Biogas upgrading with novel cellulose nano-crystals and polyvinyl amine nanocomposite membranes

A novel crystalline nano cellulose (CNC) and polyvinyl amine (PVAm) based nanocomposite membranes were synthesized and evaluated for biogas upgrading. Different concentrations of CNC was incorporated in 3 wt % PVAm solution on commercial polysulfone (PSf) sheet using dip coating method. The effect of feed pressure (5, 10 and 15 bar) was investigated for the CO₂/CH₄ separation. The incorporation of CNC increased the crystallinity of membranes. The thickness of selective layer enhanced to 2.16 μm from 1.5 μm with increasing concentration of CNC. However, degree of swelling reduced from 75.88% to 68.93 with CNC concentration at 1.5 wt%. The best results were shown by PVAm membrane with 1 wt % CNC concentration i.e. CO₂ permeance of 0.0216 m³(STP)/m².bar.hr and selectivity (CO₂/CH₄) of 41.The permeance decreased approximately 1.8 folds for PVAm/1CNC membrane with the increase in pressure from 5 to 15 bar. However, selectivity dropped from 41 to 39 for formulated membranes.     

Facilitated transport of CO2 in novel PVAm/PVA blend membrane

A defect-free ultra thin PVAm/PVA blend facilitated transport membrane cast on a porous polysulfone (PSf) support was developed and evaluated in this study. The target membrane was prepared from commercial polyvinyl amine (PVAm) and polyvinyl alcohol (PVA). Effects of experimental conditions were investigated for a CO₂–N₂ mixed gas. A CO₂/N₂ separation factor of up to 174 and a CO₂ permeance up to 0.58 m³(STP)/(m² h bar) were documented. Experimental results suggest that CO₂ is being transported according to the facilitated transport mechanism through this membrane. The fixed amino groups in the PVAm matrix function as CO₂ carriers to facilitate the transport whereas the PVA adds mechanical strength to the blend by entanglement of the polymeric chains hence creating a supporting network. The good mechanical properties obtained from the blend of PVA with PVAm, enabled an ultra thin selective layer (down to 0.3 μm) to be formed on PSf support (with MWCO of 50,000), resulted in both high selectivity and permeance. The PVAm/PVA blend membrane also exhibited a good stability during a 400 h test.     

Composite hollow fiber membranes for CO2 capture

Composite hollow fibers membranes were prepared by coating poly(phenylene oxide) (PPO) and polysulfone (PSf) hollow fibers with high molecular polyvinylamine (PVAm). Two procedures of coating hollow fibers outside and respective inside were investigated with respect to intrinsic PVAm solution properties and hollow fibers geometry and material.The influence of operating mode (sweep or vacuum) on the performances of membranes was investigated. Vacuum operating mode gave better results than using sweep because part of the sweep gas permeated into feed and induced an extra resistance to the most permeable gas the CO₂. The composite PVAm/PSf HF membranes having a 0.7–1.5 μm PVAm selective layer, showed CO₂/N₂ selectivity between 100 and 230. The selectivity was attributed to the CO₂ facilitated transport imposed by PVAm selective layer. The CO₂ permeance changed from 0.006 to 0.022 m³(STP)/(m² bar h) in direct correlation with CO₂ permeance and separation mechanism of the individual porous supports used for membrane fabrication. The multilayer PVAm/PPO membrane using as support PPO hollow fibers with a 40 nm PPO dense skin layer, surprisingly presented an increase in selectivity with the increase in CO₂ partial pressure. This trend was opposite to the facilitated transport characteristic behaviour of PVAm/porous PSf. This indicated that PVAm/PPO membrane represents a new membrane, with new properties and a hybrid mechanism, extremely stable at high pressure ratios. The CO₂/N₂ selectivity ranged between 20 and 500 and the CO₂ permeance from 0.11 to 2.3 m³(STP)/(m² bar h) depending on the operating conditions.For both PVAm/PSf and PVAm/PPO membranes, the CO₂ permeance was similar with the CO₂ permeance of uncoated hollow fiber supports, confirming that the CO₂ diffusion rate limiting step resides in the properties of the relatively thick support, not at the level of 1.2 μm thin and water swollen PVAm selective layer. A dynamic transfer of the CO₂ diffusion rate limiting step between PVAm top layer and PPO support was observed by changing the feed relative humidity (RH%). The CO₂ diffusion rate was controlled by the PPO support when using humid feed. At low feed humidity the 1.2 μm PVAm top layer becomes the CO₂ diffusion rate limiting step.     

