Texture Of Cokes Research Articles

Contribution to the study of copyrolysis. Correlation of additives analytical data with optical texture of resultant cokes

Experiments were made to correlate analytical data of co-carbonization additives with the optical texture of cokes. The fifteen additives are carbopitches low and high temperature, anthracene and chrysene oils (hydrogenated or not), petroleum pitches and an heavy petroleum oil. These are added at 10% (in weight) to the additives-coal blends (high volatile caking coal Merlebach France). The additives are characterized by physical chemical, spectroscopic and chromatographic methods providing 28 characteristic analytical data for each product. The mathematical treatment of the analytical data leads to a division of additives according to their co-carbonization reactivity (active or passive additive). The most relevant characteristics for this classification are : elemental analysis ; hydroxyl index IOH ; aromaticity factor (13C NMR) and chromatographic data. We also note that the sequence: plastometry of coal-additives blends and determination of the optical texture of resultant semi-cokes is a very convenient method to verify and/or to predict the influence of additives in co-carbonization. The analytical data of additives correlated with plastic properties of coal blends are : elemental analysis and chromatographic data.

石炭液化油蒸留残さの重質有機成分から得た炭素化生成物の性質

Organic heavy components from five kinds of coal liquid vacuum residues (CLVR) from the plant (0.1t/d) of NEDOL process were studied to obtain a basic information for their utilization to carbon materials. The textures of cokes from extracts of CLVR and crystallographic parameters of graphitized cokes were examined by means of a polarized-light microscope and X-ray diffractometer.Cokes from asphaltenes showed flow anisotropic textures and ones from preas-phaltenes showed mosaic textures, which increased in the anisotropic unit size of the texture with increasing rank of the raw coal. Graphitizability of asphaltenes was bet-ter than that of preasphaltenes. Graphitizability of preasphaltenes became better with higher rank of the raw coals.

The texture and strength of metallurgical coke

This study aimed to investigate the relationship between the tensile strength of metallurgical coke and both the textural composition of the carbon matrix and the porous structure of the coke, and further to assess the use of these structural features as bases of methods of coke strength prediction. The forty-four cokes examined were produced in a small pilot-oven from blended-coal charges based on six coals differing widely in rank. Their textural composition was assessed by incident polarized-light microscopy while pore structural parameters were measured by computerized image analysis allied to reflected light microscopy. The tensile strength of coke could be related to textural data with accuracy using several relationships, some of which were based on a model for the tensile failure of coke. Relationships between tensile strength and pore sturctural parameters were less successful, possibly because of difficulties associated with the measuring system used. Neverthless relationships involving combinations of pore structural and textural data were developed and investigated. It was shown that relationships between tensile strength and calculated textural data had promise as the basis of a method of coke strength prediction. Also, tensile strengths could be calculated from the blend composition and the tensile strength of the coke produced from component cokes. Both methods have value in different situations.

Development of coke texture by thermal pretreatment of petroleum residua

Thermal pretreatment of coker feeds at sub-carbonization temperatures can lead to considerable development of the optical texture of semi-cokes produced upon carbonization at 723 K. The extent of the development is dependent upon the nature of the residual feed and pretreatment time-temperature history. Under suitable pretreatment conditions, highly reactive feed components can be induced to react and self-stabilize. During subsequent carbonization, the slower processes required for the development of carbonaceous mesophase can then proceed relatively unhindered. These same reactive species are believed to give rise to the formation of shot coke in delayed coking and cause the production of other cokes with poorly developed mesophase.

Heavy oil from direct hydrogenation of a flame-coal as a raw material for electrode coke production

This paper presents a concept of the integration of coal liquefaction with ‘regular’ type electrode coke production. The characteristics of the parent coal, the heavy product of hydrogenation and its fractions as well as the physicochemical and textural properties of the carbonization product of heavy hydrogenated oil and its fractions are discussed. It was shown that the fractions boiling below 360 °C worsen the texture of coke and removal of these fractions from the purified raw hydrogenated oil by distillation improves the texture of carbon. However, such a modification of hydrogenated oil is not sufficient for fibrous coke production.

