Outlet Gas Composition Research Articles

Vapor-phase hydrogenation of acetoin and diacetyl into 2,3-butanediol over supported metal catalysts

Vapor-phase catalytic production of 2,3-butanediol from acetoin and diacetyl was investigated over the supported metal catalysts such as Ni, Co, Cu, and Ag. A yield of 2,3-butanediol higher than 90% can be obtained from both acetoin and diacetyl over Ni/SiO2 catalyst in an H2 flow at 150°C. Since the hydrogenation is an exothermic reaction, a low temperature is favorable to gain a full production of 2,3-butanediol. It was found that the equilibrium among 2,3-butanediol, acetoin, and diacetyl could be achieved at a contact time of the reactants with catalyst longer than 1.67h. The pressure equilibrium constants in the hydrogenation were calculated by the outlet gas composition.

Equilibrium Modeling of Sorption-Enhanced Cogasification of Sewage Sludge and Wood for Hydrogen-Rich Gas Production with in Situ Carbon Dioxide Capture

Sewage sludge disposal is troublesome because of the presence of microbes, toxins, and heavy metals in it. Co-gasification of sewage sludge with wood is a promising pathway to dispose of sewage sludge and generate usable syngas, simultaneously. By using a sorbent for in situ sorption of CO2, H2 fraction in the generated syngas can be enhanced considerably. An equilibrium model was developed taking wood and sewage sludge as the model compounds and CaO as the sorbent. This evaluation was performed by employing ASPEN PLUS (V 8.8) software. Principle of Gibbs free-energy minimization was adopted to predict the outlet gas composition and gas yield. The impact of reactor temperature (600 to 900 °C) and sludge content (0 to 100 wt % at 700 °C) in the feedstock on syngas yield and constituents were assessed. With 30 wt % sludge, maximum gas yield was observed as 0.526 kg h–1 at 900 °C while minimum CO2 fraction was achieved at 700 °C. At 700 °C, the highest gas yield of 0.251 kg h–1 was recorded at 50 wt % sludge...

Conversion of Petroleum Coke in a High-Pressure Entrained-Flow Gasifier: Comparison of Computational Fluid Dynamics Model and Experiment

High-pressure entrained-flow gasifier technology is used to convert solid carbonaceous feedstocks into synthesis gas, which can be used in an integrated gasification combined cycle power plant or as a feedstock for chemical or synthetic fuel production. Computational fluid dynamics (CFD) models, once validated, can be used to help design full-scale reactors. Model validation entails the comparison of model predictions to lab-scale or pilot-scale measurements. However, experimental measurements of high-pressure pilot-scale gasifiers usually consist only of wall temperatures and outlet gas temperature and composition, which are of limited use for model validation when the gasifier is operating well, providing information only about operating temperature, heat loss, and equilibrium gas composition. These do not provide a strong validation of the CFD model, whose main purpose is to make predictions of the flame size and shape and its ability to convert solid fuel to gas efficiently in a small volume. This paper presents a model validation based on data generated using CanmetENERGY’s 1 MWth high-pressure entrained-flow gasifier. To provide a stronger validation, the approach taken here is to compare the model predictions to the pilot-scale measurements over a range of operating conditions comprising higher (approximately 90%) carbon conversion and lower (approximately 80% or lower) carbon conversion. In effect, the comparison includes operating conditions for which gasification reactions are extended or delayed toward the outlet in order to capture key effects. It is found that the present CFD model is able to track the performance of the gasifier over the range of operating conditions and provides insight into the causes for limited carbon conversion.

Simulation of a reversible SOFC with Aspen Plus

A thermodynamic Aspen Plus simulation model for a reversible solid oxide fuel cell (RSOFC) is presented and evaluated. It is composed of an electrolysis and a fuel cell module. The latter is based on an existing non reversible SOFC model. The electrolysis model simulates water electrolysis as well as catalytic reactions of inlet gases. The model has been validated using data from literature. It has been found that the support layer on fuel electrode supported cells has to be treated differently in terms of diffusion than the active layer. Simulation results show that for the investigated cell parameters, the positive effect of adding CO2 to the steam feed on the electrolysis process is due to water–gas-shift reactions and not CO2 electrolysis. An analysis of outlet gas compositions in electrolysis mode showed that the assumption of the cell as an equilibrium reactor was justified. A parameter study has been conducted, showing that increasing the operation temperature and pressure can improve the overall performance, while changing the inlet gas compositions in general improves either fuel cell or electrolysis mode and deteriorates performance for the other mode.

