Effects of fluorination modification on pore size controlled electrospun activated carbon fibers for high capacity methane storage

Electrospun carbon fibers were prepared as a methane storage medium. Chemical activation was carried out using potassium carbonate to develop the pore structure, which can provide sites for the uptake of methane, and then fluorination surface modification was conducted to enhance the capacity of storage. Chemical activation provided a highly microporous structure, which is beneficial for methane storage, with a high specific surface area greater than 2500 m²/g. The pore size distribution showed that the prepared samples have pore sizes in the range of 0.7–1.6 nm. The effect of fluorination surface modification was also investigated. The functional groups, which were confirmed by XPS analysis, played an important role in guiding methane gas into the carbon silt pores via the attractive force felt by the electrons in the methane molecules due to the high electronegativity of fluorine. Eventually, the methane uptake increased up to 18.1 wt.% by the synergetic effects of the highly developed micropore structure and the guiding of methane to carbon pores by fluorine.     

Analysis of Relationship Between Microbial and Methanogenic Biomass in Methane Fermentation

To analyze the relationship between biomass of microorganisms and methane production, the total biomass of bacteria and archaea (BA) during methane fermentation was analyzed by the environmental DNA analysis method. In the case of using methanogenic sludge as a seed which is generally used for methane fermentation, the total BA biomass reached to 1.5 × 10⁸ to 3.6 × 10⁸ cells/ml when methane was produced. On the other hand, soil suspension was used as a seed; methane was not produced for 14-day cultivation. However, the total BA biomass reached to above 1.5 × 10⁸ cells/ml. The methanogen biomass was counted by using a fluorescence microscope (coenzyme F₄₂₀), and the methanogen biomass and the ratio of methanogens in the total of BA were analyzed during methane fermentation. At the methane-producing phase, the methanogen biomass reached to 1.3 × 10⁸ cells/ml, and the ratio of methanogens was above 70% of the total BA. When the ratio of methanogens in a seed was changed, the methane-producing phase was moved. However, the relationship between methanogens and other microorganisms at the methane-producing phase was almost similar.     

Reforming of Carbon Dioxide to Methane and Methanol by Electric Impulse Low-Pressure Discharge with Hydrogen

Basic phenomena of the reduction of carbon dioxide to reusable organic materials including methane and methanol were investigated by using a radio frequency impulse discharge in a low gas pressure range without catalysis. The discharge took place under different discharge parameters such as voltage, gas flow rate, gas-mixing ratio, and gas residence time, where the carbon dioxide was mixed with hydrogen at total gas pressure of 1–10 Torr. Organic materials such as methane and methanol were observed. Carbon monoxide was a major product from carbon dioxide. Methane was the dominant organic species produced by the discharge. The concentration of methane increased with discharge voltage, and its volume fraction attained 10–20% of the products containing carbon that came from carbon dioxide. This fraction was also dependent on the mixing ratio of carbon dioxide and hydrogen. We also observed the formation of methanol, though its fraction was low, a few %, compared with methane.     

Study on deuterium exchange in surface CHx species formed from methane over platinum, ruthenium and cobalt under non-oxidative conditions

Dissociative chemisorption of methane over ruthenium, cobalt, platinum and their bimetallic counterparts supported by alumina and NaY was investigated under a wide range of temperatures. The extent of hydrogen loss from methane was monitored by deuterium uptake of the surface CH_x species formed from methane during the course of methane chemisorption. The presence of a high average number of deuterium in the desorbing methane suggested a widespread dissociation of methane. The initial distribution of the deuterated products generally decreased in the sequence CD₄>CHD₃>CH₂D₂. The amount of chemisorbed methane during methane chemisorption increases with temperature and it follows the sequence of reducibility of the supported metals and particle size which, in turn, depends on the support and the alloy formed. CH_x (x=1) species prevailed on alumina supported catalysts, while on NaY supported metals, CH₂ species are dominant when small metal particles are stabilized inside the supercage. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

