Hydrogen production by catalytic dehydrogenation of methylcyclohexane over Pt catalysts supported on pyrolytic waste tire char

Pyrolytic waste tire char was modified to be used as support and a series of catalysts supported with 0.1-1.0 wt% Pt were prepared by conventional wetness impregnation method. TEM images show that the Pt nanoparticles are well-dispersed in any microregions in the sample view on the TEM grid. The results of methylcyclohexane dehydrogenation reaction show the Pt loadings and the reaction temperature have a significant impact on the catalytic activity.     

Ozonation of Pyrolytic Aqueous Phase: Changes in the Content of Phenolic Compounds and Color

Ozonation on the phenols present in pyrolytic aqueous phases attained from biomass thermochemical conversion was evaluated. During ozonation, the dark color of original samples was found to decrease as a function of ozonation time. The oxidation kinetics of phenols was quantified by a method based on the color changes of samples. The oxidation profiles showed different behaviors and in some cases the phenols presented a positive correlation with the relative R color parameter, except eugenol, syringol, and vanillin which were markedly different. Finally, the color changes observed seem to be associated with the changes in the overall content of phenols and with the change in the molecular weight of the heavy fractions that include lignin oligomers.     

Chemical vapor deposition of pyrolytic boron nitride ceramics from single source precursor

Pyrolytic boron nitride ceramics were prepared on graphite substrates from borazine as the single source precursor by hot-wall chemical vapor deposition in deposition temperature range from 1300 °C to 1600 °C with a total pressure of 200 Pa. The chemical composition and the effect of deposition temperature on the morphology, phase, and structure of the pyrolytic boron nitride were investigated. A high purity product with stoichiometric B/N ratio is obtained. The deposition surface of the product exhibited a pebble-like structure, and the fracture surface showed an apparent laminar structure having a preferential (002) orientation parallel to the surface of the substrate at temperatures above 1400 °C. The product contained some turbostratic and amorphous boron nitride as evidenced from XRD and FTIR examinations. With the increase of deposition temperature, the crystallinity of the pyrolytic boron nitride increased with the turbostratic and amorphous boron nitride turned into hexagonal structure, and the crystallinity of the product became higher.     

Thermal management of a proton exchange membrane fuel cell stack with pyrolytic graphite sheets and fans combined

This work characterizes the thermal management of a proton exchange membrane fuel cell (PEMFC) stack with combined passive and active cooling. A 10-cell PEMFC stack with an active area of 100 cm² for each cell is constructed. Six thermally conductive 0.1-mm-thick Pyrolytic Graphite Sheets (PGSs) are cut into the shape of flow channels and bound to the six central cathode gas channel plates. These PGSs, which are lightweight and have high thermal conductivity, function as heat spreaders and fins and provide passive cooling in the fuel cell stack, along with two small fans for forced convection. Three other cooling configurations with differently sized fans are also tested for comparisons (without PGSs). Although the maximum power generated by the stack with the configuration combining PGSs and fans was 183 W, not the highest among all configurations, it significantly reduced the volume, weight, and cooling power of the thermal management system. Net power, specific power, volumetric power density, and back work ratio of this novel thermal management method are 179 W, 18.54 W kg⁻¹, 38.9 kW m⁻³, and 2.1%, respectively, which are superior to those of the other three cooling configurations with fans.     

Magnetic carbon: Explicit evidence of ferromagnetism induced by proton irradiation

The recently found ferromagnetic signals in pure graphite and in polymerised fullerenes are received mainly with scepticism by most of the scientific community. Actually, before those results were published, there were already several reports claiming an unusually large magnetization in pyrolytic carbon and oxidised fullerenes, without attracting the attention of the community. This scepticism may be well founded since not always a careful and systematic impurity study was provided to quantify the influence of ferromagnetic impurities. In this article and after a brief review of the existing data on magnetic carbon, we present and discuss recently obtained results on the ferromagnetism (or ferrimagnetism) induced by proton irradiation on pure pyrolytic graphite, which strengthen the importance of hydrogen in the formation of the magnetic ordering. The overall results indicate that room-temperature ferromagnetism in carbon-based structures containing only p- and s-electrons is a reality.     

Effects of needle-punched felt structure on the mechanical properties of carbon/carbon composites

The effects of needle-punched felt structure, including mass ratio of non-woven cloth to short-cut fiber web, PAN-based carbon fiber types of non-woven cloth and thickness of unit (one layer of non-woven cloth and short-cut web was named as a unit), on the flexural properties of C/C composites from pressure gradient CVI are discussed. Results show that flexural strength and modulus increase when mass ratio of non-woven cloth to short-cut fiber web changes from 7:3 to 6:4 and that PAN-based carbon fiber types of non-woven cloth strongly influence the flexural properties. The strength of C/C composites is not linear with the strength of non-woven cloth carbon fiber because of the important interface between carbon fiber and matrix carbon. It is suitable to choose T300 or T700 as reinforcing carbon fiber for C/C composites in the present study. An optimum unit number per cm of the needle-punched felts for higher flexural properties exists.     

Influence of the surface area/volume ratio on the chemistry of carbon deposition from methane

The chemistry of carbon deposition from methane as a function of methane pressure was studied at a temperature of 1100 °C and surface area/volume ratios of 0.8 and 3.2 mm⁻¹ by analysis of both gaseous and condensing, i.e. aromatic reaction products. Conversion of methane as well as the yields of the hydrocarbons formed increase with increasing pressure. The surface area/volume ratio has a significant influence on the formation of aromatic hydrocarbons showing much higher yields at the lower ratio. This result, expected from preceding studies of deposition rates, confirms that a change of this ratio leads to a change of the deposition chemistry of carbon.     

Analysis of gas phase compounds in chemical vapor deposition of carbon from light hydrocarbons

Product distributions in the pyrolysis of ethylene, acetylene, and propylene are studied to obtain an experimental database for a detailed kinetic modeling of gas phase reactions in chemical vapor deposition of carbon from these light hydrocarbons. Experiments were performed with a vertical flow reactor at 900 °C and pressures from 2 to 15 kPa. Gas phase components were analyzed by both on-line and off-line gas chromatography. More than 40 compounds from hydrogen to coronene were identified and quantitatively determined as a function of the residence time varied up to 1.6 s. Product recoveries were generally more than 90%. Analysis of the kinetics of the conversion of the hydrocarbons resulted in global reaction orders of 1.2 (ethylene), 2.7 (acetylene), and 1.5 (propylene). First order dehydrogenation reactions and third order trimerization reactions leading to benzene are decisive reactions for ethylene and acetylene, respectively. Conversion of propylene should also be based on two simultaneous reactions, a first order dissociation reaction, and second order reactions such as bimolecular reaction of propylene resulting an allyl and a propyl radical. These insights should be useful to develop a reaction mechanism based on elementary reactions in forthcoming studies.