Methane Partial Pressure Research Articles

Deactivation and kinetic studies of unsupported Ni and Ni–Co–Cu alloy catalysts used for hydrogen production by methane decomposition

Metallic nickel nano-particles and Ni–Co–Cu alloy particles were prepared primarily as catalysts for the thermal decomposition of methane to produce hydrogen. A series of kinetic experiments were conducted using these two types of catalysts. The effects of methane partial pressure and reaction temperature on the maximal hydrogen formation rate were studied. The reaction order and activation energy were estimated. Based on the TEM micrographs and the deactivation process of catalyst, the widely used empirical model (general power law equation) and a phenomenological model (exponential decay model) were used to simulate the experimental results of Ni catalysts.By quantifying the relationship between the kinetic parameters and the reaction conditions (methane partial pressure and reaction temperature), the transient hydrogen formation rate over the reaction time was derived and validated by comparing with the experimental data. A detailed catalytic deactivation study of Ni and Ni–Co–Cu catalysts was also carried out. Different deactivation mechanisms of pure Ni catalyst and Ni–Co–Cu alloy catalysts were compared and discussed.

The Role of the Gas Phase in Graphene Formation by CVD on Copper

Graphene synthesis on copper foils is experimentally studied at 1000°C under various methane partial pressures. A decrease in the carbon supply permits the formation of larger graphene flakes with fewer layers and crystalline defects. An influence of the copper foil confinement on graphene nucleation and growth is shown. Then, methane pyrolysis is simulated using the Fluent Ansys® code. The model shows that, at 1000°C, CH4 is decomposed to form gaseous saturated and unsaturated species. This means that two types of unsaturated species can co‐exist during graphene synthesis, the first one arising in the reactor volume from methane pyrolysis, and the second one only forming in the vicinity of copper, thanks to its catalytic activity.

Hydrogen production from catalytic decomposition of methane over ordered mesoporous carbons (CMK-3) and carbide-derived carbon (DUT-19)

This paper presents a thermogravimetric analysis of catalytic methane decomposition using ordered mesoporous carbon nanorods (CMK-3) and ordered mesoporous carbide-derived carbon (DUT-19) as catalysts. X-ray diffraction and N2 physisorption analyses were performed for both fresh catalysts. Threshold temperatures for methane decomposition with DUT-19 and CMK-3 were estimated by three different methods found in literature. Carbon formation rate and carbon weight gain as a function of time at various temperatures and methane partial pressures were studied, and the kinetics of CMK-3 and DUT-19 as catalysts for methane decomposition were investigated. Arrhenius energy values of 187kJ/mol for CMK-3 and 196kJ/mol for DUT-19 with a reaction order of 0.5 were obtained for both catalysts. Results show that carbon deposition on the catalyst during the reaction lead to catalyst deactivation with significant surface modification. Scanning electron microscope studies of fresh and deactivated catalyst samples show the blocking of catalyst pores and the formation of agglomerates on the outer surface of the catalyst during the course of reaction. DUT-19 catalytically outperforms CMK-3 because of a lower threshold temperature, higher surface area, and higher pore volume. These results show that ordered mesoporous carbons are promising catalysts for methane decomposition.

Synthesis of carbon nanotubes by thermo catalytic decomposition of methane over Cu and Zn promoted Ni/MCM-22 catalyst

The production of carbon nanotubes (CNTs) and pure hydrogen by the thermo catalytic decomposition of methane using a nano-size Ni-Cu-Zn/MCM-22 catalyst was investigated. The effect of Cu and Zn promoters was investigated by varying the amounts of Cu and Zn from 5 to 15wt% on a 50%Ni/MCM-22 catalyst prepared by wet impregnation. The performance of these catalysts was investigated in a fixed bed tubular reactor. The catalyst 50%Ni-10%Cu-10%Zn/MCM-22 resulted highest yield of hydrogen, and bamboo-shaped CNTs compared to other catalysts. The morphology of the carbon product strongly depended on reaction temperature, the amount of copper and zinc loading, flow rate and the partial pressure of methane. At higher reaction temperatures (>750°C) methane conversion and the yield of CNTs decreased due to sintering of the Ni particles. The experimental conditions for optimizing the carbon yield were also investigated and the most favorable conditions were observed at 750°C and at a methane partial pressure of 0.25atm. The aim of this study was to investigate the influence of reaction conditions on the morphology and formation of bamboo-shaped carbon filaments on a metal nanoparticle-based catalyst at moderate temperature.

