Adsorption and separation of CO2/N2 and CO2/CH4 by 13X zeolite

Accumulation of greenhouse gases in the atmosphere is responsible for increased global warming of our planet. The increasing concentration of carbon dioxide mainly from flue gas, automobile and landfill gas (LFG) emissions are major contributors to this problem. In this work, CO₂, CH₄ and N₂ adsorption was studied on Ceca 13X zeolite by determining pure and binary mixture isotherms using a constant volume method and a concentration pulse chromatographic technique at 40 and 100°C. The experimental data were then compared to the predicted binary behaviour by extended Langmuir model. Results showed that the extended Langmuir theoretical adsorption model can only be applied as an approximation to predict the experimental binary behaviour for the systems studied. Equilibrium phase diagrams were obtained from the experimental binary isotherms. For these systems, the integral thermodynamic consistency tests were also conducted. It was found that Ceca 13X exhibits large CO₂/CH₄ and CO₂/N₂ selectivity and could find application in landfill gas purification, CO₂ removal from natural gas and CO₂ removal from ambient air or flue gas streams. © 2011 Canadian Society for Chemical Engineering     

Experimental and theoretical study of the adsorption of pure molecules and binary systems containing methane, carbon monoxide, carbon dioxide and nitrogen. Application to the syngas generation

This study takes place in the context of the use of a Synthesis Gas in Gas To Liquid process, liquid hydrocarbon production by conversion based on Fischer–Tropsch synthesis. Our aim is the process improvement by a selective recycling of the tail gas. So, we measure pure component isotherms for four gases (CO₂, CH₄, CO, N₂) of the tail gas until 2000 kPa and binary mixture (CO₂–CH₄; CO₂–N₂; CH₄–N₂) equilibria at 303.15 K and 400 and 950 kPa onto a ZSM-5 zeolite. We also predict the binary mixture equilibria by the Ideal Adsorbed Solution Theory (IAST) and the Vacancy Solution Model (VSM, Flory–Huggins and Wilson forms) and we obtain very good results. So not only binary mixture equilibria but also ternary and quaternary mixture adsorption can be predicted. With these data (experimental and simulated), we can conclude that the CO₂ is the most adsorbed component while N₂ is the least one. These two components can be separated from CH₄ and CO which are sent in the Synthesis Gas production step.     

Separation of CO2 and CH4 on CaX zeolite for use in Landfill gas separation

In this study, adsorption separation of main components of landfill gas, methane (CH₄) and carbon dioxide (CO₂) was carried out. Henry's law constants, limiting heat of adsorption values, pure and binary isotherms for CO₂ and CH₄ were determined for CaX zeolite adsorbent. Pure isotherm data were compared to those for NaX zeolite from previous studies. The CO₂ adsorption capacity of CaX was greater than that of NaX; however, NaX's separation factor was higher. The heat of adsorption for CO₂ for CaX was higher than those for NaX. © 2013 Canadian Society for Chemical Engineering     

Adsorption and separation of CH4/CO2/N2/H2/CO mixtures in hexagonally ordered carbon nanopipes CMK-5

Adsorption and separation of N₂, CH₄, CO₂, H₂ 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 CH₄ and CO₂ 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 N₂–CH₄, CH₄–CO₂, N₂–CO₂, H₂–CO, H₂–CH₄ and H₂–CO₂ 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_CO2/N2, S_CH4/H2 and S_CO2/H2, respectively. Our study shows that CMK-5 material is not only a promising candidate for gas storage, but also suitable for gas separation.     