A Uniformly Oriented MFI Membrane for Improved CO2 Separation

Membrane separation of CO₂ from natural gas, biogas, synthesis gas, and flu gas is a simple and energy‐efficient alternative to other separation techniques. But results for CO₂‐selective permeance have always been achieved by randomly oriented and thick zeolite membranes. Thin, oriented membranes have great potential to realize high‐flux and high‐selectivity separation of mixtures at low energy cost. We now report a facile method for preparing silica MFI membranes in fluoride media on a graded alumina support. In the resulting membrane straight channels are uniformly vertically aligned and the membrane has a thickness of 0.5 μm. The membrane showed a separation selectivity of 109 for CO₂/H₂ mixtures and a CO₂ permeance of 51×10^?7 mol m^?2 s^?1 Pa^?1 at ?35 °C, making it promising for practical CO₂ separation from mixtures.     

A Highly Permeable Aligned Montmorillonite Mixed‐Matrix Membrane for CO2 Separation

Highly permeable montmorillonite layers bonded and aligned with the chain stretching orientation of polyvinylamineacid are immobilized onto a porous polysulfone substrate to fabricate aligned montmorillonite/polysulfone mixed‐matrix membranes for CO₂ separation. High‐speed gas‐transport channels are formed by the aligned interlayer gaps of the modified montmorillonite, through which CO₂ transport primarily occurs. High CO₂ permeance of about 800 GPU is achieved combined with a high mixed‐gas selectivity for CO₂ that is stable over a period of 600 h and independent of the water content in the feed.     

Pebax/TSIL blend thin film composite membranes for CO_2 separation

In this study a thin film composite (TFC) membrane with a Pebax/Task-specific ionic liquid (TSIL) blend selective layer was prepared. Defect-free Pebax/TSIL layers were coated successfully on a polysulfone ultrafiltration porous support with a polydimethylsiloxane (PDMS) gutter layer. Different parameters in the membrane preparation (e.g. concentration, coating time) were investigated and optimized. The morphology of the membranes was studied by scanning electron microscopy (SEM), while the thermal properties and chemical structures of the membrane materials were investigated by thermo-gravimetric analyzer (TGA), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The CO₂ separation performance of the membrane was evaluated using a mixed gas permeation test. Experimental results show that the incorporation of TSIL into the Pebax matrix can significantly increase both CO₂ permeance and CO₂/N₂ selectivity. With the presence of water vapor, the membrane exhibits the best CO₂/N₂ selectivity at a relative humidity of around 75%, where a CO₂ permeance of around 500 GPU and a CO₂/N₂ selectivity of 46 were documented. A further increase in the relative humidity resulted in higher CO₂ permeance but decreased CO₂/N₂ selectivity. Experiments also show that CO₂ permeance decreases with a CO₂ partial pressure increase, which is considered a characteristic in facilitated transport membranes.     

