Facile CO2 Separation in Composite Membranes

CO₂ emission from anthropogenic sources has raised worldwide environmental concerns and hence proficient energy paradigm has tilted towards CO₂ capture. Membrane technology is one of the efficient technologies for CO₂ separation since it is environmentally friendly, inexpensive, and offers high surface areas. Various approaches are discussed to improve membrane performance focusing mainly on permeability and selectivity parameters. Different types of fillers are incorporated to reach the Robeson's upper bound curve. In this review, polymer‐inorganic nanocomposite membranes for the separation of CO₂, CH₄, and N₂ from various gas mixtures are comprehensively discussed. Metal organic frameworks (MOFs) and ionic liquid (ILs) mixed‐matrix membranes are also considered.     

二氧化硅膜的制备及分离CH4/CO2气体的研究

以正硅酸乙酯为前驱体,通过溶胶-凝胶法,采用多分离层镀膜工艺制备了用于分离CH4/CO2气体二氧化硅无机膜。通过TG-DSC、粒度分析仪及SEM对二氧化硅膜进行表征,结果表明分别利用HNO3、EtOH及DMF作为催化剂、助溶剂及添加剂可制备出表面性能较好的二氧化硅膜;利用多分离层镀膜工艺制备的二氧化硅膜,在0.025MPa下,对CH4/CO2气体的分离因子高达1.73,其效果明显高于利用单一溶胶涂膜的分离因子1.6,有效的提高了二氧化硅膜对气体的分离能力。     

Polyurethane-SAPO-34 mixed matrix membrane for CO2/CH4 and CO2/N2 separation

SAPO-34 nanocrystals (inorganic filler) were incorporated in polyurethane membranes and the permeation properties of CO₂, CH_4, and N₂ gases were explored. In this regard, the synthesized PU-SAPO-34 mixed matrix membranes (MMMs) were characterized via SEM, AFM, TGA, XRD and FTIR analyses. Gas permeation properties of PU-SAPO-34 MMMs with SAPO-34 contents of 5 wt%, 10 wt% and 20 wt% were investigated. The permeation results revealed that the presence of 20 wt% SAPO-34 resulted in 4.45%, 18.24% and 40.2% reductions in permeability of CO_2, CH_4, and N₂, respectively, as compared to the permeability of neat polyurethane membrane. Also, the findings showed that at the pressure of 1.2 MPa, the incorporation of 20 wt% SAPO-34 into the polyurethane membranes enhanced the selectivity of CO₂/CH₄ and CO₂/N₂, 14.43 and 37.46%, respectively. In this research, PU containing 20 wt% SAPO-34 showed the best separation performance. For the first time, polynomial regression (PR) as a simple yet accurate tool yielded a mathematical equation for the prediction of permeabilities with high accuracy (R² > 99%).     

Enhancing the CO2 Separation Performance of Matrimid 5218 Membranes for CO2/CH4 Binary Mixtures

The effect of CO₂‐philic additive polyethylene glycol (PEG) 200 in Matrimid 5218 on the separation performance of prepared membranes was evaluated in a binary gas mixture. Matrimid/PEG 200 flat‐sheet blended membranes with low PEG concentrations were prepared by the dense film‐casting method. Pure Matrimid and blended membranes were characterized by FTIR spectroscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and permeation measurements. The addition of 4–5 % of PEG enhanced considerably the CO₂ permeability of the Matrimid matrix. The best formulation, Matrimid/PEG 200 (96/4), showed in comparison to pure Matrimid a more than threefold increase in CO₂ permeability and an increase in separation factor of about 40 %.     

Influence of Particle Size on the Performance of Polysulfone Magnetic Membranes for O2/N2 Separation

Magnetic mixed-matrix membranes (MMMs) are fabricated using polysulfone (PSf) and iron oxide (Fe) for O₂/N₂ separation. The effects of Fe nanoparticle size and content on the performance of the membranes are investigated using a novel gas permeation unit in the presence of various magnetic fields. The results indicate that the O₂ permeation is improved by adding Fe nanoparticles into the PSf matrix regardless of the particle size. Furthermore, the selectivity of PSf and PSf-Fe membranes is considerably enhanced by applying a magnetic field during the permeation experiments. The O₂ permeability and O₂/N₂ selectivity of PSf-Fe50 MMMs in the presence of a magnetic field are higher than those of neat PSf membranes.     

