Methane Conversion Efficiency Research Articles

Biomethane recovery from Egeria densa in a microbial electrolysis cell-assisted anaerobic system: Performance and stability assessment

Renewable energy recovery from submerged aquatic plants such as Egeria densa (E. densa) via continuous anaerobic digestion (AD) represents a bottleneck because of process instability. Here, a single-chamber membrane-free microbial electrolysis cell (MEC) equipped with a pair of Ti/RuO2 mesh electrodes (i.e. the combined MEC-AD system) was implemented at different applied voltages (0–1.0 V) to evaluate the potential effects of bioelectrochemical stimulation on methane production and process stability of E. densa fermentation. The application of MEC effectively stabilized E. densa fermentation and upgraded overall process performance, especially solid matters removal. E. densa AD process was operated steadily throughout bioelectrochemical process without any signs of imbalance. The solubilization-removal of solid matters and methane conversion efficiency gradually increased with increasing applied voltage, with an average methane yield of approximately 248.2 ± 21.0 mL L−1 d−1 at 1.0 V. Whereas, the stability of the process became worse immediately once the external power was removed, with weaken solid matters removal along with methane output, evidencing the favorable and indispensable role in maintaining process stability. The stabilizing effect was further quantitatively demonstrated by statistical analysis using standard deviation (SD), coefficient of variance (CV) and box-plots. The syntrophic and win–win interactions between fermenting bacteria and electroactive bacteria might have contributed to the improved process stability and bioenergy recovery.

Oxidative Conversion of Methane into Syngas Using Porous Catalysts Prepared by Combustion Synthesis

Using the method of combustion synthesis, a series of porous cermet materials from nickel and oxides (such as NiO, MgO, Al2O3, ZrO2, and rare-earth oxides) was synthesized. They investigated in terms of their application as catalysts of the reaction of oxidative coupling of methane into synthesis gas. It is found out that the composites containing about 50% (NiO + Ni) and a small amount (up to 5%) of Ce, La, Nd, and Pr-oxides at the temperature 830оС ensure the conversion efficiency of methane within 92 ÷ 95% and the H2/CO ratio 2.0 ÷ 2.1 in the reaction products. The data obtained suggest that the materials manufactured can be effectively used in the systems of syngas manufacturing (for the Fischer – Tropsch process) and in the production of hydrogen from natural gas.

Heat Transfer and Energy Storage Performance of Methane Reforming with Carbon Dioxide in Semi-cavity Reactor

The heat transfer and energy storage performance of methane reforming with carbon dioxide in a semi-cavity reactor catalyzed by Ni/Al2O3 are numerically investigated. The concentrated solar energy flux is calculated by Gaussian distribution model, and the heat losses of radiation and convection in semi-cavity reactor are reduced by considering the angle factor. The simulated methane conversion and thermochemical storage efficiency have good agreements with previous experimental data. The simulation results indicate that the higher operating temperature promotes the methane reforming reaction, so the methane conversion obviously increases with the operating temperature. As DNI (direct normal irradiation) increases, the methane conversion increases, while the thermochemical storage efficiency first increases and then decreases. Compared with tubular reactor, the methane conversion of semi-cavity reactor increases for 13.2%, and the thermochemical storage efficiency get an increase of 12.9%. When the inlet velocity rises, the fluid temperature decreases with heat loss increasing, the methane conversion remarkably decreases with the residence time decreasing, and the thermochemical storage efficiency has a maximum.

Thermochemical storage performances of methane reforming with carbon dioxide in tubular and semi-cavity reactors heated by a solar dish system

