Combination of Sorption-Enhanced Steam Methane Reforming and Electricity Generation by MCFC: Concept and Numerical Simulation Analysis

Abstract

Reformed gas made by the steam methane reforming(SMR) process is used as fuel feed to MCFC, but it is not as good as pure hydrogen due to the presence of CO₂ and CO. The sorption-enhanced steam methane reforming(SE-SMR) process can reduce CO₂ and CO to a low level and produce high purity hydrogen. Considering the merits of similar operating temperatures (about 500°C) and carbon dioxide recycle, a novel concept of a six-step sorption-enhanced steam methane reforming (SE-SMR) combined with electricity generation by molten carbonate fuel cell (MCFC) is proposed. In the present paper, a cycle of the SE-SMR process, which include the steps of reaction/adsorption, depressurization, gas purges (nitrogen and reformed gas, respectively), and pressurization with reformed gas, is modeled and analyzed. The process stream in the SE-SMR process is used as anode feed in MCFC. According to the result of numerical simulation, a fuel cell grade hydrogen product (above 80% purity) at the SE-SMR temperature of 450°C can be obtained. A carbon dioxide recycle mechanism is developed for cathode feed of MCFC from flue gas by burning with excess air to achieve a proper CO₂/air ratio (about 30:70). The novel electricity generation system, which can operate at lower energy consumption and high purity hydrogen feed is helpful for the MCFC'S performance and life time.     

Pentalithium Ferrite (Li5FeO4) as Highly Active Material for Hydrogen Production in the Chemical Looping Partial Oxidation of Methane

In this work, the pentalithium ferrite was synthetized by solid-state method, and it was characterized by XRD and N₂ adsorption–desorption techniques. Then, H₂ production was obtained through a catalytic conversion process; chemical looping partial oxidation (CLPO) of methane using Li₅FeO₄ as multifunctional material. The catalytic decomposition of methane is an easy way to obtain clean energy, such as hydrogen, but in this process carbon deposition is also possible. The results showed that this material has the ability to convert methane to hydrogen, but it is also capable to donate oxygen atoms from its crystalline network, producing carbon monoxide and/or carbon dioxide, limiting the carbon deposition on the ceramic surface. In addition, it was demonstrated that this lithium-based ceramic produces hydrogen over a wide temperature range (550–900 °C), with a stable hydrogen production for 3 h at 825 °C. Furthermore, it was possible to achieve a cyclic test of methane decomposition with a pre-oxidation process between each cycle obtaining an outstanding increase in hydrogen production from 10% in cycle 1 to ~?100% in the cycle 10. This previous stage not only induces an increase in the decomposition of methane, but also avoids carbon deposition accompanied by the production of both CO_X compounds. Finally, it must be mentioned that Li₅FeO₄ is capable to chemisorb both carbon oxides produced, promoting high purity hydrogen production.

     

Effect of carbon deposition over carbonaceous catalysts on CH4 decomposition and CH4-CO2 reforming

An investigation was made using a continuous fixed bed reactor to understand the influence of carbon deposition obtained under different conditions on CH₄-CO₂ reforming. Thermogravimetry (TG) and X-ray diffraction (XRD) were employed to study the characteristics of carbon deposition. It was found that the carbonaceous catalyst is an efficient catalyst in methane decomposition and CH₄-CO₂ reforming. The trend of methane decomposition at lower temperatures is similar to that at higher temperatures. The methane conversion is high during the initial of stage of the reaction, and then decays to a relatively fixed value after about 30 min. With temperature increase, the methane decomposition rate increases quickly. The reaction temperature has significant influence on methane decomposition, whereas the carbon deposition does not affect methane decomposition significantly. Different types of carbon deposition were formed at different methane decomposition reaction temperatures. The carbon deposition Type I generated at 900°C has a minor effect on CH₄-CO₂ reforming and it easily reacts with carbon dioxide, but the carbon deposition Type II generated at 1000°C and 1100°C clearly inhibits CH₄-CO₂ reforming and it is difficult to react with carbon dioxide. The results of XRD showed that some graphite structures were found in carbon deposition Type II.     

