Dual‐Layer Hollow Fibers for Sulfur Removal from Fuels

Emission of sulfur compounds to the atmosphere is universally recognized as one key target to be reduced. For membrane pervaporation which is considered as a potential purification process of fuels, dual‐layer polyurethane (PU)/polyethersulfone hollow‐fiber membranes were prepared. A novel fabrication technique is proposed using a quadruple spinneret to produce the fiber with such morphology by simultaneous spinning of two polymer solutions in the presence of two corresponding precipitation media. Activated carbon was added into the PU solution to improve the transport properties of the selective layer. Resulting hollow‐fiber membranes showed very good adhesion between the selective layer and its support, in addition to an effective removal of a sulfur compound such as 2‐methyl thiophene from a typical model fuel, an indication of good prospects for both the fabrication technique and for sulfur removal by pervaporation of fuels.     

NI/NI‐YSZ Current Collector/Anode Dual Layer Hollow Fibers for Micro‐Tubular Solid Oxide Fuel Cells

A co‐extrusion technique was employed to fabricate a novel dual layer NiO/NiO‐YSZ hollow fiber (HF) precursor which was then co‐sintered at 1,400 °C and reduced at 700 °C to form, respectively, a meshed porous inner Ni current collector and outer Ni‐YSZ anode layers for SOFC applications. The inner thin and highly porous “mesh‐like” pure Ni layer of approximately 50 μm in thickness functions as a current collector in micro‐tubular solid oxide fuel cell (SOFC), aiming at highly efficient current collection with low fuel diffusion resistance, while the thicker outer Ni‐YSZ layer of 260 μm acts as an anode, providing also major mechanical strength to the dual‐layer HF. Achieved morphology consisted of short finger‐like voids originating from the inner lumen of the HF, and a sponge‐like structure filling most of the Ni‐YSZ anode layer, which is considered to be suitable macrostructure for anode SOFC system. The electrical conductivity of the meshed porous inner Ni layer is measured to be 77.5 × 10⁵ S m^–1. This result is significantly higher than previous reported results on single layer Ni‐YSZ HFs, which performs not only as a catalyst for the oxidation reaction, but also as a current collector. These results highlight the advantages of this novel dual‐layer HF design as a new and highly efficient way of collecting current from the lumen of micro‐tubular SOFC.     

Partial Oxidation of Methane to Syngas in a Packed Bed Catalyst Membrane Reactor

The planar membrane reactor configuration was explored for partial oxidation of methane (POM) to syngas. A supported membrane composed of yttria‐stabilized zirconia and La_0.8Sr_0.2Cr_0.5Fe_0.5O_3‐δ was sealed to a stainless holder, and a Ni/Al₂O₃ catalyst bed was placed under the membrane plane with a small slit between them. This reactor configuration would facilitate the POM reaction via oxidation‐reforming mechanism: the oxidation reaction occurring at the membrane surface and the reforming reaction taking place in the catalyst bed. At 800°C and a methane feed rate of 32 mL min^?1, the reactor attained methane throughput conversion over 90%, CO and H₂ selectivity both over 95%, and an equivalent oxygen permeation rate 1.4 mL cm^?2 min^?1. The membrane and catalyst remained intact after the POM testing. The planar membrane reactor configuration explored in this study may lead to the development of a compact reactor for syngas production. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2170–2176, 2016     

Partial oxidation of methane in hollow‐fiber membrane reactors based on alkaline‐earth metal‐free CO2‐tolerant oxide

The U‐shaped alkaline‐earth metal‐free CO₂‐stable oxide hollow‐fiber membranes based on (Pr_0.9La_0.1)₂(Ni_0.74Cu_0.21Ga_0.05)O_4+δ (PLNCG) are prepared by a phase‐inversion spinning process and applied successfully in the partial oxidation of methane (POM) to syngas. The effects of temperature, CH₄ concentration and flow rate of the feed air on CH₄ conversion, CO selectivity, H₂/CO ratio, and oxygen permeation flux through the PLNCG hollow‐fiber membrane are investigated in detail. The oxygen permeation flux arrives at approximately 10.5 mL/min cm² and the CO selectivity is higher than 99.5% with a CH₄ conversion of 97.0% and a H₂/CO ratio of 1.8 during 140 h steady operation. The spent hollow‐fiber membrane still maintains a dense microstructure and the Ruddlesden‐Popper K₂NiF₄‐type structure, which indicates that the U‐shaped alkaline‐earth metal‐free CO₂‐tolerant PLNCG hollow‐fiber membrane reactor can be steadily operated for POM to syngas with good performance. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3587–3595, 2014     