Thermochemical storage performances of methane reforming with carbon dioxide in tubular and semi-cavity reactor heated by a solar dish system have been experimentally and numerically investigated. The methane conversion and thermochemical storage efficiency of methane reforming process in tubular reactor were experimentally studied for inlet flow rate 3–6L/min and direct normal irradiation (DNI) 677.8–714.3W/m2. According to the experimental system and results, Gaussian distribution model is derived for concentrated solar energy flux from solar dish, and a 3D finite volume method coupled with volumetric reaction kinetics and unilateral concentrated solar energy flux is established by experimental verification. The simulated methane conversion and energy storage efficiency have good agreements with the experimental data, and the temperature and species concentration distributions of the reactor are also successfully predicted. In the middle region of reactor, the concentrated solar energy flux and heat loss reach maxima, while the net heat flux and reaction kinetic rate reach maxima in the front region because of high temperature and high reactant fraction. As the catalyst bed length increases, the residence time and reverse reaction rate both rise, so there exists a proper catalyst bed length. When DNI rises, the methane reforming is promoted, while the heat loss remarkably increases, which results in the maximum thermochemical storage efficiency under proper DNI. Structural and operating parameters for the present tubular reactor can be further optimized, and the proper catalyst bed length is 300mm, while the proper DNI is 250–300W/m2 (focal energy flux of 244.3–293.2kW/m2). A semi-cavity reactor is designed to reduce the heat loss and enhance the energy storage performance. According to the experimental results under inlet flow rate 2–6L/min and DNI 452.4–598.5W/m2, the methane conversion of semi-cavity reactor can be increased to 74.8%, and the thermochemical storage efficiency and total energy efficiency can be respectively increased to 19.7% and 28.9%.

A feasibility study on a novel stone dust looping process for abatement of ventilation air methane

This paper describes the development of a novel stone dust looping process that relates to the removal of ventilation air methane using stone dust. The working principle behind the stone dust looping process is incredibly simple which involves the catalytic oxidation of methane followed by carbonation and calcination reactions. In the current work, laboratory scale fluidized bed experiments and process simulations were conducted to evaluate the feasibility of the stone dust looping process. The experimental work concluded that oxidation of ventilation air methane in the stone dust looping process can be successfully achieved at temperatures between 500 and 650°C. The experimental results indicated that oxidation of methane was found to increase at higher temperatures while carbon dioxide capture efficiency showed a declining trend with increasing temperature. Furthermore, higher methane conversion and optimum (thermodynamic) carbon dioxide capture efficiency were observed for lower ventilation air methane flow rates and higher bed inventory. The concentration of methane in ventilation air methane and stone dust particle size did not have a significant effect on methane conversion or carbon dioxide capture. Also, comparison with synthetically prepared CuO and Fe2O3 catalysts has been made with CaO for VAM oxidation. CaO was found to be comparable to Fe2O3 and superior to CuO. From the process simulations, it was concluded that thermal energy generation in the carbonator was increased with higher methane and carbon dioxide concentrations. However, at the same time for higher methane and carbon dioxide concentrations, a greater CaO flux was required in the carbonator and hence a larger amount of goaf gas was required for the calcination reaction. The higher thermal energy generation in the carbonator was expected to improve the autothermicity of the stone dust looping process at concentrations of methane in the ventilation stream <0.2 vol.% (thermodynamic limit).

Effect of core and shell compositions on MeOx@LaySr1−yFeO3 core–shell redox catalysts for chemical looping reforming of methane

The chemical looping reforming (CLR) process converts methane into syngas through cyclic redox reactions of an active lattice oxygen (O2−) containing redox catalyst. In CLR, methane is partially oxidized to CO and H2 using the active lattice oxygen of a redox catalyst. In a subsequent step, the oxygen-deprived redox catalyst is regenerated by air. Such a process can eliminate the need for steam and/or oxygen in reforming, thereby improving methane conversion efficiency. A number of perovskite-structured mixed metal oxides are known to be active for CLR. However, the oxygen storage capacity of perovskites tends to be low, limiting their practical application in chemical looping. In contrast reducible metal oxides such as cobalt and iron oxides can store up to 30wt.% lattice oxygen but are less selective for syngas generation. We explore oxygen carriers that utilize the advantages of both perovskites and first-row transition metal oxides by integrating a transition metal oxide core with a mixed ionic–electronic conductive (MIEC) perovskite support/shell. MIEC perovskites facilitate countercurrent conduction of O2− and electrons, allowing facile O2− transport though the solid. It is proposed that this conduction allows rapid oxygen transport to and from the transition metal oxide cores irrespective of the porosity of the redox catalyst. In this work, we show that MeOx@LaySr1−yFeO3 can be an excellent model catalyst system for CLR. The activity, selectivity, and coke resistance of the core–shell system can be tuned by changing the ratio of La to Sr in the perovskite shell and the type of transition metal oxide in the core. Our studies indicate that lower Sr loadings can improve activity and selectivity of the catalyst for methane partial oxidation, but make the LSF shell less resistant to decomposition during the reduction step.

