CO2 separation by carbon molecular sieve monoliths prepared from nitrated coal tar pitch

The objective of the present work is to develop a simple procedure, which avoids the need of a binder, to obtain activated carbon monoliths from a waste precursor (coal tar pitch) suitable for CO₂ capture and/or separation. The main task of this process consists of a nitration process of the coal tar pitch. This nitration step over the coal tar pitch is characterised by different techniques, such as infrared spectroscopy and thermogravimetric analysis. The nitration treatment produces the oxidation of the pitch molecules, leading to hydrogen consumption and generating oxygenated and nitrogenated surface complexes. As a consequence of this oxidation, nitrated coal tar pitch is an infusible material, which allows the carbonization of monolithic pieces avoiding their fusion. Decomposition of these surface complexes during the carbonization of monoliths generates narrow microporosity, which is suitable for CO₂ capture from gas streams at room temperature. The molecular sieving properties of these materials are studied by CH₄ and CO₂ adsorption kinetics.     

煤沥青改性后流变性能的变化分析

为了探讨对苯二甲醛(TPA)对煤沥青改性后流变性能的变化,采用旋转黏度计测定了煤沥青及TPA改性的煤沥青的表观黏度,研究了表观黏度与温度的关系;采用示差扫描量热法研究了煤沥青和TPA改性的煤沥青的热行为。结果表明,TPA改性的煤沥青的黏度与温度的关系曲线呈现W型,在200℃～225℃处于低黏流区,表观黏度值200mPa.s～400mPa.s,可以作为浸渍剂煤沥青使用;TPA改性的煤沥青在高于225℃时,表观黏度值迅速上升;TPA改性的煤沥青在低黏度区域具有较低的活化能,这对煤沥青的浸渍工艺有益。     

Étude des phénomènes de mouillabilité du carbone par le brai liquide

One of the processes used in the manufacture of carbon/carbon composites makes use of impregnation with pitch of a multidirectional structure of carbon rods made of carbon fibres at high temperature followed by carbonization under high pressure. A densification of the composite is obtained by repeated impregnations.Since the mechanical properties of the composites must likely depend on the quality of the interface formed between the carbon rod and the liquid pitch matrix, the wetting properties of pitches of various origins and properties (Table 1) were studied for several carbon rods (Table 2). A tensiometric method based on the weight of pitch lifted during immersion of the carbon rod at 350°C was used (Fig. 1).Measurements of the surface energy of the pitches in the liquid state at 350°C (Table 3) and in the solid state at room temperature (Table 4) show that the surface energy is practically independent of the origin of the pitch and that the surface polarity of the pitch is negligible. On the contrary, the values of the contact angle at 350°C is higher for the petroleum pitch No. 1 than for the coal tar pitches (Table 5).The wettability criteria, i.e. the spreading coefficient S and the wetting tension τ, derived from the measured surface energy and contact angle, confirm the lower wetting ability of the petroleum pitch (Fig. 2). These criteria may explain why the densification process (number of impregnations and carbonization cycles necessary to reach an apparent density of the composite of 1.90) is much more difficult with petroleum pitch. On the contrary, the adhesion criterion factor, expressed as the reversible energy of adhesion between the liquid and the solid at 350°C, has the same value whatever the origin of the pitch. Since the degree of adhesion might influence the quality of the carbon/carbon interface in the composite, the same value of the adhesion criterion factor may explain why all composites, at equivalent density, show about the same compression and torsion strengths.The difference between the wettability and adhesion for the pitches of different origins is due to the difference in the spreading pressure π; this quantity measures the decrease of the surface energy of the carbon rod resulting from the adsorption of the pitch vapor. The calculations reveal that, whatever the surface energy of the carbon rod, the petroleum pitch leads to a larger reduction of the surface energy of the solid than the coal tar pitches (Fig. 3).The wettability and adhesion criteria adopted in this study seem to (at least to a first approximation) explain the dependence of the mechanical properties of the carbon/carbon composites on the type of pitch and on the processing conditions.     