Study on simulation of pulverized coal gasification process in the GSP gasifier

A model of entrained‐flow coal gasifier (1920 t/d and single nozzle) was established to simulate the gasification process of pulverized coal from Ningxia of China on the basis of ANSYS Fluent. In order to simulate the characteristics of the coal gasification process, the Lagrange model was adopted to obtain properties of particles, and the standard k‐ϵ turbulence model was applied to the gas phase flow. Meanwhile, the species transport model and modified eddy‐dissipation model (EDM) were used to simulate the species transport and gas phase reaction, respectively. Radiation heat transfer was modelled with the P1 model. The simulation results were in good agreement with the actual production data. In addition, the effects of the pressure, temperature, oxygen‐coal ratio, and steam‐coal ratio on the gasification process were studied using this model. It was found that increasing the gasification pressure had little effect on the composition of outlet gas. The concentration of CO and H2 increased with the increase of temperature. The best oxygen‐coal ratio range was 0.70–0.85 for this gasifier and coal sample. The steam‐coal ratio was decided by the actual operating conditions of the gasification. The simulation of the coal gasification process can predict the details of flow field, temperature field, velocity field, and concentration field in the gasifier. It is helpful to clearly understand coal gasification behaviour inside the gasifier so as to better understand the actual gasification process. Furthermore the simulation method is practicable in the gasifier design and structure optimization, and also supplies some useful data to assist the production operation.

Influence of the microstructure on the catalytic properties of SOFC anodes under dry reforming of methane

This work investigates the catalytic properties of different solid oxide fuel cell (SOFC) Ni-based anodes toward the dry reforming of CH4. The analysis is carried out in a tubular quartz micro-reactor. A mass spectrometer is used to analyze the outlet gas composition and thus to evaluate the methane conversion rate. Temperature Programmed Oxidation (TPO) experiments were also performed on the anode samples to calculate the amount of deposited carbon.Ni based anodes differing in term of microstructure, with both yttria stabilized zirconia and gadolinia doped-ceria, were tested. The investigated catalytic properties were related to the anode microstructure by measuring the specific surface area of the different samples and by means of morphological observations.It is found that the conversion rate of methane is strongly dependent on the specific surface area of the anode.

Cracking Reaction of Octane Fuel and Electrochemical Reaction on Ni-YSZ Cermet Anode of Internal Steam Reforming Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) can, in principle, use not only hydrogen but also hydrocarbon fuels which have high energy density. Then, SOFC is a promising power source for many potential mobile robot applications. Octane is a good candidate as fuel due to high boiling point enough to be in the liquid phase even at high temperatures in summer. Performance of the internal reforming SOFC is governed by anode electrode material, internal reforming method, and operating conditions. Ni-yttria stabilized zirconia (Ni-YSZ) cermet is the most promising anode material for SOFC because of its low cost, chemical stability, and closely matched thermal expansion coefficients with the dense YSZ electrolyte. Steam reforming is the first choice for the internal reforming method because it has been frequently-studied for the direct use of methane fuel. Then, operation of SOFC by internal steam reforming of octane has been studied. However, cracking reactions on the YSZ anode, which is affected by the operating conditions, have not been elucidated sufficiently. The purpose of this study is to clarify the cracking reaction of octane fuel and the electrochemical reaction of the Ni-YSZ anode electrode under various operating conditions. In this study, the fuel-cracking reaction on the Ni-YSZ anode electrode is estimated by gas chromatography with thermal conductivity detector. Anode electrode performance is studied by electrochemical measurement. Two types of octane (n-octane; linear alkane, iso-octane; branched chain alkane) are used in order to elucidate the effect of difference in carbon-chain structure. Octane and steam of equilibrium vapor pressure were supplied to the SOFC cell by bubbling carrier gas (He) at a constant rate. Temperature of the octane bubbler and the carrier gas flow rate was 30 oC and 10 ml/min, respectively. The carrier gas flow rate of the water bubbler was 83 ml/min. Steam/carbon ratio (S/C) was controlled over an S/C ratio from 0.5 to 5.5 by changing the temperature of the water bubbler from 30 to 80 oC. The cell temperature range was 700-950 oC. The octane internal steam reforming operation of SOFC was demonstrated by I-V and I-P characteristics and stable power generation property by constant current. The effects of operating conditions (S/C ratio and cell temperature) on the open circuit voltage (OCV) and power generation property were investigated. The chemicals generated by the cracking reaction of octane at various operating conditions were analyzed by gas chromatography and compared. The difference in outlet gas compositions from the cell of open circuit condition and power generation condition revealed the main species consumed for the power generation reaction on the anode electrode. The electrochemical reaction resistance of the Ni-YSZ anode was measured by ac impedance method and the rate-determining process was identified. In this study the following was revealed. When the S/C and/or the operating temperature are high, the reforming reaction rate is large. By the reforming reaction of n-octane, H2, CO, CO2, and CH4 is mainly produced. When the iso-octane is used as the fuel, small amount of C2H6 is also generated in addition to them. Only H2 and CO contribute to the power generation directly. Rate-determining process of the electrode reaction is a cracking reaction to H2 and CO.

