Heat-treated Pitch Research Articles

The effect of waste PET addition on PFO-based anode materials for improving the electric capacity in lithium-ion battery

The carbon anode material for lithium-ion battery was prepared by pyrolysis fuel oil and waste polyethylene terephthalate (PET) additive. The pitch was synthesized as a medium material for carbon anode by heat treatment. The waste PET additive improved the softening point and thermal stability of the pitch. La and Lc of the anode material (heat-treated pitch) increased at higher treatment temperature but decreased by waste PET additive. The electric capacity was evaluated based on effects of defective cavity and developed graphite interlayer, respectively. When the La and Lc of the anode material decreased, the electric capacity by cavity increased based on defective graphite structure. Therefore, the addition of waste PET causes the improved capacity by the cavity. The anode material which has a high efficiency (over 95%) and C-rate (95%, 2 C/0.1 C) was obtained by controlling the process of heat treatment and PET addition. The mechanism of lithium-ion insertion was discussed based on effects of defective cavity and developed graphite interlayer.

Effects of structure of heat-treated pitch precursors on electrochemical properties of pitch-based activated carbons

Abstract Activated carbons (ACs) prepared from heat-treated pitch precursors with KOH activation are used to fabricate electrodes for electric double-layer capacitors. The electrochemical properties of pitch-based ACs were investigated based on the structural differences between the pitch precursors prepared at different heat treatment temperatures. The high crystallite height of the pitch precursor before KOH activation resulted in improved porous structures having a high specific surface area and total pore volume, while the high crystallite width of the pitch precursors before KOH activation was responsible for the high micropore volume fraction. As a result, the A-HP1 and A-HP2, which were prepared from heat-treated pitch precursor, showed improved electrochemical properties due to the improved porous structures resulting from the high total pore volume fraction. In particular, A-HP1 has higher specific capacitance than A-HP2, because of the high micropore volume fraction of the former.

Effect of structural change of pitch on the thermal conductivity of epoxy-based composites filled with heat-treated pitch

Petroleum-based pitches were used as filler materials to study the effects of heat-treatment-induced changes in pitch structure on the thermal conductivity of epoxy-based composites. The heat treatment was performed in two steps: the first involved heating the pitch to 250 °C in order to remove the low-molecular-weight compounds from the pitch, and the second involved heating the pitch to either 430 or 450 °C. There was no significant difference in the curing behavior of the diglycidyl ether of bisphenol A (DGEBA)/pitch composites, regardless of the heat-treatment temperature. However, the thermal conductivity of the DGEBA/pitch composites improved with increasing heat-treatment temperature, and the epoxy composite prepared with pitch heat-treated at 430 °C exhibited the maximum thermal conductivity. This can be attributed to structural changes in the pitch, such as the distance between adjacent planes (d-spacing), crystallite height (Lc) and crystallite width (La). Although Lc of the pitch increased with increasing heat-treatment temperature, the d-spacings and La decreased. These results suggest that the heat treatment of the pitch led to a well-stacked crystalline structure. However, compared with the pitch heat-treated at 430 °C, that heat-treated at 450 °C exhibited lower thermal conductivity in the DGEBA/pitch composite because of the low La, resulting in the loss of basal carbon as a consequence of in situ gasification, and pyrolysis of the low-molecular-weight compounds in the pitch. © 2013 Society of Chemical Industry

Formation of Mesophase Spheres in a QI-Free Coal Tar Pitch

A QI-free coal tar pitch prepared by solvent extraction from a soft coal tar pitch was subjected to a series of thermal treatments at a predetermined temperature for different holding times. The development of mesophase was discussed in terms of its size and content in the heat-treated pitches. Results showed that the size and yield of the dispersed mesophase spheres in the isotropic matrix strongly depended on the holding temperatures. When the holding temperature was less than 400 °C, only a few of small spheres formed in the mesophase pitches. However, when the holding temperature was over 420 °C, the diameter and yield of mesophase spheres in the heat-treatment pitches increased progressively with increase of the holding time. Treatment at 440 °C for 4h led to 19.9 % of the yield and the average sphere radius was 4.5-100 . In the SEM photograph of mesocarbon microbeads obtained from the heat-treated pitches using soxhlet extraction. Many small flaky particles and sporadic rugby ball-shaped particles were observed as well as a large number of spherical particles.

