Methane-rich Mixtures Research Articles

Crystallization risk of aromatic compounds in LNG production. Part II: The solubility of p-xylene in methane-rich mixtures down to cryogenic temperatures

New measurements of solubility of solid p-xylene in solvents methane and (90%mol/mol)methane + (10%mol/mol)ethane have been carried out using a cryogenic apparatus and adopting a static-analytic method for temperatures from 273 K down to 128 K at nominal pressures of 3 and 6 MPa. Measured solid-liquid and solid-vapor equilibria have been compared to literature values of solubility of solid p-xylene in methane-rich phases and to modeling results obtained by coupling a cubic equation of state and a model for the solid phase. Results confirm the conclusions reported in our previous study of this system that evidenced of a non-monotonic variation of the solubility of p-xylene with temperature when crossing the critical region of the solvent and that binary interaction parameters regressed on vapor-liquid equilibrium can be used for predicting the solubility at cryogenic conditions.

Compact and accurate chemical mechanism for methane pyrolysis with PAH growth

A reliable and compact chemical mechanism of gas-phase methane pyrolysis leading to formation of large polycyclic aromatic hydrocarbon (PAH) molecules has been developed. This model is designed for studies of carbon nanostructure synthesis such as carbon black and graphene flakes, including soot growth kinetics. Methane pyrolysis with carbon nanostructure synthesis is a two-stage process where conversion of CH4 to C2H2 precedes the growth of PAH molecules from acetylene. We present a single chemical mechanism that accurately describes both stages. We have constructed a compact and accurate chemical mechanism capable of modeling both stages of methane pyrolysis based on the ABF [1] mechanism which was expanded with the most prominent reaction pathways from the mechanism by Tao [2] for small PAH molecules and HACA pathways for larger PAH molecules, up to 37 aromatic rings. The resulting mechanism was validated through comparison to multiple available sets of experimental data. Good agreement with the experimental data for both processes was obtained. Performance of the mechanism was tested for pyrolysis of methane-rich mixtures under long residence times leading to abundant formation of PAH molecules. It is shown that the inclusion of larger PAH species (up to A37) in the chemical mechanism is important for accurate prediction of the fraction of carbon converted to PAH molecules and, correspondingly, the residual fraction of acetylene in the mixture. The mechanism file is available upon request.

Gaseous fueling of an adapted commercial automotive spark-ignition engine: Simplified thermodynamic modeling and experimental study running on hydrogen, methane, carbon monoxide and their mixtures

In the present work, methane, carbon monoxide, hydrogen and the binary mixtures 20 % CH4–80 % H2, 80 % CH4–20 % H2, 25 % CO–75 % H2 (by volume) were considered as fuels of a naturally aspirated port-fuel injection four-cylinder Volkswagen 1.4 L spark-ignition (SI) engine. The interest in these fuels lies in the fact that they can be obtained from renewable resources such as the fermentation or gasification of residual biomasses as well as the electrolysis of water with electricity of renewable origin in the case of hydrogen. In addition, they can be used upon relatively easy modifications of the engines, including the retrofitting of existing internal combustion engines. It has been found that the engine gives similar performance regardless the gaseous fuel nature if the air–fuel equivalence ratio (λ) is the same. Maximum brake torque and mean effective pressure values within 45–89 N·m and 4.0–8.0 bar, respectively, have been obtained at values of λ between 1 and 2 at full load, engine speed of 2000 rpm and optimum spark-advance. In contrast, the nature of the gaseous fuel had great influence upon the range of λ values at which a fuel (either pure or blend) could be used. Methane and methane-rich mixtures with hydrogen or carbon monoxide allowed operating the engine at close to stoichiometric conditions (i.e. 1 < λ < 1.5) yielding the highest brake torque and mean effective pressure values. On the contrary, hydrogen and hydrogen-rich mixtures with methane or carbon monoxide could be employed only in the very fuel-lean region (i.e. 1.5 < λ < 2). The behavior of carbon monoxide was intermediate between that of methane and hydrogen.The present study extends and complements previous works in which the aforementioned fuels were compared only under stoichiometric conditions in air (λ = 1). In addition, a simple zero-dimensional thermodynamic combustion model has been developed that allows describing qualitatively the trends set by the several fuels. Although the model is useful to understand the influence of the fuels properties on the engine performance, its predictive capability is limited by the simplifications made.