Cobalt ferrite for direct cracking of methane to produce hydrogen and carbon nanostructure: Effect of temperature and methane flow rate

Cobalt ferrite (CoFe₂O₄) was used as a catalyst for direct methane cracking. The reaction was accomplished in a fixed bed reactor at normal atmospheric pressure, while gas flow rate (20–50 mL/min) and reaction temperature (800–900 °C) were varied. The fresh CoFe₂O₄ morphology is sponge-like particle with inverse spinel structure as revealed from SEM and XRD results. The methane conversions and hydrogen formation rate were increased with reaction temperature, while catalyst stability and induction period decreased. Increases of gas flow rate > 20 mL/min led to a decrease the overall catalytic activity of CoFe₂O₄ for methane cracking. The XRD results of spent catalysts revealed that CoFe alloy was the active phase of methane cracking. TGA analysis showed that the largest amount of deposited carbon was 70.46 % at (20 mL/min, 900 °C), where it was 34.40 % at (50 mL/min, 800 °C). The deposited carbon has the shape of spherical carbon nanostructures and/or nano sprouts as observed with SEM. Raman data confirmed the graphitization type of the deposited carbon.     

Low temperature conversion of methane to syngas using lattice oxygen over NiO-MgO

The conversion of methane to syngas (H₂ and CO) is an important route to produce high value-added products. Oxidize methane into syngas in the absence of gaseous oxidants is an economical route. In this work, NiO-MgO composite is successfully synthesized via an impregnation method. At 764 K, methane is directly converted to syngas on the NiO-MgO without gaseous oxidants. A synergistic effect of NiO and MgO was observed, in which NiO induced lattice oxygen of MgO mobility to oxidize methane and suppressed the formation of intermediates for side reaction. As a result, NiO-MgO exhibited enhancement of catalytic activity with the H₂ production rate of 1241.0 µmol g^?1 min^?1, which was 3.4 times higher than that of pure MgO. This work provides a direct guidance to understand of methane oxidation via lattice oxygen under low temperature (< 773 K).     

Phase equilibrium measurements and the tuning behavior of new sII clathrate hydrates

We suggest two types of new amine-type sII formers: pyrrolidine and piperidine. These guest compounds fail to form clathrate hydrate structures with host water, but instead have to combine with light gaseous guest molecules (methane) for enclathration. First, two binary clathrate hydrates of (pyrrolidine + methane) and (piperidine + methane) were synthesized at various amine concentrations. ¹³C NMR and Raman analysis were done to identify the clathrate hydrate structure and guest distribution over sII-S and sII-L cages. XRD was also used to find the exact structure and corresponding cell parameters. At a dilute pyrrolidine concentration of less than 5.56 mol%, the tuning phenomenon is observed such that methane molecules surprisingly occupy sII-L cages. At the critical guest concentration of about 0.1 mol%, the cage occupancy ratio reaches the maximum of approximately 0.5. At very dilute guest concentration below 0.1 mol%, the methane molecules fail to occupy large cages on account of their rarefied distribution in the network. Direct-release experiments were performed to determine the actual guest compositions in the clathrate hydrate phases. Finally, we measured the clathrate hydrate phase equilibria of (pyrrolidine + methane) and (piperidine + methane).     