Carbonization in the tube bomb leading to needle coke: I. Cocarbonization of a petroleum vacuum residue and a FCC-decant oil into better needle coke

The cocarbonization of a Fluidized Catalytic Cracking decant oil (FCCDO) with a petroleum low sulfur vacuum residue (LSVR) was studied at a temperature range of 460 to 480°C by evaluating the qualities of coke lumps produced in a tube bomb in terms of their CTE and anisotropic development. The cocarbonization certainly improved the orientation of flow texture and CTE of the resultant coke, providing the smallest CTE as low as 0.10 × 10 −6/° C and 0.36 × 10 −6/° C at particular FCCDO/LSVR mixing ratios of 5 5 and 7 3 according to the respective carbonization temperatures of 460 and 480°C. The natures of bulk mesophase and gas evolution at the solidification stage for the axial-rearrangement of mesophase aromatic component, both of which essentially define the coke quality, are strongly influenced by the carbonization reactivities of blended feedstocks and carbonization conditions. FCCDO may moderate the carbonization progress of reactive LSVR and LSVR supply the sufficient gas evolution during the solidification, leading to excellent flow texture of axial arrangement. The formation of mosaic coke in the bottom part of the lump which may deteriolate the quality of the coke produced in a commercial coker appeared to be caused by the phase separation between the paraffin and asphaltene fractions. Such a separation at a early stage of the carbonization was found to be controlled by the blending and the carbonization conditions.

Coke properties and their microstructure Part II: Coke carboxyreactivity: Relations to their texture

Several methods for studying coke texture are used to foresee coke reactivity to CO 2. The polarizing optical microscope allows one to assess the differential reactivity of optical textures. The transmission electron-microscope (darkfield 002) permits evaluation of the most reactive cokes and to better foresee the total coke reactivity. The processing of the complementary data through discriminant factor analysis has led to a reliable reactivity prevision of the cokes.

Carbonization behaviour of transalkylated Taiheiyo coal

Transalkylation reactions of a non-coking coal, Taiheiyo coal, using alkyl acceptors, 9,10-dihydroanthracene (DHA) or naphthalene, have been carried out in the presence of super acid catalyst of trifluoromethane sulphonic acid. The carbonization behaviour of transalkylated Taiheiyo coal was studied with respect to mesophase formation. The development of optical texture in coke was affected strongly by the nature and quantity of alkyl acceptor introduced into the coal molecule. The variation in spin concentration of transalkylated coal during the carbonization reaction was monitored using high-temperature e.s.r. The improvement of the carbonization property of transalkylated coal was discussed in terms of the stabilization of radicals. A schematic model of the carbonization reaction of transalkylated coal is proposed on the basis of these observations.

Temperature dependence of 1H n.m.r. spectra for pitch fractions using a high temperature method

Coal tar and petroleum pitches and their solvent fractions were studied by high temperature 1H n.m.r. The chemical changes and molecular motion associated with the pyrolysis have been related to the size and shape of optical textures of the resultant cokes.

Influence of pitch additions on coal carbonization: Characterization of pitches

The technique of etching polished coke surfaces and examination by SEM was used to compare the abilities of a series of pitches to modify the carbon texture of cokes prepared from two low-rank coals. Cokes prepared from the pitches were similarly examined and a numerical texture index, the magnitude of which increased with increasing content of the larger textural components, was found to provide a useful measure of the ability of the pitches to modify the coke carbon texture.

Microtexture and structure of semi-cokes and cokes

During carbonization, before the semi-coke stage, parallel local orientation of polyaromatic structures occurs (local molecular orientation or LMO). The oriented species are usually classified in decreasing order by the extent of optical isochromatic areas and are studied at molecular range by means of transmission electron microscopy. A continuous series of microtextures exist from stiff and flat lamellae to crumpled and then porous microtextures according to a decreasing curvature radius of the sheets of polyaromatic structures. This continuous degradation of coke texture, related to a continuous decrease in the local molecular orientation, brings about a decrease in carbon graphitizability. It is shown that textural and structural variations of coke depend upon the functional groups linked to polyaromatic structures, these groups having antagonistic effects of either cross-linkage (oxygen or sulphur) or saturation (hydrogen).