Preparation of CO_2 selective composite membranes using Pebax/CuBTC/PEG-ran-PPG ternary system

Three phase Pebax~? MH 1657/PEG-ran-PPG/CuBTC(polymer/liquid/solid) was successfully deposited as a selective layer on a porous Polysulfone(PSF) support. In fact, the beneficial properties of PEG(high selectivity) with those of PPG(high permeability, amorphous) have been combined with superior properties of mixed matrix membrane(MMMs). The membranes were characterized by DSC, TGA and SEM, while CuBTC was characterized by CO_2 and CH_4adsorption test. Statistically based experimental design(central composite design, CCD) was applied to analyze and optimize the effect of PEG-ran-PPG(10–50 wt%) and CuBTC(0–20 wt%) mass contents on the CO_2 permeance and CO_2/CH_4 ideal selectivity. Based on the regression coefficients of the obtained models, the CO_2 permeance was notably influenced by PEG-ran-PPG,while CuBTC has the most significant effect on the CO_2/CH_4 ideal selectivity. Under the optimum conditions(PEG-ran-PPG: 32.76 wt% and CuBTC: 20 wt%), nearly 620% increase in the CO_2 permeance and43% enhancement in the CO_2/CH_4 ideal selectivity was observed compared to the neat Pebax. The effect of pressure(3, 9 and 15 bar) on the pure and mixed gas separation performance of the composite membranes was also investigated. The high solubility of CO_2 in the membranes resulted in the enhancement of CO_2 permeability with increase in gas pressure.     

Porphyrin‐based covalent triazine frameworks: Porosity,adsorption performance,and drug delivery

Two porous porphyrin‐based covalent triazine frameworks (PCTFs), in which porphyrin is incorporated as building block, have been synthesized by the Friedel–Crafts reaction. The copolymer PCTFs show large Brunauer–Emmett–Teller specific surface area of up to 1089 m² g^?1, high CO₂ uptake capacity reaching 139.9 mg g^?1 at 273 K/1.0 bar, and good selectivity for CO₂/CH₄ adsorption attaining 6.1 at 273 K/1.0 bar. The resulting porous solids also can be used as matrices for drug delivery of ibuprofen in vitro. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2594–2600     

Covalent and electrostatic incorporation of amines into hypercrosslinked polymers for increased CO2 selectivity

Two methods of incorporating functional groups rich in nitrogen into low cost microporous hypercrosslinked polymers (HCPs) have been evaluated and the effects on the carbon dioxide CO₂/N₂ IAST selectivity were measured. Electrostatic incorporation of an ammonium salt into a sulfonic acid-containing HCP polymer afforded a static CO₂ uptake of 2.5 mmol g⁻¹ with a CO₂/N₂ IAST selectivity of 42:1 at 1 bar and 298 K. Using column breakthrough measurements with a 15:85 CO₂/N₂ mixture at 298 K and 1 bar, a selectivity of 17:1 was obtained. However, varying the counterion resulted in polymers with lower CO₂/N₂ selectivity values. Decoration of the parent polymer with CO₂-philic imidazole followed by electrostatic ammonium salt incorporation blocked some of the micropores reducing the selectivity which re-emphasizes the role and importance of pore width for CO₂/N₂ selectivity. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2513–2521     

Xenon Recovery by DD3R Zeolite Membranes: Application in Anaesthetics

Xe is only produced by cryogenic distillation of air, and its availability is limited by the extremely low abundance. Therefore, Xe recovery after usage is the only way to guarantee sufficient supply and broad application. Herein we demonstrate DD3R zeolite as a benchmark membrane material for CO₂/Xe separation. The CO₂ permeance after an optimized membrane synthesis is one order magnitude higher than for conventional membranes and is less susceptible to water vapour. The overall membrane performance is dominated by diffusivity selectivity of CO₂ over Xe in DD3R zeolite membranes, whereby rigidity of the zeolite structure plays a key role. For relevant anaesthetic composition (<5 % CO₂) and condition (humid), CO₂ permeance and CO₂/Xe selectivity stabilized at 2.0×10^?8 mol m^?2 s^?1 Pa^?1 and 67, respectively, during long‐term operation (>320 h). This endows DD3R zeolite membranes great potential for on‐stream CO₂ removal from the Xe‐based closed‐circuit anesthesia system. The large cost reduction of up to 4 orders of magnitude by membrane Xe‐recycling (>99+%) allows the use of the precious Xe as anaesthetics gas a viable general option in surgery.     