Alternative Materials for the Enrichment of Biogas with Methane.

Carbonaceous adsorbents have been pointed out as promising adsorbents for the recovery of methane from its mixture with carbon dioxide, including biogas. This is because of the fact that CO2 is more strongly adsorbed and also diffuses faster compared to methane in these materials. Therefore, the present study aimed to test alternative carbonaceous materials for the gas separation process with the purpose of enriching biogas in biomethane and to compare them with the commercial one. Among them was coconut shell activated carbon (AC) as the adsorbent derived from bio-waste, rubber tire pyrolysis char (RPC) as a by-product of waste utilization technology, and carbon molecular sieve (CMS) as the commercial material. The breakthrough experiments were conducted using two mixtures, a methane-rich mixture (consisting of 75% CH4 and 25% CO2) and a carbon dioxide-rich mixture (containing 25% CH4 and 75% CO2). This investigation showed that the AC sample would be a better candidate material for the CH4/CO2 separation using a fixed-bed adsorption column than the commercial CMS sample. It is worth mentioning that due to its poorly developed micropore structure, the RPC sample exhibited limited adsorption capacity for both compounds, particularly for CO2. However, it was observed that for the methane-rich mixture, it was possible to obtain an instantaneous concentration of around 93% CH4. This indicates that there is still much potential for the use of the RPC, but this raw material needs further treatment. The Yoon–Nelson model was used to predict breakthrough curves for the experimental data. The results show that the data for the AC were best fitted with this model.

Ruthenium-Exsolution Catalyst for Dry Reforming of Biogas

Solid oxide fuel cells have a proven efficiency for the direct conversion of biogas into electricity, and their full potential from European agricultural and waste-water sites still has to be fully evaluated and harnessed. Biogases are methane-rich mixtures whose composition and trace contaminants, especially of sulfur compounds, can vary greatly.To avoid carbon deposition from the carbon-rich CH4-CO2 mixtures, some amount of steam and/or extra CO2 needs to be added to process the biogas. Ideally this can be recovered from the SOFC exhaust. In a preparatory work, biogas/SOFC integrated systems were studied and compared using Aspen Plus[1]. Best performances are reached with a catalytic methane pre-reformer when a fraction of the anode off-gas is recirculated for mixing with the biogas feed. This work provided the guidelines for the present catalytic study and predicted thermodynamic equilibria of gas mixtures.Here, the overall performance of a ruthenium exsolution catalyst[2] for the reforming of methane was evaluated for these different biogas compositions at various gas hourly space velocities. Gas chromatography and material balance calculations enabled the full measurement of inlet and outlet gas compositions which, in turn, permitted to calculate precise conversion rates, reforming ratio, and the deviation from thermodynamic equilibrium. Methane conversion reached >95 % for a dry-dominant reforming mixture, which simplifies the overall system. The longer-term stability of the catalyst as well as its tolerance towards different sulfur traces that occur in biogas was then evaluated and analyzed. [1] Shuai Ma, Gabriele Loreti, Ligang Wang, Andrea L. Facci, Stefano Ubertini, Changqing Dong, François Maréchal, and Jan Van herle, E3S Web of Conferences 2021 238:04002DOI: 10.1051/e3sconf/202123804002 [2] Muhammad A. Naeem, Paula M. Abdala, Andac Armutlulu, Sung Min Kim, Alexey Fedorov, and Christoph R. Müller, ACS Catalysis 2020 10 (3), 1923-1937DOI: 10.1021/acscatal.9b04555

Liquefied Synthetic Natural Gas Produced through Renewable Energy Surplus: Impact Analysis on Vehicular Transportation by 2040 in Italy

