Coal Science - ACS Publications

---

31 Studies on the Structure of Coals of Different Rank Hydrogen Distribution of Depolymerization Products

Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 11, 2015 | http://pubs.acs.org Publication Date: January 1, 1966 | doi: 10.1021/ba-1966-0055.ch031

LASZLO A. HEREDY, ANDREW E. KOSTYO, and MARTIN B. NEUWORTH Research Division,

Consolidation

Coal Co., Library,

Pa.

The distribution of hydrogen types in the soluble fractions from the depolymerization of a series of coals has been determined by NMR analysis. The aromatic hydrogen content varies from 20 to 32% of the total hydrogen, and no simple relationship exists with coal rank. β-Paraffinic plus naphthenic hydrogens, the major type, exceed the α-hydrogens and comprise 38-66% of the nonaromatic hydro­ gens. The most striking variation in the structure of the six coals is the number of methylene bridges. The degree of depolymerization with phenol-BF can 3

be correlated directly with the number of methylene bridges found in the soluble fractions. A general coal structure in accord with our results consists of large units (MW > 4000) and smaller units (MW, 300-600) connected by methylene bridges.

J h e distribution of hydrogen types in coals continues to be a subject of con­ siderable interest i n coal structure studies. Published data indicate that the fraction of aromatic hydrogens usually increases with increasing rank, but the absolute values depend on the specific analytical method used ( 7 ) . Hydrogen type analysis of a single coal based on the application of N M R spectroscopy to the soluble fraction from depolymerization with phenol-BFa has been re­ ported by us ( 3 ) . T h e conversion of coal to soluble fragments i n substantial yields under very m i l d conditions permits a reliable determination of the hydrogen types b y N M R analysis, and these results can be extrapolated to the parent coal with considerable confidence. This procedure has now been extended to a series of coals varying i n rank from lignite ( 7 0 % C ) to a l o w volatile bituminous coal ( 9 1 % C ) . In addition to determining the amount of aromatic and aliphatic hydrogens, the aromatic group w i l l be further subdivided into monocyclic and polycyclic types. A more 493

In Coal Science; Given, P.; Advances in Chemistry; American Chemical Society: Washington, DC, 1966.

494

COAL SCIENCE

detailed breakdown of the aliphatic hydrogens into methylene, «, 0, and 0* types will be reported.

Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 11, 2015 | http://pubs.acs.org Publication Date: January 1, 1966 | doi: 10.1021/ba-1966-0055.ch031

Experimental Details of the depolymerization, solvent separations, and product analyses were described previously (3, 4). Molecular weights of the benzene-, methanol-, and phenol-soluble fractions were determined cryoscopically using sulfolane as the solvent (11). A l l N M R spectra were recorded on a Varian A - 6 0 spectrometer at room temperature by Nuclear Magnetic Resonance Specialties, Inc., N e w Kensington, Pa. Benzene soluble fractions were recorded in deuterated chloroform solution ( C D C l s ) while dimethyl sulfoxide-do (DMSO-c/r.) was the solvent employed for other fractions. (Deuterated chloroform with enrichment of 99.8% was purchased from Bio-Rad Laboratories and dimethyl sulfoxide-dr, with enrichment of 99.6% from Merck, Sharp, and Dohme of Canada.) The internal standard used with the C D C l a solutions was tetramethylsilane and hexamethyldisiloxane (chemical shift 7 c.p.s.) with DMSO-d«. Prior to preparation for N M R recording, the samples were thoroughly dried in a vacuum at 110°C. T h e N M R tubes were sealed to minimize the absorption of atmospheric moisture. The chemical shifts given in c.p.s. are referred to tetramethylsilane. A planimeter was used for area measurement. Corrections were made for hydrogen in C D C l a , D M S O - d o , and chemically combined radioactive phenol so that the final data represent only the hydrogen associated with the coal. A correction for hydrogen in the solvents could be made from the known weight and the deuterium enrichment. The quantity of combined radioactive phenol in each sample was determined from the radioactivity count, and with these data the appropriate correction was made in the aromatic and hydroxyl proton regions. Total hydroxyl proton content was determined by titration w i t h sodium aminoethoxide in ethylenediamine. The resonance line for the hydroxyl proton in C D C l a is in the 390-370 c.p.s. region. In DMSO-d