Separation of co2-ch4 and co2-n2 systems using ion-exchanged fau-type zeolite membranes with different si/al ratios

FAU-type zeolite membranes with different Si/Al ratios were hydrothermally synthesized on the outer surface of a porous α-Al₂O₃ support tube. The permeances of the membranes to CO₂, CH₄ and N₂ were then measured at 308 K for single-component and equimolar binary systems. The separation properties were dependent on both the Si/Al ratio and the ion-exchange treatment. For single-component systems, a lower Si/Al ratio resulted in the incorporation of a larger number of Na⁺ ions. For a CO₂-CH₄ mixture, both CO₂ permeances and CO₂/CH₄ selectivities were approximately half the values obtained for a binary CO₂-N₂ mixture. The highest selectivities, obtained using the NaX(1) zeolite membrane, were 28 for CO₂/CH₄ and 78 for CO₂/N₂. The RbY, RbX(1) and RbX(2) zeolite membranes showed larger CO₂ permeances, compared with those of the original Na-type membranes. Ion-exchange with K⁺ ions was the most effective for the NaY zeolite membrane in that both the CO₂ permeance and the CO₂/CH₄ selectivity were increased.     

Single and Multicomponent Sorption of CO2, CH4 and N2 in a Microporous Metal-Organic Framework

Abstract

Single and multicomponent fixed-bed adsorption of CO₂, N₂, and CH₄ on crystals of MOF-508b has been studied in this work. Adsorption equilibrium was measured at temperatures ranging from 303 to 343 K and partial pressures up to 4.5 bar. MOF-508b is very selective for CO₂ and the loadings of CH₄ and N₂ are practically temperature independent. The Langmuir isotherm model provides a good representation of the equilibrium data. A dynamic model based on the LDF approximation for the mass transfer has been used to describe with good accuracy the adsorption kinetics of single, binary and ternary breakthrough curves. It was found that the intra-crystalline diffusivity for CO₂ is one order of magnitude faster than for CH₄ and N₂.     

CO2/CH4/N2在沸石13X-APG上的吸附平衡

采用磁悬浮热天平测量了CO₂、CH₄与N₂在沸石13X-APG上的吸附等温线,温度为293、303、333和363 K,压力为0～500 kPa。对吸附平衡实验数据采用multi-site Langmuir模型和Sips模型进行拟合,均得到良好的拟合效果,非线性回归得到吸附热等模型参数,可为变压吸附工艺过程的开发提供基础热力学数据。将沸石13X-APG吸附分离性能与文献中报道的吸附材料(如沸石分子筛、活性炭、金属有机骨架材料和介孔硅分子筛)性能相比较。通过比较CO₂、CH₄与N₂吸附容量以及相对分离系数,探讨CO₂/CH₄(垃圾填埋气或者CO₂强化煤层甲烷回收气)体系、CO₂/N₂(燃煤电厂、水泥厂以及焦炭厂烟道气)体系以及CH₄/N₂(煤层气)体系吸附分离的高效材料,为未来二氧化碳吸附捕集和甲烷吸附回收提供基础数据。     

Equilibrium Adsorption Studies of CO2, CH4, and N2 on Amine Functionalized Polystyrene

Adsorption of CO₂, CH₄, and N₂ has been investigated using amine functionalized polymeric resins having diethanolamine, imidazole, dimethylamine, and N-methyl piperazine covalently attached to the styrene-divinyl benzene copolymer (PS) matrix. The equilibrium adsorption of CO₂, CH₄, and N₂ was examined on these functionalized polymers at pressures from atmospheric to 40 atm for CO₂ and N₂ while up to 10 atm for CH₄ at 303 K. PS-Imidazole showed the highest adsorption capacity for CO₂ as compared to other functionalized polymers. No significant uptake of CH₄ and N₂ was observed at low pressures by any of the functionalized polymers. The adsorption isotherms were analyzed using dual mode sorption model and Ideal Adsorbed Solution Theory (IAST).     

Transient measurements of adsorption and diffusion in H-ZSM-5 membranes

A transient permeation method presented here not only determines the adsorption and diffusion properties of the pores that are the transport pathways through zeolite membranes, but nondestructively estimates the effective thickness of the membrane. Transient responses of the permeate concentration to step changes in the feed were measured on two H-ZSM-5 tubular membranes and modeled assuming Maxwell-Stefan diffusion and Langmuir adsorption. The adsorption isotherms determined from these transient measurements at 298 K of N₂ and CO₂ were nearly identical to those measured by calorimetry on H-ZSM-5 powders. The CH₄ isotherm at 298 K was similar to isotherms measured by calorimetry and gravimetric techniques on Na-ZSM-5 and silicalite powders. The similarity of the isotherms indicates that transport of these light gases occurs mainly through zeolite pores. The Maxwell-Stefan diffusion coefficients D_MS depended on concentration and were higher for higher feed partial pressures. Average D_MS values for the two membranes were 7.5, 5 and 1.5×10⁻¹⁰ m²/s for N₂, CH₄, and CO₂, respectively; these are in the same range and order as diffusion coefficients measured in zeolite crystals.     