Properties of graphitized pitch cokes: Influence of the precarbonization treatment of pitch on the formation of graphitic structure

X-ray analysis, an abradability test, and porosimetric measurements were used to study the effect of the original texture of pitch cokes on properties of graphitization products obtained by their thermal processing at 2100 °C. It has been established, from the interlayer spacing d 002, crystallite dimension L c , relative peak intensity I rel , and parameters of abradability, that the product F 2100 prepared from pitch coke with highly directional structure, obtained by two stage filtration of molten pitch during the pre-carbonizing treatment, was characterized by the properties most suitable for its intended purpose. Comparing them with the graphitization products of quinoline extract (QS), pitch coke from unprocessed pitch containing quinoline - insoluble (QI) substances, and of the petroleum coke, the evidence could be brought that the transition into the graphitic structure could be ‘thermally accelerated’, for the sample F 2100, by 200 to 250 K. There could be found, in all graphitized samples, a new conspicuous region of mesopores with maxima of radii of 7.5 or 22.5 nm, respectively, corresponding to slots formed during the destruction of the lamellar structure.

Carbonization of hydrogenated ethylene tar pitch; study of the pitch molecular compactness factor and coke optical texture

Compactness factors of aromatic molecules in hydrogenated ethylene tar pitch were calculated as a parameter to relate to properties of mesophase of the carbonization system. Compactness factors, φ, derived from structural analyses of hydrogenated ethylene tar pitch were also related to the size and shape of optical textures of resultant cokes. Hydrogenated ethylene tar pitches having values of φ 〉 0.5 gave cokes with flow type anisotropy and relate to formation of peri-condensed structures. The spin-lattice relaxation times, T 1, for the cokes derived from hydrogenated ethylene tar pitch, are related to their optical texture.

Development of anisotropic texture in co-carbonization of low rank coal with pitch-evaluation from hydrogen donor and acceptor abilities of coal and pitch

The extent of development of anisotropic texture in cokes prepared from various coals or blended coals in co-carbonization systems was assessed by using the ratio of hydrogen donor ability to acceptor ability. A parameter D/ A, corresponding to the amount of hydrogen transfer during carbonization in the system of blended coal and pitch additive has been proposed to give a measure of the aforesaid development of anisotropic texture in resultant cokes. In pitch A/non-caking coal systems, blending the pitch A with coal to a value of D/ A − 0.22, D/ A − 0.28 and D/ A − 0.40 gives mainly fine-granted mosaics, medium-grained mosaics and coarse-grained mosaics, respectively. The Gieseler plastometry and high-temperature 1H-NMR were also used to obtain informations about the mobility of the co-carbonization system. A good relation was found between D/ A, and the solidification temperature determined by the Gieseler plastometry. Such an approach based on the concept of D/ A parameter provides a guideline for selecting pitch as a modifier for low rank coal carbonization.

Hydrogen transfer reaction during carbonization of coal and pitch.

The extent of hydrogen donor and acceptor ability of the respective coals and pitches was evaluated experimentally. The hydrogen donor ability (Da) o f coal depends on coal rank (reflectance) and correlates with the development of optical texture in cokes. The mild oxidations of coal and coal blends were also characterized with respect to hydrogen donor ability. The extent of anisotropic texture in cokes from co-carbonization of Akabira coal with various pitch systems was assessed by using hydrogen donor and acceptor ability of coals and pitches. Materials with a value of D/A=0.12-0.14 produce fine grained mosaic texture [Mf].

Characterization of carbonization reaction of petroleum residues by means of high-temperature ESR and transferable hydrogen

An attempt has been made to characterize the carbonization reaction of petroleum residues through measurements of high temperature ESR, hydrogen donor ability and optical texture of resultant cokes. Good correlations were found between hydrogen donor ability and change in spin concentration. Residues forming cokes with large sizes of optical texture have a high ability as a hydrogen donor and show a low spin concentration at high temperatures. Similar results were obtained also for some model compounds. A model for the mechanism of carbonization is proposed on the basis of these observations.

