Separation of CO2 and N2 on Zeolite Silicalate-1 Membrane Synthesized on Novel Support

This paper reports on the properties of an MFI-type zeolite (silicalite-1) membrane synthesized on a novel tubular support with a 0.45 µm-pore size active layer consisting of zirconium and titanium oxides. Even though the membrane was synthesized by a pore plugging method, apart from penetrating into the support, the silicalite-1 crystals formed a 1.5 µm layer on top of the support. After the zeolite synthesis, the Si constituted more than 35% of the active layer of the support, which implies small size and close packing of the silicalite-1 crystals in the pores of the active layer.

Single gas permeation tests with N₂ and CO₂ revealed comparable N₂ and CO₂ permeances. On the other hand, CO₂/N₂ gas separation tests performed at different total feed pressures and feed compositions lead to CO₂/N₂ permselectivities as high as 26.0, with the corresponding CO₂ permeance of 6 × 10^?8 mol/m² Pa s. The effects of changing the partial pressure gradient of CO₂ across the membrane by means of varying the total feed pressure and the feed composition on the CO₂ permeance and CO₂/N₂ permselectivity are discussed.     

Microwave synthesis of tubular zeolitic imidazolate framework ZIF-8 membranes for CO2/CH4 separation

The separation of CO₂/CH₄ is reported in detail by using zeolitic imidazolate framework (ZIF-8) membrane which was prepared on 3-aminopropyltriethoxysilane modified Al₂O₃ tube through microwave heating synthesis. Attributed to the preferential adsorption affinity of CO₂ over CH₄ and a narrow pore window of 0.34 nm, the ZIF-8 membrane shows high separation performances for the separation of CO₂/CH₄ mixtures. For the separation of equimolar CO₂/CH₄ mixture at 100°C and 2 bar feed (1 bar permeate) pressure, a CO₂ permeance of 1.02 × 10^?8 mol/m²· s· Pa and a CO₂/CH₄ selectivity of 6.8 are obtained, which is promising for CO₂ separation.     

Effect of dodeca‐tungstophosphric acid on morphology and performance of polyvinyl alcohol membrane for gas separation

In this article, organic/inorganic membrane was prepared for gas separation by incorporating dodeca‐tungstophosphric acid (PWA) into the base polymer. Flat‐sheet composite membranes were produced via dry‐phase inversion method. In the first stage, the effects of PWA concentration on morphology and performance of polyvinyl alcohol (PVA) membranes were elucidated. For this stage, the preparation of membranes was carried out at constant temperature of 40°C. The porosity of the prepared membrane was slightly increased with addition of PWA. By increasing the PWA concentration up to 6 wt % in the membrane recipe, the permeability of N₂, O and air was improved from 50,000 (for no addition of PWA) to around 160,000, 140,000, and 80,000 L m^?2 h^?1, respectively. For H this was enhanced from 110,000 to 230,000 L m^?2 h^?1. The ideal selectivity of the membrane was slightly improved for N₂/air (from 1 to 1.2). For N₂/O₂ pair, the initial drop (from 2.5 to 1.5) was followed by a slight increase (1.5–1.9). Moreover, the selectivity was decreased for H₂/air (from 2.8 to 1.8) and H₂/N₂ (from 2.2 to 1.7) by increasing the PWA concentration. The 10 wt % PVA membrane with 6 wt % PWA demonstrated superior performance compared with the other compositions. In summary, the presence of PWA in the casting solution results in lower flux for O₂ and higher selectivity for H₂/O₂ pair. In the second stage, the effects of solvent evaporation temperature (10, 27, 40, and 80°C) on morphology and performance of the membranes were studied. By increasing the temperature, the number and size of voids were increased. The permeation of gases was improved from 100,000 L m^?2 h^?1 (at 10°C) to 150,000 (O₂), 250,000 (air), 380,000 (N₂), and 600,000 L m^?2 h^?1 (H₂) by increasing the temperature up to 80°C. This increment resulted in selectivity alteration either increment or diminishment. The selectivity was changed from 1.3 to 3.2 (H₂/O₂), 0.8–2.5 (N₂/O₂), 1.2–2.4 (H₂/air), 0.6–1.5 (N₂/air) and 2.0–1.5 (H₂/N₂). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Theoretical and experimental study on the emission characteristics of waste plastics incineration by modified O2/RFG combustion technology