Adsorption of CO2 from dry gases on MCM-41 silica at ambient temperature and high pressure. 2: Adsorption of CO2/N2, CO2/CH4 and CO2/H2 binary mixtures

Adsorption equilibrium capacity of CO₂, CH₄, N₂, H₂ and O₂ on periodic mesoporous MCM-41 silica was measured gravimetrically at room temperature and pressure up to 25 bar. The ideal adsorption solution theory (IAST) was validated and used for the prediction of CO₂/N₂, CO₂/CH₄, CO₂/H₂ binary mixture adsorption equilibria on MCM-41 using single components adsorption data. In all cases, MCM-41 showed preferential CO₂ adsorption in comparison to the other gases, in agreement with CO₂/N₂, CO₂/CH₄, CO₂/H₂ selectivity determined using IAST. In comparison to well known benchmark CO₂ adsorbents like activated carbons, zeolites and metal-organic frameworks (MOFs), MCM-41 showed good CO₂ separation performances from CO₂/N₂, CO₂/CH₄ and CO₂/H₂ binary mixtures at high pressure, via pressure swing adsorption by utilizing a medium pressure desorption process (PSA-H/M). The working CO₂ capacity of MCM-41 in the aforementioned binary mixtures using PSA-H/M is generally higher than 13X zeolite and comparable to different activated carbons.     

Force fields for classical atomistic simulations of small gas molecules in silicalite-1 for energy-related gas separations at high temperatures

High temperature (>573 K) molecular dynamics studies of gas diffusion in microporous zeolites require consideration of the zeolite framework flexibility. Pore windows can expand and contract at high temperatures, affecting phase space and material properties. No studies to date have addressed the application of the condensed-phase optimized molecular potentials for atomistic simulation studies or the consistent valence force field to simulate gas diffusion and adsorption in siliceous MFI (silicalite-1). The current study seeks to validate these intramolecular and intermolecular potentials along with another zeolite-specific force field reported by Nicholas et al. (JACS 113:4792–4800, 1991) for silicalite-1, one of the most extensively investigated zeolites, with respect to diffusion of several gas molecules. The experimental diffusion coefficients of H₂, CO₂, CH₄, O₂ and N₂ in silicalite-1 obtained using pulse-field gradient-nuclear magnetic resonance and quasi-elastic neutron scattering methods were compared to theoretically derived diffusion coefficients employing these force fields in molecular dynamics simulations. The diffusion coefficients obtained using the three force fields for H₂, CO₂, CH₄, O₂ and N₂ agreed well with these experimental data. The zeolite-specific force field of Nicholas et al. was employed in grand canonical Monte Carlo simulations to obtain adsorption isotherms of these gases. The adsorption isotherms and isosteric heats of adsorption predicted were also in agreement with the expected range of available experimental and theoretical adsorption data reported in the literature.     

Modeling interfacial tension of (CH4+N2)+H2O and (N2+CO2)+H2O systems using linear gradient theory

The linear gradient theory (LGT) of fluid interfaces in combination with the cubic-plus-association equation of state (CPA EOS) is applied to determine the interfacial tensions of (CH₄+N₂)+H₂O and (N₂+CO₂)+H₂O ternary mixtures from 298–373 K and 10–300 bar. First, the pure component influence parameters of CH₄, N₂, CO₂ and H₂O are obtained. Then, temperature-dependent expressions of binary interaction coefficient for (CH₄+H₂O), (N₂+H₂O) and (CO₂+H₂O) are correlated. These empirical correlations of pure component influence parameters and binary interaction coefficients are applied for ternary mixtures. For (CH₄+N₂)+H₂O and (N₂+CO₂)+H₂O mixtures, the predictions show good agreement with experimental data (overall AAD～1.31%).     

