Methanol synthesis from CO2 using a silicone rubber/ceramic composite membrane reactor

A one-dimensional isothermal pseudo-homogeneous parallel flow model was developed for the methanol synthesis from CO2 in a silicone rubber/ceramic composite membrane reactor. The fourth-order Runge-Kutta method was adopted to simulate the process behaviors in the membrane reactor. How those parameters affect the reaction behaviors in the membrane reactor, such as Damkohler number Da, pressure ratio p(r), reaction temperature T, membrane separation factor alpha, membrane permeation parameter phi , as well as the non-uniform parameter of membrane permeation L-1, were discussed in detail. Parts of the theoretical results were tested and verified; the experimental results showed that the conversion of the main reaction in the membrane reactor increased by 22% against traditional fixed bed reactor, and the optimal non-uniform parameter of membrane permeation rate, L-1.opt ,does exist. (C) 2003 Elsevier B.V All rights reserved.

The effect of methanol and ethanol cross-over on the performance of PtRu/C-based anode DAFCs

In the present work, the cross-over rates of methanol and ethanol, respectively, through Nafion(R)-115 membranes at different temperatures and different concentrations have been measured and compared. The changes of Nafion(R)-115 membrane porosity in the presence of methanol or ethanol aqueous solutions were also determined by weighing vacuum-dried and alcohol solution-equilibrated membranes. The techniques of anode polarization and adsorption stripping voltarnmetry were applied to compare the electrochemical activity and adsorption ability, respectively. To investigate the consequences of methanol and ethanol permeation from the anode to the cathode on the performance of direct alcohol fuel cells (DAFCs), single DAFC tests, with methanol or ethanol as the fuel, have been carried out and the corresponding anode and cathode polarizations versus dynamic hydrogen electrode (DHE) were also performed. The effect of alcohol concentration on the performance of PtRu/C anode-based DAFCs was investigated.

Synthesis of NaA zeolite membrane on a ceramic hollow fiber

NaA zeolite membrane was successfully synthesized on a ceramic hollow fiber with an outer diameter of 400 mum, a thickness of 100 mum and an average pore radius of 0.1 mum. The as-synthesized membranes were characterized by XRD, SEM as well as gas permeation. A continuous C NaA zeolite membrane formed after a three-stage synthesis. The membrane thickness was similar to5 mum. Gas permeation data indicated that a relatively high quality NaA zeolite membrane formed on the ceramic hollow fiber support. (C) 2003 Elsevier B.V. All rights reserved.

Influence of drying method on morphology and properties of asymmetric cellulose hollow fiber membrane

Using a dry/wet spinning process, asymmetric cellulose hollow fiber membranes (CHFM) were prepared from a dope composed of cellulose/N-methylmorpholine-N-oxide/water. The formation mechanism for the finger-like macrovoids at the inner portion of as-spun fibers was explained. Naturally drying and three solvent exchange drying methods were tried to investigate their influence on morphology and properties of CHFM. It was found that the ethanol-hexane exchange drying was an appropriate method to minimize morphology change of the as-spun CHFM, whereas the naturally drying caused the greatest shrinkage of the fibers that made the porous membrane become dense. The result, CHFM from ethanol-hexane exchange drying performed the highest gas permeation rate but gas permeation of the naturally dried membrane could not be detectable. The resultant CHFM from the ethanol-hexane exchange drying also showed acceptable, mechanical properties, thus it was proposed to be an appropriate method for gas separation purpose. The experimental results supported the proposed drying mechanism of CHFM. The free water would evaporate or be replaced by a solvent that subsequently would evaporate but the bonded water would remain in the membrane. What dominated the changes of membrane morphology during drying should be. the molecular affinities of cellulose-water, water-solvent and solvent-solvent. (C) 2004 Elsevier B.V. All rights reserved.

Catalytic partial oxidation of gasoline to syngas in a dense membrane reactor

In our previous work, it was shown that LiLaNiO/gamma-Al2O3 was an excellent catalyst for partial oxidation of heptane to syngas in a fixed-bed reactor at high temperature and the selectivity of CO was about 93%. However, pure oxygen was used as the oxidant. We have developed a dense oxygen permeation membrane Ba0.5Sr0.5Co0.8Fe0.2O3 that can supply pure oxygen for the reaction. In this work, the membrane was combined with the catalyst LiLaNiO/gamma-Al2O3 in one rector for the partial oxidation of heptane that is typical component of gasoline. A good performance of the membrane reactor has been obtained, with 100% n-heptane conversion and >94% hydrogen selectivity at the optimized reaction conditions. (C) 2004 Elsevier B.V. All rights reserved.

