A thin-film (700 nm) DDR zeolite disc membrane was evaluated for separating a 1/1 CO2/CH4 mixture in a wide temperature range (−35 to 180 °C). The highest selectivity of 2325 paired with a high CO2 permeance of 34 × 10−7 mol/(m2·s·Pa) was observed at −30 °C and a feed pressure of 3 bar. At the same feed pressure, the highest CO2 permanence was recorded at + 10 °C reaching 44 × 10−7 mol/(m2·s·Pa), while selectivity remained remarkably high at 1118. High permeance and selectivity were also observed at higher feed pressures. These results surpass all previously published data on CO2/CH4 separation using DDR zeolite membranes and indicate that the membranes have strong potential for upgrading natural gas and biogas. A model describing mass transfer while considering adsorption, surface barrier, and surface diffusion was fitted to experimental single gas permeation data and showed that it can accurately describe the mass transfer in the zeolite pores while indicating that the limiting step was the surface barrier. These findings highlight the potential of DDR membranes for industrial gas purification across a broad range of temperatures and feed pressures.

The adsorption equilibrium isotherms of the common components of natural gas and biogas, CO2, CH4, N2, and He were experimentally measured over wide temperature ranges on all-silica MFI, CHA, and DDR zeolite crystals. First, large zeolite crystals, suitable for adsorption measurements, were synthesized and characterized by XRD and SEM. In the next step, gas adsorption data was recorded and the Toth equation was fitted to the measured adsorption data, and the adsorption capacity at saturation (Csat), affinity constant (b), and Toth heterogeneity parameter (t) were estimated. Finally, the van't Hoff equation was used to calculate the isosteric enthalpy of adsorption and adsorption entropy for all gases on each zeolite. The results reveal that the Toth equation can accurately predict the adsorption of gases on the studied microporous zeolite crystals in the investigated temperature range. To the best of our knowledge, the saturation adsorption capacity and adsorption enthalpy for helium on CHA and DDR zeolites have been determined experimentally for the first time in the present work. The estimated adsorption parameters presented in this work are accurate, primarily due to the large crystals used for the adsorption measurements and the recording of low-temperature adsorption equilibrium isotherms over broad temperature ranges. These factors are crucial for the reliability of our results, which are invaluable for understanding adsorption and mass transfer in zeolite materials, as well as for advancing the development of zeolite materials for gas separation.

Adsorption of carbon dioxide and other gases on a novel acetate functionalized silica adsorbent under various conditions is investigated experimentally and theoretically by grand-canonical Monte Carlo (GCMC) simulations. The acetate functional group has the capability to interact with the carbon atoms in CO2 molecules due to the electron-donating properties of the carbonyl and ether groups. However, the acetate functional group has not yet been examined for CO2 adsorption on silica. Adsorption of CO2, CH4, N2, and H2 was measured experimentally in the temperature range of 253–373 K and pressure range of 0–100 kPa. CO2 showed significantly higher adsorption compared to other gases with maximum adsorption of ca. 32 cc/gr at standard condition (STP) at a pressure of 100 kPa and a temperature of 253 K. The recorded adsorption data could be fitted by Freundlich isotherms, indicating heterogeneous adsorption sites. To better understand the heterogeneous adsorption sites, GCMC simulations were used to examine the effects of pore size, temperature, pressure, concentration of functional groups in the silica matrix, and competitive adsorption. The GCMC data was in good agreement with the experimental data and suggested the oxygen-containing moieties (i.e., carbonyl and ether groups) on the acetate group as the adsorption sites. These sites displayed high Lewis acid-base interaction with the CO2 molecules. The GCMC data indicated selective adsorption of CO2 over N2 and a CO2/N2 binary gas mixture selectivity of 20 for a 10/90 CO2/N2 feed. To the best of our knowledge, this is the first report on the experimental adsorption of CO2 over acetate functionalized silica adsorbent coupled with an investigation of the adsorption sites through GCMC simulations.

