Early Stage Of Carbonization Research Articles

Industrial byproduct Iron ore tailings as ecofriendly materials in the utilization of cementitious composites

Iron ore tailings (IOT)—industrial byproducts—are un-floating minerals in the flotation process of raw ore. Their large stockpiles and low utilization rates have become pressing challenges. This study provides a cleaner production solution for the potential usage of IOT as ecofriendly fine aggregates in the cementitious composite. The mechanical properties, carbonation resistance, and freeze–thaw (F–T) cycle resistance of iron ore tailings cementitious composites (IOTCC) with different IOT replacement ratios were evaluated rigorously. The pore-fluid distribution and pore-three-dimensional distribution of IOTCC were investigated using nuclear magnetic resonance (NMR) and industrial computer technology (CT). The micro-morphologies of the IOTCC was characterized using scanning electron microscopy (SEM). Finally, the environmental impact of IOTCC was assessed. Results indicated that, compared to ordinary cementitious composites, the IOTCC exhibited the most remarkable mechanical properties, carbonation resistance, and F–T resistance, and had the lowest porosity as well as a denser, more homogeneous interfacial transition zone (ITZ) between the fine aggregate and the matrix under a IOT replacement ratio of 25 %. This was further confirmed by SEM observations. The porosities of the IOTCC decreased faster in the early stage of carbonization than in the subsequent stage. Otherwise, the porosities of the IOTCC increased with increasing number of F–T cycles. The gradual increase in the number of larger pores and deteriorated pore morphology was the main factor affecting their F–T resistance. The life cycle assessment further indicated that the IOT could help reduce environmental overload. The successful application of IOT as ecofriendly materials will further promote the sustainable development of the construction industry.

Effects of olefinic compounds on the thermal transformation for FCC slurry oil: Evolution pattern and mechanism

FCC decant oil was always used as the raw material for the preparation of high-value-added carbonaceous materials. There is little disagreement that the free radical mechanism induces thermal polymerization reactions between reactant molecules and intermediate species, which leads to the formation of carbonaceous mesophase in the early stage of carbonization. Olefinic hydrocarbons were recently found to be widely distributed in FCC decant oil in our previous research, and these chemically active compounds usually possess weak π-bonds in molecules and thus potentially form free radicals easily, which may impact the carbonization performance dramatically. This research investigated the effects of olefinic compounds on the preparation of needle coke from FCC decant oil, as well as the corresponding mechanism in depth combined with the evolution pattern of the intermediate species during liquid carbonization. ESR analyses were adopted to evaluate the variation of the concentration of stable free radicals. Stable free radical concentration varied greatly in diverse polymerizing systems along with the carbonization process. Olefin showed a significant effect on the stable free radical concentration during carbonization. The stable free radical concentration of the polymerizing system derived from FCC decant oil was 3.32 × 1020 spins/g when the reaction time was 4 h. But with 3 wt% addition of 2-vinylnaphthalene and squalene in FCC decant oil, the stable free radical concentration increased to 2.14 × 1021 spins/g and 1.33 × 1021 spins/g, respectively, with the same reaction time. Meanwhile, the olefins conjugated with aromatic rings shown more obvious effect on the generation of free radicals. Olefinic compounds can lead to a high generation rate of free radicals and significantly high stable free radical concentration in the polymerizing system which then promote the formation of disordered carbon materials. Besides, plenty of fine particles appeared between mesophase spheres with the addition of olefinic hydrocarbons, and then impeded the coalescence between mesophase spheres. Effect mechanism for olefin on the development of carbonaceous mesophase was proposed accordingly. In sum, the content of olefinic compounds in raw materials should be limited for reaching the requirements of the synthesis of carbon materials with superior structures, in which the content of olefinic compounds should be less than 1 wt% at least based on the research in this paper.

Sequential pretreatments of an FCC slurry oil sample for preparation of feedstocks for high-value solid carbon materials

FCC slurry oil (SO) is an important and yield-rich by-product of the FCC process, which can be regarded as the raw material of high-value-added carbonaceous products due to its abundant concentration of aromatic components, but essential pretreatments and purifications for SO are required before carbonization to eliminate the adverse factors. Appropriate sequential pretreatments aimed at achieving the high-value utilization of SO have been developed, and two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC-TOFMS), Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H NMR, 13C NMR) were implemented for the systematical properties analyses of SO and its derivatives after sequential pretreatments. Polarized-light microscope, scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to evaluate the microstructures and microcrystal parameters of intermediate species and final products during carbonization. Through the varying degrees of sequential pretreatments, the comprehensive properties of feedstocks were improved gradually which further led to the diverse development of carbonaceous mesophase at the early stage of carbonization. Furthermore, ordinary or superior needle coke can be synthesized from the obtained oil samples during sequential pretreatments. The synthesized needle coke had suitable performance for the application in anode material of lithium-ion batteries.