Time mismatch between renewable energy production and consumption, grid congestion issues, and consequent production curtailment lead to the need for energy storage systems to allow for a greater renewable energy sources share in future energy scenarios. A power-to-liquefied synthetic natural gas system can be used to convert renewable energy surplus into fuel for heavy duty vehicles, coupling the electric and transportation sectors. The investigated system originates from power-to-gas technology, based on water electrolysis and CO2 methanation to produce a methane rich mixture containing H2, coupled with a low temperature gas upgrading section to meet the liquefied natural gas requirements. The process uses direct air CO2 capture to feed the methanation section; mol sieve dehydration and cryogenic distillation are implemented to produce a liquefied natural gas quality mixture. The utilization of this fuel in heavy duty vehicles can reduce greenhouse gases emissions if compared with diesel and natural gas, supporting the growth of renewable fuel consumption in an existing market. Here, the application of power-to-liquefied synthetic natural gas systems is investigated at a national level for Italy by 2040, assessing the number of plants to be installed in order to convert the curtailed energy, synthetic fuel production, and consequent avoided greenhouse gases emissions through well-to-wheel analysis. Finally, plant investment cost is preliminarily investigated.

Density Measurements of (0.99 Methane\u2009+\u20090.01 Butane) and (0.98 Methane\u2009+\u20090.02 Isopentane) over the Temperature Range from (100 to 160) K at Pressures up to 10.8\xa0MPa

Densities of two methane-rich binary mixtures were measured in the homogeneous liquid and the supercritical region at temperatures between (100 and 160) K using a low-temperature single-sinker magnetic-suspension densimeter. For each mixture, four isotherms were studied over the pressure range from (0.3 to 10.8) MPa. Molar compositions of the gravimetrically prepared methane-rich binary mixtures were approximately 0.01 butane and 0.02 isopentane, respectively, with the balance being methane. The relative expanded combined uncertainty (k = 2) of the experimental densities was estimated to be in the range of (0.02 to 0.06) %. Due to a supercritical liquefaction procedure and the integration of a special VLE-cell, it was possible to measure densities in the homogeneous liquid phase without changing the composition of the liquefied mixture. Based on the supercritical liquefaction procedure, a new time-saving measurement procedure was developed and applied. Moreover, saturated-liquid densities were determined by extrapolation of the experimental single-phase liquid densities to the vapor pressure calculated with an equation of state (EOS); here, the relative expanded combined uncertainty (k = 2) is less than 0.05 % in most cases. The new experimental results were compared with the GERG-2008 equation of state, the EOS-LNG and the enhanced revised Klosek and McKinley (ERKM) method.

Stratification Dynamics of Titan's Lakes via Methane Evaporation.

Saturn's moon Titan is the only extraterrestrial body known to host stable lakes and a hydrological cycle. Titan's lakes predominantly contain liquid methane, ethane, and nitrogen, with methane evaporation driving its hydrological cycle. Molecular interactions between these three species lead to non-ideal behavior that causes Titan's lakes to behave differently than Earth's lakes. Here, we numerically investigate how methane evaporation and non-ideal interactions affect the physical properties, structure, dynamics, and evolution of shallow lakes on Titan. We find that, under certain temperature regimes, methane-rich mixtures are denser than relatively ethane-rich mixtures. This allows methane evaporation to stratify Titan's lakes into ethane-rich upper layers and methane-rich lower layers, separated by a strong compositional gradient. At temperatures above 86K, lakes remain well-mixed and unstratified. Between 84 and 86K, lakes can stratify episodically. Below 84K, lakes permanently stratify, and develop very methane-depleted epilimnia. Despite small seasonal and diurnal deviations (<5K) from typical surface temperatures, Titan's rain-filled ephemeral lakes and "phantom lakes" may nevertheless experience significantly larger temperature fluctuations, resulting in polymictic or even meromictic stratification, which may trigger ethane ice precipitation.