Analysis and modeling of mesophase sphere generation, growth and coalescence upon heating of a coal tar pitch

The present study has been undertaken aiming: (1) to provide an experimental procedure for measurement of characteristics of mesophase sphere formation from a coal tar pitch upon heating at 673–723 K in terms of the time-dependent changes in the population density and the radius distribution of the spheres and (2) to prove that the nucleation, growth and coalescence of the spheres are essential for quantitative explanation of the time-dependent changes. In regard to (1), this paper describes the conditions that are required in microscopic analysis of cross-sections of the bulk of heat-treated pitch for the conversion of the population density and the radius distribution of the cross-sectional circles into those of spheres on volume basis. Regarding (2), a model analysis demonstrates that the change in the radius distribution with time, as well as that in the population density of spheres, can quantitatively be predicted. The analysis also reveals that the spheres grow without undergoing coalescence in the early period, and the sphere coalescence commences after termination of sphere generation while the growth continues.

Modification of synthetic mesophase pitch with iron oxide, Fe 2O 3

Iron oxide (Fe 2O 3) was examined as an additive to improve the yield of the insoluble fraction in the synthetic mesophase pitch and to inhibit the expansion of the pitch during the heat-treatment and the successive carbonization of the insoluble fraction. The pitch was heat-treated at 350°C for 4 h under 500 rev./min stirring by adding 0, 6, 17, and 25 wt.% Fe 2O 3. The heat-treated pitch without additive produced swollen semi-coke with the flow domain texture whereas the heat-treated pitch with Fe 2O 3 produced porous but non-swollen semi-coke with the mosaic texture. Fe 2O 3 increased the yield of pyridine insoluble (PI) in the heat-treated pitch and inhibited completely swelling of the extracted insoluble fraction at its carbonization. The iron oxide is believed to enhance the oxidative polymerization of the lighter fraction in the pitch and to allow smooth liberation of evolving gases to suppress the expansion of the pitch and its PI during the carbonization. The successive calcination and graphitization gave spherical powders of the graphite. According to X-ray diffraction, Fe 2O 3 was transformed into Fe 3O 4, and then to elemental Fe and Fe 3C by calcination at 1000°C. At the graphitization stage, elemental Fe was only present in the carbon, catalyzing the graphitization to a limited extent.

Carbon/carbon composites with heat-treated pitches: II. Development of porosity in composites

C/C composites made with carbon fibres and coal tar pitch as matrix precursor were characterised in relationship with the properties of the pitch. The influence of pitch pretreatment in nitrogen and in air on the development of porosity in the C/C composites during a first impregnation–carbonisation step is studied. The amount of voids present in the final composite as well as the pore size distribution have been determined using quantitative image analysis. Results indicate that the pretreatment in air induces a significant change in the porosity of the C/C composite since the pore size distribution of the intertow and intratow porosity becomes narrower and the fraction of closed voids increases. Thermal annealing at 2000°C of the composite also affects significantly its porosity in a way depending on the pitch properties due to the propagation of microfissures. Thermal programmed desorption of C/C composite and carbon precursors provides informations on the carbonisation behaviour of the composite and therefore confirms the results obtained by image analysis.

Carbon/carbon composites with heat-treated pitches: I. Effect of treatment in air on the physical characteristics of coal tar pitches and the carbon matrix derived therefrom

Coal tar pitch has been heat treated at 350°C in the presence of air and nitrogen for different times. The treatment temperatures have been pre-estimated from the behaviour of pitch during heat treatment in the presence of air. The modified pitches so obtained have been characterised by FTIR, TGA, DTG, DSC, elemental analysis, etc. FTIR studies reveal that the aromaticity of the pitches increases with heat treatment in air at 350°C up to 5 h. TGA studies also exhibit characteristic differences in pyrolysis behaviour of these pitches. C/H ratio and the coke yield have been found to initially increase with treatment time but decrease with longer heat treatment. Comparison of thermal analysis data, C/H ratio and FTIR studies show that during heat treatment of pitch in air, polymerization dominates volatilization of low molecular weight compounds in the pitch.

96/01486 Mechanical properties of binderless carbon mould prepared from heat-treated mesophse pitch of controlled grain size

96/01486 Mechanical properties of binderless carbon mould prepared from heat-treated mesophse pitch of controlled grain size

95/06431 Carbon disc of high density and strength prepared from heat-treated mesophase pitch grains

95/06431 Carbon disc of high density and strength prepared from heat-treated mesophase pitch grains

Formation of mesophase spherules in low-Ql coal tar pitches and development of monolithic carbons therefrom

Three coal tar pitches having different and low contents of primary quinoline insolubles (Ql) were subjected to a series of thermal treatments at a predetermined temperature for different periods of soaking. The development of mesophase, in terms of its size and content in the heat-treated pitches, was studied as a function of the soaking time and content of primary quinoline insolubles in the original pitches. Mesophase spherules, with an average size of about 5 μm, formed in one of the coal tar pitches were separated using solvent extraction employing a suitable tar oil. These spherules, also called “mesocarbon microbeads (MCMB)”, after being moulded into small rectangular plates, were carbonized at temperatures of 950 and 2700 °C to obtain fine textured monolithic carbons possessing apparent densities of 1.66 and 1.85 g cm−3, respectively, at these heat-treatment temperatures.