高温煤焦油沥青黏结剂碳化固结作用在炭质型材中的应用与研究进展

高温煤焦油沥青（high temperature coal tar pitch,HTCTP）具有优良的润湿性和黏结性,可用作黏结剂。HTCTP黏结剂能与炭质颗粒物料产生良好的固结作用,因此在不同类型炭质型材的制备中获得广泛的应用与研究,HTCTP高温过程的黏结性能及碳化固结作用效果决定了炭质型材的机械强度和理化性能。本文综述了HTCTP作黏结剂制备炭质型材的一般工艺过程和相关研究进展,梳理了不同应用领域对HTCTP碳化固结作用的共性机制和个性特点,总结了HTCTP的性能影响因素及碳化固结作用机理。通过分析HTCTP不同组分在碳化固结过程中的作用及转化过程,揭示HTCTP碳化固结作用与炭质型材机械强度的关联机制及影响碳化固结强度的关键因素,提出强化HTCTP碳化固结作用的措施,提升HTCTP黏结剂在炭质型材制备中的应用效果。     

炭/炭复合材料用浸渍剂煤沥青研究进展

本文介绍了炭/炭复合材料用浸渍剂煤沥青的结构组成与性能特点,分析了影响煤沥青浸渍性能的关键因素,总结对比了近几年浸溃用煤沥青改性方法的优缺点.指出煤沥青的开发和生产应该兼顾残炭率、流动性、黏度和软化点等因素,从而减少浸渍次数,降低炭/炭复合材料的生产成本.     

改性煤沥青浸渍增密C/C复合材料的研究

为降低C／C复合材料制造成本,采用表面活性剂对煤沥青进行改性．实验结果表明,加入少量表面活性剂后,煤沥青的软化点、黏度等流变性能得到较大幅度的改善,而残炭率变化不大,同时QI含量降低、颗粒变小、渗透率增大．以改性后的煤沥青为浸渍剂对C／C复合材料进行增密处理,经六次浸渍一炭化后,C／C复合材料的密度可达到1．61g／cm^3以上．     

贫煤与煤沥青共炭化研究

进行了不同配比的煤沥青和贫煤的共炭化研究,研究表明,煤沥青与贫煤共炭化时的相互作用是物理融合和化学相互作用的共同作用。其中物理融合表现在使焦炭界面结合状态改善,化学相互作用表现在煤沥青使贫煤的炭化性能发生变化。随煤沥青配比的增加,配煤黏结性有较大改善,焦炭OTI值增大,ISO值减小。煤沥青通过增大焦炭光学组织各向异性程度,使焦炭的反应性降低,反应后强度提高。     

Production of petro/coal tar pitch by joint distillation of coal tar and heavy pyrolytic oil

The properties of petro/coal tar pitch and distillate fractions obtained in the joint distillation of coal tar and heavy pyrolytic oil from ethylene production are described. The petro/coal tar pitch is particularly reactive in heat treatment and air-blowing. The petro/coal tar pitch may be used as less carcinogenic binder and impregnating electrode pitch.     

煤沥青基功能碳材料的研究现状及前景

我国煤沥青资源丰富,但深加工技术落后,产品附加值低,实现煤沥青高附加值利用是亟待解决的重大课题。本文介绍了以煤沥青为原料合成高性能功能碳材料的主要技术,重点阐述了以煤沥青为原料制备中间相沥青、多孔碳材料、碳纤维、二维纳米碳材料及碳基复合材料的研究进展。分析表明,高芳香性和高缩合度分子结构所引起的强π-π相互作用是阻碍煤沥青基高性能功能碳材料设计合成的瓶颈问题。通过催化聚合、氧化、共热解等技术手段可有效改善煤沥青分子结构及其物理、化学性质。结合模板复制、物理/化学活化、界面诱导以及催化石墨化等技术可实现多种功能性碳材料结构设计与表面化学性质调控。发展煤沥青分子结构调控新技术作为改善煤沥青基碳材料性能的重要策略,需要系统深入研究。     

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.     