Microwave-assisted hydrothermal synthesis of hydroxy-sodalite zeolite membrane

A high quality pure hydroxy-sodalite zeolite membrane was successfully synthesized on an alpha-Al2O3 support by a novel microwave-assisted hydrothermal synthesis (MARS) method. Influence of synthesis conditions, such as synthesis time, synthesis procedure, etc., on the formation of hydroxy-sodalite zeolite membrane by MAHS method was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas permeation measurements. The synthesis of hydroxy-sodalite zeolite membrane by MAHS method only needed 45 min and synthesis was more than 8 times faster than by the conventional hydrothermal synthesis (CHS) method. A pure hydroxy-sodalite zeolite membrane was easily synthesized by MAHS method, while a zeolite membrane, which consisted of NaX zeolite, NaA zeolite and hydroxy-sodalite zeolite, was usually synthesized by CHS method. The effect of preparation procedures had a dramatic impact on the formation of hydroxy-sodalite zeolite membrane and a single-stage synthesis procedure produced a pure hydroxy-sodalite zeolite membrane. The pure hydroxy-sodalite zeolite membrane synthesized by MARS method was found to be well inter-grown and the thickness of the membrane was 6-7 mum. Gas permeation results showed that the hydrogen/n-butane permselectivity of the hydroxy-sodalite zeolite membrane was larger than 1000. (C) 2004 Elsevier Inc. All rights reserved.

Structure and oxygen permeability of a dual-phase membrane

The dual-phase membrane of La0.15Sr0.85Ga0.3Fe0.7O3-delta-Ba0.5Sr0.5Fe0.2Co0.8O3-delta (LSGF-BSCF) was prepared successfully. This membrane was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe micro-analyzer (EPMA). This membrane has a dense dual-phase structure: LSGF being the dense body of this membrane and BSCF as another phase running along the LSGF body. This structure is favorable for the oxygen permeation through the membrane. The oxygen permeation test shows that the oxygen permeation flux of LSGF-BSCF membrane (Jo(2) = 0.45 ml/min cm(2), at 915 degreesC) is much higher than that of LSGF membrane (Jo(2) = 0.05 ml/min cm(2)). Thickness dependence of oxygen permeation indicates that the oxygen permeation is controlled by the bulk diffusion. Compared to pure BSCF the dual-phase membrane of LSGF-BSCF is stable in reducing atmosphere. (C) 2003 Elsevier B.V. All rights reserved.

Gas permeability of a novel cellulose membrane

A novel cellulose membrane was prepared by using amine oxides as the solvent and its mechanical performance was measured. Steady-state permeation rates of carbon dioxide, hydrogen, methane, nitrogen, oxygen, argon and helium in the homogeneous dense cellulose membrane were measured in the temperature range of 298-353 K and under gas pressures up to 1 MPa. The effect of swelling on hydrophilic membrane permeability was studied in some detail on the cellulose membrane. The difference in gas permeability between the "dry" cellulose membrane and the "water-swollen" cellulose membrane was investigated, and the gas permeability between the cellulose membrane and the Cellophane was compared. In this paper, the separation performance Of CO2 over H-2 in a "water-swollen" cellulose membrane is reported for the first time and the separation factor Of CO2/H-2 can be up to 15. (C) 2002 Elsevier Science B.V. All rights reserved.

Anodic Stripping Voltammetry at Bismuth-Coated and Uncoated Carbon Microdisk Electrodes:Application to Trace Metals Analysis in Flood Samples

This article reports on the performance of a bismuth-coated carbon microdisk electrode (BiFμE) for the determination of trace heavy metals by anodic stripping voltammetry (ASV). The BiFμE was prepared by electrodeposition of a metallic bismuth film onto the microdisk, by applying an in-situ electroplating procedure. To test the performance of the BiFμE, ASV measurements were performed on synthetic solutions containing Cd2+, Pb2+, and Cu2+ as target ions. The results indicated that cadmium and lead gave well-defined ASV peaks with no interference, and their quantitative determination could be carried out straightforwardly. In particular, linear calibration curves over the range 5.0 x 10-8-1.0 x 10-6M for both ions, and detection limits of 7.8 and 2.9 nM, for cadmium and lead, respectively, after applying a 60 sec preconcentration step, were obtained. The reproducibility was also satisfactory, the relative standard deviation (RSD) being within 2.5% for both ions. Copper, instead, gave an ASV response that. in most experimental conditions, overlapped with that of bismuth. This circumstance made the determination of copper at the BiFμE difficult. Since the latter element could be detected reliably at the uncoated carbon microdisk electrode (CμE), both BiFμE and CμE were employed, respectively, for the determination of lead and copper ions in drinking water, wine, and tomato sauce.

Synthesis and Aqueous Solution Properties of Hydrophobically Modified Anionic Acrylamide Copolymers

In this investigation, hydrophobically modified polyacrylamide with low amounts of anionic long-chain alkyl was synthesized by the free radical polymerization in deionized water. This water-soluble copolymerization method is more convenient compared with the traditional micellar copolymerization methods. The copolymers were characterized using Fourier transform infrared, H-1 NMR, and the molecular weight and polydispersity were determined using gel permeation chromatography. The solution behavior of the copolymers was studied as a function of composition, pH, and added electrolytes. As NaCl was added to solutions of AM/C(11)AM copolymers or pH was lowered, the shielding or elimination of electrostatic repulsions between carboxylate groups of the C(11)AM unit lead to coil shrinkage.

