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A micro-structured 5kW complete fuel processor for iso-octane as hydrogen supply system for mobile auxiliary power units: Part II—Development of water–gas shift and preferential oxidation catalysts reactors and assembly of the fuel processor
Abstract
Microstructured reactors for water–gas shift and the preferential oxidation of carbon monoxide were developed for a fuel processing/fuel cell system running on iso-octane and designed for an electrical power output of 5 kWel. The target application was an automotive auxiliary power unit (APU). The work covered both catalyst and reactor development. A platinum/ceria catalyst was applied for water–gas shift, while platinum on zeolite/alumina carrier served as catalyst for preferential oxidation. These catalysts were introduced into the final full size prototype reactors, which were constructed from microstructured stainless steel foils. Testing in a pilot scale test rig revealed conversion close to the thermodynamic equilibrium for the water–gas shift reactors at a WHSV range of 17–41 Ndm3/(h gcat). The preferential oxidation, which was performed at higher WHSV in the range of 48–98 Ndm3/(h gcat) revealed up to 90% conversion in a first stage, while in the second stage reactor the carbon monoxide content of the reformate was decreased to less than 50 ppm. The reactors were then incorporated into a complete bread-board fuel processor of 5 kWel power equivalent, which comprised also of an autothermal reformer reactor. The fuel processor was operated at a steam to carbon ratio of 3.3 and an oxygen to carbon ratio of 0.67. Under these conditions, it converted the iso-octane feed completely to purified reformate with an overall efficiency of 74%.
... Moreover, the water produced in the PEM-FC stack can be used in other items of the APU [13]. APUs can be used for mobile applications (trucks, recreational vehicles, and marine leisure), as well for stationary ones (power supply to antennas in remote locations as Uninterruptible Power Supply (UPS) units) [10,[13][14][15][16][17][18][19][20]. ...
... The complexity of a fuel-cell-based APUs is liable of the actual general situation: in the open literature there are not experimental validations of the whole apparatus, but at least of the fuel processing section [14][15][16]28,30], most of the time realized with heavy governmental grants [61]. Various companies, investing money and resources, are working on the development of reliable APUs to enter the selling markets (see the EU situation in [10], and [30]), but they are slowed down by technical and economic difficulties (in the EU area only one company possesses a marketable apparatus [10]). ...
... An overall APU power of 5 kW e net is assumed. Typical requirements of the APUs for trucks and passengers vehicles are, in fact, based on the delivery of 5 kW e net [14,15,[77][78][79][80][81][82][83][84][85][86]. ...
... However, of interest is the advantage that a declining temperature gradient along microchannels could pose for an exothermic reaction such as water-gas shift [55,56] or CO 2 methanation [51,52]. Typically, the majority of reactants are converted in the high temperature region, while the lower temperature near the reactor outlet acts as a conditioning stage to reach favourable conversions (improved equilibrium) [51,54,57,58]. A similar observation was made by Kolios et al. [59,60], in which the lower downstream temperature was utilised as a water-gas shift stage to condition methanol steam reforming products. ...
... The addition of gas diffusers to the inlet and outlet sections of microchannel reactors will provide improved subdivision of the feed gas to the microchannels [57]. ...
The thermal coupling of endothermic and exothermic reactions is an important pathway for integrated thermal management within chemical reactors, which supports process intensification. Microchannel reactors are unique in the sense that they provide various design and operational characteristics that benefit high throughput and millisecond contact time chemical conversions. These include high microchannel aspect ratios, improved heat transfer (via thin and thermally conductive reactor substrates), and enhanced mass transfer (due to limited diffusional effects). In this review of experimental and simulated microchannel reactors, focus is put on improved designs and operating strategies to support thermal conduction across microchannel walls, yet keep chemical products from the respective reactions separate using spatially-segregated reaction chambers. Three common flow configurations (counter-current, co-current and cross-flow designs) are critically discussed as a result of their abilities to distribute ‒ and in some cases recirculate ‒ reaction heat, the steady-state temperature profiles established within them as a result of flow direction, and reactant conversions/product yields as a result of their thermal characteristics. Special attention is devoted to microchannel design aspects, including wall thermal conductivity, channel dimensions, catalyst positioning and other design strategies (distribution manifolds and heat recirculative reactor designs) to improve heat and mass flows within microchannel reactors.
... The platinum has been widely employed in reforming processes. It is a well-known active metal for reactions involving oxidation processes like water gas-shift (WGS) [4,5] and also catalyzes in a very effective way feeds containing oxygen, like partial oxidation of methane (POM) [6][7][8]. In addition, Pt is widely employed in SR and dry reforming (DR) as summarized in [9]. ...
... Prior to start with the experiments, a sensitivity analysis was carried out using Aspen Plus software in order to determine the most appropriate O 2 /CH 4 and S/C feed ratios (vol%) to obtain the highest hydrogen yield, at a constant CH 4 /CO 2 ratio of 1.5 (vol%) [4]. Based on the results of this study, Fig. 3, it was concluded that the ratios of O 2 / CH 4 = 0.25 and S/C = 1.0 are the most suitable ones, which is in good agreement with previous investigation of the authors [27]. ...
In this work, Pt based mono and bimetallic catalysts were tested under conditions of tri-reforming (TR). All the catalysts contained 25% of CeO2 and a metal loading of 2.5 or 5.0% (wt%). The bimetallic catalysts contained 2.5% Pt and 2.5% of Me, where Me = Ni, Co, Mo, Pd, Fe, Re, Y, Cu or Zn. For all the experiments, a synthetic biogas which consisted of 60% CH4 and 40% CO2 (vol.) was mixed with water, S/C = 1.0, and oxygen, O2/CH4 = 0.25, and fed to a fixed bed reactor (FBR) system or a microreactor. The 2.5Pt catalyst was used in order to compare the performance of each reaction system. The tests were performed at reaction temperatures between 700 and 800 °C, and at volume hourly space velocities (VHSV) between 100 LN/(h gcat) and 200 LN/(h gcat) for the FBR system and between 1000 LN/(h gcat) and 2000 LN/(h gcat) for the microreactor, at atmospheric pressure. Then, all catalysts were deposited into microchannel reactors and tested at a constant VHSV of 2000 LN/(h gcat) and reaction temperatures between 700 and 800 °C. Catalysts under investigation were characterized applying the following techniques: inductively coupled plasma optical emission spectroscopy (ICP-OES), N2 Physisorption, Temperature Programmed Reduction (TPR), CO chemisorption, Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). The microreactor was identified as the most efficient and promising reaction system, and the 2.5(Pt–Pd) catalyst as the bimetallic formulation with the highest activity. Therefore its activity and stability was compared with the reference 5.0Pt catalyst at 700 °C and VHSV of 2000 LN/(h gcat) for more than 100 h. Although slightly lower activity was measured operating with the 2.5(Pt–Pd) catalyst, a significant reduction of the Pt content compared to the reference 5.0Pt catalyst was achieved through the incorporation of Pd.
... Miniaturization of chemical reactors has become an object of extensive research in the fields of chemistry, biochemistry, science of nanomaterials, nanotechnology etc. [1]. Recently, microchannel reactors (MCR) that have a large number of parallel submillimeter channels, slots or membranes [2] were successfully applied in hydrogen energetics, in autothermal conversion of heavy hydrocarbons [3], in partial oxidation of methane [4], in organic synthesis [5], and in other industrially important processes [6][7][8][9][10]. ...
... BET surface 8 m 2 /g) was used in the experiments. Initially, the catalyst was in the form of rings 5 Â 2.5 Â 5 mm (outer dia., inner dia., height), then the catalyst pellets were crushed and sieved to the fractures d p = 0.15-0.25 mm, bulk density c = 1.07 g/cm 3 . The ratio of the channel diameter to the average diameter of the catalyst fracture was ID c /d p % 5. ...
... An integrated reactor is needed to convert the liquid propellant, such as hydrogen peroxide and methyl naphthalene, to the gas phase. Bubble generation and flow-pattern evolution of gas-liquid two-phase flows have been investigated in these gas releasing microreactors, in order to achieve high conversion and production stability [10][11][12][13]. Especially, surface catalytic reactions that release oxygen like the H 2 O 2 decomposition encounter a tricky problem. ...
