Feed Gas Pressure Research Articles

Synthesis and optimization of high-performance amine-based polymer for CO2 separation

• Optimal conditions were ascertained to obtain PVAm with high molecular weight and low crystallinity. • The effect of molecular weight and crystallinity on CO 2 separation performance of PVAm was systematically discussed. • The pilot scale synthesis of PVAm was successfully attempted for continuous preparation of composite membranes with high CO 2 separation performance. Membrane technology features inspiring excellence from numerous separation technologies for CO 2 capture from post-combustion gas. Polyvinylamine (PVAm)-based facilitated transport membranes show significantly high separation performance, which has been proven promising for industrial scale-up. However, commercialized PVAm with low molecular weight and excessive crystallinity is not available to prepare high-performance membranes. Herein, the synthesis process of PVAm was optimized by regulating polymerization and acidic hydrolytic conditions. The membranes based on PVAm with a molecular weight of 154 kDa and crystallinity of 11.37% display high CO 2 permeance of 726 GPU and CO 2 /N 2 selectivity of 55 at a feed gas pressure of 0.50 MPa. Furthermore, we established a PVAm synthesis reactor with an annual PVAm solution (1%(mass)) capacity of over 7000 kg and realized the scaled-up manufacture of both PVAm and composite membranes.

Simple scalable approach to advanced membrane module design and hydrogen separation performance using twelve replaceable palladium-coated Al2O3 hollow fibre membranes

A phase-inversion approach was used to manufacture Al2O3 hollow fibre supports, which were then sintered at 1723 K. The electroless plating technique is developed to prepare palladium-coated Al2O3 hollow fibre membranes for hydrogen separation. Three different scaling-up configurations were produced and tested: single membrane, membrane unit obtained by assembling three membranes, and advanced membrane module obtained by assembling twelve replaceable membranes. The hydrogen flux was investigated under vacuum and without vacuum using a feed gas of pure H2 (100%) and a binary feed gas mixture of H2 (80%) and CO2 (20%) at different feed gas pressures (100–800 kPa), feed gas rate (0.2–6.0 L min−1), and temperature (673–723 K). The hydrogen flux increases from 0.2162 mol m−2 s−1 (feed gas pressure = 600 kPa, feed gas rate = 0.2 L min−1) to 0.4487 mol m−2 s−1 (feed gas pressure = 800 kPa, feed gas rate = 6.0 L min−1) under the binary gas mixture at 723 K by switching from a single to the advanced membrane module, while the hydrogen purity remains above 97.5% throughout the experiment. Some aspects about the scalability of palladium-coated Al2O3 hollow fibre membranes for hydrogen separation are discussed.

Molecular Characterization of Membrane Gas Separation under Very High Temperatures and Pressure: Single- and Mixed-Gas CO2/CH4 and CO2/N2 Permselectivities in Hybrid Networks.

