Coal model

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. 

Note. In a recent paper, Miller and Stein have provided values for both C-C and C-0 bonds for a variety of coal model compounds, including bibenzyl and benzyl phenyl ether (11). Their rate constant for bibenzyl provides half-life values at 335°C and 400°C even larger than those discussed here, and it would seem on the basis of their data that at those low temperatures C-C scission in bibenzyl itself is too slow for thermal scission to be significant. 

A number of basic studies in the area of donor solvent liquefaction have been reported (2 -9). Franz (10J reported on the interaction of a subbituminous coal with deuterium-labelled tetra-lin, Cronauer, et al. (11) examined the interaction of deuterium-labelled Tetralin with coal model compounds and Benjamin, et al. (12) examined the pyrolysis of Tetralin-l-13C and the formation of tetralin from naphthalene with and without vitrinite and hydrogen. Other related studies have been conducted on the thermal stability of Tetralin, 1,2-dihydronaphthalene, cis-oecalin and 2-methylin-dene (13,14). 

CAMD modeling has been used in this study to compare and partially to differentiate several postulated bituminous coal models based on their physical structures, minimum energies, and other characteristics. It is clear from the folding of the CAMD structures after molecular dynamics (especially in Figures 3c and 4c) that simple two-dimensional representations cannot adequately represent the structure of coal. Inter-cluster bonding has a powerful influence on coal structure when three-dimensional models are employed. 

Solvent Effects During the Reaction of Coal Model Compounds... 

For the bituminous coal, most of this water is formed at temperatures below 400°C before any other products are observed. For the lignite, neither pyrolytic water nor more than a small amount of hydrocarbons (Figure 3) (7,8) is evolved until temperatures of around 600°-700°C are attained. This behavior supports the view, based on work with coal model substances (27), that water production from phenolic hydroxyl groups deprives the pyrolyzing coal of hydrogen which could otherwise stabilize hydrocarbon species (e.g., tar). 

To probe the presence of synergistic effects in more detail, experiments with polyethylene and coal model compounds have been carried out in our own laboratory. Tetradecane (C14H30) was used as a polyethylene mimic, and 4-(naphthylmethyl)bibenzyl (NBBM) was used as a coal model compound. Reaction temperatures were 693 and 773 K, and batch reaction times ranged from 5-150 min. Reactions of binary mixtures of tetradecane and NBBM revealed interactions between the reactants and synergistic effects. Tetradecane conversion was increased in the presence of NBBM, which was rationalized in terms of kinetic coupling. The internal carbon-carbon bonds of tetradecane have a higher... 

On the molecular level, coal is an extremely complex substance and in spite of extensive research in this area the exact structure of coal has yet to be determined (Chapter 10). Different authors have proposed various coal models from time to time. Broadly it is agreed that coal consists of heterogeneous polyaromatic clusters in a complex array resulting in a highly cross-linked macromolecular gel structure. Another opinion that coal has a highly associated structure also exists. 

A. Terentis, A. Doughty, and J. C. Mackle, Kinetics of pyrolysis of a coal model compound, 2-picoline, the nitrogen heteroaromatic analog of toluene. 1. Product distributions, J. Phys. Chem. 96(25), 10334-10339 (1992). 

E. Ikeda and J. C. Mackie, Thermal decomposition of two coal model compounds— pyridine and 2-picoline kinetics and product distributions, J. Anal. Appl. Pyrol. 34(1), 47-63 (1995). 

The hrst hve chapters (Part 1) present an overview of some methods that have been used in the recent hterature to calculate rate constants and the associated case studies. The main topics covered in this part include thermochemistry and kinetics, computational chemistry and kinetics, quantum instanton, kinetic calculations in liquid solutions, and new applications of density functional theory in kinetic calculations. The remaining hve chapters (Part II) are focused on apphcations even though methodologies are discussed. The topics in the second part include the kinetics of molecules relevant to combustion processes, intermolecular electron transfer reactivity of organic compounds, lignin model compounds, and coal model compounds in addition to free radical polymerization. 

Later studies showed that the mechanism of reactions, in particular ionic versus free-radical, could vary. Townsend [15] has studied the reaction of a series of coal model compounds (alkyl-aryl hydrocarbons and ethers) in supercritical water. For the hydrocarbons a free-radical pyrolysis route does not take advantage of the medium. However, for the ethers enhanced rates of reaction through a hydrolysis route occurs. As a result of different possible pathways, decomposition products of some organics in supercritical water have been shown by several workers to vary with solvent strength. In the absence of water, Pr(H20) = 0, pyrolysis is dominant and yields a variety of products including polycondensates. The main products of decomposition of neat methoxy... 

Mirrata S, Nomrrra M, Nakamura K, Kumagai H, Sanada Y (1993) CAMD study of coal model molecrrles. 

Density simirlation for four Japanese coals. Eneigy Fuels 7 469-472 Mrrrgich J, Rodriguez M, Aray Y (1996) Molecrrlar recognition and molecular mechanics of micelles of some model asphaltenes and resins. Energy Fuels 10 68-76 Nakamirra K, Mirrata S, Nomura M (1993) CAMD study of coal model molecules. 1. Estimation of physical density of coal model molecules. Energy Fuels 7 347-350 Olah GA, Molnar A (1995) Hydrocarbon Chemistry, John Wiley Sons, Inc. 

---