Novel micro-scale reaction devices are progressing in various applications. Whereas, specialized gas-producing reactors of high conversion at micro/mini scale remain challenging and are rarely explored, but are needed urgently in new generation vehicles and aerospace applications. In this work, two kinds of high-aspect-ratio flat channel (200 μm depth, 5.0 mm width, and 40.0 mm length) microreactors with platinum foil catalyst, named as inlet reactors and outlet reactors, are designed and tested for H2O2 decomposition. The wavelet transform method is applied to analyze the effects of reactant flow rate and pin–fin configuration on flow instability in both the time domain and the frequency domain. The inlet reactors utilize periodic flow pattern transitions to achieve an independence of conversion on reactant flow rate. For outlet reactors, the upstream compressible slug volume and the backflow are restricted by the pin–fin array, and thus the H2O2 decomposition reaches a conversion of 59.0% at 5 ml/h reactant flow rate. This conversion is 300% higher than those of H2O2 decomposition in microchannel reactors ever reported in the literature. The results from this work can be used for the design and manufacturing of micro-scale reactors for gas involved applications.
... For all catalysts, an increase of both CH 4 and CO 2 conversions with temperature is observed, in accordance with the endothermic behavior of the DRM reaction. A slightly higher CO 2 than CH 4 conversion is also depicted over the entire temperature range accounting for some but limited occurrence of RWGS (Reverse Water Gas Shift) that consumes CO 2 and increases its conversion level 37,38 . ...
A catalyst made of Ni 0 nanoparticles highly dispersed on a lamellar alumina support was prepared by an environmentally-friendly route. The latter involved the synthesis of an aluminum-containing metal-organic framework (MOF) MIL-53(Al) in which the linkers were derived from the depolymerization of polyethylene terephthalate (PET) originating from plastic wastes. After demonstrating the purity and structure integrity of the PET-derived MIL-53(Al), this MOF was impregnated with nickel nitrate salt and then calcined to form a lamellar Ni-Al 2 O 3 mixed metal oxide with a high surface area (S BET = 1276 m 2 g-1 , N 2 sorption). This mixed oxide consisted of nickel aluminate nanodomains dispersed within amorphous alumina, as revealed by PXRD and TPR analyses. Subsequent reduction under H 2 resulted in the formation of well-dispersed 5 nm Ni 0 nanoparticles homogeneously occluded within the interlamellar porosity of the γ-alumina matrix, as attested by electron microscopy. This waste-derived catalyst displayed catalytic performances in the reaction of dry reforming of methane (DRM) as good as its counterpart made from a MOF obtained from commercial benzene-1,4-dicarboxylic acid (BDC). Thus, under similar steady state conditions, at 650 °C and 1 bar, the PET-derived catalyst led to CH 4 and CO 2 conversions as high as those on the BDC-derived catalyst, and its catalytic stability and selectivity towards DRM were excellent as well (no loss of activity after 13 h and H 2 :CO products ratio remaining at 1). Moreover, both catalysts were much better than those of a reference nickel alumina catalyst prepared by conventional impregnation route. This work therefore demonstrates the possibility of using plastic wastes instead of commercial chemicals to prepare efficient porous nickel-alumina DRM catalysts from MOFs, fostering the concept of circular economy.
... The final goal of a green energy market is the full exploitation of renewable energy sources (with H 2 production via water electrolysis); however, the development of a decentralized H 2 -production and supply chain based on small scale processors represents a realistic transition strategy [4][5][6][7]. Small-scale reformers have also been proposed for the on-board applications of H 2 (fueling of auxiliary power units based on fuel cells, the injections in the combustion chamber, and the regeneration of catalytic traps) in view of an improvement of the vehicle efficiency [8][9][10][11]. ...
Catalytic partial oxidation (CPO) of logistic fuels is a promising technology for the small-scale and on-board production of syngas (H2 and CO). Rh coated monoliths can be used as catalysts that, due to Rh high activity, allow the use of reduced reactor volumes (with contact time in the order of milliseconds) and the achievement of high syngas yield. As the CPO process is globally exothermic, it can be operated in adiabatic reactors. The reaction mechanism of the CPO process involves the superposition of exothermic and endothermic reactions at the catalyst inlet. Thus, a hot spot temperature is formed, which may lead to catalyst deactivation via sintering. In this work, the effect of the flow rate on the overall performance of a CPO-reformer has been studied, using iso-octane as model fuel. The focus has been on thermal behavior. The experimental investigation consisted of iC8-CPO tests at varying total flow rates from 5 to 15 NL/min, wherein axially resolved temperature and composition measurements were performed. The increase of flow rate resulted in a progressive increase of the hot spot temperature, with partial loss of activity in the entry zone of the monolith (as evidenced by repeated reference tests of CH4-CPO); conversely, the adiabatic character of the reformer improved. A detailed modelling analysis provided the means for the interpretation of the observed results. The temperature hot spot can be limited by acting on the operating conditions of the process. However, a tradeoff is required between the stability of the catalyst and the achievement of high performances (syngas yield, reactants conversion, and reactor adiabaticity).
... This value of CO residual concentration is comparable with literature data concerning microchannel reactors despite the fact that compositions of the initial reaction mixture and inlet CO concentration differ strongly. For example, Kolb et al. [33] used a catalyst 1% Pt/CeO 2 /Al 2 O 3 deposited on the microchannel plate made of metallic foil. The initial mixture was comprised of 10.0% CO, 20.0% ...
This paper reports the results of a study of a water–gas shift reaction over nickel–ceria catalysts with different metal loading. Within this study, the overall CO conversion and observed kinetic behavior were investigated over the temperature range of 250–550 °C in different reactor configurations (fixed-bed and microchannel reactors). The quasi-steady state kinetics of the CO water–gas shift reaction was studied for fractions of Ni-containing cerium oxide catalysts in fixed-bed experiments at lab-scale level using a very dilute gas (1% CO + 1.8% H2O in Не). A set of experiments with a microchannel reactor was performed using the feed composition (CO:H2O:H2:N2 = 1:2:2:2), representing a product gas from methane partial oxidation. The results were interpreted using computational models. The kinetic parameters were determined by regression analysis, while mechanistic aspects were considered only briefly. Simulation of the WGS reaction in the microreactor was also carried out by using the COMSOL Multiphysics program.
... The ATR was not used to recuperate heat from. Similar prototype systems have been designed and operated [40][41][42] where heat is recuperated by use of heat exchanger between reactor components to increase thermal efficiency. ...
Liquid hydrocarbons are high energy density fuels, and micro-reactor based fuel processors are viable alternatives to generate hydrogen for portable fuel cell applications. Micro-reactors have high mass and heat transfer rates due to their small length scales. However, they suffer from thermal heat retention problems due to large surface area to volume ratios. This thesis attempts to explore methodologies to make micro-reactors thermally efficient.
A simulation of the preferential oxidation catalytic reaction is setup in a channel which is contained within a counterflow heat exchanger to recuperate excess heat. Performance of the system is evaluated by using the concepts of reactive length and thermal efficiency. The ratio of the channel used for 95% conversion of CO is defined as reactive length. The PrOx reaction model is verified by comparing simulation with experimental data.
A parametric study is performed using parameters such as mass flow rates, inlet temperatures, conductivity, selectivity, mass of catalyst and concentration. Significant parameters by which the system can be controlled effectively are identified. Parameters that directly affect the systems enthalpy are found to be most effective. The remaining parameters can be used to tune the operation of the system.
Simulation is employed to understand characteristics of two types of micro-reactors: silicon and channel based. For silicon micro-reactor, it is found that flow redistributes itself due to high mass transfer limits. CFD simulation is able to predict these temperatures within 5% accuracy. The silicon micro-reactor is compared against packed-bed reactor and operates comparable due to similar length and time scales. A 1-D reaction model is able to predict the conversion trends in both packed-bed and silicon micro-reactors.
The channel based micro-reactor design consists of three generations of fuel processors. The first generation is a proof of concept, while the second generation uses discrete reactors for each processor stage. The third generation combines these separate stages into a single package giving a thermally integrated fuel processor with heat recuperation and is demonstrated over extended periods of time. There are potential applications for such micro-reactor based fuel processors as portable electronics, military hardware, quick recharge devices and more.
