1,721,219 research outputs found
Methanol steam reforming and ethanol steam reforming in membrane reactors: An experimental study
No full textIn this work a comparison between methanol steam reforming reaction (MSR) and ethanol steam reforming reaction (ESR) to produce hydrogen in membrane reactors (MRs) is discussed from an experimental point of view . Both reaction systems have been investigated by considering the influence of the membrane characteristics as well as the influence of the operating temperature. In the case of the dense membrane, the sweep gas flow rate and the different fluxes configurations have also been analysed. Experimental results, in terms of reactants conversion as well as hydrogen production and gases selectivity in MRs and in a traditional reactor (TR), are presented. The catalyst stability in both reaction systems was also tested
On the study of catalytic membrane reactor for water detritiation: Membrane characterization
No full textTritium waste recycling is a real economic and ecological issue. Generally under the non-valuable Q2O form (Q = H, D or T), waste can be converted into fuel Q2 for a fusion machine (e.g. JET, ITER) by isotope exchange reaction Q2O + H2 = H2O + Q2. Such a reaction is carried out over Ni-based catalyst bed packed in a thin wall hydrogen permselective membrane tube. This catalytic membrane reactor can achieve higher conversion ratios than conventional fixed bed reactors by selective removal of reaction product Q2 by the membrane according to Le Chatelier's Law. This paper presents some preliminary permeation tests performed on a catalytic membrane reactor. Permeabilities of pure hydrogen and deuterium as well as those of binary mixtures of hydrogen, deuterium and nitrogen have been estimated by measuring permeation fluxes at temperatures ranging from 573 to 673 K, and pressure differences up to 1.5 bar. Pure component global fluxes were linked to permeation coefficient by means of Sieverts' law. The thin membrane (150 μm), made of Pd-Ag alloy (23 wt.% Ag), showed good permeability and infinite selectivity toward protium and deuterium. Lower permeability values were obtained with mixtures containing non permeable gases highlighting the existence of gas phase resistance. The sensitivity of this concentration polarization phenomenon to the composition and the flow rate of the inlet was evaluated and fitted by a two-dimensional model. © 2013 Elsevier B.V. All rights reserved
Catalytic reforming of olive mill wastewater and methane in a Pd-membrane reactor
No full textOlive mill wastewater (OMW) is a biomass by-product of the olive oil industry. To treat this waste, reforming has been studied as a means of both producing hydrogen/syngas and reducing the pollution resulting from OMW. This study investigated a process in which OMW was added to methane and fed into a membrane reformer. The goal was to use the large water excess in OMW for reforming the methane. The results of the experiment showed that the combined reforming of methane and OMW is characterized by high hydrogen yields, with all the organic matter (the total organic carbon of both the OMW and the methane) reacting to produce hydrogen. Particularly, at 450°C and 500 kPa with a space velocity of 0.17 mol h-1 gCAT -1 and a steam-to-carbon ratio of 16.6, hydrogen yields around 45 g per 100 g of TOC fed were measured. This corresponds to the production of 12.3 kg of ultra-pure hydrogen per ton of treated OMW. Also, it was demonstrated that adding methane to OMW does not affect the ability of the reforming process to reduce the pollution from the wastewater. Finally, the optimum operating conditions of the membrane reformer were defined by analyzing the effect of the space velocity and steam-to-carbon ratio on hydrogen production. Copyright © 2016 Hydrogen Energy Publications, LLC
Membranes and membrane reactors for tritium separation
