Thermodynamic Analysis of the Effect of Green Hydrogen Addition to a Fuel Mixture on the Steam Methane Reforming Process

Steam methane (CH4–H2O) reforming in the presence of a catalyst, usually nickel, is the most common technology for generating synthesis gas as a feedstock in chemical synthesis and a source of pure H2 and CO. What is essential from the perspective of further gas use is the parameter describing a ratio of equilibrium concentration of hydrogen to carbon monoxide H/C=xH2/xCO. The parameter is determined by operating temperature and the initial ratio of steam concentration to methane SC= xH2O0/xCH40. In this paper, the author presents a thermodynamic analysis of the effect of green hydrogen addition to a fuel mixture on the steam methane reforming process of gaseous phase (CH4/H2)–H2O. The thermodynamic analysis of conversion of hydrogen-enriched methane (CH4/H2)–H2O has been performed using parametric equation formalism, allowing for determining the equilibrium composition of the process in progress. A thermodynamic condition of carbon precipitation in methane reforming (CH4/H2) with the gaseous phase of H2O has been interpreted. The ranges of substrate concentrations creating carbon deposition for temperature T = 1000 K have been determined, based on the technologies used. The results obtained can serve as a model basis for describing the properties of steam reforming of methane and hydrogen mixture (CH4/H2)–H2O.

Promoting Role of Amorphous Carbon and Carbon Nanotubes Growth Modes of Methane Decomposition in One-Pot Catalytic Approach

We report the simultaneous production of hydrogen fuel and carbon nanotubes (CNTs) via methane dehydrogenation catalyzed with Ni/SBA-15. Most Ni nanoparticles (NPs) with size between 10 and 30 nm were highly dispersed on SBA-15 and most of them had a strong interaction with the support. At temperatures ranging from 500 to 800 °C, methane could be decomposed to release hydrogen with 100% selectivity at conversion between 51 and 65%. There was no CO or CO2 detectable in the reaction fluent. In the initial stage of the reaction, amorphous carbon and dehydrogenated methane species adsorbed on the Ni NPs promoted the CH4 decomposition. The amorphous carbon atoms were then transformed into carbon nanotubes which chiefly consisted of a multiwall structure and grew towards different orientations via a tip-growth or a base-growth modes, controlled by the interaction strength between the Ni NPs and the SBA-15 support. Reaction temperature affected not only methane conversion, but also the diffusion of carbon atoms on/in the Ni NPs and their precipitation at the interfaces. At higher temperature, bamboo-like CNTs or onion-like metal-encapsulated carbons were formed, mainly due to the rate of carbon atom formation greater than that of carbon precipitation for CNTs construction. The CNTs formation mechanisms are discussed and their growth modes under different conditions are proposed.

Effects of carbon nano-additives on characteristics of TiC ceramics prepared by field-assisted sintering

Five carbonaceous nano-additives (graphite, graphene, carbon black, carbon nanotubes, and diamond) had different impacts on the sinterability, microstructural evolution, and properties of titanium carbide. In this research, the sintering by spark plasma was employed to produce the monolithic TiC and carbon-doped ceramics under the sintering parameters of 1900 ºC, 10 min, 40 MPa. The carbon black additive had the best performance in densifying the TiC, thanks to its fine particle size, as well as its high chemical reactivity with TiO2 surface oxide. By contrast, the incorporation of nano-diamonds resulted in a considerable decline in the relative density of TiC owing to the graphitization phenomenon, together with the gas production at high temperatures. Although carbon precipitation from the TiC matrix occurred in all samples, some of the added carbonaceous phases promoted this phenomenon, while the others hindered it to some extent. Amongst the introduced additives, carbon black had the most contribution to grain refining, so that a roughly halved average grain size was attained in comparison with the undoped specimen. The highest values of hardness (3233 HV0.1 kg), thermal conductivity (25.1 W/mK), and flexural strength (658 MPa) secured for the ceramic incorporated by 5 wt% nano carbon black.

Bioclimatic Regularities of Change in the Density of Organic Carbon of the Steppe Soil in Different Regions of the World

The bioclimatic regularities between the average annual precipitation, average annual temperatures and the density of organic carbon in the soil layer of 0-30 cm of the steppes in the regions of the world are given. They are distinguished by a high certainty of quantization by asymmetric wave equations. It turned out that, due to the vibrational adaptation of organic carbon, precipitation and temperature are dependent on each other. For example, the model of the influence of precipitation on temperature includes the first term in the form of Laplace's law (in mathematics), Mandelbrot's law (in physics), Zipf-Perl (in biology), and Pareto (in econometrics). The second term is the biotechnical law of the author of the article, which gives the maximum change in the indicator. Both components form a trend that makes it possible to divide the precipitation interval into three stages: 1) with an increase in precipitation from 0 to 60 mm, the temperature decreases according to Mandelbrot's law from 23.25 to 0.5 0С; 2) from 60 to 2100 mm, the temperature rises to 24 ° C; 3) with a further increase in precipitation over 2100 mm, a slow decrease in temperature occurs. The third term is an asymmetric wavelet with a constant half-period of 367.8 mm. A positive sign shows that in the steppes there is a positive oscillatory adaptation of temperature to changes in precipitation. In the interval of precipitation 0-350 mm, an oscillatory decrease in temperature occurs. It turns out that the first oscillation at 0 mm precipitation begins with a very high temperature gradient of thermal energy. The first interval includes Mongolia and Inner Mongolia. In the second interval of 350-750 mm, an oscillatory increase in temperature occurs. Then, in the third interval 750-1050 mm, the temperature drops again. The second oscillation with a correlation coefficient of 0.9685 has clear precipitation boundaries in the range of 200-2000 mm. Due to the negative sign, the fluctuation is a crisis, inhibiting the rise in temperature. And the third fluctuation has a positive effect on the temperature. The mechanism of oscillatory adaptation in the steppe soil is so perfect that it changes for itself the conditions of the place where the grass grows. An amplitude-frequency analysis of each oscillation will make it possible to determine the specific particular effects of precipitation and temperature on each other and on the density of organic carbon. It was found that two-factor modeling of the change in the soil organic carbon density makes it possible to achieve an identification error even less than the absolute measurement error.

Structural and Electrochemical Analysis of Decarburized Graphene Electrodes for Supercapacitor Applications

In this research, a facile and cost-effective method of graphene synthesis by the modified carburization process and its applications for supercapacitor electrodes is reported. In this simple approach, carbon was diffused into nickel foam and naturally cooled to obtain carbon precipitation for the in situ growth of graphene by decarburization. Phase-structure and surface-morphology analysis revealed the presence of a highly reduced structure of the graphene layer. Furthermore, the large-intensity D, substantial G, and 2D bands in Raman spectra were attributed to disordered multilayer graphene. The three-electrode systems were used to measure electrochemical efficiency. The electrode sample exhibited enhanced current density of 0.6 A/g, electrode energy of 1.0008 Wh/kg, and power density of 180 W/kg, showing significant electrochemical performance for supercapacitor electrode applications.