Pitch Fractions Research Articles

Insight into the effect of structural differences among pitch fractions on sodium storage performance of pitch-derived hard carbons

Pitch is an excellent precursor of hard carbons (HCs) with low-cost and high carbon content, enabling its commercial-scale application in sodium-ion batteries. Pre-oxidation is the key to obtaining pitch-derived HCs with disordered microstructures. However, pitch is a mixture of fractions with different molecular weights and structures. With the introduction of oxygen, the cross-linked structure established by each fraction could be different, the effect of which on the microstructure and sodium storage performance of HCs remains unclear. Here, we separate pitch into three fractions and further pre-oxidize and carbonize to produce HCs, in order to systematically investigate the effects of structural differences among pitch fractions on the cross-linking mechanism and microstructure of as-obtained HCs. It is found that tetrahydrofuran-insoluble (THFI) enables the enrichment of polar oxygen functional groups, thus enhancing its oxidative activity to obtain more oxygen for the construction of abundant three-dimensional cross-linked structure. It is conducive to preventing the rearrangement of carbon layers and promoting the development of micropores during high-temperature carbonization process, which facilitates the storage of sodium ions in the low-voltage plateau region. The resulting hard carbon (THFI-1400) has significantly improved overall sodium storage performances. This work provides a new strategy to prepare low-cost and high-performance HCs.

Light fraction of pitch realizes robust coating on silicon anodes: The inhibition of volume expansion by self-delithiation

Extreme volume expansion upon lithiation remains a key challenge for Silicon (Si)-based anode materials, which commonly results in electrochemi-mechanical degradation and subsequent fast capacity fading. Pitch-derived carbon coating is an efficient strategy to alleviate the expansion of Si. However, clarifying the relationship between the microstructures of pitch-derived carbon and its expansion confinements properties is still difficult due to the complexity of pitch composition. Herein, we develop core-shell Si@C anode materials with robust protective pitch-derived carbon coating by pitch fraction separation and confirm the expansion confinements properties is connected to molecular structure and weight of pitch fractions. Small and disordered microcrystalline units of light fractions confer high resilience to the derived carbon coating which is less prone to rupture. The compressive stress from resilience coating leads to the transformation of lithium-silicon alloys to amorphous silicon during the early stages of lithiation, which allows for reduction in the expansion of Si. The composites of light fractions derived carbon with Si exhibits the best cycling stability. This work provides new insights into the understanding of expansion confinements in silicon-carbon anode materials.

Evaluation of the utility of isotropic pitches as solvent components of spinnable mesophase pitch precursors for highly graphitizable functional carbon materials

Spinnable mesophase pitch (SMP) is an important graphitizable precursor for high-performance carbon materials. Generally, SMPs show fully developed anisotropic texture, and the pitches contain isotropic contents more than 30 wt%, which plays the role of solvent for the mesogenic components in the lyotropic liquid crystalline system of the pitch. Here, we prepared SMP by blending the mesogenic components of AR mesophase pitch with various isotropic pitches to evaluate the usability of isotropic pitches as solvents. The mesogenic components were prepared by tetrahydrofuran fractionation of AR mesophase pitch. Isotropic pitches with a softening point of 140–220 °C were prepared separately by simple heat treatment of slurry oil (SO) and coal tar pitch (CTP). SMPs were prepared by thermal blending of the above mentioned mesogenic components and isotropic pitches in various blending ratios. CTP-derived isotropic pitch showed better solvent performance than a SO-derived pitch in terms of anisotropic texture. SMP prepared by blending of the mesogenic components and CTP-derived isotropic pitch with a softening point of 180 °C at the ratio of 4/6 (w/w) showed almost 100% anisotropic texture; the carbon fiber derived from the pitch showed tensile strength of 2.7 GPa and Young’s modulus of 470 GPa after graphitization at 2,800 °C.