UV-visible and near-IR spectra of heat-treated pitches during mesophase formation

Heat-treatment processes of various pitches have been monitored by the UV-visible and near-IR spectra measured with the diffuse reflectance method. The shape and intensity of the observed absorption bands changed with the heat treatment of the pitches, reflecting the size of the aromatic molecules and the degree of the intermolecular interactions. For pitches exhibiting spherical mesophase and flow optical texture, some parts of the isolated aromatic hydrocarbons are converted into the agglomerates with lamellar structure by the heat treatment and both fractions are present in a considerable amount with proper ratio. On the other hand, in the case of pitch exhibiting the mosaic optical texture, the isolated aromatic hydrocarbons are unstable, converting to the disordered carbon.

In situ ESR measurement of mesophase formation during the heat treatment and cooling processes of pitches

Both heating and cooling processes for mesophase formation from various pitches have been followed by in situ ESR measurements. In addition to signal intensity and linewidth, the saturation phenomenon of the signal intensity with changing microwave power was measured during heat treatment and cooling processes. As a convenient measure of the saturation factor, l/ P max ( P max is the microwave power at which the signal shows maximum intensity) was employed. In general, 1/ P max decreased with an increase in heat-treatment temperature; this change seems to correspond to a decrease in the viscosity of pitch. When pitches were heat treated at 500°C for 2 h, the carbonization reactions and the rearrangement of molecules may occur, which irreversibly changes 1/ P max . Pronounced differences in the behavior of 1/ P max measured during cooling of the heat-treated pitches were found to depend upon pitch optical texture (isotropic, flow and mosaic).

Raman microprobe study of heat-treated pitches

Recently, Raman spectroscopy has evolved as a useful technique for a rapid and nondestructive characterization of carbonaceous materials. In this article, a series of heat-treated pitches from the same coal-tar precursor is investigated by means of a Raman microprobe. Separated Raman spectra are obtained for the isotropic phase and the mesophase. The evolutions observed are characteristic of the structural rearrangement change in the two phases. They correlate well with the observations reported in literature and obtained by using different methods of structural investigations.

Molten storage and carbonization characteristics of premium grade coal-tar pitch: Influence of crude tar type and distillation conditions

A growing trend towards the transport and use of molten rather than solidified pitch has caused tar distillers to examine the relative stability of pitches while held in storage tanks. The scope of laboratory storage-stability tests can be extended to higher temperatures as a method of studying the earliest stages of pitch polymerization/carbonization. Some indications of the ultimate performance of the pitch in the end-use process can be gained. Crude tar has a strong influence on the ultimate properties and performance of a pitch. Seven tars have been made into 120 °C Mettler softening-point pitches by two distillation methods to study their subsequent storage and carbonization behaviour. The behaviour exhibited by each pitch allows a judgement on overall ‘reactivity’ and on the sensitivity to thermal conditions in the distillation of each tar. Two distillation schemes were adopted: batch distillation followed by heat treatment; and batch distillation at a pressure which was progressively reduced. The results show that time at elevated temperature has a major effect on the properties and performance of the resulting pitch. Vacuum distillation allows lower processing temperatures. Larger amounts of secondary quinoline-insolubles were formed under the ‘distillation with heat treatment’ scheme. Complete wetting of coke by pitch took place at lower temperatures for the vacuum-distilled pitches. Heat-treated pitches increased more rapidly in softening point and lost more mass when thermally soaked. Distillation under vacuum conditions resulted in significantly modified pitch carbonization characteristics.

CARBONACEOUS MESOPHASE

The study of carbonaceous mesophase began with a study in coking process of coals. Many studies about mesophase in heat-treated pitches have been done since those of Brooks and Taylor.Mesophase has a soluble one and a fusible one in addition to an insoluble and infusible one. These have been cleared up with the physicochemical properties of quinoline-soluble and quinoline-insoluble mesophase, and the heat-treating properties of mesophase by polarized micrograph observation under heating stage.As an utilization of mesophase now, there are high performance pitch-based carbon fiber and meso-carbon microbeads as a filler of high performance liquid chromatography.The future utilization of mesophase will depend on the control of mesophase properties.

