Average Stacking Height Research Articles

Comparative study on devolatilization behavior, microstructural evolution and resultant properties during calcination of petroleum coke with distinct mesophase texture

Petroleum coke as an affordable and abundant material represents significant opportunities for using in both traditional and emerging fields, whereas a lack of understanding transformation chemistry during essential calcination hampers its development. Herein, relevance among devolatilization behavior, microstructural evolution and resultant properties during calcination of green coke were investigated. Calcination is found to be roughly distinguished into three regimes according to average stacking height (Lc) and average interlayer spacing (d002) obtained by analysis of WAXS as well as appearance of D2 peak in Raman spectra. The first regime below 800ºC shows starting transformation from semi-coke to coke, mainly induced by volatilization of low-molecular-weight components, dealkylation and intramolecular dehydro-condensation. Simultaneously, progressive healing of in-plane defects, gradual increase of mesogen-layer size and decrease of interlayer spacing was accompanied, causing significant growth of real density. Thereafter, intermolecular dehydro-polymerization and heteroatoms elimination become dominant in 800–1400 °C, leading to removal of interstitial defects. Consequently, larger stacking height and more homogeneous stacking of well-developed hexagonal carbon layers are formed, further promoting microstrength and electric-conductivity of resultant coke. Next, graphite-like microcrystallites would be rearranged into polyhedral configuration in 1400–1600ºC, indicating a transition from coke to semi-graphite. Notably, the mode of arrangement of mesophase units in the green coke would largely predetermine the coke microstructure. This work could give a guidance for regulating structural evolution via selection of green coke and calcination condition according to application.

Effect of supercritical CO2 transient high-pressure fracturing on bituminous coal microstructure

Carbon dioxide phase change fracturing is an effective permeability enhancement technology, and its influence mechanism on the coal microstructure remains to be further investigated. To explore the impact of CO2 fracturing on the coal chemical structure, the self-developed transient high-pressure fracturing of CO2 test platform was independently developed. Based on X-ray photoelectron spectrometer (XPS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), the elemental morphology, functional group and crystal structure of the two bituminous coal samples before and after fracturing were analyzed. The results showed that the fracturing process resulted in the disruption of hydrogen bonds within coal, leading to a reduction in the cross-linking density of the coal structure. Moreover, it facilitated the breaking of fatty alkyl side chains and oxygen-containing functional groups, causing the detachment of side chains and shortening of the fatty chains. The interlayer spacing of aromatic layers (d200) of fractured coal decreased, and the average transverse dimension (La), the average stack height (Lc) and the aromaticity (fa) increased. With the improvement of aromaticity, the arrangement between aromatic layers was looser. The volume and basic unit structure of coal crystal nucleus became larger, and the flattening degree increased. The research results contribute to the understanding of the change of coal microstructure under supercritical CO2 transient high-pressure fracturing and provide theoretical support for exploring the methane adsorption capacity of fractured coal.

Relationships between Combustion Behavior in Air and the Chemical Structure of Bituminous Coal during Combustion Processes

The structural parameters of five bituminous coals were analyzed by using X-ray diffraction and attenuated total reflection–Fourier transform infrared spectroscopy. The combustion behavior of coal was investigated by using a thermogravimetric analyzer under air conditions. Furthermore, the relationships between combustion parameters and the coal structure were established. The results show that bituminous coals contain crystalline and amorphous carbon. The aromaticity, interlayer spacing, average stacking height, aliphatic chain length, and the hydrocarbon-generating potential varied with the different bituminous coals. The coal samples exhibited similar weight changes during the combustion process, and the combustion parameters increased with increments in heating rate. The maximum combustion rate and activation energy increased with declining interlayer spacing and hydrocarbon-generating potential and increasing aromaticity, average stacking height, and aliphatic chain length. The bituminous coal for the utilization of combustion should have high aromaticity, a degree of graphitization, crystalline, long aliphatic chain length, and weak hydrocarbon-generating potential.