Evaluating of the oxidative behaviors of isotropic pitch fractions for optimal the mechanical properties of isotropic pitch-based carbon fibers

Oxidative stabilization plays an extremely important role in maintaining shape and structural integrity and preventing inter-filament fusing of isotropic pitch fibers during the subsequent carbonization. However, the actual chemical processes and mechanism of the stabilization reaction are complex and as yet poorly defined because of the complexity of the isotropic pitch. In the study, an isotropic pitch synthesized through the co-carbonization of aromatic-rich distillate oil and polyethylene glycol was fractioned into seven fractions by n-heptane, toluene, and their mixtures. The chemical structure and oxidative reaction features of each pitch fraction were systematically analyzed and investigated by FT-IR, 13C NMR, TG-DSC, SEM, etc. The results revealed that the light pitch fractions with more and longer alky side chains attached to the aromatic nucleus exhibit higher oxidative reactivity and appear to induce a higher content of oxygen uptake to achieve stabilization as compared with the heavy pitch fractions. The stabilization reactions of the pitch fractions were carried out in multiple stages, which was confirmed by the conversion of oxygen-containing functional groups ketones and aldehydes to anhydrides and esters as oxidation temperature increased from 150 ℃ to 290 ℃. Three commercial isotropic pitches produced from petroleum-based raw material were oxidized under different conditions. The results confirmed that it is feasible to predict and optimize the stabilization process by tailoring the pitch components.

Coking of the α2 Fraction of Coal Pitch and the Structure of Its Coke Residue

Coking of the α2 Fraction of Coal Pitch and the Structure of Its Coke Residue

Study of the Molecular-Weight Distribution of Binder Pitches for Carbon Blocks

The present study aimed to identify the required characteristics of binder pitches in the filler-binder mixing process to effectively manufacture graphite blocks. To this end, a binder pitch was separated into pitch fractions of varying molecular-weight segments. The role and effectiveness of each pitch fraction were then analyzed with respect to their molecular-weight distribution. As a result, the optimal molecular-weight distribution was determined. More specifically, a coal-tar pitch was separated into solvent-soluble and solvent-insoluble fractions. The molecular-weight distribution was determined according to this classification, and the characteristics of each pitch fraction were examined. The pitch separation process was conducted using three solvents: hexane, toluene, and quinoline. The resulting pitch was separated into the following pitch fractions: hexane-soluble (HS), hexane-insoluble-toluene-soluble (HI-TS), toluene-insoluble-quinoline-soluble (TI-QS), and quinoline-insoluble (QI). Fourier transform infrared (FT-IR) spectrum, matrix-assisted laser desorption ionization-time of flight (MALDI-TOF), and softening point of each pitch fraction were measured. Also, pitch samples were refabricated while varying the mixing ratio of these pitch fractions, and carbon blocks were then prepared using them. The compressive strength and porosity of these blocks were measured and compared. The P154_B pitch with a high content of TI-QS was used to fabricate a green block. Due to the high viscosity of the binder used, the fluidity was not sufficiently high, and thus, the green block made of this pitch had relatively low strength. The other blocks had similar levels of strength. After the carbonization process, the carbon block with a high content of HS (P352_B-C) and the carbon block with the HS content removed (P073_B-C) showed lower compressive strength than their respective green-block counterparts (P352_B and P073_B). However, their strength was higher compared to those of the other carbon blocks. In the case of carbon block P073_B-C, the HS content was completely removed, and thus, the content of TI-QS (β-resin) was relatively high. Accordingly, this carbon block ended up with large amounts of components that had high coking values (CVs), and this contributed to limiting the formation of pores. Therefore, the compressive strength of this carbon block was high. In the case of the carbon block with a high content of HS (P352_B-C), a suitable level of viscosity was achieved because the HS components ensured high fluidity. As a result, blocks with higher density and compressive strength could be fabricated. The major findings of the present study confirm that producing carbon blocks with high mechanical properties requires binder pitches with a balanced combination of suitable viscosity to ensure sufficiently high fluidity and a proper level of CV to effectively suppress the formation of pores in the mixing and molding process.

