Morphology Of Carbon Deposits Research Articles

Pyrolysis and coking behavior of CxHy with different structures in microchannel continuous flow reactor

Coking with carbon deposition in hydrocarbon fuel (CxHy) pyrolysis at high temperature is a serious problem to be considered. In this work, single component CxHy with different structures was used as the probe of the carbon deposition. Thirteen simple and representative of alkanes, cycloalkanes, aromatics and O-containing CxHy were selected as the model compounds to decompose and coking in microchannel continuous flow reactor under the same conditions. The distributions of gas, liquid and solid phase products formed by CxHy pyrolysis were characterized by GC, GC-MS, SEM and TPO-IR respectively. The results demonstrate that the molecular structure of CxHy has a great influence on pyrolysis and coking behavior. For all alkanes, CH4, C2H4, C3H6 and C4H8 are the most abundant in gaseous products, and their total content exceeds 70 %. For cycloalkanes, monocyclic cyclohexane pyrolysis tends to produce C2H4, C4H8 and 1,3-C4H6, while bicyclic decahydronaphthalene pyrolysis tends to produce CH4, C2H4 and C3H6. For aromatics, CH4 and C2H4 are the main products in the pyrolysis gas phase of benzene, toluene and ethylbenzene. Interestingly, in the liquid phase of the pyrolysis of O-containing CxHy (ethanol, acetone and tetrahydrofuran), most of the products are oxygenated compounds and no aromatics. SEM and TPO-IR revealed that at least three carbon species were formed by cracking of CxHy molecules with different structures, including amorphous, filamentous and granular carbon. However, due to the great and complex influence of CxHy molecular structure on the micro morphology of carbon deposition, it is difficult to classify all carbon species at present, which needs further experiments and researches.

Characteristic, Structure, and Morphology of Carbon Deposit From Biodiesel Blend

Characteristic, Structure, and Morphology of Carbon Deposit From Biodiesel Blend

Highly efficient conversion of methane using microsecond and nanosecond pulsed spark discharges

Plasma-assisted methane (CH4) activation is a promising way for a hydrogen (H2) production. In this paper, we describe our studies of microsecond and nanosecond pulsed spark discharge plasmas use in a CH4 pyrolysis for a H2 production. The dependence of CH4 conversion and gas discharge product composition on discharge power, discharge gap length and gas flow rate are studied. The electrical and optical characteristics of the discharges are also studied to reveal discharge plasma parameters and chemical reactions leading to CH4 pyrolysis. Experimental results show that H2 and acetylene (C2H2) are the major gas discharge products accompanied by trace gas discharge products, such as ethane (C2H6), ethylene (C2H4) and carbon. The highest CH4 conversion and H2 yield, 91.2% and 38.4%, respectively, are achieved with an energy conversion efficiency of 44.3% using the microsecond pulsed spark discharge at a gap length 6 mm and a gas flow rate 50 mL/min. The carbon balance under the studied operating parameters varies from 66.7% to 92.8%. The morphology of carbon deposition is presented by two crystal forms identified by SEM and Raman spectral analyses. Finally, comparatively low electron temperature and high vibrational molecular temperature are observed in our experiments, which suggests that V-V transition for CH4 excitation process and V-T transition for CH4 heating process play important roles in CH4 pyrolysis sustained by the pulsed spark discharge.

Probing the structural organisation of sp2 carbons obtained by the Boudouard reaction using in situ Raman scattering in reducing conditions

The catalytic decomposition of carbon monoxide from a mixture of CO and H2 in the presence of iron or iron oxides has been the subject of many studies since the end of 1950s. The Boudouard reaction (2CO→CO2+C) produces solid carbon deposition in many high temperature industrial processes in which carbon monoxide is a reactant. The aim of this study was to determine whether the oxidation degree of iron has a significant effect in the quantity and in the morphology of carbon deposit. Original in situ Raman device using controlled temperature and gas mixture was developed to explore the evolution of the morphology of the carbon formation during Boudouard’s reaction. The results show two types of carbon morphologies (well-structurally organized sp2 carbons in the form of shells and nano-fibers) depending on the content of H2 in the gas mixture. The abundant production of carbon nano-fibers could be responsible for the destruction of refractory materials operating in CO+H2 atmospheres. This study is of outstanding importance to provide helpful observation and basic information on the involved mechanisms for solving this industrial problem.