We explore the separation of H2 from CH4 using ultrathin DDR membranes across various temperatures and feed pressures. Using a membrane that featured a zeolite film around 700 nm thick, we measured an H2 permeance of 7.2 × 10–7 mol/(m2·s·Pa), equivalent to 2.2 × 103 GPU, for a 1/1 H2/CH4 gas mixture at 3 bar(a) under ambient temperature. This permeance exceeds previously reported values for DDR membranes by more than 10-fold and is comparable to the permeance reported for the best palladium membranes. Under the same conditions, H2/CH4 separation selectivity reached 207, well above values earlier reported for DDR membranes. These membranes also demonstrate outstanding performance under high pressures and temperatures of up to 180 °C, and high feed pressure is needed for achieving high H2/CH4 selectivities at elevated temperatures. Interestingly, the experimental data fit a mass-transfer model that incorporates surface diffusion and surface barriers, indicating that the selective surface barrier governs the overall selective transport; meanwhile, the important parameters related to the mass transfer of H2 and CH4 in DDR zeolite are explored.

The low water flux and high production cost of ceramic membranes for vacuum membrane distillation (VMD) are among the factors limiting their feasibility for desalination applications. To address this challenge, highly permeable anodic alumina membranes were modified and evaluated for their properties in VMD using a highly permeable support. Owing to the nanostructures on its surface, the anodic alumina membrane displayed superhydrophobic characteristics with water contact angles and liquid entry pressure values higher than 150° and 4 bar, respectively. A superior water flux of 316 kg/(m2·h) was observed in VMD along with NaCl rejection above 99% for a 3 wt.% NaCl feed at 80 °C. The high flux is attributed to the highly permeable support and the short vapor transport path of the thin and open pores structure of the anodic alumina material, being cylindrical with a thickness of 55 μm. For benchmark comparison, a commercial polytetrafluoroethylene (PTFE) and conventional asymmetric α-alumina membranes were also evaluated under similar conditions. In addition, variation of the support porosity allowed for validation of the effective transport area of the membranes. Considering the inexpensive synthesis method of the anodic alumina material, this study provides important perspectives on the development of novel membrane materials, paving the way for overcoming the challenges associated with desalination using VMD.

Aromatic hydrocarbons are important components of jet fuels mainly due to their effects on lowering the freeze point, enhancing the lubricity, and preventing the fuel leakage in the engines and fueling systems by interacting with their polymer seals. Produced from fossil resources, jet fuel consumption contributes to rising atmospheric CO2 levels. Therefore, efficient utilization of renewable resources, such as biomass, to produce jet fuel components is an important step toward building a sustainable society. Hence, structure-modified zeolite catalysts that determine a high selective production of aromatic HCs in the range of jet fuel chemicals from biomass via catalytic pyrolysis were synthesized and engineered in a PyroGC-MS/FID system. The structure-modified catalysts of hierarchical HBeta (HRCHY HBeta) and defect-free nano-sized crystals ZSM-5 (ZSM-5-F) were used to selectively deoxygenate the reactive species in biomass pyrolysis vapors leading to a high production of renewable jet fuels (bio jet fuels; BJFs). The morphology of zeolites were designed for an enhanced diffusion of biomass pyrolysis vapors and upgraded products, in and out of the catalyst, to selectively produce monoaromatic HCs. A comprehensive comparison of the experimental and theoretical results obtained from biomass pyrolysis using the commercial catalyst of HBeta and the structure-modified catalysts of hierarchical HBeta and defect-free ZSM-5 was accomplished in in-situ and ex-situ catalytic configurations. Meanwhile, the catalytic performance of the ZSM-5-F catalyst in the conversion of a biomass pyrolysis oil model into jet fuel chemicals was investigated using a fixed bed catalytic reactor.

Ethylene/ethane separation is a critical and energy-consuming process in the chemical industry due to the similar properties of the compounds and the great need of ethylene for e.g., polymer production. Many materials have been studied for their implementation as membranes as an energetically favorable alternative to conventional distillation and adsorption processes. Metal-organic frameworks (MOF) have revealed promising properties as highly permeable and selective membranes. Among the most studied and promising MOF candidates is ZIF-8, known for its thermal stability and small pores connected by narrow-sized windows. In this work, we present an analysis of the influence of parameters such as temperature, feed pressure and feed flowrate on the separation of ethylene/ethane through a thin ZIF-8/alumina disc membrane. We observed that the temperature has a significant effect on the separation. The ethylene permeance increased with decreased temperature and reached 8.1 × 10−7 mol/(m2·s·Pa) at −30 °C. At this temperature, the ethylene/ethane selectivity was 2.5. The study concluded with a considerable enhancement of the permeance of ZIF-8 membranes for ethylene/ethane separations, while maintaining a good selectivity compared to the reported values in the literature. The results have important implications for the development of more cost-effective and energy-efficient membrane-based separation technologies for ethylene purification.