For mitigating the emission of greenhouse gas CO₂ from general air combustion systems, a clean combustion technology O₂/RFG is in development. The O₂/RFG combustion technology can significantly enhance the CO₂ concentration in the flue gas; however, using almost pure oxygen or pure CO₂ as feed gas is uneconomic and impractical. As a result, this study proposes a modified O₂/RFG combustion technology in which the minimum pure oxygen is mixed with the recycled flue gas and air to serve as the feed gas. The effects of different feed gas compositions and ratios of recycled flue gas on the emission characteristics of CO₂, CO and NO_x during the plastics incineration are investigated by theoretical and experimental approaches.Theoretical calculations were carried out by a thermodynamic equilibrium program and the results indicated that the emissions of CO₂ were increased with the O₂ concentrations in the feed gas and the ratios of recycled flue gas increased. Experimental results did not have the same trends with theoretical calculations. The best feed gas composition of the modified O₂/RFG combustion was 40% O₂ + 60% N₂ and the best ratio of recycled flue gas was 15%. As the O₂ concentration in feed gas and the ratio of recycled flue gas increased, the total flow rates and pressures of feed gas reduced. The mixing of solid waste and feed gas was incomplete and the formation of CO₂ decreased. Moreover, the emission of CO was decreased as the O₂ concentration in feed gas and the ratio of recycled flue gas increased. The emission of NO_x gradually increased with rising the ratio of recycled flue gas at lower O₂ concentration (<40%) but decreased at higher O₂ concentration (>60%).     

CO2 recovery from flue gas by PSA process using activated carbon

An experimental study was performed for the recovery of CO₂ from flue gas of the electric power plant by pressure swing adsorption process. Activated carbon was used as an adsorbent. The equilibrium adsorption isotherms of pure component and breakthrough curves of their mixture (CO₂ : N₂ : O₂=17 : 79 : 4 vol%) were measured. Pressure equalization step and product purge step were added to basic 4-step PSA for the recovery of strong adsorbates. Through investigation of the effects of each step and total feed rate, highly concentrated CO₂ could be obtained by increasing the adsorption time, product purge time, and evacuation time simultaneously with full pressure-equalization. Based on the basic results, the 3-bed, 8-step PSA cycle with the pressure equalization and product purge step was organized. Maximum product purity of CO₂ was 99.8% and recovery was 34%.     

Improving membrane performance for nitrogen production from air

Using a portion of the product N₂ to purge the permeate side of a membrane module in order to reduce the membrane area for the separation of air for nitrogen production is considered. A simulation program was developed and used to compare a purge system to a conventional non-purge permeator. Both the selectivity of the membrane and the feed/permeate pressure ratio were found to affect the ability of the purge stream to reduce the membrane area. The purge stream reduces the recovery of nitrogen, which results in a minimum in the membrane area per unit of product flow.     

Effects of Synthesis Temperature and Support Material on CO2 and CH4 Permeation through SAPO-34 Membranes

In this research, continuous SAPO-34 membranes were synthesized via secondary growth method onto both α-Al₂O₃ and mullite supports at three levels of synthesis temperature: 185, 195, and 220°C for 24 h. The synthesized membranes were characterized using XRD and SEM analysis and single gas permeation experiments. It was found out that support material and synthesis temperature both have significant effects on the membrane performance. At higher synthesis temperature, SAPO-34 crystals grown over the mullite support become more uniform and smaller in size but those grown on the α-Al₂O₃ support become larger. Effect of synthesis temperature on single gas permeation properties of the synthesized SAPO-34 membranes was also studied. For the mullite supported membranes, the CH₄ and CO₂ permeances decrease as synthesis temperature increases; but in the case of the alumina supported membranes, by increasing synthesis temperature, CH₄ and CO₂ permeances first decrease up to 195°C and then increase up to 220°C. Even in equal membrane thicknesses, the mullite supported membrane shows lower gas permenaces. Increasing synthesis temperature decreases CO₂/CH₄ ideal selectivity for the α-Al₂O₃ supported membranes, while increases for the mullite supported membranes. Under optimum synthesis conditions, at room temperature and 2 bar feed pressure, the CO₂ permeance through the α-Al₂O₃ and the mullite supported SAPO-34 membranes are 8.2 × 10^?7 and 8.5 × 10^?8 (mol/m² · s · Pa), respectively, and CO₂/CH₄ ideal selectivities are 51 and 61, respectively.     

