Computer Science
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........44d&link_type=abstract
Thesis (PH.D.)--SOUTHERN ILLINOIS UNIVERSITY AT CARBONDALE, 1993.Source: Dissertation Abstracts International, Volume: 55-09, S
Computer Science
Coals, Lignite
Scientific paper
In order to understand the coal-water interactions and to elucidate the structure of water in low-rank coal, comprehensive temperature (100 K < T < 300 K) dependent specific heat, in-situ temperature (98 K < T < 295 K) dependent Fourier transform infrared (ISTD-FTIR), in-situ desorption kinetics via the differential scanning calorimetry (DSC) at 295 K < T < 480 K, and in-situ desorption via FTIR (ISD-FTIR) (at 296 K, 348 K, and 383 K) measurements on Beulah-Zap lignite coal and Wyodak sub-bituminous coal were performed. Our temperature dependent specific heat and ISTD-FTIR measurements have led us to propose a model of water in low-rank coals. According to our model, there are four types of water in a low-rank coal. The surface adsorbed water, strongly hydrogen bonded (H-bonded) to the hydrophilic sites on the coal surface, attained extra mobility as the temperature increased to around 180 K. The grain water, located next to the surface adsorbed water layer and acting as a transition region between the surface adsorbed water and the center bulk water, began to melt at around 232 K. The bulk like water, at the center of a small pore, showed the depressed melting transition at T < 273 K (such as 257 K and 267 K). Pure bulk water, mechanically held between coal particles and present in the macropores, exhibited the normal melting transition at 275 K. Our in-situ desorption kinetics (via DSC technique) studies indicate that water is lost from Beulah-Zap lignite coal, of particle sizes <841 mum, < 106 mum, and <37 mum, by two independent but simultaneously operative kinetic mechanisms. The unimolecular decay kinetics are obeyed by those water molecules which are near the mouths of large pores and/or surround the coal particles. Most of the water was removed via a 2nd-order diffusion mechanism. Finally, the ISD-FTIR studies on Beulah-Zap lignite coal suggest that the water molecules present on the coal surface are in form of H-bonded water clusters. Within these water clusters, the five O-H stretching frequency components, corresponding to the different strength of H-bonds were observed. The experimental results also disclosed the irreversible changes of H-bonding structure in coal after the sample was vacuum dried at 383 K.
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