Optimization of carbonization conditions for needle coke production from a low-sulphur petroleum vacuum residue

The optimum carbonization conditions for converting a low-sulphur petroleum vacuum residue in a tube bomb in terms of pressure and temperature into better needle coke of low CTE, with less production of poor bottom coke, were studied by observation of the resultant cokes and sequential analyses of carbonization intermediates by means of solvent fractionation and gas evolution. Carbonization at 460°C under 15 kg cm^–2 G produced the best needle coke. The quality of the resultant needle coke was strongly influenced by viscosity changes of the system, the solidification range and gas evolution in the carbonization progress. The first two characteristics reflect the rates of condensation (such as QI formation) and devolatilization of soluble fractions, strongly influencing the growth of anisotropic units. The last characteristic reflects the pyrolytic cracking reaction to define the timing of gas evolution during carbonization, influencing the axial orientation of anisotropic texture as well as the porosity in the resultant coke. Both profiles varied very much, depending on the carbonization temperature. Finally, the formation of a bottom coke of fine mosaic texture is discussed from the viewpoint of the co-carbonization concept.     

Some factors for the high performances of mesophase pitch based carbon fibre

The tensile strength and Young's modulus of the carbon fibres prepared from naphthalene derived mesophase pitch were studied by varying the spinning temperature, heating rate and final temperature of the stabilization and graphitization temperatures to find the best properties obtainable from the particular pitch. The heating rate was very influential on the tensile strength of the fibre; a slow heating of 0.5° C min^–1, provided the highest strength, as high as 5 GPa at the optimum final temperature of stabilization. A higher or lower final temperature reduced the strength. Insufficient oxygen uptake or decomposition of oxygen groups at the surface of the fibre could induce defects, reducing the strength. In contrast, Young's modulus of the fibres was rather insensitive to preparation conditions. The carbonization and graphitization temperature influenced the mechanical properties as follows: the strength increased stepwise with the carbonization temperature, whereas the modulus increased sharply with the graphitization temperature. The structural factors most influential differed with these properties.     

Preparation of activated carbon fibers from polyvinyl chloride

Waste polyvinyl chloride (PVC) contains high content of chlorine, which is believed to liberate dioxine at its combustion. Efficient removal of chlorine from PVC achieved by selecting the heat-treatment conditions provided free-chlorine PVC based pitch by a two-stage heat-treatment process. The obtained pitch (softening point: 218 °C) was spun, stabilized, carbonized and activated to prepare activated carbon fibers (ACF) whose DeSO_x activity was tested preliminarily and found comparable to other ACF.     

Carbonization of coal-tar pitch into lump needle coke in a tube bomb

The carbonization of coal-tar pitches and their QI (quinoline insoluble)-free fractions was studied by evaluating their lump cokes produced in a tube bomb at various temperatures (470 to 550° C) and pressures (0 to 75 kg cm^–2 gauge). The lump coke from QI-free fractions had a comparable anisotropic development and coefficient of thermal expansion (CTE). The carbonization temperature and pressure were found to influence strongly the properties of the cokes. At the highest temperature of 550° C, the most appropriate pressure for the best needle coke was 15 kg cm^–2 G (gauge). Either higher or lower pressure increased the CTE value of coke. In contrast, at a moderate temperature of 500° C, the higher pressure produced the better coke. At the lowest temperature of 470° C, it took 10 h to complete the carbonization, and the lowest pressure allowed the best extent of uniaxial arrangement. Among the cokes prepared under the present conditions, the Carbonization at 500° C under 40 kg cm^–2 G produced the best needle coke with a CTE value as low as 0.1 × 10^–6° C^–1. The carbonization scheme leading into the needle coke is discussed for a better understanding of how the carbonization temperature and pressure cooperatively influence the quality of the resultant coke, in relation to the carbonization reactivity of coal-tar pitch.     

Predicting the strength reduction of particleboard subjected to various climatic conditions in Japan using artificial neural networks

Particleboard specimens were subjected to various climatic conditions in Japan, and the relationships between climatic factors and internal bond strength (IB) were investigated using multiple regression analysis (MRA) or artificial neural networks (ANN). At low- and middle-temperature sites, the IB predicted using MRA (IB_MRA) and ANN (IB_ANN) decreased linearly with increasing exposure time. In addition, at high-temperature sites, with increasing exposure time, IB_MRA decreased linearly, whereas IB_ANN decreased exponentially. The trend of IB_ANN was almost identical to that of the measured IB of the specimens subjected to various climatic conditions. Moreover, IB_MRA and IB_ANN for 1-, 3-, and 5-year exposures were predicted using nationwide climatic factors. The minimum IB is zero when the particleboard is deteriorated; however, negative IB was predicted using MRA when the exposure time increased in the high-temperature area. In addition, the IB for 1-year exposure in the low-temperature area near site 1 was higher than the initial IB of 0.833 MPa. MRA is not always valid because of the assumption of linearity. However, negative IB even for 5-year exposure in the high-temperature area and high IB even for 1-year exposure in the low-temperature area were not predicted using ANN. The IB reduction was predicted correctly using ANN, and the correct IB reduction could be mapped.     

