沥青球在空气中的不熔化及炭化

以空气为氧化介质，以０．５℃／ｍｉｎ的升温速度，在不同氧化终温及氧化时间下，对沥青球进行不熔化处理。利用元素分析及红外光谱研究了不熔化过程及其对炭化性质的影响；并利用ＴＧ－ＤＴＧ分析了沥青球的炭化过程。     

沥青球空气氧化不熔化的研究

采用空气氧化实现了０．１５４～１．００ｍｍ范围四种球径沥青球的不熔化。并应用差示扫描量热法ＤＳＣ谱图表征沥青球的不熔化程度。概述沥青球空气氧化增重和炭化收率间的关系，应用红外光谱初步探讨了沥青球空气氧化不熔化的机理。     

沥青纤维不熔化过程的研究—空气中沥青纤维的氧化

通过在空气中加热沥青纤维,分析纤维在不熔化过程中析出的气相组分,同时采用付里叶变换红外光谱测定不同氧化温度下纤维的特征基因,结合热重分析和元素分析数据,对沥青纤维在空气中的氧化进行了研究,将沥青纤维的氧化大致分为三个阶段。     

添加硫促进沥青球的不熔化

制备了不同硫含量的各种粒级的添加硫沥青球,并且选择合适的工艺条件进行氧化稳定化处理,结果表明：硫的添加能有效地促进沥青球的不熔化,缩短不溶化时间,对于０．６～１．０ｍｍ的沥青球,添加硫后使其不熔化时间由原来的３０ｈ以上缩短到３．１ｈ。     

添加硫沥青球不熔化机理的研究

为了阐明硫促进沥青球不熔化的原因,利用红外光谱（IR）、X－射线光电子能谱（XPS）、气相色谱（GC）及元素分析等方法研究了添加硫沥青球不熔化过程的机理,证明硫与沥青发生了反应,在沥青球内部形成了硫醇、硫酸、亚砜和砜等含硫官能团,促进了沥青分子的交联,提高了沥青的软化点．缩短了沥青球的不熔化时间。同时添加硫沥青球在不熔化过程中生成了H2S、COS、CS2等含硫组分。     

煤焦油沥青纤维的不熔化过程研究

以硫化法制得的高软化点（２５５ ℃） 煤焦油沥青为原料,通过熔融纺丝、氧化不熔化及炭化处理制备煤焦油基沥青纤维。探讨了不熔化终温对产品炭纤维抗拉强度的影响,借助于元素分析、气相色谱分析（ＧＡ）、ＤＴＡ、ＴＧ 和红外光谱分析等表征手段,对沥青纤维的不熔化过程进行了研究。结果表明：氧化终温强烈影响着炭纤维的抗拉强度;煤焦油沥青纤维在空气中的不熔化过程在低于３４０ ℃时表观上表现为恒重恒热,氧化反应主要发生于２００～３４０ ℃之间。     

煤沥青纤维的不熔化处理

采用空气预氧化方法进行煤沥青纤维的不熔化处理,用红外光谱定性描述了预氧化过程,并运用动力学进行了定量计算,求出了增重为3％时,不同直径的纤维在不同温度下所需的预氧化时间。     

不熔化炭化对大直径中间相沥青炭纤维结构和性能的影响

本文研究了大直径中间相沥青炭单丝的不熔化过程。不同恒温时间的不熔化过程中元素量的变化及其红外光谱分析指出了不熔化的原理。研究结果表明不同的不熔化条件使最终的大直径中间相沥青炭单丝的力学性能及横截结构产生了明显的差异;随着恒温时间的加长(直至恒温4h)以及升温速率的减少,大直径中间相炭单丝的取向度增加,此趋向与大直径中间相沥青炭单丝的强度变化相一致。     

沥青球的空气氧化稳定化反应特性研究

用 TGA、 DTG和 DTA法研究了石油沥青球和煤沥青球在空气中的热反应特性,研究了沥青球氧化稳定化的反应特点及其与沥青球组成与结构的关系。结果表明：石油沥青球由于与氧气的反应活性较强,更难于不熔化;增加萘含量和提高原沥青的软化点有利于沥青球的不熔化。     