Novel thin-film composite membranes with improved water flux from sulfonated cardo poly(arylene ether sulfone) bearing pendant amino groups

A new class of polymeric amine, namely, sulfonated cardo poly(arylene ether sulfone) (SPES-NH2) was synthesized and used for the preparation of thin-film composite membrane. The TFC membranes were prepared on a polysulfone supporting film through interfacial polymerization with trimesoyl chloride (TMC) solutions and amine solutions containing SPES-NH2 and m-phenylenediamine (MPDA). The resultant membranes were characterized with water permeation performance, chemical structure, hydrophilicity of active layer and membrane morphology including top surface and cross-section.

Formation of reversible shell cross-linked micelles from the biodegradable amphiphilic diblock copolymer poly(L-cysteine)-block-poly(L-lactide)

A novel biodegradable diblock copolymer, poly(L-cysteine)-b-Poly(L-lactide) (PLC-b-PLLA), was synthesized by ring-opening polymerization (ROP) of N-carboxyanhydride of beta-benzyloxycarbonyl-L-Cysteine (ZLC-NCA) with amino-terminated Poly(L-lactide) (NH2-PLLA) as a macroinitiator in a convenient way. The diblock copolymer and its precursor were characterized by H-1 NMR, Fourier transform infrared (FT-IR), gel permeation chromatography (GPC), and X-ray photoelectron spectroscopy (XPS) measurements. The length of each block polymer could be tailored by molecular design and the ratios of feeding monomers.

Effect of Copolymerization Time on the Microstructure and Properties of Polypropylene/Poly(ethylene-co-propylene) In-Reactor Alloys

Three Polypropylene/Poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys produced by a two-stage slurry/gas polymerization had different ethylene contents and mechanical properties, which were achieved by controlling the copolymerization time. The three alloys were fractionated into five fractions via temperature rising dissolution fractionation (TRDF), respectively. The chain structures of the whole samples and their fractions were analyzed using high-temperature gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), C-13 nuclear magnetic resonance (C-13 NMR), and differential scanning calorimetry (DSC) techniques. These three in-reactor alloys mainly contained four portions: ethylenepropylene random copolymer (EPR), ethylene-propylene (EP) segmented and block copolymers, and propylene homopolymer. The increased copolymerization time caused the increased ethylene content of the sample. The weight percent of EPR, EP segmented and block copolymer also became higher.

Macrocycle-Terminated Core-Cross-Linked Star Polymers: Synthesis and Characterization

We have synthesized macrocyclic polystyrene- (PS-) terminated PS star polymers via a core-cross-linking approach in this work. A tadpole-shaped macrocyclic PS-linear-PS copolymer was synthesized at first via click chemistry and ATRP polymerization method. The "living" ATRP initiating chain-ends of the tadpole-shaped copolymers were linked together via ATRP polymerization with divinylbenzene to form a core-cross-linked macrocyclic star polymer. The number of arms attached to the macrocyclic star polymers was measured with NMR. and absolute molecular weights with gel permeation chromatography (GPC) with multiangle laser light scattering detector. These macrocyclic star polymers had a highly cross-linked core and many radiating arms. The shorter tadpole-shaped precursors caused core-cross-linked star polymers with higher molecular weights and more arm numbers. The macrocycle-terminated core-cross-linked star polymers showed two glass transition temperatures, one arising from the linear branches and another from the macrocycles.

A Novel Strategy to Branched Polyacrylonitrile Via One-Pot RAFT Copolymerization of Acrylonitrile and an Asymmetrical Divinyl Monomer

Branched polyacrylonitriles were prepared via the one-pot radical copolymerization of acrylonitirle and an asymmetric divinyl monomer (allyl methacrylate) that possesses both a higher reactive methacrylate and a lower reactive allyl. RAFT technique was used to keep a low-propagation chain concentration via a fast reversible chain transfer euilibration and thus the cross-linking was prevented until a high level of monomer conversions. This novel strategy was demonstrated to engenerate a branched architecture with abundant pendant functional vinyl and nitrile groups, and controlled molecular weight as a behavior of controlled/living radical polymerization characteristics. The effect of the various experimental parameters, including temperature, brancher to monomer molar ratio, and chain transfer agent to initiator molar ratio, on the control Of moleculer dimension (molecular weight and polydispersity indices) and the degree of branching were investigated in detail. Moreover, H-1 NMR and gel permeation chromatography confirm the branched architecture of the resultant polymer. The intrinsic viscosity of the copolymer is also lower than the linear counterpart.