... The channels with a depth of 650 µm and a width of 1000 µm were manufactured by wet chemical etching into stainless steel plates. The etched plates were then coated with a Pt/ceria/alumina catalyst (Kolb et al. , 2008). The reactor comprised 84 plates which were stapled and sealed by laser welding. ...
The water-gas shift (WGS) reaction is an equilibrium-limited reaction at higher temperatures, usually kinetically limited below 250 °C. This requires development of more active low-temperature catalysts and advanced reactor concepts to overcome limitations related to low CO conversions in the range 250-350 °C. This chapter reviews novel WGS catalysts and modern reactor concepts proposed during the last decade. The novel catalyst compositions include Cu-containing bulk mixed metal oxides, noble metals supported on mesoporous oxides and molybdenum carbides. The advantages of advanced WGS reactor concepts including monolithic reactors, microstructured reactors/heat-exchangers and membrane reactors are discussed. The effect of reaction conditions on the kinetics of low-temperature WGS reactions are presented for the main catalyst types.
... The fuel processing unit converts a long chain hydrocarbon into a hydrogen rich gas mixture. Considered hydrocarbons are, for example: methane [93,122], methanol [65,70,157], iso-octane [94,95], gasoline [133], JP-8 [44] and diesel [9,10,136,137,154]. It is possible to build multi-fuel processors [33]. ...
Fuel cell systems (FCS) are considered to be upcoming technology for electrical power generation. They can be used for portable, stationary and transportation applications. Fuel cells are run on hydrogen. Hydrogen can be produced either by electrolysis using electricity from renewable energy or by converting conventional hydrocarbons into a hydrogen rich gas. Among others, a FCS incorporates two main components, the fuel processing unit and the fuel cell stack. The use of hydrocarbon fueled FCS as auxiliary power units (APU) in transportation applications is a possible entry market for this technology that utilizes the existing infrastructure of fuel supply.
Hydrocarbon fueled FCSs are complex multi-domain systems combining aspects from various energetic regimes, like electro-chemical, electrical, pneumatical and thermal. These systems work only in a narrow and well defined range of operation. Therefore, this application requires a well adapted system control to respect these constraints. Classical control structure development often requires the transfer function of the system. This can be difficult or even impossible to derive for complex systems. Therefore, control structure development for complex multi-domain systems is often based on empirical observation and experience. It is desireable to find an approach that allows the development of a control structure based on system description. Such an approach will simplify control structure development and ensure that the control structure is adapted to the system needs. Model based control structure design is an approach that can meet these demands.
This thesis presents a complete model of a low temperature FCS fueled by commercial diesel, and is well adapted for model based control development. The studied FCS provides 25kW electric power, and at the same time the system waste heat is used for climatization.
In chapter 2 several modeling methodologies are introduced. Each is evaluated to see if it can be used to model a complex multi-domain system and if it can be used for model based control structure development. Energetic Macroscopic Representation (EMR) is identified as the best adapted methodology and is applied to chemical reactions and mass transfer.
In chapter 3 a model of the fuel processor is presented and implemented in Matlab/Simulink\texttrademark. To obtain a hydrogen rich gas, the supplied hydrocarbon has to be broken up. Subsequently, the gas has to be purified in order to avoid contamination of the fuel cell with sulfur and carbon monoxide.
In chapter 4 a model of the fuel cell stack is presented. It takes into account the gas flows in the different layers, describing membrane humidification as well as the voltage supplied by the fuel cell. The model also takes into account the influence of the membrane humidity on the stack voltage.
Among low temperature fuel cells, two technologies are available. The model is developed for the more common (Polymer Electrolyte Fuel Cell - PEFC), but the emerging technology (High Temperature Proton Exchange Membrane Fuel Cell - HTPEMFC) shows advantages with regard to system volume and heat use. Therefore, the models of the fuel processor and the fuel cell stack have been adapted to this emerging technology. The demonstrated adaptability underlines the advantage of using a modular modeling approach.
The models are validated successfully against measurements, literature values and values supplied by system manufacturer.
To confirm that the model can be used for model based control development, the control structure with regard to the temperature and the mass flow control for the FCS is developed in chapter 5. It is shown that the control structure of the system can be obtained by block wise inversion of the model. This approach gives the control structure; the choice of the controllers and their parameterization is up to the developer. The application of control proves that, using EMR, it is possible to derive a control structure from the model of a complex multi domain system without the need to derive its transfer function.
The presented work is accomplished in cooperation with the French national project GAPPAC from the PAN-H program of the French National Agency for Research (ANR). It gathers N-GHY, Airbus and Nexter as industrial partners and LMFA, Armines, IFFI, INRETS LTN and FCLAB Institute as research institutes.
... To increase the overall hydrogen production, the volume and the weight of catalysts must be dramatically increased, with considerable increasing of costs. For this reason process intensification is still required to achieve good performance targets for small-scale applications such as for distributed or mobile hydrogen production [22,25,70]. Different configurations (foams, honeycombs, gauze, microchannels) were proposed as alternative to traditional packedbed reactors [71][72][73][74][75][76][77][78]. ...
... Nevertheless, the devices that unite the scientific interest recently are undoubtedly the microstructured reactors or also called microreactors [46][47][48][49][50]. As its name indicates the microreactors are composed by multiple parallel channels with diameters between 10 and several hundred micrometers. ...
... In particular, a low CO content in hydrogen stream generated by reforming process deteriorates the efficiency of the Pt anode catalyst via CO poisoning [8,9]. Many types of fuel processing systems were developed to produce pure hydrogen that is fast enough to supply the PEM fuel cell operation by passing through auxiliary units [10,11]. These auxiliary units were integrated into the H 2 production unit (reformer) in order to effectively remove CO from the H 2 stream and also to minimize H 2 loss in the H 2 -rich stream. ...
Preferential CO oxidation in a H2-rich stream was studied over Au/ZnO and Au/ZnO–Fe2O3 catalysts prepared by photodeposition under UV–vis light. The high catalytic activities of both Au/ZnO and Au/ZnO–Fe2O3 catalysts are presented over a temperature range of 30–130°C. TEM results revealed that the average particle size of Au over the Au/ZnO and Au/ZnO–Fe2O3 catalysts, is in the range of 3–5nm. Moreover, DR/UV–vis spectra showed that the prepared catalysts contained Auδ+ and Au0 (active sites for the PROX reaction) on the catalyst support. Based on the experiment observations, it can be concluded that the catalysts prepared by a photodeposition exhibited excellent catalytic activity, even when both CO2 and H2O were added to the simulated stream.
... As concerned the preparation of coated metal plates, the procedure consisted in the deposition of the precursors solution (AlðNOÞ 3 Á 9H 2 O, urea, RhðNO 3 Þ 3 and zeolite as suspension) into the plate channels by filling them with a syringe (infusion-pump method) [9]. After filling the channels, the catalyst layer onto the surface of the channels was developed by SCS by placing the plates stack in oven set up at 500 1C. ...
CO preferential oxidation (CO-PROX) can lead to a reduction of the CO content in the hydrogen-rich gas
derived from hydrocarbon re-forming down to at least 10 ppmv or below, so as to enable its direct feed to
standard polymer electrolyte membrane fuel cells (PEM FCs). Rh-based catalysts supported on A zeolites
(3A, 4A, and 5A), alumina, titania, and ceria were prepared and tested for potential application in CO-PROX
operating over a temperature range compatible with PEM FCs (80-100 °C). Among the prepared catalysts,
the 1% Rh-zeolite 3A catalyst, tested with a weight space velocity (WSV) of 0.66 N·L· min-1 · gcat-1, was
found to be the most suitable one for the CO-PROX at low temperature: it reduced the inlet CO concentration
below 10 ppmv within a temperature range of at least 80-120 °C without the appearance of undesirable side
reactions. Tests at progressively lower O-to-CO feed ratio and the same WSV value were carried out for the
sake of reducing H2 consumption and improving CO-PROX selectivity. For 1% Rh-3A zeolite the minimum
λ value, ensuring a sufficiently wide temperature range of a nearly complete CO conversion at temperatures
compatible with PEM FCs operation, was found to be equal to 3. Finally, to decrease the catalyst cost, the
Rh load on the catalyst was tentatively reduced from 1 to 0.5%. A better distribution of the active element
crystallites over the support surface was even obtained for this last catalyst. When operating at λ= 3 and at
WSV= 0.66 N·L· min-1 · gcat-1, the 0.5% Rh-3A catalyst could effectively reduce the inlet CO concentration
below 10 ppmv within a temperature range of 100-140 °C, without the appearance of undesired side reactions.
