Utilisation of the binders prepared from coal tar pitch and phenolic resins for the production metallurgical quality briquettes from coke breeze and the study of their high temperature carbonization behaviour

To reduce the cost of the formed coke briquettes which can be used as a substitute fuel to the metallurgical coke for the blast furnace from the coke breeze alternative binders and their blends were used. The high temperature behavior was investigated. The binders tested were: the nitrogen blown, air blown coal tar pitch and the blend of air blown coal tar pitch with the phenolic resins blends. The phenolic resin blends were prepared by mixing equal amount of resole and novalac. From the results, nitrogen blowing resulted in the weakest briquettes. The air blowing procedure should be preferred in place of nitrogen blowing for this purpose. When the air blown coal tar pitch was used alone as a binder, the briquettes must be cured at 200 °C for 2 h, then carbonized at a temperature above 670 °C. Since it requires higher temperature at carbonization stage, using air blown coal tar pitch alone as a binder was not economical. Therefore, the briquettes were prepared from the blended binder, containing air blown coal tar pitch and phenolic resins blend. The optimum amount of air blown coal tar pitch was found to be 50% w/w in the blended binder. Curing the briquettes at 200 °C for 2 h was found to be sufficient for producing strong briquettes with a tensile strength of 50.45 MN/m². When these cured briquettes were carbonized at temperatures 470 °C, 670 °C and 950 °C, their strength were increasing continuously, reaching to 71.85 MN/m² at the carbonization temperature of 950 °C. These briquettes can be used as a substitute for the metallurgical coke after curing; the process might not require un-economical high temperature carbonization stage.     

Primary carbonization of an anisotropic ‘mesophase’ pitch compared to conventional isotropic pitch

The evolution during carbonization treatments of a 100% anisotropic pitch (pitch C) was compared to that of Ashland 240 (100% γ resins). The anisotropic pitch C results from a gas-sparge preparation leading to a composition of 93% β resins (QS-TI) and 7% γ resins (QS). It is made of a major component (QS-TI), in which droplets (100-300 nm in size) partially toluene soluble are distributed. The physicochemical, textural and microtextural evolutions of the two pitches were studied. During pitch C primary carbonization, anisotropic droplets grow by coalescence, then decompose into Brooks and Taylor mesophase spheres suspended in isotropic drops. These drops develop at the expense of the anisotropic matrix by a continuous regeneration of the small anisotropic droplets which feed the isotropic drops by diffusion process. Then inside these drops, mesophase spheres grow then coalesce and the behaviour of a conventional pitch is restored. These various molecular associations are due to absence of chemical events below 450 °C, leading to the global mass spectrum being constant. At 500 °C the material is homogeneously anisotropic though plastic, the metastable system is destroyed and the evolution of conventional pitches is recovered, i.e. above 550 °C macropores develop up to solidification at 600 °C (semi-coke stage).     

Effect of densification parameters on the low-energy tribological behavior of carbon/carbon composites

The low-energy tribological behavior was investigated in carbon/carbon composites fabricated by processing with different densification parameters. In the densification process, different impregnating precursors and carbonization temperatures were used to investigate the influence on physical and mechanical properties, microstructure and tribological behavior. Experimental results indicate that the density and hardness of resin-based specimens are higher than those of pitch-based specimens after four densification cycles. When increasing carbonization temperature in the specimens based on coal tar pitch, the open porosity increases whereas both the bulk density and the hardness decrease. When comparing the tribological properties of the specimens with different impregnating precursors, coal tar pitch specimens show lower and more stable friction coefficients and exhibit lower weight losses. This is because the pitch matrix is transferred to the preferred orientation structure carbon after carbonization. The different carbonization temperatures do influence the tribological properties; specimens carbonized at 700 °C exhibit the lowest weight loss and the most stable friction coefficient.     

A graphite foam reinforced by graphite particles

Graphite foam was obtained after carbonization and graphitization of a pitch foam formed by the pyrolysis of coal tar based mesophase pitch mixed with graphite particles in a high pressure and temperature chamber. The graphite foam possessed high mechanical strength and exceptional thermal conductivity after adding the graphite particles. Experimental results showed that the thermal conductivity of modified graphite foam reached 110 W/m K, and its compressive strength increased from 3.7 MPa to 12.5 MPa with the addition of 5 wt% graphite particles. Through the microscopic observation, it was also found that fewer micro-cracks were formed in the cell wall of the modified foam as compared with pure graphite foam. The graphitization degree of modified foam reached 84.9% and the ligament of graphite foam exhibited high alignment after carbonization at 1200 °C for 3 h and graphitization at 3000 °C for 10 min.     

