Optimizing the parameters of the steam-carbon dioxide conversion of methane by Gibbs energy minimization

The thermodynamic equilibrium for the steam-carbon dioxide conversion of methane was studied by Gibbs energy minimization. The degree of coke formation, the content of methane and carbon dioxide in the synthesis gas, and the synthesis gas H₂/CO ratio were plotted as functions of the molar ratios of CO₂/CH₄ and H₂O/CH₄ in the initial mixture at different temperatures and pressures. The regions of the optimum CH₄/CO₂/H₂O molar ratios for steam-carbon dioxide conversion were discovered, with no coke formation taking place in these regions. The optimized CH₄/CO₂/H₂O molar fractions characterized by the minimum content of methane and carbon dioxide in the synthesis gas were found for each region.     

Sulfur gas tolerance and toxicity of co-utilizing and methanogenic bacteria

Anaerobic bacteria have been shown to be capable of converting CO, H₂, and CO₂ in synthesis gas to valuable products, such as acetate, methane, and ethanol. However, synthesis gas also contains small quantities of sulfur gases such as H₂S and COS, that may inhibit the performance of these organisms. This paper compares the performance of several CO-utilizing and methanogenic bacteria in converting CO, CO₂, and H₂ to products in the presence of various concentrations of H₂S and COS. The sulfur gas toxicity levels, growth, substrate uptake, and product formation for each organism are compared.     

甲烷三重整制合成气

甲烷三重整是利用CO₂-H₂O-O₂ 同时重整甲烷的过程。该工艺既可以生产H₂/CO 为1.5 —2.0的合成气,又可以缓解甚至消除催化剂的积炭,适合于更廉价地生产用于合成甲醇、二甲醚以及清洁燃料等下游产品的合成气。本文重点评述了近年来国内外甲烷三重整制合成气在热力学、催化剂、反应器、动力学等方面的研究进展,指出甲烷三重整反应在电厂烟气、煤层气、天然气综合利用方面具备良好前景,但要通过该过程实现廉价合成气的生产,仍需研制高活性、抗积炭性能强的催化剂,并对反应器进行改进,以及进行反应机理和反应动力学的深入研究。     

Wet Conversion of Methane and Carbon Dioxide in a DBD Reactor

The influence of water on the plasma assisted conversion of methane and carbon dioxide in a dielectric barrier discharge (DBD) plug flow reactor was studied. The plasma at atmospheric pressure was ignited by a power supply at a frequency of 13.56?MHz. Product formation was studied at a power range between 35 and 70?W. The concentrations of the three gases were altered and diluted with helium to 3?%. FTIR spectroscopy and mass spectroscopy were applied to analyze the inlet and the product streams. The main product of this process are hydrogen, carbon monoxide and ethane. Ethene, ethine, methanol and formaldehyde are generated beside the main products in this DBD in lower concentrations. The conversion of methane, the ratio of the synthesis gas components (n(H₂):n(CO)), and the yield of oxygenated hydrocarbons and hydrogen increases by adding water. The total consumed energy reaches lower values for small amounts of water. Additional water does not influence the generated amount of C2 hydrocarbons and of CO, but decreases the carbon dioxide conversion.     

DC-Pulsed Plasma for Dry Reforming of Methane to Synthesis Gas

The carbon dioxide reforming of methane to synthesis gas under DC-pulsed plasma was investigated. The effects of specific input energy and feed ratio on the product distribution and also feed conversion was studied. At the input energy of about 11 eV/molecule per methane and/or carbon dioxide the feed conversion of 38% for CH₄ and 28% for CO₂ and product selectivity of 74% has been attained for H₂ and CO at feed flow rate of 90 ml/min. The energy consumption in this work displays potential to further study and optimization of the process. The importance of the electron impact reactions in the process was discussed. The results show that by prudent tuning of system variables, the process be able to run in the way of synthesis gas, instead of hydrocarbon production.     

Computational fluid dynamics study of the dry reforming of methane over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in a membrane reactor. Coke deposition

This work investigates the dry reforming of CH₄ as an important process for the conversion of greenhouse gases to synthesis gas. The mixture of methane and CO₂ is readily available in the greenhouse gas which makes realization of dry reforming of methane process more convenient. The paper is an attempt to numerically analyse by computational fluid dynamics (CFD) the coking and gasification mechanisms in the lab-scale membrane module with a fixed-bed supported nickel catalyst (Ni/Al₂O₃). The concentrations and molar fluxes obtained by the simulation are compared with the experimental profiles to validate the CFD model. It was found that working in a catalytic fixed-bed membrane reactor, in the case of the dry reforming of methane and under specific conditions, was not critical, from the point of view of catalyst deactivation.     