Methane Steam Reforming Kinetics on a Ni/Mg/K/Al2O3 Catalyst

The kinetics of methane steam reforming were studied on a Ni/Mg/K/Al2O3 catalyst that was developed for conditioning of biomass-derived syngas. Reactions were conducted in a packed-bed reactor while the concentrations of reactants (methane and steam) and products (hydrogen, carbon monoxide, and carbon dioxide) were varied at atmospheric pressure, with the effects of temperature (525–700 °C) and residence time also being investigated. A power law rate model was developed using nonlinear regression to provide a predictive capability for the rate of methane conversion over this catalyst, to be used for reactor design and technoeconomic analysis of process designs. In order to provide some mechanistic insight, and to compare this catalyst to other non-promoted Ni/Al2O3 catalysts reported in the literature, a reaction mechanism consisting of five elementary steps, using a Langmuir–Hinshelwood type approach, was also considered. These five steps included: (i) CH4 adsorption, (ii) H2O adsorption, (iii) surface reaction of adsorbed CH4 and H2O to form CO and H2, (iv) CO desorption, and (v) H2 desorption. Nonlinear regression was then used to fit each of the rate laws to the experimental data. From these results, the model that assumed CH4 adsorption to be the rate determining step provided the best fit of the experimental data. This finding is consistent with literature studies on non-promoted Ni/Al2O3 catalysts, in which methane adsorption has been proposed to be the rate determining step during catalytic methane steam reforming. Both the power rate laws and the rate law assuming CH4 adsorption to be the rate determining step can be used as predictive tools for determining methane conversion for a given set of process conditions. Additionally, a rate expression that assumed the rate was only a function of methane partial pressure was considered, namely, \(rate = k*P_{{CH_{4} }}\), where \(k = k_{0} *e^{{^{{ - {\text{Ea}}/{\text{RT}}}} }}\), with PCH4 in units of Torr. This first-order-methane rate expression fit the data well, yielding an apparent activation energy over this catalyst of Ea = 93 kJ/mol and the pre-exponential rate constant of k0 = 7.67 × 105 mol/(g-cat s Torr CH4).

Kinetic and autocatalytic effects during the hydrogen production by methane decomposition over carbonaceous catalysts

The reaction kinetics of methane decomposition to yield hydrogen and carbon has been investigated comparing different types of carbonaceous catalysts: two ordered mesoporous carbons (CMK-3 and CMK-5) and two commercial carbon blacks (CB-bp and CB-v). The evolution of the reaction rate along the time has been analyzed concluding that it is governed by different and opposite events: reduction of active sites by carbon deposition, autocatalytic effects of the carbon deposits and pore blockage and diffusional constraints. A relatively simple kinetic model has been developed that fits quite well the experimental reaction rate curves in spite of the complexity of the involved phenomena.Both CMK carbons, and particularly CMK-5, present the highest initial reaction rates and the longest stability at long reaction times. In these materials, a part of the active sites remains accessible, since the carbon deposits formed from methane are capable of growing through the catalyst mesopores toward the outer part of the particles. The activation energies calculated from the initial reaction rates follow the sequence CMK-3 < CMK-5 < CB-bp < CB-v, whereas in all cases the reaction order was estimated to be 0.5 with respect to the methane partial pressure.

