/CH4/CO in graphite nanofiber and C60 intercalated graphite

We performed grand canonical Monte Carlo (GCMC) simulations to investigate the adsorption separation of H2, N2, O2, CO and CH4 gas mixtures in graphite nanofibers (described by slit pore model), and C60 intercalated graphite (CIG). The presence of C60 molecules between the layers resulted in less than half of the adsorption of O2 and CH4 in CIG, compared to the slit pore. However, the adsorption selectivity of O2/N2, CH4/N2, CH4/H2, and CO/H2 systems in CIG is much higher than that of slit pores. These observations indicate that the slit pore and CIG are suitable for gas storage and gas separation, respectively. We used the two-dimensional Zhou-Gasem-Robinson (2D ZGR) EOS and the dual-site Langmuir-Freundlich (DSLF) to correlate the pure component adsorption isotherms simulated by GCMC method, and further predicted the adsorption of the binary gas mixtures by the ZGR model and ideal adsorbed solution theory (IAST), respectively. We found that neither adsorption model can accurately predict the adsorption properties of the four gas mixtures in the two materials simulated by GCMC method. IAST has a satisfactory predictive effect on the adsorption of N2-O2, N2-CH4 and H2-CO gas mixtures in CIG, while ZGR can accurately predict the gas adsorption of N2-O2, H2-CH4 and H2-CO in CIG. However, both models perform poorly in predicting gas adsorption in the slit pore. Consequently, experimental study or molecular simulation should be carried out for the validation of the results, when using the adsorption theory such as IAST and 2D EOS to predict the adsorption of a gas mixture.

Highly CO selective Cu(I)-doped MIL-100(Fe) adsorbent with high CO/CO2 selectivity due to π complexation: Effects of Cu(I) loading and activation temperature

Cu(I) doping of octahedral MIL-100(Fe) was successfully performed by means of impregnation and consequent reduction under vacuum conditions. Although MIL-100(Fe) adsorbed CO2 better than CO, Cu(I)@MIL-100(Fe) showed selective CO adsorption compared to CO2 owing to π complexation between CO and Cu(I). Effects of Cu(I) loading concentration, activation temperature, and adsorption temperature upon CO/CO2 adsorption properties were systematically investigated. The adsorption behaviors of CO and CO2 on MIL-100(Fe) and Cu(I)@MIL-100(Fe) were well described by the dual-site Langmuir–Freundlich (DSLF) model. Ideal adsorbed solution theory (IAST) was used to predict adsorption isotherms of equimolar CO and CO2 mixtures and to predict CO/CO2 selectivities as a function of bulk pressure. The obtained results showed that 45 wt% Cu(I)-doped MIL-100(Fe) had CO adsorption capacity of 3.10 mmol g−1 and CO/CO2 selectivity of 420 at 298 K and 1 bar. In addition, a large CO working capacity of 1.39 mmol g−1 was observed for 45 wt% Cu(I)-doped MIL-100(Fe) in the pressure range of 10–100 kPa. Cu(I)-doped MIL-100(Fe) thus appears promising as an adsorbent material for effective CO/CO2 separation.

A new MOF-505@GO composite with high selectivity for CO2/CH4 and CO2/N2 separation

Novel MOF-505@GO composites comprised of a copper-based metal-organic framework and graphite oxide (GO) were synthesized by a solvothermal method for effective separation of CO2/CH4 and CO2/N2, which are challenging chemical separations in industry. The composites were characterized by various techniques including powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and porosity measurement through nitrogen adsorption at cryogenic temperature. Single component adsorption isotherm measurements of CO2, CH4 and N2 were performed at different temperatures. The selectivities of CO2/CH4 and CO2/N2 were estimated on the basis of ideal adsorbed solution theory (IAST). MOF-505@GO composites showed higher porosity and enhanced CO2 adsorption compared to its parent compound MOF-505. MOF-505@5GO exhibited the highest CO2 uptake of 3.94mmol/g at 298K and 100kPa, having an increase of 37.3% in comparison with the parent MOF-505. The significant improvement of CO2 uptakes could be attributed to not only new micropores and unsaturated metal sites formed in the MOF-505@GO, but also enhanced surface dispersive forces of the composites. The experimental adsorption isotherms of CO2, CH4 and N2 were well fitted with dual site Langmuir-Freundlich (DSLF) model. The CO2/CH4 and CO2/N2 adsorption selectivities were up to 8.6 and 37.2 at 298K and 100kPa, respectively, predicted by IAST. More strikingly, the composites showed excellent moisture stability, which was confirmed by PXRD analysis. These superior performances suggested that the MOF-505@GO composites are promising candidates for industrial CO2 capture.