Optimization of Methanotrophic Growth and Production of Poly(3-Hydroxybutyrate) in a High-Throughput Microbioreactor System.

Production of poly(3-hydroxybutyrate) (P3HB) from methane has economic and environmental advantages over production by agricultural feedstock. Identification of high-productivity strains and optimal growth conditions is critical to efficient conversion of methane to polymer. Current culture conditions, including serum bottles, shake flasks, and agar plates, are labor-intensive and therefore insufficient for systematic screening and isolation. Gas chromatography, the standard method for analysis of P3HB content in bacterial biomass, is also incompatible with high-throughput screening. Growth in aerated microtiter plates coupled with a 96-well Nile red flow-cytometric assay creates an integrated microbioreactor system for high-throughput growth and analysis of P3HB-producing methanotrophic cultures, eliminating the need for individual manipulation of experimental replicates. This system was tested in practice to conduct medium optimization for P3HB production in pure cultures of Methylocystis parvus OBBP. Optimization gave insight into unexpected interactions: for example, low calcium concentrations significantly enhanced P3HB production under nitrogen-limited conditions. Optimization of calcium and copper concentrations in the growth medium increased final P3HB content from 18.1% to 49.4% and P3HB concentration from 0.69 g/liter to 3.43 g/liter while reducing doubling time from 10.6 h to 8.6 h. The ability to culture and analyze thousands of replicates with high mass transfer in completely mixed culture promises to streamline medium optimization and allow the detection and isolation of highly productive strains. Applications for this system are numerous, encompassing analysis of biofuels and other lipid inclusions, as well as analysis of heterotrophic and photosynthetic systems.

High temperature energy storage performances of methane reforming with carbon dioxide in a tubular packed reactor

High temperature heat transfer and energy storage performances of methane reforming with carbon dioxide in tubular packed reactor are investigated under different operating conditions. Experimental results show that the methane reforming in tubular packed reactor can efficiently store high temperature thermal energy, and the sensible heat and heat loss besides thermochemical energy storage play important role in the total energy storage process. When the operating temperature is increased, the thermochemical storage efficiency first increases for methane conversion rising and then decreases for heat loss rising. As the operating temperate is 800°C, the methane conversion is 79.6%, and the thermochemical storage efficiency and total energy efficiency can be higher than 47% and 70%. According to the experimental system, the flow and reaction model of methane reforming is established using the laminar finite-rate model and Arrhenius expression, and the simulated methane conversion and energy storage efficiency fit with experimental data. Along the flow direction, the fluid temperature in the catalyst bed first decreases because of the endothermic reaction and then increases for the heat transfer from reactor wall. As a conclusion, the maximum thermochemical storage efficiency will be obtained under optimal operating temperature and optimal flow rate, and the total energy efficiency can be increased by the increase of bed conductivity and decrease of heat loss coefficient.

Numerical study on catalytic combustion of methane with ozone using Pd-exchanged zeolite X

A steady-state 1D macro-homogeneous model is developed to illustrate the combustion process of methane with ozone in the reactor composed of Pd-exchanged zeolite X. The model is validated by comparing the predicted results with the measured data. The methane conversion increases with decreasing the inlet methane concentration and gas space velocity and increasing the inlet ozone concentration and temperature. As the reactor length reduces, the methane conversion varies little if the reactor is too long but decreases when the reactor is too short. Therefore, the reactor should be properly designed to balance costs and the methane-conversion efficiency.