Reduced model of chemical kinetic and two-dimensional structure of detonation wave in rich mixtures of methane with oxidizer

Two-step reduced model of chemical kinetics of detonation combustion of methane mixtures is presented. The possibility of condensed carbon (soot) microparticles formation in reaction products is taken into account for the first time. The model is simple (only one ordinary differential equation in a main heat release zone) and physically grounded. It is in consistent with the second law of thermodynamics and Le Chatelier’s principle. The model verification has been performed via numerical calculations of parameters and two-dimensional structure of detonation wave in the fuel-rich methane-oxidizer mixture. The irregular cellular structure of the wave with all its main features, observed in the experiments, was reproduced in the calculations. The dominant size of the detonation cell is in good agreement with experimental data and corresponding estimations in the frames of generally accepted Vasil’ev-Nikolaev model of detonation cell.

Low-temperature steam conversion of flare gases for various applications

The present work aims at studying low-temperature steam conversion of model flare gas mixtures containing C2H6-C5H12 in methane excess over industrial Ni-based catalyst. It is shown that at 250–350 °C and H2O/CC2+ molar ratio of 0.7–1.0, steam conversion can be applied to convert C2+-hydrocarbons into CH4, CO2 and H2, which results in the lowering net calorific value, the Wobbe index and dew point temperature of the gas obtained. However, complete conversion is not necessary for certain applications. In these cases, kinetically controlled partial conversion of ethane and propane enables one to obtain methane-rich mixtures with desired calorific properties for various applications. This idea has been experimentally verified. Kinetic study of C2H6-C5H12 low-temperature steam conversion has been performed. A simple macrokinetic model, which included irreversible first-order kinetics for C2H6-C5H12 steam conversion and quasi-equilibrium mode for CO2 methanation, has been suggested. The model adequately describes the experimental data on the conversion of model flare gas mixtures at various temperatures and flow rates and has been applied to predict the reaction conditions which would allow one to obtain methane-rich mixtures with the desired properties for various applications.

Effective Design of a Vacuum Pressure Swing Adsorption Process To Recover Dilute Helium from a Natural Gas Source in a Methane-Rich Mixture with Nitrogen

The conventional method of helium production is a cryogenic process, which is installed downstream of a liquefied natural gas (LNG) plant, where a helium extraction unit (HeXU) would be usually developed as the byproduct unit, due to the high cost of the process. In this study, pressure swing adsorption method accompanied by a relative vacuum condition for the bed regeneration (PVSA) was investigated as an alternative method for recovery of helium from natural gas source. The PVSA design was studied for a continuous product, utilizing zeolite 13X as the adsorbent, through a formerly validated model, for a dilute feed of 1.5 vol % He, mainly comprised of methane in 82.5 vol % accompanied by nitrogen. The impacts of repressurizing medium and equalization steps of the design conditions on the He purity and recovery were investigated. It was revealed that, generally, the bed repressurizing step should be performed by the feed as compared to the product. However, at high space velocities, a combination of the ...

Lanthanum chromite based composite anodes for dry reforming of methane

Composite anodes containing La0.6Sr0.4CrO3-δ (LSCr) and Ce0.9Gd0.1O2 (GDC) infiltrated with 5 or 10 wt% Ni were investigated as potential catalysts for dry reforming of methane (DRM) reaction in methane rich mixtures. Powders were characterized and tested as catalysts for DRM reaction. Ni-infiltrated composite anodes were used for fuel cell tests and compared to Ni-free anodes. Electrochemical tests were performed in different gas mixtures to evaluate the anodic performance in externally reformed biogas (external reforming mode). The design of an external layer of composite anode achieved the internal DMR reaction (internal reforming mode).