Graphyne nanostructure as a potential adsorbent for separation of H2S/CH4 mixture: Combining grand canonical Monte Carlo simulations with ideal adsorbed solution theory

The adsorption performances of multilayer graphyne-n (n=1–3) nanostructures (abbreviated as MGN-n) for pure H2S, CH4 and their mixture are explored by the Grand canonical Monte Carlo (GCMC) simulations combined with ideal adsorbed solution theory (IAST). The effects of pressure, temperature, gaseous composition and content of pre-adsorbed water on the adsorption and separation behaviors are examined. For the pure H2S and CH4 adsorption, the dual-site Langmuir-Freundlich (DSLF) model can be used to exactly fit the results of GCMC simulation. Compared with CH4, H2S molecules are preferentially adsorbed in all cases. Due to the effect of adsorbent’s structure, the loading of H2S in MGN-1 with smaller free volume (0.662cm3g−1) is greater than that in MGN-2 with free volume 0.933cm3g−1. For the mixture adsorption, the IAST can accurately predict the loading of two species in MGN-1 and MGN-2, but it has a slight deviation for the selectivity predictions. For the MGN-3, due to the strong adsorbate-adsorbate interactions and heterogeneity surface, the IAST can’t predict the loading and selectivity precisely. Besides, the separation performances of MGN are compared with zeolites and found that the MGN-1 has the highest H2S adsorption capacity and selectivity, in which the loading and selectivity reaches up to 15.493mmolg−1 and 60.8 at 1MPa and 300K, respectively. Rising temperature has adverse influence on the H2S/CH4 mixture separation. The H2S selectivity in MGN-1, MGN-2 and MGN-3 reduces 93.51%, 78.24% and 87.46% respectively as the temperature rises from 300K to 500K. When the molar fraction of H2S in mixture is low, pre-adsorbed some water is beneficial to the mixture separation. This work demonstrates that the MGN-1 can act as a delightful separation material.

Selective Hysteretic Sorption of Light Hydrocarbons in a Flexible Metal–Organic Framework Material

Porous MFM-202a (MFM = Manchester Framework Material, replacing the NOTT designation) shows an exceptionally high uptake of acetylene, 18.3 mmol g–1 (47.6 wt %) at 195 K and 1.0 bar, representing the highest value reported to date for a framework material. However, at 293 K and 10 bar C2H6 uptake (9.13 mmol g–1) is preferred. Dual-site Langmuir-Freundlich (DSLF)- and Numerical Integration (NI)-based IAST methods have been used to analyze selectivities for C1 to C3 hydrocarbons. MFM-202a exhibits broadly hysteretic desorption of acetylene; such behavior is important for practical gas storage since it allows the gas to be adsorbed at high pressure but stored at relatively low pressure. Stepwise uptake and hysteretic release were also observed for adsorption of other unsaturated light hydrocarbons (ethane and propene) in MFM-202a but not for saturated hydrocarbons (methane, ethane, and propane). MFM-202a has been studied by in situ synchrotron X-ray powder diffraction to reveal the possible phase transition ...

Enhanced separation performance of a novel composite material GrO@MIL-101 for CO2/CH4 binary mixture

A novel GrO@MIL-101 composite consisting of graphene oxide (GrO) and MIL-101(Cr) was synthesized, characterized and tested for separation of CO2/CH4 mixture. GrO@MIL-101 had higher BET surface area and better porosity than parent MIL-101. CO2 and CH4 isotherms were separately measured at different temperatures using a gravimetric method, and were fitted using the dual-site Langmuir–Freundlich (DSLF) model. The adsorption capacity of GrO@MIL-101 for CO2 was significantly improved over MIL-101, reaching 22.4mmolg−1 at 25bar and 298K, much higher than traditional adsorbents and most other MOFs. The isotherms and selectivities of CO2/CH4 binary mixture were estimated using the ideal adsorbed solution theory (IAST). While calculated isotherms indicated CO2 was more favorably adsorbed on GrO@MIL-101 than CH4, the adsorption selectivity of GrO@MIL-101 composite was dramatically enhanced over pristine MIL-101. At 1.5bar, the selectivity of GrO@MIL-101 for CO2/CH4 (10:90) mixture with a characteristic of natural gas was up to 32, which was more than three times of that of MIL-101. Isosteric heats of adsorption for CO2 and CH4 on GrO@MIL-101 were slightly above those on parent MIL-101. GrO@MIL-101 also displayed remarkable quasi-reversibility for CO2 adsorption, showing more than 95% desorption efficiency over five cycles.