No full textMembrane technologies are being increasingly applied to the processes followed for separating hydrogen and its isotopes. In the fusion fuel cycle, the most important applications of the membranes for tritium purification and recovery are as follows: plasma exhaust treatment, tritium extraction from the breeding blanket and water detritiation. In this chapter, several kinds of membranes that are currently used for separating tritium are being described, with particular focus on the dense Pd-based membranes, which exhibit infinite selectivity to the hydrogen isotopes. In particular, the hydrogen/metal interaction, the hydrogen mass transfer mechanisms through metals and the related isotopic effects are being reported. Beside permeation, other chemical and physical properties of the commercial Pd-Ag alloy used for manufacturing the membrane permeators are being discussed with special regard to the membrane synthesis and the reactor module design. Finally, the process applications of the membrane devices used for the detritiation treatments in the fusion fuel cycle are also being presented. ©2013 Nova Science Publishers, Inc. All rights reserved
Surface effects and CO/CO2 influence in the H2 permeation through a Pd-Ag membrane: A comprehensive model
No full textThe 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. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
COx free hydrogen production through water-gas shift reaction in different hybrid multifunctional reactors
No full textHigh-purity H2 production from the water-gas shift (WGS) reaction was assessed. Since the WGS is limited by the equilibrium, different reactor types that allow to extract one or more products from the reaction medium, namely membrane reactor (MR; for H2 separation), sorption-enhanced reactor (SER; for CO2 capture) and sorption-enhanced membrane reactor (SEMR; for simultaneous CO2 and H2 removal), were used and compared with fixed-bed traditional reactor (TR). Experimental results were obtained with commercial materials, namely WGS Cu-based catalyst and K-doped hydrotalcite for CO2 capture. Additionally, in the MR and SEMR, a self-supported Pd-Ag membrane for separating H2 selectively from the reaction zone was used. Experimental tests were performed at different temperatures and pressures, and the results obtained were compared with those predicted by theoretical simulations at the thermodynamic equilibrium. Moreover, in the case of SER, different methods for the hydrotalcite regeneration and the evaluation of its working sorption capacity under cycling conditions were also assessed. Not all sorbed CO2 can be desorbed under dry conditions (pure nitrogen purging stream); however, if steam is used during the regeneration step, all sites can be effectively regenerated, allowing to have a stable working sorption capacity. Concerning the performance of the different hybrid reactors tested, i.e. MR, SER and SEMR, it was found that all are able of overcoming the TR limitations, with performances reaching conversion above the equilibrium for the feed composition. Nonetheless, only the SER and SEMR configurations allow to obtain high-purity H2 in all reactor exiting streams under the operating conditions herein assessed. © 2018 Elsevier B.V
Optimal Pt load of a Pt/La2O3·SiO2 highly selective WGS catalyst used in a Pd-membrane reactor
No full textDifferent catalytic tests were carried out in a tubular Pd-membrane reactor feeding a reformer outlet type stream with a molar composition of 40% H2, 40% H2O, 12% CO2 and 8% CO. They were performed between 673 and 723 K and at pressures ranging from 100 kPa to 800 kPa. At 723 K and 800 kPa, the CO conversion and H2 recovery values were 96% and 88%, respectively. A stability test including several start-up and shut-down cycles showed high stability of the Pt(0.1) catalyst.Pt(wt%)/La2O3(27)·SiO2 catalysts with wt% = 0.02 up to 1.2 were synthesized and tested in a conventional fixed-bed reactor. In differential mode, the Pt(0.1)/La2O3(27)·SiO2 catalyst showed higher activity per gram of Pt than the other solids. XPS showed the presence of only surface metallic platinum, in both the fresh and used Pt(0.1 wt%) formulation, which could be responsible for the high catalytic activity. At higher Pt loads both Ptδ+ and Pt° species were present at the surface. The presence of La2Si2O7 in all solids was detected by XRD. Graphitic carbon in the used catalysts was not detected through laser Raman spectroscopy
A novel procedure for the preliminary design of dense metal membrane modules for hydrogen separation