The effect of substrate to inoculum ratios on the anaerobic digestion of human faecal material

Abstract The anaerobic digestion (AD) of human faecal material (HFM) was investigated to consider the effect different substrate to inoculum ratios (SIR) from 0.5 to 4 on the rate and extent of methane production as well as impact on pathogen numbers. The AD process was monitored by measuring pH, total volatile fatty acid, bicarbonate alkalinity, ammonium and methane production. The results showed that the highest amounts of methane production with a value of 254.4 ±12.6 ml CH 4 g VS added − 1 and highest pathogen removal with a value of 2.7×10 4 ±40 and 2.5×10 3 ±0.5 CFU/ml, respectively, for E.coli and faecal coliform bacteria was achieved by the 0.5 SIR incubation. However, the highest organic loading found in the 4.0 SIR incubation showed the lowest methane yield with a value of 110 ±1.3 ml CH 4 g VS added − 1 and the lowest pathogen removal with a value of 3.2×10 5 ±19 and 3.2×10 4 ±3.5 CFU/ml, respectively for E.coli and faecal coliform bacteria. The empirical equation was used to calculate the theoretical methane and compare this with the actual values of methane production. The relatively high methane conversion efficiency between theoretical and actual values for 0.5 SIR, further suggest that this operational condition was the most effective.

Effect of Geometric Scale on Heat Recirculation and Syngas Production in a Noncatalytic Counter-Flow Reformer

Hydrogen-based systems, such as fuel cells, are a promising means to satisfy portable and remote power demands. Hydrogen transportation and storage challenges can be met with point-of-use reforming of hydrocarbon fuels to hydrogen-rich syngas. Applications may require geometric scaling of system components, including the fuel reformer. This study computationally investigates, via a two-dimensional computational fluid dynamics (CFD) model, the effect of scaling on a noncatalytic counter-flow reformer that utilizes heat recirculation to convert hydrocarbon fuels to syngas. The dimensions of the counter-flow reactor studied previously are used as reference values, and the reactor volume is scaled relative to the reference volume by varying either channel height or length. Operating range maps are developed that indicate where reactor operation is obtained as a function of equivalence ratio and inlet velocity. Heat recirculation, hydrogen, carbon monoxide, and methane conversion efficiencies are quantified over a range of inlet velocities and equivalence ratios. Computationally determined peak gas and wall temperatures are compared to adiabatic equilibrium temperatures. This analysis relates the degree of superadiabicity, the extent to which the temperature exceeds that predicted by equilibrium in the reactor to the more readily measured wall temperatures, which have previously been shown to be important indicators of reactor performance.

Dynamic Methane Partial Oxidation Using a Fe2O3@La0.8Sr0.2FeO3-δ Core–Shell Redox Catalyst in the Absence of Gaseous Oxygen

Chemical looping reforming partially oxidizes methane into syngas through cyclic redox reactions of an active lattice-oxygen (O2–) containing redox catalyst. The avoidance of direct contact between methane and steam and/or gaseous oxygen has the potential to eliminate the energy consumption for generating these oxidants, thereby increasing methane conversion efficiency. This article investigates redox catalysts comprised of iron oxide core covered with lanthanum strontium ferrite (LSF) shell. The iron oxide core serves as the primary source of lattice-oxygen, whereas the LSF shell provides an active surface and facilitates O2– and electron conductions. These core–shell materials have the promise to provide higher selectivity for methane conversion with lower solid circulation rates than traditional redox catalysts. Methane oxidation by this catalyst exhibits four distinct regions, i.e. deep oxidation; competing deep and selective oxidation; selective oxidation with autoactivation; and methane decomposition. Further investigations indicate that the evolution of “loose” lattice oxygen from the bulk contributes to deep oxidation, whereas reduced surface iron species are responsible for selective methane oxidation.

Methane Catalytic Cracking to Make Hydrogen and Graphitic Nano Carbons (Nanotubes, Microfibers, Microballs, Onions) with Zero Emission

Methane was catalytically decomposed to hydrogen and highly graphitic carbon nanotubes, microfibers, microballs, and nano onions. Over Mo x –Ni(Fe,Co) y –MgO z , single-walled carbon nanotubes (SWNTs) and thin-walled carbon nanotubes (TWNTs) were produced; over Ni/Y, individually separated SWNTs were generated; over La2NiO4, multiwalled carbon nanotubes (MWNTs) were made. Over Ni/MCM-41, with the addition of benzene, the carbon microballs (CMBs) were produced. Over Fe–Cr alloy and LaNi0.9Co0.1O3, the carbon nano onions (CNOs) and carbon microfibers (CMFs) were produced, respectively. The methane conversion efficiency and carbon growth rate followed the order: CNOs > CMBs > CMFs > MWNTs > TWNTs > SWNTs.