Effect of carbon deposition over carbonaceous catalysts on CH<Subscript>4</Subscript> decomposition and CH<Subscript>4</Subscript>-CO<Subscript>2</Subscript> reforming

An investigation was made using a continuous fixed bed reactor to understand the influence of carbon deposition obtained under different conditions on CH₄-CO₂ reforming. Thermogravimetry (TG) and X-ray diffraction (XRD) were employed to study the characteristics of carbon deposition. It was found that the carbonaceous catalyst is an efficient catalyst in methane decomposition and CH₄-CO₂ reforming. The trend of methane decomposition at lower temperatures is similar to that at higher temperatures. The methane conversion is high during the initial of stage of the reaction, and then decays to a relatively fixed value after about 30 min. With temperature increase, the methane decomposition rate increases quickly. The reaction temperature has significant influence on methane decomposition, whereas the carbon deposition does not affect methane decomposition significantly. Different types of carbon deposition were formed at different methane decomposition reaction temperatures. The carbon deposition Type I generated at 900°C has a minor effect on CH₄-CO₂ reforming and it easily reacts with carbon dioxide, but the carbon deposition Type II generated at 1000°C and 1100°C clearly inhibits CH₄-CO₂ reforming and it is difficult to react with carbon dioxide. The results of XRD showed that some graphite structures were found in carbon deposition Type II.     

Pyrolysis of methane in the presence of hydrogen

The kinetics of methane pyrolysis were studied in a tubular flow reactor in the temperature range 1200 to 1500°C at atmospheric pressure. To avoid excessive carbon formation the reaction time was short and the methane feed was diluted with hydrogen. Ethene, ethyne, benzene and hydrogen were the main gaseous products. Ethane was observed as a product at very low conversions of methane. More than 90% selectivity was obtained for C₂ products. The ratio of ethyne to ethene increased with increasing temperature. The yield of C₂ products is limited by gas-phase equilibrium at lower temperatures. Formation of carbon was strongly depressed by hydrogen at higher temperatures. The maximum yield of ethyne was found to increase from about 10% to about 50% when the temperature was increased from 1200 to 1500°C, with hydrogen dilution H₂: CH₄ = 2: 1. A mechanistic reaction model was used to simulate the pyrolysis of methane at the actual conditions. A sensitivity analysis was performed to evaluate the elementary reactions which influence the formation and consumption of the species in the model system.     

Methane Steam Reforming in Hydrogen-permeable Membrane Reactor for Pure Hydrogen Production

Steam reforming of methane over a ruthenium catalyst has been carried out at 500 °C in a membrane reactor equipped with a palladium membrane supported on a porous stainless steel tube. Hydrogen and carbon dioxide are mainly produced in the reaction, while hydrogen is selectively permeated through the membrane. Since equilibrium-shift takes place by hydrogen separation from the reaction mixture, the methane conversion significantly exceeds the equilibrium value, which is low at 500 °C. The selectivity to carbon monoxide by-produced in the reaction is lower than that expected from the equilibrium. Although the equilibrium conversion decreases with an increase in the reaction pressure, the conversion with the membrane reactor can increase because the hydrogen separation is promoted by the pressure increase. The catalytic activity is an important factor to produce a sufficiently high methane conversion and it is enhanced at a high reaction pressure.     

Upgrading of low rank coal with solvent

In this study, thermal upgrading of low-rank coal with solvent at 380–440 °C under an initial nitrogen pressure of 2 MPa was studied as a possible method for producing clean solid fuel with a high heating value and less spontaneous ignition behavior. Upgrading of Buckskin coal (USA, subbituminous coal) in the presence of t-decalin (non hydrogen-donor solvent) at 440 °C gave 11.4 wt.% of gas, 5.3 wt.% of oil and 74.1 wt.% of upgraded solid product with a small amount of water. The gaseous product consisted mainly of carbon dioxide (67 wt.%), methane, carbon monoxide, hydrogen and a trace of C₂ and C₃ hydrocarbon gases. The oil product from coal contained BTX, phenol, and their alkyl-derivatives. The heating value of the upgraded solid product from the Buckskin coal increased to 31.0 MJ/kg in dry base as compared to the heating value of wet base of the untreated raw coal, which was 19.3 MJ/kg. Spontaneous ignition behavior was greatly reduced by the upgrading. The effect of catalyst and additives on the upgrading was investigated in terms of product distribution and the quality of the solid product. Taiheiyo (Japan, subbituminous) and Yallourn (Australia, brown) coals were also studied.     