No full textThe paper introduces a procedure for the preliminary design and optimization of membrane modules made of dense metal permeator tubes for hydrogen separation from gas mixtures. Based on the mass transfer mechanisms of hydrogen into the metal lattice, the design procedure establishes the relationships among the dimensionless parameters related to the geometry (tube diameter, length and wall thickness) and the operating conditions (pressure, temperature, flow rates of feed and permeate streams, etc.). The concept of maximum hydrogen recovery and its dependence on pressure and dilution of feed stream is introduced and discussed. Similarly, the decrease of the driving force with the increase of the required hydrogen recovery factor is showed. The influence of the operative conditions on the minimum required tube wall thickness is also determined. Particularly, the operation at high temperature reduces significantly the Pd-alloy tensile strength thus increasing the minimum Pd-tube thickness. Finally, the model is applied to a case study of a Pd-membrane module separating ultra-pure hydrogen from a gas stream coming from the methane reforming. A sensitive analysis is carried out by using the expressions and the graphs of dimensionless parameters defined by the design procedure introduced in this paper. © 2016 Hydrogen Energy Publications LL
Production of hydrogen in a Pd-membrane reactor via catalytic reforming of olive mill wastewater
No full textOlive mill wastewater (OMW) contributes to environmental issues in Mediterranean regions because of its poor biodegradability and high phytotoxicity. Among the different processes proposed for the treatment of OMW, thermochemical treatments are advantageous as they can recover hydrogen-rich gas mixtures; thus, they can convert a waste into an energetic source. In this work, a noble metals based catalyst supported on rare earth mixed oxides was studied for its ability to reform OMW in a Pd-Ag tubular membrane reactor. The experimental results were compared with those obtained in a previous study using a Pt/Al2O3 catalyst. After filtration and concentration via distillation, OMW was treated in a Pd-Ag tube of thickness 0.143. mm, diameter 10. mm, and length 146. mm. The membrane tube was filled with 4.8. g of catalyst. The reaction tests were performed at 450. °C in the pressure range 100-500. kPa and demonstrated the capability of the membrane reactor to produce up to 3.25. kg of hydrogen per ton of OMW. Higher values of hydrogen recovery and hydrogen yield were measured at 500. kPa when the hydrogen permeated in the shell side was up to 80% of all the hydrogen produced and about 35. wt% of the total organic carbon (TOC) fed. Investigation of carbon formation showed that only 1.2% of the fed carbon was responsible for coke formation by demonstrating that the new catalyst, although tested at low temperature, was effective to limit this phenomenon. When compared to the commercial Pt-based catalyst, the new catalyst exhibited higher selectivity toward the reforming reaction, allowing it to significantly reduce the formation of methane and coke; thus, it exhibited higher hydrogen yield and greater durability. © 2015 Elsevier B.V
Enhancing the low temperature water-gas shift reaction through a hybrid sorption-enhanced membrane reactor for high-purity hydrogen production
No full text(Figure Presented). The low temperature water-gas-shift reaction (LT-WGS) has been assessed by means of a hybrid sorption-enhanced membrane reactor (HSEMR) that combines both CO2 and H2 removal from the reaction zone. The performance of this reactor has been compared with that obtained by (i) a traditional and (ii) a sorption-enhanced (only CO2 is removed) reactor operating in the same operational conditions. Cu/ZnO-Al2O3 and K2CO3-promoted hydrotalcite materials have been used as a catalyst and CO2 sorbent, respectively. A self-supported Pd-Ag membrane tube has been used in order to selectively separate the H2. The CO2 sorption capacity, in the presence and absence of water vapour, of the potassium-promoted hydrotalcite has been determined by means of breakthrough experiments. The presence of water vapour enhanced the sorption capacity of the hydrotalcite in the experimental conditions used. Concerning the performance of the HSERM, results clearly show that when both CO2 and H2 are removed from the reaction zone, the hydrogen production through the reversible LT-WGS reaction is enhanced compared to either a traditional or a sorption-enhanced reactor, allowing overcoming equilibrium limitations and obtain a pure H2 stream. © 2015 Elsevier Ltd. All rights reserved
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