A review of the control of pore structure in MgO-templated nanoporous carbons

Nanoporous carbons with a high surface area were directly prepared from various carbon precursors without any stabilization and activation processes. Various carbon precursors, including poly(vinyl alcohol), poly(ethylene terephthalate), polyimide, coal tar pitch, were used and MgO itself, Mg acetate, Mg citrate, Mg gluconate and Mg hydroxy-carbonate were employed as MgO precursor. Carbon precursor was mixed with MgO precursor in different ratios either in powder (powder mixing) or in solution (solution mixing), and heat-treated at 900 °C in inert atmosphere. MgO formed in the carbonization products was dissolved out using a diluted acid. BET surface area of the carbons obtained could be reached to high value, as high as 2000 m²/g, even though any activation process was not applied. Most carbons prepared through this method were rich in mesopores. Size of mesopores in the resultant carbons was tunable by selecting MgO precursor and relative volume between mesopores and micropores was controlled by carbon precursor.     

Structural and electrochemical characterisation of nitrogen enriched carbons produced by the co-pyrolysis of coal-tar pitch with polyacrylonitrile

Carbonaceous materials ranging from soft carbons of moderate nitrogen content (up to 2.5 wt.%) to typical hard carbons with an excess of nitrogen (up to 6 wt.%) were produced by carbonisation at 1050 °C of coal-tar pitch (CTP)—polyacrylonitrile blends with various ratio of the components. The resultant carbons were characterised by elemental analysis, optical and transmission electron microscopy (TEM), X-ray diffraction, X-ray photoelectron spectroscopy and sorption of nitrogen and carbon dioxide. The electrochemical lithium insertion has been investigated in these carbons by a galvanostatic technique, using carbon/lithium two-electrode cells. Independently of the nitrogen content, the electrochemical performance of the soft carbons is comparable. The nitrogen enriched hard carbons demonstrate a relatively low value of reversible capacity, due to the absence of available nanopores. On the other hand, the irreversible capacity increases with the proportion of nitrogen, especially in the form of pyridinic groups. The lone pair of electrons contribute to the trapping of solvated lithium cations on these groups which act as active sites for the electrolyte decomposition during the first reduction, leading to an enhanced irreversible capacity.     

KOH activation of pitch-derived carbonaceous materials—Effect of carbonization degree

Two series of mesophase pitches and semi-cokes of different carbonization degree were produced by heat treatment of anthracene oil derived pitches P1 and P4 in the temperature range of 460-700 °C. These carbonaceous materials were activated with potassium hydroxide at 700 °C using 1:3 reagents ratio to assess the effects of the precursor optical texture and carbonization degree on the activation behavior. The results show that the increase in the pitch pretreatment temperature suppresses propensity to the pore generation while enhancing particle breaking. The effect can be illustrated by decreases in the BET surface area S_BET from ~ 2700 to ~ 1500 m² g⁻¹ and the micropore volume V_DR from ~ 0.85 to ~ 0.45 cm³ g⁻¹. These parameters are inversely related with the H/C atomic ratio of precursor. In contrast, the anisotropic development of pitch coke, varying from flow type to mosaics, has a slight effect on the activation behaviour. The mechanism of porosity generation, that is proposed, stresses the role of hydrogen occurring at the edges of graphene layers and potassium metal insertion/deinsertion on the porosity development and particle disintegration during KOH activation of pitch-derived carbons.     

Surface functional groups of carbons and the effects of their chemical character, density and accessibility to ions on electrochemical performance

Wood origin activated carbon was oxidized and then treated with melamine and urea followed by carbonization at 950 °C in an inert atmosphere. The samples were characterized using elemental analysis, adsorption of nitrogen, Boehm titration, FTIR and XPS. Testing the carbons as the electrode materials in supercapacitors indicated that the electrochemical behavior of modified samples is governed mainly by the specific types of functional groups. Both surface chemistry and texture of carbons are affected by the nitrogen source and the type of oxygen functionalities preexisting on the surface. The modified carbons revealed significantly enhanced capacitances in 1 M H₂SO₄ reaching 300 F/g and the capacitance retention ratio is 86% at the current load of 1 A/g. Perfect correlations were found between the number of basic groups and the gravimetric capacitance and between the normalized capacitance in micropores and the distribution of quaternary and pyridinic-N-oxide nitrogen species on the surface of the micropores. The pseudocapacitance on N and O atoms is particularly dominant at higher current loads and the charge on quaternary nitrogen and pyridinic-N-oxide enhances the electron transport through the electrode improving the rate performance of treated samples. The micropores were found to be most effective in a double-layer formation.     