Influence of K2CO3 catalyst on rate of hydrogen gasification of carbon black

Kinetic rate measurements of the hydrogen gasification of a graphiticed carbon black at 865°C and 500 psig hydrogen are reported for K₂CO₃ loadings of 0, 1, 5 and 10 wt. %. Potassium loss was measured during reaction; surface area and catalyst loading of residual samples were measured after experiment. A twentyfold increase in gasification rate at 50%–70% conversion is observed upon addition of 10 wt. % K₂CO₃. Specific reaction rate is approximately constant in the presence of 5% and 10% catalyst but decreases for the uncatalyzed sample. These results, as well as the results of experiments in which the carbon is first degassed, support the postulate that surface oxygen is the primary catalytic entity in the hydrogen gasification and that K₂CO₃ merely stabilizes and provides additional oxygen on the surface.     

Effect of steam and sodium hydroxide for the production of hydrogen on gasification of dehydrochlorinated poly(vinyl chloride)

Dehydrochlorinated poly(vinyl chloride) (PVC) and activated carbon were pyrolyzed with sodium hydroxide in a flow of steam and nitrogen at 3.0 MPa and 560–660 °C. In both cases, hydrogen and sodium carbonate were the main products, and methane, ethane, and carbon dioxide were minor products. The gasification rate increased with partial steam pressure, and the reaction order with respect to steam partial pressure was 0.69. For both dehydrochlorinated PVC and activated carbon, the gasification rate increased with the NaOH/C molar ratio. However, the rate became saturated at NaOH/C ratios higher than 2.0. The activation energy of gasification of dehydrochlorinated PVC or activated carbon was 178 kJ/mol, assuming first-order reaction rate. These experimental results indicate that hydrogen was produced from the reaction: C+2NaOH+H₂O→Na₂CO₃+2H₂.     

Hydrothermal reforming of bio-diesel plant waste: Products distribution and characterization

A viscous waste derived from a bio-diesel production plant, in the form of crude glycerol, was reacted under subcritical and supercritical water conditions and the product composition determined in relation to process conditions. Preliminary analysis of the original sample showed that the main constituent organic compounds were methanol (20.8 wt.%), glycerol (42.3 wt.%) and fatty acid methyl esters (33.1 wt.%). Uncatalyzed reforming experiments were carried out in a 75 ml Hastelloy-C batch reactor at temperatures between 300 °C and 450 °C and pressures between 8.5 MPa and 31 MPa. Oil/wax constituted more than 62 wt.% of the reactions products. At 300 °C, the main product was a waxy material containing mainly glycerol and fatty acid methyl esters. As the temperature increased to supercritical water conditions, low viscosity oils were produced and all of the glycerol was reacted. The oils contained mainly saturated and unsaturated fatty acid esters as well as their decomposition products. The gaseous products were carbon dioxide, hydrogen and methane and lower concentrations of carbon monoxide and C₂-C₄ hydrocarbons. No char formation was observed. However, during alkaline gasification with sodium hydroxide at 380 °C, the reaction products included a gaseous effluent containing up to 90% by volume of hydrogen, in addition to oil and significant amount of whitish solid residue (soap). Sodium hydroxide influenced the production of hydrogen via water-gas shift by the removal of carbon dioxide as sodium carbonate, but also decreased oil product possibly through saponification.     

Low temperature hybrid plasma-catalytic methanation over Ni-Ce-Zr hydrotalcite-derived catalysts

The activity of Ceria and Zirconia-promoted Ni-containing hydrotalcite-derived catalysts was assayed in a hybrid plasma-catalytic process for the hydrogenation of carbon dioxide into methane at low temperatures and in the presence of a cold dielectric barrier discharge (DBD) plasma. High methane yields, around 80%, were measured under hybrid plasma-catalytic conditions, even at very low temperatures (110 °C, adiabatic conditions). In the absence of plasma, acceptably high CO₂ conversions and methane yields were only observed at temperatures higher than 330 °C. The presence of completely reduced Ni-crystallites of intermediate size, more readily available on the non-promoted catalysts was found to enhance the methanation reaction. Ce and Zr addition did not result in a noticeable improvement of the catalytic activity.     