Comparison of the composition and structure for coal-derived and petroleum heavy subfraction by an improved separation method

The property of coal-derived asphaltene and resin shows remarkable differences from petroleum one, such as the molecular aggregation and thermal cracking characteristics. It is significant to make deep-level analysis of their composition and structure to provide detailed molecule information for coal tar deep processing. In this paper, an improved separation method, which innovatively developed two-stage asphaltene extraction and two-stage silica gel separation coupling process, was built to obtain the purified asphaltene and resin components derived from coal tar (C-asp and C-res) and petroleum (P-asp and P-res). All samples were analyzed comparatively through Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), solid state cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy (13C-CP/MAS-NMR), thermogravimetric analysis (TG) and scanning electron microscopy (SEM). It is found that C-asp and C-res contain more OH groups resulting in stronger aggregate effect and OH-OH and OH-ether O are the main hydrogen bond. C-asp and C-res have more C-O of phenols and C = O of COOH group. C-asp and C-res have fewer and shorter alkyl side chains. The aromatic ring substitutive degree (σ) of C-asp and C-res is higher while the alkyl branching degree of P-asp and P-res is higher. Besides, asphaltene has higher σ, alkyl substituents number (n), average stack height of aromatic sheet (Lc), average number of aromatic sheets associated in per stacked cluster (M) and shorter average substituted alkyl chain length (L) compared with resin. Finally, the average molecular structure models of C-asp, P-asp, C-res and P-res are obtained.

Strength degradation mechanism of iron coke prepared by mixed coal and Fe2O3

Iron coke, as a new type of blast furnace burden is helpful for energy saving, emission reduction and green production of iron making. This study aims to investigate the strength degradation mechanism of iron coke prepared by mixed coal and Fe2O3 to provide a theoretical direction to improve its strength. Coking and pyrolysis experiments of mixed coal and Fe2O3 were carried out between 400 and 500 ℃ temperature. Gieseler plastometer and derivative thermogravimetric (DTG) showed that added Fe2O3 inhibited the thermoplasticity and pyrolysis process of mixed coal during coking. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) results showed that added Fe2O3 decreased the aromaticity and average stacking height, but increased the interlayer spacing of crystallite, aliphatic chain length and hydrocarbon-generating potential of mixed coal during coking. Further, gas chromatography-mass spectrometer (GCMS) analysis suggested that the added Fe2O3 inhibited the cleavage of CalO, CalS, CalN, CalCar and CalCal bonds, reduced the generation of ethylbenzene, o-xylene and unbranched alkanes with carbon atoms in 24–26, thus decreased the amount of fluid phase generated in coking and ultimately degraded the strength of iron coke.

Formation mechanism of solid product produced from co-pyrolysis of Pingdingshan lean coal with organic matter in Huadian oil shale

A mixture of Pingdingshan lean coal and acid-treated Huadian oil shale was co-pyrolyzed in a drop-tube fixed-bed reactor in the temperature range of 300 °C–450 °C. To reveal the formation mechanism of the solid co-pyrolysis product, changes in some physico-chemical properties were investigated, using analysis by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, pore analysis, thermogravimetry, and electron spin resonance. X-ray diffraction showed that the lattice plane spacing for the co-pyrolyzed mixture decreased from 0.357 nm to 0.346 nm and the average stacking height increased from 1.509 nm to 1.980 nm in the temperature range of 300 °C–450 °C, suggesting that pyrolysis treatment increased its degree of metamorphism. The amount of oxygen-containing functional groups and pore volume decreased with increasing temperature. Thermogravimetry and electron spin resonance results showed that synergistic effects occurred during the copyrolysis process. A formation mechanism for the solid product was proposed. Hydrogen-rich radicals generated from the pyrolysis of the oil shale were trapped by hydrogen-poor macromolecular radicals of the intermediate metaplast produced from coal pyrolysis, thereby increasing the yield of solid product.