Full load performance and emission characteristics of hydrogen-compressed natural gas engines with valve overlap changes

Natural gas vehicle engines are preferred over diesel engines because they release significantly lower amounts of nitrogen oxides (NOx) and carbon dioxide emissions. Hydrogen-compressed natural gas (HCNG) technology is a promising alternative to that used in conventional compressed natural gas engines because hydrogen possesses stable lean combustion characteristics. Although the NOx emissions requirements are satisfied, methane emissions must be filtered using an oxidation catalyst. An alternative is required for methane reduction because improving the conversion efficiency of methane is expensive. In this study, the strategy of varying the valve overlap was employed to reduce methane emissions. Although a torque valve cannot meet engine emission specifications, the hydrocarbon and methane emissions were reduced by approximately 41% by decreasing the valve overlap duration while using HCNG fuel. The level of NOx emissions was approximately equivalent to or slightly higher than that of a conventional camshaft.

Textural and catalytic properties of Mo loaded hierarchical meso-/microporous lamellar MFI and MWW zeolites for direct methane conversion

The consequences of meso-/microporous zeolite structures on distribution and activity of active sites (Brønsted acid and metal sites) in molybdenum (Mo) impregnated lamellar MFI and lamellar MWW zeolites were investigated in direct methane aromatization (DMA) reactions. In comparison with their microporous analogies (Mo/MFI and Mo/MWW), the mesopores in the Mo/lamellar MFI and Mo/lamellar MWW zeolites facilitated the dispersion of Mo in zeolite micro-channels. The catalytic DMA reactions showed that the Mo loaded lamellar MFI and lamellar MWW zeolites enabled efficient methane conversion, aromatic product formation, and coke accumulation in the initial stage of reaction, while their performances were similar to those of Mo/MFI and Mo/MWW catalysts in the long term run. A plausible explanation to this scenario is that active sites in Mo/lamellar MFI and Mo/lamellar MWW can be accessed by reactants through both micropores and mesopores. The facilitated transport and accessibility to active sites by mesopores accounted for initial fast reaction and deactivation rates of Mo loaded lamellar zeolites. After mesopores were clogged by deposited coke in DMA reactions, micropores of zeolites were responsible for the long term catalyst performances, which were similar to Mo loaded microporous zeolites.

Development of the Tricopper Cluster as a Catalyst for the Efficient Conversion of Methane into MeOH

AbstractFollowing recent progress towards understanding the structure of the particulate methane monooxygenase in methanotrophic bacteria, it is now possible to attempt the development of laboratory catalysts for the conversion of methane into MeOH under ambient conditions. To this end, a class of tricopper complexes that are capable of efficiently oxidizing small hydrocarbon substrates at room temperature has recently been developed. In this Minireview, we describe the development of a tricopper cluster to accomplish the catalytic conversion of methane into MeOH, as well as a number of small n‐alkanes into their corresponding alcohols and ketones, with high efficiencies. The properties of this robust catalytic system are discussed.

Efficient Methane Conversion to Hydrogen by the Force-Activated Oxides on Iron Particle Surfaces

Mechanochemically activated iron oxide formation on α-iron (Fe) microparticles for the efficient reaction with methane (CH4) was investigated using a simple milling process to successfully clarify the efficient CH4 adsorption as well as the C–H bonding dissociation. First, the oxides with different oxidation degrees (i.e., disordered or ordered iron oxides) were formed on the Fe by mechanochemical milling under an oxygen atmosphere. The surface analyses by X-ray diffraction, Raman, and X-ray photoelectron spectroscopy (XPS) revealed that the surface iron oxides consisted of two phases (α-Fe2O3 and Fe3O4), and the Fe2O3-like structure was dominantly grown on the near-surface of the disordered iron oxides during the initial oxidation time (0.08 and 0.80 h). Furthermore, the signals from an electron spin resonance analysis suggested dangling bondings on the disordered oxides, indicating the successful formation of the active O sites. Second, the mechanochemical reaction of the resultant iron oxide surfaces with CH4 was investigated. As a result, the efficient CH4 adsorption as well H2 generation were prominently observed on the disordered oxides, indicating an effectively dissociative adsorption. XPS analysis of the resultant particles revealed that the C–H bonding dissociation dominantly occurred on the near-surface oxygen atoms. Furthermore, using a molecular orbital calculation analysis, the activated O atoms with dangling bondings in the disordered iron oxides were found to affect the C–H dissociation of the adsorbate molecules (e.g., CH4 and CH3•) and exhibit an efficient H2 generation. On the other hand, the O atoms in the ordered lattice could not induce the C–H dissociation of CH3• to produce the equilibrium adsorption/desorption states and lower H2 generation amount, suggesting the importance of both the force-induced activated O atoms and closest interatomic distances. Therefore, we first achieved the efficient mechanochemical decomposition of CH4 and CH3• to generate H2 by the disordered iron oxide surfaces on α-Fe particles.