Octane Steam Reforming and Electrochemical Reaction on Cu-GDC Cermet Anode of Internal Reforming Solid Oxide Fuel Cell

A small and high-performance solid oxide fuel cell (SOFC) system is promising as a power source for many potential mobile robot applications. To realize the small SOFC system, the direct use of liquid hydrocarbon fuel, which has high energy density and is easy to storage and carry, is desirable. The optimization of type of fuel, operating conditions, and a fuel electrode (anode electrode) is essential. In the view point of the use at high temperatures in summer outdoor, octane having high boiling temperature is a good candidate as the fuel. Steam reforming is the first choice for the internal reforming method because it has been frequently-studied for the direct use of methane fuel. A porous cermet of Ni and yttria-stabilized zirconia (YSZ), which has widely been studied as an anode electrode for the internal reforming operation SOFC, is one of promising anode electrode materials, however, performance degradation due to sulfur poisoning and carbon deposition on the anode electrodes surface is concerned. A porous cermet of Cu and gadolinium oxide-doped ceria (Cu-GDC), which, respectively, have excellent sulfur tolerance and oxygen ion supply property, has high potential for the anode electrode of SOFC operated by internal reforming of methane. Therefore, in this study, the Cu-GDC cermet was focused as an alternative anode electrode for the octane-direct use SOFC. The aim of this study is to clarify the effects of operating conditions on the reforming reaction and electrochemical reaction on the Cu-GDC cermet anode electrode. In this study, the fuel-cracking reaction, which occurs at elevated temperature in the presence of excess steam, was estimated. In order to understand the effect of difference in branching of carbon chain, n-octane (linear alkane) and iso-octane (branched chain alkane) were used. Octane and steam were supplied to the SOFC cell by bubbling carrier gas (He or Ar) at a constant rate. Temperature of the octane bubbler and the carrier gas flow rate was 30 oC and 10 ml/min, respectively. The carrier gas flow rate of the water bubbler was 83 ml/min. Steam/carbon ratio (S/C) was controlled over a S/C ratio from 0.5 to 5.5 by changing the temperature of the water bubbler from 30 to 80 oC. The cell temperature range was 700-850 oC. I-V and I-P characteristics, and stable power generation property by constant current were investigated to demonstrate the octane direct internal reforming operation of SOFC. The effects of S/C ratio and cell temperature on the open circuit voltage (OCV) and I-V and I-P characteristics were investigated. In order to identify the chemicals generated by the fuel cracking reaction, outlet gas compositions from the cell of open circuit condition and power generation condition were analyzed by gas chromatography. The following are the main findings that we have revealed in the present study. By raising the S/C ratio and/or the cell temperature, the reforming reaction is facilitated, but fluctuation of the OCV is increased. Chemical species and their ratio generated by the cracking reaction are changed by the difference in the carbon-chain of octane. Mainly H2, CO, CO2, CH4, and C2H6 are generated in the reforming reaction of n-octane, and C3H8, CH3OH, and C4H10 are also generated in addition to those in the reforming reaction of iso-octane. However, the main electrode reaction to generate electrical power is only the electrochemical oxidation of H2 and/or CO. By using the n-octane fuel, the carbon deposition is reduced. The rate-determining process is dissociation to H and CO.