On the chemistry of the oxidative stabilization and carbonization of carbonaceous mesophase

Two mesophase samples, one derived from a coal-tar pitch (M-A) and the other from a naphthalene-based pitch (M-B), were stabilized with air in a temperature range of 200-300 °C and then carbonized to 1000 °C. Elemental analysis and FTIR spectroscopy were used to monitor the changes produced by oxygen in the chemical composition of the mesophase samples at different stages of stabilization (from 200 to 300 °C) and after carbonization of the stabilized samples (from 300 to 1000 °C). The results show that oxidative stabilization is a dehydrogenative process, where the hydrogen removed is predominantly aliphatic and the oxygen uptake is mainly in the form of C-O-C and CO groups. The more aliphatic character of M-B accelerates the stabilization process with respect to M-A. M-B shows a higher weight gain and also a greater variety of oxygen-containing functional groups. As a result, the plasticity of M-B is more affected by changes in the stabilization temperature than that of M-A. Thus, the stabilization process is easier to control in the case of M-A. On carbonization, oxygen and hydrogen are removed from the stabilized samples and the carbons generated exhibit an increase in interlayer spacing and a decrease in crystallite size as the carbonization temperature increases.     

Molasses and air blown coal tar pitch binders for the production of metallurgical quality formed coke from anthracite fines or coke breeze

The effect of the type and the amount of hardeners, such as ammonium nitrate, ammonium carbonate and nitric acid on the molasses bonded briquettes prepared from anthracite fines or coke breeze were investigated. Amongst the hardener studied the best results were obtained with 2.5% ammonium nitrate hardener. The briquettes produced with this hardener were highly water resistant but not waterproof and their tensile strengths were not adequate to be used as a substitute for the metallurgical coke. Therefore, the briquettes were prepared with molasses containing 2.5% ammonium nitrate hardener and air blown coal tar pitch blended binder. When the blended binder was used for the production of anthracite fines or coke breeze briquettes, after curing at 200 °C for 2 h, they became waterproof and their tensile strengths were found to be sufficient to be used as a substitute for coke oven coke. The briquettes after curing could be directly charged into the blast furnace without carbonizing them at high carbonization temperatures. Since molasses and coal tar pitch, are relatively cheap and readily available materials, the process investigated could be economical way of producing high quality formed coke.     

Preparation of microporous sorbents from cedar nutshells and hydrolytic lignin

Carbon nutshells and hydrolytic lignin were used as starting materials for the preparation of microporous active carbons. Optimum parameters for cedar nutshell carbonization have been selected (temperature of carbonization 700-800 °C, rate of heating less than 3 °C/min) for the preparation of microporous carbons (average pore width 0.56 nm). The textural characteristics of microporous carbons made from nutshell are similar to those of a ‘Coconut’ carbon molecular sieve, but the latter has both a higher CO₂ adsorption capacity and a higher coefficient of N₂/O₂ separation. The influence of carbonization and steam-activation parameters on the microtexture and molecular-sieve properties of granular carbons made from hydrolytic lignin was also investigated. A low rate of heating (less 3 °C/min) promotes the formation of micropores with average sizes around 0.56-0.58 nm at carbonization temperature 700 °C. At the same carbonization temperature the average sizes of micropores were 0.7-0.78 nm at rates of heating more than 3 °C/min. The activation of lignin-char with steam at 800 °C resulted in the formation of active carbons with more developed micropore volume (0.3-0.35 cm³ g⁻¹) and with micropores of widths around 0.6-0.66 nm which are able to separate He from a He-CH₄ mixture. The size of the micropores was varied as a function of burn off value.     