Continuous Porous Aromatic Framework Membranes with Modifiable Sites for Optimized Gas Separation

Continuous microporous membranes are widely studied for gas separation, due to their low energy premium and strong molecular specificity. Porous aromatic frameworks (PAFs) with their exceptional stability and structural flexibility are suited to a wide range of separations. Main-stream PAF-based membranes are usually prepared with polymeric matrices, but their discrete entities and boundary defects weaken their selectivity and permeability. The synthesis of continuous PAF membranes is still a major challenge because PAFs are insoluble. Herein, we successfully synthesized a continuous PAF membrane for gas separation. Both pore size and chemistry of the PAF membrane were modified by ion-exchange, resulting in good selectivity and permeance for the gas mixtures H₂/N₂ and CO₂/N₂. The membrane with Br^? as a counter ion in the framework exhibited a H₂/N₂ selectivity of 72.7 with a H₂ permeance of 51844 gas permeation units (GPU). When the counter ions were replaced by BF₄^?, the membrane showed a CO₂ permeance of 23058 GPU, and an optimized CO₂/N₂ selectivity of 60.0. Our results show that continuous PAF membranes with modifiable pores are promising for various gas separation situations.     

Separation of carbon dioxide from nitrogen using ion-exchanged faujasite-type zeolite membranes formed on porous support tubes

Faujasite-type zeolite membranes were reproducibly synthesized by hydrothermal reaction on the outer surface of a porous α-alumina support tube of 30 or 200 mm in length. The membrane properties were evaluated by CO₂ separation from an equimolar mixture of CO₂ and N₂ at a permeation temperature of 40°C. CO₂ permeance and CO₂/N₂ selectivity of the NaY-type membranes were in the ranges of 0.4×10⁻⁶–2.5×10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ and 20–50, respectively. The NaY-type membranes were ion-exchanged with alkali and alkaline earth cations. The LiY-type membrane showed the highest N₂ permeance and the lowest CO₂/N₂ selectivity. The KY-type membrane gave the highest CO₂/N₂ selectivity. The NaY-type membrane was stable against exposure to air at 400°C. NaX-type zeolite membranes, formed by decreasing the ratio of SiO₂/Al₂O₃ in the starting solution, exhibited lower CO₂ permeances and higher CO₂/N₂ selectivities than those of the NaY-type zeolite membranes.     

Syntheses and permselectivity properties of polysulfones based on bisphenol A and 1, 1 bi‐2 naphthol

Polysulfone copolymers based on mixtures of bisphenol A, BPA, and 1,1 bi‐2 naphthol, BN, diols have been synthesized and their gas permeability coefficients and selectivity separation factors for O₂/N₂ and CO₂/CH₄, at 5 atm and 35 °C, have been measured in a standard permeation cell. The polysulfone copolymers can form flexible thin films suitable for gas separation membranes. The gas selectivity for O₂/N₂ measured for the polysulfone copolymers synthesized with 50 and 70 mol % of BN, with the rest being BPA, in the initial mixture of diols are 6.4 and 6.8, respectively. The corresponding gas permeability coefficients for O₂ are 1.24 and 1.09 Barrers. Compared to the corresponding selectivity and permeability balance reported for polysulfones based on pure BPA, BPA–PSF, the copolymers show a balance that moves in the direction of higher selectivity with small losses in the permeability of the fastest gas. From the glass transition temperature determinations, it is observed that the incorporation of BN in the repeating unit of BPA–PSF inhibits large‐scale segmental motions that are reflected in reductions in the diffusivity coefficients for all gases. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 226–231, 2004     

Crosslinking of gelatin membranes with ferulic acid or glutaraldehyde: Relationship between gas permeability and renaturation level of gelatin triple helices