Current Status and Future Prospect of Polymer‐Layered Silicate Mixed‐Matrix Membranes for CO2/CH4 Separation

The mixed‐matrix membrane (MMM), a state‐of‐the‐art polymer‐inorganic hybrid, is a relatively recent addition to the membrane family which adopts the synergistic advantages of the polymer and inorganic phase. Although marked improvement has been achieved by MMMs in CO₂/CH₄ separation, the development of a defect‐free structure to transcend the Robeson upper bound limit remains a challenge. In previous years, a number of inorganic materials with diverse nature have been studied for CO₂/CH₄ separation; however, layered silicates have not attracted much attention despite their superior thermal and mechanical properties. Analyses of the potential of using layered silicates as inorganic fillers in MMM fabrication for CO₂/CH₄ separation are reviewed. Additionally, the immediate challenges toward successful formation of layered silicate‐based MMM and future prospects are addressed.     

PBI/Clinoptilolite mixed-matrix membranes for binary (N2/CH4) and ternary (CO2/N2/CH4) mixed gas separation

In this work, polybenzimidazole (PBI)-based mixed matrix membranes (MMMs) with natural zeolite were prepared and their transport properties for binary (N₂/CH₄) and ternary (CO₂/N₂/CH₄) mixed-gas separation were studied. The MMMs, were prepared with PBI as polymeric matrix and Mexican natural zeolite clinoptilolite enriched with cations of Ca²⁺ as filler. The thermal properties analysis of the PBI and MMMs studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicates that the MMMs membranes have Tg higher than 350°C and decomposition temperatures above 600°C compared with the pristine membranes. PBI membrane and MMMs were analyzed by X-Ray Diffraction (XRD) and the diffraction patterns showed the zeolite signals combine with the amorphous dome from the polymeric matrix. In addition, the perm-selectivity properties of the polymeric membranes and MMMs were tested with binary (N₂/CH₄; 10/90 mol%) and ternary (CO₂/N₂/CH₄; 5/10/85 mol%) gas mixtures at different pressure rates (50, 150 and 300 psi). The perm-selectivity properties of the MMMs membranes show an improvement in their values about 30% higher compared to the PBI polymeric membranes, favoring the permeation of CO₂ and N₂.     

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     

Atmospheric CO2/CH4 permeability of EVA copolymer/SiO2 composite membrane for biogas purification

The CO₂ and CH₄ permeabilities of poly(ethylene-co-vinyl acetate) (EVA)/SiO₂ composite membrane were investigated at atmospheric pressure. The membranes were fabricated by compression molding and characterized by Fourier transformed infrared spectroscopy, differential scanning calorimetry, a universal testing machine, and a contact angle analyzer. The effect of vinyl acetate content (18–33 wt%) was evaluated for both single-gas and mixed-gas permeation systems. A non-pressurized homemade-permeation cell was used for the single-gas permeation of CO₂ and CH₄, while a tubular membrane was utilized for a continuous separation of CO₂/CH₄ mixture. CO₂ flux was readily increased (from 0.7 to 2.0 ml/m².s) with vinyl acetate content (18–33 wt%). The enhanced CO₂ permeability is attributed to the increase in polarity and also the decrease in crystallinity of the membrane. A satisfied gas separation selectivity (CO₂/CH₄) of 4.31 could be obtained from tubular membrane with 28 wt% VA content. The incorporation of SiO₂ as a filler (0.5–2.0 wt%) especially increased the membrane polarity and hence the CO₂ flux up to 6.0 ml/m².s. However, the CH₄ flux was not affected by VA and SiO₂ contents.     

Synthesis of dual-functionalized mixed matrix membrane with amino-GO-Bent/PVDF for efficient separation of CO2/CH4 and CO2/N2

Mixed matrix membranes (MMMs), which combine the characteristics of inorganic nanofillers and organic matrices, have received wide attention because of their good permeability and selective performance for separating CO₂ from industrial waste gases. In this work, the amino-GO-loaded bentonite (amino GO-Bent) was prepared by loading  NH₂ on the GO surface with a large number of functional sites. Firstly, by introducing  NH₂ on the surface of GO and then interacting with bentonite (Bent) organically modified by silane coupling agents through amide bonding. Mixed matrix membranes (MMMs) with an area of 623.7 cm² and homogeneous texture were prepared using amino-GO-Bent as inorganic filler to improve the membrane selectivity for CO₂/N₂ and CO₂/CH₄ separation. The results show that the introduction of amino GO-Bent in MMMs can greatly improve the CO₂ permeability and obtain high CO₂ permeation performance: 2.67945 × 10⁻⁷ cm³ (STP)·cm/s/cm²/cmHg, and the selectivity of CO₂/N₂ and CO₂/CH₄ can reach 307.28 and 325.97, respectively. The two selective values were 14 and 18 times higher than those of pure PVDF membranes, and the performance of MMMs far exceeded the Robeson upper limit in 2008, respectively.     