煤沥青基微晶炭的制备及其储锂性能

以工业副产物煤沥青（coal tar pitch, CTP）为原料,采用高温炭化法制备煤沥青基微晶炭,利用XRD、Raman光谱、SEM、TEM和XPS等手段对其微观结构和表面化学性质进行表征,并探究微晶炭用作锂离子电池负极材料的储锂特性。结果表明,煤沥青经不同温度（800~1100℃）炭化处理后可制备出石墨微晶和无定形炭共存的微晶炭。炭化温度是影响煤沥青基微晶炭的微晶片层、纳米孔道和结构缺陷等微观结构特征和表面化学性质的重要因素。当炭化温度为800℃时,煤沥青基微晶炭CTP-800具有较为有序的石墨微晶片层和丰富的纳米孔道、结构缺陷等无定形炭,且两者有机结合,相互镶嵌,构筑成三维网络结构,同时炭基体表面含有适量氧/氮官能团。该微晶炭用作锂离子电池负极材料时具有优异的储锂特性,在50mA/g电流密度下可逆容量可达305mA·h/g,1000mA/g大电流密度下仍可维持在174mA·h/g,经100次循环后可逆容量保持率超过99.0%,显示出良好的倍率性能和优异的循环稳定性,是一种较为理想的锂离子电池负极材料。煤沥青基微晶炭 CTP-800优异的储锂特性与其炭基体中含有石墨微晶片层与纳米孔道、结构缺陷等无定形炭和炭表面富含氧/氮官能团等因素密切相关。     

Capacitance behaviour of brown coal based active carbon modified through chemical reaction with urea

The capacitive performance of activated carbons with different contents of nitrogen obtained from brown coal has been investigated. Nitrogen enrichments have been made by exposing the samples to urea without overpressure in oxidizing conditions. The effect of different temperatures of carbonization (500 and 700 °C) and the influence of the sequence of nitrogenation and activation processes have been investigated. Electrochemical study has been performed on microporous carbonaceous materials with high surface areas (BET) ranging from 2209 to 3268 m²/g, and chemical structures with different content of nitrogen (0.2-5.6 wt.%) and oxygen heteroatoms (4.5-11.1 wt.%) and different type of species formed.The presence of nitrogen heteroatoms in carbonaceous materials considerably increases their capacitance, particularly if they work as the negative electrode in alkaline capacitor. Capacitance of the same materials used as a positive electrode is characteristically reduced. Such specific influence of nitrogen has been observed even at their low content implied by the chemical composition of natural brown coal giving capacitance of negative and positive electrode of 341 and 264 F/g, respectively. The similar effect of nitrogen in the acidic medium has been much lower; capacitance of the material used for both electrodes has been of about 300 F/g. Carbonaceous materials containing nitrogen reveal different behaviour, mainly in respect of charge exchange dynamics, if they are used as capacitor electrodes of the opposite polarity.     

Swelling and related mechanical and physical properties of carbon nanofiber filled mesophase pitch for use as a bipolar plate material

Mesophase pitch was investigated as a melt processable precursor to a compression or injection moldable all carbon bipolar plate. After shaping, carbonization to 1000 °C or greater is required to achieve the desired electrical and mechanical properties, but gases evolved during this step lead to swelling. Carbon nanofiber was added to suppress swelling during carbonization and bypass the typical oxidation steps used when processing mesophase pitch. The addition of carbon nanofiber decreased swelling by increasing the viscosity of the melt. Carbonized materials with carbon nanofibers can show strengths (30-50 MPa) and conductivities (20-80 S cm⁻¹) consistent with composite bipolar plate materials. The materials show conductivities below Department of Energy target values at the current carbonization temperatures, which were limited to 1000 °C. The use of glass fibers as a secondary filler led to reduced gas permeability in porous samples.     

Effect of graphitization on fluorination of carbon nanocones and nanodiscs

The reactivity with pure fluorine gas of a mixture of carbon nanodiscs and nanocones was investigated. The starting materials were the as-prepared mixture, which results from cracking of heavy oils, and the sample post-treated at 2700 °C in argon atmosphere in order to increase the graphitization degree. The effect of this graphitization on the resulting fluorinated carbons was highlighted in terms of structural and morphological features using ¹³C and ¹⁹F solid-state nuclear magnetic resonance, electron paramagnetic resonance, Raman spectroscopy, atomic force microscopy and scanning electron microscopy. These characterizations were used to explain the electrochemical properties of these materials when used as an electrode in a primary lithium battery.     

Electrochemical reaction of the SiMn/C composite for anode in lithium ion batteries

The SiMn-graphite composite powder was prepared by mechanical ball milling and its electrochemical performances were evaluated as the candidate anode materials for lithium ion batteries. It is found that the cyclic performance of the composite materials is improved significantly compared to SiMn alloy and pure silicon. The heat treatment of the electrodes is beneficial for enhancing the cyclic stabilities. The SiMn-20 wt.% graphite composite electrode after annealing at 200 °C has an initial reversible capacity of 463 mAh g⁻¹ and a charge-discharge efficiency of 70%. Moreover, the reversible capacity maintains 426 mAh g⁻¹ after 30 cycles with a coulomb efficiency of over 97%. The phase structure and morphology of the composite were analyzed by X-ray diffraction (XRD) and scanning electron microscopy. The lithiation/delithiation behavior was investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The composite materials appear to be promising candidates as negative electrodes for lithium rechargeable batteries.     