Catalytic Membrane Reactors – Chemical Upgrading and Pollution Control

This article presents an overview on oxygen permeation, oxidative activation of light hydrocarbons and splitting of various molecules (H₂O, N₂O, NO_x) containing oxygen in a hollow fiber catalytic membrane reactor made of BaCo_xFe_yZr_zO_3–δ (BCFZ, x+y+z = 1) which is used to separate oxygen from oxygen containing gases. Innovative reactor concepts are introduced and performances for the various applications are discussed. A detailed view is also given on the thermodynamic and kinetic background with regard to the above mentioned reactions. The potentials in terms of product intensification and energy saving by usage of the BCFZ hollow fibers as reaction vessels are evaluated. However, there are still technological challenges that prevent the described processes from being practiced on commercial scale by now.     

Dual‐layer PBI/P84 hollow fibers for pervaporation dehydration of acetone

Acetone dehydration via pervaporation is challenging, because acetone and water have close molecular sizes, and acetone has a much higher vapor pressure than water. Acetone is also a powerful solvent, which dissolves or swells most polymers. We have developed novel polybenzimidazole/BTDA‐TDI/MDI (PBI/P84) dual‐layer hollow fibers for pervaporation dehydration of acetone for industrial and biofuel separations. Both thermal and chemical crosslinking modifications were applied to the membranes to investigate their effectiveness to overcome acetone‐induced swelling. Thermal treatment can effectively enhance separation performance, but performance stability can only be achieved through the crosslinking modification of PBI. Crosslinking by p‐xylene dichloride followed by a thermal treatment above 250°C show significant effectiveness to improve and stabilize pervaporation performance. The fractional free volume of the PBI selective layer reduces from 3.27 to 1.98% and 1.33%, respectively, after thermal treatment and a combination of chemical/thermal crosslinking modifications characterized by positron annihilation spectroscopy. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

钙钛矿型混合导体透氧膜SrFe0.6Cu0.3Ti0.1O3－δ的制备与表征

Dense membrane with the composition of SrFe0.6Cu0.3Ti0.1O3-δ （SFCTO） was prepared by solid state reaction method. Oxygen permeation flux through this membrane was investigated at operating temperature ranging from 750℃ to 950℃ and different oxygen partial pressure. XRD measurements indicated that the compound was able to form single-phased perovskite structure in which part of Fe was replaced by Cu and Ti. The oxygen desorption and the reducibility of SFCTO powder were characterized by thermogravimetric analysis and temperature programmed reduction analysis, respectively. It was found that SFCTO had good structure stability under low oxygen pressure at high temperature. The addition of Ti increased the reduction temperature of Cu and Fe. Performance tests showed that the oxygen permeation flux through a 1.5 mm thick SFCTO membrane was 0.35-0.96 ml·min ^-1·cm^-2 under air/helium oxygen partial pressure gradient with activation energy of 53.2 kJ·mol^-1. The methane conversion of 85%, CO selectivity of 90% and comparatively higher oxygen permeation flux of 5 ml·min^-1·cm^- 2 were achieved at 850℃, when a SFCTO membrane reactor loaded with Ni-Ce/Al2O3 catalyst was applied for the partial oxidation of methane to syngas.     