Methyl mercaptan removal from natural gas using MIL-53(Al)

MIL-53(Al) was synthesized using hydrothermal method with various synthesis and calcination conditions. The synthesized materials were characterized by Powder X-ray Diffraction (PXRD), Thermal Gravimetric Analysis (TGA) and N2 adsorption-desorption isotherms (BET surface area measurement) methods. The results showed that synthesis time and calcination time can be decreased two days and one day, respectively, with respect to the usual method with no significantly decrement in the BET surface area and the crystallinity of materials. The sorption equilibrium, thermodynamic and kinetic of methyl mercaptan (MeSH) and methane adsorption on the MIL-53(Al) were studied by the volumetric method using a home-made apparatus. The sorption isotherm of MeSH revealed type IV according to IUPAC classification, while a type I was observed in the profile of the methane sorption isotherm. The synthesized MIL-53(Al) displayed high methyl mercaptan adsorption capacity (more than 9 mmol/g) which is about 2–3 times more than 13X, the usual industrial adsorbent for mercaptan removal from natural gas. The various models such as Langmuir, Sips and Thoth were successfully used to fit the adsorption experimental data. The Extended Langmuir (EL) and Ideal Adsorbed Solution Theory (IAST) models along with the pure component isotherm fitted to the Langmuir model were used to predict the removal of MeSH from methane-rich mixture. MIL-53(Al) presented high selectivity (EL selectivity of 263) for MeSH over methane. The isosteric heat of MeSH and CH4 adsorption on the MIL-53(Al) were within the range of 26–50 and about 18 kJ mol−1 respectively. Multiple adsorption–desorption cycles showed that the MeSH adsorption on the MIL-53 was highly reversible with a desorption efficiency of up to 95%. The diffusion time constants of MeSH and CH4 in the MIL-53(Al) at 298 K were estimated to be 1.48 × 10−2 and 1.99 × 10−2 s−1, respectively, leading to relatively equal adsorption kinetics of both molecules. High adsorption capacity, good kinetics, easy regeneration and reversible process of MeSH adsorption, suggested that the MIL-53(Al) can be used as a favorable adsorbent for purification of natural gas or biogas in the Pressure Swing Adsorption (PSA) process.

Controlled-Freeze-Zone Technology for the Distillation of High-CO2 Natural Gas

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 171508, “Controlled-Freeze-Zone Technology for the Commercialization of Australian High-CO2 Natural Gas,” by Jaime A. Valencia, Robert D. Denton, P. Scott Northrop, Charles J. Mart, and Ransdall K. Smith, ExxonMobil, prepared for the 2014 SPE Asia Pacific Oil and Gas Conference and Exhibition, Adelaide, Australia, 14–16 October. The paper has not been peer reviewed. The simple separation of carbon dioxide (CO2) from natural gas by distillation would involve cryogenic temperatures at which CO2 solidifies. Most CO2-separation processes instead use solvents that bind to CO2 molecules. For solvent regeneration, the binding process is reversed. The technology described by the authors provides the simplicity of a single-step distillation process for the separation of CO2 from natural gas. The technology has shown the potential to separate CO2 and other impurities from natural gas more efficiently and more cost-effectively. The Process In the gas industry, separations based on differing relative volatility and phase behavior are relatively simple, easy to implement, and widely used. The significant difference in relative volatility of methane and CO2 makes this system an ideal candidate for separation by distillation, were it not for some cold-temperature conditions leading to solidification of CO2. At 600 psig, conventional distillation is interfered with, for liquid-methane concentrations between approximately 25 and 85%, by the presence of this solid phase. Raising the pressure to 800 psig shifts the operating conditions away from the solidification boundary but into a new limitation: critical conditions. The critical pressure of pure methane is 667 psia; thus, methane-rich mixtures become supercritical. A high-purity methane-product stream cannot be obtained by distillation at 800 psig, and the overhead product purity is limited to 80 to 85% methane with a residual CO2 content of 15 to 20%. This is the basis for CO2 bulk fractionation. The technology described in this paper, rather than avoiding the solidification of CO2, allows CO2 to freeze, though under carefully controlled conditions and in a specially designed section of an otherwise conventional distillation tower. The tower normally incorporates three zones: the specially designed section that addresses the solidification region and two conventional distillation sections, one for rectifying and one for stripping, which cover the vapor/liquid areas above and below the CO2-solidification region. The relationship between the three sections of the column and the methane/ CO2 phase diagram is illustrated in Fig. 1.