Resonant frequency study of tensile and shear elasticity moduli of carbon fibre reinforced composites (CFRC)

The dynamic elastic properties are important characteristics of composite materials. They control the vibrational behaviour of composite structures and are also an ideal tool for monitoring of the development of CFRCs’ mechanical properties during their processing (heat treatment, densification). The present studies have been performed to explore relations between the dynamic tensile and shear moduli and some structural features (viz., fibre fraction, fibre type, porosity, weave pattern of woven reinforcement) of various unidirectional or bi-directional fibre reinforced carbon/carbon composites, made out of PAN- or pitch-based fibres as reinforcements and phenolic resin or coal tar pitch as matrix precursors. The dynamic tensile and in-plane shear moduli were determined from resonant frequencies of a beam with free ends. The longitudinal dynamic Young’s modulus of unidirectional CFRC composites – besides its dependence on the original fibre modulus and fibre volume contents – also reflects changes induced in matrix and fibres by heat treatment. The in-plane shear modulus does not depend on the fibre type but there exists its distinct tendency to increase with increasing fibre fraction. For bi-directionally reinforced composites, the longitudinal tensile modulus is more sensitive to the fabric weave pattern than to the fibre type. Tensile modulus of diagonally cut specimens and in-plane shear modulus of longitudinally cut ones are mutually correlated and, therefore, simultaneously controlled by densification steps and graphitisation heat treatment.     

Influence of oxidative stabilization on the electrochemical behaviour of coal tar pitch derived carbons in lithium batteries

A commercial coal tar pitch was thermally treated at 430 °C for 4 h and then submitted to hot filtration in order to separate the isotropic phase from the mesophase developed during the treatment. Each phase was then oxidatively stabilized in order to preserve its structure during carbonization and then carbonized at temperatures ranging from 700 to 1000 °C. The effect of the microstructure, particle morphology and chemical composition of the carbons and also the influence of their carbonization temperature on the electrochemical behaviour as electrode materials in lithium cells were studied.Galvanostatic cycling of lithium test cells using the carbon materials as positive electrodes showed the improvement of the electrochemical performance in both isotropic and anisotropic phases by stabilization with air previous to carbonization. More subtle differences between isotropic and anisotropic samples were evidenced and interpreted in terms of their textural properties. Moreover, the electrochemical impedance spectroscopy (EIS) has been demonstrated to be an interesting technique to elucidate the changes occurred in the electrode interfaces when these coal tar pitch based carbons are cycled.     

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。     

Mechanical behavior of two-dimensional carbon/carbon composites with interfacial carbon layers

Effect of interfacial carbon layers on the mechanical properties and fracture behavior of two-dimensional carbon fiber fabrics reinforced carbon matrix composites were investigated. Phenolic resin reinforced with two-dimensional plain woven carbon fiber fabrics was used as starting materials for carbon/carbon composites and was prepared using vacuum bag hot pressing technique. In order to study the effect of interfacial bonding, a carbon layer was applied to the carbon fabrics in advance. The carbon layers were prepared using petroleum pitch with different concentrations as precursors. The experimental results indicate that the carbon/carbon composites with interfacial carbon layers possess higher fracture energy than that without carbon layers after carbonization at 1000°C. For a pitch concentration of 0.15 g/ml, the carbon/carbon composites have both higher flexural strength and fracture energy than composites without carbon layers. Both flexural strength and fracture energy increased for composites with and without carbon layers after graphitization. The amount of increase in fracture energy was more significant for composites with interfacial carbon layers. Results indicate that a suitable pitch concentration should be used in order to tailor the mechanical behavior of carbon/carbon composites with interfacial carbon layers.     

Reactivity and related microstructure of 3d carbon/carbon composites

Four carbon/carbon composites fabricated with either PAN fibers or coal tar pitch fibers were examined. Detailed analysis of composite properties and structure included total surface area by Kr adsorption at 77 K, active surface area, porosity, crystallite parameters, as well as SEM and optical microscopic observations. Rates of composite gasification were measured at 1123 K in 3.1 kPa of steam. Under these experimental conditions the composites fabricated with PAN fibers are roughly three times as reactive as those fabricated with pitch fibers. Microscopic examination of the composites provides detail on two different microstructures for each fiber and respective composite. Binder associated with the fibers is influenced by the fiber microstructure, and a continuation of structure is developed throughout the composite body. Even though the fiber fraction is only approximately 50% of the composite by weight, it is clear that fiber microstructure influences overall composite microstructure and, hence, composite physical properties and subsequent composite gasification behavior.     