Nano‐engineered nickel catalysts supported on 4‐channel α‐Al2O3 hollow fibers for dry reforming of methane

A nickel (Ni) nanoparticle catalyst, supported on 4‐channel α‐Al₂O₃ hollow fibers, was synthesized by atomic layer deposition (ALD). Highly dispersed Ni nanoparticles were successfully deposited on the outside surfaces and the inside porous structures of hollow fibers. The catalyst was employed to catalyze the dry reforming of methane (DRM) reaction and showed a methane reforming rate of 2040 Lh^?1gNi^?1 at 800°C. NiAl₂O₄ spinel was formed when Ni nanoparticles were deposited on alpha‐alumina substrates by ALD, which enhanced the Ni‐support interaction. Different cycles (two, five, and ten) of Al₂O₃ ALD films were applied on the Ni/hollow fiber catalysts to further improve the interaction between the Ni nanoparticles and the hollow fiber support. Both the catalyst activity and stability were improved with the deposition of Al₂O₃ ALD films. Among the Al₂O₃ ALD coated catalysts, the catalyst with five cycles of Al₂O₃ ALD showed the best performance. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2625–2631, 2018     

La0.6Sr0.4Co0.8Ga0.2O3‐δ (LSCG) hollow fiber membrane reactor: Partial oxidation of methane at medium temperature

In this study, La_0.6Sr_0.4Co_0.8Ga_0.2O_3‐δ (LSCG) hollow fiber membrane reactor was integrated with Ni/LaAlO₃‐Al₂O₃ catalyst for the catalytic partial oxidation of methane (POM) reaction. The process was successfully carried out in the medium temperature range (600–800°C) for reaction of blank POM with bare membrane, catalytic POM reaction and swept with H₂:CO gas mixture. For the catalytic POM reaction, enhancement in selectivity to H₂ and CO is obtained between 650–750°C when O₂:CH₄ <1. High CH₄ conversion of 97% is achieved at 750°C with corresponding H₂ and CO selectivity of about 74 and 91%. The oxygen flux of the membranes also increased with the increase in oxygen partial pressure gradient across the membrane. The postreacted membranes were tested via XRD and FESEM‐EDX for their crystallinity and surface morphology. XPS analysis was further used to investigate the O1s, Co 2p and Sr 3d binding energies of the segregated elements from the reducing reaction environment. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3874–3885, 2013     

Performance of mix‐impregnated CeO2‐Ni/YSZ Anodes for Direct Oxidation of Methane in Solid Oxide Fuel Cells

CeO₂‐Ni/YSZ anodes for methane direct oxidation were prepared by the vacuum mix‐impregnation method. By this method, NiO and CeO₂ are obtained from nitrate decomposition and high temperature sintering is avoided, which is different from the preparation of conventional Ni‐yttria‐stabilised zirconia(YSZ) anodes. Impregnating CeO₂ into the anode can improve the cell performance, especially, when CH₄ is used as fuel_. The investigation indicated that CeO₂‐Ni/YSZ anodes calcined at higher temperature exhibited better stability than those calcined at lower temperature. Under the testing temperature of 1,073 K, the anode calcined at 1,073 K exhibited the best performance. The maximum power density of a cell with a 10 wt.‐%CeO₂‐25 wt.‐%Ni anode calcined at 1,073 K reached 480 mW cm^–2 after running on CH₄ for 5 h. At the same time, high discharge current favoured cell operation on CH₄ when using these anodes. No obvious carbon was found on the CeO₂‐Ni anode after testing in CH₄ as revealed from SEM and corresponding linear EDS analysis. In addition, cell performance decreased at the beginning of discharge testing which was attributed to the anode microstructure change observed with SEM.     

Fick's First Law of Diffusion and Binary Gas Separation by Hollow‐Fiber Asymmetric Membrane

For calculating mass transfer through a hollow‐fiber asymmetric membrane, a fundamentally new theoretical method based on Fick's first law of diffusion is proposed. The main features of this method, and the ones currently used for the same purpose, have been compared. The current methods, also based on Fick's first law of diffusion, are shown to be theoretically less than adequate. Recommendations are given for the practical implementation of the new method.     

Two‐Dimensional Model for Oxidative Coupling of Methane in a Packed‐Bed Membrane Reactor

A two‐dimensional (2D) model of a packed‐bed membrane reactor was developed to describe ethylene production by oxidative coupling of methane (OCM). The model covers all relevant energy and mass transport processes in the reactor and allows a more precise prediction of the temperature and conversion patterns. It is demonstrated that the fast OCM reaction leads to oxygen depletion in the vicinity of the membrane, causing strong radial concentration gradients in the bed. Further results indicate that the detailed 2D model can provide more accurate predictions of experimental data than the simplified one.     