Features of Early Stages of Carbonization of Polyimide Films Containing Carbon Nanoparticles

Features of Early Stages of Carbonization of Polyimide Films Containing Carbon Nanoparticles

Modified Effects of Additives to Petroleum Pitch on the Mesophase Development of the Carbonized Solid Products

Comparative studies in carbonization behaviors of petroleum pitch (SS70 pitch) and SS70-pitch–additive mixtures were conducted to develop a better understanding of the modified mechanisms of additives. The carbonization of solvent fractions in SS70 pitch was also investigated to reveal the relationships among solvent fractions and the additives. The characterization of resultant solid products by X-ray diffraction and scanning electron microscope analysis showed that samples obtained from co-carbonization of SS70–aromatic oil (P1) and SS70–aromatics enriched fractions of FCC slurry (P2) mixtures respectively had higher stacking layer numbers of mesogens and flatter morphology than those of specimens produced by carbonization of SS70 pitch and SS70–deasphalt oil (P3) mixtures. Adding additives P1 and P2 into SS70 pitch lowered not only the rates of carbonization but also the aromaticity and size of aromatic molecules in toluene insolubles formed in the early stage of carbonization, both jointly contributing to the formation of well-developed mesophase. The asphaltenes of SS70 pitch were prone to forming the poorly developed mesophase due to its high reactivity and also interfered with the carbonized performance of maltenes. Additives P1 and P2 played the “dominant partner effect” on mesophase development by providing physical fluidity of the reaction system and some chemical stability for asphaltenes via their dilution effect and H-transfer reactions.

Transmission electron microscopy investigation of microtwins and double positioning domains in (111) 3C-SiC in relation with the carbonization conditions

In this work, transmission electron microscopy is used to investigate the influence of the carbonization conditions on the formation of crystal defects in 3C-SiC layers deposited on (111) silicon. We focus on two kinds of defects; (1) the stacking faults and microtwins lying in the (1¯1¯1) planes, and (2) the double positioning domains. While the density of the stacking faults and microtwins is found independent on the carbonization conditions, the size of the double positioning domains is strongly influenced by the propane flow rate and can be related to the substrate sealing at the early stage of carbonization.

Hetero-Epitaxial Growth of 3C-SiC with Smooth Surface on Si(001) Using Acetylene Gas

The carbonization conditions (acetylene pressure and heating rate) to obtain close carbonized layer covered on Si(001) substrate without thermal pits is studied. Subsequent hetero-epitaxial 3C-SiC with smooth surface have been grown by low-pressure CVD. Single-crystalline carbonized layers could be grown at 1050°C by using suitable carbonization processes. The surfaces of Si were covered with single-crystalline 3C-SiC layers at an early stage of carbonization, preventing out-diffusion of Si atoms from Si substrates. 3C-SiC epi-film have RMS = 0.4nm but no single domain. The protrusion density of the film was an order of 1000 cm-2.

Analysis of Hydrocarbons and Sulfur Compounds in Two FCC Decant Oils and Their Carbonization Products

Two decant oils (DO A and DO B) which produce coke with different optical textures were quantitatively analyzed before and at several stages of carbonization. The differences observed in mesophase development and sulfur incorporation in the semicokes were related to differences in the molecular composition of the two decant oils, including hydrocarbons and sulfur compounds. The analysis of the GC-amenable fractions of the decant oils showed that DO A contains an abundance of pyrene and substituted pyrenes, while DO B is dominated by high concentrations of polymethylphenanthrenes. In general, DO B has a much higher proportion of alkyl-substituted PAHs and a higher concentration of n-alkanes. The presence of more reactive hydrocarbons in DO B is considered to be responsible for the inferior texture development and rapid incorporation of sulfur in the semicoke. Extensive methylation/demethylation reactions appear to occur during the early stages of carbonization; the role of these reactions in mesophase development and sulfur incorporation is addressed further in the companion papers (Energy Fuels 1997, 11, 631, 637).

Carbonization and graphitization behavior of decacyclene

Decacyclene was carbonized in a glass tube or a molten salt at various temperatures and the products were analyzed by means of Raman spectroscopy, X-ray diffractometry, ESR and FT-IR spectroscopies in order to investigate the influence of contained pentagonal aromatic rings on the change of carbon structures with heat-treatment. It was found that the presence of the pentagonal rings disturbs the growth of planar aromatic layers at the early stage of carbonization and that the development of the layer stacking to c-axis with further heat-treatment is influenced predominantly by the phase during the carbonization stage rather than by the pentagonal rings.

