Coal, structure

R. A. Durie, ed.. The Science of Victorian Brown Coal Structure, Properties and Consequencesfor Utilisation, Butterworth Heinemann, Oxford, 1991. An excellent reference not only for Victorim Brown Coal, but for lignitic coals of the world. 

Coal, structure of, 517 Coal tar, compounds from, 517 Cocaine, specific rotation of, 296 structure of. 64, 916 structure proof of. 875 synthesis of, 915... 

Conversion of coal to benzene or hexane soluble form has been shown to consist of a series of very fast reactions followed by slower reactions (2 3). The fast initial reactions have been proposed to involve only the thermal disruption of the coal structure to produce free radical fragments. Solvents which are present interact with these fragments to stabilize them through hydrogen donation. In fact, Wiser showed that there exists a strong similarity between coal pyrolysis and liquefaction (5). Recent studies by Petrakis have shown that suspensions of coals in various solvents when heated to 450°C produce large quantities of free radicals (. 1 molar solutions ) even when subsequently measured at room temperature. The radical concentration was significantly lower in H-donor solvents (Tetralin) then in non-donor solvents (naphthalene) (6). 

The significance of the above-described work is that in all of the presently developing coal liquefaction processes, the initial step in the conversion is thermal fragmentation of the coal structure to produce very fragile molecules which are highly functional, low in solubility, and extremely reactive toward dehydrogenation and char formation. A more detailed discussion of the chemical nature of these initial products has been presented elsewhere (4). ... 

In catalytic coal liquefaction processes, reaction temperatures must be high in order to insure that thermal reactions disrupt the coal structure to the point that the catalyst can act on the products. 

The Effect of Coal Structure on the Dissolution of Brown Coal in Tetralin... 

The important elementary reactions of coal liquefaction are the decomposition of coal structure with low bond dissociation energy, the stabilization of fragments by the solvent and the dissolution of coal units into the solution. 

While, oxygen containing structures of coal must be playing important parts in the course of coal liquefaction. It will be key points that what kinds of oxygen containing structure are decomposed and what kinds of structure are formed in the course of reaction. It has been proposed (5,6) and recently stressed (2-11) that the units of coal structure are linked by ether linkage. 

Thermal Treatment of Various Aromatic Compounds. In order to study the reaction of coal structure, various aromatic compounds were chosen as the coal model and treated at 450°C. 

It has been often proposed that the units of coal structure are linked by ether linkages. Recently, Ruberto and his coworkers (7,8), Ignasiak and Gawlak (9) concluded that a significant portion of the oxygen in coal occurs in ether functional groups. 

These results strongly suggest that in coal structure the covalent bond of benzyl ethers composed of aliphatic carbon and oxygen will be entirely cleaved at temperatures lower than 400°C, and the covalent bond composed of aromatic carbon and oxygen will be considerably decomposed at 450°C, since the unit structure of bituminous coal is considered to be composed of polynucleus of several benzene rings. 

In outline of what follows we will begin by brief reference to previous work on coal liquefaction. The present approach will then be motivated from considerations of coal structure and hydro-gen-donor activity. A theoretical section follows in the form of a pericyclic hypothesis for the coal liquefaction mechanism, with focus on the hydrogen transfer step. Experiments suggested by the theory are then discussed, with presentation of preliminary results for hydrogen transfer among model substrates as well as for the liquefaction of an Illinois No. 6 coal to hexane-, benzene-, and pyridine-solubles by selected hydrogen donors. 

The present approach to the coal liquefaction mechanism evolved from contemporary knowledge of coal structure (e.g. 11,... 

The dialin donor solvents were also used directly in coal liquefaction studies. Inasmuch as details of coal structure are unknown, the present theory can only be tested in a qualitative way, as follows. First, if the liquefaction of coal occurs under kinetic control with hydrogen-transfer from the donor solvent involved in the rate-determining step, then we should expect the dialin donors to be more effective than the control solvent T.et-ralin (and also Dfecalin). This is suggested by the theory because the dialins possess higher energy HOMOs than Tetralin and... 

It is necessary to notify, that the critical analysis of the Flory theory application for the determination of molecular mass and the crossing density of the coal structure has been done in the Painter s works [16], Authors assert, that the possible formation of hydrogen bonds between the hydroxy groups of low-metamorphized coal has an important role here that is why, even a lot of empirical amendments introduction into calculations leads to obtaining the understated values of molecular masses of clusters. 

Advances in the understanding of coal structure and its evolution during devolatilization have led to the development of several coal network models... 

Solomon, P. R., Coal Structure and Thermal Decomposition, in New Approaches in Coal Chemistry, ACS Symposium Series No. 169 (B. D. Blaustein, B. C. Bockrath, and... 

One of the dominant issues in coal structure to re-emerge in the past decade is the two-phase concept of coal structure. A very spirited discussion of this topic was a feature of the 1989 symposium (48-52V Peter Given played a central role in the recent work on the two-phase concept, particularly in fostering the usage of the terms "mobile phase" and "macromolecular network" (23.53-551 and in organizing the "debate in print" (54V which has become a landmark papers in coal structure. In particular, the debate in print (24) was cited by all of die contributors to the 1989 discussion of the mobile phase (48-52V Given s work on the mobile phase was a... 

Meyers, R.A., Coal Structure, Academic Press, New York 1982. 

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