This work illustrates the potential of using atomistic molecular dynamics (MD) and grand-canonical Monte Carlo (GCMC) simulations prior to experiments in order to pre-screen candidate membrane structures for gas separation, under harsh conditions of temperature and pressure. It compares at 300 °C and 400 °C the CO2/CH4 and CO2/N2 sieving properties of a series of hybrid networks based on inorganic silsesquioxanes hyper-cross-linked with small organic PMDA or 6FDA imides. The inorganic precursors are the octa(aminopropyl)silsesquioxane (POSS), which degrades above 300 °C, and the octa(aminophenyl)silsesquioxane (OAPS), which has three possible meta, para or ortho isomers and is expected to resist well above 400 °C. As such, the polyPOSS-imide networks were tested at 300 °C only, while the polyOAPS-imide networks were tested at both 300 °C and 400 °C. The feed gas pressure was set to 60 bar in all the simulations. The morphologies and densities of the pure model networks at 300 °C and 400 °C are strongly dependent on their precursors, with the amount of significant free volume ranging from ~2% to ~20%. Since measurements at high temperatures and pressures are difficult to carry out in a laboratory, six isomer-specific polyOAPS-imides and two polyPOSS-imides were simulated in order to assess their N2, CH4 and CO2 permselectivities under such harsh conditions. The models were first analyzed under single-gas conditions, but to be closer to the real processes, the networks that maintained CO2/CH4 and CO2/N2 ideal permselectivities above 2 were also tested with binary-gas 90%/10% CH4/CO2 and N2/CO2 feeds. At very high temperatures, the single-gas solubility coefficients vary in the same order as their critical temperatures, but the differences between the penetrants are attenuated and the plasticizing effect of CO2 is strongly reduced. The single-gas diffusion coefficients correlate well with the amount of available free volume in the matrices. Some OAPS-based networks exhibit a nanoporous behavior, while the others are less permeable and show higher ideal permselectivities. Four of the networks were further tested under mixed-gas conditions. The solubility coefficient improved for CO2, while the diffusion selectivity remained similar for the CO2/CH4 pair and disappeared for the CO2/N2 pair. The real separation factor is, thus, mostly governed by the solubility. Two polyOAPS-imide networks, i.e., the polyorthoOAPS-PMDA and the polymetaOAPS-6FDA, seem to be able to maintain their CO2/CH4 and CO2/N2 sieving abilities above 2 at 400 °C. These are outstanding performances for polymer-based membranes, and consequently, it is important to be able to produce isomer-specific polyOAPS-imides for use as gas separation membranes under harsh conditions.

Performance of Multilayer Composite Hollow Membrane in Separation of CO2 from CH4 in Mixed Gas Conditions.

Composite membranes comprising NH2-MIL-125(Ti)/PEBAX coated on PDMS/PSf were prepared in this work, and their gas separation performance for high CO2 feed gas was investigated under various operating circumstances, such as pressure and CO2 concentration, in mixed gas conditions. The functional groups and morphology of the prepared membranes were characterized by Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM). CO2 concentration and feed gas pressure were demonstrated to have a considerable impact on the CO2 and CH4 permeance, as well as the CO2/CH4 mixed gas selectivity of the resultant membrane. As CO2 concentration was raised from 14.5 vol % to 70 vol %, a trade-off between permeance and selectivity was found, as CO2 permeance increased by 136% and CO2/CH4 selectivity reduced by 42.17%. The membrane produced in this work exhibited pressure durability up to 9 bar and adequate gas separation performance at feed gas conditions consisting of high CO2 content.

New sterically hindered polyvinylamine-containing membranes for CO2 capture from flue gas

Amine-containing facilitated transport membranes can have both high permeability and selectivity due to the reversible reaction between CO 2 and amino groups for effective carbon capture from flue gas. We have developed an improved method for the synthesis of high-molecular-weight sterically hindered polyvinylamine (PVAm) as the new fixed-site carrier in thin-film composite membranes for CO 2 capture. Commercially available PVAm was N -monomethylated into poly- N -methyl- N -vinylamine (PVAm-CH 3 ) using the stepwise reductive amination with a highly polar fluorinated alcohol as the solvent to enhance the equilibrium shift to the formation of the imine intermediate. The method prevented over-alkylation, resulting in the increased yield of the target product. PVAm-CH 3 exhibited excellent CO 2 facilitation with a CO 2 permeability of 445.7 Barrer (1 Barrer = 3.349 × 10 −16 mol m m −2 s −1 Pa −1 ) and a CO 2 /N 2 selectivity of 70.3, which are above the Robeson 2008 upper bound. The PVAm-CH 3 solution retained a sufficiently high viscosity after incorporating the amino acid salt, 2-(1-piperazinyl)ethylamine sarcosinate (PZEA-Sar), as the mobile carrier for the membrane coating on nanoporous polyethersulfone (PES) substrates without any penetration issues. The resultant thin-film composite PVAm-CH 3 /PZEA-Sar membrane with a thickness of approximately 170 nm exhibited a superior CO 2 performance of 1071 GPU (1 GPU = 3.349 × 10 −10 mol m −2 s −1 Pa −1 ) and a CO 2 /N 2 selectivity of 183 at 57 °C and a feed gas pressure of 111.64 kPa (1.5 psig). This PVAm-CH 3 /PZEA-Sar membrane surpassed the latest redefined 2019 CO 2 /N 2 upper bound and outperformed other polymer-based membranes. Density functional theory calculations also demonstrated that PVAm-CH 3 showed a stronger preference, relative to PVAm, toward the more efficient bicarbonate pathway. Thus, the steric hindrance effect of PVAm-CH 3 enhanced the solubility of CO 2 in the polymer matrix and resulted in the higher CO 2 permeance. • Hindered polyvinylamine (PVAm-CH 3 ) synthesized using stepwise reductive amination. • The reaction conditions optimized for the highest N -methylation degree of 39%. • PVAm-CH 3 fixed-site carrier membrane exhibited excellent CO 2 facilitation. • The improved performance of PVAm-CH 3 was illustrated by DFT calculations. • A composite membrane showed 1071 GPU CO 2 permeance and 183 CO 2 /N 2 selectivity.