This study investigated the gas separation membranes made with gelatin, crosslinked with ferulic acid (FA) and blended with polyethylene glycol (PEG) 200, by using a solvent‐free procedure. Gas permeation properties (He, N₂, O₂, and CO₂) of these “green membranes” were studied and discussed in relation with their structure. Differential scanning calorimetric measurements were carried out to determine the gelatin triple helical renaturation level. The lowest permeability values [He and CO₂ permeability (4.5 × 10^?2 Barrer) with CO₂/O₂ selectivity of 14.5] were reached with gelatin/PEG 200 uncrosslinked membranes showing the highest renaturation level (40%). Crosslinking with FA lead to less rigid and brittle materials than GTA and to 10 times more permeable membranes compared with uncrosslinked membranes. Membranes crosslinked with glutaraldehyde broke during gas permeation measurements. Results demonstrated that higher gas permeability values were closely related to lower renaturation level of gelatin. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 280–287     

Synthesis and behaviour of hybrid polymer-silica membranes made by sol gel process with adsorbed carbonic anhydrase enzyme,in the capture of CO<Subscript>2</Subscript>

Thin nylon-SiO₂ membranes made by sol–gel SiO₂ coating of a nylon weaving were impregnated in a second step with an aqueous carbonic anhydrase solution. The biocatalytic hybrid membranes obtained were applied to the capture of CO₂ from a N₂–CO₂ gas mixture containing 10% CO₂, under a total pressure ≈ 1 atm. The CO₂ permeance of these membranes was at least similar to those previously reported for liquid membranes. When impregnated with a 0.2 mg mL⁻¹ enzyme solution in a pH ≈ 8 NaHCO₃ buffer, the permeance of a nylon-SiO₂ membrane was multiplied by a factor ≈ 3 when the buffer molarity was increased from 0.1 to 1 M. By comparison, this permeance only increased by a factor ≈ 1.3 without any enzyme in the same buffers. The permeance was also higher with the enzyme than without it: respectively ≈3.7 10⁻⁸ and ≈4.7 10⁻⁹ mol \textm_{\textmembrane} ^{- 2} {\text{m}}_{\text{membrane}}^{{^{ - 2} }} s⁻¹ Pa⁻¹ with and without enzyme, in a 1 M NaHCO₃ buffer. A maximum permeance was observed for an enzyme concentration of ≈0.2 mg mL⁻¹, possibly due to a competition between the H⁺ ions produced from CO_2,aq by the enzyme and the H⁺ captured by the buffer. Besides, when the SiO₂–CO₂ contact was enhanced by the membrane architecture, SiO₂ improved the CO₂ permeance. The influence of an in situ CaCO₃ deposit was also investigated and it improved the CO₂ permeance when no enzyme was added.     

Preparation and characterization of a novel water soluble amino chitosan (amino-CS) derivative for facilitated transport of CO<Subscript>2</Subscript>

With the goal of obtaining a water soluble polymeric carrier for preparation of fixed facilitated transport membranes, a water soluble amino containing chitosan derivative was prepared through Michael-addition reaction between chitosan and ethyl acrylate followed by amidation of the ester groups with an appropriate diamine. This derivative was characterized using ¹H-NMR spectroscopy. Then, facilitated transport membranes were prepared by casting a thin layer of chitosan derivative/poly(vinyl alcohol) blend on a porous polysolfune support; and the effect of fixed carrier’s content, feed temperature and feed pressure on the CO₂ permeance, and CO₂/CH₄ selectivity of produced membranes were studied. A facilitated transport mechanism for CO₂ through this membrane was concluded.     

Preparation and characterization of (Pebax 1657 + silica nanoparticle)/PVC mixed matrix composite membrane for CO<Subscript>2</Subscript>/N<Subscript>2</Subscript> separation