Silanol-free ZSM-5 nanosheet with merely 35 nm thickness in the b-axis was synthesized by seeded growth from defect-free 10 nm silicalite-1 in a fluoride medium (denoted as F35). Submicron-scaled stöber sol silica beads were introduced into the gap between nanosheets to serve as a spacer for the prevention of neighboring crystals' close contact with each other, which can improve the heat and mass transportation during the catalytic reactions when compared to the aggregated zeolite crystals. Methanol-to-hydrocarbons (MTH) and model bio-oil upgrading were conducted by using dispersed F35, respectively, and the results were compared to the aggregated ZSM-5. The effluent from bio-oil upgrading through dispersed F35 contains no heavier compound, which was considered as the coke precursor, and significantly reduced amount of unreacted feeding molecule. GC–MS revealed that the coke solution from dispersed F35 contains a considerably reduced (61 %) amount of heavier carbon species. Among them, some species have molecular configurations highly consistent with the zeolite channel structure. The dispersed F35 shows a 33 % longer life in catalytic reactions and a 60 % decreased amount of external thermal cock. An unconventional ‘temperature-determined flexible channel’ mechanism that explains the ‘host–guest’ interactive behavior under catalytic reaction was proposed.

In this study, DDR membranes with a layer thickness of approximately 700 nm were studied for separation feeds comprising mixtures of CO2 and CH4. The membranes displayed the highest CO2 over CH4 permselectivity and CO2 permeability reported in literature. This was ascribed to a defect-free and ultra-thin zeolite film as well as an open and highly permeable support. For equimolar mixtures, the highest CO2 over CH4 permselectivity of 727 was observed when the pressure at the feed side was 5 bar(a) and the permeate pressure was 1 bar(a) at 25 °C. At these conditions, the CO2 permeability was very high at 45 × 10−7 mol/(m2 s Pa). Separation experiments for 80/20 and 20/80 mixtures were also performed, and in these cases, CO2 over CH4 permselectivities of 1011 and 622 were observed, respectively. For all feeds, the membrane permselectivity decreased slightly at higher temperature and in all cases, higher permselectivity was observed when vacuum was applied at the permeate side. One-stage membrane processes for upgrading biogas to biomethane at three different operating pressures were designed based on the experimental data. In all cases, a quite low membrane area, methane slip and power need were observed.

Large (100 cm² membrane area) tubular chabazite (CHA) zeolite membranes (450 nm thick) were experimentally evaluated for the separation of CO₂/CH₄ in an industrial laboratory. An industrially relevant feed flow rate of 250 Ndm³/min was used. The feed pressure and temperature were varied in the ranges of 5–18 bar and 292–318 K, respectively. For a CO₂/CH₄ feed with a molar ratio of 1:1, the experimental CO₂/CH₄ selectivity was high at 205, and the CO₂ permeance arrived at 52 × 10^–7 mol/(m²·s·Pa) at 5 bar and 292 K. As far as we know, there is no report in the literature on large CHA membranes with such high permeability and selectivity. A high CO₂/CH₄ selectivity was also observed for a 1:4 CO₂/CH₄ feed. However, as indicated by mathematical modeling, concentration polarization was still an issue for membrane performance, especially at high operating pressures, even though the flow rate of the feed was relatively high. Without concentration polarization, the theoretical CO₂/CH₄ selectivity was 41% higher than the experimental value for a 1:1 CO₂/CH₄ feed at 18 bar. The corresponding CO₂ permeance without concentration polarization was 23% higher than the experimentally observed value, reaching 34 × 10^–7 mol/(m²·s·Pa). CHA membrane processes for the removal of CO₂ from CH₄ were designed, and the electricity consumption and module cost of the process were also estimated. All of the results in this study indicate a great potential of the large CHA membranes for biogas and natural gas upgrading; however, concentration polarization should be minimized in industrial processes.