Decorated Traditional Zeolites with Subunits of Metal–Organic Frameworks for CH4/N2 Separation

Metal–organic frameworks (MOF) materials are promising materials for gas separation, but their application still faces various challenges. A strategy is now reported for introducing subunits of MOFs into traditional zeolite frameworks to obtain applicable adsorbents with advantages of both zeolites and MOFs. The subunits of ZIFs were introduced into zeolite Y and zeolite ZSM‐5 for CH₄/N₂ separation. Both the molecular simulation and experimental results validated that the IAST CH₄/N₂ selectivity of the resulting samples greatly improved (above 8, at 100 kPa and 25 °C) with the incorporation of ZIF subunits into zeolites structure, and the selectivities were obviously higher than that of zeolites and even better than that of ZIFs. This strategy not only gave rise to an efficient adsorbent for CH₄/N₂ separation but also provided ideas for design of other adsorption and separation materials.     

Pure and binary adsorption isotherms of ethylene and ethane on zeolite 5A

Pure and binary adsorption equilibrium data of ethylene and ethane on zeolite 5A were collected with a volumetric method for the temperature range 283 K to 323 K and pressure up to 950 kPa. The applicability of the binary adsorption prediction by the vacancy solution theory (VST) was investigated. Further individual adsorption and selectivity were obtained by VST prediction. According to the experimental results, zeolite 5A has a high adsorption capacity and selectivity for ethylene in the ethylene/ethane system. VST predicts that ethylene selectivity increases with pressure; it also shows that the amount of ethylene separated by zeolite 5A increases as the temperature decreases at a specified pressure.     

CuCl改性Y型分子筛的CO吸附性能研究

利用自发单层分散原理,讨论了在NaY,NH4Y,CuY分子筛上CuCl分散改性情况,并对所得到的改性分子筛进行了CO吸附性能研究。实验结果表明,在低CuCl担载量时,CuCl可在这三种载体表面达到原子水平分散,其分散容量分别为0.58g/gNaY,0.68g/gNH4Y和0.41g/gCuY。由于CO与Cu^+可生配位化合物,经CuCl改性的Y型分子筛对CO显示出较高吸附性能。其中,0.6gCuCl/gNH4Y分子筛表现出最高的CO吸附容量,在室温、常压下可达123mL/gNH4Y.     

Host-Guest Interaction in Ethylene and Ethane Separation on Zeolitic Imidazolate Frameworks as Revealed by Solid-State NMR Spectroscopy

The separation of ethane/ethylene mixture by using metal-organic frameworks (MOFs) as adsorbents is strongly associated with the pore size-sieving effect and the adsorbent-adsorbate interaction. Herein, solid-state NMR spectroscopy is utilized to explore the host-guest interaction and ethane/ethylene separation mechanism on zeolitic imidazolate frameworks (ZIFs). Preferential access to the ZIF-8 and ZIF-8-90 frameworks by ethane compared to ethylene is directly visualized from two-dimensional ¹H-¹H spin diffusion MAS NMR spectroscopy and further verified by computational density distributions. The ¹H MAS NMR spectroscopy provides an alternative for straightforwardly extracting the adsorption selectivity of ethane/ethylene mixture at 1.1∼9.6 bar in ZIFs, which is consistent with the IAST predictions.     

Fixed bed adsorption of benzothiophene over zeolites with faujasite structure

This work addresses the adsorption of benzothiophene (BT), as a model heterocyclic and aromatic sulphur compound present in road fuels, over agglomerated zeolites with faujasite structure. Several adsorbents based on zeolites with FAU structure have been prepared with different Si/Al molar ratios and exchange cations and then agglomerated. The influence of the zeolite basicity has been studied, both in equilibrium and dynamic liquid phase adsorption experiments. Basicity of the adsorbent increased as the Si/Al molar ratio and the electronegativity of the exchange cation decreased. In equilibrium experiments, the affinity towards the adsorbent increased as the Si/Al molar ratio decreased, showing the highest affinity for exchanged low silica X zeolites with medium basicity (A-KLSX-02). Dynamic experiments showed that the less zeolite basicity, the higher fractional bed utilization and adsorption capacity at breakthrough time. Besides, zeolites with high basicity did not reach the equilibrium capacity due to the low diffusivity of BT into the micropores. Thermogravimetric analyses of the spent adsorbents showed a stronger BT adsorption onto the more basic zeolites. As main conclusion, adsorbents with medium basicity could present the best performance in fuel desulphurization due to their high affinity with sulphur compounds, although diffusion problems should be taken into account.     