Hydrogen production from glycerol by reforming in supercritical water over Ru/Al2O3 catalyst

Supercritical water is a promising medium for the reforming of hydrocarbons and alcohols for the production of hydrogen at high pressures in a short reaction time. Water serves both as a dense solvent as well as a reactant. In this work, hydrogen is produced from glycerol by supercritical water reforming over a Ru/Al₂O₃ catalyst with low methane and carbon monoxide formation. Experiments were conducted in a tubular fixed-bed flow reactor over a temperature range of 700–800 °C, feed concentrations up to 40 wt% glycerol, all at short reaction time of less than 5 s. Glycerol was completely gasified to hydrogen, carbon dioxide, and methane along with small amounts of carbon monoxide. At dilute feed concentrations, near-theoretical yield of 7 mol of hydrogen/mol of glycerol was obtained, which decreases with an increase in the feed concentration. Based on a kinetic model for glycerol reforming, an activation energy of 55.9 kJ/mol was observed.     

Hydrogen Yield from Low Temperature Steam Reforming of Ethanol

Low temperature steam reforming of ethanol in the temperature range of 200–360°C was studied to maximize the production of H₂. The optimum reaction conditions in presence of a suitable catalyst can produce mainly the desired products H₂ and CO₂. Cu/Al₂O₃ catalysts with six different concentrations ranging from 0 to 10 wt.% Mn, were prepared, characterized and studied for the ethanol-steam reforming reaction. Maximum ethanol conversion of 60.7% and hydrogen yield of 3.74 (mol H₂ / mol ethanol converted) were observed at 360°C for catalyst with 2.5 wt.% Mn loading.     

Supercritical water gasification of aqueous fraction of pyrolysis oil in the presence of a Ni‐Ru catalyst

This study demonstrated that aqueous fraction of pyrolysis oil can be efficiently gasified into fuel gases methane and hydrogen via supercritical water gasification (SCWG) at moderate temperatures (500–700°C) over Ni_20%Ru_2%/γ‐Al₂O₃ catalyst. All experiments were performed in a bench‐scale continuous down‐flow tubular reactor packed with the catalyst. Carbon gasification efficiency of 0.91 mol/mol‐C (converted into CH₄ and CO₂) was achieved in SCWG of the aqueous fraction of pyrolysis oil (containing 2.98 wt % C) at 700°C in the presence of the catalyst. A similar carbon gasification efficiency (approx. 0.89 mol/mol‐C) was obtained at a lower temperature (600°C) with a diluted feedstock (0.7 wt %C). Scanning Electron Microscopy coupled with Energy Dispersive x‐ray and inductively coupled plasma analysis results confirmed that this catalyst was stable during SCWG of aqueous fraction of pyrolysis oil after 6 h on‐stream. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2786–2793, 2016     

HYDROGENOLYSIS OF DIPHENYL ETHER

Hydrogenolysis of diphenyl ether was investigated at 550°C and 620°C and at pressures up to 1850 psig. Primary interest was the elucidation of cracking patterns at a hydrogen to diphenyl ether molar ratio of 2:1.

The primary reaction was C—O—C bond cleavage resulting in the formation of benzene and phenol. The secondary reaction was ring cracking resulting in the formation of gaseous components namely, carbon monoxide, carbon dioxide and lighter hydrocarbons.     

Synthesis of nickel catalysts supported on Zr-doped ordered mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and their catalytic performance for low-temperature CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

A series of Zr-doped ordered mesoporous Al₂O₃ with various Zr contents were synthesized by evaporation-induced self-assembly strategy and the Ni-based catalysts supported on these Al₂O₃ materials were prepared by impregnation method. These catalysts with large specific surface area, big pore volume, uniform pore size possess excellent catalytic performance for the low-temperature carbon dioxide reforming of methane. The activities of these catalysts were tested in carbon dioxide reforming of methane reaction with temperature increasing from 500 to 650?°C and the stabilities of these catalysts were evaluated for long time reaction at 650?°C. It was found that when Zr/(Zr?+?Al) molar ratio?=?0.5%, the Ni/0.5ZrO₂–Al₂O₃ catalyst showed the highest activity, and exhibited superior stabilization compared to the Ni-based catalyst supported on traditional ordered mesoporous Al₂O₃. The “confinement effect” from mesoporous channels of alumina matrix is helpful to stabilize the Ni nanoparticles. As a promoter, Zr could stabilize the ordered mesoporous framework by reacting with Al₂O₃ to form ZrO₂–Al₂O₃ solid solution. Since ZrO₂ enhances the dissociation of carbon dioxide, more oxygen intermediates are given to remove the carbon formed during the reaction.     