Synthetic carbons activated with phosphoric acid: II. Porous structure

Synthetic activated carbons were prepared by H₃PO₄ activation of a chloromethylated and sulfonated copolymer of styrene and divinylbenzene, using an impregnation weight ratio of 0.75 and carbonization temperatures in the 400-1000 °C range. Other impregnation ratios (0.93 and 1.11) were also used at a carbonization temperature of 800 °C. The porous texture of the resulting carbons was characterized by N₂ adsorption at −196 °C and CO₂ adsorption at 0 °C. All carbons exhibited a multimodal pore size distribution with maxima in the micropore and meso/macropore regions. Maxima in pore volume were attained at 900 °C for micropores and at 500 and 900 °C for mesopores. The mesopore volume was less sensitive than the micropore volume to changes in the impregnation ratio. It is concluded that the porous texture is not a prime factor in determining the outstanding cation exchange capacities of these carbons.     

High power supercapacitors using polyacrylonitrile-based carbon nanofiber paper

Porous carbon nanofiber paper has been obtained by one-step carbonization/activation of PAN-based nanofiber paper at temperatures from 700 to 1000 °C in CO₂ atmosphere. The paper was used as supercapacitor electrode without any binder or percolator. At low temperature, e.g., ?900 °C, nitrogen enriched carbons with a poorly developed specific surface area (S_BET ? 400 m²/g) are obtained. In aqueous electrolytes, these carbons withstand high current loads without a noticeable decrease of capacitance, and the normalized capacitance reaches 67 μF/cm². At 10 s time constant, the values of energy and power densities are 3-4 times higher than for activated carbons (AC) presenting higher specific surface area. By carbonization/activation at 1000 °C, subnanometer pores are developed and S_BET = 705 m²/g. Despite moderate BET specific surface area, the capacitance reaches values higher than 100 F/g in organic electrolyte. At high power densities, the nanofiber paper obtained at 1000 °C outperforms the energy density retention of ACs in organic electrolyte. The high power capability of the carbon nanofiber papers in the two kinds of electrolytes is attributed both to the high intrinsic conductivity of the fibers and to the high diffusion rate of ions in the opened mesopores.     

Carbon foam derived from various precursors

A series of carbon foams was developed by using low-cost precursors, such as coal, coal tar pitch and petroleum pitch. The properties of the resultant carbon foams cover a wide range, e.g., bulk density, 0.32-0.67 g/cm³, compressive strength, 2.5-18.7 MPa, isotropic and anisotropic microstructure, etc. The investigation of foaming mechanism and the relationship between properties and structure indicate that the fluidity and dilatation of the foaming precursors significantly affect the foaming performance and foam structure. Raw coal samples were foamed directly without pretreatment in this work. However, for the pitch based foaming precursor, a thermal pretreatment is necessary to adjust its thermoplastic properties to meet the foaming requirement. The mechanical strength of carbon foam is found to be related to not only the foam cell structure, but also the fluidity and anisotropic domain size of the foaming precursors. In addition, the micro and mesopore structure in carbon foam matrix was investigated by gas adsorption and it was found that it also affects the strength of carbon foam and is related to the fluidity of foaming precursor.     

Coal carbonization with addition of hydrochloric acid as a way of improving coke quality

The possibility to expand the base of raw materials for carbonization using more lower grade and noncoking coals has been examined. Plastometric indices of the parent coals (C=79.0-87.2 wt% daf): x, shrinkage of coal and y, thickness of the thermoplastic layer were determined. It was established that the addition of 1 M HCl to coal increases the thickness of the thermoplastic layer (y) of gaseous (C=82.7 wt% daf) and rich (C=87.2 wt% daf) coals by 15-20% and the strength of the solid carbonized residue from 64 up to 84% and from 92 up to 94 %, respectively. A comparative evaluation of gaseous (C=82.2-82.7 wt% daf) coal according the degree of its restorativity is given. The strength of the coke is obtained from untreated gaseous coal and with HCl additive in the temperature region of carbonization of 450-800 °C. It is established that the greatest increase of coke strength takes place in the temperature region of 550-750 °C. Data of X-ray diffraction show that structural changes take place at coal carbonization.