Carbon Deposition during CO2 Electrolysis in Ni-Based Solid-Oxide-Cell Electrodes

Local gradients within an operating solid oxide electrolyzer cell were studied using current-potential measurements and electrochemical impedance spectroscopy. The cells and operating conditions were closely related to commercial applications. The cells with fuel electrodes of nickel and yttria-stabilized zirconia (Ni-YSZ) cermets were supplied by Haldor Topsoe A/S and the operating conditions were chosen so as to take stack relevant considerations into account. Formation of carbon nanotubes in Ni containing fuel electrodes has previously been observed in co-electrolysis of H2O and CO2 [1]. Hence, the carbon formation threshold in an operating cell was investigated during electrolysis of an idealized reactant atmosphere of CO and CO2. The electrolysis current was gradually increased in steps until the cell voltage spontaneously increased, thereby indicating cell degradation and possibly the onset of carbon deposition. The outlet gas composition at each current step was estimated based on the inlet gas composition and the reactant conversion using Faraday's law. The increase in voltage was observed at lower pCO/pCO2 ratios than that corresponding to the thermodynamic threshold for carbon formation. Electrochemical impedance spectroscopy in both H2/H2O and CO/CO2 revealed an increase in resistance of the fuel electrode after each CO2 electrolysis current-voltage curve, indicating possible carbon deposition. The difference in partial oxygen pressure between inlet and outlet was analyzed to verify carbon deposition. The increase in voltage is likely due to either blocking of the reaction sites by the deposited carbon, or due to the microstructural damage caused by the carbon, or a combination of these. Moreover, the current step-size and step-length was varied to investigate the time-dependence of the detection of carbon deposition. Initial results indicate that for longer current steps, carbon formation is observed at lower pCO/pCO2 ratios. This is related to the rate of carbon deposition and the averaged nature of the cell voltage measurements. Possible reasons for these observations will be discussed in detail. In an attempt to mitigate the degradation due to carbon deposition, the Ni-YSZ electrode was infiltrated with a gadolinium doped ceria (CGO) solution. Initial results indicate that the coking tolerance was not enhanced, but it is still unclear whether infiltrated cells degrade less. However, infiltrated cells display a significant performance enhancement before coking, especially under electrolysis current. The investigation thus indicated carbon formation in the Ni containing fuel electrode before the thermodynamically calculated threshold for average measurements of the cell was reached. The deviation from the average threshold was reproduced on several cells and quantified (figure 1). The observation of carbon formation on a local, microstructural level before the expected thermodynamic threshold for average measurements on the cell level, is of crucial importance when choosing operating conditions for commercial systems. The effect would be even more severe on stack level, where the gas diffusion and temperature gradients are more pronounced. Initial results of the mitigation strategy of infiltrating CGO are negative, but increased performance prior to coking was observed. [1] Y. Tao, S. D. Ebbesen, and M. B. Mogensen, “Carbon Deposition in Solid Oxide Cells during Co-Electrolysis of H2O and CO2” Journal of the Electrochemical Society, vol. 161, pp. F337–F343, Jan. 2014. Figure 1

An Analysis of Biogas Reforming Process on Ni/YSZ and Ni/SDC Catalysts

The conversion of biogas to electricity presents an attractive niche application for fuel cells. Thus attempts have been made to use biogas as a fuel for high temperature fuel cell systems such as SOFC. Biogas can be converted to hydrogen-rich fuel in a reforming process. For hydrocarbon-based fuel, three types of fuel conversion can be considered in reforming reactions: an external reforming system, an indirect internal reforming system and a direct internal reforming system. High-temperature SOFC eliminates the need for an expensive external reforming system. The possibility of using internal reforming is one of the characteristics of high temperature fuel cells like SOFC. However, for high-temperature operation, thermal management of the SOFC system becomes an important issue. To properly carry out thermal management, both detailed modeling and numerical analyses of the phenomena occurring inside the SOFC system is required. In the present work, the process of reforming biogas on a Ni/YSZ and a Ni/SDC catalyst has been numerically and experimentally investigated. Measurements including different thermal boundary conditions, steam-to-carbon ratios and several different fuel compositions were taken. A numerical model containing methane/steam reforming reaction, dry reforming reaction and shift reaction has been proposed to predict the gas mixture composition at the outlet of the reformer. The results of the numerical computation were compared with experimental data and good agreement has been found. The results indicate the importance of combined, numerical and experimental studies in the design of SOFC reformers. The combined approach used leads to the successful prediction of the outlet gas composition for different modelling conditions.