Autothermal reforming of methane to syngas for Fischer-Tropsch synthesis with promoted palladium and a fast start-up device

In this study, a Pd catalyst was prepared with promoters such as CeO₂, BaO and SrO in a washcoated form on a metallic monolith for autothermal reforming of methane to syngas for the Fischer-Tropsch synthesis. A reactor was installed with an electric heater in the form of the metallic monolith as a start-up device instead of a burner with which stable and fast start-ups (within 4 min) were achieved. Gas hourly space velocity and O₂/CH₄ governed, methane conversion, while H₂O/CH₄ controlled H₂/CO ratio. A methane conversion of approx. 96%, H₂+CO selectivity of approx. 85%, and H₂/CO of approx. 2.6 were obtained under the conditions of gas hourly space velocity (GHSV) at 103000 h^?1, O₂/CH₄=0.7 and H₂O/CH₄=0.35.     

Oscillations during partial oxidation of methane to synthesis gas over Ru/Al2O3 catalyst (Special column of methane transformation, Article)

Oscillations in temperatures of catalyst bed as well as concentrations of gas phase species at the exit of reactor were observed during the partial oxidation of methane to synthesis gas over Ru/Al₂O₃ in the temperature range of 600 to 850 °C. XRD, H₂-TPR and in situ Raman techniques was used to characterize the catalyst. Two types of ruthenium species, i.e. the ruthenium species weakly interacted with Al₂O₃ and that strongly interacted with the support, were identified by H₂-TPR experiment. These species are responsible for two types of oscillation profiles observed during the reaction. The oscillations were the result of these ruthenium species switching cyclically between the oxidized state and the reduced state under the reaction condition. These cyclic transformations, in turn, were the result of temperature variations caused by the varying levels of the strongly exothermic CH₄ combustion and the highly endothermic CH₄ reforming (with H₂O and CO₂) reactions (or the less exothermic direct partial oxidation of methane to CO and H₂), which were favored by the oxidized and the metallic sites, respectively. The major pathway of synthesis gas formation over the catalyst was via the combustion-reforming mechanism.     

Catalytic Conversion of Simulated Biogas Mixtures to Synthesis Gas in a Fluidized Bed Reactor Supported by a DBD

The catalytic conversion of methane and carbon dioxide was studied in a fluidized bed reactor supported by a 13.56?Hz driven coaxial DBD-reactor. Palladium or cupper catalyst which are covered on Al₂O₃ particles were used. The goal was to test whether biogas can be used for the production of synthesis gas. The influences of discharge power, catalysts and temperature of the catalyst bed on the product yield were studied. The starting material and product stream was analyzed by quadrupole mass spectrometry and infrared spectroscopy. H₂/CO ratios can be adjusted in a range between 0.65 (without a catalyst) and 1.75 (using a copper catalyst). The process is highly selective for hydrogen production (up to 83%, using a Palladium catalyst). A copper catalyst increases the H₂/CO ratio can from 1.04 to 1.16 and the palladium catalyst from 1.11 to 1.43 by heating the catalyst to a temperature of 250°C.     

Intensification of the oxidation of rich methane/air mixtures by O2 molecules excited to the a 1Δg state

Methane oxidation in rich CH₄/air mixtures can be intensified by exciting O₂ molecules to the a ¹Δ_g state. Even small amounts of O₂(a ¹Δ_g) molecules reduce the ignition temperature and shorten the induction period. As compared to the oxidation of ordinary methane/air mixtures, oxidation in the presence of excited oxygen makes it possible to convert methane into synthesis gas (H₂ + CO) at low initial temperatures of ≈600 K and atmospheric pressure and to raise the H₂ and CO yields at a fixed reactor length.     

Application of copper sulfate pentahydrate as an ammonia removal reagent for the determination of trace impurities in ammonia by gas chromatography

Rapid analysis of trace permanent gas impurities in high purity ammonia gas for the microelectronics industry is described, using a gas chromatograph equipped with a phtoionization detector. Our system incorporates a reactive precolumn in combination with the analytical column to remove the ammonia matrix peak that otherwise would complicate the measurements due to baseline fluctuations and loss of analytes. The performance of 21 precolumn candidate materials was evaluated. Copper sulfate pentahydrate (CuSO₄·5H₂O) was shown to selectively react with ammonia at room temperature and atmospheric column pressures, without affecting the hydrogen, oxygen, nitrogen, methane or carbon monoxide peak areas. To prevent loss of trace carbon dioxide, an additional boron trioxide reactant layer was inserted above the copper sulfate pentahydrate bed in the reactive precolumn. Using the combined materials, calibration curves for carbon dioxide proved to be equivalent in both ammonia and helium matrix gases. These curves were equivalent in both matrix gases. The quantitative performance of the system was also evaluated. Peak repeatabilities, based on eight injections, were in the range of 4.1–8.2% relative standard deviation; and detection limits were 6.9 ppb for H₂, 1.8 ppb for O₂, 1.6 ppb for N₂, 6.4 ppb for CH₄, 13 ppb for CO, and 5.4 ppb for CO₂.     