... As concerned the preparation of coated metal plates, the procedure consisted in the deposition of the precursors solution (AlðNOÞ 3 Á 9H 2 O, urea, RhðNO 3 Þ 3 and zeolite as sus- pension) into the plate channels by filling them with a syringe (infusion-pump method) [9]. After filling the channels, the catalyst layer onto the surface of the channels was developed by SCS by placing the plates stack in oven set up at 500 1C. ...
Even traces of CO in the hydrogen-rich gas fed to PEMFC can poison the platinum anode and dramatically decrease the cell power output.Micro-chemical technology (MCT) is a new direction of chemical engineering originated in the early 1990s. The application of MCT can greatly improve the efficiency of systems and diminish their volumes and weights. The novel reaction conditions such as the very low residence times in micro-structured reactors create the need for adopting or even improving conventional catalyst technology according to the requirements of this new application. On top of the improved heat and mass transfer, micro-structured reactors allow for a better temperature control of the reaction.In the present paper, a screening of powder Rh-based catalysts, was carried out for CO preferential oxidation reaction, and then the more promising catalyst was deposed and tested in a microchannel reactor.
The pinch-off dynamics during hydrogen bubble formation was experimentally investigated in a cross-junction microchannel. A binarization interface recognizing and key frame tracking method was established. By analyzing the breakup dynamics through spatial and time domains, the effects of interfacial tension and viscosity on hydrogen bubble pinch-off were revealed. A transitional stage between a liquid squeezing stage and a free pinch-off stage was newly observed and the transitional stage was named as the wave model stage because of the long-wave approximation of the interface at this stage. The time criteria between the three stages are proved to be around 1/10 of tcap (capillary time) and around tcap to the pinch-off moment, respectively. However, the power law exponents of the minimum radial radius R0 for hydrogen - liquid flow, larger than those for nitrogen - liquid flow, are consistent with literature works in terms of both range and tendency.
A novel tanks-in-series-reactor (TSR) model has been developed for auto-thermal reforming of hydrocarbons in a monolithic reactor carrying microchannels. The model is based on the dynamic mass and heat balance equations defined for the channel and catalyst layer. The description of chemical reactions is based on a simplified multi-step surface reaction mechanism under the assumption of the rate-determining step. The predicted steady-state concentration profiles are consistent with experimental literature data.
Powder and structured catalysts based on CuO–CeO2 nanoparticles dispersed on different silica are studied in CO preferential oxidation. Silica of natural origin (Celite) and fumed silica (aerosil), both commercial materials, and synthesized mesoporous SBA-15 with 20, 200 and 650 m²g⁻¹ respectively, are selected as supports. CuCe/Celite coated on cordierite monolith displays the highest activity, reaching CO conversion above 90% between 140 and 210 °C and more than 99% around 160 °C. The addition of 10% CO2 and 10% H2O partially deactivates the monolithic catalyst.
The lower surface area of CuCe/Celite favors the contact between CuO and CeO2 nanoparticles promoting a better interaction of Cu⁺²/Cu⁺ and Ce⁺³/Ce⁺⁴ redox couples. Raman spectroscopy reveals oxygen vacancies and XPS results show high metal lattice surface oxygen concentration and surface enrichment of Cu and Ce which promote the catalytic activity.
Catalytic processing of light hydrocarbons provides fuels and raw chemicals, and is thus of paramount importance for the energy and chemical industry. However, the harsh conditions and significant heat effects cause undesirable inefficiency, high power consumption and carbon emission of conventional reactors. Microstructured catalytic reactors enable excellent heat and mass transfer and potentially lower the pressure drop with a compact design, thus allowing high-throughput light hydrocarbons processing under strict control of temperature and concentration as demanded by distributed production. This paper summarizes the fabrication technology and key R&D activities with regard to microstructured reactors for intensifying gas-solid catalytic reactions. Representative examples of light hydrocarbons processing in microstructured reactors are reviewed including the endothermic steam methane reforming and the exothermic methanation and ethane oxidative dehydrogenation processes. It is believed that innovative and efficient reactor-catalyst integration could boost even wider applications of the emerging reactor technology, which would eventually reshape the energy and chemical industry.
For the first time the influence of CO, CO2 and H2O content on the performance of chlorinated NiCeO2 catalyst in selective or preferential CO methanation was studied systematically. It was shown that the rate of CO methanation over Ni(Cl)/CeO2 increases with the increasing H2 concentration, is independent of CO2 concentration and decreases with increasing CO and H2O concentrations; the rate of CO2 methanation is weakly sensitive to H2 and CO2 concentrations and decreases with increasing CO and H2O concentrations. High catalyst selectivity was attributed to Ni surface blockage by strongly adsorbed CO molecules and ceria surface blockage by Cl, which both inhibit CO2 hydrogenation.
For the first time, selective CO methanation over Ni(Cl)/CeO2 was studied for deep CO removal from formic acid derived hydrogen-rich gases characterized by high CO2 (40–50 vol%), low CO (30–1000 ppm) content and trace amounts of water. Composite Ni(Cl)/CeO2-η-Al2O3/FeCrAl wire mesh catalyst was demonstrated to be effective for this process at temperatures of 180–220°С, selectivity 30–70%, WHSV up to 200 L (STP)/(g∙h). The catalyst provides high process productivity, low pressure drop, uniform temperature distribution, and appears highly promising for the development of a compact CO cleanup reactor. Selective CO methanation was concluded to be a convenient way to CO-free hydrogen produced by formic acid decomposition.
The current scenario where the effects of global warming are more and more evident, has motivated different initiatives for facing this, such as the creation of global policies with a clear environmental guideline. Within these policies, the control of Greenhouse Gase (GHG) emissions has been defined as mandatory, but for carrying out this, a smart strategy is proposed. This is the application of a circular economy model, which seeks to minimize the generation of waste and maximize the efficient use of resources. From this point of view, CO2 recycling is an alternative to reduce emissions to the atmosphere, and we need to look for new business models which valorization this compound which now must be considered as a renewable carbon source. This has renewed the interest in known processes for the chemical transformation of CO2 but that have not been applied at industrial level because they do not offer evident profitability. For example, the methane produced in the Sabatier reaction has a great potential for application, but this depends on the existence of a sustainable supply of hydrogen and a greater efficiency during the process that allows maximizing energy efficiency and thermal control to maximize the methane yield. Regarding energy efficiency and thermal control of the process, the use of structured reactors is an appropriate strategy. The evolution of new technologies, such as 3D printing, and the consolidation of knowledge in the structing of catalysts has enabled the use of these reactors to develop a wide range of possibilities in the field. In this sense, the present review presents a brief description of the main policies that have motivated the transition to a circular economy model and within this, to CO2 recycling. This allows understanding, why efforts are being focused on the development of different reactions for CO2 valorization. Special attention to the case of the Sabatier reaction and in the application of structured reactors for such process is paid.
A structured Ni(Cl)/CeO2/η-Al2O3/FeCrAl catalyst was developed and tested for the reaction of selective methanation of CO in the presence of CO2. The use of a FeCrAlloy wire mesh with a η-Al2O3 protective coating as a support of Ni(Cl)/CeO2 enabled production of a catalyst with the ability of high rates of heat removal, that is similar in performance to the most efficient powder catalysts. In a hydrogen-rich gas mixture of composition (vol%): 1.0 CO, 65 H2, 10 H2O, 20 CO2, He - balance, at WHSV of 29 L g⁻¹ h⁻¹, the Ni(Cl)/CeO2/η-Al2O3/FeCrAl catalyst reduced the CO concentration to a level of <10 ppm in the temperature range of 230–270 °C with a selectivity larger than 70%.
Solution combustion synthesis (SCS) is a preparation technique that can be used to synthesize a variety of inorganic nanomaterials and structured catalysts. It is based on a self-propagating exothermic redox reaction between organic salts and a fuel mixed together in an aqueous solution, which results in the formation of nanocrystalline and highly pure solid nanomaterials. SCS can be considered as an attractive synthesis method for catalysts due to the simple nature of the synthetic route and short reaction times. The process is easily scaled up to any kind of application which makes it economically attractive. This mini-review provides a short overview on the synthesis of structured catalysts by SCS and their recent utilization for energy applications and pollution control.