Helium recovery and purification by dual reflux pressure swing adsorption

Global demand for helium has risen over the past few decades driven by a vast range of applications based on its unique properties. Helium is often produced industrially from the vent streams of nitrogen rejection units (NRU) in liquefied natural gas (LNG) plants, where it accumulates because of its low boiling point. Further deep cryogenic processing stages are then required to upgrade its concentration to saleable levels. We report here an experimental and simulation-based investigation of an alternative, non-cryogenic process based on dual reflux pressure swing adsorption (DR PSA) cycles to recover and purify helium from model binaries including a 1 mol% He + 99 mol% N2 mixture representative of NRU vent streams. Binderfree zeolite 13X was used as the adsorbent in an experimental campaign employing a laboratory-scale DR PSA apparatus. The experimental runs validated a non-isothermal numerical model with an average deviation of 1 mol% between the simulated and experimental product compositions. The single-stage DR PSA experiments produced helium product streams with purities ranging from (30 to 99) mol% from feeds with concentrations ranging from (1 to 50) mol% He. Two DR PSA stages were required to upgrade mixtures containing 1 mol% He to a target product purity of > 99 mol%. A cascade arrangement of two DR PSA systems with a waste recycle enabled a 99.999 mol% He purity product at 95 % recovery, which is competitive with conventional cryogenic systems. This cascade DR PSA process used either two or three compressors depending on the feed gas pressure, with associated duty costs of 1.5 MJ∙(mol He produced)–1. This is lower than several membrane processes described in the literature and could be more cost-effective for smaller-scale applications than cryogenic processes with similar levels of separation performance.

Simulation Model for Prediction of Gas Separation in Membrane Contactor Process.

The purpose of this study is to establish a practical simulation model based on mass balance, mass transport equations and equilibrium equation between gas and liquid phases across a porous membrane in membrane contactor process in order to predict the separation behavior by the gassing process of gas mixture in membrane contactor. The established simulation model was verified by comparison between the simulated values and real process values in the separation of CH4/CO2 mixture, showing an excellent agreement between them. The parameter R-value in the model, which is a kind of the permeability of permeant across porous membrane, has been determined by fitting a numerical solution of the model equation to the experimental data to obtain a practical value of the parameter. A parametric study on the gassing process of N2/CO2 mixture in membrane contactor was made with the help of the practical simulation model to investigate the effects of operation parameters on separation performance and to characterize the separation behavior of membrane contactor process. A series of simulations of the separation of N2/CO2 mixture in membrane contactor were conducted, and the optimization on the membrane process was discussed to maximize the separation performance in terms of N2 recovery percent in retentate and CO2 permeation rate. It was observed from the analysis of the result of the simulation that liquid flow rate has a negative effect on N2 recovery percent in retentate but a positive effect on the separation of CO2, while R-value affects the separation performance in the other way. It is confirmed in this study that the developed simulation can be used as a tool to optimize the parameters, i.e., feed gas pressure, liquid flow rate and R-value to maximize the separation performance.