Performance of a mixed-conducting ceramic membrane reactor with high oxygen permeability for methane conversion

A mixed-conducting perovskite-type Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) ceramic membrane reactor with high oxygen permeability was applied for the activation of methane. The membrane reactor has intrinsic catalytic activities for methane conversion to ethane and ethylene. C₂ selectivity up to 40–70% was achieved, albeit that conversion rate were low, typically 0.5–3.5% at 800–900°C with a 50% helium diluted methane inlet stream at a flow rate of 34 ml/min. Large amount of unreacted molecular oxygen was detected in the eluted gas and the oxygen permeation flux improved only slightly compared with that under non-reactive air/He experiments. The partial oxidation of methane to syngas in a BSCFO membrane reactor was also performed by packing LiLaNiO/γ-Al₂O₃ with 10% Ni loading as the catalyst. At the initial stage, oxygen permeation flux, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation flux to reach its steady state. 98.5% CH₄ conversion, 93.0% CO selectivity and 10.45 ml/cm² min oxygen permeation flux were achieved under steady state at 850°C. Methane conversion and oxygen permeation flux increased with increasing temperature. No fracture of the membrane reactor was observed during syngas production. However, H₂-TPR investigation demonstrated that the BSCFO was unstable under reducing atmosphere, yet the material was found to have excellent phase reversibility. A membrane reactor made from BSCFO was successfully operated for the POM reaction at 875°C for more than 500 h without failure, with a stable oxygen permeation flux of about 11.5 ml/cm² min.     

The oxidative stream reforming of methane to syngas in a thin tubular mixed-conducting membrane reactor

The oxidative stream reforming of methane (OSRM) to syngas, involving coupling of exothermic partial oxidation of methane (POM) and endothermic steam reforming of methane (SRM) processes, was studied in a thin tubular Al₂O₃-doped SrCo_0.8Fe_0.2O_3−δ membrane reactor packed with a Ni/γ-Al₂O₃ catalyst. The influences of the temperature and feed concentration on the membrane reaction performances were investigated in detail. The methane and steam conversions increased with increasing the temperature and high conversions were obtained in 850–900 °C. Different from the POM reaction, in the OSRM reaction the temperature and H₂O/CH₄ profoundly influenced the CO selectivity, H₂/CO and heat of the reaction. The CO selectivity increased with increasing the temperature or decreasing the H₂O/CH₄ ratio in the feed owing to the water gas shift reaction (H₂O + CO → CO₂ + H₂). And the H₂ selectivity based on methane conversion was always 100% because the net steam conversion was greater than zero. The H₂/CO in product could be tuned from 1.9 to 2.8 by adjusting the reaction temperature or H₂O/CH₄. Depending on the temperature or H₂O/CH₄, furthermore, the OSRM process could be performed auto-thermally with idealized reaction condition.     

Effect of Electrical Pulse Forms on the CO2 Reforming of Methane Using Atmospheric Dielectric Barrier Discharge

Methane conversion using an electric discharge has been studied for many years. Recently, many research groups have developed high-frequency pulsed plasma reaction for methane conversion to higher hydrocarbons and synthesis gas. CO₂ reforming of methane to synthesis gas has also attracted considerable interest as a method of utilization of the greenhouse gases, CO₂ and CH₄, which occupy most of man-made greenhouse gases. In this study, the influence of pulse form of applied voltage on methane and carbon dioxide conversions and product selectivity has been investigated using a cylindrical type DBD reactor. For this purpose, two kinds of power supply were compared, that is, AC power supply which has a high-frequency sinusoidal wave form, and AC pulse power supply which has modified AC pulse wave form. The conversions of methane and carbon dioxide were enhanced using pulsed plasma. The lower pulse width was more profitable economically.     

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.     

Methane oxidation by green oxidant to methanol over zeolite-based catalysts

To reduce greenhouse gas emission from oil and gas production,it is essential to better convert methane to useful chemicals（rather） than to flare it.Conversion of methane to liquid oxygenates（mainly methanol） has attracted extensive attention and countless efforts have been made;however,running this reaction in a green,efficient,and practical way has remained elusive.The novel catalyst and oxidants play a critical role in activating methane and converting it to oxygenates（methanol）.In this revie...     