煤沥青球的氧化不熔化过程特性

氧化不熔化过程是煤沥青基球状活性炭制备中的核心工艺,对其过程特性和动力学机理的认识是实现氧化过程工艺优化的关键。本文以煤沥青萃取球为原料,通过实验研究,重点探讨了粒径范围、升温速率和氧化温度对其氧化不熔化过程的影响,并确定氧化动力学参数及其反应机理函数。结果表明：氧化不熔化过程可分为轻组分热解、初步氧化、氧化增重和恒温氧化失重4个阶段。煤沥青球经过氧化不熔化后,C、H含量减少,O含量增加,表面光滑平整。减小粒径并选取合适的升温速率（0.25～0.5℃·min^-1）以及氧化温度（275～325℃）,更有利于氧化不熔化快速稳定地进行。粒径范围为0.3～0.6 mm的煤沥青球在升温速率为0.5℃·min^-1、氧化温度为300℃的条件下活化能最小,各个阶段的值分别为83.34、293.19、302.25和357.05 kJ·mol^-1。     

Chemistry of pitch carbonization

The conversion of pitch to carbon is a complex process encompassing a multitude of physical and chemical transformations among the many pitch components. Studies on both individual aromatic compounds and pitches have shown that polymerization through loss of side chains and hydrogen is the main chemical reaction. Molecular rearrangements are also prevalent. A continual increase in molecular weight through polymerization and loss of low molecular weight volatiles results in the transformation of pitch to mesophase, coke and ultimately carbon. Stable free-radicals are formed during both the polymerization and rearrangement processes. These various aspects are reviewed to develop a general mechanistic sequence for pitch carbonization.     

Oxidative coupling of methane in a bubbling fluidized bed reactor

The oxidative coupling of methane to higher hydrocarbons (C₂₊) was studied in a bubbling fluidized bed reactor between 700°C and 820°C, and with partial pressures of methane from 40 to 70 kPa and of oxygen from 2 to 20 kPa; the total pressure was ca 100 kPa. CaO, Na₂CO₃/CaO and PbO/γ-Al₂O₃ were used as catalytic materials. C₂₊ selectivity depends markedly on temperature and oxygen partial pressure. The optimum temperature for maximizing C₂₊ selectivity varies between 720 and 800°C depending on the catalyst. Maximum C₂₊ selectivities were achieved at low oxygen and high methane partial pressures and amounted to 46% for CaO (T = 780°C; P_CH4 = 70 kPa; P_O2 = 5 kPa), 53% for Na₂CO₃/CaO (T = 760°C; P_CH4 = 60 kPa; P_O2 = 6 kPa) and 70% for PbO/γ-Al₂O₃ (T = 720°C; P_CH4 = 60 kPa; P_O2 = 5 kPa). Maximum yields were obtained at low methane-to-oxygen ratios; they amounted to 4.5% for CaO (T = 800°C; P_CH4 = 70 kPa; P_O2 = 12 kPa), 8.8% for Na₂CO₃/CaO (T = 820°C; P_CH4 = 60 kPa; P_O2 = 20 kPa) and 11.3% for PbO/γ-Al₂O₃ (T 2= 800°C; P_CH4 = 60 kPa; P_O2 = 20 kPa).     

The bubble behavior in the gas-solids fluidized bed

The bubbling frequency in a gas-solids fluidized bed and its stochastic variation along the axial direction of the bed were determined by means of the capacitance method. The stochastic model proposed, more specifically a pure-death process, appears to be capable of describing the resultant data well.     

Solids mixing behavior in a nano-agglomerate fluidized bed

The nano-particles mixing behavior in a nano-agglomerate fluidized bed (NAFB) using R972, a kind of nano-SiO₂ powder, was investigated by the nano-particle coated phosphors tracer method. The axial and radial solids dispersion coefficients in this system were two orders of magnitude lower than those in fluid catalytic cracking (FCC) catalyst systems. The axial solids dispersion coefficient increased with increasing superficial gas velocities, and ranged between 9.1 × 10^− 4 and 2.6 × 10^− 3 m²/s. There was a step increase in the axial solids dispersion coefficient between the particulate fluidization regime and bubbling and turbulent fluidization regimes. As the superficial gas velocity increased, the radial solids dispersion coefficient increased gradually, from 1.2 × 10^− 4 to 4.5 × 10^− 4 m²/s. The much smaller D_a and D_r, compared to regular fluidized systems, is mainly due to the reduced density difference between the fluidized particles and fluidizing medium. To validate this, the solids dispersion coefficients in the NABF were compared with literature values for liquid-solid particulate systems in the particulate fluidization regime and FCC systems in the bubbling and turbulent fluidization regimes. The density difference between the fluidized particles and fluidizing medium and kinetic viscosity of the fluidizing medium, and other hydrodynamic factors like the superficial velocity of the fluidizing medium and the average diameters of the fluidized particles, were the key factors in the solids mixing in the fluidized beds. Empirical correlations are given to describe the results.     