Competitive adsorption and selectivity of benzene and water vapor on the microporous metal organic frameworks (HKUST-1)

Abstract Competitive adsorption and selectivity of benzene and water vapor were studied on the microporous metal organic frameworks (HKUST-1). The adsorption equilibrium and kinetics of pure component as well as binary mixtures of benzene and water vapor were systematically investigated on the HKUST-1. Their binary adsorption selectivity and permeation selectivity are predicted via the IAST method. Results showed that the equilibrium data of benzene and water vapor depicted the Langmuir–Freundlich and Dual Site Langmuir–Freundlich (DSLF) type adsorption isotherms, respectively. Benzene exhibited much higher isosteric heat and desorption activation energy than water vapor, indicating a stronger interaction with the HKUST-1. The adsorption selectivity of benzene/water on the HKUST-1 was of about ∼8.32 at 318 K and 1.0 mbar, and its diffusivity selectivity was about 17.6 at 298 K and 1.5 mbar, respectively. Breakthrough curves of benzene showed a remaining capacity of about 94.7% and 72.9% in the presence of 13 and 34 RH%. Thus, the HKUST-1 is more selective or preferential adsorption for benzene molecules in comparison to water molecules at high temperature and low pressure. Also, it shows the advantage of kinetic separation for VOCs and water vapor.

Preparation and Adsorption Performance of GrO@Cu-BTC for Separation of CO2/CH4

Composites (GrO@Cu-BTC) based on Cu-BTC and graphene oxide were synthesized by a solvothermal method for the separation of CO2/CH4 binary mixtures. The as-synthesized composites were then characterized. The isotherms of CO2 and CH4 on the as-synthesized materials were measured by the volumetric method. The isotherms and adsorption selectivities of CO2/CH4 binary mixtures were estimated on the basis of ideal adsorbed solution theory (IAST). The results showed that the composite 1GrO@Cu-BTC had a higher BET surface area and pore volume compared to the parent Cu-BTC. More importantly, its adsorption capacity for CO2 improved significantly in comparison with that of Cu-BTC, which was up to 8.19 mmol/g at 1 bar and 273 K. The dual-site Langmuir–Freundlich (DSLF) model was applied favorably for fitting experimental isotherm data of CO2 and CH4 adsorption on the samples. The predicted isotherms of the binary mixture based on IAST showed that CO2 was more favorably adsorbed than CH4 on the sample 1GrO@Cu-BTC. TPD...

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.

Covalent-organic polymers for carbon dioxide capture

Reducing anthropogenic carbon dioxide emission has become an urgent environmental and climate issue of our age. Here, a series of covalent-organic polymers (COPs) are synthesized, and the adsorption properties of these COPs for H2, CO2, CH4, N2 and O2 are studied. The H2 uptake of COP-2 reaches 1.74 wt% at 77 K and 1 bar, which is among the highest reported uptakes in the field of microporous organic polymers under similar conditions, and CO2 and CH4 adsorption capacities are 594 mg g−1 and 78 mg g−1, respectively, at 298 K and 18 bar. Then, based on the single component isotherm, the dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is used to predict the selectivity of the COP materials for post-combustion (CO2–N2) and pre-combustion (O2–N2) gas mixtures. The IAST predicted results indicate that COP-1 exhibits significantly higher selectivity compared to COP-2, 3 and 4, due to its smaller pore size. In particular, the adsorption selectivity of COP-1 for the CO2–N2 mixture reaches 91 at a CO2 : N2 ratio of 15 : 85 at 298 K and 1 bar, and 2.38 for the 21 : 79 O2–N2 mixture at 298 K and 1 bar. Furthermore, these COPs also show robust properties for the removal of CO2 from natural gas. The adsorption selectivity of COP-1 for CO2–CH4 is in the range of 4.1–5.0 at a CO2 : CH4 ratio of 15 : 85 at 0 < P < 40 bar.

