Semi-coke

Coals mesophase pitch coal chars coal tar pitch carbon mesocarbon microbeads, carbon fibers semi-coke, calcined coke activated carbons premium cokes, carbon fibers, binder and matrix... 

Fig. 12. A, Schematic representation of parallel arrays of polynuclear aromatic hydrocarbon molecules in a mesophase sphere. B, a) isolated mesophasc spheres in an isotropic fluid pitch matrix b) coalescence of mesophase c) structure of semi-coke after phase inversion and solidification.

Solid Anthracite coal bituminous coal lignite peat wood Coke charcoal petroleum coke breeze semi-coke (low-temperature coal distillate) pulverized coal... 

Carbonaceous solids appear as a result of retrogressive reactions, in which organic thermal fragments recombine to produce insoluble semi-cokes (59,65). Coke formation is observed during liquefaction of all coals and its extent can vary widely according to the coal, the reaction solvent, and reaction conditions. The predominant inorganic species produced during the process of coal... 

For these types of reactor solids, the carbonaceous solids content varies usually from about 20 to 40%. The components of these solids are listed in Table VII. Optical examination of the solids has shown that they are primarily composed of mixtures of semi-cokes formed during liquefaction by retrogressive reactions with chars derived from macerals. Unreacted macerals comprise only a small fraction of these solids (65,74,75). 

Pitch-like solids and isotropic semi-cokes Anisotropic semi-cokes... 

The following natural precursors have been selected for KOH activation coal (C), coal semi-coke (CS), pitch semi-coke (PS) and pitch mesophase (PM). An industrial activated carbon (AC) was also used. Activation was performed at 800°C in KOH with 4 1 (C KOH) weight ratio, for 5 hours, followed by a careful washing of the samples with 10% HC1 and distilled water. The activation process supplied highly microporous carbons with BET specific surface areas from 1900 to 3150 m2/g. The BET surface area together with the micro and the total pore volume of the KOH-activated carbons are presented in Table 1. The mean micropore width calculated from the Dubinin equation is designed as LD. 

High porosity carbons ranging from typically microporous solids of narrow pore size distribution to materials with over 30% of mesopore contribution were produced by the treatment of various polymeric-type (coal) and carbonaceous (mesophase, semi-cokes, commercial active carbon) precursors with an excess of KOH. The effects related to parent material nature, KOH/precursor ratio and reaction temperature and time on the porosity characteristics and surface chemistry is described. The results are discussed in terms of suitability of produced carbons as an electrode material in electric double-layer capacitors. 

Materials used in the activation with KOH include high volatile bituminous coal C, coal semi-coke CS, pitch mesophase PM, pitch semicoke PS and commercial activated carbon AC. The semi-cokes CS and PS were produced by the heat treatment of corresponding parent materials at 520°C with a heating rate of 5°C/min and 2 hours soaking time. The preparation of mesophase PM comprised the soaking of coal-tar pitch at 450°C for 7 h with a continuous stirring. All the treatments were performed under argon in a vertical Pyrex retort of 45 mm diameter. 

Varying KOH ratio in the mixture is a very effective way of controlling porosity development in resultant activated carbons. The trend in the pore volume and BET surface area increase seems to be similar for various precursors (Fig. la). It is interesting to note, however, a sharp widening of pores, resulting in clearly mesoporous texture, when a large excess of KOH is used in reaction with coal semi-coke (Fig. lb). Increase in the reaction temperature within 600-900°C results in a strong development... 

The treatment of semi-coke or mesophase (3 1 mixture) for 2 h at 600°C gives a material of pore volume VT about 0.7 cm3/g and surface area Sbet about 1700 m2/g which is typically microporous with rather narrow micropores (average size LD below 1.2 nm). Activated carbons produced within the temperature range of 700-800°C have fairly similar porosity characteristics, VT about 1 cm3/g and Sbet near 2500 m2/g. It is interesting to note that within the wide temperature range of 600-800°C the bum-off is at a reasonably low level of 20-23 wt%. 