Homogeneous precipitation synthesis and thermoelectric properties of Ca2Co2O5 ceramics

Abstract

Homogeneous precipitation method was applied to synthesise Ca₂Co₂O₅ powders using calcium nitrate, cobalt nitrate and urea as raw materials. Uniform plate-like Ca₂Co₂O₅ powders with an average grain size of 1 μm can be obtained by calcining the precursor for 8 h at 1073 K in the air. The Ca₂Co₂O₅ ceramics were gained after sintering for 4 h at 1083 K using uniaxial pressure moulding and then sintering technique. The thermoelectric properties of ceramic samples were measured from 303 to 973 K, and the result shows that the electrical conductivity, Seebeck coefficient, thermal conductivity and figure of merit of the sample are 2236·85 S m^?1, 175·95 μV K^?1, 1·01 W m^?1 K^?1 and 0·69 at 973 K respectively.     

Adsorption and desorption characteristics of CF<Subscript>4</Subscript> on fixed bed column

Adsorption and desorption characteristics of CF₄, which is considered a significant global warming compound, were experimentally investigated. Dynamic behavior of feed gas mixture of CF₄ and N₂ was observed by breakthrough curve. Effects of CF₄ concentrations in the feed gas were investigated, and three pressurization methods were compared. Desorption experiments were carried out using vacuum blowdown and purge. Desorption curves with various N₂ flow rates, feed compositions, and purge time were obtained. The enrichment factor was high for low concentration of CF₄. However, the time required for complete desorption was independent of CF₄ concentration. In the operation of separate vacuum blowdown and purge steps, a short period of vacuum blowdown followed by the purge step was effective.     

Understanding the performance of membrane for direct air capture of CO2

Direct air capture (DAC) of CO₂ is becoming increasingly important for reducing greenhouse gas concentrations in the atmosphere. However, the cost and energy requirements associated with DAC make it less economically feasible than carbon capture from flue gases. While various methods like solid sorbents and gas–liquid absorption have been explored for DAC, membrane processes have only recently been investigated. The objective of this study is to examine the separation performance of a membrane unit for capturing CO₂ from ambient air. The performance of a membrane depends on several factors, including the composition of the feed gas, pressure ratio, material selectivity, and membrane area. The single-stage separation process with the co-current flow and constant permeability flux model is evaluated using a commercial module integrated with a process simulator to separate a binary mixture of carbon dioxide and nitrogen to assess the sensitivity of selectivity on purity and recovery of CO₂ in permeate, and power requirement. Additionally, three levels of CO₂ reduction from the feed stream to the retentate stream (25%, 50%, and 75%) are studied. A trade-off between purity and recovery factor is observed, and achieving high purity in permeate requires high concentration in the retentate.     

Ultraviolet‐ray treatment of polysulfone membranes on the O2/N2 and CO2/CH4 separation performance

UV irradiation on polysulfone (PSF) membranes was studied to improve their gas‐separation properties. Membranes with 19–25% PSF contents were prepared by the phase‐inversion method, and the membrane surface was modified with UV rays with a wavelength of 312 nm and a power of 360 µw/cm². Measurements of gas permeation were conducted with pure carbon dioxide (CO₂), methane (CH₄), oxygen (O₂), and nitrogen (N₂) gases under 3–8 bar pressure at 25°C. Fourier transform infrared spectrometry revealed that the polar functional groups of hydroxyl and carbonyl were introduced by UV irradiation. The water contact angle of the treated membrane was reduced from 70–75° to 10–12° after 12 h of UV exposure. Scanning electron microscopy observation showed that the dense skin layer increased as the polymer concentration increased. After UV treatment, the permeation of O₂ decreased from 0.4–3.4 to 0.2–2.3 m³ m^?2 h^?1 bar^?1, whereas that of N₂, CO₂, and CH₄ increased for all of the pressures used from 0.1–1.7 m³ m^?2 h^?1 bar^?1 to about 0.1–3.4 m³ m^?2 h^?1 bar^?1; this depended on the applied pressure and the PSF content. As a result, the selectivity ratio of O₂/N₂ decreased from 1.9–7.8 to 0.6–1.5, whereas that of CO₂/CH₄ increased from 0.9–2.6 to 1.1–6.1. Moreover, the O₂/N₂ and CO₂/CH₄ of the untreated and the treated membranes decreased with increasing pressure and increased with increasing polymer concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42074.     