CNT@Cu3(BTC)2 and Metal–Organic Frameworks for Separation of CO2/CH4 Mixture

Effectively separating CO2 from the natural gas, which is one of alternative “friendly” fuels, is a very important issue. A hybrid material CNT@Cu3(BTC)2 has been prepared to separate CO2 from the CO2/CH4 mixture. For comparison of separation efficiency, a series of representative metal–organic frameworks (MOF-177, UMCM-1, ZIF-8, MIL-53 (Al), and Cu3(BTC)2) have also been synthesized by the solvothermal method. Adsorption isotherms of CO2 and CH4 pure gases are measured by Hiden Isochema Intelligent Gravimetric Analyzer (IGA-003). The dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is used to predict adsorption of each component in the CO2/CH4 mixture. The IAST-predicted results show that the hybrid material CNT@Cu3(BTC)2 exhibits the greatest selectivity among the six materials, and its selectivity keeps in the range of 5.5 to 7.0 for equimolar CO2/CH4 mixture at 1 < p < 20 bar, which is higher than activated carbons. Moreover, the selectivity of CNT@Cu3(BTC)2 for the C...

Adsorption and separation of CH 4/CO 2/N 2/H 2/CO mixtures in hexagonally ordered carbon nanopipes CMK-5

Adsorption and separation of N 2, CH 4, CO 2, H 2 and CO mixtures in CMK-5 material at room temperature have been extensively investigated by a hybrid method of grand canonical Monte Carlo (GCMC) simulation and adsorption theory. The GCMC simulations show that the excess uptakes of pure CH 4 and CO 2 at 6.0 MPa and 298 K can reach 13.18 and 37.56 mmol/g, respectively. The dual-site Langmuir–Freundlich (DSLF) model was also utilized to fit the absolute adsorption isotherms of pure gases from molecular simulations. By using the fitted DSLF model parameters and ideal adsorption solution theory (IAST), we further predicted the adsorption separation of N 2–CH 4, CH 4–CO 2, N 2–CO 2, H 2–CO, H 2–CH 4 and H 2–CO 2 binary mixtures. The effect of the bulk gas composition on the selectivity of these gases is also studied. To improve the storage and separation performance, we finally tailor the structural parameters of CMK-5 material by using the hybrid method. It is found that the uptakes of pure gases, especially for CO 2, can be enhanced with the increase of pore diameter D i , while the separation efficiency is apparently favored in the CMK-5 material with a smaller D i . The selectivity at D i =3.0 nm and 6.0 MPa gives the greatest value of 8.91, 7.28 and 27.52 for S CO 2 / N 2 , S CH 4 / H 2 and S CO 2 / H 2 , respectively. Our study shows that CMK-5 material is not only a promising candidate for gas storage, but also suitable for gas separation.

Adsorption of CO2, CH4, CO2/N2 and CO2/CH4 in novel activated carbon beads: Preparation, measurements and simulation

AbstractA series of high performance carbonaceous mesoporous materials: activated carbon beads (ACBs), have been prepared in this work. Among the samples, ACB‐5 possesses the BET specific surface area of 3537 m2 g−1 and ACB‐2 has the pore volume of 3.18 cm3 g−1. Experimental measurements were carried out on the intelligent gravimetric analyzer (IGA‐003, Hiden). Carbon dioxide adsorption capacity of 909 mg g−1 has been achieved in ACB‐5 at 298 K and 18 bar, which is superior to the existing carbonaceous porous materials and comparable to metal‐organic framework (MOF)‐177 (1232 mg g−1, at 298 K and 20 bar) and covalent‐organic framework (COF)‐102 (1050 mg g−1 at 298 K and 20 bar) reported in the literature. Moreover, methane uptake reaches 15.23 wt % in ACB‐5 at 298 K and 18 bar, which is better than MOF‐5. To predict the performances of the samples ACB‐2 and ACB‐5 at high pressures, modeling of the samples and grand canonical Monte Carlo simulation have been conducted, as is presented in our previous work. The adsorption isotherms of CO2/N2 and CO2/CH4 in our samples ACB‐2 and 5 have been measured at 298 and 348 K and different compositions, corresponding to the pre‐ and postcombustion conditions for CO2 capture. The Dual‐Site Langmuir‐Freundlich (DSLF) model‐based ideal‐adsorbed solution theory (IAST) was also used to solve the selectivity of CO2 over N2 and CH4. The selectivities of ACBs for CO2/CH4 are in the range of 2–2.5, while they remain in the range of 6.0–8.0 for CO2/N2 at T = 298 K. In summary, this work presents a new type of adsorbent‐ACBs, which are not only good candidates for CO2 and CH4 storage but also for the capture of carbon dioxide in pre‐ and postcombustion processes. © 2011 American Institute of Chemical Engineers AIChE J, 2011