Fuel processing is the conversion of fossil and regenerative fuels to hydrogen-containing gas mixtures. The chemical conversion is performed in most cases in the gas phase, normally heterogeneously catalyzed in the presence of a solid catalyst. The first step of the conversion procedure is named reforming. It has been established in large-scale industrial processes for many decades. The industrial applications most commonly use natural gas as feedstock. The product of the natural gas reforming process is synthesis gas, a mixture of carbon monoxide and hydrogen, which is then used for numerous processes in large-scale chemical production which are not subject of this section but rather the technology, which provides a hydrogen-containing gas mixture, named reformate, which is a feed suitable for a fuel cell. The fuel cell then converts hydrogen to electrical energy. Depending on the fuel cell type, removal of carbon monoxide might be required, which is achieved by water-gas shift and preferential oxidation reactions performed downstream the reformer. The reactor types suitable for mobile and decentralized applications are, apart from conventional fixed-bed reactors, ceramic and metallic monoliths, (microchannel) plate heat exchangers, and membrane reactors which allow the combination of membrane separation with the reactions mentioned previously.
The current paper provides an overview of recent and past research activities in the field of microreactors for selective oxidation reactions. The majority of the research efforts are currently focussing on the direct synthesis of hydrogen peroxide, aldehydes and carboxylic acids and the preferential (selective) removal of carbon monoxide out of hydrogen rich reaction mixtures. Catalyst development, process optimisation and reactor design are under investigation. Numerous examples demonstrate the advantages of microstructured reactors for the reaction systems envisaged through the improved catalyst utilization, heat management and potential operation under hazardous conditions, especially in the explosive regime.
A CFD model of a copper-ceria based micro-reactor for the CO preferential oxidation reaction is developed. Simulations are performed by changing the thermal conductivity of the support and the oxygen inlet concentration. It is found that the value of the wall thermal conductivity has a significant role on the temperature profiles, hot-spot and selectivity. On increasing the O2 content, the CO selectivity decreases. An increase of the oxygen content anticipates the activation of the H2 oxidation, thus competing with CO oxidation. Conversely, at low values of the O2 content, the H2 oxidation is activated only after an almost complete CO oxidation is obtained. From the results it appears that the temperature control and management in the reactor is a key for increasing the CO selectivity at high CO conversion.
A discussion on fuel processing technology covers the early development of fuel cell systems; fuel cell automobile programs; options for fuel cell automobile commercialization; the idea of on-board reforming for automobiles; developments in stationary and portable fuel cell system products using hydrocarbons, alcohol, and oxygenated fuels including diesel fuel, dimethyl ether, ethanol, methanol, propane, and natural gas; improvements in overall efficiency and reductions in pressure drop through the bed; coupling of heat transfer; catalytic kinetics and mass transfer limitations in conjunction with the discovery of new classes of catalysts that meet the requirements of hydrocarbon fuel processing; and new directions in fuel processor design. This is an abstract of a paper presented at the 2012 AIChE Annual Meeting (Pittsburgh, PA 10/28/2012-11/2/2012).
At IMM, all development steps required for building a fuel processor have been addressed. Reactor and system design, catalyst development and set-up/testing of complete fuel processors are realised for systems up to 5 kW power output of the corresponding fuel cell. The applications standing behind the development work are manifold. Having demonstrated the feasibility of compact fuel processing, the aspects of future mass production of such devices for consumer applications are discussed. Complete fuel processor systems will be presented and discussed.Emphasis will also be made on manufacturing technologies applicable, which greatly depend on the production scale and on the market potential of the application. Microreactiontechnology, fuel processors.
Chemical intensification aims to enhance chemical processes by employing harsh reaction conditions, such as high temperatures, high pressures, solvent effects, high concentration of the reactants, handling of hazardous compounds and novel chemical transformations. The process design intensification field is directed toward the complete production design aspect of chemical manufacturing. It intends to simplify and integrate the different reaction and purification steps of a chemical reaction sequence in a single streamlined and continuous-flow process. Although the concept is relatively new, novel process windows have had already a significant impact on flow chemistry applications, as well as on the process engineering aspect. This chapter discusses each aspect of novel process windows and provides several literature examples. It concludes by providing two verified in-house laboratory experiments.
Catalysts for biofuels reforming based on two types of nanocomposite active components (Ni + Ru/La0.8Pr0.2Mn0.2Cr0.8O3/Y0.08Zr0.92O2−δ, Ni + Ru/Sm0.15Pr0.15Ce0.35Zr0.35O2) supported on microchannel substrates (Ni–Al alloy foam plates, Fechraloy plates protected by a thin corundum layer) were developed. Applied procedures for the active components loading on substrates provide thermochemical stability of supported layers of active components in tough operation conditions not affecting their reactivity/catalytic activity. Effects of the nature of nanocomposite active component, type of fuel (ethanol, ethyl acetate, acetone and glycerol), feed composition and contact time on the yield of syngas/byproducts and performance stability are considered and compared with results of calculations of the equilibrium composition of reaction mixtures. For nanocomposite active components with a high oxygen mobility and reactivity, reforming of such typical fuel as ethanol is described by the step-wise red-ox mechanism. Preliminary results of the mathematical modelling of the ethanol steam reforming on a stack of microchannel Fechraloy plates loaded with Ni + Ru/Sm0.15Pr0.15Ce0.35Zr0.35O2 active component revealed that this process can be satisfactorily described by the isothermal model without any impact of the heat/mass transfer.
The auto-thermal reforming (ATR) performance of diesel blended with biodiesel (e.g., B5, B10, B20, B40, and B80) was investigated and compared to pure diesel and biodiesel ATR in a single-tube reformer with ceramic monolith wash-coated rhodium/ceria-zirconia catalyst. The initial operating condition of the ATR of all studied fuels was set as total moles of oxygen from air, water, and fuel per mole of carbon (O/C) = 1.47, moles of water to carbon (H2O/C) = 0.6, and gas hourly space velocity = 33,950 h(-1) at 1223 K reformer temperature, to achieve the same syngas (H-2 + CO) production rate. A direct photo-acoustic micro-soot meter was applied to quantify the dynamic evolution of carbon formation and a mass spectrometer was used to measure the gas composition of reformer effluents. The blends with more biodiesel content were found to have a lower syngas production rate and reforming efficiency, and require more air and higher reformer temperature to avoid carbon formation. Strong correlations between ethylene and solid carbon concentration were observed in the reformation of all the fuels and blends, with more biodiesel content tending to have higher ethylene production. This study is one component of a three-part investigation of bio-fuel reforming, also including fuel vaporization and reactant mixing (Part 1) and biodiesel (Part 2). Copyright
Microchannel reactors and heat exchangers have been developed by application of a novel laser welding technique, which generates durable sealing of the reactors for operating temperatures up to 1000 °C. A microreactor for exhaust gas cleaning purposes has been operated for 35 000 h in a laboratory environment. Results from the operation of a diesel oxidative steam reformer in combination with a hot gas driven evaporator are presented.
Two types of flow distributors, that is, a jet-flow-splitter and a simplified constructal distributor, were designed to equalize the gaseous reagents in the inlet of a microreformer packed with catalyst supported on ceramic foam. The effects of type and geometry of distributors on flow, temperature distributions, and reaction performance over the catalyst during the autothermal reforming of ethanol were investigated experimentally and computationally. It was found that the jet flow splitter in the shape of cone or hemisphere can effectively equalize the flow distribution on the lower surface of catalyst, thereby improving the temperature distribution and performance of the microreformer. A microreformer with a hemisphere jet-flow-splitter in optimal geometry can convert 91% of ethanol with a selectivity to hydrogen of 74%, equivalent to yielding 3.3 mol of hydrogen per mol ethanol. Such a distribution device can be used to fabricate an efficient microreformer with simple structure for the hydrogen production orienting the portable fuel cell application.