Adsorption of ethane, ethylene, propane, and propylene on a magnesium-based metal-organic framework

Separation of olefin/paraffin is an energy-intensive and difficult separation process in petrochemical industry. Energy-efficient adsorption process is considered as a promising alternative to the traditional cryogenic distillation for separating olefin/paraffin mixtures. In this work, we explored the feasibility of adsorptive separation of olefin/paraffin mixtures using a magnesium-based metal-organic framework, Mg-MOF-74. Adsorption equilibria and kinetics of ethane, ethylene, propane, and propylene on a Mg-MOF-74 adsorbent were determined at 278, 298, and 318 K and pressures up to 100 kPa. A dual-site Sips model was used to correlate the adsorption equilibrium data, and a micropore diffusion model was applied to extract the diffusivities from the adsorption kinetics data. A grand canonical Monte Carlo simulation was conducted to calculate the adsorption isotherms and to elucidate the adsorption mechanisms. The simulation results showed that all four adsorbate molecules are preferentially adsorbed on the open metal sites where each metal site binds one adsorbate molecule. Propylene and propane have a stronger affinity to the Mg-MOF-74 adsorbent than ethane and ethylene because of their significant dipole moments. Adsorption equilibrium selectivity, combined equilibrium and kinetic selectivity, and adsorbent selection parameter for pressure swing adsorption processes were estimated. The relatively high values of adsorption selectivity suggest that it is feasible to separate ethylene/ethane, propylene/propane, and propylene/ethylene pairs in a vacuum swing adsorption process using Mg-MOF-74 as an adsorbent.     

Advanced adsorbents for the separation of the ortho- and para-hydrogen spin isomers at cryogenic temperatures

Improved adsorbent types and compositions have been developed for the challenging separation of the ortho- and para-hydrogen spin isomers at 77 K. From a systematic study of commercially available adsorbent types, it has been found that zeolites of type X offer the largest capacity and selectivity towards ortho-hydrogen and that performance is significantly impacted by the cation type and the number of cations present in the zeolite. For the present separation improved performance was obtained with larger Group I cations, especially K and Cs. Another key property of the adsorbents addressed in the present work is the need to control the adsorbent composition to avoid unwanted catalytic conversion of the para- to ortho-hydrogen. A common source of unwanted catalytic activity in many adsorbent compositions was identified as the presence of unwanted transition metal impurities, especially iron associated with the natural clays, commonly employed as binding agents in the commercial agglomerated zeolite products. To avoid this, equivalent adsorbent compositions were agglomerated instead using colloidal silica binding agents which successfully minimize back conversion of the para- to ortho-hydrogen and produced adsorbents with higher capacities and selectivities for the ortho component at the test temperature of 77 K. These advanced adsorbents can be applied in more efficient hydrogen liquefaction processes.     

Zeolites modified by CuCl for separating CO from gas mixtures containing CO2

Although zeolites such as NaY and 13X adsorb CO₂ much more than CO, the adsorption amount of CO₂ and CO can be reversed if the zeolites are modified with CuCl. When zeolite NaY or 13X is mixed with CuCl and heated, high CO adsorption selectivity and capacity can be obtained. Isotherms show the adsorbents have CO capacity much higher than CO₂. This is because CuCl has dispersed onto the surface of the zeolites to form a monolayer after the heat treatment and the monolayer dispersed CuCl can provide tremendous Cu(I) to selective adsorb CO and inhibit the CO₂ adsorption. The monolayer dispersion of CuCl is confirmed by XRD and EXAFS studies. The loading of CuCl on the zeolites has a threshold below which the CuCl forms monolayer after heating and crystalline phase of CuCl can not be detected by XRD. An adsorbent of CuCl/NaY with CuCl content closed to the monolayer capacity shows very high CO selective adsorbability for CO₂, N₂, H₂ and CH₄. At temperature higher than room temperature, the adsorbent has even better CO selectivity for CO₂. Using the adsorbent, a single-stage 4 beds PSA process, working at 70°C and 0.4 MPa to 0.013 MPa, can obtain CO product with purity >99.5% and yield >85%.     