Thin film nanocomposite (TFN) membrane comprising Pebax®1657 and porous organic polymers (POP) for favored CO2 separation

Global warming is a public alarming issue caused by extreme CO2 emissions. Thus, CO2 removing using TFN membranes is an effective method to improve the CO2 separation performance. Thin film nocomposite membranes composed of Pebax 1657 embedded by porous organic polymers over the porous polysulfone support used to separate CO2 from CH4 and N2 gases. Porous organic polymers were synthesized via Friedel-Crafts one-step reaction. The obtained results from field emission scanning electron microscopy and thermal gravimetric analysis revealed that the TFN membranes declared a superior compatibility between Pebax and fillers. Permeation properties of membranes were tested over various feed pressure with the range of 2–10 bar. Pure gases permeability, CO2/CH4 and CO2/N2 selectivities improved via adding porous organic polymers into the Pebax. At porous organic polymers loading of 5wt% and feed pressure of 2 bar, the CO2, CH4 and N2 permeability raised to 310.6, 27.6 and 4.5 Barrer, respectively; which exhibited a significant improvement compared to thin film composite membrane. Moreover, the CO2/CH4 and CO2/N2 selectivities also increased to 11.25 and 70.04; respectively. Obtained results reveladed that the membranes performance was enhanced as the feed gas pressure increased. TFN containing 5wt% porous organic polymers implies a CO2 permeability of 348.4 Barrer at feed pressure of 10 bar.

Optimization Design and Analysis of Single-Stage Mixed Refrigerant Liquefaction Process

Small-scale natural gas liquefaction processes have several clear advantages, particularly in the exploitation of ‘unconventional’ natural gas (NG) from sources such as difficult-to-access and offshore gas fields. Moreover, conventional liquefaction processes have a number of disadvantages such as high energy consumption, large cooling loads required in the refrigeration cycle, and non-uniform matching of cold and hot flows in liquified natural gas (LNG) heat exchanger (HE). The main objective of this study was to optimize the most commonly used mixed refrigerant process. The liquefaction performance of the optimized process was analyzed and the influence of gas parameters on the power consumption, exergy loss, freezing mixture circulation, and cooling water load were investigated. The results show that compressor power consumption can be reduced by 29.8%, the cooling water load can be reduced by 21.3%, and the system exergy efficiency can be increased by 41% with the optimized process. Furthermore, throttling and compression of the freezing mixture were increased during the refrigeration stage. It can be concluded that reducing the feed gas temperature and increasing the feed gas pressure can reduce the total power consumption, exergy loss, freezing mixture circulation, and cooling water load, which can significantly improve liquefaction performance.

Magnetic field-induced improvement in O2/N2 gas separation applications of simultaneously co-casted superparamagnetic mixed matrix membranes

For industrial purposes and current challenges facing the world, the selective separation of oxygen and nitrogen gases from the air by polymer mixed matrix membranes is crucial. Due to the diamagnetic nature of water molecules used in the fabrication of the polymer membranes, the magnetic field (H) may affect the resulting separation performance. Here, using a simultaneous co-casting method, empty and superparamagnetic Fe3O4 nanoparticle-filled double-layer polyethersulfone (PES)/Pebax®1657 mixed matrix membranes are fabricated under different external magnetic field intensities in the range of H = 0–5000 Oe. The O2 and N2 permeances of the PES/Pebax® membranes are found to increase with increasing the magnetic field intensity, arising from an enhancement in the polymer chain mobility. The Fe3O4 nanoparticles form thick root-like superparamagnetic channels on the double-layer PES/Pebax® surface at a magnetic field intensity of 4000 Oe, resulting in an O2/ N2 ideal selectivity of 3.59 at a feed gas pressure of 10 bar. This indicates an improvement of 40% in the selectivity compared to a single-layer Pebax® membrane filled with Fe3O4 nanoparticles.