Heterogeneous Methane Conversion Processes Induced by a Pulse Microwave Discharge Near a Metal Surface

The degradation of methane in the batch mode by the action of a one-atmosphere pulse microwave discharge excited in a quartz reactor partially filled by a nickel gauze was studied. The fashion of gauze layout ensuring the sustainable excitation of discharge at an average power of 60–150 W and a pulse on/off ratio of 10 was described. Measurements of a pressure rise in the system simultaneously with the chromatographic analysis of the gas mixture sampled from the reactor showed that the product buildup kinetics were determined by the discharge character: when the discharge was maintained in the form of multiple sparks throughout the gauze-filled volume, the highest degradation rate was observed and all the products detected, including benzene, accumulated linearly with respect to the amount of methane decomposed. In the case of the formation of a local discharge zone in which the gauze was heated to a yellow heat, the benzene buildup followed a nonlinear law, its formation rate increased a few times with an increase in the degree of methane conversion. Although the total methane decomposition rate was lower in this case, conversion into benzene turned out to be a few times greater than in the previous experiment. For example, no more than 10–20% of methane decomposed within a discharge time of 10 min, whereas its conversion to benzene reached 10–15%.     

Solubility of methane in water and in a medium for the cultivation of methanotrophs bacteria

Solubility of methane in water and in an aqueous growth medium for the cultivation of methanotrophs bacteria was determined over the temperature range 293.15 to 323.15 K and at atmospheric pressure. The measurements were carried out in a Ben-Naim/Baer type apparatus with a precision of about ±0.3%. The experimental results were determined using accurate thermodynamic relations. The mole fractions of the dissolved gas at the gas partial pressure of 101.325 kPa, the Henry coefficients at the water vapour pressure and the Ostwald coefficients at infinite dilution were obtained. A comparison between the solubility of methane in water and those observed in fermentation medium over the temperature range of 298.15 to 308.15 K has shown that this gas is about ±2.3% more soluble in water.The temperature dependence of the mole fractions of methane was also determined using the Clarke-Glew-Weiss equation and the thermodynamic quantities, Gibbs energy, enthalpy and entropy changes, associated with the dissolution process were calculated.Furthermore, the experimental Henry coefficients for methane in water are compared with those calculated by the scaled particle theory. The estimated Henry coefficients are about ±4% lower than the experimental ones.     

Mesophilic Digestion Kinetics of Manure Slurry

Anaerobic digestion kinetics study of cow manure was performed at 35°C in bench-scale gas-lift digesters (3.78 l working volume) at eight different volatile solids (VS) loading rates in the range of 1.11–5.87 g l⁻¹ day⁻¹. The digesters produced methane at the rates of 0.44–1.18 l l⁻¹ day⁻¹, and the methane content of the biogas was found to increase with longer hydraulic retention time (HRT). Based on the experimental observations, the ultimate methane yield and the specific methane productivity were estimated to be 0.42 l CH₄ (g VS loaded)^–1 and 0.45 l CH₄ (g VS consumed)^–1, respectively. Total and dissolved chemical oxygen demand (COD) consumptions were calculated to be 59–17% and 78–43% at 24.4–4.6 days HRTs, respectively. Maximum concentration of volatile fatty acids in the effluent was observed as 0.7 g l^–1 at 4.6 days HRT, while it was below detection limit at HRTs longer than 11 days. The observed methane production rate did not compare well with the predictions of Chen and Hashimoto’s [1] and Hill’s [2] models using their recommended kinetic parameters. However, under the studied experimental conditions, the predictions of Chen and Hashimoto’s [1] model compared better to the observed data than that of Hill’s [2] model. The nonlinear regression analysis of the experimental data was performed using a derived methane production rate model, for a completely mixed anaerobic digester, involving Contois kinetics [3] with endogenous decay. The best fit values for the maximum specific growth rate (μ _m) and dimensionless kinetic parameter (K) were estimated as 0.43 day^–1 and 0.89, respectively. The experimental data were found to be within 95% confidence interval of the prediction of the derived methane production rate model with the sum of residual squared error as 0.02.     

Continuous Process for Obtaining Carbon Nanofibers

A continuous laboratory installation with a horizontal reactor for obtaining carbon nanofibers by catalytic pyrolysis of methane was developed and tested. The conversion of methane at 600°C was studied and the nanofiber output capacity of the continuous installation under the optimal conditions on a Ni-La₂O₃ catalyst was determined.     