An improved algorithm for the three‐fluid‐phase VLLE flash calculation

The VLLE flash is important in water and hydrocarbons mixtures, hydrocarbon and CO2 rich mixtures, and hydrocarbon methane rich mixtures that are encountered in reservoir performance and recovery studies. A robust VLLE flash algorithm is proposed. The equilibrium and mass balance equations are solved as a constrained minimization problem. An inverse barrier function is used to handle the inequality constrains to solve for the phase fractions. It warrants always arriving to the solution. The challenging cases analyzed showed that the initialization procedure proposed, together with successive substitution iteration in the outer loop, is a good method for a stable VLLE flash algorithm, even near critical points. Whenever the result is in the region outside the three‐phase physical domain, the solution suggests that the system has fewer phases. In one of the cases analyzed, a region with three liquid phases was encountered and the algorithm found two different solutions with positive phase fractions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3081–3093, 2015

Selective catalytic reduction of N2O with CH4 on Ni-MOR: A comparison with Co-MOR and Fe-MOR catalysts

The selective catalytic reduction of N2O with CH4 in the presence of excess O2 (CH4-SCRN2O) and CH4+O2 reaction were studied on Ni-MOR, Co-MOR and Fe-MOR, prepared from H-MOR or Na-MOR, by ion-exchange or CVD.FTIR showed that transition metal ions (tmi) were well dispersed, mainly isolated with at least two coordinative vacancies. For CH4-SCRN2O, irrespective of Brønsted acid site and Na+ amount, catalysts were active in the order Fe-MOR>Ni-MOR>Co-MOR. Using a methane-poor mixture, on all samples CH4-SCRN2O consisted of two nearly independent reactions: CH4+N2O and CH4+O2. Using a methane-rich mixture, CH4-SCRN2O consisted of a CH4+N2O+O2 reaction, whose stoichiometric ratios depended on the tmi. Whereas on Ni-MOR methane combustion occurred as side reaction, on Co-MOR and Fe-MOR no side reactions occurred. Accordingly, for CH4+O2 Co-MOR and Fe-MOR were poorly active, whereas Ni-MOR were highly active.We conclude that in CH4-SCRN2O a monoatomic oxygen form activates methane on Co-MOR and Fe-MOR catalysts, whereas both a monoatomic oxygen form and a molecular oxygen form activate methane on Ni-MOR. Being active for the CH4-SCRN2O and CH4-SCRNOx and forming CO only in traces, Ni-MOR are promising catalysts for the simultaneous SCR of N2O and NOx using CH4 as reducing agent.

Catalytic partial oxidation of methane rich mixtures in non-adiabatic monolith reactors

In this work the partial oxidation of hydrocarbons on a rhodium-based catalyst is studied experimentally and numerically. A unidimensional heterogeneous mathematical model for catalytic partial oxidation of hydrocarbons is applied to adiabatic and non-adiabatic honeycomb monolith reactors. The model is validated for the non-adiabatic case with good agreement against experimental measurements of temperature and species concentrations for three fuel compositions over a wide range of operating conditions.The influence of radiative heat losses on the non-adiabatic reactor performance is numerically investigated under varying operating conditions: fuel flow rate, air to fuel equivalence ratio and fuel composition. The radiative heat losses change the heat release relatively to the adiabatic configuration and a slightly more exothermic reaction pathway is observed. This higher chemical heat release points out a lower importance of endothermic reforming reactions in the overall chemical scheme justifying the lower outlet fuel conversion registered. It is also observed during non-adiabatic operation that the H2 selectivity can present higher values than in adiabatic conditions.The potential of the non-adiabatic reactor configuration to improve catalyst thermal stability is confirmed since a significant decrease of surface hot spots in relation to adiabatic operation may occur.

