Catalytic Membrane Reactor for Extraction of Hydrogen from Bioethanol Reforming

This research explores a novel application of catalytic membrane reactors for high- purity hydrogen extraction from bioethanol reforming. Conventional membrane systems employ hydrogen permselective materials such as palladium, polymer membranes, which present several material challenges including embrittlement, thermal degradation and poisoning by hydrocarbons when used for high-temperature hydrocarbon reforming. Thus, the present work is motivated by an interest in employing reactor design concepts to alleviate our reliance upon permselective materials. Catalytic membrane reactor with segregated reactant(s) is employed to demonstrate the hypothesis that high-purity hydrogen with competitive hydrogen recoveries can be achieved by manipulating the reaction and diffusion phenomena, and corresponding thermal gradients inside the catalytic membrane, in the absence of any permselective materials. The hypothesis is demonstrated in two designs: (1) a single functional layer design for water-gas-shift catalytic membrane reactor, and (2) a multi-layer design for bioethanol reforming. A two-dimensional model is developed to describe reaction and diffusion in the catalytic membrane coupled with plug-flow equations in the retentate and permeate volumes using shell and tube architecture. Simulation results for a typical diesel reformate mixture (9 mol% CO, 3 mol% CO2, 28 mol% H2 and 15 mol% H2O) demonstrate that H2:CO permselectivities of 90:1 to > 200:1 with permeate hydrogen recoveries of 20% to 40% can be achieved through appropriate catalytic membrane design. This single reaction simulation results are used to establish a clear rubric of design rules that are then used as a base for designing catalytic membrane reactor for extraction of hydrogen from bioethanol (16 mol% ethanol). The two-dimensional catalytic membrane reactor for bioethanol reforming is simulated, using a network of ethanol reforming reactions and a composite iicatalyst with unique catalytic layers active for one or more reactions. The isothermal simulation results show that an apparent H2:CO permselectivity of 100:1 with hydrogen recovery of 15% can be achieved at appropriate design and flow configuration. This model is extended to a non-isothermal design, which predicted a decrease in membrane performance owing to endothermic reforming reaction. An autothermal design with an additional combustion catalyst layer to counteract the endothermic thermal gradients enhanced the non-isothermal membrane performance. Experiments were conducted to validate the water-gas-shift catalytic membrane reactor model using a gas permeation system; results qualitatively agree with the modeling results and quantitively with an error

CO2-SELECTIVE MEMBRANE FOR FUEL CELL APPLICATIONS

We have developed CO2-selective membranes to purified hydrogen and nitrogenfor fuel cell processes. Hydrogen purification impacts other industries such as ammoniaproduction and flue gas purification at reduced costs.Dense chitosan membranes were used for the first time to separate CO2 from amixture of 10% CO2, 10% H2, and 80% N2 at temperatures of 20 – 150oC and feedpressures of 1.5 atm – 5 atm. At 1.5 atm and 20 – 150oC, dry chitosan membranesachieved CO2 permeabilities, CO2/N2 and CO2/H2 separation factors of 0.383 – 24.3barrers, 10.7 – 3.40, and 4.54 – 1.50, respectively. The dry chitosan acted as an ordinarysolution-diffusion membrane: permeability increased with temperature but selectivitydecreased. The CO2/H2 and CO2/N2 separation factors at all temperatures enhanced CO2removal, making this membrane a candidate for fuel cell processes. The dual modetransport model fitted the transport data well.To achieve higher CO2 transport properties, chitosan was swollen with water.Water mediated the reaction of chitosan\u27s amino groups with CO2. Humidifing the feedand sweep gases increased the membrane\u27s performance. At 1.5 atm and 20 – 110 –150oC, CO2 permeabilities, CO2/N2 and CO2/H2 separation factors were 213 – 483 – 399barrers, 69.4 – 250 – 194, and 18.9 – 43.4 – 29, respectively. The presence of free waterand bound water facilitated the transport of CO2. Increasing feed pressure removed themaxima in permeability and selectivities at 110oC, but led to reduced CO2 permeabilities,CO2/N2 separation factors, and CO2/H2 separation factors to 156 – 286 barrers, 44.2 –131, and 12.0 – 16.7, respectively.To acquire higher CO2 transport properties, arginine-sodium salts wereincorporated in chitosan membranes as additional sites for facilitated transport. The salt\u27spercolation threshold was 40 wt %. At 1.5 atm and 20 – 110 – 150oC, CO2 permeabilities,CO2/N2 and CO2/H2 separation factors were 403 – 1498 – 1284 barrers, 122 – 852 – 516,and 31.9 – 144 – 75.5, respectively. Increasing feed pressure to 5 atm resulted indeclining CO2 permeabilities, CO2/N2 and CO2/H2 separation factors to 118 – 1078barrers, 21.6 – 352, and 5.67 – 47.9, respectively.Chitosan was characterized in terms of morphology, solution properties, thermalproperties, crystallinity, and degree of deacetylation