Adsorption isotherms and ideal selectivities of hydrogen sulfide and carbon dioxide over methane for the Si-CHA zeolite: comparison of carbon dioxide and methane adsorption with the all-silica DD3R zeolite

Adsorption isotherms of H₂S, CO₂, and CH₄ on the Si-CHA zeolite were measured over pressure range of 0–190 kPa and temperatures of 298, 323, and 348 K. Acid gases adsorption isotherms on this type of zeolite are reported for the first time. The isotherms follow a typical Type-I shape according to the Brunauer classification. Both Langmuir and Toth isotherms describe well the adsorption isotherms of methane and acid gases over the experimental conditions tested. At room temperature and pressure of 100 kPa, the amount of CO₂ adsorption for Si-CHA zeolite is 29 % greater than that reported elsewhere (van den Bergh et al. J Mem Sci 316:35–45 (2008); Surf Sci Catal 170:1021–1027 (2007)) for the pure silica DD3R zeolite while the amounts of CH₄ adsorption are reasonably the same. Si-CHA zeolite showed high ideal selectivities for acid gases over methane at 100 kPa (6.15 for H₂S and 4.06 for CO₂ at 298 K). Furthermore, H₂S adsorption mechanism was found to be physical, and hence, Si-CHA can be utilized in pressure swing adsorption processes. Due to higher amount of carbon dioxide adsorbed and lower heats of adsorption as well as three dimensional channels of Si-CHA pore structure, this zeolite can remove acid gases from methane in a kinetic based process such as zeolite membrane.     

Thermal analyses of four adsorption materials for environmental pollution by DSC and TG

In view of loss prevention and hazard control, traditional engineers use adsorbents to adsorb volatile organic compounds (VOCs) in the semiconductor, photonics, and petrochemical industries. To save funds and promote green energy application, industries usually apply a zeolite processing desorption step under high temperature in the zeolite rotor-wheel system. Many thermal runaway accidents and flame incidents have occurred in the desorption step. Zeolite has been used to adsorb VOCs and applied in the processing desorption step in a reactor without considering oxygen concentration situation, which could easily lead to a flame followed by thermal explosion. Nitrogen is a critically important purge gas regarding passive action for avoiding an accident. Home-made zeolite was investigated for the best manufacturing ratio, which was 20. Brunauer–Emmett–Teller of zeolite (Si/Al = 20) was analyzed to be 400 m² g^?1, which is easy for adsorbing pollutants. According to our previous studies, home-made zeolite has prominent adsorption capacities on VOCs. Zeolite rotor-wheel system was developed to desorb the pollutants of interest. Zeolite was applied to analyze the thermal stability, runaway reaction under various oxygen concentrations, reuse rates, etc. Zeolite is a thermally stable material under room temperature to 650 °C. An endothermic reaction (30–100 °C) of home-made zeolite was analyzed by differential scanning calorimetry and thermogravimetric analyzer. Clearly, water has a significant effect on deteriorating for the zeolite adsorption. Home-made zeolite is a suitable adsorbent and catalyst in the petrochemical and environmental industries. As far as pollution control and loss prevention are concerned, versatility in the analysis of recycled adsorbents is required and is useful for various industrial applications.     