The present manuscript provides a panoramic overview of the most recent work carried out at a European level on the research and development of fuel processor (FP) units for various type of fuel cells (FCs), with an update on actual existing commercial products manufactured in Europe, namely auxiliary power units (APUs) and combined heat and power systems (CHPs). An increasing number of integrated complete FP units has been developed for a large variety of fuels: natural gas, biogas, low sulphur road diesel, propane, butane, liquefied petroleum gas (LPG), methanol, and ethanol. Some FP, APU and CHP systems are at present available on the European market.
The in situ deposition of 1.5 wt.% Ru/γ-Al2O3 catalytic layers on cordierite monoliths (400 cpsi, diameter 1 cm, length 1.5 cm), combining Solution Combustion Synthesis (SCS) with Wet Impregnation (WI), was addressed. First of all, the physicochemical properties of the catalyst at powder level were investigated by X-ray Diffraction (XRD), N2 adsorption (BET), and H2 chemisorption, while the morphology of final structured catalysts was evaluated by SEM analysis and mechanical strength tests by sonication. The catalytic activity towards methane Oxy-Steam Reforming (OSR) reaction was studied after the choice of the most suitable catalyst load, carrying out tests varying the temperature (500 - 800°C), the oxygen-to-carbon ratio (O/C = 0.45 - 0.75, oxygen as moles), the steam-to-carbon ratio (S/C = 1.0 - 2.4), and the weight space velocity (WGS = 34,000 - 400,000 Nml gcat–1 h–1), in order to identify the optimum operative conditions. The results showed that a total catalytic layer load (active metal plus oxide carrier) equal to 6.5 mg cm–2 was enough to achieve excellent performances, while no substantial improvements were obtained at higher catalytic layer loads. Moreover, the coated Ru/γ-Al2O3 monolith exhibited a good catalytic activity towards the studied reaction also at considerably high WSV values (till 400,000 Nml gcat–1 h–1).
The catalytic systems of new generation and microstuctured heat-exchanger reactors for the water-gas shift reaction have been considered.
Portable electronic devices are behind the interest in fuel cell (FC) technology to replace or supplement batteries in portable applications. H2-feeded polymer electrolyte membrane fuel cells (PEMFCs) should be coupled to hydrocarbon fuel processors when the PEMFC are applied for use in vehicles’ power traction and auxiliary power units. Cleanup of the H2-rich reformate gases is mandatory since Pt or Pt-Ru catalysts at the FC anode may be poisoned by the strong irreversible adsorption of carbon monoxide (CO) molecules; therefore, the CO levels in the hydrogen stream must be in the parts per million range (<50 ppm for Pt–Ru anodes or <10 ppm for Pt ones).
The current paper provides an overview of recent and past research activities in the field of microreactors for energy related topics. The main research efforts in this field are currently focussing on fuel processing as hydrogen source, mostly for distributed consumption through fuel cells. Catalyst development, reactor design and testing for reforming and removal of carbon monoxide through water-gas shift, preferential oxidation, selective methanation and membrane separation are therefore under investigation. An increasing number of integrated complete micro fuel processors has been developed for a large variety of fuels, assisted by static and dynamic simulation of these systems. The synthesis of liquid fuels is another emerging topic, namely Fischer-Tropsch synthesis, methanol and dimethylether production from synthesis gas and biodiesel production.
In this work we have studied the effect of the addition of Sn to alumina-supported Pt catalysts towards the catalytic performance in CO-PROX reaction. Monometallic Pt and Sn catalysts supported on alumina, and bimetallic Pt–Sn supported on alumina (with Pt/Sn atomic ratios of 1.92, 0.53 and 0.28) was prepared by successive impregnation, with high dispersion of the metal. The addition of Sn to Pt does not substantially increase the activity in CO-PROX at low temperatures; however, the temperature interval where the CO conversion is maximum was significantly increased. The optimum Pt/Sn atomic ratio was found to be 0.53. In a wide operation window with respect to temperature, the catalyst with optimum Pt to Sn ratio shows a maximum CO conversion of 78% for λ=2 with constant selectivity (about 40%) and with 31%CO yield. In the presence of either CO2 or H2O the performance of Sn promoted catalyst was seen to show improved activity.
This paper presents a panoramic overview of the experimental work carried out at Politecnico di Torino on the development of structured catalytic reactors for the production of H2-rich streams from hydrocarbons, to be fed to PEM-FCs: short contact time catalytic partial oxidation (SCT-CPO) reactor for syngas production, micro-channelled reactors for syngas CO clean-up, water gas shift (WGS) and preferential oxidation (PROX). Concerning the reactor for methane SCT-CPO, 10% Ni deposited on irregular γ-Al2O3 particles presented the best performance (CH4 conversion>90%; H2 selectivity>95%) compared to 0.5% Rh deposited over γ-Al2O3 spheres. As regards the HT-WGS reaction, the best performance was obtained with the catalyst 1% Pt/(CeO2+TiO2): it reached the thermodynamic equilibrium (inlet CO: 10% b.v.; WHSV=40Nlh−1gcat−1) in the temperature range 450–525°C, allowing the abatement of almost 60% of the CO present in the fed gas stream. Finally, the best performance towards CO-PROX reaction was obtained with the catalyst 1% Rh/(Al2O3+3A zeolite): it reached the complete CO conversion (inlet CO: 0.5% b.v.; WHSV=40Nlh−1gcat−1; λ=3) in the temperature range 130–160°C, thus assuring an easy controllability of the system.
A brief review of water gas shift (WGS) catalysis is provided. An overview of the four general classes of WGS catalysts is presented, which include: 1) high temperature shift (HTS), 2) low temperature shift (LTS), 3) sulfur-tolerant shift catalysts, and 4) precious metal-based shift catalysts. A review of WGS utilizing monoliths or other reactor technologies that pertain to fuel cell applications, an area of increasing interest over the past several years, is also presented. Ratnasamy and Wagner have recently provided an outstanding and comprehensive review of WGS catalysis. A particular emphasis of that work is catalyst surface structures, active sites, reaction intermediates, and mechanisms, particularly for noble metal-based catalysts1. The summary provided here is a succinct review of water gas shift catalysis and reactors, with an emphasis on fuel processing applications for fuel cells, and is not intended to provide a comprehensive review of WGS technology.
The last CO clean-up step based on the preferential oxidation (CO-PROX) can lead to a reduction of the CO
concentration in the hydrogen-rich gas derived from hydrocarbons reforming down to at least 10 ppmv
or below, so as to enable its direct feeding to standard PEM fuel cells. In this paper, a screening of powder
Pt-based catalysts for CO preferential oxidation reaction was carried out; then the more active catalyst
(1% Pt on 50% 3A zeolite and 50% �-Al2O3, i.e. 1% Pt-MIX) was deposed by precursors solution spraying
followed by in situ combustion synthesis (SCS) in a micro-channel metal plate reactor and the obtained
structured system was tested with a synthetic feed stream simulating the WGS outlet composition. The
1% Pt-MIX catalyst was laid out on metal plates previously coated with thin �-Al2O3 layer (15�m thickness)
by plasma spray technique to improve the catalytic material adhesion. A studywas then carried out
at �=2O2/CO= 4 by varying the GHSV and the superficial catalyst load in a range values characterized by
a satisfactory performance for a CO-PROX prototype reactor. The following results were, in fact, obtained
with a catalyst load of 0.50mgcm−2: with GHSV equal to 2000 h−1 and 4800 h−1 the complete CO conversion (residual CO concentration less than 2ppmv) with simultaneous O2 conversion equal to 1 was
obtained in the temperature range 194–214 ◦C and 215–225 ◦C, respectively.
The present paper deals with the study concerning the CO removal from reforming H2-rich gas stream
through WGS reaction over Rh-based catalysts supported on CeO2 carriers. CeO2 was prepared by two
different methods: solution combustion synthesis (SCS) and hard template (HT); incipient wetness
impregnation method was used to deposit the active metal on the carriers. The screening at powder
level in a fixed bed micro-reactor highlighted that feeding 5% CO and 20% H2O (N2 balance) with the
HT-prepared catalyst, CO conversion started at slightly lower temperature, but CH4 outlet concentrations
were higher than those of the SCS-prepared one. With a simulated reformate mixture (5% CO + 20%
H2O + 11% CO2 + 40% H2, N2 balance), the equilibrium WGS curve was exceeded for both catalysts (for the
HT-prepared catalyst, CO conversion started at lower temperature and reached 100%), due to the parasite
methanation reactions of both CO and CO2, favoured by the presence of a large hydrogen concentration
in the reactor. A very high CH4 outlet concentration (max 18.6%) was measured for the HT-prepared
catalyst. Then, tests at different weight space velocities WSV were carried out: with the SCS-prepared
catalyst the best performance was obtained by lowering WSV.
