精制沥青中间相热转化的研究

用程序升温对精制沥青中间相热转化过程进行研究，揭示了中间相转化的机理，发现了中间相热转化过程的规律。     

萘沥青的合成条件与其中间相热转化行为的关系研究

以萘为原料,采用AlCl3催化合成和热转化处理二步法制备了高软化点、低QI含量的优质萘系中间相沥青。通过分析表征不同条件下合成的萘沥青经热转化后所得中间相沥青的性质和中间相织构形态,重点研究了萘沥青的合成条件与其中间相热转化行为间的内在关系,以确定合成萘沥青的最佳工艺参数。结果表明,在合成温度240℃、合成时间6 h、催化剂用量10%的条件下合成的萘沥青在390℃恒温8 h后能得到100%的广域流线型的体中间相沥青,其软化点为244.6℃,QI含量仅为10.32%。     

精制沥青结构对中间相热转化过程的影响

采用Brown-Ladner法计算出沥青的结构参数,通过中间相热转化试验获得转化的特征温度和所得生焦的光学显微组分来分析精制沥青的结构对中间相热转化过程的影响.     

精制沥青中间相热转化的动力学计算与分析

用程序升温对中间相热转化过程进行动力学参数计算,并对计算结果作了简要分析。根据推导的动力学方程,计算出Sp1和Sp2的反应活化能,Sp2的反应活性大于Sp1,但在同一温度下,Sp1反应速率受温度影响的程度比Sp2大。这一结果对选择合适的精制沥青具有一定的指导意义。     

中间相热转化行为研究

研究了经预处理FCC油浆的组织、结构和组成变化对热聚合过程中生成中间相行为的影响,实验发现,原料经预处理去除了部分轻组分,体系稠环度增加,芳香度增大,有利于热聚合过程中中间相的形成.未经处理的原料只观察到了小球的出现与固化,而预处理FCC油浆可以观察到中间相小球出现、长大、融并及固化的完整过程.实验结果进一步说明油浆本身的组成、结构和性质对中间相形成有很大影响.同时观察到体系黏度变化和保护性气体的流动作用对中间相有序融并的影响.     

二乙烯基苯改性煤沥青的中间相转化行为研究

进行了二乙烯基苯(DVB)改性煤沥青的中间相转化行为研究．采用偏光显微镜研究DVB改性煤沥青的光学结构；采用FT-IR和元素分析研究改性煤沥青的热解过程．研究表明，改性煤沥青的光学组织结构显著改善，随交联剂DVB用量的不同，可得到超镶嵌(SM)、广域(D)和小域(SD)三种光学结构；随热解温度的升高，改性沥青中的甲基和亚甲基特征峰的吸收强度逐渐减弱，C／H原子比增加，芳构化程度提高．     

对甲基苯甲醛改性煤沥青的中间相转化行为

进行了对甲基苯甲醛（PMB）改性煤沥青的中间相转化行为的研究，采用FT-IR和元素分析研究改性煤沥青的热解过程；采用偏光显微镜研究PMB改性煤沥青的光学结构，研究表明，改性沥青含有大量的甲基和亚甲基，随热解温度的升高，改性沥青中的甲基和亚甲基特征峰的吸收强度逐渐减弱，C／H原子比增加，芳构化程度提高；此外，改性煤沥青的光学结构为广域（D）组织。     

两种煤焦油沥青恒温热转化过程研究

通过对两种煤焦油沥青恒温热转化过程的研究,得出了中间相转化的特征时间和动力学参数,试验表明,在中间相产率约１５％之前,主要产生中间相小球体的生成反应,活化能较高,而后期反应活化能较低。     

中间相沥青的调制及其性能研究

以沥青为原料,采用热缩聚法合成了一系列不同各向异性组分含量的中间相沥青(MP)。以不同各向异性组分含量的中间相沥青为原料,采用KOH活化法制备了中间相沥青基活性炭(MP-AC)。使用透反射偏振光显微镜对中间相沥青的显微结构进行静态观察,考察了不同恒温时间中间相沥青的收率和光学显微形态的变化,使用物理吸附仪对MP-AC的比表面积进行了考察。结果表明:反应温度在410℃,恒温6.5 h时可以得到各向异性组分含量约为100%的优质广域型中间相沥青;MP中各向异性组分含量的不同对MP-AC的比表面积影响不大。     

Modified characteristics of mesophase pitch prepared from coal tar pitch by adding waste polystyrene

The toluene soluble of coal tar pitch was carbonized with waste polystyrene. The properties of mesophase pitches were characterized using polarized light optical microscope, apparent viscometer, FT-IR, ¹H NMR and X-ray diffractometer. After adding the waste polystyrene into the toluene soluble of coal tar pitch, the soluble mesophase were was increased from about 9% to 52% and the mesophase pitches were changed from 74% with coarse mosaic texture to 100% with flow domain texture. The mesophase pitches were transformed from thixotropy to unthixotropy. By waste polystyrene added into the toluene soluble of coal tar pitch, the methylene group was increased a lot. The presence of more alkyl groups modified the characteristics of mesophase pitches and improved the assembly of mesophase pitch molecules.     