ПАРАМЕТРЫ ГАЗОВОЙ ФАЗЫ И РЕЖИМЫ РЕАКТИВНО-ИОННОГО ТРАВЛЕНИЯ Si И SiO2 В БИНАРНЫХ СМЕСЯХ Ar + CF4/C4F8

The comparative study of plasma electro-physical parameters, steady-state gas phase compositions and reactive-ion etching kinetics for Si and SiO2 in binary CF4 + Ar and C4F8 + Ar gas mixtures were studied under conditions of 13.56 MHz inductive RF discharge. As fixed input parameters, we used the total pressure of feed gas (6 mTorr) as well as power levels supplied by plasma excitation source (700 W) and bias source (200 W). The investigation approach combined plasma diagnostics experiments with double Langmuir probe and 0-dimensional (global) model for the chemistry of neutral species. It was shown that investigated gas mixtures exhibit quite close properties in respect to both ions-related parameters and electron gas while are characterized by sufficient differences in kinetics of atoms and radicals. The features of C4F8 + Ar gas under the given set of processing conditions are the higher density of polymerizing radicals, the lower density of F atoms as well as the weaker sensitivity the last parameter to the change in Ar fraction in a feed gas. Etching experiments indicated that a) an increase in Ar fraction in CF4 + Ar and C4F8 + Ar gas mixtures results in qualitatively different changes in Si and SiO2 etching rates; and b) obtained dependencies of etching rates on Ar fraction in both gas mixtures contradict with the behavior of F atom flux. Obviously, such situation corresponds to the change in reaction probability of F atoms with the treated surface. It was suggested that an increase of Ar fraction in the low-polymerizing CF4 + Ar plasma activates the heterogeneous chemical reaction through the intensification of ion-stimulated desorption of etching products and/or surface amorphization. The similar effect for the high-polymerizing C4F8 + Ar plasma may be related to decreasing fluorocarbon film thickness that provides the better access of F atoms to the etched surface.

A systematic study on the effects of synthesis conditions of polyamide selective layer on the CO2/N2 separation of thin film composite polyamide membranes

AbstractDifferent top layer fabrication methods (amine‐first, acid‐first, spin coating), organic phase solvents (hexane, heptane, mixed hexane/heptane), acid acceptors (triethylamine, sodium carbonate, sodium hydroxide), and surfactant sodium dodecyl sulfate concentrations (0, 0.05, and 0.1 wt%) were utilized to fabricate thin film composite polyamide membranes for CO2/N2 separation. The results, according to an L9 orthogonal array of Taguchi approach, showed that employing acid‐first method increases both CO2 permeance and CO2/N2 selectivity of the membranes at a feed gas pressure of 3 bars. On the other hand, sodium hydroxide, and triethylamine should be used, as acid acceptors, to maximize CO2 permeance and CO2/N2 selectivity, respectively. Moreover, the use of hexane solvent and 0 wt% surfactant led to maximum permeance, while, hexane solvent and 0.1 wt% surfactant were needed to reach the highest selectivity. The above level setting of synthesis parameters also resulted in the minimum sensitivity of the fabrication process to the noise factors effects. As shown by the analysis of variance, acid acceptor, and organic solvent types were the most influential parameters on CO2 permeance and CO2/N2 selectivity, respectively. The effects of fabrication method and surfactant concentration, as single factors, on permeation/selectivity responses were also investigated.