Effects of Fe2O3 addition on the thermoplasticity and structure of coking coal matrix during thermoplastic stage of pyrolysis

Effects of Fe2O3 addition on the thermoplasticity and structure of coking coal matrix were performed by blending Fe2O3 with coking coal matrix during thermoplastic stage of pyrolysis. Thermoplasticity and thermal behavior of coal matrix were characterized by Gieseler plastometer and Thermogravimetry analyzer. Structure of coal matrix at different pyrolysis temperatures during thermoplastic stage was investigated by using X-ray diffraction and Fourier transform infrared spectroscopy. Fluid phase collected from the coal matrix by two-stage extraction was identified by Gas chromatography-mass spectrometer analysis. The results show that the added Fe2O3 decreased the plastic range, maximum Gieseler fluidity and weight loss rate of coal matrix, and inhibited the cleavage of Cal-Cal, Cal-Car, Cal-O, Cal-S and Cal-N bonds during thermoplastic stage. Further, the inhibiting effect resulted from the added Fe2O3 made the decrease of aromaticity and average stacking height, increase of interlayer spacing of the crystallite, and ascending of aliphatic chain length and hydrocarbon-generating potential of coal matrix. Consequently, the formed fluid phase would be reduced, reflected in the disappearance of ethylbenzene, o-xylene and unbranched alkanes with carbon atoms in 24–26, resulting in coal thermoplasticity declining. This contributes to a better understanding of coke strength decrease in producing highly reactive iron coke.

Experimental study on gasification mechanism of unburned pulverized coal catalyzed by alkali metal vapor

The catalytic behavior of alkali vapor on unburned pulverized coal (UPC) prepared from bituminous coal, anthracite, semi coke and coke have been investigated. Experiment results show that the alkali metal vapor has catalytic effect on the gasification reaction of UPC. The catalytic effect of coke UPC is the most obvious, followed by anthracite UPC and bituminous coal UPC. Semi coke UPC is the least catalyzed by alkali metals but its gasification reactivity is the best. As the concentration of alkali metal vapor increases, the alkali metal content adsorbed by UPC increases, and there may be a phenomenon of saturated adsorption. The amount of alkali metal adsorbed is between 2% and 6%. AUPC has the highest ability to adsorb alkali metals, and SUPC is the weakest, which may be related to the minerals (CaO, Al2O3) in the coal ash. Changes in stomatal parameters are not the main factors affecting the catalytic effect. The results of X-ray diffraction experiments show that alkali metal aluminosilicate exists in the ash of coal after adsorption of alkali metal, and the average stack height of carbon atoms decreases significantly. The alkali metal catalytic gasification reaction is mainly achieved by destroying the carbon basic structural unit. The alkali metal nepheline and the interlayer compound may be the main catalytic substances, and the destructive ability of alkali intercalation is obviously stronger than that of alkali nepheline. The catalytic mechanism of alkali metals on unburned coal and the destruction mechanism of alkali metals on carbon crystals were discussed. It can provide reference for reducing alkali metal corrosion on coke and improving pulverized coal utilization rate.

Research on the Combustion Characteristics and Kinetic Analysis of the Recycling Dust for a COREX Furnace

Thermogravimetric analysis of recycling dust (RD) from the melter gasifier of COREX, coke1 (C-1), coke2 (C-2) and coal char (CC) under 70% oxygen atmosphere was carried out using thermal balance. The chemical composition and physical structure of the samples were investigated. The characteristic temperatures and comprehensive combustion characteristic indexes were calculated and kinetic parameters during the combustion process were calculated as well using a distributed activation energy model (DAEM). The results show that the carbon in the recycling dust originates from unconsumed CC and coke fines, and the average stacking height of carbon in RD is larger than that of C-1, C-2 and CC. The conversion curves of RD are different from those of C-1, C-2 and CC, and there are two peaks in the RD conversion rate curves. The combustion profiles of RD moves to a higher temperature zone with increasing heating rates. The average activation energies of their combustion process for RD, C-1, C-2 and CC range from 191.84 kJ/mol to 128.31 kJ/mol. The activation energy for recycling dust increases as the fractional conversion increases, but the value for C-1, C-2 and CC decreases with increasing conversion, indicating different combustion mechanisms.