Parametric Study of Methane Catalytic CVD into Single‐walled Carbon Nanotubes Using Spin‐coated Iron Nanoparticles

AbstractThe effects of reaction temperature, methane partial pressure, and reaction period on growing single‐walled carbon nanotubes (SWCNTs) are demonstrated in the present study. Simple methane CVD is carried out using a homemade iron nanoparticles catalyst. The iron nanoparticles are prepared by spin‐coating a colloidal mixture of iron(III) nitrate, PEG‐400, and absolute ethanol on silicon wafers. The experimental results show that the effects of all three reaction parameters studied, on the morphology and the topography of the SWCNT arrays, are significant. There is no evidence showing that the diameter of SWCNTs is correlated with these three reaction parameters.

Establishing and verifying of model for methane mass transfer in DAMO process

Denitrification anaerobic methane oxidation (DAMO) is a discovery in environmental science and engineering field. DAMO process releases a large of free energy, but DAMO microbial growth is extremely slow. The doubling time is as long as one month or more, which makes it difficult to attain DAMO enrichment culture. Methane is thought to be the key element on DAMO bacteria enrichment, because it is insoluble in water. A mathematical model describing methane behavior in gas-liquid-bacteria phases was set up to study the effect of methane on DAMO bacteria enrichment. Based on the model analysis, a relational expression between DAMO specific activity, methane partial pressure in gas phase and resistance of mass transfer was obtained, which was confirmed by DAMO specific activity test.

Hydrogen production by methane cracking using Ni-supported catalysts in a fluidized bed

Nickel, supported on porous alumina (γAl2O3), non-porous alumina (αAl2O3), and porous silica, was used to catalyze methane cracking in a fluidized bed reactor for hydrogen production. The effects of temperature, PCH4, and particle diameter, and their interactions, on methane conversion were studied with each catalyst. Temperature was the dominant parameter affecting the hydrogen production rate for all catalysts and particle diameter had the strongest effect on the total amount of carbon deposited. Maximum methane conversion as a function of support type followed the order Ni/SiO2 > Ni/αAl2O3 > Ni/γAl2O3. Nonetheless, better fluidization quality was obtained with Ni/γAl2O3. Methane conversion was increased by increasing temperature and particle size from 108 to 275 μm due to better fluidization achieved with 275 μm particles. Increasing the flow rate and methane partial pressure (PCH4) caused a drop in methane conversion. Tests were also run in a fixed bed reactor, and at constant weight hourly space velocity (WHSV), higher conversion was achieved in the fixed bed, but at the same time faster deactivation occurred since a higher methane conversion led to increase in carbon filament and encapsulating carbon formation rates. A critical problem with the fixed bed was the pressure build-up inside the reactor due to carbon accumulation. Finally, a series of cracking/regeneration cycle experiments were carried out in the fluidized bed reactor. The regeneration was performed through product carbon gasification in air. Ni/αAl2O3 and Ni/γAl2O3 activity decreased significantly with the first regeneration, which is attributed to Ni sintering during exothermic regeneration/carbon oxidation. However, Ni/SiO2 was thermally stable over at least three cracking/regeneration cycles, but mechanical attrition was observed.

Development of Sinter-Resistant Core–Shell LaMnxFe1–xO3@mSiO2 Oxygen Carriers for Chemical Looping Combustion

