Evaluation of Drying Induced Changes in the Molecular Mobility of Coal by Means of Pulsed Proton NMR

Abstract

Drying induced changes in the molecular properties of six different as-received coals with water contents ranging from 8 to 60 wt % of their wet weight were investigated on the basis of the mobility of the coal hydrogen and the distribution of different types of water. When dried at 303 K, a brown coal releases water in the following order: free water identical to bulk water, bound water that froze at around 226 K, finally, nonfreezable water that never froze even at 123 K. According to 1 H NMR criteria, a portion of the coal hydrogen was found to be mobile. The amount of the mobile coal hydrogen (C MH ) varied inversely with the amount of the nonfreezable water, while the release of the free and bound water had little effect on the reduction of C MH . For coals with water contents of up to 32 wt %, C MH in the as-received samples agreed well with the hydroxylic hydrogen content, C DH , which was determined by a hydrogen-deuterium exchange technique. However, in coals with higher water content, C MH was approximately twice as great as C DH .

Nondestructive quantification of moisture in powdered low-rank coal by a unilateral nuclear magnetic resonance scanner

“…The similar overestimate has been observed using a different low-field bilateral NMR spectrometer, JNM-MU25 (25 MHz for proton; JEOL Ltd., Tokyo, Japan), with respect to the same coal samples (Nakashima Y., unpublished data). This systematic overestimation by the three different NMR spectrometers compared with thermogravimetry is not an artifact but probably attributable to non-water mobile hydrogen (e.g., hydroxyl groups) in solid coal (Lynch, Barton, and Webster 1991;Norinaga et al 1998b), which is undetectable in principle by thermogravimetry at 107°C. Thus, "water" or "moisture" measured by unilateral/bilateral NMR includes signals from the small amount of non-water mobile hydrogen as well as those from H 2 O molecules.…”

“…ESM4. Signals from the mobile protons (e.g., water molecules) were extracted and converted into water fraction values according to the conventional technique Webster 1979, 1980;Norinaga et al 1998aNorinaga et al , 1998bUnsworth et al 1988), which is described in the caption of Fig. ESM4.…”

“…The low-field time-domain NMR with a bilateral magnetic circuit has been used for the moisture quantification of coal samples (Graebert and Michel 1990;Webster 1979, 1980;Norinaga et al 1998aNorinaga et al , 1998bUnsworth et al 1988;Yao et al 2010). Although specific sample preparation (inserting samples into tubes) is required, the bilateral NMR ensures reliable moisture measurements with high S/N ratios.…”

Quantitative Analyses of Chemical Structural Change and Gas Generation Profile of Coal upon Heating toward Gaining New Insights for Coal Pyrolysis Chemistry

“…AD possesses higher amounts of oxygen functional groups that hold water via hydrogen bonds. 18,19) The strongly sorbed water mainly contributes the higher temperature for the water release upon heating than the boiling point of pure water. Based on this measurement, it is possible to quantify the hydrogen and pyrolytic water generated by pyrolysis.…”

A Study of the Hydrogen Exchange Reactions Occurring during Loy Yang Lignite Pyrolysis Using Deuterium-Labeled Water and Gas Chromatography–Mass Spectrometry Analysis

“…The plot for the m/z 18 ion shows an initial peak extending from approximately 85 to 225°C (apex at 125°C) that can be assigned to the drying of "sorbed" water. In this context, sorbed water is defined as the free (bulk), bound, and nonfreezable water described by Noringa et al 21,22 A second peak beginning at approximately 340°C whose apex is at approximately 500°C can be assigned to chemically formed pyrolytic water observed by other researchers. 1,20 Similar sorbed water drying peaks are observed in the m/z 20 trace (D 2 O) and m/z 19 (HDO) trace.…”