Combustion synthesis (CS) is becoming one of the most important ways to produce a wide range of advanced porous ceramic or metallic materials. These include ceramic oxide like nanostructured catalysts. In CS, the heat released from the redox chemical reaction is used to produce useful materials. Depending upon the nature of the reactants, and the amount of heat made available during reaction, CS is in general mainly described as self-propagating high temperature synthesis (SHS), solution combustion synthesis (SCS), and flame synthesis (FS). Among these, SCS is an attractive alternative for the production of particular materials of high value compared to the more conventional and expensive preparation routes.
A micro-structured autothermal reformer was developed for a fuel processing/fuel cell system running on iso-octane and designed for an electrical power output of 5 kWel. The target application was an automotive auxiliary power unit (APU). The work covered both catalyst and reactor development. In fixed bed screening, nickel and rhodium were identified as the best candidates for autothermal reforming of gasoline. Under higher feed flow rates applied in microchannel testing, a catalyst formulation containing 1 wt.% Rh on alumina prepared by the sol–gel synthesis route proved to be stable at least in the medium term. This catalyst was introduced into the final prototype reactor designed to supply a 5 kW fuel cell, which was based upon micro-structured stainless steel foils. The reactor was optimised for equipartition of flows by numerical simulation. Testing in a pilot scale test rig, which was limited to a specified power equivalent of 3.5 kWel, revealed more than 97% conversion of gasoline at 124 Ndm3/min total flow-rate of reformate, which corresponded to a WHSV of 316.5 Ndm3/(h gcat).
Birch [57] ABSTRACT The invention relates to a process for purifying human von Willebrand factor from a cryoprecipitated plasma fraction, which comprises a combination of three chro matographic separation steps. The ?rst chromato graphic separation step comprises contacting a cryo precipitated fraction with a large-pore vinyl polymer resin having DEAE group. The ef?uent from this sepa ration step is again contacted with a large pore vinyl polymer resin having DEAE groups in the second chromatographic step. In the third chromatographic separation step, the ef?uent from the second step is subjected to af?nity chromatography by contacting with gelatin-Sepharose. The concentrate obtained has very high speci?c activity and a high percentage of high molecular weight multimers. The concentrate is intended, in particular, for therapeutic use.
A micro-reformer was fabricated and its performance investigated using copper-zinc catalysts with differing compositions and loadings at various operating conditions. A catalyst with 3:1 copper-to-zinc ratio and 8 wt% loading produced enough hydrogen to power a 28W PEM fuel cell when using a third of the reformer's volume (8 cm 3 ) and assuming 64% fuel cell efficiency. Methanol conversion was 65% while hydrogen content in the off-gas was 45% at a temperature of 275°C and residence time of 0.11s. Carbon monoxide levels were approximately 1.45%. Higher methanol conversions (80%) and hydrogen content in the off-gas (50%) were achieved by a second catalyst with 16 wt% at 290°C while utilizing the entire reformer volume. Hydrogen yield and selectivity were high (78 and 98% respectively). Extrapolating from present results, the maximum power output possible to be achieved by this device is 84 W.
This paper deals with reviewing on the application of micro-structured reactors for heterogeneously catalysed gas phase reactions. After a brief introduction covering some estimation criteria for the performance of micro-structured reactors, an overview of the work performed to date in the field is given. The reactors are classified by the type of catalyst applied (porous or non-porous) and according to their basic design criteria. At the end, a small chapter is dedicated to applications employing reactors combined with other micro-structured devices like heat exchangers. Finally, some alternative ways of achieving micro-structures, besides relying on micro-fabrication, are discussed.Diverse gas-phase reactions have been investigated in micro-reactors, among them (partial) oxidations, hydrogenations, dehydrogenations, dehydrations, and reforming processes. Particular attention has been drawn to achieve excellent temperature control and to prevent hot-spots. So, for many reactions increases in selectivity were found. Especially, many examples of partial oxidations were described, including processes of utmost industrial importance such as ethylene oxide synthesis. Within consecutive processes, as e.g. given for multiple hydrogenations, high selectivity was achieved for species that are thermodynamically not the most stable molecule of all species serially generated such as monoenes yielded by hydrogenation of polyenes. Also, increases in conversion were achieved, e.g. by processing at high pressure and high temperature, often in the explosive regime. As a consequence, high space–time yields were reported as well. In many cases, reactor performance better compared to fixed-bed technology was achieved. Process safety was found to be high when using micro-reaction devices; intrinsic safety in former explosive regimes was ascribed. With respect to process optimisation, fast serial screening of process parameter variation was conducted, at low sample consumption.
Wash-coated alumina catalysts introduced into micro-channels were applied for the water-gas shift reaction. The application standing behind this work was catalytic CO clean-up of reformate with the aim of hydrogen generation for mobile fuel cell systems. Bimetallic Pt/CeO2/Al2O3, Pt/Rh/CeO2/Al2O3, Pt/Pd/CeO2/Al2O3 and Pt/Ru/Al2O3 catalysts were tested in a standard screening protocol under the conditions of high-temperature shift (9.1% CO, 290, 315 and 340°C reaction temperature) and low-temperature shift (2.6% CO, 290, 315 and 340°C reaction temperature) at a WHSV of 100Ndm3/(hgcat). Methane, was formed as the only by-product. Pt/CeO2/Al2O3 was identified as the best candidate concerning selectivity and activity. The optimum platinum content was found to range between 3 and 5wt.%, whereas the optimum ceria content ranged between 12 and 24wt.%. The calcination temperature and platinum metal salt solution applied during catalyst preparation had a drastic effect on the activity of the Pt/CeO2/Al2O3 catalyst.
Laboratory and industrial results are used to elucidate the general features of the deactivation of supported copper metal catalysts in hydrogenation reactions. Hydrogenations with copper catalysts are milder than with their nickel or platinum counterparts, and they have selectivities that are exploited commercially. They are used in single stream plants for production of hydrogen via the low-temperature water shift gas reaction, and for methanol manufacture from synthesis gas, and also in hydrogenation of speciality organic compounds. Common catalyst types are based on Cu/Cr2O3 (copper chromite) or Cu/ZnO formulations that contain stabilisers and promoters such as alkaline earth oxides and Al2O3. These have several roles, including inhibition of sintering, and poison traps that prevent poisoning of the active metal surface. The best understood are Cu/ZnO formulations that have improved sulphur resistance due to formation of thermodynamically stable ZnS. Copper catalysts are susceptible to thermal sintering via a surface migration process and this is markedly accelerated by the presence of even traces of chloride. Care must be, therefore, taken to eliminate halides from copper catalysts during manufacture, and from the reactants during use. Operating temperatures must be restricted, usually to below 300°C when catalyst longevity is important with large catalyst volumes.
Even traces of CO in the hydrogen-rich feed gas to proton exchange membrane fuel cells (PEMFC) poison the platinum anode electrode and dramatically decrease the power output. In this work, a variety of catalytic materials consisting of noble metals supported on A zeolites were synthesised, characterised and tested under realistic conditions in the quest of a catalyst for the removal of CO via the CO preferential oxidation (CO-PROX) reaction. Pt, Pd and Ru-based catalysts, prepared by wet impregnation and characterised by XRD and HRTEM, were investigated in a fixed bed reactor, by determining CO conversion and selectivity through the outlet concentrations of CO and O2. In contrast to supported Pd and Ru catalysts, Pt-catalysts showed complete CO-conversion and a comparatively high selectivity. The 1% Pt-3A catalyst showed the best performance: it kept the complete CO-conversion in a wide temperature range, showing the highest selectivity for CO oxidation with minimal involvement in side reactions, such as H2 oxidation and RWGS reaction. Experimental data proved that the RWGS outcome is directly related to the support structure. The rather high temperature (≈260°C) at which complete CO conversion is achieved by the 1% Pt-3A catalyst enables to locate the CO-PROX unit immediately after the low temperature water-gas shift unit of the fuel processor converting hydrocarbons into hydrogen-rich gas.