Phosphonates Meet Metal−Organic Frameworks: Towards CO2 Adsorption

Here we report a new highly microporous zirconium phosphonate material synthesized under solvothemal conditions. The specific Brunauer-Emmett-Teller (BET) surface area of the “unconventional metal−organic framework” (UMOF) is measured to be ∼900 m²/g, after following an appropriate activation protocol. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) shows that the material bears a free −OH functionality on the phosphonate linker that may interact with CO₂. CO₂ adsorption isotherms were collected and a measured heat of adsorption of 31 kJ/mol was obtained. In addition, adsorption isotherms of CO₂, N₂, and CH₄ at 298 K combined with Ideal Adsorbed Solution Theory (IAST) show that the material can be expected to display high selectivities for uptake of CO₂ versus N₂ or CH₄.     

Adsorption prediction for three binary supercritical gas mixtures on activated carbon based on a NDFT/PSD approach

A non-local density functional theory (NDFT) in combination with the pore size distribution (PSD) analysis has been applied to make a comprehensively theoretical study for correlating and predicting the adsorption equilibria of pure supercritical gases and the corresponding binary supercritical gas mixtures on activated carbon. In this approach, the required PSDs were determined from an input of experimental adsorption data of pure components. By comparing with the experimental data of three different binary systems, CH₄/N₂, CH₄/CO₂, and CO₂/N₂, at high pressure up to 13.6 MPa and temperature 318.2 K with various concentration ranges, the predictive performance of the theoretical approach was evaluated. The adsorption of the mixtures has also been predicted by applying the ideal adsorbed solution (IAS) theory. It was shown that the NDFT/PSD method could be used to predict the mixture adsorption behaviors under high pressure. The developed method has greater superiority over the IAS theory in the prediction of the mixture adsorption.     

Separation of CO2/CH4 mixtures with the MIL-53(Al) metal–organic framework

Adsorptive separation of CH₄/CO₂ mixtures was studied using a fixed-bed packed with MIL-53(Al) MOF pellets. Such pellets of MIL-53(Al) were produced using a polyvinyl alcohol binder. As revealed by N₂ adsorption isotherms, the use of polyvinyl alcohol as binder results in a loss in overall capacity of 32%. Separations of binary mixtures in breakthrough experiments were successfully performed at pressures varying between 1 and 8 bar and different mixture compositions. The binary adsorption isotherms reveal a preferential adsorption of CO₂ compared to CH₄ over the whole pressure and concentration range. The separation selectivity was affected by total pressure; below 5 bar, a constant selectivity, with an average separation factor of about 7 was observed. Above 5 bar, the average separation factor decreases to about 4. The adsorption selectivity is affected by breathing of the framework and specific interaction of CO₂ with framework hydroxyl groups. CO₂ desorption can be realised by mild thermal treatment.     

Sorption studies of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, N<Subscript>2</Subscript>, CO,O<Subscript>2</Subscript> and Ar on nanoporous aluminum terephthalate [MIL-53(Al)]

Aluminum terephthalate, MIL-53(Al), metal–organic framework synthesized hydrothermally and purified by solvent extraction method was used as an adsorbent for gas adsorption studies. The synthesized MIL-53(Al) was characterized by powder X-Ray diffraction analysis, surface area measurement using N₂ adsorption–desorption at 77 K, FTIR spectroscopy and thermo gravimetric analysis. Adsorption isotherms of CO₂, CH₄, CO, N₂, O₂ and Ar were measured at 288 and 303 K. The absolute adsorption capacity was found in the order CO₂>CH₄>CO>N₂>Ar>O₂. Henry’s constants, heat of adsorption in the low pressure region and adsorption selectivities for the adsorbate gases were calculated from their adsorption isotherms. The high selectivity and low heat of adsorption for CO₂ suggests that MIL-53(Al) is a potential adsorbent material for the separation of CO₂ from gas mixtures. The high selectivity for CH₄ over O₂ and its low heat of adsorption suggests that MIL-53(Al) could also be a compatible adsorbent for the separation of methane from methane–oxygen gas mixtures.     