Effect of air gap on gas permeance/selectivity performance of BTDA‐TDI/MDI copolyimide hollow fiber membranes

Fabrication, morphology evaluation , and permeance/selectivity properties of three asymmetric BTDA‐TDI/MDI copolyimide hollow fiber membranes (HFM s ) are reported. The asymmetric HFM s were spun using the dry/wet phase inversion process. The effect of one of the major spinning parameters, the air gap, on the permeance/selectivity properties of the produced HFM was investigated. Scanning e lectron m icroscopy was used to evaluate the morphological characteristics and the macroscopic structure of the developed HFM. The permeance values of He, H₂, CH₄, CO₂, O₂, and N₂ gases were measured by the variable pressure method at different feed pressures and temperatures and the permselectivity coefficients were calculated. The higher selectivity values were evaluated for the Μ1 membrane and were found to be 49.33, 2.99, 5.13, 5.57 , and 9.61 for H₂/CH₄, O₂/N₂, CO₂/CH₄, CO₂/N₂ , and H₂/CO₂ gas mixtures , respectively. The selectivity experiments of H₂/CH₄, CO₂/CH₄ , and O₂/N₂ mixtures were performed at 25 ° C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4490–4499, 2013     

Catalytic partial oxidation of CH4 over bimetallic Ni‐Re/Al2O3: Kinetic determination for application in microreactor

The activity of a novel Ni‐Re/Al₂O₃ catalyst toward partial oxidation of methane was investigated in comparison with that of a precious‐metal Rh/Al₂O₃ catalyst. Reactions involving CH₄/O₂/Ar, CH₄/H₂O/Ar, CH₄/CO₂/Ar, CO/O₂/Ar, and H₂/O₂/Ar were performed to determine the kinetic expressions based on indirect partial oxidation scheme. A mathematical model comprising of Ergun equation as well as mass and energy balances with lumped indirect partial oxidation network was applied to obtain the kinetic parameters and then used to predict the reactant and product concentrations as well as temperature profiles within a fixed‐bed microreactor. H₂ and CO production as well as H₂/CO₂ and CO/CO₂ ratios from the reaction over Ni‐Re/Al₂O₃ catalyst were higher than those over Rh/Al₂O₃ catalyst. Simulation revealed that much smoother temperature profiles along the microreactor length were obtained when using Ni‐Re/Al₂O₃ catalyst. Steep hot‐spot temperature gradients, particularly at the entrance of the reactor, were, conversely, noted when using Rh/Al₂O₃ catalyst. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1691–1701, 2018     

Selective Production of C4 Hydrocarbons from Syngas Using Fe‐Co/ZrO2 and SO42—/ZrO2 Catalysts

Modified Fischer‐Tropsch (MFT) syntheses were carried out to convert synthesis gas to C₄ hydrocarbons over Fe‐Co/ZrO₂ (FT) and SO₄^2—/ZrO₂ (SZ) catalysts in a dual reactor system, keeping the FT to SZ catalysts ratio at 1:1.5. Five Fe‐Co/ZrO₂ catalysts with different Fe and Co loading, and SZ with 15 wt% SO₄^2— were prepared and extensively characterized using various physico‐chemical methods. The FT synthesis process was initially performed using a Fe‐Co/ZrO₂ catalyst in a single reactor and the effects of Fe and Co mass ratio, reaction temperature, space velocity on the production of C₄ hydrocarbons and C₂‐C₄ olefins were investigated. Results indicated that a 3.71% Fe—8.76% Co/ZrO₂ mixed oxide catalyst alone at 260°C and 5 h^—1 gave high selectivities of C₂‐C₄ olefins (～26.1 wt%) and total C₄ hydrocarbon product (～16.2 wt%). The MFT process 150°C gave higher C₄ (～31.6 wt%), isobutane (～22.9 wt%) and C₂‐C₄ (31.1 wt%) selectivities.