The selective CO oxidation reaction on Pt/-Al2O3insimulated reformer gas (75% H2; the rest is N2) was investigated over a wide range of CO concentrations (0.021.5%)at low stoichiometric O2excess (pO2/pCO=0.51.5). Integral flow measurements in a microreactor showed that the optimumtemperature for the PROX process (preferential oxidation) was200°C; rates of CO methanation in this range wereinsignificant. At higher temperatures a significant loss inselectivity was observed. The quantitative determination of COoxidation rates and selectivities as a function of CO and O2concentration between 150 and 250°C by differential flow measurements led to reaction orders of -0.4 forpCOand +0.8 forpO2at an apparentactivation energy of 71 kJ/mol. These kinetics are consistentwith the selective CO oxidation reaction occurring in thelow-rate branch, on a surface predominantly covered withadsorbed CO. Its ramifications on the observed dependence of theselectivity on both CO concentration and temperature arediscussed. A H2-induced increase in the CO oxidation rate by afactor of 2 was observed. Comparison of the kinetic rateexpression for the selective CO oxidation with the performanceof a plug-flow reactor (variable flow rates) led to quantitativeagreement.
Platinum/ceria/alumina catalysts have been prepared in the microchannels of stainless steel platelets. These catalysts are very active for the water-gas shift reaction between 250–400°C. The use of microreactors as kinetic devices has a clear advantage that the thin catalyst film allows the determination of the intrinsic kinetics even in the case of fast reactions. However, the channel design should be such that plug flow conditions are favored. The kinetics of the water-gas shift reaction, free from internal diffusion limitations, have been studied over thin catalyst layers over a large range of operation conditions. The reaction rate is almost zero-order in carbon monoxide and strongly inhibited by the partial pressure of hydrogen and to a lesser extent to that of carbon dioxide. An overall activation energy of 76.8 ± 2 kJ/mol has been measured. The data are best described by a dual-site mechanism, where platinum provides an adsorption site for carbon monoxide and ceria an adsorption site for water. The rate-determining step involves the formation of a complex between a carboxyl species and a hydroxyl group that decomposes over a free platinum site into carbon dioxide and hydrogen. © 2006 American Institute of Chemical Engineers AIChE J, 2006
Carbon monoxide is known to be poisonous to the proton exchange membrane fuel cell catalyst. Selective oxidation of carbon monoxide in a hydrogen-rich reformate stream is considered to be a practical method with the most potential for reducing concentrations down to tolerant levels. In the present work, nine different noble metal catalysts were investigated using a microstructured reactor in the presence of excess hydrogen and carbon dioxide at a GHSV of 15 500 h−1 and at temperatures up to 160 °C. The most active were Pt–Ru/γ-Al2O3, Rh/γ-Al2O3 and Pt–Rh/γ-Al2O3 yet the most stable was Pt–Rh/γ-Al2O3. Its activity was also investigated using a wet feed and also at a GHSV of 31 000 h−1. Water was found to promote the catalyst activity while at higher GHSV higher temperatures were required to achieve full carbon monoxide conversion. The catalyst exhibited steady performance in the microstructured reactor for 50 h while reducing 1.12% carbon monoxide to 10 ppm with inlet oxygen to carbon monoxide ratio of 4.
Due to the increasing demand for electrical power in today's passenger vehicles, and with the requirements regarding fuel consumption and environmental sustainability tightening, a fuel cell-based auxiliary power unit (APU) becomes a promising alternative to the conventional generation of electrical energy via internal combustion engine, generator and battery. It is obvious that the on-board stored fuel has to be used for the fuel cell system, thus, gasoline or diesel has to be reformed on board. This makes the auxiliary power unit a complex integrated system of stack, air supply, fuel processor, electrics as well as heat and water management. Aside from proving the technical feasibility of such a system, the development has to address three major barriers:start-up time, costs, and size/weight of the systems. In this paper a packaging concept for an auxiliary power unit is presented. The main emphasis is placed on the fuel processor, as good packaging of this large subsystem has the strongest impact on overall size.
Combustion synthesis has emerged as a facile and economically viable technique for the preparation of advanced ceramics, catalysts and nanomaterials. Recent innovations in the combustion and processing parameters have resulted in a better understanding of combustion phenomena and control of microstructure and property of the products.
On-board fuel processors are being developed to provide hydrogen-rich gas to the polymer electrolyte fuel cell automotive propulsion systems. Whereas the anode catalyst in the fuel cell has low tolerance for carbon monoxide, 10–100 ppm, reforming of gasoline and other hydrocarbon fuels generally produces 1–2% of CO. Of the many methods of removing CO from the reformer gas, preferential oxidation (PrOx) of CO over noble-metal catalysts is practiced most frequently. In this paper, we present experimental data for CO conversion on a Pt-based catalyst that is active at room temperature and was coated on a ceramic monolith. The data is used to develop an empirical correlation for selectivity for CO oxidation as a function of CO concentration and oxygen stoichiometry at 30,000–80,000/h space velocity. The selectivity correlation is used in a model to analyze the performance of multi-stage, adiabatic PrOx reactors with heat exchange between the stages to cool the reformate to 100 °C. An optimization algorithm is used to determine the operating conditions that can reduce CO concentration to 10 ppm while minimizing parasitic loss of H2 in the reformate stream. It is found that the 10 ppm constraint limits the maximum inlet CO concentration to 1.05% in a single-stage reactor and to 3.1% in a two-stage reactor. The results clearly show the incremental reduction in parasitic H2 loss by addition of second and third stages.
There are large efforts in exploring the on-board reforming technologies, which would avoid the actual lack of hydrogen infrastructure and related safety issues. From this view point, the present work deals with the comparison between two different 10 kWe fuel processors (FP) systems for the production of hydrogen-rich fuel gas starting from diesel oil, based respectively on autothermal (ATR) and steam-reforming (SR) process and related CO clean-up technologies; the obtained hydrogen rich gas is fed to the PEMFC stack of an auxiliary power unit (APU). Based on a series of simulations with Matlab/Simulink, the two systems were compared in terms of FP and APU efficiency, hydrogen concentration fed to the FC, water balance and process scheme complexity. Notwithstanding a slightly higher process scheme complexity and a slightly more difficult water recovery, the FP based on the SR scheme, as compared to the ATR one, shows higher efficiency and larger hydrogen concentration for the stream fed to the PEMFC anode, which represent key issues for auxiliary power generation based on FCs as compared, e.g. to alternators.
Microreactor technology creates opportunities for the development of miniature chemical devices, in which several unit operations are integrated. In this paper, we describe the design, model simulation, and experimental validation and operation of a microdevice for the preferential oxidation of carbon monoxide in hydrogen-rich reformate gas. The microdevice integrates two heat exchangers and one reactor, all consisting of welded stacks of microstructured plates. We show that the device is able to reduce the carbon monoxide concentration to 10 ppm in combination with a high heat recovery efficiency of 90%. The design of the microstructured plates was based on a combination of three-dimensional computational fluid dynamics simulations of the flow pattern and a two-dimensional heat transfer model, in which the flow pattern was approximated. An integral one-dimensional micro heat exchange model was then used to design the integrated device. This approach may be well suited for designing microstructured reaction systems.
Special catalysts — Pt supported zeolites — for the selective oxidation of carbon monoxide in reformed fuels from methanol or natural gas were proposed. They can be applied for the application to polymer electrolyte fuel membrane cells of which anode Pt catalysts suffer serious poisoning by the presence of trace carbon monoxide. The proposed Pt-supported zeolite catalysts can oxidize carbon monoxide much more selectively in a large excess of hydrogen with the addition of a low concentration of oxygen than a conventional Pt-supported alumina catalyst. The selectivity was affected by supports, in the order A type zeolite mordenite X type zeolite alumina. With decreasing oxygen content, an enhanced selectivity was obtained on Pt-zeolite catalysts (approaching 100%). Pt supported on mordenite showed the highest selectivity, with high conversion from carbon monoxide to carbon dioxide among the catalysts examined. It was demonstrated that the oxygen addition can be minimized almost to the stoichiometric amount required for the complete oxidation of carbon monoxide in a large excess of hydrogen.
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