Membrane and Membrane Reactors Operations in Chemical Engineering

This Special Issue is aimed at highlighting the potentialities of membrane and membrane reactor operations in various sectors of chemical engineering, based on application of the process intensification strategy. In all of the contributions, the principles of process intensification were pursued during the adoption of membrane technology, demonstrating how it may lead to the development of redesigned processes that are more compact and efficient while also being more environmental friendly, energy saving, and amenable to integration with other green processes. This Special Issue comprises a number of experimental and theoretical studies dealing with the application of membrane and membrane reactor technology in various scientific fields of chemical engineering, such as membrane distillation for wastewater treatment, hydrogen production from reforming reactions via inorganic membrane and membrane photoassisted reactors, membrane desalination, gas/liquid phase membrane separation of CO2, and membrane filtration for the recovery of antioxidants from agricultural byproducts, contributing to valorization of the potentialities of membrane operations

Multiphysics Modeling of a Microchannel Methanol Steam Reformer for High Temperature Polymer Electrolyte Membrane Fuel Cell Systems

One of the main challenges facing power generation by fuel cells is the difficulties of hydrogen fuel storage. Several methods have been suggested and studied by researchers to overcome this problem. Among these methods, using a fuel reformer as one of the components of the fuel cell system is considered a practical and promising alternative to hydrogen storage. Among many hydrogen carrier fuels that can be used in reformers, methanol is one of the most attractive due to its distinctive properties. Methanol reformate gas is ideal for feeding high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Therefore, methanol reformate gas fueled HT-PEMFC systems are currently available in the market for portable, stationary and marine applications. Although there are various reformer types to convert methanol to hydrogen rich syn-gas, microchannel plate heat exchanger reformers have some advantages that increase the system efficiency and decrease the system size. In particular, the microchannel plate heat exchanger methanol reformer can be a promising candidate to meet size demands and improve the system efficiency and start-up time to produce power in the range of 100 to 500 W for auxiliary unit power (APU) applications. Furthermore, recent improvements in new catalyst types for methanol reforming can enable the next generation of microchannel methanol reformers with less weight and higher efficiency to be designed. Modeling of the microchannel reformers can be helpful to design next generation reformers. In this thesis, firstly, a methanol reformer system to produce power using HT-PEMFC for portable power generation applications is studied. This study is required for selecting inlet parameters for the multiphysics modeling of the microchannel methanol steam reformer in the second and the third studies. In this study, a detailed parametric study using computer simulations is conducted to estimate the effects of steam-to-carbon (SC) ratio, reformer temperature, current density of the fuel cell, fuel cell temperature, cathode stoichiometric ratio, hydrogen utilization, and rate of power production on the reformate gas composition, fuel cell performance, input fuel flow rate, and heat duties of the system components. In particular, the effects of the reformate gas composition at various fuel cell temperatures on HT-PEMFC performance were examined. The results confirm that the CO molar ratio in the reformate gas increases by decreasing the SC ratio and increasing the reformer temperature. However, the adverse effect of CO molar ratio on fuel cell performance decreases at elevated fuel cell temperatures. The fuel cell voltage decreases by ͠ 78% with the variation of the current density from 0.1 A/cm₂ to 1 A/cm₂ for 160°C fuel cell temperature and 0.9% CO molar ratio in the reformate gas, while it decreases by ͠ 61% for 180°C fuel cell temperature. In addition, an increase in the fuel cell temperature from 160°C to 180°C, the input fuel flow rate to produce a given power generation from the system decreases, while enough heat is still available in the system to provide the heat requirement of different system components. In the second study, a steady state multiphysics model of a microchannel methanol reformer for hydrogen production is developed and validated for the purpose of studying the effects of catalyst layer structural parameters and heat supply strategies on the reformer performance. The aim of this study is to generate hydrogen from the reformer that can be used in HT-PEMFCs. The dimensions of the reformer and inlet flow rate of methanol are selected to produce enough hydrogen to feed fuel cells in the range of 100 to 500 W. This study considers a 2-dimensional domain for the thin coating of the reforming catalyst to account for the internal diffusion limitations and the coating layer structural parameters. The multicomponent Maxwell-Stefan diffusion equation is implemented to account for diffusion fluxes inside the porous structure of the catalyst. The multiphysics model is validated using the reported experimental data by implementing four different reaction kinetics models of methanol steam reforming. This study considers the best fit kinetics model to evaluate the performance of the microchannel methanol reformer. The results show that the catalyst effectiveness factor is relatively low only at the entrance of the reformer for a catalyst layer thickness greater than 50 µm. In addition, this study reveals that for efficient use of the catalyst, the effective heat supply strategy should be improved. Additionally, the design feasibility of the segmented catalyst layer to achieve a certain amount of methanol conversion with less catalyst is demonstrated. It is revealed that for the same inlet conditions, the segmented catalyst layer design required 25% less reforming catalyst to achieve 90% conversion compared to the conventional continuous coating design. In the last study, a numerical model is developed to predict the performance of a microchannel methanol steam reformer with different catalyst layer configurations to produce hydrogen-rich syngas for a HT-PEMFC. A solution schema is developed to compare continuous catalyst layer configurations and various segmented catalyst layer configurations without any convergence issue in the numerical analysis. In this work, heat is provided to the endothermic reforming-side via methanol combustion. The results show that higher heat transfer rates can be provided by applying segmented catalyst layer configurations, thus resulting in significant performance improvement of the microchannel methanol steam reformer. The results reveal that methanol conversion can be increased by ͠ 25% by using segmented catalyst layer configurations with less catalyst in the reforming and combustion sides. The results also indicate that even though there is no significant improvement in methanol conversion with increasing catalyst layer thickness, the greater catalyst layer thickness provides the advantage of reduced high temperature elevations across the reformer length. Overall, the segmented catalyst layer configurations can play an important role in designing the next generation of microchannel reformers for fuel cell power generation systems to maximize power, minimize reformer size, and decrease the required quantity of catalyst