Matrimid‐based carbon tubular membranes: The effect of the polymer composition

In this article, we present a development study of new membrane materials and enhancements of productive membranes to improve the current performance of polymeric membranes. Carbon membranes are a promising material for this matter as they offer an improvement in the gas‐separation performance and exhibit a good combination of permeability and selectivity. Carbon membranes produced from the carbonization of polymeric materials have been reported to be effective for gas separation because of their ability to separate gases with almost similar molecular sizes. In this study, a carbon support membrane was prepared with Matrimid 5218 as a polymeric precursor. The polymer solution was coated on the surface of a tubular support with the dip‐coating method. The polymer tubular membrane was then carbonized under a nitrogen atmosphere with different polymer compositions of 5–18 wt %. The carbonization process was performed at 850°C at a heating rate of 2°C/min. Matrimid‐based carbon tubular membranes were fabricated and characterized in terms of their structural morphology, thermal stability, and gas‐permeation properties with scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and a pure‐gas‐permeation system, respectively. Pure‐gas‐permeation tests were performed with the pure gases carbon dioxide (CO₂) and N₂ at room temperature at a pressure of 8 bar. On the basis of the results, the highest CO₂/N₂ selectivity of 75.73 was obtained for the carbon membrane prepared with a 15 wt % polymer composition. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42394.     

The kinetics of gasification of carbon deposited on nickel catalysts

The kinetics of gasification of carbon deposited on nickel foils and nickel-alumina catalysts by steam, carbon dioxide and hydrogen are reported for the temperature range 450–850°C. At atmospheric pressure steam is the most effective gasifying agent. In all cases, the kinetic data obtained at lower temperatures (below 600°C) is consistent with control of the process by the chemical reaction. As the temperature increases, the rates of gasification by steam and carbon dioxide are limited by mass transfer effects. The concentration of methane near reaction sites affects the rate of hydrogen gasification above 650°C.     

Effects of Thermal Treatment on Gas Transport Through Porous Silica Membranes

Abstract

The effects of thermal treatment from 180°C to 1150°C on the gas transport properties of porous silica membranes were systematically studied for various gases. The permeance of all gases, except for CO₂, has a maximum at 800°C. The CO₂ permeance was constant from 180°C to 600°C and then decreased monotonically. Membranes thermally treated at 1150°C did not exhibit any gas permeation because of pore collapse. The gas transport behavior follows a combination of Knudsen diffusion and surface diffusion for all gases tested except for carbon dioxide. The permeation of carbon dioxide is strongly affected by capillary condensation. We propose a new transport model composed of two components; that is, the Knudsen diffusion factor, α, and the surface diffusion factor, β. A transition was observed for α and β at around 800–900°C, which is close to the strain point of the membrane. This transition treatment temperature can be correlated with the changes in gas permeance. The model allows qualitative evaluation of gas transport through porous membranes regardless of their actual microporous structures.     

Enhancing co‐production of H2 and syngas via water splitting and POM on surface‐modified oxygen permeable membranes

In this article, we report a detailed study on co‐production of H₂ and syngas on La_0.9Ca_0.1FeO_3?δ (LCF‐91) membranes via water splitting and partial oxidation of methane, respectively. A permeation model shows that the surface reaction on the sweep side is the rate limiting step for this process on a 0.9 mm‐thick dense membrane at 990°C. Hence, sweep side surface modifications such as adding a porous layer and nickel catalysts were applied; the hydrogen production rate from water thermolysis is enhanced by two orders of magnitude to 0.37 μmol/cm²?s compared with the results on the unmodified membrane. At the sweep side exit, syngas (H₂/CO = 2) is produced and negligible solid carbon is found. Yet near the membrane surface on the sweep side, methane can decompose into solid carbon and hydrogen at the surface, or it may be oxidized into CO and CO₂, depending on the oxygen permeation flux. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4427–4435, 2016