This work investigates the possibility of using LaMn0.7Fe0.3O3.15@mSiO2 as oxygen carriers for chemical looping combustion (CLC). CLC is a new combustion technique with inherent separation of CO2 from atmospheric N2. LaMn0.7Fe0.3O3.15@mSiO2 core–shell materials were prepared by coating a layer of mesostructured silica around the agglomerated perovskite particles. The oxygen carriers were characterized using different methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 sorption, hydrogen temperature-programmed reduction (H2-TPR), and temperature-programmed desorption of oxygen (TPD-O2). The reactivity and stability of the carrier materials were tested in a special reactor, allowing for short contact time between the fluidized carrier and the reactive gas [Chemical Reactor Engineering Centre (CREC) fluidized riser simulator]. Multiple reduction–oxidation cycles were performed. TEM images of the carriers showed that a perfect mesoporous silica layer was formed around samples with 4, 32, and 55 nm in thickness. The oxygen carriers having a core–shell structure showed higher reactivity and stability during 10 repeated redox cycles compared to the LaMn0.7Fe0.3O3.15 core. This could be due to a protective role of the silica shell against sintering of the particles during repeated cycles under CLC conditions. The agglomeration of the particles, which occurred at high temperatures during CLC cycles, is more controllable in the core–shell-structured carriers, as confirmed by SEM images. XRD patterns confirmed that the crystal structure of all perovskites remained unchanged after multiple redox cycles. Methane conversion and partial conversion to CO2 were observed to increase with the contact time between methane and the carrier. Indeed, more oxygen from the carrier surface, grain boundaries, and even from the bulk lattice was released to react with methane. Upon rising the contact time, less CO was formed, which is desirable for CLC application. Increasing the reaction temperature and methane partial pressure lead to enhanced conversions of CH4 under CLC conditions.

Methane cracking using Ni supported on porous and non-porous alumina catalysts

Porous and non-porous alumina catalysts were used as nickel supports to catalyze methane cracking. Different operating parameters were studied in a thermal gravimetric analyzer, including methane and hydrogen partial pressures, temperature and flow rate. During CH4 cracking, carbon builds up on the catalyst surface and therefore the catalyst requires periodic regeneration. Cycling tests were performed, using air during the regeneration phase to burn off the carbon. The results showed that the non-porous catalyst performed better than the porous catalyst in terms of cracking during the first cycle. Full regeneration of the catalysts by oxidizing the deposited carbon was achieved at 550 °C, while oxidation was very slow at 500 °C. After full regeneration, the performance of the porous catalyst became considerably better than the non-porous. The porous catalyst kept its activity for 24 cracking/regeneration cycles, while the non-porous catalyst lost half of its activity by the second cracking cycle and almost all of its activity after six cycles. NiAl2O4 formation and Ni sintering caused the non-porous catalyst activity loss. TPO results showed that two carbon types were deposited on the catalysts, namely Cβ and Cγ, where Cβ is more active than Cγ.

Modeling and simulation of an industrial secondary reformer reactor in the fertilizer plants

In this paper, the industrial secondary reformer reactor has been modeled and simulated at steady-state operation conditions. It aims to modify a complete mathematical model of the secondary reformer design. The secondary reformer is a part of a subprocess in a higher scale unit of ammonia synthesis. It is located after the primary reformer in the ammonia plant where it is used in the synthesis of ammonia. The reactions in the secondary reformer reactor are assumed to be carried inside two reactors in series. The first reactor, upper section, is the combustion zone, while the second reactor, bottom section, is the catalyst zone with nickel catalyst based on the alumina. In order to create a reactor design model for the secondary reformer in the industrial ammonia plant, combustion and catalyst zones have been studied. The temperature and compositions of gas in the combustion zone are predicted using the atomic molar balance and adiabatic flame temperature model. In the catalyst zone, the temperature and composition profiles along the axial distance are predicted using a one-dimensional heterogeneous catalytic reaction model with the assumption that the reactions are first order in methane partial pressure.

Substrate-specific pressure-dependence of microbial sulfate reduction in deep-sea cold seep sediments of the Japan Trench.