Structure of anisotropic spheres obtained in the course of needle coke formation

Three kinds of spheres obtained from the heat-treated pitches which gave needle-like cokes were examined by means of an X-ray diffractometer (Diamond's method), an electron microscope and a magnetic balance to get their structural information. The precise chemical analyses were also obtained for spheres solubilized by the method of reductive alkylation. The planar condensed-ring compounds of relatively small size (6 ~ 15 Å) were revealed to align with preferred orientation to form the anisotropic sphere by these instrumental analyses. The molecular weight measurement showed that the sphere contained the molecules of molecular weight distributed from 400 to 3000 or more, and that the average molecular weight remained constant through the stages of their appearance, growth and initial coalescence in spite of the enlargement of the anisotropic domains. These results indicated that the smaller molecules are anchored to the larger ones by the π-π van der Waals forces to form the insoluble sphere. It can be also assumed that the growth of the spheres is not attained by their coalescence but by incorporation of smaller molecules in the matrix into the sphere at an adequate rate to increase their diameter as large as possible for the formation of a needle-like coke. The structural model of the sphere component was tried to be described by the chemical terms based on the results.

Influence of Coexistent Materials on the Formation of Carbonaceous Mesophase in Pitch (3)

The effect of ferrocene in pitch on nucleation and growth processes of mesophase was investigated from the behavior of iron. The quinoline soluble coal-tar pitch to which ferrocene was added, was heat-treated at 430°C for a certain period. Quinoline insoluble part in the heat-treated pitch was separated by solvent extraction with quinoline. Then, the quinoline insoluble part was treated with HCl. Iron contents in the heat-treated pitch, the quinoline insoluble part, and the quinoline insoluble part treated with HCl were examined. The obtained results are as follows.Ferrocene added in pitch was already decomposed at 430°C and changed into the fine crystals of α-Fe and FeS, which covered the surface of mesophase spherules formed in pitch. The mesophase spherules were found to have almost the same size. Amounts of mesophase formation in the ferrocene-added pitch were larger than those in the pitch having no ferrocene content. From these results, it is considered that the iron crystals controll the size of mesophase spherules and accelerate the mesophase formation. Furthermore, when the mesophase coalesces each other, the crystals not only covers the surface of the coalesced mesophase but also exists inside the mesophase.It is also made clear that the shape of mesophase spherules changes from lemon-like form to spherical form with growth of mesophase spherules.

Production of Carbon Solids from Coke covered with Mesophase

It is attempted to produce carbon solids from coke powder covered with mesophase without binder pitch. The coke powders used were a calcined coke and a green coke (not calcined), and the pitches were a coal-tar pitch and the petroleum heavy oils. A mixture of coke powder of 5 or 10 wt% and pitch was heat-treated at 430°C for a certain period. The mesophase in the heat-treated pitch exists on the surface of the coke powder and this coke covered with the mesophase was separated from the heat-treated pitch by quinoline treatment as quinoline insoluble part. Carbon solids were prepared by carbonization of the molding made of quinoline insoluble part (QI) and measured these physical properties.The obtained results are as follows;1) Compressive strength of the carbon solids increased with increasing the mesophase content in QI. When the mesophase content in QI was 50 wt%, the compressive strength was 600-1300 kg/cm2 at HTT 1000°C and 300-500 kg/cm2 at 2800°C.2) The carbon solids made of the green coke covered with the mesophase from coal-tar pitch had the highest strength and bulk density. Also, high strength carbon solids could be obtained from the coke much covered with the mesophase from petroleum heavy oils.3) The values of the electric resistance and the coefficient of thermal expansion were comparable to those of carbon solids prepared from coke and binder pitch, and were varied with the mesophase content in QI.From these results, it is confirmed that high strength carbon solids are prepared from the coke powder covered with mesophase.

Shapes of Meso-Carbon Microbeads

Quinoline-soluble coal-tar pitch, coal-tar pitch containing 3.4% free-carbon (quinolineinsoluble particles) and petroleum asphalt containing 5.4% sulphur were heat-treated for 120 min., 90 min. and 60 min. at 430°C respectively. Formation of mesophase spherules was observed by using a polarized-light microscope.The mesophase spherules were separated by solvent extraction from heat-treated pitches. The separated mesophase spherules were named meso-carbon microbeads and classified into type C, type M and type P according to above mentioned raw pitches. The shapes of meso-carbon microbeads were studied with a scanning electron microscope.The shapes of type C and type P can be divided into two classes, that is, the shapes of meso-carbon microbeads having larger size than about 5μm are approximately true spheres and those having smaller size than about 3μm are lemon-like spheroid. It is not obvious that the meso-carbon microbeads showing lemon-like shapes have the same lamellae structure as those larger than about 5μm, because the sensitive-tint technique can not be used for the meso-carbon microbeads smaller than about 3μm according to the resolving power of optical microscope.The shapes of type M are irregular, although their sizes are almost the same, and the free-carbon smaller than about 1μm are retained over the surface of mesophase.