Effect of silica nanoparticles on carbon dioxide separation performances of PVA/PEG cross-linked membranes

Novel PVA/PEG cross-linked membranes were prepared with (0–20 wt. %) of silica nanoparticles. The presence of both the polymers and additive was confirmed by FTIR analysis. The thermal properties of the membranes were analyzed by TGA and DSC analysis. The morphological and mechanical properties of the membranes were studied by SEM analysis and tensile testing, respectively. The gas permeation performances of the membranes were examined using state-of-the-art gas permeability cell. It was found that permeability of all the gases increased with the increase of silica loading, whereas ideal selectivity of carbon dioxide with respect to nitrogen and methane increased up to 10 wt. % loading and then became nearly constant on further loading. 20 wt. % silica loaded membrane was found to be the best performance membrane. The gas permeability of CO2 was also compared with different gas permeation models and was found to be in close agreement with Maxwell Model. The effect of temperature and pressure of feed gas pressure was also studied on permeation performances and optimum performances were achieved around 65 °C. The gas permeation performances were observed to decrease slightly with the increase in feed gas pressure up to 20 bar which confirms the absence of plasticization phenomenon up to 20 bar. Finally, gas permeation performances were compared with 2008 Robeson trade-off lines and it was found that at 20 wt. % loading, gas permeation performances surpassed the trade-off line for CO2/N2, and for CO2/CH4, the gas permeation performances approached the trade-off line.

Theoretical investigation of ZIFs as adsorbents or membranes for separating noble gas mixtures: applying a newer method for predicting performances

Zeolitic imidazolate frameworks (ZIFs) possess similar topological structures with zeolites, however a number of characteristic properties of the ZIFs, such as easy incorporation of desired linkers to their structures, tunable pore sizes, high porosities, and large surface areas make them better option for targeted engineering applications. In this respect, cheaper, highly efficient, and selective separation of syngas mixtures using ZIFs has been already shown in the literature. Separation and purification of noble gases, on the other hand, have been achieved using energy demanding cryogenic distillation of air and currently we know little about noble gas separation performances of the ZIFs. Replacing energy intensive gas separation techniques with adsorbent and/or membrane based separation technologies, indeed, have been motivated for decreasing the operational costs, price of the pure noble gases, as well as opening new application areas for the noble gases. In this respect, we theoretically investigate Xe/Kr and Xe/Ar separation performances of eight ZIFs, namely ZIF-6, ZIF-11, ZIF-60, ZIF-67, ZIF-69, ZIF-78, ZIF-79, and ZIF-81 using Grand Canonical Monte Carlo and Molecular Dynamics simulations and calculate Xe permeability and permeation selectivity using a newer method suggested previously by our group. While ZIF-11 shows significant Xe uptake from the noble gas mixtures, ZIF-81 and ZIF-79 show exceptional Xe adsorption selectivities for two gas mixtures at low pressures, 22.5 and 21 for the Xe/Kr and 128 and 120 for the Xe/Ar mixture, respectively. ZIF-69 and ZIF-79 show high Xe permeability (4. $$2\times 1$$ 0 $$^5$$ and 3. $$2\times 1$$ 0 $$^5$$ Barrers) as well as high Xe permeation selectivity (17.35 and 15.85) for the Xe/Ar mixture at 2 bar feed gas pressure. For the Xe/Kr mixture, on the other hand, we observe high Xe permeability and moderate Xe permeation selectivity, especially at low pressures. Comparing with the limited literature available, these ZIFs show promise for selective separation of Xe from its binary mixtures of Kr and Ar at room temperature. We also compare the permeability and permeation selectivity predictions using different approaches, namely the new method and the approximate approach which is commonly used in the literature. Results reveal significant deviations of the approximate approach with respect to the new method, especially for the permeability calculations. Thus, using the new method for determining membrane performances is highly suggested.