On the decarbonization of chemical and energy industries: Power-to-X design strategies

Tesis por compendio de publicaciones[ES]Hoy en día, la preocupación por la sostenibilidad está dando lugar a todo un nuevo sistema económico. Este nuevo paradigma afecta a todos los sectores como la agricultura, la industria, el sector financiero, etc. Dos de los más afectados son la industria química y el sistema energético debido a su configuración actual y, estos dos sectores son particularmente estudiados en esta tesis. En cuanto a la industria química, la producción electroquímica es uno de los métodos más atractivos para producir productos químicos de forma sostenible dejando atrás la producción tradicional no renovable. En esta tesis se ha prestado especial atención a la producción sostenible de amoníaco. Se han evaluado dos rutas diferentes, la primera utiliza la electrólisis del agua y evalúa diferentes tecnologías de separación del aire en función de la escala, y la segunda utiliza la biomasa como materia prima. Utilizando estos productos electroquímicos, es posible construir una nueva industria química sostenible. En esta tesis se propone la síntesis de carbo- nato de dimetilo (DMC) utilizando metanol renovable, amoníaco y dióxido de carbono capturado. En cuanto al sector energético, la introducción de fuentes renovables es esencial para alcanzar los objetivos propuestos. En este punto, el almacenamiento de energía será crucial para garantizar la satisfacción de la demanda debido a las fluctuaciones inherentes a las energías solar y eólica. Esta tesis se centra en la evaluación de productos químicos como forma potencial de almacenamiento o como vectores de energía. Se estudia la transformación del amoníaco en electricidad a escala de proceso proporcionando los resultados necesarios para implementar esta alternativa a escala de red. El diseño y el funcionamiento de las insta- laciones basadas en renovables se abordan simultáneamente, incluyendo la ubicación de las unidades debido a que los recursos renovables estan distri- buidos. Se propone un sistema integrado para utilizar productos químicos como vectores energéticos para diferentes aplicaciones energéticas en una región de España, calculando las capacidades, la operación y la ubicación óptima de las instalaciones. Además, se realiza la integración de diferentes energías renovables intermitentes y no intermitentes junto con diferentes tecnologías de almacenamiento desde una perspectiva económica y social para satisfacer una determinada demanda eléctrica. Todos estos sistemas y herramientas propuestos contribuyen a crear un escenario futuro en el que los sectores químico y energético se transforman para ser menos impactantes en el medio ambiente que nos rode