Characterization of char from high temperature fluidized bed coal pyrolysis in complex atmospheres

The physiochemical properties of chars produced by coal pyrolysis in a laboratory-scale fluidized bed reactor with a continuous coal feed and char discharge at temperatures of 750 to 980°C under N2-based atmospheres containing O2, H2, CO, CH4, and CO2 were studied. The specific surface area of the char was found to decrease with increasing pyrolysis temperature. The interlayer spacing of the char also decreased, while the average stacking height and carbon crystal size increased at higher temperatures, suggesting that the char generated at high temperatures had a highly ordered structure. The char obtained using an ER value of 0.064 exhibited the highest specific surface area and oxidation reactivity. Relatively high O2 concentrations degraded the pore structure of the char, decreasing the surface area. The char produced in an atmosphere incorporating H2 showed a more condensed crystalline structure and consequently had lower oxidation reactivity.

Investigation of the Microstructure of Disordered, Non‐graphitic Carbons by an Advanced Analysis Method for Wide‐Angle X‐ray Scattering

AbstractThe analysis of the wide‐angle X‐ray scattering (WAXS) data of non‐graphitic carbons is challenging due to the broad and overlapped (hk)‐ and (00l)‐reflections. A recently developed advanced analysis method developed by Ruland and Smarsly allows for the fitting of the WAXS data by a continuous model function, providing a detailed insight into the sp2‐carbon microstructure. Obtaining parameters like the graphene layer extent La, the average stack height Lc and disorder effects permits the quantification of microstructural features. Firstly, this publication gives a brief review over historical und recent developments regarding the evaluation of the WAXS of disordered carbons. Secondly, the applicability of this algorithm to carbon samples possessing a substantial degree of disorder is tested by investigating activated carbons, heat treated coal tar pitch and furfuryl alcohol. It is seen that several structural parameters are determined with reasonable accuracy and thereby the influence of the precursor and the temperature on the resulting carbon microstructure is identified. The decrease in disorder within the 2D graphene lattice and in the stacking of the layers at higher synthesis temperatures is quantified. Moreover, this study reveals that the graphene layer extent La is only about a few nanometers in size, showing that typical non‐graphitic carbons used for diverse applications possess quite small dimensions of graphene stacks.

Carbon-stabilized mesoporous MoS2 — Structural and surface characterization with spectroscopic and catalytic tools

Structural and surface properties of carbon-containing mesoporous MoS2 and of a reference MoS2 were studied with various techniques including XRD, elemental analysis, TEM, XPS, EXAFS, nitrogen physisorption, oxygen chemisorption (OCS), determination of exchangeable surface hydrogen, and kinetic study of test reactions like ethene hydrogenation and H2/D2 exchange. The study was made before and after use of these catalysts in the hydrodesulfurization of dibenzothiophene. The microstructure of carbon-stabilized MoS2 is characterized by nanoslabs of ≈ 2 nm average stacking height embedded in an amorphous matrix with a very broad pore-size distribution. Thermal stress induced a collapse of the microporous structure leading to the formation of mainly mesopores. The carbon is well-distributed over the bulk, without any signature of carbide species detected neither in XPS nor in EXAFS measurements. The activity patterns of both materials (related to the OCS capacity) were similar despite the differing sulfur content, with the carbon-stabilized MoS2 being more sulfur deficient. This suggests that the catalytic properties of the latter material were caused by near-stoichiometric MoS2 apparently present in the nanoslabs, whereas the sulfur vacancies in the sulfur-deficient amorphous phase were blocked by strongly adsorbed carbon residues. Interestingly, the HDS reaction did not cause significant changes of the properties of the carbon-stabilized MoS2. Conversely, the reference MoS2 was strongly activated, in particular with respect to ethene hydrogenation, which can be explained by a pronounced sulfur loss during the HDS reaction, without significant site blockage by the coke deposited.

Inference on carbon atom arrangement in the turbostatic graphene layers in Tikak coal (India) by X-ray pair distribution function analysis

This paper communicates the distribution of carbon atoms in a single poly-cyclic aromatic (PCA) layer (graphene) in Tikak coal from Assam, India. The pair distribution function (PDF) analysis performed indicates no evidence of any graphite like structure in this coal. The aromatic fraction is observed to be 74% with the aliphatic fraction correspondingly estimated to be 26% in this coal. The average carbon atom has 2.5 nearest carbon atom neighbours at an average bond distance of 1.50 Å. The average stacking height of the parallel aromatic layers (Lc) and the average diameter of the aromatic layers (La) are estimated to be 9.86 Å and 4.80 Å, respectively. For this coal, the average number of stacking layers and the average number of atoms per layer are estimated to be four and eight respectively. In addition, the gamma band is observed at a d-value of 4.34 Å. The comparison of the atom-pair correlation function to simulated one-dimensional structure function calculated for a model compound benzene (C6H6) also indicates that C6 unit is the major components in this coal. The average carbon atom has at least one and one nearest aryl and alkyl C-C atom pairs separated by 1.39 and 1.54 Å respectively. [Received: January 30, 2010; Accepted: March 21, 2010]

