Abstract:A mathematical modelling of one-dimensional, stationary and isothermic membrane reactor for methane steam reforming was developed to compare the maximum yield for methane conversion in this reactor with that in a conventional fixed-bed reactor. Fick's first law was used to describe the mechanism of hydrogen permeation. The variables studied include: reaction temperature, hydrogen feed flow rate and membrane thickness. The results show that the membrane reactor presents a higher methane conversion yield than th… Show more
“…The use of hydrogen as a clean energy vector is every day more recurrent: combustion of hydrogen results in water and, particularly, its environmental impact is very limited when produced from renewables [3][4][5]. Currently, the principal source of hydrogen is the reforming of hydrocarbons, mainly methane [6]. As a result of the methane steam reforming some compounds like CO, CO2, H2O, etc.…”
The permeability of a 0.175 mm thick Pd-Ag tubular membrane to pure H2 and binary mixtures of H2/CO or H2/CO2 was studied. The tests were performed in a wide range of temperature (523-723 K) and pressure (200-800 kPa).Pure H2-permeation through a dense metal membrane is described by the Sieverts' law. However, it was already found that the H2 permeation does not follow the Sieverts' law when other components are present in the feed and namely CO or CO2. In this work, it is proposed a new permeation model based on the Sieverts' law considering: i) the mass transfer resistance due to the surface effects and ii) the barrier effect due to the presence of either CO or CO2. The model was successfully validated against experimental data of hydrogen permeation for binary (H2/CO and H2/CO2) experiments for every working temperature and pressure.
“…The use of hydrogen as a clean energy vector is every day more recurrent: combustion of hydrogen results in water and, particularly, its environmental impact is very limited when produced from renewables [3][4][5]. Currently, the principal source of hydrogen is the reforming of hydrocarbons, mainly methane [6]. As a result of the methane steam reforming some compounds like CO, CO2, H2O, etc.…”
The permeability of a 0.175 mm thick Pd-Ag tubular membrane to pure H2 and binary mixtures of H2/CO or H2/CO2 was studied. The tests were performed in a wide range of temperature (523-723 K) and pressure (200-800 kPa).Pure H2-permeation through a dense metal membrane is described by the Sieverts' law. However, it was already found that the H2 permeation does not follow the Sieverts' law when other components are present in the feed and namely CO or CO2. In this work, it is proposed a new permeation model based on the Sieverts' law considering: i) the mass transfer resistance due to the surface effects and ii) the barrier effect due to the presence of either CO or CO2. The model was successfully validated against experimental data of hydrogen permeation for binary (H2/CO and H2/CO2) experiments for every working temperature and pressure.
“…Membrane microreactors are an important class of microreactors that combine reaction and separation in one single device. Thus, for example, a thin palladium membrane can be included which separates hydrogen from the reformate gas mixture (Alfadhel and Kothare, 2005;Assaf et al, 1998;Karnik et al, 2003). Assaf et al (1998) modeled the methane steam reforming in an isothermal membrane reactor and concluded that the membrane reactor, besides providing purified hydrogen still presents a higher methane conversion yield than the conventional fixed-bed reactor.…”
Section: Microreactorsmentioning
confidence: 99%
“…Thus, for example, a thin palladium membrane can be included which separates hydrogen from the reformate gas mixture (Alfadhel and Kothare, 2005;Assaf et al, 1998;Karnik et al, 2003). Assaf et al (1998) modeled the methane steam reforming in an isothermal membrane reactor and concluded that the membrane reactor, besides providing purified hydrogen still presents a higher methane conversion yield than the conventional fixed-bed reactor. This work presents a two-dimensional mathematical model of an isothermal membrane microreactor operating under steady-state conditions for use as a source of pure hydrogen for a PEM fuel cell from ethanol steam reforming catalyzed by Ni/Al 2 O 3 .…”
-Microreactors are miniaturized chemical reaction systems, which contain reaction channels with characteristic dimensions in the range of 10-500 μm. One possible application for microreactors is the conversion of ethanol to hydrogen used in fuel cells to generate electricity. In this paper a rigorous isothermal, steady-state two-dimensional model was developed to simulate the behavior of a membrane microreactor based on the hydrogen yield from ethanol steam reforming. Furthermore, this membrane microreactor is compared to a membraneless microreactor. A potential advantage of the membrane microreactor is the fact that both ethanol steam reforming and the separation of hydrogen by a permselective membrane occur in one single microdevice. The simulation results for steam reforming yields are in agreement with experimental data found in the literature. The results show that the membrane microreactorpermits a hydrogen yield of up to 0.833 which is more than twice that generated by the membraneless reactor. More than 80% of the generated hydrogen permeates through the membrane and, due to its high selectivity, the membrane microreactor delivers high-purity hydrogen to the fuel cell.
“…The development of oxygen permeable membranes has opened up a new possibility to enhance the partial oxidation of methane process. New improvements are been done in membrane materials and structures, which supports the selective compound in porous alumina, porous ceramic substrate, and in nanostructured carbides, and several works suggests the oxygen-permeating dense membranes have potential applications in partial oxidation of methane (Balachandran et al, 1997;Tsai et al, 1997;Kao et al, 1997).…”
Section: Introductionmentioning
confidence: 99%
“…The modeling and simulation of catalytic membrane reactors for methane conversion to syngas has been done by some authors, specially on steam reforming of methane and oxidative coupling of methane (Shu et al, 1994;Wang and Lin, 1995;Kao et al, 1997;Assaf et al, 1998;Chen et al, 2003;Lin et al, 2003;Gallucci et al, 2004). Very few works have dealt with partial oxidation of methane in membrane reactors (Tsai et al, 1997;Jin et al, 2000) and none dealing with the production of syngas for gas-to-liquid (GTL) processes.…”
Partial oxidation of methane is one of the most important chemical processes for the production of syngas. In recent years, the abundant availability of natural gas and the increasing demand of hydrogen have led to high interest to further develop this process increasing the yield of syngas. In this work the partial oxidation of methane was studied from a modeling point of view in a membrane reactor and in a conventional reactor. A mathematical model of a membrane reactor used for partial oxidation of methane, assuming steadystate conditions, was developed to simulate and compare the maximum yields and operating conditions in the reactor with that in a conventional reactor. Simulation results show that different parameters affect methane conversion and H /CO ratio, such as temperature, operating conditions, and membrane 2 parameters such as membrane permeance. In a membrane reactor an increase in the operating pressure corresponds to an increase in methane conversion, since allows for a greater partial pressure gradient between the reaction and permeate zone, thus contributing to shift the equilibrium towards the products. As such, the membrane reactors are a good alternative to produce syngas especially for GTL processes. Operating conditions can be set to control the H2/CO ratio to a desired value, and high conversions at mild temperatures can be achieved reducing capital and operational costs.
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