Dibenzo-21-crown-7-ether contained 6FDA-based polyimide membrane with improved gas selectivity

In the present work, a novel crown ether contained polyimide membrane was synthesized by 4, 4′- (hexafluoro - isopropylidene) diphthalic anhydride, 1, 4 - Bis (4 - aminophenoxy) benzene, and di(aminobenze)-21-Crown-7 ether. The physical property and chemical structure were studied by FTIR, 1HNMR, XRD, TGA, GPC, and tensile testing. Molecular dynamic simulations were applied to investigate the effects of crown ether content on free volume property of membranes. The permselectivity was studied employing He, H2, CO2, N2, and CH4 pure gas as feed. The effects of crown ether content, operation temperature, feed gas pressure, and aging effect on membranes were investigated. Results show that introducing crown ether into polymeric backbone can increase the chains packing density, which lead to reduce d-spacing as well as accessible fractional free volume. These permeabilities followed the order of He > H2 > CO2 > N2 > CH4, indicating a typical molecular sieving separation mechanism in membranes. The introduction of DB21C7 can improve the diffusion selectivity and solubility selectivity. For example, CO2/N2 and CO2/CH4 diffusion selectivity display impressing increase of 53% and 84% respectively by incorporation of 30 mol% DB21C7. As a consequence, the membrane with 30 mol% DB21C7 exhibit remarkable selectivity increase of about 173.5% (for He/CH4), 156.9% (for H2/CH4), 109.4% (for CO2/N2), 88.5% (for CO2/CH4) than non-crown ether contained polyimide membrane. Hence, future membrane material design for high purity gas requirement may be considered as a promising alternative membrane by introducing the crown ether moiety into the polymeric backbone.

Efficient Facilitated Transport Polymer Membrane for CO2/CH4 Separation from Oilfield Associated Gas.

CO2 enhanced oil recovery (CO2-EOR) technology is a competitive strategy to improve oil field economic returns and reduce greenhouse gas emissions. However, the arbitrary emissions or combustion of the associated gas, which mainly consists of CO2 and CH4, will cause the aggravation of the greenhouse effect and a huge waste of resources. In this paper, the high-performance facilitated transport multilayer composite membrane for CO2/CH4 separation was prepared by individually adjusting the membrane structure of each layer. The effect of test conditions on the CO2/CH4 separation performance was systematically investigated. The membrane exhibits high CO2 permeance of 3.451 × 10−7 mol·m−2·s−1·Pa−1 and CO2/CH4 selectivity of 62 at 298 K and 0.15 MPa feed gas pressure. The cost analysis was investigated by simulating the two-stage system. When the recovery rate and purity of CH4 are 98%, the minimum specific cost of separating CO2/CH4 (45/55 vol%) can be reduced to 0.046 $·Nm−3 CH4. The excellent short-to-mid-term stability indicates the great potential of large industrial application in the CH4 recovery and CO2 reinjection from oilfield associated gas.

Study of separation factor and product extraction ratio in hydrogen isotope separation with displacement chromatography

Abstract A numerical method is proposed to simulate the protium-deuterium (H D) separation with the displacement chromatography technique, considering the coupling of the gas diffusion and chemical reactions inside the pores. Different fractal pore models are generated to describe different filling methods of the separation materials. The effects of the pore structure parameters (porosity θ, specific surface area Sg and fractal dimension Df) and operating conditions (separation material length L and feed gas pressure P) on the separation performance are studied. A smaller modulus χ' (a combination of θ, Sg and Df) or a larger L leads to a higher separation factor (α). α increases with P increasing when χ' 9.3350 × 10−11. The effects of these factors on the product extraction ratio (β) are opposite to those on α. The quantitative expressions of α and β are obtained by a theoretical derivation and data correlations, which are helpful to instruct how to arrange the separation materials for the displacement chromatography method. Two separation columns filled with the sponge palladium are used in H D separation experiments. The measured values of α and β match well with the predicted values which validates these quantitative expressions.