A high CO2 permselective mesoporous silica/carbon composite membrane for CO2 separation

Ordered mesoporous silica/carbon composite membranes with a high CO₂ permeability and selectivity were designed and prepared by incorporating SBA-15 or MCM-48 particles into polymeric precursors followed by heat treatment. The as-made composite membranes were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and N₂ adsorption, of which the gas separation performance in terms of gas permeability and selectivity were evaluated using the single gas (CO₂, N₂, CH₄) and gas mixtures (CO₂/N₂ and CO₂/CH₄, 50/50 mol.%). In comparison to the pure carbon membranes and microporous zeolite/C composite membranes, the as-made mesoporous silica/C composite membranes, and the MCM-48/C composite membrane in particular, exhibit an outstanding CO₂ gas permeability and selectivity for the separation of CO₂/CH₄ and CO₂/N₂ gas pairs owing to the smaller gas diffusive resistance through the membrane and additional gas permeation channels created by the incorporation of mesoporous silicas in carbon membrane matrix. The channel shape and dimension of mesoporous silicas are key parameters for governing the gas permeability of the as-made composite membranes. The gas separation mechanism and the functions of porous materials incorporated inside the composite membranes are addressed.     

Simulation of CO2/CH4 high pressure separation on microporous activated carbon

Abstract

Pure component adsorption equilibrium of CH₄ and CO₂ on activated carbon have been studied at three different temperatures, 298, 323, and 348?K within a pressure range of 10–2000?kPa. Binary adsorption equilibrium isotherm was described using extended Sips equation and ideal adsorbed solution theory (IAST) model. Experimental breakthrough curves of CO₂/CH₄ (40:60 in a molar basis) were performed at four different pressures (300, 600, 1200, and 1800?kPa). The experimental results of binary isotherms and breakthrough curves have been compared to the predicted simulation data in order to evaluate the best isotherm model for this scenario. The IAST and Sips models described significantly different results for each adsorbed component when higher pressures are set. These different results cause a significant discrepancy in the estimation of the equilibrium selectivity. Simulated and experimental equilibrium selectivity data provided by IAST presented values of around 4, for CO₂/CH₄, and extended Sips presented values of around 2. Also, simulated breakthrough curves showed that IAST fits better to the experimental data at higher pressures. According to the simulations, in a binary mixture at total pressure over 800?kPa, extended Sips model underestimated significantly the CO₂ adsorbed amount and overestimated the CH₄ adsorbed amount.     

Pure and Binary Adsorption Equilibria of Methane and Carbon Dioxide on Silicalite

Abstract

For the separation of CH₄ and CO₂ from landfill gas, pure and binary adsorption behavior of these gases were studied up to 5 atmosphere pressure at 40, 70, and 100°C for silicalite as the adsorbent. Pure and binary adsorption isotherms were determined experimentally and compared to predicted isotherms by several equilibrium models, as well as the other available data in the literature. Experimental binary isotherms at different concentrations were determined by using three concentration pulse methods (CPM). HT–CPM (Harlick‐Tezel CPM) was observed to be the best one to describe the behavior of this binary system. Equilibrium phase diagrams and separation factors were obtained from the experimental binary isotherms. For this system, the integral thermodynamic consistency tests were also shown and discussed.     

Effect of temperature on gas adsorption and separation in ZIF-8: A combined experimental and molecular simulation study

In this work, the effect of temperature on adsorption of CO₂, CH₄, CO, and N₂ and separation of their binary mixtures in ZIF-8 were investigated using experimental measurements combining with molecular simulations. The results show that for pure gas adsorption, the effect of temperature is large when strong adsorption occurs, mainly due to the variation of the interaction energy between adsorbate molecules with temperature; while for gas mixtures, systems with large selectivity are more sensitive to temperature. In addition, this work shows that temperature influences the working capacity of CO₂ in temperature swing adsorption (TSA) process with the interplay of pressure, which should be considered in the design of TSA process in practical applications.