Recent Developments and Applications of Ionic Liquids in Gas Separation Membranes

Flue gas emissions and the harmful effects of these gases urge to separate and capture these unwanted gases. Ionic liquids due to negligible vapor pressure, thermal stability, and wide electrochemical stability have expanded its application in gas separations. A comprehensive overview of the recent developments and applications of ionic liquid membranes (ILMs) for gas separation is given. The three general classifications of ILMs, such as supported ionic liquid membranes (SILMs), ionic liquid polymeric membranes (ILPMs), and ionic liquid mixed‐matrix membranes (ILMMMs) along with their applications, for the separation of various mixed gases systems is discussed in detail. Furthermore, issues, challenges, computational study, and future perspectives for ILMs are also considered.     

Recent Applications of Polymer Blends in Gas Separation Membranes

Polymeric membranes are extensively used for gas separations but their performance is limited by the upper bound trade‐off discovered by Robeson in 1991. Among the attractive modifications available to increase the performance of polymeric membranes, polymer blending is a unique technique because it offers a time‐ and cost‐effective method of tuning the properties of membranes. A variety of polymer blends has been explored in recent years. The application of polymer blends in gas separation membranes is described by critically analyzing the performance of polymer blend membranes. Polymer blend membranes of different polymer pairs are reviewed and evaluated in terms of phase behavior, permeability, and selectivity.     

Selective Removal of Carbon Dioxide from Wet CO2/H2 Mixtures via Facilitated Transport Membranes containing Amine Blends as Carriers

The selective separation of carbon dioxide (CO₂) from a wet gaseous mixture of CO₂/H₂ through facilitated transport membranes containing immobilized aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), ethylenediamine (EDA) and monoprotonated ethylenediamine (EDAH⁺) and their blends was experimentally investigated. The effect of CO₂ partial pressure, amine concentration, feed side pressure and amine species on the CO₂ and H₂ permeances were studied. The CO₂ permeability through amine solution membranes decreased with increasing CO₂ feed partial pressure but the H₂ permeance was almost independent of the H₂ partial pressure. A comparison of experimental results showed that single or blended amines with low viscosity and a moderate equilibrium constant, i.e., large forward and reverse reaction rate of CO₂‐amine, are suitable for effective separation of CO₂. The permeability of CO₂ generally increased with an increase in amine concentration, although this increase may be compromised by the salting out effect and decrease in diffusivities of species. The results obtained indicated that CO₂ permeance across a variety of amines are in the order of DEA (2 M) > MD (2 M) > MD (1 M) > MEA (2 M) > MEA (4 M) > MD (4 M) > DEA (1 M) > DEA (4 M) > MEA (1 M) for various concentrations of MEA + DEA blend and are in the order of EDAH⁺ (2 M) > DEA (2 M) > MH (2 M) > DH (2 M) > ED (2 M) > EDA (2 M) > MEA (2 M) for various blends of amine.     

Ceramic Supported PDMS and PEGDA Composite Membranes for CO2 Separation

Composite membranes have attracted increasing attentions owing to their potential applications for CO2 separation. In this work, ceramic supported polydimethylsiloxane （PDMS） and poly （ethylene glycol） diacrylate （PEGDA） composite membranes were prepared. The microstructure and physicochemical properties of the compos- ite membranes were characterized. Preparation conditions were systematically optimized. The gas separation performance of the as-prepared membranes was studied by pure gas and binary gas permeation measurement of CO〉 N2 and H〉 Experiments showed that PDMS, as silicone rubber, exhibited larger permeance and lower separation factors. Conversely, PEGDA composite membrane presented smaller gas permeance but higher ideal selectivity for CO2/N2. Compared to the performance of those membranes using polymeric supports or freestanding membranes, the two kinds of ceramic supported composite membranes exhibited higher gas permeance and acceptable selectivity. Therefore, the ceramic supported composite membrane can be expected as a candidate for CO2 separation from light gases.     