Analysis of container dwell time on marine terminal throughput and rehandling productivity

When port authorities or terminal operators set the free time or increase storage density, the decision is often made without a clear understanding of their effects on throughput and rehandling productivity. This is partly because practical methods that deal specifically with the effect of dwell time on throughput and productivity are limited in the literature; hence the motivation for this work. This paper introduces simple methods to evaluate the effect of container dwell time and storage policies on import throughput, storage density, and rehandling productivity. The analysis considers two import storage strategies 1) non-mixed - no stacking of new import containers on top of old ones, and 2) mixed - stacking of new import containers on top of old ones. The results highlight the effect dwell time has on throughput and rehandling productivity. For the non-mixed storage policy, the increasing container dwell time lowers throughput and average stack height - resulting in an increase in rehandling productivity. On the other hand, for the mixed storage policy, the increasing container dwell time raises throughput and average stack height - resulting in a decrease in rehandling productivity. Using the presented methods, port authorities and terminal operators are able to assess and quantify the benefits of their decisions regarding container free time and subsequently make an informed decision.

Analysis of container dwell time on marine terminal throughput and rehandling productivity

When port authorities or terminal operators set the free time or increase storage density, the decision is often made without a clear understanding of their effects on throughput and rehandling productivity. This is partly because practical methods that deal specifically with the effect of dwell time on throughput and productivity are limited in the literature; hence the motivation for this work. This paper introduces simple methods to evaluate the effect of container dwell time and storage policies on import throughput, storage density, and rehandling productivity. The analysis considers two import storage strategies 1) non-mixed - no stacking of new import containers on top of old ones, and 2) mixed - stacking of new import containers on top of old ones. The results highlight the effect dwell time has on throughput and rehandling productivity. For the non-mixed storage policy, the increasing container dwell time lowers throughput and average stack height - resulting in an increase in rehandling productivity. On the other hand, for the mixed storage policy, the increasing container dwell time raises throughput and average stack height - resulting in a decrease in rehandling productivity. Using the presented methods, port authorities and terminal operators are able to assess and quantify the benefits of their decisions regarding container free time and subsequently make an informed decision.

X-ray scattering study of the average polycyclic aromatic unit in Ledo coal

This report is an attempt to understand the short-range structural features, to determine the relationship(s) between the aryl/alkyl carbon ratio, and to determine the size of the average polycyclic aromatic unit in Ledo coal from Makum coalfield, Assam, India. An X-ray scattering analysis of the average polycyclic aromatic unit in the coal indicates that the aromatic fraction in this coal is 74% with the aliphatic fraction correspondingly estimated to be 26%. The average carbon atom has 2.3 nearest carbon atom neighbours at an average bond distance of 1.50 (1) Å. The average stacking height of the parallel aromatic layers and the average diameter of the aromatic layers are estimated to be 7.58 Å and 4.86 Å, respectively. For this coal, the average number of stacking layers and the average number of atoms per layer are estimated to be 2 and 8, respectively. In addition, the Gamma band is observed at advalue of 4.42 Å.

The average height of binary trees and other simple trees

The average height of a binary tree with n internal nodes is shown to be asymptotic to 2√ πn. This represents the average stack height of the simplest recursive tree traversal algorithm. The method used in this estimation is also applicable to the analysis of traversal algorithms of unary-binary trees, unbalanced 2–3 trees, t-ary trees for any t, and other families of trees. It yields the two previously known estimates about average heights of trees, namely for labeled nonplanar trees (a result due to Renyi and Szekeres) and for planar trees (a result of De Bruijn, Knuth, and Rice). The method developed here, which relies on a singularity analysis of generating functions, is new and widely applicable.