摘要:

Some aspects of the structure of coal are discussed. Emphasis is placed on the changes occurring during coalification and on the macromolecular structure of coal. The various forms of oxygen in coals are described, and the limitations to our knowledge of heteroatom functional groups are discussed. Some aspects of coal structure especially relevant to the chemical reactivity of coals are described. Much more must be learned about coal structure, both physical and chemical before realistic attempts to develop structure‐reactivity relationships are possible.

ISSN:0094-243X    

DOI:10.1063/1.32967

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Ample evidence from physicochemical experiments suggests that bituminous coals can be described as highly crosslinked and entangled networks of macromolecular chains of irregular structure. Theoretically these structures can be analyzed by statistical mechanical models considering non‐Gaussian distribution of the macro‐molecular chains along with departure from the Flory theories of crosslinked macromolecules. The models of Kovac (1978) and Peppas and Lucht (1979) have been developed in order to describe non‐extractable coal matrices and their behavior during swelling in appropriate swelling agents. The molecular weight between cross‐links Mcand the crosslinking density &rgr;xcan be determined for various solvents and equilibrium swelling ratios. Few experimental data are available to which these models can be applied. Thus, in view of these new theoretical models, experimental research must be directed towards the reexamination of extraction and swelling behavior of bituminous coals. Some of the important parameters to be determined for characterization of the physical structure of coals include the thermodynamic interaction parameter &khgr;, the crosslinking parameters Mcand &rgr;xand the molecular weight distribution of the extractable coal portion.

ISSN:0094-243X    

DOI:10.1063/1.32944

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Coal as viewed microscopically is seen to be composed largely of discrete organic components referred to as macerals. Each maceral responds differently in carbonization, and each develops into a particular form of carbon in the coke product and has its own characteristic effects on coke microstructure. A classification of macerals has been developed and a number of correlations of this classification with coking behavior and coke properties have been established. Examples of how this classification serves in coal‐blend formulation and for predictive purposes are given. Basic knowledge about the chemical and physical constitution of coal and of the mechanisms involved in the response of coal to process conditions is stressed as a requirement in the development of new coke‐making technology.

ISSN:0094-243X    

DOI:10.1063/1.32909

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

13C nmr spectra that approach high‐resolution quality can now be obtained on solids by using high‐power 1H decoupling (for eliminating the major line broadening due to1H‐13C dipole‐dipole interactions),1H‐13C cross polarization (for circumventing the13C T1bottleneck) and magic‐angle spinning (for eliminating line broadening due to chemical shift anisotropy).13C spectra with rather sharp lines are obtained for crystalline samples. For coals and other very complex mixtures, the occurrence of many different, but very similar, chemical architectures renders for most samples two rather broad resonances bands (the aromatic/olefinic carbon band and the aliphatic carbon band). Additional structural information can be obtained from the13C nmr spectrum if the coal has an unusually simple distribution of carbon bypes or if more sophisticated techniques are employed. Progress, limitations and propsects for solving important problems in coal science by the13C nmr technique are discussed.

ISSN:0094-243X    

DOI:10.1063/1.32910

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Protonated heteroatom functionalities (COOH, OH, Sh, NH) have a major impact on the chemical and physical properties of coal materials. Characterization of these functionalities will, therefore, be important to efficient development of new coal utilization technologies. Silicon‐29 NMR spectroscopy of the trimethysilyl derivatives of these functional groups is a powerful new tool for this characterization. Preparation of the trimethylsilyl derivatives is carried out in the NMR sample tube and the29Si NMR spectrum of the products is accumulated under conditions similar to those routinely used in13NMR. Studies on derivatized model compounds show that29Si chemical shifts are generally segraged into three regions characteristic of COOh, OH and SH, and NH functionalities. The29Si resonances of aromatic OH derivatives are further differentiated so that the major oxygenated components of coal liquids can be monitored as a function of processing and distillation conditions. Quantitative29Si NMR results are used to calculate total OH and COOH concentrations in several solutions. Comparison of these results with the elemental oxygen content permits an estimated of the percentage oxygen present in non‐derivatizable (e.g., ether) groups. The technique is illustrated using soluble coal liquid distillate fractions boiling in the range of initial boiling point to 1050°F (566 °C).

ISSN:0094-243X    

DOI:10.1063/1.32911

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

This paper provides an overview of the nature, behavior and significance of free radicals in coals, coal components and fractions during coal conversion processes. Special emphasis is placed on the characterization of free radicals and their dependence on pyrolyis and liquefaction process conditions. Some preliminary results are provided from the recently developed technique for the in situ observations of free radicals under preheater/reactor conditions.

ISSN:0094-243X    

DOI:10.1063/1.32961

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Fourier Transform Infrared Spectroscopy (FTIR) is being used to provide understanding of the organic structure of coals and coal thermal decomposition products. The research has developed a relationship between the coal organic structure and the products of thermal decomposition. The work has also led to the discovery that many of the coal structural elements are preserved in the heavy molecular weight products (tar) released in thermal decomposition and that careful analysis of these products in relation to the parent coal can supply clues to the original structure. Quantitative FTIR spectra for coals, tars and chars are used to determine concentrations of the hydroxyl, aliphatic and aromatic hydrogen. Concentrations of aliphatic carbon are computed using an assumed aliphatic stoichiometry; aromatic carbon concentrations are determined by difference. The values are in good agreement with date determined by13C and proton NMR. Analysis of the solid produ ts produced by successive stages in the thermal decomposition provides information on the changes in the chemical bonds occurring during the process. Time resolved infrared scans (129 msec/scan) taken during the thermal decomposition provide data on the amount, composition and rate of evolution of light gas species. The relationship between the evolved light species and their sources in the coal is developed by comparing the rate of evolution with the rate of change in the chemical bonds. With the application of these techniques, a general kinetic model has been developed which relates the products of thermal decomposition to the organic structure of the parent coal.

ISSN:0094-243X    

DOI:10.1063/1.32962

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The photoacoustic microsope is shown to be an effective tool for the study of lower rank coals. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.32963

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Trifluoroperoxyacetic acid chemically fragments coals at 25–80°. The reagent is so selective for oxidizing aromatic rings and is so inert towards benzylic hydrogen that isopropylbenzene, tetralin, indan, and dihydrophenanthrene have their benzene ring(s) totally destroyed without any evidence of oxidation at the benzylic hydrogen. The fragments contain more and different structural information relative to conventional oxidataions with Mn (7+), Cr (6+), HNO3, and O2. These latter selectively oxidize benzylic hydrogen. Produces from 27 selected coals show that 9,10‐dihydroanthracene and 9,10‐dihydrophenanthrene units are prominent features in most bituminous coals in accord with Given’s structure of coal. Their frequency accounts for the fact that no continuous fused ring structure or graphite exists. The only simple alkyl substituent is methyl. Liquefaction (solvent refining) sharply increases the amount of arylmethyl and aromatic structure and causes the appearance of unsubstituted phenyl groups. Nitric acid degradations have been reinvestigated and are developed into a premier method for analyzing the amounts and lengths of linear alkane chains in coals. Generally the amounts of such chains represent –2% of the carbon in coal, but in one Utah coal they account for about 42% of the carbons.

ISSN:0094-243X    

DOI:10.1063/1.32912

出版商:AIP    

年代:1981

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.32964

出版商:AIP    

年代:1981

数据来源: AIP