Lucy M. Lucht

Macromolecular structure of coals: 2. Molecular weight between crosslinks from pyridine swelling experiments

Abstract The effective macromolecular structure of ten coals was investigated by application of a modified Gaussian network equation to the results of equilibrium vapour-swelling studies using pyridine as the penetrant. Using data at 35 °C it was found that the effective number N of repeating units between crosslinks varied from 7.0 to 8.5, corresponding to a molecular weight M c between crosslinks of 990 to 1280, over the coal rank range 69.9–82.4 wt%C (dmmf). At 86.0 wt%C, N fell to 4.6, corresponding to a molecular weight between crosslinks of 780, and continued to decline to 2.2, corresponding to M c = 814 , at 91.5 wt%C. An increase in swelling temperature from 35 to 60 °C had little effect on the analysis; however, at 80 °C substantially increased equilibrium swelling values were obtained, which indicated a change in coal structure, increased thermodynamic interaction or attack on the hydrogen-bonded structure of the coal by pyridine.

MACROMOLECULAR STRUCTURE OF COALS. I. THE ORGANIC PHASE OF BITUMINOUS COALS AS A MACROMOLECULAR NETWORK

The organic phase of bituminous coals may be represented as a three-dimensional macromolecular network, with chains consisting of aromatic or heterocyclic clusters and smaller connecting bonds, usually of etheric, sulfidicor methylenic nature. The crosslinks are covalently bonded bridges or hydrogen-bonded structures. The molecular weight between crosslinks, [Mbar]C, and other parameters of the crosslinked structure can be calculated using the results of various experiments and applying theories widely used for the analysis of polymeric networks, albeit with significant modifications.

TRANSPORT OF PENETRANTS IN THE MACROMOLECULAR STRUCTURE OF COALS. I. ANOMALOUS TRANSPORT IN UNTREATED AND PYRIDINE-EXTRACTED COALS

Dynamic swelling of coals using pyridine vapors was investigated in an effort to elucidate the mechanisms of penetrant transport in coal sections and particles. Anomalous (non-Fickian) and Case-II transport were observed in much the same way as witb penetrant transport in glassy polymers. This anomalous transport was a function of ihe crosslinked structure of the organic phase of the coal samples.

Crosslinked macromolecular structures in bituminous coals: Theoretical and experimental considerations

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 Mc and the crosslinking density ρx can 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 ...

Macromolecular structure of coals

SummaryThe Flory thermodynamic interaction parameter, X, was calculated for a range of solvents interacting with the crosslinked macromolecular structure of coals of a wide range of carbon content.