Effects of the molecular structure from pitch fractions on the properties of pitch‐based electrospun nanofibers

AbstractMesophase pitch was separated into different pitch fractions to investigate the effect of pitch fractions on the properties of their nanofibers prepared by electrospinning. The evolution of different pitch fractions‐derived nanofibers during stabilization and carbonization were explored, and the properties of the resultant carbon nanofibers (CNFs) as electrode materials for supercapacitor were compared. Results indicated that the hexane insoluble‐toluene soluble (HI‐TS) and toluene insoluble‐tetrahydrofuran (THF) soluble (TI‐THFS) fractions had good spinnability due to their narrow molecular weight distribution. Moreover, compared with HI‐TS and THF insoluble (THFI), TI‐THFS consisted of appropriate aromaticity and branched alkyl groups which promoted the stabilization and carbonization behaviors of its nanofibers, resulting in maintaining ideal fiber morphology of TI‐THFS‐derived nanofiber due to the mitigation of their exothermic reactions. Meanwhile, the TI‐THFS‐derived CNFs presented the highest surface area of 543 m2 g−1 and exhibited an excellent specific capacitance of 167 F g−1 at 0.5 A g−1 in 6 M KOH electrolyte.

Thread turn milling simulation

The study shows that the high-performance thread turn-milling process with a synchronous rotation of the helical milling cutter and the workpiece is not widely adopted since there are no reliable methods to estimate the organic thread formation errors. The thread is machined as an envelope curve along the elementary surfaces of each cut shifted along the workpiece axis by a fraction of the thread pitch inversely proportional to the number of the cutter teeth. Domestic and international researchers tried to analytically estimate the thread formation errors at the part face. Such an approach failed to produce acceptable results since thread turn-milling is a three-dimensional process. We analyzed the thread formation errors in 3D using COMPAS 3D CAD system and developed a simulation model. We modelled a reference 3D thread machined on the workpiece; a 3D resulting thread; a single cutter tooth path in the plane perpendicular to the workpiece axis; 3D cut by a single cutter tooth. We also simulated the entire process and made a 3D model of the machining errors by subtracting the reference part geometry from the 3D thread model, and estimated the errors. The results were checked for consistency (max deviations) and acceptability for each dimension. The undercut dimensions were obtained by subtracting the 3D part model from the 3D reference model. Conversely, the overcut dimensions were obtained by subtracting the 3D reference model from the 3D part model.

Heat Transfer and Pressure Drop Investigations of the Compact Exhaust Heat Exchanger With Twisted Tape Inserts for Automotive Waste Heat Utilization

Abstract Thermoelectric-based waste heat recovery is a competent technique to reduce the exhaust emissions and fuel consumption of automobiles. Thermal and hydraulic characteristics of the exhaust heat exchanger plays a decisive role in the extent of waste heat recovery from the exhaust gas. In this study, the exhaust heat exchanger having twisted tape inserts is proposed to increase the internal heat transfer coefficient. The dimensionless Nusselt number and friction factor were evaluated experimentally for different designs of the twisted tapes. The experiments were performed for the Reynolds number in the range 2300–25000. The considered geometric parameters of the twisted rib explored were the pitch fraction, twist fraction, and slope. The obtained results were compared to reveal the best feasible design of the twisted tape. The maximum net thermohydraulic efficiency factor achieved for the system in the present analysis is 1.93. With the use of twisted tapes, the area of the exhaust heat exchanger can be greatly reduced for the same power output as flat geometry. This would help for the integration of the waste heat recovery with the engine, where the space available is very limited.

Precursors for the Synthesis of Carbon Materials from Coal Pitch

The functional and group composition and structure of β and α2 fractions of medium-temperature coal pitch fraction (in powder form) are investigated by methods such as elemental analysis, electron microscopy, IR spectroscopy, ESR, X-ray diffraction analysis, derivatographic analysis, and chromatography and mass spectrometry. The morphology and structure of the coke residues from the thermal destruction of the pitch’s α2 fraction are studied at different stages of thermolysis. It is found that the polycyclic aromatic hydrocarbons in the volatile thermolytic products of the coal pitch are generated on decomposition of the β fraction. The data obtained by different methods are relatively consistent and more completely characterize the functional and group composition and structure of the β and α2 fractions of medium-temperature coal pitch. On that basis, new methods are proposed for the use of individual pitch fractions as precursors for the synthesis of carbon materials or selective sorbents.