Innovatory boronated carbons (manufactured in the Institute of Chemistry and Technology of Petroleum and Coal, Wroclaw University of Technology, Poland) were obtained by co-pyrolysis of coal-tar pitch with a pyridine-borane complex. In the first stage of pyrolysis (520°C) the so-called semi-coke is obtained. Further carbonization at 2500°C leads to obtaining boron-doped carbonaceous material (sample labeled 25B2). 

Coals coal chars semi-coke, calcined coke activated carbons... 

It can also identify texture of the semi coke formed as illustrated in Figure 6. If a binder is used with a coal, the Plastofrost technique can determine the coal-binder interaction and the texture of coke formed from the binder phase. Although not considered in studies undertaken at Waterloo, the axial location of the thermocouples in the sample holder makes the Plastofrost procedure capable of measuring coal-coke conductivity as a function of coal, temperature and compaction pressure, with just a modest redesign of the heating slab. 

Carbonization of the oxidized Phalen Seam coal at 550°C resulted in a non-agglomerated char. Dilatation and FSI results for this coal are given in Table II and confirm its non-coking character. The semi-coke obtained from dilatation experiments had an isotropic structure, as shown in Figure 1. 

Oxidized Phalen Seam coal hydrogenated at 450°C for 3 hours at different hydrogen pressures gave the dilatation results presented in Table III. Optical micrographs of the semi-cokes obtained from dilatation experiments are shown in Figures 5 to 8. 

A severely weathered bituminous coal from eastern Canada was treated by thermal hydrogenation under various reactor conditions. The coking properties of this coal were found to be restored under appropriate hydrogenation conditions. The semi-coke of the hydrogenated coal exhibited an anisotropic coke structure. The size of the anisotropic domains in the semi-coke was found to depend on reactor temperature and hydrogen pressure during hydrogenation. 

Semi-coke, or coke ash residue. This waste material accumulates when oil shale is retorted. The residues and their leachates contain organic contaminants, most importantly phenolic species, for example, phenol, cresols, xylenols, and resorcinols (Raidma 1994 Kahru et al. 1999). 

Fig. 5. View of two mounds of semi-coke in the vicinity of Kivioli. The mound in the foreground is about 100 m tall (Photo Courtesy L. Michelson, from http //virumaa.kolhoos.ee/discuss/msg).

Tabic 7. Chemical nrm/rusifrni of semi-coke and ash tensie from Kividli. KoiuUi-Jiirve. ami Nan o areas in Estonia... 

Elements Unit Kivjoli semi-coke Kuhtla-Jiirvc Narva ... 

Fresh < 20 y old >40 y old Semi-coke fresh Ash front powerplant Ash from cyclone Ash from filter... 

As regards organic contaminants, leachates from semi-coke contain compounds such as phenols, for example, cresols, resorcinols, and xylenols, which occur at mg/L concentrations. Indeed, Kahru et al. (2002) found total phenols at concentrations up to 380 mg/L in semi-coke dump leachates. Phenols also volatilize from such leachates, depending on temperature and pH (Kundel Liblik 2000). Atmospheric phenol concentrations of 4-50 xg/m3 have been observed in the proximity of leachate ponds (Koel 1999). Generally, aliphatic hydrocarbons, carboxylic acids, and organo-nitro and organo-sulpho compounds do not occur at elevated concentrations in leachates from Estonian semi-coke (Koel 1999). 

Retorting of oil shales to produce shale oil results in wastes (condensate water and solid semi-coke residue) that are heavily contaminated with organic compounds, especially phenolic compounds. Semi-coke leachate is typically alkaline (Kundel Liblik 2000) and can contain several hundred mg/L phenol in Estonia, in addition to potentially toxic heavy metals and trace elements, for example, As, B, F, Mo, and Se, which might be mobilized during leaching by water. Volatilization of phenols from leachate lagoons can also impact atmospheric quality. 

Arro, H., Prikk, A., Pihu, T. Opik, I. 2002. Utilization of semi-coke of Estonian shale oil industry. Oil Shale, 19, 117-125. 

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