Carbon Deposition during CO2 Electrolysis in Ni-Based Solid-Oxide-Cell Electrodes

The carbon formation threshold in an operating cell was investigated during electrolysis of an idealized reactant atmosphere of CO and CO2. The electrolysis current was gradually increased in steps until the cell voltage spontaneously increased, thereby indicating cell degradation and possibly the onset of carbon deposition. The outlet gas composition at each current step was estimated based on the inlet gas composition and the reactant conversion using Faraday's law. The increase in voltage was observed at lower outlet pCO/pCO2 ratios than that corresponding to the expected thermodynamic threshold for carbon formation. The degradation observed was related to the fuel electrode, as confirmed by electrochemical impedance spectroscopy. Mitigation of the degradation mechanism was attempted by infiltrating gadolinium doped ceria. The onset of carbon deposition was largely unaffected, but the polarization resistance of the electrode during electrolysis was significantly decreased.

Formation of hydrogen from the CO–H2O system using porous Gd-doped ceria electrochemical cell with MnO cathode and Fe3O4 anode

This paper reports the outlet gas composition and phase change of electrodes during the CO–H2O reaction (CO + H2O → H2 + CO2) using an electrochemical cell with MnO–GDC (Gd-doped ceria: Ce0.8Gd0.2O1.9) cathode/porous GDC electrolyte/Fe3O4–GDC anode system. In the cathode, oxidation of MnO by H2O (3MnO + H2O → Mn3O4 + H2) and electrochemical reduction of Mn3O4 occurred (Mn3O4 + 2e− → 3MnO + O2−). In the anode, reduction of Fe3O4 by CO (Fe3O4 + CO → 3FeO + CO2) and electrochemical oxidation of FeO occurred (3FeO + O2− → Fe3O4 + 2e−). H2 and CO2 gases were produced through the above catalytic reactions. The fraction of H2 gas in the outlet gas increased at a high heating temperature and was 30–50% at 700 °C. As a parallel reaction of the CO–H2O reaction, the supplied CO gas was decomposed to CO2 and solid carbon over Fe3O4 in the anode at low temperatures (disproportion of CO, 2CO → CO2 + C).

Waste Gypsum Board and Ash-Related Problems during Combustion of Biomass. 1. Fluidized Bed

This paper is the first in a series of two describing the use of waste gypsum boards as an additive during combustion of biomass. This paper focuses on experiments performed in a bench-scale bubbling fluidized-bed reactor (5 kW). Three biomass fuels were used, i.e., wheat straw (WS), reed canary grass (RC), and spruce bark (SB), with and without addition of shredded waste gypsum board (SWGB). The objective of this work was to determine the effect of SWGB addition on biomass ash transformation reactions during fluidized bed combustion. The combustion was carried out in a bed of quartz sand at 800 or 700 °C for 8 h. After the combustion stage, a controlled fluidized–bed agglomeration test was carried out to determine the defluidization temperature. During combustion experiments, outlet gas composition was continuously measured by means of Fourier transform infrared spectroscopy. At the same place in the flue gas channel, particulate matter was collected with a 13-stage Dekati low-pressure impactor. Bottom and cyclone fly ash samples were collected after the combustion tests. In addition, during the combustion tests a 6-h deposit sample was collected with an air-cooled (430 °C) probe. All ash samples were analyzed by means of scanning electron microscopy combined with energy dispersive X-ray spectrometry for elemental composition and with X-ray powder diffraction for the detection of crystalline phases. Decomposition of CaSO4 originating from SWGB was mainly observed during combustion of reed canary grass at 800 °C. The decomposition was observed as doubled SO2 emissions. No significant increase of SO2 during combustion of SB and WS was observed. However, the interaction of SWGB particles with WS and SB ash forming matter, mainly potassium containing compounds, led to the formation of K2Ca2(SO4)3.

Accurate predictions of H2O and CO2 co-electrolysis outlet compositions in operation

This work highlights an experimental and modeling approach devoted to a better understanding of H2O and CO2 co-electrolysis mechanisms at 800°C. A standard Cathode Supported Cell (CSC) was used in this study. Through numerical adjustments on experimental polarization curves, the cathode microstructural parameters and exchange current densities for H2O and CO2 reductions were determined and subsequently implemented in an in-house co-electrolysis model. Additionally, micro gas chromatography (μGC) analyses were performed in co-electrolysis operating mode for different cell polarizations (from i = 0 to i = −1.75 A cm−2). μGC analyses at Open Circuit Voltage (OCV) were used to validate the kinetic constants of the Water Gas Shift (WGS) reaction implemented in the model. Predictions of both co-electrolysis polarization curves and outlet gas compositions were then compared to the experimental measurements. The good agreement between simulated and experimental data proves the relevance of the macroscopic representation of electrochemical processes through a “surface ratio” that takes into account the H2O and CO2 electrolyzes competition. A sensitivity analysis was performed to ensure a better understanding of co-electrolysis mechanisms and further investigate the influence of the reverse WGS reaction over CO production.