Analysis of the Anode Paste Charge Composition

Anode pastes are widely used in the production of ferroalloys and primary aluminum and in other processes in the metal and chemical industries. In consideration that their manufacturing involves dosing and mixing, the properties and performance of the commercial product are determined by the type of initial charge components and their ratio. This study analyzed the composition of the initial charge mixtures of two anode pastes. At the initial stage, the solid carbon filler was separated from the pitch binder. The filler separated was classified by the components based on the difference in their physical properties and then divided into size classes. A comprehensive thermal analysis of the initial samples and the filler fractions was performed to evaluate the thermal transformations in the samples and to determine the filler–binder ratio in the charge. The extraction results of individual pitch fractions in the corresponding solvents were considered in the analysis. The charge mixture for two anode paste samples was analyzed to determine the possibility of using this approach. This approach can be developed further for possible applications in metal industry enterprises and in laboratory studies.

Experimental Investigation on Thermal Performance in Three-Sided Solar Air Heaters Having an Alignment of Multi-v and Transverse Wire Roughness on the Absorber Plate

Abstract The use of artificial roughness is an efficient and commercial way to appreciate the thermal performance from the collector to the air in solar air heater ducts, for numerous applications such as space-heating, crop-drying, and seasoning of timber industrial purpose. In this paper, the tentative inquiry on thermal enactment using new-fangled of three-sided roughened quadrilateral duct solar air heater having an alignment of multiple-v and transverse wire is performed and compared the outcomes with smooth duct air heater under similar operational circumstances. The modification of an arrangement and operational constraints is inspected within the restrictions, the moral of four-sided duct aspect ratio (W/H) = 8, the Reynolds number occupied from 3000 to 12,000, fraction of pitch to roughness height, P/e in the range of 10–25; ratio of roughness height to hydraulic diameter, e/D in the range of 0.018–0.042; at flow attack angle, α = 60 deg for constant moral of relative roughness width, (W/w) = 6. The augmentation on thermal efficiency in three-sided rugged duct is found to be 23–86% when compared to smooth duct, and the maximum thermal efficiency can occur at P/e = 10 and e/D = 0.042. The enhancement in air temperature flowing under three-sided roughened duct is found to be 49.27% more than that of a smooth duct. The instant innovative form of three-sided roughened solar air warmer would be preferable to those of a smooth solar air heater with respect to heat assignment.

Suspended core microstructured optical fibers with diverse arrangements of gold-filled holes: study of the polarization characteristics and resonance strength

We study the dispersion and polarization properties as well as the coupling characteristics of suspended core microstructured optical fibers (SC-MOFs) having constant pitch and air-filling fraction with a varying suspension factor (SF) and diverse arrangements of gold-filled holes. The interaction between the core-guided fundamental mode and the surface plasmon polaritons (SPPs) generated on the surface of the gold-filled hole creates surface plasmon resonance (SPR) at the phase-matching wavelengths. It is observed that such plasmonic SC-MOF designs exhibit very high birefringence and an increased number of complete coupling points for high SF values. In addition, for all the arrangements of gold-filled holes, the coupling occurs for a higher order of the SPP for structures having greater SF. The resonance strength of such SC-MOFs is significantly enhanced and considerable reduction in full width at half maximum (FWHM) bandwidth of the SPR peak is achieved for the ${ x}$x-axis with suitable arrangement of gold-filled holes. The values of the coupling strength and FWHM achieved for the proposed SC-MOF structures are better compared to all the data reported until now to the best of our knowledge. The results suggest that such SC-MOF structures may be beneficial for developing polarizers or in-fiber polarization splitters with improved performance.