Plasma-Enhanced Chemical-Vapor-Deposition Synthesis of Photoredox-Active Nitrogen-Doped Carbon from NH3 and CH4 Gases

Earth's primordial atmosphere was rich in ammonia and methane. To understand the evolution of the atmosphere, these two gases were used to make photoredox-active nitrogen-doped carbon (NDC). Photocatalysts such as NDC might play an important role in the development of geological and atmospheric chemistry during the Archean era. This study describes the synthesis of NDC directly from NH₃ and CH₄ gases. The photocatalyst product can be used to selectively synthesize imines by photo-oxidization of amines, producing H₂O₂ simultaneously in the photoreduction reaction. Our findings shed light on the chemical evolution of the Earth.     

Partial Oxidation of Methane into Syngas with Oxygen Permeating Ceramic Membrane Reactors

Partial oxidation of methane (CH₄ +1/2O₂ CO + 2H₂) is considered as an alternative reforming reaction to steam reforming for production of syngas. This reaction is a slightly exothermic reaction and produces syngas of H₂/CO = 2, which is suitable for the synthesis of hydrocarbon or methanol. In this paper, the catalytic partial oxidation of CH₄ with a membrane reactor using oxygen permeating ceramic, in particular, LaGaO₃-based oxide, is reported. Supported Ni or Rh catalysts are active and selective for this reaction. On the other hand, a mixed ionic and electronic conducting (MIEC) ceramic membrane is useful for obtaining pure oxygen from air when the gradient in oxygen partial pressure is obtained. As for a MIEC membrane, mixed electronic–oxide ionic conductors of Fe- or Co-based perovskite oxides are widely investigated. However, the improvement in stability in a reducing atmosphere is critically required for the MIEC membrane for the application to the membrane reactor for CH₄ partial oxidation. Perovskite oxides of LaGaO₃ doped with Sr for a La site and a Fe, Co, or Ni for a Ga site, respectively, are promising as the oxygen-separating membrane for CH₄ partial oxidation because of high stability in a reducing atmosphere as well as high permeability of oxygen. The partial oxidation of CH₄ with solid oxide fuel cells (SOFCs) is also described. Simultaneous generation of electrical power and syngas is demonstrated by the fabricated fuel cell type reactor using a LaGaO₃-based oxide electrolyte.     

Syngas Production from Propane Using Atmospheric Non-thermal Plasma

Propane steam reforming using a sliding discharge reactor was investigated under atmospheric pressure and low temperature (420 K). Non-thermal plasma steam reforming proceeded efficiently and hydrogen was formed as a main product (H₂ concentration up to 50%). By-products (C₂-hydrocarbons, methane, carbon dioxide) were measured with concentrations lower than 6%. The mean electrical power injected in the discharge is less than 2 kW. The process efficiency is described in terms of propane conversion rate, steam reforming and cracking selectivity, as well as by-products production. Chemical processes modelling based on classical thermodynamic equilibrium reactor is also proposed. Calculated data fit quiet well experimental results and indicate that the improvement of C₃H₈ conversion and then H₂ production can be achieved by increasing the gas fraction through the discharge. By improving the reactor design, the non-thermal plasma has a potential for being an effective way for supplying hydrogen or synthesis gas.     

Negative ion chemical ionization mass spectra of (η6-arene)Cr(CO)3

The negative ion chemical ionization mass spectra, with ammonia and methane as reagent gases, of the (η⁶-arene)Cr(CO)₃ complexes, where the arene is C₆H₅COCH₃, C₆H₅COC₂H₅, C₆H₅COC₃H₇, C₆H₅COC(CH₃)₃, 2-CH₃C₆H₄COC₃H₇, C₆H₅COOCH₃, C₆H₅CH₃, 1,3,5-(CH₃)₃C₆H₃ and C₆H₅CH₂COC₂H₅, are reported. Similar behaviour is observed with the two reagent gases, but ammonia shows a much higher abundance for the ions produced by reactions of [NH₂]^? with sample molecules. The compounds containing the C₆H₅CO group display an abundant [M]^{? ˙}, whereas the other compounds exhibit [M? H]^? as base peak, produced by ion/molecule reactions. A comparison of the negative ion chemical ionization mass spectra of the (η⁶-arene)Cr(CO)₃ complexes with those of the corresponding ligands shows the strong electron withdrawing power of the Cr(CO)₃ group in the gas phase.