一维直孔道MOFs对CH4/N2和CO2/CH4的分离

非常规天然气未来可以作为常规天然气的有效补充,其中低浓度煤层气和生物质燃气分别需要脱除大量的N₂ 和CO₂以达到富集和纯化CH₄的目的。本研究针对CH₄/N₂这一对较难分离的气体组合,选取了具有一维菱形孔道的MOFs材料Cu(INA)₂作为吸附剂,将合成的样品做了XRD和TG表征,测试了纯气体CO₂、CH₄和N₂的吸附曲线,利用巨正则系综蒙特卡罗(GCMC)分子模拟和理想吸附溶液理论(IAST)计算了气体的吸附热和该材料对于CH₄/N₂和CO₂/CH₄的吸附选择性系数;3 MPa压力下制备的颗粒样品填装吸附分离装置,进行了混合气体CH₄/N₂ (50%/50%)和CO₂/CH₄ (50%/50%)的穿透试验,分离的结果显示,Cu(INA)₂不仅高选择性地吸附CH₄/N₂混合物中的CH₄(S_CH4/N2=10),而且对CH₄/N₂的分离效果优于CO₂/CH₄。     

Single and Binary CO2/CH4 Separation of a Zeolitic Imidazolate Framework‐8 Membrane

The performance of a zeolitic imidazolate framework‐8 (ZIF‐8) membrane in single and binary CO₂/CH₄ gas separation was investigated by means of a gas transport model that included generalized Maxwell‐Stefan and binary friction models. The model concerns gas diffusion through the membrane layer, gas flow through membrane intercrystalline pores, and resistance of the support layer. The effective membrane area considering the actual area for the gas permeated through the membrane was also introduced in this model. The selective ZIF‐8 membrane was successfully synthesized using a microwave‐assisted solvothermal method on an α‐alumina support pre‐attached with ZIF‐8 seeds by solvent evaporation. The simulated data agreed well with the experimental data. The model revealed that the membrane intercrystalline pores and its effective area significantly affected the CO₂/CH₄ gas permeation and separation performance.     

Polysulfone/zinc oxide nanoparticle mixed matrix membranes for CO2/CH4 separation

Preparation and characterization of novel polysulfone/zinc oxide (PSf/ZnO) mixed matrix membranes (MMMs) with different ZnO loadings for high selective CO₂/CH₄ separation were aimed in this study. Scanning electron microscopy photographs demonstrated that spongy and small tear like pores in plain PSf membrane (0 wt % of ZnO) replaced with large tear like pores close to surface layer by increasing ZnO content up to 0.1 and 1 wt %. In contrast, a dense and less free volume structure was obtained in membranes having 3 and 5 wt % of ZnO. Membrane porosity increased from 28.68 to 50.51% with increasing ZnO content from 0 to 1 wt %. Then, a reduction in porosity was observed for membranes containing 3 and 5 wt % of ZnO. Atomic force microscopy images presented variation in membrane surface roughness. Surface roughness decreased from 67.64 nm for plain PSf to 47.86 nm for membrane containing 1 wt % of ZnO. While, surface roughness increased and reached to 115.5 and 122.4 nm for MMMs having 3 and 5 wt % of ZnO. Gas separation properties of PSf/ZnO MMMs were examined and CO₂/CH₄ selectivity of MMMs containing 3 and 5 wt % of ZnO were 22.29 and 54.29, respectively, in 1 bar feed pressure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39745.     

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     

Separation of CO2/N2 Gas Mixture through Carbon Membranes: Monte Carlo Simulation

Abstract

Monte Carlo simulation method is employed to investigate separation behavior of gas mixture composed of carbon dioxide and nitrogen through a model carbon membrane under the different conditions. The simulation gives insight into the separation mechanism to a certain extent, which is based on the loading and diffusion of carbon dioxide and nitrogen in the carbon membrane with different pore size. The simulation results indicate that the carbon dioxide can be adsorbed on the surface of membrane wall more strongly, whereas the diffusion rate of nitrogen is more prominent. When the separation condition alters, the influence of the two main factors mentioned above on transport of gas molecules in membranes becomes different. Therefore, the equilibrium selectivity of nitrogen and carbon dioxide changes correspondingly.