Methane decomposition under a corona discharge to generate COx-free hydrogen

A non-thermal plasma reforming unit operating at atmospheric pressure has been developed for converting methane to COx-free hydrogen. Argon was used to provide additional electrons and photons for higher reaction rates. A series of experiments was performed for positive corona discharge at a fixed inter-electrode distance (15 mm) to study the effects of discharge power (range of 14–20 W) and residence time (60, 120, 180 and 240 s). A second series of experiments studied the effect of inter-electrode distance on hydrogen production, with distances of 15, 20, 25, 30 and 35 mm tested. The analysis of the results shows that both discharge power and residence time, have a positive influence on methane conversion, hydrogen selectivity and energy conversion efficiency. Longer discharge gaps favour hydrogen production. A final series of experiments on corona polarity showed that a positive discharge was preferable.

Non-thermal plasma catalysis of methane: Principles, energy efficiency, and applications

The reaction mechanism and energy efficiency analysis of non-thermal plasma assisted methane conversion are presented. Plasma catalysis is an innovative next-generation green technology that satisfies needs for energy and materials conservation, and environmental protection. Non-thermal plasma uniquely generates reactive species almost independently of reaction temperature. Those species initiate chemical reactions at remarkably lower temperatures than conventional thermochemical reactions. Low-temperature methane conversion is important because it minimizes exergy destruction accompanied by combustion of the initial feed, or production of high-temperature thermal energy, necessary for thermochemical methane reform. Non-thermal plasma has great flexibility to tune the process parameters so that energy and material consumption are minimized. This article explains aspects of plasma-assisted fuel reforming including arc plasma to non-thermal plasma. We specifically examine dielectric barrier discharge (DBD) as viable non-thermal plasma for practical fuel reforming. Second, the energy efficiency of non-oxidative methane conversion using DBD is analyzed. That energy efficiency determined by experimentation was 1%, although theoretical analysis suggested 8%, implying that DBD alone is invariably more inefficient. Finally, DBD-catalysts hybrid reaction is proposed and a synergistic effect between plasma-generated reactive species and catalysts is clarified, suggesting that vibrationally excited species are important for enhancing overall methane conversion efficiency with catalysts.

Optimization geometries of a vortex gliding-arc reactor for partial oxidation of methane

The effects of the geometry of gliding-arc reactor – such as distance between the electrodes, outlet diameter, and inlet position – on the reactor characteristics (methane conversion, hydrogen yield, and energy efficiency) have not been fully investigated. In this paper, AC gliding-arc reactors including the vortex flow configuration are designed to produce hydrogen from the methane by partial oxidation. The influence of vortex flow configuration on the reactor characteristics is also studied by varying the inlet position. When the inlet of the gliding-arc reactor is positioned close to the outlet, reverse vortex flow reactor (RVFR), the maximum energy efficiency reaches 50% and the yields of hydrogen and carbon monoxide are 40% and 65%, respectively. As the distance between electrodes increases from 5 mm to 15 mm, both hydrogen yield and energy efficiency increase approximately 10% for the RVFR. The energy efficiency and hydrogen yield are highest when the ratio of the outlet diameter to the inner diameter is 0.5 for the RVFR. Experimental results indicate that the flow field in the plasma reactor has an important influence on the reactor performance. Furthermore, hydrogen production increases as the number of feed gas flows in contact with the plasma zone increases.