Влияние состава газовой среды при проведении каталитического пиролиза метана на морфологию углеродных отложений

Влияние состава газовой среды при проведении каталитического пиролиза метана на морфологию углеродных отложений

CARBON PRECURSOR DEPENDENCE OF CARBON NANOFIBERS SYNTHESIZED BY CATALYST-FREE ULTRASONIC SPRAY-PYROLYSIS METHOD

In this paper, we report the growth of carbon nanofibers (CNFs) by catalyst-free ultrasonic spray-pyrolysis of methanol, ethanol and 2-propanol. We found that the morphology of carbon deposition on the substrate strongly depended on the position of the substrate in the reaction tube and the carbon source species. When ethanol and 2-propanol were used as the carbon source, a slightly hollow structure CNFs were formed downstream in the reaction tube, whereas when the carbon source was methanol, an amorphous structure CNFs were formed at the center of the reaction tube. We consider the difference in CNFs growth between the alcohol types is presence of alkyl groups in alcohol.

Carbon deposition on Ni/ZrO2–CeO2 catalyst during steam reforming of acetic acid

Steam reforming of acetic acid, one model compounds of bio-oil, was studied on the Ni/ZrO2–CeO2 catalysts which were prepared by the impregnation method. The results showed that high acetic acid conversion and hydrogen yield were obtained in the temperature range of 650–750 °C when H2O/HAC ratio was 3. Nevertheless, the catalyst deactivation was caused by carbon deposition eventually with time-on-stream. In order to discuss the behavior of the carbon deposition on the Ni/ZrO2–CeO2 catalyst during steam reforming of bio-oil, the structure and morphology of carbon deposition were investigated by BET, XRD, TG/DTA, TPR, SEM and EDX techniques. All the experimental results showed acetone and CO were the important carbon precursors of acetic acid reforming and the graphitic-like carbon was the main type of carbon deposition on the surface of the deactivated 12%Ni/CeO2–ZrO2 catalyst.

Effect of hydrocarbons precursors on the formation of carbon nanotubes in chemical vapor deposition

High-temperature decomposition of hydrocarbons may lead to the formation of carbon deposits. However in our present studies, we found that the morphology of carbon deposits over MgO supported Fe catalyst during chemical vapor deposition (CVD) process was closely related to the thermodynamic properties and chemical structures of hydrocarbon precursors. Six kinds of hydrocarbons (methane, hexane, cyclohexane, benzene, naphthalene and anthracene) were used as carbon precursors in this study. Methane which has a pretty simple composition and is more chemically stable was favorable for the formation of high-purity single walled carbon nanotubes (SWNTs). For high-molecular weight hydrocarbons, it was found that the chemical structures rather than thermodynamic properties of carbon precursors would play an important role in nanotube formation. Specifically, the CVD processes of aromatic molecules such as benzene, naphthalene and anthracene inclined to the growth of SWNTs. While the cases of aliphatic and cyclic hydrocarbon molecules seemed a little more complicated. Based on different pyrolytic behaviors of carbon precursors and formation mechanism of SWNTs and multi-walled carbon nanotubes (MWNTs), a possible explanation of the difference in CVD products was also proposed.

The thermal properties of carbon-silica adsorbents (carbosils) prepared by methylene chloride pyrolysis

The thermal properties of complex carbon-silica adsorbents (carbosils) were investigated using differential thermal analysis. The adsorbents were prepared by pyrolysis of methylene chloride. Pyrolysis reaction on silica surface was carried out at different temperatures (400–700 °C) and at different pressures of CH2Cl2 vapours. Thermal analysis was carried out in air atmosphere. The following parameters characterizing the properties of the adsorbents were determined: carbon content, specific surface area, carbon layer thickness, pore volume, mean pore radius, differential of heats of adsorption ofn-hexane and benzene, and micrographs. The correlation between topography and morphology of carbon deposits (dependent on the parameters of the pyrolysis process) and the courses of DTA and TG curves corresponding to individual carbosils have been determined.

Microscopic investigations of the surface of carbon-silica adsorbents with consideration of heterogeneity of carbon layer studied by transmission electron microscopy, and its correlation with adsorption data

Transmission electron microscopy has been used to study the morphology and topography of carbon deposits (films) on the surface of silica gels. Complex carbon-silica adsorbents were obtained by pyrolysis of n-heptyl alcohol, benzyl alcohol and α-phenylethyl alcohol on the surface of silica gel and also by pyrolysis of other compounds (i.e. acenaphthene, p-chlorotoluene) and by pyrolysis of mixtures of the above compounds. We have found distinct correlations between the morphology of carbon deposit (microscopic image of the carbon layer) and the composition of the carbonized matter, and surface properties of the composed adsorbent, i.e. heat of adsorption, the adsorption shape of the energy distribution function, selectivity in chromatography and the like. The adsorption shape of the potential distribution function also correlates with the replicas of the complex adsorbent surface.