CO2 Capture by Using a Membrane-absorption Hybrid Process in the Nature Gas Combined Cycle Power Plants

ABSTRACT This study’s main objective was to optimize the design parameters of the hybrid membrane-absorption CO2-capture process in natural gas steam cycle (NGCC) power plants. To calculate the CO2 concentration in the permeating gas and the required area for the separating membrane, a mass transfer model of a membrane for separating CO2, N2 and H2O was developed in Aspen Plus. The effects of the CO2 recovery rate of the membrane, the ratio of the feed gas pressure to the permeating-side gas pressure and the flow rate of the flue gas on the required area for the membrane, the power consumption of the compressor and the heat duty for the solvent regeneration were then analyzed. The optimal feed-gas-to-permeating-side-gas pressure ratio and the flue gas flow rate were found to be 10:1 and 50%, respectively. Furthermore, compared to traditional chemical absorption, the solvent regeneration’s heat duty decreased by more than 20.7% when the gas flow rate and the CO2 recovery rate were 100% and 20%, respectively.

A study on highly active Cu-Zn-Al-K catalyst for CO2 hydrogenation to methanol

Excellent CO2 hydrogenation activity results were obtained on Cu-Zn-Al-K (CZA-K) catalyst with 10% of CO2 conversion and 98% of methanol selectivity at 220 °C. The CZA-K catalyst was precipitated by using 4 M K2CO3/KOH solution. For comparison purpose, CZA-Na and CZA catalysts were synthesized by using 4 M solutions of Na2CO3/NaOH and (NH4)2CO3/NH4OH respectively. Characterization of these catalysts was done by using BET-poresize, XRD, FTIR-DRIFTs, high pressure-TPR, CO2-TPD-mass, XPS and HAADF-STEM-EDX techniques. Among the catalysts studied maximum methanol space time yield of 14.4 mmol·gcat−·h− was obtained on CZA-K at 240 °C with 2400 h− GHSV of CO2/H2 mole ratio equals to 1:4. Greater methanol yield was associated with superior surface Cu+/Cu0 content in CZA-K was obtained through K2CO3/KOH precipitation. Further, FTIR-DRIFTs spectra suggests the interaction of CO2 with the potassium existed in the CZA framework (0.65% K, EDX) led to the formation of KO(CO)O surface species. To some extent, CO2 dissociation to CO and subsequent CH4 formation was limited by this species in presence of H2. At 240 °C, steady catalytic activity was observed for 100 h of continuous operation on CZA-K. It was associated with fewer carbon deposits formation and segregated active metals in CZA-K catalyst. The decreasing order of CO2 hydrogenation activity at 240 °C with 3.0 MPa feed-gas pressure as follows: CZA-K (14% CO2 conversion and 96% methanol selectivity) > CZA-Na (11% and 94%) > CZA (9% and 92%).

CO2/H2 separation through poly(ionic liquid)–ionic liquid membranes: The effect of multicomponent gas mixtures, temperature and gas feed pressure

This work presents mixed gas separation performance through PIL–IL membranes bearing pyrrolidinium-based PILs with [NTf2]– and [C(CN)3]– anions and different weight percentages of the corresponding ILs using a ternary mixture of H2, CO2 and N2 and different feed pressures ranging from 1 to 4 bar and temperatures from 20 to 80 °C. COSMO-RS was successfully used to understand the separation behavior of the PIL–IL composites for the H2 + CO2 + N2 mixture. The effect of temperature between 20 °C and 80 °C and feed pressure between 1 bar and 4 bar was also studied and is here discussed. The increased of the mixed H2, CO2 and N2 permeabilities with increasing temperature was shown to be due to dominant role of gas solubility at low temperature, and diffusivity at high temperature. The small pronounced differences between mixed and ideal CO2/H2 permselectivities through the prepared PIL–IL composites indicated that membrane separation efficiency can be maintained, despite the competition effect between gases in mixed gas experiments. Depending on the operating conditions, the best mixed separation performance was obtained for PIL C(CN)3–60 [C2mim][C(CN)3], with a CO2 permeability of 324.7 Barrer and a CO2/H2 permselectivity of 11.4. The great potential of the studied PIL–IL membranes for biohydrogen separation is here clearly evidenced, since they revealed mixed CO2/H2 separation performances above the Robeson upper bound even at the highest temperature and feed pressure tested.