Adsorption and separation of carbon dioxide and methane in new zeolites using the Grand Canonical Monte Carlo method

The adsorption and separation behaviors of CO₂ and CH₄ in new siliceous zeolites (IFO, JSR, OKO, SEW) were simulated using the Grand Canonical Monte Carlo method in the paper. The adsorption isotherms for pure components and binary mixtures of CO₂ and CH₄ in four siliceous zeolites were obtained. The adsorption thermodynamic properties including Gibb’s free energy change, enthalpy change and entropy change were investigated. The results demonstrate that the adsorbed amount of pure components increases with an increase in pressure, and larger pore volume and surface area are beneficial to improve the adsorption capacity. The adsorption amount of CO₂ and CH₄ in the JSR zeolite is 7.08 and 2.27 mmol g^?1 at 1000 kPa, respectively. In view of the thermodynamic results, the new siliceous zeolites show a higher affinity for CO₂. The adsorption capacities of CO₂ in all zeolites were five times more than those of CH₄ in binary mixtures based on the ratios of equilibrium adsorption capacity. Considering the adsorption uptake and selectivity for CO₂/CH₄, the JSR zeolite is a good candidate for the separation of CO₂/CH₄ at low pressure.     

Factors affecting drug adsorption on beta zeolites

The adsorption behaviour of three commonly used drugs, namely ketoprofen, hydrochlorothiazide and atenolol, from diluted aqueous solutions on beta zeolites with different SiO₂/Al₂O₃ ratio (i.e. 25, 38 and 360) was investigated by changing the ionic strength and the pH, before and after thermal treatment of the adsorbents. The selective adsorption of drugs was confirmed by thermogravimetry and X‐ray diffraction. The adsorption capacity of beta zeolites was strongly dependent on both the solution pH and the alumina content of the adsorbent. Such a remarkable difference was interpreted as a function of the interactions between drug molecules and zeolite surface functional groups. Atenolol was readily adsorbed on the less hydrophobic zeolite, under pH conditions in which electrostatic interactions were predominant. On the other hand, ketoprofen adsorption was mainly driven by hydrophobic interactions. For undissociated molecules the adsorption capability increased with the increase of hydrophobicity.     

Adsorptive Separation of Acetylene from Light Hydrocarbons by Mesoporous Iron Trimesate MIL‐100(Fe)

A reducible metal–organic framework (MOF), iron(III) trimesate, denoted as MIL‐100(Fe), was investigated for the separation and purification of methane/ethane/ethylene/acetylene and an acetylene/CO₂ mixtures by using sorption isotherms, breakthrough experiments, ideal adsorbed solution theory (IAST) calculations, and IR spectroscopic analysis. The MIL‐100(Fe) showed high adsorption selectivity not only for acetylene and ethylene over methane and ethane, but also for acetylene over CO₂. The separation and purification of acetylene over ethylene was also possible for MIL‐100(Fe) activated at 423 K. According to the data obtained from operando IR spectroscopy, the unsaturated Fe^III sites and surface OH groups are mainly responsible for the successful separation of the acetylene/ethylene mixture, whereas the unsaturated Fe^II sites have a detrimental effect on both separation and purification. The potential of MIL‐100(Fe) for the separation of a mixture of C₂H₂/CO₂ was also examined by using the IAST calculations and transient breakthrough simulations. Comparing the IAST selectivity calculations of C₂H₂/CO₂ for four MOFs selected from the literature, the selectivity with MIL‐100(Fe) was higher than those of CuBTC, ZJU‐60a, and PCP‐33, but lower than that of HOF‐3.     

短链烷烃二元混合物在分子筛上吸附分离的分子模拟

用巨正则是系综Monte Carlo(GCMC)与构型偏倚(CBMC)相结合的方法模拟了 MFI分子筛对甲烷-丙烷、乙烷-丙烷体系(300K，345kPa)的吸附平衡，模拟结果与 文献实验结果相吻合，分别模拟了FER，ISV，MEL，MFI，MOR，TON等六种分子筛对 甲烷－丙烷、乙烷－丙烷体系（300K，345kPa）的吸附，得出甲烷－丙烷体系中分 子筛对较长链烷烃的选择性大小顺序（气相乙烷摩尔分数为0.5时）为ISV＞MEI＞ MEL＞FER＞TON＞MOR,对乙烷－丙烷体系选择性大小顺序（气相乙烷摩尔分数为0. 5时）为ISV＞MOR＞MFI＞FER＞MEL＞TON. MOR型分子筛对两个不同体系的吸附行为 表现出明显的不同，两个体中ISV的吸附量均最大，MFI，MEL，FER次之，此三种分 子筛具有相拟的吸附量，MOR和TON型分子筛吸附量较低。     