Self-Organization of Hexane-Insoluble Asphaltenes of Coal Pitch

Recently, there has been growing interest in asphaltenes, which are byproducts of petroleum processing and coal liquefaction. However, most data on the macromolecular structure and morphological characteristics of asphaltene aggregates relate to the petrochemical industry. We know that the concentration of asphaltene in solution affects the structure of their associates, which is also modified by the presence of various additives. The formation of planar associates of asphaltenes and condensed graphite-like structures are of particular interest. In order to optimize the graphitization of the anode mass, coal pitch (the β fraction) is investigated. In the heat treatment of the anode mass, the best binder is pitch with a high content of β fraction. The structuring of the asphaltene macromolecules in solution has not been studied for coal pitch. In the present work, in order to investigate the self-assembly of molecular aggregates of coal-pitch asphaltenes, the morphology and structure of powder particles for coal-pitch asphaltenes are investigated by various methods. The β fraction of pitch containing asphaltenes is separated by means of selectively soluble groups. Toluene and hexane are used as the selective solvents. On the basis of X-ray phase analysis, the coke residue of coal-pitch asphaltenes contains crystallites of naphthene–aromatic layers. The crystalline properties of the deposited asphaltene particles hardly depend on the deposition conditions. The powder mainly consists of turbostratic carbon structures.

Selective hydrogenation of quinolines over a CoCu bimetallic catalyst at low temperature

Quinoline derivatives are widely exist in the environment, and mainly separated from the coal tar pitch fraction. Hydrogenation of these compounds to 1,2,3,4-tetrahydroquinolines, an important class of natural products and medicinal agents, is a significant transformation of waste to valuable chemicals. In the present work, we developed a cheap and highly efficient Co3Cu1Ox bimetallic catalyst and used it for the hydrogenation of quinolines at a temperature down to 60 °C. The introduction of Cu into Co catalyst changed the physical and chemical features of Co catalyst, which was characterized by Raman spectra, N2-adsorption/desorption isotherms, H2-TPR and H2-TPD tests. The recycling experiments indicated the catalyst was stable and possessed good reusability. Importantly, the gram-scale experiment provided a high yield (92%) to the target product, demonstrating that the catalytic system has a potential practical application.

Valuable Products from Coal Tar

Research on the production and properties of coal pitch is conducted in the laboratory at PAO Koks. One topic of interest is the distillation of coal tar to produce a broad tar and pitch fraction, whose quality is analyzed. It is possible to regulate the characteristics of pitch: its ash content and content of components insoluble in toluene (the α fraction) and components insoluble in quinoline (the α1 fraction).

Insight into the oxidative reactivity of pitch fractions for predicting and optimizing the oxidation stabilization of pitch

Oxidative stability is of particular importance to maintain the morphology and adjust physicochemical properties of pitch-based carbon products. Due to the complex composition of pitch, the oxidative reactivity of the pitch components has rarely been reported to date, so that the oxidative stabilization conditions of pitch have been mainly selected from experience. In the study, a coal tar pitch was fractionated into toluene-soluble (TS), toluene-insoluble and pyridine-soluble (PS), pyridine-insoluble and quinoline-soluble (QS), and quinoline-insoluble (QI) fractions. The molecular structural features of each fraction and their reactivity with oxygen at varying oxidation temperature were characterized and evaluated. The results reveal that light fractions (TS and PS) with more alkyl side chains exhibit a higher reactivity at the low oxidation temperature range from 200 to 250 °C, leading to the formation of more cross-linked structures. Meanwhile heavy fractions (QS and QI), with relatively rich isolated aromatic hydrogen, seem to be remarkable in O2 uptake and the formation of C–O structures until the oxidation temperature rises above 250 °C. Insight into group composition of the pitch allows predicting its oxidative stability characteristics and further allowing it to quickly fine-tune operational conditions for time-effective and energy-saving stabilization.