Enhanced reactivity of some lignites by deashing pretreatment in hydrogen-transferring liquefaction under atmospheric pressure

The reactivities of five lignites were studied in the hydrogen-transfer liquefaction process undet atmospheric pressure, using a hydrogenated petroleum pitch (HA240). Although asphaltene yield from Yallourn brown coal was as high as 70%, other lignites showed inferior yields. Pretreatment in boiling 0.4N hydrochloric acid enhanced the liquefaction reactivity significantly to the extent that the asphaltene yield from Berga lignite increased to as much as 70%.     

Carbonization of coals to produce anisotropic cokes: 5. Structural factors of coals influencing carbonization properties

The carbonization properties are studied of two particular coals (Zontag Vlei and Metla coals) which are markedly different despite their similar coalification rank, maceral composition, and oxygen and exinite contents. These coals possess different structural features which influence their carbonization. A demineralizing pretreatment improves the properties of Metla coal. However, this is still inferior to the Zontag Vlei coal. O-alkylation of the Metla coal improves fusibility in single carbonizations and susceptibilities, equalling those of the Zontag Vlei coal. Preheat-treatment differentiates between the coals: Metla coal loses its susceptibility at lower temperatures. The chemical analyses of oxygen functionalities of both the original and preheated coals show that their hydroxyl groups behave differently in carbonizations at lower temperatures, indicating that oxygen functionality may be another influential factor. Hydrogen shuttling within the coal may be a third factor as it may remove the oxygen functionality.     

Oxygen distribution in the mesophase pitch fibre after oxidative stabilization

The oxygen distribution in the transverse section of 30m diameter mesophase pitch fibres after oxidative stabilization was measured by using EPMA (electron probe X-ray microanalyser) to clarify the progress of the oxidative reaction and diffusion of the oxidant during the stabilization. Oxygen was distributed in shallow gradients regardless of the stabilization time from the surface to the centre of the mesophase pitch (MP) fibres stabilized at 230° C, suggesting sufficient diffusion of the oxidant to the centre of the fibre at this temperature. In contrast, steeper gradients of distribution were observed in the MP fibres stabilized at 270° C although oxygen up-take of the centre increased steadily with the longer stabilization time to decrease the gradient. Much steeper gradients of the oxygen distribution were observed in the cross-sectioned surface of the fibres stabilized at 300° C for 15 and 30min. The gradient became much steeper with longer stabilization, suggesting some barriers in the deeply oxidized zone which may block the oxygen diffusion. The PVC-10 fibres, whose reactivity was enhanced by blending PVC pitch of 10wt%, showed steeper distributions of oxygen after the stabilization at 270° C comparing to those of the MP fibres stabilized under the same conditions. It showed steeper gradient with the longer stabilization time. In conclusion, stabilization at a lower temperature (230° C) allows relatively rapid diffusion of the oxidant into the centre of the MP fibre during rather slow stabilization but, a higher temperature of stabilization (at 300° C) and/or higher reactivity of the mesophase pitch accelerates the oxidation much more rapidly than the diffusion, providing a blockade zone for the oxygen diffusion near the fibre surface. The extensive oxidation may cross-link three dimensionally the mesophase molecules thus allowing no diffusion of oxygen among the molecules. Such diffusion control tends to provide skin-core structure in the carbonized fibre.It should be noted that fibre thinner than 10m showed no skin-core structure. Diffusion within 5m from the surface may be rapid under any conditions.     

Carbonization of coals to produce anisotropic cokes. 2. Up-grading of modification activities of petroleum process residues and their correlation with structural parameters

Modifying activities of petroleum pitches and up-graded pitches in the co-carbonization with a range of coals have been examined with the object of proposing an effective co-carbonization process for blast-furnace coke production. Up-grading of additives was attempted using thermal, acidic and oxidative reactions. Acidic reactions with aluminium chloride were most effective with lighter petroleum residues of initially poor modifying activity, this being attributed to dealkylation, ring-closure and ring condensation reactions. The relation between modifying activity and structural indices is discussed. The aromaticity (f_a) and the naphthenic ring number in the unit structure T_n,us can be used as appropriate parameters for the activity when the coking yield is taken into account.