Rheostructural studies on a synthetic mesophase pitch during transient shear flow

The steady, shear viscosities of a synthetic mesophase pitch (Mitsubishi AR-HP) obtained from rate-sweep experiments at 0.1-10 s⁻¹ exhibited shear-thinning (region I) and plateau responses (region II), but displayed a hysteresis during the decreasing rate sweep. Transient tests revealed that the shear stress (and consequently the shear viscosity) displayed a local maximum and a minimum before approaching a steady state. Following steady flow at 1 s⁻¹, a reversal of flow direction or a very short interruption in flow did not lead to the maxima or minima in the transient shear stress, but the maxima and the minima reappeared in the transient stress after a rest time of ∼1000 s. An experimental protocol was developed to preserve the rheological samples, and their microstructure was characterized in three orthogonal planes for the initial and final states. The initial microstructure was found to have a weak, but preferred, orientation of mesophase layers in the radial direction of the rheometer cone-plate (due to the initial squeezing flow). The initial microstructure changed to a flow-aligned fibrous structure after shearing in the viscometric flow.     

A two-stage preparation of mesophase pitch from the vacuum residue of FCC decant oil

The preparation of mesophase pitch as a precursor for the high-performance carbon fiber from a vacuum residue of FCC-decant oil (FCC-DOVR) was studied, applying a two-stage heat treatment to improve the pitch yield as well as its liquid crystal properties. The present two-stage preparation consisted of the pressurized heat treatment (1–5 MP) of the first stage at 430–480°C and the successive heat treatment under 13–260 Pa at 430°C. Such a two-stage preparation increased the yield of the spinnable mesophase pitch of 100% domain texture with lower softening point to 45% from 22% by the single-stage one from the same feedstock. Spinning properties of the mesophase pitch were excellent to allow smooth spinning for longer than 15 min and random orientation of mesogen molecules in the tranverse section of the fiber perpendicular to the fiber axis. The chemistry of the two-stage preparation for the higher yield and better properties as the fiber precursor is briefly discussed.     

Chemical, microstructural and thermal analyses of a naphthalene-derived mesophase pitch

A detailed characterisation of a synthetic naphthalene-derived mesophase pitch, in its as-received state and during pyrolysis, has been performed. The study has been conducted by means of various techniques and with a particular attention to Raman microspectroscopy. The Raman spectra show features in common with the naphthalene precursor, i.e., a broad and complex band at 1150-1500 cm⁻¹ and a multicomponent G band at 1600 cm⁻¹. These features correspond to the vibration modes of the molecules of the pitch and more especially to the non-aromatic C-C bonds involved in alkyl groups, aryl-aryl bonds or naphthenic rings. The pyrolysis of the pitch into coke takes place within a narrow temperature range (480-500 °C) through the elimination of hydrogen and light alkanes resulting from the breaking of homolytic C-H bonds and naphthenic cycles, respectively. This process initiates a swelling of the pitch. The analysis of the Raman features shows that the structure of the pitch is only slightly affected within this temperature range. Conversely, significant structural changes of the material (as shown by the vanishing of the multicomponent bands at 1600 and 1150-1500 cm⁻¹) are evidenced beyond 750 °C, simultaneously with a hydrogen release and an increase of the true density. This phenomenon corresponds to the extension of the graphene layers of the coke and the formation of a distorted carbon network.     

Liquid crystal surface anchoring of mesophase pitch

Mesophase pitch, in common with other liquid crystalline substances, exhibits preferred angles of molecular orientation at its boundaries with other phases. These orientations, or surface anchoring states, are important because they influence the ultimate graphene layer arrangement in a variety of carbon materials where the pitch precursor encounters a composite filler, a free surface, a bubble cavity, or the surfaces of processing equipment such as a fiber spinneret. This paper presents experimentally determined anchoring states for two mesophase pitches at free surfaces, and on twenty solid substrates. Edge-on anchoring is found to be the most common state, occurring on the free surface, on some metals, on PTFE, and on all oxides with the exception of the lamellar material mica. The optical texture associated with the edge-on films is observed to be stable during carbonization up to 1200 °C. Face-on anchoring is observed on carbon graphene planes, mica and the metals Pt, Ni, and Ag. Trends in the data are discussed in terms of the strength of pitch/substrate intermolecular forces relative to π-π bonding between large discotic mesogens within the pitch. The implications for the structure and properties of carbon materials are discussed.     

A novel method to obtain a petroleum-derived mesophase pitch suitable as carbon fibre precursor

This paper studies a novel method for the preparation of mesophase pitches suitable as carbon fibre precursors. A series of thermally treated petroleum pitches with mesophase contents ranging from 10.8 to 52.2 vol.% was obtained from pitch A-240. Separation of the phases was initially attempted by hot filtration, a suitable method for separating the phases in thermally treated coal-tar pitches. Although filtration failed for the petroleum samples, the behaviour observed led to the development of a new separation method that consists in the sedimentation of the mesophase. This method, after optimisation, yielded pitches with mesophase contents up to 97 vol.%, which were easily spun into carbon fibres of reasonable mechanical properties.     

Analysis of the carbonization and formation of coal tar pitch mesophase under dynamic conditions

Thermokinetic analysis of three pitch samples was carried out: coal tar pitch obtained from light coke oven tar (P), mesophase pitch after 10.5 h (MP1), and mesophase pitch after 12 h (MP2) thermopreparation at 410 °C. The process was realized in a continuous system with a 10 kg mass being charged to the reactor. It was demonstrated using Kissinger’s law that the temperature criterion, the first-order thermokinetics and the calculated Arrhenius law parameters fulfill the isokinetic effect when the classical routes of thermokinetic analysis of the samples prepared under dynamic conditions (at three heating rates) are used, which makes the qualitative interpretation of differences between these samples difficult. An alternative solution was proposed using the relative rate of thermal decomposition. The temperature ranges of the chemical reactions leading to the formation of mesophase structures, as well as the temperature ranges of the coking processes of the Fixed Carbon phase, were determined.