以煤焦油沥青为原料制备高性能活性炭的研究

以煤焦油沥青为原料,使用KCNS溶液活化处理,选择适宜的工艺条件,制备出优质的活性炭。讨论了煤焦油沥青热处理温度、中间相沥青的粒径、KCNS溶液的浓度、KCNS溶液与中间相沥青的液固比、炭化温度、炭化时间、活化温度、活化时间等主要因素对活性炭性能的影响。结果表明,在该适宜的工艺条件下制备的活性炭,强度为90.8%,比表面积为2 601.5 m2/g,吸碘值为2 217.0 mg/g,吸苯值为1 099.3mg/g,吸亚甲基蓝值为397.8mg/g,产品性能优良。     

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.     

Rheological characteristics of coal tar and petroleum pitches with and without additives

An extensive study of rheological characteristics of coal tar and petroleum pitches with and without additives, namely, petroleum coke, natural graphite and carbon black has been made. It is found that all pitches, pure or mixed with a carbon additive are not Newtonian as reported in the literature, but behave Theologically as Bingham plastics with certain yield stress and plastic viscosity at all temperatures of measurement between 85–180°C. The yield stress and plastic viscosity both decrease with increase in temperature of the pitch. A pure petroleum pitch having the same softening point as that of a coal tar pitch is found to have a lower viscosity compared to that of the latter at all temperatures of measurement. This suggests that the criterion of softening point as a measure of suitability of a coal tar pitch binder in the manufacture of artificial carbon is not sufficient for petroleum pitches. Addition of ten parts of carbon black by weight of pitch results in a considerable decrease in viscosity change with temperature of the coal tar pitch compared to almost insignificant change in the case of the petroleum pitch of the same softening point. However, the addition of petroleum coke or natural graphite makes the pitch more viscous but does not change the temperature dependence of viscosity of either of the two types of pitches. The implications are discussed.     

Microstructure of carbon/carbon composites reinforced with pitch-based ribbon-shape carbon fibers

Carbon/carbon composites were prepared with ribbon-shape pitch-based carbon fibers serving as reinforcement and thermosetting PFA resin and thermoplastic pitch as matrix precursors. The composites were heat treated to 1000, 1600 and 2700 °C. Microstructural transformations taking place in the reinforcement, carbon matrix, and the interface were studied using polarized optical and scanning electron microscopy. The fiber/matrix bond and ordering of the carbon matrix in heat-treated composites was found to vary depending on the heat treatment temperature of the fibers. Stabilized fiber cleaved during carbonization of resin-derived composites. In contrast, fibers retain their shape during carbonization of pitch matrix composites. Optical activity was observed in composites made with carbonized fibers; the extent decreases with increased heat treatment of the fibers. Studies at various heat treatment temperatures indicate that ribbon-shape fibers developed ordered structure at 1600 °C when co-carbonized with thermosetting resin or thermoplastic pitches.     

Carbon/carbon composites based on a polyimide matrix with coal tar pitch

Blending of coal tar pitch with a polyimide precursor based on acetyl derivatives of aromatic diamines during its synthesis leads to a homogeneous, highly thermostable matrix for carbon fibre reinforced composites. If the weight content of the pitch in the polyimide matrix does not exceed 40%, the mechanical properties (flexural strength, shear modulus and fracture toughness) of these composites are comparable to those of similar composites based on a pure polyimide matrix. Carbonisation and graphitisation of the composites with a properly blended matrix precursor leads to carbon fibre reinforced carbon composites with lower open porosity and higher density, elastic modulus and flexural strength than those of composites based on a pure polyimide matrix.