The influence of hydrostatic pressure on microbial sulfate reduction (SR) was studied using sediments obtained at cold seep sites from 5500 to 6200 m water depth of the Japan Trench. Sediment samples were stored under anoxic conditions for 17 months in slurries at 4°C and at in situ pressure (50 MPa), at atmospheric pressure (0.1 MPa), or under methanic conditions with a methane partial pressure of 0.2 MPa. Samples without methane amendment stored at in situ pressure retained higher levels of sulfate reducing activity than samples stored at 0.1 MPa. Piezophilic SR showed distinct substrate specificity after hydrogen and acetate addition. SR activity in samples stored under methanic conditions was one order of magnitude higher than in non-amended samples. Methanic samples stored under low hydrostatic pressure exhibited no increased SR activity at high pressure even with the amendment of methane. These new insights into the effects of pressure on substrate specific sulfate reducing activity in anaerobic environmental samples indicate that hydrostatic pressure must be considered to be a relevant parameter in ecological studies of anaerobic deep-sea microbial processes and long-term storage of environmental samples.

Kinetic study of double-walled carbon nanotube synthesis by catalytic chemical vapour deposition over an Fe-Mo/MgO catalyst using methane as the carbon source

A kinetic study was performed to describe experimental reaction rates of double-walled carbon nanotube (DWNT) synthesis by catalytic chemical vapour deposition (CCVD) over an Fe-Mo/MgO catalyst using methane as the carbon source. Initial reaction rates were determined by mass spectrometry for methane partial pressures ranging from 0.01 atm to 0.9 atm and for three temperatures: 900 °C, 950 °C and 1000 °C. Mass transfers from the bulk of the fluid to the external surface of the catalytic bed and through the catalytic bed were negligible as determined experimentally and confirmed by the methane mass balance. A detailed kinetic study was carried out to discriminate between phenomenological kinetic models and to validate the good agreement between the chosen model and the experimental data. The best model was found to involve the irreversible dissociative adsorption of methane followed by the irreversible decomposition of the adsorbed methyl group, which is the rate-determining centre. Activation energy of adsorbed methyl decomposition was found to be equal to 58 kJ mol −1. The catalytic deactivation by coking was expressed by a decreasing function of coke content, which leads to a sigmoid equation.

Role of Hydrogen in Chemical Vapor Deposition Growth of Large Single-Crystal Graphene

We show that graphene chemical vapor deposition growth on copper foil using methane as a carbon source is strongly affected by hydrogen, which appears to serve a dual role: an activator of the surface bound carbon that is necessary for monolayer growth and an etching reagent that controls the size and morphology of the graphene domains. The resulting growth rate for a fixed methane partial pressure has a maximum at hydrogen partial pressures 200-400 times that of methane. The morphology and size of the graphene domains, as well as the number of layers, change with hydrogen pressure from irregularly shaped incomplete bilayers to well-defined perfect single layer hexagons. Raman spectra suggest the zigzag termination in the hexagons as more stable than the armchair edges.

Thermocatalytic decomposition of methane using activated carbon: Studying the influence of process parameters using factorial design

The thermocatalytic decomposition of methane over activated carbon (AC) is proposed as a potential alternative for the production of hydrogen. The experiments were divided into two parts; the first part was conducted using thermogravimetric analyzer (TGA) while the second part was conducted in a bench-scale unit. For the first part, the research objective is to study the main and interaction effects of decomposition temperature (800–950 °C) and methane partial pressure (0.03–0.63 atm) on the initial specific rate of carbon formation by using statistical method. The experiments were carried out as a general full factorial design consisting of 20 experiments. Quadratic model was developed for initial specific rate of carbon formation in term of temperature and methane partial pressure using response surface methodology. The model’s results show that not only the effects of the main parameters are important, but also the interaction effects between them are significant. For the second part, the main effects of decomposition temperature (775–850 °C) and AC weight (20–120 g) on the initial rate of methane decomposition by using the analysis of variance (ANOVA) were investigated. The results showed that AC weight has higher mean effects than decomposition temperature on the initial rate of methane decomposition.