Effect on selective adsorption of ethane and ethylene of the polyoxometalates impregnation in the metal-organic framework MIL-101

Impregnation of ionic nanostructured units in the pores of metal-organic frameworks (MOFs) is one approach to modify their host–guest interactions. Although, the effect of this approach is well investigated in catalysis, drug delivery, and bio imaging, still little is known about its impact on the selective adsorption properties of MOFs. Here we report the impregnation of two different polyoxometalate (POM) nanoclusters (PW₁₁ and SiW₁₁) into chromium terephthalate-based MOF, MIL-101(Cr), to investigate the post-impregnation changes in selective adsorption behavior, which are observed in terms of an important paraffin–olefin separation, using ethane and ethylene, at high pressure. The PW₁₁ and SiW₁₁ POMs bring π-accepting tendency and highly electronegative oxygen atoms on their surface to MIL-101 structure that selectively increases the affinity of material for ethylene, which is confirmed from isosteric heats of adsorption and selectivity calculation. Impregnated samples retain about 74–81 % of working adsorption capacity, after regeneration by decreasing the pressure. This study shows that anionic metal-oxide nanoclusters (POMs) may be used to change the selectivity of MOFs for olefin molecules.     

Separation of CO2-CH4 mixtures in the mesoporous MIL-100(Cr) MOF: experimental and modelling approaches

Carbon dioxide is the main undesirable compound present in raw natural gas and biogas. Physisorption based adsorption processes such as pressure swing adsorption (PSA) are one of the solutions to selectively adsorb CO(2) from CH(4). Some hybrid crystalline porous materials that belong to the family of metal-organic frameworks (MOFs) show larger CO(2) adsorption capacity compared to the usual industrial adsorbents, such as zeolites and most activated carbons, which makes them potentially promising for such applications. However, their selectivity values have been most often determined using only single gas adsorption measurements combined with simple macroscopic thermodynamic models or by means of molecular simulations based on generic forcefields. The transfer of this systematic approach to all MOFs, whatever their complex physico-chemical features, needs to be considered with caution. In contrast, direct co-adsorption measurements collected on these new materials are still scarce. The aim of this study is to perform a complete analysis of the CO(2)-CH(4) co-adsorption in the mesoporous MIL-100(Cr) MOF (MIL stands for Materials from Institut Lavoisier) by means of a synergic combination of outstanding experimental and modelling tools. This solid has been chosen both for its fundamental interests, given its very large CO(2) adsorption capacities and its complexity with a combination of micropores and mesopores and the existence of unsaturated accessible metal sites. The predictions obtained by means of Grand Canonical Monte Carlo simulations based on generic forcefields as well as macroscopic thermodynamic (IAST, RAST) models will be compared to direct the co-adsorption experimental data (breakthrough curve and volumetric measurements).     

Alkali metal cation doping of metal-organic framework for enhancing carbon dioxide adsorption capacity

Metal-organic frameworks （MOFs） have attracted much attention as adsorbents for the separation of CO2 from flue gas or natural gas. Here, a typical metal-organic framework HKUST-I（also named Cu-BTC or MOF-199） was chemically reduced by doping it with alkali metals （Li, Na and K） and they were further used to investigate their CO2 adsorption capacities. The structural information, surface chemistry and thermal behavior of the prepared adsorbent samples were characterized by X-ray powder diffraction （XRD）, thermo-gravimetric analysis （TGA） and nitrogen adsorption-desorption isotherm analysis. The results showed that the CO2 storage capacity of HKUST-1 doped with moderate quantities of Li＋, Na＋ and K＋, individually, was greater than that of unmodified HKUST-1. The highest CO2 adsorption uptake of 8.64 mmol/g was obtained with 1K-HKUST-1, and it was ca. 11% increase in adsorption capacity at 298 K and 18 bar as compared with HKUST- 1. Moreover, adsorption tests showed that HKUST-1 and 1K-HKUST-1 displayed much higher adsorption capacities of CO2 than those of N2. Finally, the adsorption/desorption cycle experiment revealed that the adsorption performance of 1K-HKUST-1 was fairly stable, without obvious deterioration in the adsorption capacity of CO2 after 10 cycles.     