In this work, the films of poly(ether-block-amide) (Pebax 1657) and hydrophilic/hydrophobic silica nanoparticles (0–10 wt%) were coated on a poly(vinyl chloride) (PVC) ultrafiltration membrane to form new mixed matrix composite membranes (MMCMs) for CO₂/N₂ separation. The membranes were characterized by SEM, FTIR, DSC and XRD. Successful formation of a non-porous defect-free dense top layer with ~4 μm of thickness and also uniform dispersion of silica nanoparticles up to 8 wt% loading in Pebax matrix were confirmed by SEM images. The gas permeation results showed an increase in the permeance of all gases and an increase in ideal CO₂/N₂ selectivity with the increase in silica nanoparticle contents. Comparison between the incorporation of hydrophilic and hydrophobic silica nanoparticle into Pebax matrix revealed that the great enhancement of CO₂ solubility is the key factor for the performance improvement of Pebax + silica nanoparticle membranes. The best separation performance of the hydrophilic silica nanoparticle-incorporated Pebax/PVC membrane for pure gases (at 1 bar and 25 °C) was obtained with a CO₂ permeability of 124 barrer and an ideal CO₂/N₂ selectivity of 76, i.e., 63 and 35% higher than those of neat Pebax membrane, respectively. The corresponding values for hydrophobic silica nanoparticle-incorporated Pebax/PVC membrane were 107 barrer for CO₂ permeability and 61 for ideal CO₂/N₂ selectivity. Also the performances of MMCMs improved upon pressure increase (1–10 bar) owing to the shift in plasticizing effect of CO₂ towards the higher pressures. In addition, an increase in permeabilities with a decrease in ideal selectivity was observed upon temperature increase (25–50 °C) due to the intensification of chain mobility.     

Polyacrylamide hydrogel membranes with controlled pore sizes

We developed a method to characterize polymer‐supported polyacrylamide crosslinked hydrogel networks using a range of well‐defined poly(N, N‐dimethylacrylamide)‐coated gold nanoparticles with diameters ranging from 3 to 48 nm under ultrafiltration conditions of 16 bar. The membranes resulted in permeabilities ranging between 0.199 and 6.343 × 10^?18 m². There was a direct correlation between the size exclusion and the permeability rate coefficient, k_m; the higher the k_m value the larger the average pore size. Our results further demonstrate that the gold nanoparticles could be trapped within the membrane at the end of a cul‐de‐sacs found within the gel network, which often leads to membrane fouling. We believe that this method of using gold nanoparticles to characterize crosslinked membranes provides insight into the gel network, and will provide a unique tool to analyze new membranes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Formation of Ultrathin,Continuous Metal–Organic Framework Membranes on Flexible Polymer Substrates

Metal–organic framework (MOF) materials have an enormous potential in separation applications, but to realize their potential as semipermeable membranes they need to be assembled into thin continuous macroscopic films for fabrication into devices. By using a facile immersion technique, we prepared ultrathin, continuous zeolitic imidazolate framework (ZIF‐8) membranes on titania‐functionalized porous polymeric supports. The coherent ZIF‐8 layer was surprisingly flexible and adhered well to the support, and the composite membrane could sustain bending and elongation. The membranes exhibited molecular sieving behavior, close to the theoretical permeability of ZIF‐8, with hydrogen permeance up to 201×10^?7 mol m^?2 s^?1 Pa^?1 and an ideal H₂/CO₂ selectivity of 7:1. This approach offers significant opportunities to exploit the unique properties of MOFs in the fabrication of separation and sensing devices.     

Formation of Ultrathin,Continuous Metal–Organic Framework Membranes on Flexible Polymer Substrates

Metal–organic framework (MOF) materials have an enormous potential in separation applications, but to realize their potential as semipermeable membranes they need to be assembled into thin continuous macroscopic films for fabrication into devices. By using a facile immersion technique, we prepared ultrathin, continuous zeolitic imidazolate framework (ZIF‐8) membranes on titania‐functionalized porous polymeric supports. The coherent ZIF‐8 layer was surprisingly flexible and adhered well to the support, and the composite membrane could sustain bending and elongation. The membranes exhibited molecular sieving behavior, close to the theoretical permeability of ZIF‐8, with hydrogen permeance up to 201×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ and an ideal H₂/CO₂ selectivity of 7:1. This approach offers significant opportunities to exploit the unique properties of MOFs in the fabrication of separation and sensing devices.