Fluidized bed electrodes Part IV. Electrodeposition of copper in a fluidized bed of copper-coated spheres

The effective resistivity of the discontinuous metal phase in a fluidized bed copper electrode is derived from measurements of the potential distribution in the solution. The values are similar to those which have been previously observed for a fluidized bed of silver-coated particles and are compared with a theoretical expression based on a model of charge sharing during single particle elastic collisions. It is shown that the metal resistivity follows the predicted dependence on bed expansion and solution resistivity; the constant of proportionality is, however, different and this is attributed to a stagnation zone close to the feeder electrode. Such a stagnant zone is also indicated by comparison of the experimental and theoretically predicted distribution of potential in the metal phase.The diffusion controlled removal of copper from 10^–4 M copper sulphate is also shown to follow the theoretically predicted behaviour; the mass transfer coefficient indicates a high degree of turbulence within the bed. It is shown that scale-up factors of the order of 300 can be achieved in the processing of such dilute solutions. In view of the relatively high resistivity of the metal phase it is suggested that practical systems would arrange for a current and fluid flow to be at right angles to each other.Glossary A surface area per unit volume of electrode (cm^–1) - C double layer capacity (Farads cm^–2) - c ₀ concentration (moles cm^–3) - D diffusion coefficient (cm² s^–1) - F the Faraday (coulombs mole^–1) - I total current (A cm^–2) - i local current density (A cm^–2) - i _o exchange current density (A cm^–2) - K _m mass transfer coefficient (cm s^–1) - n equivalents per mole - R gas constant (volt coulomb deg^–1 mole^–1) - r particle radius (cm) - T absolute temperature - u superficial solution velocity (cm s^–1) - V voidage - v _p mean particle velocity (cm s^–1) - x distance from feeder in direction of current flow (cm) - electrochemical transfer coefficient for an anodic reaction - Young's modulus (dynes cm^–2) - Solution-metal diffusion layer thickness (cm) - electrode length normalized w.r.t. the static bed length - local overpotential (volts) - characteristic length (cm) - solution-particle density difference (g cm^–3) - _m effective specific resistivity of the discontinuous metal phase ( cm) - _s effective specific resistivity of the solution phase ( cm) - _m metal potential (volts) - _s solution potential (volts)     

Oxidative stabilization of pitch-polyacrylonitrile composite nanofibers electrospun by incorporating high-percentage inexpensive pitch

Polyacrylonitrile (PAN)-based composite nanofibers incorporated with high-percentage inexpensive pitch were successfully prepared by a simple electrospinning technique. Low-softening-point naphthalene pitch (NP) has the merit of high solubility but inevitably brings about preoxidation problem. Thus the influence of different preoxidation strategies on the morphology, composition, and structure of composite nanofibers was systematically investigated. The results show that there exists a ternary phase diagram consisting of PAN-pitch-solvent and a suitable apparent viscosity of homogeneous solution, which favors the smooth electrospinning and good adjustment for the diameter of carbon nanofibers (100–500 nm). The crystallinity, crystalline order, and electrical conduction of composite nanofibers are enhanced by incorporating graphitizable NP, for example, the electrical resistance of 50% NP-PAN composite nanofiber films after 800°C carbonization decreases about 30%. Both increasing the oxidation temperature and extending the oxidation time are beneficial to the oxidative stabilization of composite nanofibers with a suitable NP percentage below 50%. Gradient heating (240–340°C) and pressurized (0.08 MPa) preoxidations could accelerate the oxidative stabilization of composite nanofibers with a high NP percentage up to 110% and significantly shorten the oxidation time by half. Therefore, this study paves the road for facile preparation of cost-competitive carbon nanofibers with controllable morphology, structure, and properties.     

The axial hydrodynamic behavior in a liquid-solid circulating fluidized bed

Based on experimental results from a 7.6 cm I. D. and 3 m high liquid–solid circulating fluidized bed, the liquid–solid circulating fluidization regime has been separated into two zones: the initial circulating fluidization zone and the fully developed circulating fluidization zone. The distinct hydrodynamic behavior and the influence of particle properties in the two circulating fluidization zones have been studied. The overall flow structure in LSCFB, although still somewhat non–uniform, is much more uniform than that in a gas-solid CFB. Our experimental results also show that the axial flow characteristics and the regime transition can be strongly affected by the particle density. The stable operation range of the circulating fluidization system and the influences of some associated factors, such as the solids inventory and the particle density, were also investigated for the first time.