Modification of ABS Membrane by PEG for Capturing Carbon Dioxide from CO2/N2 Streams

Carbon dioxide capture and storage (CCS) has been propounded as an important issue in greenhouse gas emissions control. In this connection, in the present article, the advantages of using polymeric membrane for separation of carbon dioxide from CO₂/N₂ streams have been discussed. A novel composition for fabrication of a blend membrane prepared from acrylonitrile-butadiene-styrene (ABS) terpolymer and polyethylene glycol (PEG) has been suggested. The influence of PEG molecular weight (in the range of 400 to 20000) on membrane characteristics and gas separation performance, the effect of PEG content (0–30 wt%) on gas transport properties, and the effect of feed side pressure (ranging from 1 to 8 bar) on CO₂ permeability have been studied. The results show that CO₂ permeability increases from 5.22 Barrer for neat ABS to 9.76 Barrer for ABS/PEG20000 (10 wt%) while the corresponding CO₂/N₂ selectivity increases from 25.97 to 44.36. Furthermore, it is concluded that this novel membrane composition has the potential to be considered as a commercial membrane.     

Selective separation of low concentration CO2 using hydrogel immobilized CA enzyme based hollow fiber membrane reactors

This paper reported the results of developing a novel hollow fiber membrane reactor contained immobilized enzyme for selective separation of low concentration CO₂ from mixed gas streams. In the reactor, two bundles of poly(vinylidene fluoride) (PVDF) hollow fiber membranes were aligned staggered parallel in a tube module, and lab-made poly(acrylic acid-co-acrylamide)/hydrotalcite (PAA-AAm/HT) nanocomposite hydrogel was filled between fibers, in which carbonic anhydrase (CA enzyme) was immobilized. The effects of CA concentration, buffer concentration, the flow rate of sweep gas, operational temperature, and CO₂ concentration on separation performance were investigated in detail. The results showed that the transport resistance was mainly from the hydrogel layer, and decreased greatly with immobilization of carbonic anhydrase in hydrogel. Moreover, immobilized CA could retain over 76% enzymatic activity and thermal stability was also improved. The data showed that this enzyme-based membrane reactor could effectively separate CO₂ at low concentration from mixed gas streams. For the feed with 0.1% (v/v) of CO₂, the selectivity of CO₂/N₂ was 820, CO₂/O₂ was 330, and CO₂ permeance was 1.65×10^?8 mol/m² s Pa. Prolonged runs lasting 30 h showed that separation performances of the membrane reactor were quite stable.     

Influence of vent air valve opening on combustion characteristics of a down-fired pulverized-coal 300 MWe utility boiler

Industrial experiments have been performed on a down-fired pulverized-coal 300 MWe utility boiler with vent air valve opening of 100% and 40%. The gas temperature distribution along the primary air and coal mixture flow, gas temperature distribution in the furnace, and gas components such as O₂, CO, CO₂ and NO_x in the near-wall region were measured for the first time. The influence of vent air valve opening on coal combustion in the furnace was determined. The results indicate that ignition of the primary air and pulverized-coal mixture is delayed. The position of the gas temperature peak is above the arches. Emission of NO_x is up to 2101 mg/m³ (at 6% O₂ dry) with vent valve opening of 40%.     

Modeling and economic analysis of CO<Subscript>2</Subscript> separation process with hollow fiber membrane modules

The main purpose of the study was to develop a model using ASPEN and Excel simulation method to establish optimum CO₂ separation process utilizing hollow fiber membrane modules to treat exhaust gas from LNG combustion. During the simulation, optimum conditions of each CO₂ separation scenario were determined while operating parameters of CO₂ separation process were varied. The characteristics of hollow fibers membrane were assigned as 60 GPU of permeability and 25 of selectivity for the simulation. The simulation results illustrated that 4 stage connection of membrane module is required in order to achieve over 99% of CO₂ purity and 90% of recovery rate. The resulted optimum design and operation parameters throughout the simulation were also correlated with the experimental data from the actual CO₂ separation facility which has a capacity of 1,000 Nm³/day located in the Korea Research Institute of Chemical Technology. Throughout the simulation, the operating parameters of minimum energy consumption were evaluated. Economic analysis of pilot scale of CO₂ separation plant was done with the comparison of energy cost of CO₂ recovery and equipment cost of the plant based on the simulation model. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Performance of Pd composite membrane prepared by organic–inorganic method in WGS membrane reactor

H₂ production via water–gas shift (WGS) reaction in a Pd membrane reactor prepared by the electroless plating technique (ELP) “organic–inorganic” method was investigated. Pd nanoparticles embedded polyethylene glycol (PEG) was used as a polymer template during the activation step. Gas permeation results showed an infinite selectivity for H₂/N₂ with a H₂ flux of 0.004–0.016 mol/m²·s depending on operating conditions while it decreased until 0.0005 mol/m²·s for gas mixtures. Furthermore, WGS membrane reactor experiments showed a maximum CO conversion of 98.5% with a H₂ recovery of 16% at 450°C. The membrane performance was consistent during WGS catalytic membrane reactors (CMR) tests, thereby confirming the stability of the obtained membrane.     