Fuel Cell Handbook, Fifth Edition

Progress continues in fuel cell technology since the previous edition of the Fuel Cell Handbook was published in November 1998. Uppermost, polymer electrolyte fuel cells, molten carbonate fuel cells, and solid oxide fuel cells have been demonstrated at commercial size in power plants. The previously demonstrated phosphoric acid fuel cells have entered the marketplace with more than 220 power plants delivered. Highlighting this commercial entry, the phosphoric acid power plant fleet has demonstrated 95+% availability and several units have passed 40,000 hours of operation. One unit has operated over 49,000 hours. Early expectations of very low emissions and relatively high efficiencies have been met in power plants with each type of fuel cell. Fuel flexibility has been demonstrated using natural gas, propane, landfill gas, anaerobic digester gas, military logistic fuels, and coal gas, greatly expanding market opportunities. Transportation markets worldwide have shown remarkable interest in fuel cells; nearly every major vehicle manufacturer in the U.S., Europe, and the Far East is supporting development. This Handbook provides a foundation in fuel cells for persons wanting a better understanding of the technology, its benefits, and the systems issues that influence its application. Trends in technology are discussed, including next-generation concepts that promise ultrahigh efficiency and low cost, while providing exceptionally clean power plant systems. Section 1 summarizes fuel cell progress since the last edition and includes existing power plant nameplate data. Section 2 addresses the thermodynamics of fuel cells to provide an understanding of fuel cell operation at two levels (basic and advanced). Sections 3 through 8 describe the six major fuel cell types and their performance based on cell operating conditions. Alkaline and intermediate solid state fuel cells were added to this edition of the Handbook. New information indicates that manufacturers have stayed with proven cell designs, focusing instead on advancing the system surrounding the fuel cell to lower life cycle costs. Section 9, Fuel Cell Systems, has been significantly revised to characterize near-term and next-generation fuel cell power plant systems at a conceptual level of detail. Section 10 provides examples of practical fuel cell system calculations. A list of fuel cell URLs is included in the Appendix. A new index assists the reader in locating specific information quickly

Micro-structured functional catalytic eramic hollow fibre membrane reactor for methane conversion

The most significant issue associated with the oxidative methane conversion processes is the use of pure oxygen, which is extremely expensive. By using a dense oxygen permeable membrane reactor, a possible decrease in the air separation cost can be expected due to the elimination of oxygen plants. Besides, higher reaction yields can be attained due to the selective dosing of oxygen into the reaction zone. This thesis focuses on the development and potential application of functional micro-structured catalytic ceramic hollow fibre membrane reactor (CHFMR) in oxidative methane conversion to syngas (known as partial oxidation of methane (POM)) and to ethane and ethylene (known as oxidative coupling of methane (OCM)). As the membrane reactor performance is crucially dependant on the oxygen permeation rate and good contact between oxygen and methane, two types of membrane reactor designs were proposed in this study. The first design involves the development of CHFMR that consists of two layers i.e.: an outer oxygen separation layer and an inner catalytic substrate layer, known as dual-layer catalytic hollow fibre membrane reactor (DL-CHFMR). The DL-CHFMR was fabricated via a novel single-step co-extrusion and co-sintering technique, in which the thickness and the composition of each functional layer can be controlled in order to improve reactor performance. The second design involves the development of CHFMR with an outer dense separation layer integrated with conical-shaped microchannels open at the inner surface, created via a viscous fingering induced phase inversion technique. Besides substantially reducing resistance across the membrane, the microchannels can also act as a structured substrate where catalyst can be deposited for the catalytic reaction to take place, forming a catalytic hollow fibre membrane microreactor (CHFMMR). Although the CHFMRs discussed in this study are designed particularly for POM and OCM, there are general advantages of such membrane structures and reactor designs for improving the overall reaction performance. Therefore, these reactor designs can be transferred to other important catalytic reactions.Open Acces

An air-breathing, portable thermoelectric power generator based on a microfabricated silicon combustor

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections."February 2011." Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 224-237).The global consumer demand for portable electronic devices is increasing. The emphasis on reducing size and weight has put increased pressure on the power density of available power storage and generation options, which have been dominated by batteries. The energy densities of many hydrocarbon fuels exceed those of conventional batteries by several orders of magnitude, and this gap motivates research efforts into alternative portable power generation devices based on hydrocarbon fuels. Combustion-based power generation strategies have the potential to achieve significant advances in the energy density of a generator, and thermoelectric power generation is particularly attractive due to the moderate temperatures which are required. In this work, a portable-scale thermoelectric power generator was designed, fabricated, and tested. The basis of the system was a mesoscale silicon reactor for the combustion of butane over an alumina-supported platinum catalyst. The system was integrated with commercial bismuth telluride thermoelectric modules to produce 5.8 W of electrical power with a chemical-to-electrical conversion efficiency of 2.5% (based on lower heating value). The energy and power densities of the demonstrated system were 321 Wh/kg and 17 W/kg, respectively. The pressure drop through the system was 258 Pa for a flow of 15 liters per minute of air, and so the parasitic power requirement for air-pressurization was very low. The demonstration represents an order-of-magnitude improvement in portable-scale electrical power from thermoelectrics and hydrocarbon fuels, and a notable increase in the conversion efficiency compared with other published works. The system was also integrated with thermoelectric-mimicking heat sinks, which imitated the performance of high-heat-flux modules. The combustor provided a heat source of 206 to 362 W to the heat sinks at conditions suitable for a portable, air-breathing TE power generator. The combustor efficiency when integrated with the heat sinks was as high as 76%. Assuming a TE power conversion efficiency of 5%, the design point operation would result in thermoelectric power generation of 14 W, with an overall chemical-to-electrical conversion efficiency of 3.8%.by Christopher Henry Marton.Ph.D