Growth of single-walled carbon nanotubes on a Co–Mo–MgO supported catalyst by the CVD of methane in a fixed bed reactor: Model setting and parameter estimation

In this work methane was decomposed to hydrogen and carbon to determine its kinetic behavior during reaction over a Co–Mo–MgO supported catalyst using the CVD (Chemical Vapor Deposition) technique. Decomposition of methane molecules was performed in a continuous fixed bed reactor to obtain data to simulate methane decomposition in a gas phase heterogeneous media. The products and reactants of reaction were analyzed by molecular sieve column followed by GC-analysis of the fractions to determine the amount of product converted or reactant consumed. The synthesis of single-walled carbon nanotubes was performed at atmospheric pressure, different temperatures and reactant concentrations. The experimental data analyzed to suggest the formula for calculation of the initial specific reaction rate of the carbon nanotubes synthesis, were fitted by several mathematical models derived from different mechanisms based on Longmuir-hinshelwood expression. The suggested mechanism according to dissociation adsorption of methane seems to explain the catalytic performance in the range of operating conditions studied. The apparent activation energy for the growth of SWNTs was estimated according to Arrhenius equation. The as grown SWNTs products were characterized by SEM, TEM and Raman spectroscopy after purification. The catalyst deactivation was found to be dependent on the time, reaction temperature and partial pressure of methane and indicated that the reaction of deactivation can be modeled by a simple apparent second order of reaction.

Synthesis of carbon nanotubes by methane decomposition over Co–Mo/Al 2O 3: Process study and optimization using response surface methodology

Systematic studies of various process variables on the formation of carbon nanotubes (CNTs) by methane decomposition over a Co–Mo/Al 2O 3 catalyst were performed using a three-level factorial design in response surface methodology. A quadratic polynomial model for carbon yield was developed by multiple-regression analysis. The optimum conditions for CNT production within the experimental ranges were found at a reaction temperature of 761 °C, a methane partial pressure of 0.75 atm and a catalyst weight of 0.4 g. The carbon yield predicted at the optimum process conditions was 607%. Examination by electron microscopy revealed that the CNTs grown under optimum conditions had diameters of 11.8 ± 1.9 nm (average diameter ± standard deviation) and possessed an open-tip morphology.

A parametric study of methane decomposition into carbon nanotubes over 8Co-2Mo/Al 2O 3 catalyst

Abstract The effects of reaction temperature, partial pressure of methane, catalyst weight and gas hourly space velocity (GHSV) on methane decomposition were reported. The decomposition reaction was performed in a vertical fixed-bed reactor over 8Co-2Mo/Al 2O 3 catalyst. The experimental results show that these four process parameters studied had vital effects on carbon yield. As revealed by the electron microscopy and Raman spectroscopy analyses, the reaction temperature and GHSV governed the average diameter, the diameter distribution and the degree of graphitization of the synthesized carbon nanotubes (CNTs). Also, an evidence is presented to show that higher temperatures and higher GHSV favored the formation of better-graphitized CNTs with larger diameters.

Catalytic performance of La1−xErxCoO3 perovskite for the deoxidization of coal bed methane and role of erbium in a catalyst

The effective utilization of coal bed methane (CBM) is very significant for energy utilization and environmental protection, reducing significantly greenhouse gas methane emission. In this paper, La1−xErxCoO3 perovskite (0 ≤ x ≤ 0.4) catalysts for the catalytic deoxidization of CBM were prepared by a co-precipitation method and were characterized by X-ray diffraction (XRD), laser Raman spectroscopy (LRS), H2 and CH4 temperature-programmed reduction (H2, CH4-TPR), CO pulse and N2adsorption/desorption techniques. The results show that the amount of Er affects obviously the physicochemical and catalytic properties of La1−xErxCoO3, and when x = 0.2, La0.8Er0.2CoO3 exhibits the best activity for deoxidization of CBM, because Er doping promotes the activity and migration of the lattice oxygen of La0.8Er0.2CoO3. The influences of the operation parameters (methane concentration, oxygen concentration and space velocity) on the catalytic deoxygenation of CBM and the kinetics behaviours were investigated. The reaction order of removing oxygen is 0.9 for methane partial pressure and −0.6 for oxygen partial pressure.