96/05997 The role of carbon black/coal-tar pitch interactions in the early stage of carbonization

96/05997 The role of carbon black/coal-tar pitch interactions in the early stage of carbonization

乾留初期におけるコークス炉内炉幅方向水分移動機構

In order to clarify the moisture transfer mechanism, moisture distribution across the oven width at the early stage of carbonization has been investigated using the test coke oven with the upper heating wall. There is a region having a maximum moisture content below 100°C because of moisture condensation. Subsequently, as temperature is elevated close to 100°C, remarkable moisture vaporization has taken place so that the moisture in coal decreases rapidly. However, there remains a little moisture in coal beyond 100°C.Two dimensional coke oven mathematical model was hence updated by introducing this moisture transfer mechanism.

The role of carbon black/coal-tar pitch interactions in the early stage of carbonization

This study was undertaken to gain further insight into the types of interaction between pitch and carbon black (CB) occurring during thermal treatment in the initial stages of carbonization, and the effects on subsequent coke structure. A commercial coal-tar pitch was blended with CB and then thermally treated at temperatures between 400–450 °C, for 5 hours—except for 430 °C, where the time of treatment was for 10 hours. The same thermal treatments were applied in the absence of CB to test the effects of temperature alone. Parent and treated pitches were characterized by elemental analysis, optical microscopy, thermomechanical analysis (TMA) and sequential solvent extraction. Additionally, some of the fractions were characterized by FTIR, GC and 1H-NMR. Cokes obtained at 900 °C were characterized by optical microscopy in terms of their porosity and optical texture. Results show that the type of CB/pitch interactions are temperature dependent, these interactions being more significant at lower temperatures (below 425 °C). Hydrogenation and polymerization reactions have successively occurred along the range of temperatures used. CB produced an increase of pitch carbon yield without affecting pitch fluidity at the lower temperatures. The effect on the reduction of coke porosity was pronounced at the initial stages of the treatment. Coke optical texture was also affected by the presence of CB showing smaller sizes.

Carbonization behavior of petroleum pitch— In situ high-temperature 13C-NMR measurements

The carbonization behavior of petroleum pitch have been investigated by in situ high-temperature 13C-NMR at 390°C. The changes in the chemical structure, molecular mobility, and mesophase formation process of the pitch have been quantitatively monitored simultaneously using in situ high-temperature 13C-NMR. The initial stage of mesophase formation could be monitored at around the content level of 2%. The changes of aliphatic structure were clearly observed using NMR spectra of long-side-chain carbons and α-methyl carbons. The early stage of carbonization was divided into several steps and characterized. The changes in molecular mobility and in chemical structure were closely related to the mesophase transformation.

Heteroepitaxial growth of single crystalline 3C-SiC on Si substrates by gas source molecular beam epitaxy

Heteroepitaxial growth of 3C-SiC on Si substrates by gas source molecular beam epitaxy was investigated. Both Si(001) and Si(111) surfaces were carbonized using a C2H2 gas molecular beam to convert the surface region into single crystalline 3C-SiC prior to crystal growth. The supply of C2H2 was started at 400 °C, and the substrate temperature was raised at a rate of 7 °C/min. An amorphous-like layer was observed at 870 °C. Raising the temperature at a rate of 2 °C/min from 870 to 970 °C, a single crystalline 3C-SiC layer was obtained. In the case of Si(001), increase of C2H2 supply resulted in improvement of crystallinity, because of a thin (∼50 Å) 3C-SiC layer formed at an early stage of carbonization, which prevented outdiffusion of Si atoms. The thickness of the 3C-SiC layer did not increase for prolonged time of carbonization after formation of the thin layer. In the case of Si(111), the increase of C2H2 supply resulted in a thicker layer of 3C-SiC with a rough surface, because the channels of Si outdiffusion were not sealed off. Epitaxial growth of 3C-SiC was carried out using alternate supply of Si2H6 and C2H2 gas molecular beams on 3C-SiC layers obtained by carbonization under optimum conditions. Single crystalline 3C-SiC layers were obtained at 1075 °C, both on (001) and (111) surfaces.

Characterization of pitch/oxygen plasma treated carbon black systems by means of high temperature ESR

The change in extent of generation of radicals during the early stage of carbonization in A240 pitch with addition of carbon black treated by oxygen plasma was investigated by means of high temperature ESR. The increase of radical concentration of pitch with addition of plasma treated carbon black is explained by the reduction in transferable hydrogen to stabilize the free radicals created in pitch. This is caused by the abstraction of transferable hydrogen by the oxygenated functional groups on the surface of plasma treated carbon black.

