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Hydrogen Selectivity (hydrogen + selectivity)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Innentitelbild: Molecular Sieve Membrane: Supported Metal,Organic Framework with High Hydrogen Selectivity (Angew. Chem.

ANGEWANDTE CHEMIE, Issue 3 2010
3/2010)
Eine neue Kategorie von Molekularsieben umfasst Membranen, die sich von Metall-organischen Gerüsten ableiten. Wie Y. Li, J. Caro et,al. in der Zuschrift auf S.,558,ff. beschreiben, weist eine trägergestützte zeolithische Imidazolatgerüst(ZIF-7)-Membran eine hohe H2 -Selektivität auf, indem sie als Molekularsieb fungiert. Im Bild ist die Synthese der ZIF-7-Membran zu sehen, die Keimbildung an der Oberfläche und mikrowellengestützte Solvothermalsynthese einschließt. [source]

Molecular Sieve Membrane: Supported Metal,Organic Framework with High Hydrogen Selectivity,

ANGEWANDTE CHEMIE, Issue 3 2010
Yan-Shuo Li Prof.
Molekularer Seiher: Das ultramikroporöse zeolithische Imidazolatgerüst ZIF-7 wurde bezüglich seiner Eignung zur Gastrennung an Membranen untersucht. Dazu wurde es mithilfe von mikrowellengestütztem gezieltem Wachstum auf einen asymmetrischen Aluminiumoxidträger aufgebracht. Die erhaltene Membran war thermisch stabil und als Molekularsieb hoch H2 -selektiv. [source]

Pd,Ag membranes for auto-thermal ethanol reforming

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010
Silvano Tosti
Abstract The auto-thermal ethanol reforming was carried out at 200 kPa by a two-step process consisting of a traditional reformer operating at high temperature (700,740 °C) and a Pd,Ag multitube membrane module where the separation of hydrogen took place at 350,380 °C. The membrane module was a bundle of 11 thin-wall Pd,Ag tubes of wall thickness 50,60 µm, diameter 10 mm, and length 270 mm: permeation tests were performed at 300,395 °C with lumen pressure of 150,200 kPa, and nitrogen sweep flow rates in the shell side ranged from 10 to 30 l min,1 at atmospheric pressure. A hydrogen permeance Pe = 1.317 × 10,2 exp (,3.622 × 103/T(K)) mol m,2 s,1 Pa,0.5 was measured and complete hydrogen selectivity was verified. A water/ethanol mixture of molar ratio 2.50/1.00 was used as feed stream for carrying out ethanol reforming in the traditional fixed-bed reactor filled with a Ni on alumina catalyst. As a second step, the water gas shift (WGS) membrane reaction was carried out in the multitube membrane reactor: the Pd,Ag alloy of the membrane tubes worked for both catalyzing the reaction and for separating all the hydrogen produced in the reformer and in the membrane reactor itself. The hydrogen separated through the membrane was collected in the shell side of the membrane module: by operating with a water/ethanol feed flow rate of 200 g h,1, up to 1.2 l min,1 of pure hydrogen was produced. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Effect of surface defects in Pd-based membranes on the performance of a membrane reactor

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010
Alessio Caravella
Abstract In this work, the influence of superficial defects over the surface of a Pd-based membrane is analyzed in a membrane reactor for the methane steam-reforming process. In order to include the presence of defects in the permeation, a previous model of a defect-free Pd-based membrane reactor is extended and integrated to include a variable portion of area with defects in the form of pinholes. As a consequence, two different permeation mechanisms are taken into account, one through the Pd-based surface and the other one through the pinholes, where a Knudsen-like transport is considered to occur. The presence of the Knudsen transport causes the membrane separation factor between the hydrogen and the other species involved in the process to decrease, affecting the reactor performances significantly. Three reactor performance indices are investigated as functions of the fraction of the defected area and the mean pore diameter of defects, namely methane conversion, the hydrogen recovery factor, the hydrogen recovery yield and the net purity of hydrogen in the permeate. The results show that the hydrogen recovery factor is positively influenced by the decrease in hydrogen selectivity, whilst methane conversion and hydrogen net purity decrease significantly with it. On the contrary, regarding the hydrogen recovery yield, it is shown that in certain conditions (low furnace temperature, , 550 °C) it decreases with hydrogen selectivity. However, it increases again at higher furnace temperatures (,650 °C). Globally, this investigation helps in identifying acceptable defect levels on a Pd-based membrane for methane steam-reforming applications and highlights that even a very small defect level (in terms of the pinhole diameter and/or amount of the defected area) can importantly compromise the reactor performances. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Thermodynamic Equilibrium Calculations for the Reforming of Coke Oven Gas with Gasification Gas

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2007
B. Li
Abstract Thermodynamic analyses of the reforming of coke oven gas with gasification gas for syngas were investigated as a function of coke oven gas-to-gasification gas ratio (1,3), oxygen-to-methane ratio (0,1.56), pressure (25,35,bar) and temperature (700,1100,°C). Thermodynamic equilibrium results indicate that the operating temperature should be approximately 1100,°C and the oxygen-to-methane ratio should be approximately 0.39, where about 80,% CH4 and CO2 can be converted at 30,bar. Increasing the operating pressure shifts the equilibrium toward the reactants (CH4 and CO2); increasing the pressure from 25 to 35,bar decreases the conversion of CO2 from 73.7,% to 67.8,%. The conversion ratio of CO2 is less than that in the absence of O2. For a constant feed gas composition (7,% O2, 31,% gasification gas, and 62,% coke oven gas), a H2/CO ratio of about 2 occurs at temperatures of 950,°C and above. Pressure effects on the H2/CO ratio are negligible for temperatures greater than 750,°C. The steam produced has an effect on the hydrogen selectivity, but its mole fraction decreases with temperature; trace amounts of other secondary products are observed. [source]