Formation of acetaldehyde via photocarbonylation of methane with CO

Direct photocarbonylation of methane to give acetaldehyde occurred when a mixture of methane and CO dissolved in benzene was subjected to UV irradiation at λ < 290 nm. The reaction was accelerated by rhodium RhCl(CO)(PR₃)₂ complexes, where R = alkyl, Ph, or OPh.     

Determination of triazine herbicides with GC/MS under EI, methane CI and ammonia CI conditions detecting positive and negative ions

Summary Mass spectra of 26 triazine herbicides including a few metabolites were measured with a Finnigan 4000 applying electron impact and chemical ionization using methane and ammonia as reactant gases monitoring both positive and negative ions. Chemical ionization was studied to find out possible advantages of ammonia over other reactant gases. Detection limits with SIM were measured with methane and ammonia. For most of the triazines ammonia was found to be superior to methane with respect to detection sensitivity.Part of this paper was presented at the Seventh International Congress of Pesticide Chemistry, Hamburg, August 5–10, 1990     

Suppression of methane explosion in pipeline network by carbon dioxide-driven calcified montmorillonite powder

To minimize the damage and loss caused by methane explosions, and improve the safety of methane extraction, transportation, and utilization, we conducted a study on the explosion suppression performance of carbon dioxide-driven calcified montmorillonite powders with different particle sizes in a custom-designed experimental platform. The explosion suppression performance under different working conditions was evaluated according to the peak explosion overpressure, explosion power index, and the time required to reach the two outlets of the pipe network, and the explosion suppression mechanism was analyzed and discussed. The results indicated that calcified montmorillonite powder showed excellent explosion suppression performance. When the particle size of the powder was 21–32 μm and successively increased to 61–72 μm, both the explosion overpressure and explosion flame were effectively suppressed. In addition, when the particle size of the powder continued to increase to 81–92 μm, it had little enhanced suppression effect on the methane explosion. Therefore, considering the cost of use in practical applications, the calcified montmorillonite powder with a particle size of 61–72 μm was the optimal detonation inhibitor. Based on calcified montmorillonite, compound explosion suppression using carbon dioxide could serve as a theoretical reference and support for further improving the safety of methane extraction, transportation, and utilization.     

Carbon Nano-Flakes Produced by an Inductively Coupled Thermal Plasma System for Catalyst Applications

Carbon material was produced using an inductively coupled thermal plasma torch system of 35 kW and a conical shape reactor. The carbon nanopowders were obtained by plasma decomposition of methane at various flow rates and show a uniform microstructure throughout the reactor. The product has a crystalline graphitic structure, with a stacking of between 6 and 16 planes and a nano-flake morphology with particles dimensions of approximately 100 nm long, 50 nm wide and 5 nm thick. Nitrogen was also introduced in some synthesis experiments along with the methane precursor using flow rates of 0.1 and 0.2 slpm. The resulting product has the same structural properties and the nitrogen is incorporated into the graphitic structure through pyridinic type bonds.     

Tuning methane content in gas hydrates via thermodynamic modeling and molecular dynamics simulation

Storage and transportation of natural gas as gas hydrate (“gas-to-solids technology”) is a promising alternative to the established liquefied natural gas (LNG) or compressed natural gas (CNG) technologies. Gas hydrates offer a relatively high gas storage capacity and mild temperature and pressure conditions for formation. Simulations based on the van der Waals–Platteeuw model and molecular dynamics (MD) are employed in this study to relate the methane gas content/occupancy in different hydrate systems with the hydrate stability conditions including temperature, pressure, and secondary clathrate stabilizing guests. Methane is chosen as a model system for natural gas. It was found that the addition of about 1% propane suffices to increase the structure II (sII) methane hydrate stability without excessively compromising methane storage capacity in hydrate. When tetrahydrofuran (THF) is used as the stabilizing agent in sII hydrate at concentration between 1% and 3%, a reasonably high methane content in hydrate can be maintained (∼85–100, v/v) without dealing with pressures more than 5 MPa and close to room temperature.     