Self-healing and Oxidation Resistance of B-Si Doped Carbon Materials Derived from Modification Coal Tar Pitch

AbstractWith toluene soluble fraction of coal tar pitch, polycarbosilane and pyridine borane as raw materials, the modification coal tar pitch was synthesized by a liquid method. The B-Si-doped carbon materials were obtained by carbonization treatment at 800–1,600 °C for 1 h. The effects of carbonization temperatures on the composition, microstructure and oxidation resistance of the B-Si-doped carbon materials were investigated by XRD, SEM and TG-DSC. The results showed that the B-Si-doped carbon materials were composed of B2O3 and carbon. SiC crystal grains appeared when the carbonization temperatures were over 1,200 °C. The higher the carbonization temperatures were, the larger the SiC grain sizes of B-Si-doped carbon materials became. But oxidation rate of larger grain sizes of SiC was slow during oxidation. It was difficult to form a protective glassy film on the surface of the materials rapidly. Therefore, the B-Si-doped carbon materials obtained by carbonization at 1,200 °C showed better oxidation resistance. Oxidation resistance mechanism of B-Si-doped carbon materials was illustrated. The SiO2 produced by the oxidation of SiC and B2O3 formed protective glassy film, which had self-healing and anti-oxidation synergism.

Structural Modification of Petroleum Pitch Induced by Oxidation Treatment and Its Relevance to Carbonization Behaviors

Structural modifications of petroleum pitch and its subfractions induced by mild air-blowing modification have been monitored by elemental analysis, average molecular weight, Fourier transform infrared spectrometer (FTIR), 1H nuclear magnetic resonance (1H NMR), and carbon residue. Combined with the investigation into carbonization behaviors of as-prepared oxidized pitch, the relationship between oxidized modification and carbonization behaviors has also been discussed. With the air blowing treatment process, average molecular weight and oxygen content grow rapidly in the petroleum ether-insoluble fraction of the air-blown pitch in comparison with those of corresponding petroleum ether-soluble fractions, which gradually enlarges the distinction in carbonization reactivity and mutual solubility between these two subfractions. As a result, although the yield of carbonized residue is dramatically increased from 36.1 wt % to 64.5 wt % during the direct thermal carbonization process, the air blowing treatment produces an adverse effect on mesophase development of oxidized pitches, leading to the optical texture index (OTI) significantly decreasing from 35.9 to 0.6. While adding the hydrogen-donor aromatic oil (HAO) into the air-blown pitches is able to effectively improve the mutual compatibility among the solvent subfractions via H-transfer reactions and dilution effect, consequently contributing to mesophase development during the co-carbonization process accompanied by increasing OTI value of mesophase residues to about 65, except 33.6 of the PP25-HAO mixture, simultaneously the co-carbonization process still maintains the relatively high carbonized residue yield between 42.1 and 61.8 wt %. Hence, a possible combined process including air blowing modification and subsequent co-carbonization process can obtain mesophase products with high residue yield and excellent anisotropic texture by controlling the degree of oxidation and selecting compatible co-carbonization additives.

Experimental study on the coal tar hydrocracking process over different catalysts

In the paper, the results of the study on a laboratory process of hydrocracking of coal tar are presented. High-temperature coal tar was hydrocracked in an autoclave reactor, at 400–413 °C and 7,3–9,6 MPa over 5 different, hydrocracking catalysts to study the yields and characteristics of the products. Liquid products were obtained with a yield of 88–92 wt.% and gas products with a yield of 12–8 wt.%. After dehydration by azeotropic distillation, liquid products were separated on the oil fraction boiling below 360 °C, and pitch fractions boiling above this temperature. In the balance of distillation, it is clear that only the cracking activity of NiW/Al2O3 and Y zeolite catalysts is so high that the raw material containing 5 vol.% fraction boiling below 200 °C provides a product comprising approx. 12,5 vol.% of this fraction. The influence of five different catalysts on the yield of 18 poly aromatic hydrocarbons (PAHs) in the hydrocracking products have been investigated by GC/MS. The results indicate that NiW/Al2O3 and Y zeolite catalysts have the highest catalytic activity for light aromatic formation (the highest yield of fraction boiling below 200 °C) and aromatic condensed aromatic cracking (PAHs). After the hydrocracking NiW/Al2O3 catalyst, the total yields of PAHs decrease 52.7% as that of raw coal tar.