Computer simulations for the adsorption and separation of CO2/CH4/H2/N2 gases by UMCM-1 and UMCM-2 metal organic frameworks

The adsorption of pure N2/H2/CH4/CO2 along with the adsorption and separation of mixtures thereof in two metal organic frameworks (MOFs) of UMCM-1 and UMCM-2 have been extensively studied using a hybrid method of computer simulation and adsorption theory. It is found that the excess adsorption isotherms from grand canonical Monte Carlo (GCMC) simulations basically agree with the available experimental data of pure gases, except for H2 adsorption in UMCM-1 at 298 K. Moreover, the GCMC results show that both MOF materials exhibit an excellent storage capacity for pure CH4 and CO2 at room temperature. The excess uptakes of CH4 by UMCM-1 and UMCM-2 for at 5000 kPa are 12.53 and 15.06 mmol g−1, while those of CO2 at 4500 kPa are 30.13 and 36.04 mmol g−1, respectively, which approaches and even exceeds the 30.82 mmol g−1 of MOF-177. In addition, dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is also used to correlate the simulated adsorption isotherms of pure gases and further predict the separation of equimolar mixtures. IAST shows a good agreement with the GCMC results in most cases studied here. The selectivities of both MOF materials in CH4/H2 and CH4/N2 are insensitive to the pressure. The selectivities of both MOF materials for CH4/H2 are almost the same having a value of 4, while they are 2 for CH4/N2. By contrast, the selectivities for CO2/H2, CO2/N2 and CO2/CH4 apparently rely on the pressure, showing 16.4 and 26.9, 5.4 and 7.8, and 2.9 and 4.7 at 4000 kPa for UMCM-1 and UMCM-2, respectively. Compared with other MOFs materials, their separation ability is not prominent, but they are suitable for gas storage.

Adsorption and Separation of CO&lt;sub&gt;2&lt;/sub&gt;/CH&lt;sub&gt;4&lt;/sub&gt;/N&lt;sub&gt;2&lt;/sub&gt; Binary Mixtures in an Ordered Mesoporous Carbon Material CMK-3

The adsorption and separation of natural gas in the ordered mesoporous carbon material CMK-3 was investigated by molecular simulation and adsorption theory.Grand canonical ensemble Monte Carlo(GCMC) simulations show that a maximum excess uptake of 10.07 and 14.85 mmol·g-1 is obtained at the optimum temperature and pressure of 208 K,4 MPa for CH4 and 298 K,6 MPa for CO2 adsorption,respectively.Based on the dual-site Langmuir-Freundlich(DSLF) model,ideal adsorption solution theory(IAST) was used to predict the adsorption and separation of binary mixtures.The adsorption selectivity of [SCO2/CH4] is approximately the same as that of [SCH4/N2],with a value of about 3 at 298 K and 4 MPa while the highest CO2 selectivity of 7.5 was found in the N2-CO2 system under the same conditions.This indicates that the CMK-3 material is a promising candidate for natural gas separation.

Computational Study on Purification of CO2 from Natural Gas by C60 Intercalated Graphite

By combining grand canonical Monte Carlo (GCMC) simulations with adsorption theory, we perform a computational study on adsorption of CH4 and CO2 gases and purification of CO2 from the CH4−CO2 and N2−CO2 binary mixtures by the C60 intercalated graphite. The adsorption isotherms, isosteric heats and snapshots of pure gases have been examined extensively. It is found that the maximum excess uptakes at 298 K are relatively low, only giving 4.04 and 4.96 mmol/g for CH4 and CO2, respectively, due to a low porosity of 0.45 and a large crystal density of 1.57 g/cm3 of this material. It indicates that the pristine material is not suitable for gas storage. However, this material provides excellent selectivity for CO2, and the selectivity at ambient condition can reach 8 and 50 for the CH4−CO2 and N2−CO2 mixture, respectively. Furthermore, the selectivity of CO2 is almost independent of the bulk gas composition for P > 0.1 MPa. The dual-site Langmuir−Freundlich (DSLF) equation is used to fit the adsorption isotherm...