Activities of δ-Al2O3-supported bimetallic Pt?NiO and Co?NiO catalysts for methane autoreforming: Oxidation studies

The methane oxidation activities of Pt−NiO and Co−NiO bimetallic catalysts have been investigated as part of a larger research program on the autothermal reforming of methane (combined methane oxidation and steam reforming) in a fluidized bed reactor. Experiments at atmospheric pressure and 783–1023 K for both catalysts showed that the reaction was more selective towards H₂ production at CH₄∶O₂ ratios greater than unity. Light-off temperature increased with decreasing CH₄∶O₂ ratios, but increase in gas velocity (beyond minimum fluidization) increased the light-off temperature. Co−NiO was as promising as the more expensive Pt−NiO catalyst for the oxidation.     

Reaction of peroxide radicals with methane on the titanium oxide surface: Effects of the composition of the initial mixture

The reaction of TiO₂-adsorbed methyl peroxide radicals with methane, accompanied by transfer of the products into the gas phase at ∼20°C, was studied by the kinetic methods and EPR spectroscopy. In a definite range of methane concentrations, the reaction was accompanied by an increase in the total concentration of free radicals; i.e., these active species became not only regenerated, but also multiplied. The increase in the number of peroxide radicals was explained by the chain consumption of methane initiated by the reaction being studied.     

Highly effective methane conversion to aromatic hydrocarbons by means of microwave and rf-induced catalysis

Conversion of methane to higher hydrocarbon products, in particular, aromatic hydrocarbons has been achieved with good methane conversion and selectivity to aromatic products over heterogeneous catalysts using both high power pulsed microwave and rf energy. For example, under microwave irradiation > 85% conversion of methane and 60% selectivity to aromatics could be achieved. Cu, Ni, Fe and Al metallic materials are highly effective catalysts for the aromatization of methane via microwave heating; however, with a variety of supported catalysts the major products were C₂ hydrocarbons and the conversion of methane was low. The use of sponge, wire and net forms of these metal catalysts was found advantageous in effective methane conversion. The reactions are considered to be free radical in nature and to proceed through an intermediate stage involving formation of acetylene. The influence of catalyst nature and configuration, as well as the microwave and rf irradiation parameters on the reaction efficiency and product selectivity has been examined in both batch and continuous flow conditions.     

Non-oxidative conversion of methane into various petrochemical grades over tunable tri-metallic Fe-W-Mo/HZSM-5 catalyst systems

Most mono-metallic catalysts applied in non-oxidative conversion of methane exhibit low catalyst activity and limited selectivity towards useful petrochemicals. In this study, a series of thermally stable and tunable 5.4 wt% metal/support Fe-W-Mo/HZSM-5 catalyst systems were synthesized, characterized, and applied in non-oxidative conversion of methane in a custom-made stainless-steel reactor at various process conditions. Analysis of products from the reactor was done using Shimadzu 2014 gas chromatograph. Varying the amount of Fe, W, and Mo on HZSM-5 greatly influenced catalyst activity in terms of methane conversion and product distribution. When the quantities of Fe and W were increased to 2.25 wt% each and the quantity of molybdenum reduced to 0.9 wt% in the overall 5.4 wt% metal/ HZSM-5 catalyst, the resultant catalyst system became most active in methane conversion (17.4%) at 800 °C. Reducing the quantity of Fe and W each to 1.35 wt% and increasing Mo to 2.7 wt% in the overall 5.4 wt% catalyst, the resultant catalyst system became less selective towards C₂ hydrocarbons and coke, but highly selective towards xylene and benzene. Therefore, this study demonstrates that varying metal loading presents an opportunity to tune the 5.4 wt% binary Fe, W, and Mo on HZSM-5 to achieve desired methane conversion and product distribution.