Reduction Mechanism of Composite Consisted of Coal and Hematite Ore by Volatile Matter at 700–1100 K

In the drive to mitigate global warming, the iron and steel industry has made efforts to reduce carbon dioxide gas emissions. Utilization of a composite material consisting of carbonaceous material and iron ore is expected to be an effective way to solve the issue. Volatile matters in carbonaceous materials have a potential to reduce emissions by lowering the reduction temperature.In this study, the reduction by volatile matter in a coal/hematite ore composite was fundamentally examined. Different kinds of coal were chosen as carbonaceous material samples. The reduction experiment using the prepared composites was conducted by varying the heating rate as 0.08, 0.17, and 0.33 K/s, up to a temperature of 1473 K under Ar–5%N2 gas flow. The outlet gas composition was analyzed and the results were used to calculate the reduction degree.Reduction degree of hematite ore initially increases with increasing content of volatile matter in coal. However, beyond a certain point, further increase in the volatile matter content of the coal did not give a significant change in the reduction degree. For the evaluated coals, the amounts and types of gases generated are not different each other. H2 gas seems to form together with solid carbon via decomposition of hydrocarbon gases. Such gases and solid carbon may contribute to the reduction. Moreover, reduction by H2 was promoted in the early stage of the reactions by decreasing heating rate. The data indicate that control of the heating rate is a possible way to promote reduction at low temperature.

Effect of Operating Conditions on the Electrochemical Performance of Ni-YSZ Cermet Anode for Solid Oxide Fuel Cells Using Octane Fuel

Ni-yttria stabilized zirconia (YSZ) cermet is evaluated as anode material for the solid oxide fuel cells operated by the direct internal steam reforming of iso-octane. Effect of the cell temperature and the steam/carbon ratio in the fuel was examined from the point of view of the cracking reaction performance, identification of the elementary process which governs power generation and durability. When both steam/carbon ratio and cell temperature are high enough, iso-octane is cracked to generate H2 and CO. The cracking reaction of iso-octane on the surface of the Ni-YSZ anode governs the reaction rate of the anode electrode. Outlet gas composition from the cell was analyzed by gas chromatography, and the single cell property was measured by the electrochemical method.

PEMFC Cathode Contamination Evaluation with Membrane Conductivity Cell, CA, CP, CV, EIS, GC/MS and ISE - Acetonitrile

Air pollution is a challenge for the commercialization of proton exchange membrane fuel cells (PEMFCs) because exposure to pollutants has been shown to be detrimental to the performance and durability of the cell (1). Recently, 21 species were down selected from a list of more than 200 airborne pollutants for single cell evaluations (2). Results showed that contaminants differently affected cell performance. Acetonitrile and 6 other species were down selected for detailed studies. Acetonitrile adsorbs on the Pt/C catalyst surface, impacts the oxygen reduction reaction and causes a significant cell performance loss. Acetonitrile is also the only specie that affects the fuel cell membrane and ionomer proton conductivity. However, tests completed with a membrane conductivity cell did not show any impact of acetonitrile in an inert and saturated gaseous mixture. These results suggest the conductivity effect of acetonitrile in an operating PEMFC originate from conversion products.The proton conductivity impact of acetonitrile was investigated by operating membrane/electrode assemblies (MEAs) with H2/N2 and H2/air in the absence and presence of acetonitrile in the cathode stream. Acetonitrile was injected at a concentration of 20 ppm for approximately 10 hours. The cell current was measured (chronoamperometry, CA) with two different potential control methods. For H2/N2, the N2 electrode potential was controlled with the H2 electrode acting as the reference electrode. During each test, before, during and after contamination, cyclic voltammograms (CV) were acquired to detect the presence of adsorbates or reactions on the Pt surface. For H2/air, the cell voltage was controlled. Acetonitrile conversion products were also analyzed by measuring cell inlet and outlet gas compositions by gas chromatography/mass spectrometry (GC/MS).Figure 1 shows H2/air experiments. Before acetonitrile injection, as expected, the current was larger for lower cell voltages. The evolution of the open circuit voltage case (OCV) is also depicted. After the acetonitrile injection was initiated, the currents decreased by 71, 92 and ~100 % within approximately 10 hours for cell voltages of respectively 0.55, 0.65 and 0.85 V. For the OCV test, a 9 % decrease is observed in approximately 15 min followed by a steady state. These current and voltage decreases are partly due to acetonitrile adsorption on the Pt surface. Ohmic resistance changes also played a role with a contribution that increased with the cell potential, which is indicative of an acetonitrile oxidation product being absorbed by the membrane and ionomer. These results and membrane conductivity cell, CV and GC/MS data will be synthesized into a reaction mechanism.ACKNOWLEDGMENTSThis work is supported by the Department of Energy (DE-EE0000467) and the Office of Naval Research (N00014-11-1-0391). Authors are also grateful to the Hawaiian Electric Company for their ongoing support to the operations of the Hawaii Sustainable Energy Research Facility.REFERENCESJ. St-Pierre, in Polymer Electrolyte Fuel Cell Durability, F. N. Büchi, M. Inaba, and T. J. Schmidt, Editors, p. 289, Springer (2009).J. St-Pierre, M. S. Angelo, and Y. Zhai, J. Electrochem. Soc., 161, F280 (2014).