On the formation of spinning flames and combustion completeness for premixed fuel–air mixtures in stepped tube microcombustors

Various premixed fuel–air mixtures are introduced in stepped tube microcombustors. The experimental investigations show the formation of various steady and unsteady spinning flame propagation modes for a range of flow rates and mixture ratio conditions due to thermal-wall coupling. The spinning flames of very high frequency, ∼150 Hz have been observed for the first time with various fuel–air mixtures. The spinning frequency of these flames is almost twice that of flames observed in earlier work. The spinning flames were observed for both lean and rich mixtures of methane-, LPG- and propane–air mixtures. The formation of these spinning flames depends on the mixture flow rate, equivalence ratio and number of steps in the microcombustor. Exhaust gas analysis was carried out for different operating conditions. It was observed that contrary to general perception of low combustion efficiency and high CO emissions associated with such rotating and spinning flames, these high frequency spinning flames led to complete combustion with almost zero CO emissions.

Steam reforming of biogas mixtures with a palladium membrane reactor system

A fundamental study of the steam reforming of biogas and that derived from supercritical water gasification of glucose was conducted with a hydrogen-permeable palladium–silver membrane reactor. The hydrogen permeabilities for H 2 – H 2 O (4:1), H 2–CO 2 (4:1) and H 2 – N 2 (4:1) mixtures from 573 to 673 K were compared with those in the presence of hydrogen only. Water and nitrogen did not affect hydrogen permeability, whereas carbon dioxide tended to suppress its permeation in the high pressure region. Steam reforming of test gas 1 (moles H 2 : CH 4 : CO 2 = 50 : 10 : 40 ) and test gas 2 (moles H 2 : CH 4 : CO 2 = 10 : 40 : 50 ) mixtures having compositions expected from supercritical water gasification was carried out in the presence of 2 wt% Ru / Al 2 O 3 at 723 K and pressures up to 0.5 MPa. Methanation was dominant and slightly decreased as hydrogen permeated through the membrane in the steam reforming of the hydrogen rich mixture (test gas 1), whereas there was almost no effect of the membrane reactor for methane rich mixture (test gas 2). A new system combined the supercritical water gasification system and steam reforming system was developed and gas formation from glucose was carried out at 673 K and 10 MPa for supercritical gasification and from 0.1 to 0.5 MPa of reaction pressure. The experiments changing the order of catalytic bed and Pd–Ag membrane in the membrane reactor for steam reforming revealed that the elevated high pressures and hydrogen removal before catalytic steam reforming are advantageous for high hydrogen recovery.

Influence of weakly bound adduct ions on breath trace gas analysis by selected ion flow tube mass spectrometry (SIFT-MS)

This paper describes how weakly bound adduct ions form when the precursor ions used in selected ion flow mass spectrometry, SIFT-MS, analyses, viz. H 3O +, NO + and O 2 +, associate with the major components of air and exhaled breath, N 2, O 2 and CO 2. These adduct ions, which include H 3O +N 2, H 3O +CO 2, NO +CO 2, O 2 +O 2 and O 2 +CO 2, are clearly seen when dry air containing 5% CO 2 (typical of that in exhaled breath) is analysed using SIFT-MS. These adduct ions must not be misinterpreted as characteristic product ions of trace gases; if so, serious analytical errors can result. However, when exhaled breath is analysed these adduct ions are partly removed by ligand switching reactions with the abundant water molecules and the problems they represent are alleviated. But the small fractions of the adduct ions that remain in the SIFT-MS spectra, and especially when they are isobaric with genuine characteristic product ion of breath trace gases, can result in erroneous quantifications; such is the case for H 3O +N 2 interfering with breath ethanol analysis and H 3O +CO 2 with breath acetaldehyde analysis. However, these difficulties can be overcome when the isobaric adduct ions are properly recognised and excluded from the analyses; then these two important compounds can be properly quantified in breath. The presence of O 2 +CO 2 in the product ion spectra interferes with the analysis of CS 2 present at low levels in exhaled breath. It is likely that similar problems will occur as other trace compounds are detected in exhaled breath when consideration will have to be given to the possibility of overlapping between their characteristic product ions and ions produced by hitherto unknown reactions. Similar problems are evident in other systems; for example, H 3O +CH 4 adduct ions are observed in both SIFT-MS analyses of methane rich mixtures like biologically generated waste gases and in model planetary atmospheres.