Co-carbonization of hard coals and coal extracts 2. The co-carbonization of medium- and high-rank coals with extracts

Studies on the influence of anthracene coal extracts on the carbonization process of medium- and high-rank coals were undertaken. Extracts from flame coal (Int. Class. 900) and gas-coking coal (Int. Class. 632) were used as additives. The blends prepared from the examined coals and the extracts exhibited better coking properties than the parent coals. The addition of extract to the coals gave an increase in the microstrength of the resultant cokes. The effects of co-carbonization of coking coals with extracts were increases in the size of the optical texture as well as in the degree of structural ordering of cokes. In the co-carbonization of semicoking coal with addition of coal extracts, a reduction in the size of the anisotropic units and a decrease in the crystallite height of cokes were observed. No modification of the basic anisotropy of coke from anthracite by coal extract was observed. With increasing extract content in anthracite/extract blends there was an increase in the degree of structural ordering of co-carbonization products. Extract addition was unable to modify the behaviour of fusinite. Based on the results of investigation of the influence of coal extracts on the carbonization of different-rank coals, a division of coals according to the modification of the optical texture of coke is given.

Pitch coke structure and its transition into graphite: Influence of the separation process of quinoline-insoluble matter

It has been established that the texture of pitch coke depends on the pre-carbonization treatment of the pitch and the separation of the primary quinoline-insoluble matter (OI). Scanning electron microscopy was used to examine the texture of fracture surfaces of pitch cokes prepared from the raw pitch and from pitches deprived of their QI fractions by quinoline extraction or filtration, three basic structures, lamellar, globular and composite, being determined. The arrangement of the lamellar structure is affected by the method of separation of QI and results in different graphitizable products. In pitch, filtered at 350 °C, the first symptoms of lamellar arrangement were already observed at heat treatment ∗ > 450 °C .

低石炭化度炭の水素加圧炭化

Carbonization of low rank coal under high hydrogen pressure was studied. Our interest is to clarify the effects of hydrogen pressure and soaking time on the resultant cokes. The longer the: soaking time at 748 K under 5 MPa, the more extensive the development of anisotropic texture and the greater the size of optical texture. The effect of hydrogen pressure on the resultant cokes was found to be optimal at 5 MPa. However, no significant change in the anisotropic texture of the resultant cokes was observed when the hydrogen pressure was increased from 5 to 13 MPa.The effect of partial pressures of hydrogen on the carbonization reaction was also examined. When the partial pressure of hydrogen decreases, the extent of the anisotropic texture is reduced.The carbonization of Yubarishinko coaking coal was also carried out under high hydrogen pressure. The optical texture of resultant cokes for a hydrogen pressure of 8 MPa shows flow anisotropy.Moreover, the effect of selenium oxide catalyst on pressure carbonization was also studied. SeO2, which is especially effective in the early stage of carbonization, enhanced the mesophase development for Taiheiyo coal.

Enhancement of hydrogen transfer in petroleum residue with catalysts during carbonization.

The influence of the addition of metal oxide catalysts on transferable hydrogen in petroleum residue was studied by 1H-NMR technique with a particular focus on mesophase development. Solid catalysts such as SiO2-Al2O3, MoO3-TiO2 and β-Al2O3 decreased the transferable hydrogen from Wafra vacuum residue on heating up to 673K and reduced the size of optical texture of the resultant cokes. On the other hand, SeO2 markedly revealed the promotion of hydrogen transfer in vacuum residues and considerably enlarged the size of optical texture. The catalytic activity in vacuum residue/D2O systems over catalyst was investigated by D-NMR technique. Deuterium incorporation of D2O into petroleum residue in the region of aliphatic hydrogens was recognized with SeO2 catalyst, whereas exchange in the aromatic region was noted for SiO2-Al2O3 catalyst. Transferable hydrogen associated with the skeleton of hydrocarbons is one of the keys controlling the carbonization reaction of petroleum residues and pitches.