Amine-functionalized mesoporous ZSM-5 zeolite adsorbents for carbon dioxide capture

ZSM-5 type zeolite with mesoporous structure was prepared and then amine-functionalized with tetraethylenepentamine (TEPA) by wet impregnation method to form a series of CO₂ adsorbents (ZTx). The structural properties of ZSM-5 and ZTx were characterized by XRD, FTIR, TGA/DTG, nitrogen adsorption/desorption, SEM and EDX techniques. The adsorption capacity of the adsorbents with different amine loading was measured at a temperature from 40 to 100 °C and the adsorption capacity of ZT7 was 1.80 mmol/g at 100 °C. The adsorption process and mechanism were studied by fitting the experimental data used the three adsorption kinetic models, and a complex physical and chemical mixing process was produced as the amine entered the surface and pore size of the zeolite. The high adsorption selectivity at 10% CO₂ concentration and the stability of the five adsorption desorption cycles indicated that ZT7 is a suitable and promising CO₂ adsorbent for the purification of industrial flue gas.     

Dimensional stability of adsorbents subjected to thermal cycling

The dimensional stability of adsorbent beads subjected to varying temperature conditions must be understood to assess the effect of thermal cycling on both the adsorbent and the structure that contains it. Most of the literature on the coefficient of thermal expansion (CTE) of adsorbents relates to zeolite crystals or clusters of crystals with application to membranes. Such crystals or powder materials have been shown to exhibit both positive and negative volume expansion coefficients depending upon the temperature range. This duality in the CTE with increasing temperature and the large variation in the CTE magnitude for a given zeolite structure suggest that the dimensional stability of zeolite crystals under varying thermal conditions is not likely a good indicator of the thermal stability of agglomerated zeolites. In this study, a method has been developed and applied to measure the CTE of activated alumina and 13X molecular sieve adsorbent beads. A McBain gravimetric microbalance was modified in a simple manner to be used as a dilatometer. The method was validated by measuring the CTE of a 316 stainless steel rod and showing that the measured CTE of this study agreed with the published CTE within 3.3 %. Average CTEs for alumina and 13X adsorbents were determined as 4.88 × 10^?6 and 2.96 × 10^?6 mm/mm/ °C, respectively for the range of temperature 20–400 °C.     

Alkali metal cation doping of metal-organic framework for enhancing carbon dioxide adsorption capacity

Metal-organic frameworks (MOFs) have attracted much attention as adsorbents for the separation of CO₂ from flue gas or natural gas. Here, a typical metal-organic framework HKUST-1(also named Cu-BTC or MOF-199) was chemically reduced by doping it with alkali metals (Li, Na and K) and they were further used to investigate their CO₂ adsorption capacities. The structural information, surface chemistry and thermal behavior of the prepared adsorbent samples were characterized by X-ray powder diffraction (XRD), thermo-gravimetric analysis (TGA) and nitrogen adsorption-desorption isotherm analysis. The results showed that the CO₂ storage capacity of HKUST-1 doped with moderate quantities of Li⁺, Na⁺ and K⁺, individually, was greater than that of unmodified HKUST-1. The highest CO₂ adsorption uptake of 8.64 mmol/g was obtained with 1K-HKUST-1, and it was ca. 11% increase in adsorption capacity at 298 K and 18 bar as compared with HKUST-1. Moreover, adsorption tests showed that HKUST-1 and 1K-HKUST-1 displayed much higher adsorption capacities of CO₂ than those of N₂. Finally, the adsorption/desorption cycle experiment revealed that the adsorption performance of 1K-HKUST-1 was fairly stable, without obvious deterioration in the adsorption capacity of CO₂ after 10 cycles.