Parameter identification and state estimation of a microalgae dynamical model in sulphur deprived conditions: Global sensitivity analysis, optimization criterion, extended Kalman filter

In this article, a dynamic model describing the growth of the green microalgae Chlamydomonas reinhardtii, under light attenuation and sulphur‐deprived conditions leading to hydrogen production in a photobioreactor is presented. The strong interactions between biological and physical phenomena require complex mathematical expressions with an important number of parameters. This article presents a global identification procedure in three steps using data from batch experiments. First, it includes the application of a sensitivity function analysis, which allows one to determine the parameters having the greatest influence on model outputs. Secondly, the most influential parameters were identified by using the classical least‐squares cost function. This stage is applied to the experimental data collected from a lab‐scale batch photobioreactor. Finally, the implementation of an Extended Kalman Filter estimating the biomass concentration, extracellular and intracellular sulphur concentrations is presented. Thereby, the observer uses on‐line measurements provided by a mass spectrometer measuring the outlet gas composition (O2, CO2). Software sensor performances and limits are illustrated in simulation and with experimental data.

Correlation between hydrogen production rate, current, and electrode overpotential in a solid oxide electrolysis cell with La0.6Sr0.4FeO3-δ thin-film cathode.

A solid oxide electrolysis cell (SOEC) with a model-type La0.6Sr0.4FeO3−δ thin-film cathode (working electrode) on an yttria-stabilized zirconia electrolyte and a porous La0.6Sr0.4Co0.2Fe0.8O3−δ counterelectrode was operated in wet argon gas at the cathode. The hydrogen formation rate in the cathode compartment was quantified by mass spectrometry. Determination of the current as well as outlet gas composition revealed the electrochemical reduction of some residual oxygen in the cathodic compartment. Quantitative correlation between gas composition changes and current flow was possible. At 640 °C a water-to-hydrogen conversion rate of ca. 4 % was found at −1.5 V versus a reversible counterelectrode in 1 % oxygen. Onset of hydrogen formation could already be detected at voltages as low as −0.3 V. This reflects a fundamental difference between steam electrolysis and electrolysis of liquid water: substantial hydrogen production in a SOEC is already possible at pressures much below ambient. This causes difficulties in determining the cathodic overpotential of such a cell.Graphical

Methanation catalytic reactor

Storing renewable electricity in a natural gas grid is a new approach for seasonal storage. Using the existing natural gas infrastructure, a chemical energy source (methane) is stored efficiently, distributed and made available for use as required. Thus, the main step in the storage process is CO methanation. Modelling of an isothermal methanation catalytic reactor based on a kinetic scheme was carried out with Aspen plus™ software in a temperature range between 520 and 600 K and a H2/CO molar ratio of 3, in the presence of CO2 and steam. The model was validated by comparing simulation results with experimental ones. The maximum relative error is 10.87%. The effects of temperature, pressure and CO2 addition in feed gas (syngas) on CO conversion and the outlet gas composition were carefully investigated.