Aliphatic structures in coal

It is evident, therefore, that the aromatic carbon alone yields coke, and hydroaromatic carbon yields tar. Since neither appears to contribute substantially to the formation of gases (during the low temperature pyrolysis), it seems certain that the gases of low temperature pyrolysis owe their origin largely to the aliphatic structure in coal. At least it is now certain that methane formation is quite independent of the aromatic and hydroaromatic structures in coal. 

MAZIHADAft ET 41. Aliphatic Structure in Coal and Hydrogen undor Atmospheric Pressure... 

MAZUMDAR FT Al. Aliphatic Structures in Coal (Assussud From Pyrolysis) with Othor Forms of Carbon in Coal... 

Our knowledge of the aliphatic structures in coals is currently inadequate. In many low-rank coals, there is a significant amount of long-chain aliphatic material. There is a debate as to whether this material is bound to the coal macromolecular structure or whether it is simply tangled up with it and thus trapped. 

Product distribution data (Table V) obtained in the hydrocracking of coal, coal oil, anthracene and phenanthrene over a physically mixed NIS-H-zeolon catalyst indicated similarities and differences between the products of coal and coal oil on the one hand and anthracene and phenanthrene on the other hand. There were differences in the conversions which varied in the order coal> anthracene>phenanthrene coal oil. The yield of alkylbenzenes also varied in the order anthracene >phenanthrene>coal oil >coal under the conditions used. The alkylbenzenes and C -C hydrocarbon products from anthracene were similar to the products of phenanthrene. The most predominant component of alkylbenzenes was toluene and xylenes were produced in very small quantities. Methane was the most and butanes the least predominant components of the gaseous product. The products of coal and coal oil were also found to be similar. The most predominant components of alkylbenzenes and gaseous product were benzene and propane respectively. The data also indicated distinct differences between products of coal origin and pure aromatic hydrocarbons. The alkyl-benzene products of coal and coal oil contained more benzene and xylenes and less toluene, ethylbenzene and higher benzenes when compared to the products from anthracene and phenanthrene. The gaseous products of coal and coal oil contained more propane and butanes and less methane and ethane when compared to the products of anthracene and phenanthrene. The differences in the hydrocracked products were obviously due to the differences in the nature of reactants. Coal and coal oil contain hydroaromatic, naphthenic, heterocyclic and aliphatic structures, in addition to polynuclear aromatic structures. Hydrocracking under severe conditions yielded more BTX as shown in Table VI. The yields of BTX obtained from coal, coal oil, anthracene and phenanthrene were respectively 18.5, 25.5, 36.0, and 32.5 percent. Benzene was the most... 

Until recently, there have been only a few reports of aliphatic sulfur structures in coal (1,12). These results together with the experiments of Gorbaty et al. (11), give further support for the presence of labile (presumably aliphatic) sulfur moieties in high-organic sulfur-containing coals. In the previous sulfur study (1), one bituminous coal was analyzed for organic sulfur forms both by the... 

The following comments are made with regard to a correlation of the depolymerization product yields with the relative reactivities of aliphatic-aromatic carbon and oxygen-carbon bridge structures in coal ... 

Just as oxidation methods have been applied to delineation of the aliphatic (and the alicyclic) structures in coal, they have also been applied to the determination of the aromatic systems in coal. In fact, a particular oxidizing agent may produce data relating to either the aliphatic or the aromatic moieties in coal (or even relating to the lack of such systems). 

Spectroscopic methods have been applied to the elucidation of the structures in coal from very early in the development of the methods (Speight, 1978). In the initial stages of the evolution of the spectroscopic methods, the data derived by their application to coal were more of a diagnostic nature as, for example, determination of functional entities or carbon-hydrogen bonds by means of infrared spectroscopy or determination of aromatic and aliphatic hydrogen by proton magnetic resonance spectroscopy. However, virtually all of the methods have at one time or another been applied to coal as a means of deriving more detailed information about coal structure with special emphasis on the... 

Nuclear magnetic resonance spectroscopy has also been used to derive structural parameters for the distribution of aliphatic hydrogen in coal and its extraction products. A ratio of four methylene groups per methyl group was noted also, the methyl group content was higher in the soluble material and varied with the solvent power of the solvent. 

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. 

Currently, there are no accurate methods available for quantifying the aliphatic bridges in the coal macromolecule. Quantitative nature of the application of infrared (IR) spectroscopy is limited to certain general types of functional groups or bond types. Nuclear magnetic resonance spectroscopy, despite the success of dipolar dephasing techniques to decipher the extent of substitution on carbon atoms, is still inadequate to distinguish distinct structural entities . 

For the above reaction to occur, the aromatic nuclei in compound 1 should carry activating groups, such as hydroxyl, alkoxy, or fused ring aromatics". As a result of reaction with BF3 and phenol, the macromolecular structure of coal should undergo rupture at the aliphatic bridges, and these bridges are transferred to phenol molecules to produce bisphenols. Analysis of the bisphenols should provide information on the aliphatic bridges present in coal structure. 

Growth of the 1700 cm.-1 band is accompanied by reduction in the intensity of all absorptions associated with nonaromatic C-H groups. Currently held views are that aliphatic structures are destroyed during the oxidation of coal, and the changes in absorption pattern support this. 

Aliphatic structures are still of major importance in the second group of resinites, those of the bituminous coals, but aromatic structures are present in significant amounts. The spectra of these resinites display the type of absorption pattern that has come to be associated with other coal macerals, particularly the sporinites and to a large extent the vitrinites. This pattern is established in the resinites of the high volatile bituminous coals. Furthermore, resinites of this group are reactive during carbonization and oxidation processes in which their behavior parallels that of similarly affected vitrinites of equivalent rank. 

A decade of work on the distribution of carbon (and also hydrogen) has now led to a fair assessment of the aromatic and hydroaromatic contents of coals although there may still be differences of opinion about the accuracy of these values (16). Our information on the aliphatic structures present in coal is, however, less complete. 

A second requirement of the Tronov postulates—formation of acid anhydrides—is met by evidence from infrared spectra of oxidized coal samples periodically withdrawn from the reactor. As a matter of experimental record, it should be observed that such anhydrides did not appear until the later stages of reaction, by which time -COOH concentrations were already quite high. However, since initial carboxyl formation probably occurs in aliphatic structures present in the parent coal (9), appearance of anhydrides after rather... 

Concepts of the compositions of coals influenced many in considerations of the structures of soil HS. For example, the proposal of Fuchs (1931) for structures of coal HAs (Figure 1.1) influenced soil humic scientists. The proposed structure is composed of heterocyclic aliphatic functionalities, some phenol-derived units, and considerable amounts of carboxylic and hydroxyl acidic functionalities. It may be possible that such structures could arise under conditions of elevated temperature and pressure, with oxidation taking place subsequently. Whereas such conditions might prevail during the synthesis of coals, they would be most unlikely to take place during the transformations of organic materials in the soil environment. 

Of particular interest in this study is the nature of the non-aromatic structures in the three main maceral groups. It should be noted that the exinites in both the coals separated by float-sink are 90% sporinite. It has been theorized that small molecules, especially the aliphatics, are fairly mobile at some period during the formation of coal (5,6). The studies which support this theory were done on coals that are very rich in exinites and some contained alginite. Two of the coals chosen in the present work (PSOC 828 and 1103) have a more normal distribution of macerals and yet the pyrolysis results indicate that migration of molecules from the exinites to vitrinite and then incorporation into the macromolecular structure might have occurred. 

---