Formation of highly oriented graphite from poly(acrylonitrile) prepared between the lamellae of montmorillonite

An attempt was made to prepare a carbon sample having a highly oriented structure from poly(acrylonitrile) by using a two-dimensional opening between the lamellae of montmorillonite as the field of carbonization. The carbon prepared t 700 /degrees/C was liberated from montmorillonite and then it was subjected to heat treatment at various temperatures up to 2800/degrees/C. The characteristics of the resulting carbon were determined by microscopic, diffractometric, spectroscopic, and magnetoresistance methods. The graphitizability of the carbon is very high, and the carbon heat-treated at 2800/degrees/C has almost the same characteristics as the ideal graphite crystal. It consists of graphitic films with L/sub c/ value of about 40 nm and very large L/sub a/ value of more than 1 ..mu..m in many cases. The reason for such a high graphitizability was ascribed to the formation of a two-dimensional carbon precursor in the early stages of carbonization.

Carbonization behaviour of pitch in the presence of inert material

The influence of silica gel (< 45 μm) as an inert additive on the carbonization reactions of A240 pitch was investigated by optical microscopy, measurements of transferable hydrogen, high-temperature e.s.r. and high-temperature 1H n.m.r. Additions of silica gel have the effect of reducing the size of the optical texture of mesophase which appears in the early stages of carbonization. The higher the concentration of silica gel, the smaller is the amount of transferable hydrogen. The spin concentration of pitch increases with increasing silica gel content. Measured values of ΔH 1 2 , using high-temperature 1H n.m.r., suggest that the molecular motions in the pitch become restricted on addition of silica gel. The effect of silica gel on the physical properties and chemical reactivity of carbonizing pitch is discussed.

低石炭化度炭の水素加圧炭化

Carbonization of low rank coal under high hydrogen pressure was studied. Our interest is to clarify the effects of hydrogen pressure and soaking time on the resultant cokes. The longer the: soaking time at 748 K under 5 MPa, the more extensive the development of anisotropic texture and the greater the size of optical texture. The effect of hydrogen pressure on the resultant cokes was found to be optimal at 5 MPa. However, no significant change in the anisotropic texture of the resultant cokes was observed when the hydrogen pressure was increased from 5 to 13 MPa.The effect of partial pressures of hydrogen on the carbonization reaction was also examined. When the partial pressure of hydrogen decreases, the extent of the anisotropic texture is reduced.The carbonization of Yubarishinko coaking coal was also carried out under high hydrogen pressure. The optical texture of resultant cokes for a hydrogen pressure of 8 MPa shows flow anisotropy.Moreover, the effect of selenium oxide catalyst on pressure carbonization was also studied. SeO2, which is especially effective in the early stage of carbonization, enhanced the mesophase development for Taiheiyo coal.

Heavy petroleum products: Microtexture and ability to graphitize

Various asphalts extracted from crude oils by light n-alcanes were studied by elemental analysis, conventional transmission microscopy and X-ray diffraction. Like most carbonaceous materials, asphalts contain planar aromatic structures (4–12 rings in dia.) single or piled up by twos or threes (basic structural units). These units are distributed at random in the bulk and linked by non-aromatic groups. Heat-treatment was carried out under inert gas flow from room temperature to 3000°C. In the early stages of carbonization, the structural units acquire a local parallel orientation (just before the end of the tar release). The extent of the molecular orientation depends only on the opposing influence of the hydrogens and of heteroatoms such as oxygen, sulfur and nitrogen. The extent of orientation increases drastically from less than 50 Å to a few μm as the percentage of cross-linking agents (oxygen and sulfur) and of nitrogen decreases. At the same time the ability to graphitize increases progressively. All kinds of intermediates between non-graphitizing and graphitizing carbons are found after heat-treatment.

High temperature 1H-NMR study of coal and pitch at the early stages of carbonization

The temperature dependence of the 1H-NMR absorption in coals and pitches have been obtained using a pulsed Fourier transform NMR spectrometer with a high temperature probe. The samples as received were heated in the high temperature probe and NMR spectra were obtained simultaneously. With increasing temperature, the value of the line width at half-height (ΔH 1/2) of a brown coal decreases and then increases rapidly. On the other hand, tar pitch and the γ component of a coal indicate that the values of ΔH 1/2 remain small over a wide temperature range. It is found that there is an excellent relation between the temperature dependence of ΔH 1/2 and the optical texture of the mesophase.