Metal‐organic framework membrane process for high purity CO2 production

Gas separation by metal‐organic framework (MOF) membranes is an emerging research field. Their commercial application potential is, however, still rarely explored due in part to unsatisfied separation characteristics and difficulty in finding suitable applications. Herein, we report “sharp molecular sieving” properties of high quality isoreticular MOF‐1 (IRMOF‐1) membrane for CO₂ separation from dry, CO₂ enriched CO₂/CH₄, and CO₂/N₂ mixtures. The IRMOF‐1 membranes exhibit CO₂/CH₄ and CO₂/N₂ separation factors of 328 and 410 with CO₂ permeance of 2.55 × 10^?7 and 2.06 × 10^?7 mol m^?2 s^?1 Pa^?1 at feed pressure of 505 kPa and 298 K, respectively. High grade CO₂ is efficiently produced from the industrial or lower grade CO₂ feed gas by this MOF membrane separation process. The demonstrated “sharp molecular sieving” properties of the MOF membranes and their potential application in production of value‐added high purity CO₂ should bring new research and development interest in this field. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3836–3841, 2016     

Gas absorption of carbon dioxide in a hollow fiber contained liquid membrane absorber

Experiments on the absorption of CO₂ into a hollow fiber contained liquid membrane absorber were performed. The feed gas was a mixture of CO₂ and N₂, absorbent liquid was 2-amino-2-methyl-l-propanol and the hollow fiber was a microporous hydrophobic polytetrafluoroethylene membrane. Outlet concentration of CO₂ from the absorber decreased as absorbent concentration increased, gas flow rate increased and were held constant for speed of agitation, but had a maximum value in the range of inlet concentration of CO₂ from 5 to 40 mole%. The reaction rate constant obtained for CO₂-amine system was 231 I/mol · s at 25 °C using a flat stirred vessel, and the membrane-side-mass-transfer coefficient was 1.217 × 10⁻⁵ mol/cm² · s · atm in CO2/N2-amine system. A diffusion model based on mass transfer with fast-reaction was proposed to predict the performance of the absorber.     

Design of metallic nickel hollow fiber membrane modules for pure hydrogen separation

Cost‐effective and robust nickel (Ni) membrane for H₂ separation is a promising technology to upgrade the conventional H₂ industries with improved economics and environmental benignity. In this work, Ni hollow fibers (HFs) with one closed end were fabricated and assembled into a membrane module for pure H₂ separation by applying vacuum to the permeate side. The separation behavior of the HF module was investigated both experimentally and theoretically. Results indicate that H₂ recovery can be improved significantly by changing the operation conditions (temperature or feed pressure). Ni HF is a promising membrane geometry, but the negative effect of pressure drop when H₂ passes through the lumen cannot be ignored. Under the vacuum operation mode, there is little difference in term of H₂ recovery efficiency whether the feed gas flow is controlled in countercurrent or recurrent operation. This work provides important insight to the development of superior membrane H₂ separation system. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3662–3670, 2018     

High-speed CO2 transport channel containing carboxymethyl chitosan/hydrotalcite membrane for CO2 separation

A comprehensive understanding of carboxymethyl chitosan (CMC)-based mixed matrix membrane (MMM) has been critically investigated. The present work elaborates the compatibility of hydrotalcite (HT) and CMC in terms of CO₂ separation application. Various spectroscopic and microscopic techniques have been utilized to characterize the respective properties of the prepared membrane. The temperature stability and moisture retention behavior of the membrane recognized itself as the flue gas separation membrane. The CO₂/N₂ separation experiment was performed on the MMM at different temperature (60–110 °C) and sweep/feed water flow to the saturator ratio (0.33 to 3). The membrane exhibited the optimum CO₂ permeance of 70 GPU at 90°C pertaining to water flow ratio of 2.33 (sweep/feed). The CO₂/N₂ selectivity observed at that same operating condition was 13. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48715.