Infrared absorption spectra of coals with different degrees of coalification

Abstract

We have used Fourier transform IR spectroscopy to study structural changes in coals of different degrees of coalification when stored for prolonged periods under normal conditions. As a result of reaction of the surface of the coals with atmospheric oxygen and water vapor, the intensities of characteristic absorption bands were enhanced which, when we considered elemental analysis data for the coals, allowed us to obtain additional information about their structure and impurity composition.Introduction. Coals consist of complex, high molecular weight, structurally organized systems [1], and so IR spectroscopy is a convenient and informative method for studying them. Using a Fourier transform IR (FTIR) spectrometer makes it possible to highly accurately determine the position of the absorption bands and to carry out semiquantitative analysis of the hydroxyl (OH) groups, aromatic and aliphatic CH groups, carboxyl COOH groups, mineral components, and other functional groups in coals and coal extracts [2,3].The degree of coalification (the carbon atom content), which varies during the natural process of coal formation, and the reflection coefficient of light, depending on the molecular structure of the coals, are usually used to characterize coals [4]. In an optical study of coals, we need to take into account the nonuniformity of their chemical composition and their porosity. Study of the optical properties of coals with high carbon content (≥70 at.%) is made difficult by the low intensity of spectrally poorly resolved absorption bands in the IR region [5].There have been many attempts to study the structure of coals after vacuum annealing [6], thermal decomposition [7], oxidation [8], treatment in acids and bases [9] in order to modify the intensity of individual IR absorption bands of the coals and to obtain additional information about their composition, structure, and properties. The aim of this work was to use IR spectroscopy to determine the effect of the degree of coalification on the structure of coals during their prolonged oxidation under normal conditions. In addition, we used x-ray spectral microanalysis to characterize the samples.Experimental Section. Samples and study procedure. Samples of natural coals (lumps weighing ≈15 g) from the Donetsk field were stored for 20 years at room temperature in air away from light. X-ray spectral microanalysis of the samples was carried out on a scanning electron microscope (LEO1455VP, Carl Zeiss, Germany) using an energy dispersive SiLi detector (Rontec, Germany). The content of a number of chemical elements in the samples was determined by x-ray microanalysis. We should note that in the x-ray microanalysis, with electron beam energy 20 keV the near-surface region of the oxygen-enriched coal was studied (electron penetration depth down to 10 µm). Hydrogen atoms were not detected by this method. Four samples were numbered by Roman numerals in order of decrease of the atomic carbon concentration in them: from 81 to 65 at.% (see Table 1).For the FTIR measurements, piec...

Phenolic Composition, Isolation, and Structure of a New Deoxyloganic Acid Derivative from Dhokar and Gemri‐Dhokar Olive Cultivars

“…The IR spectrum showed 5 major bands at 1078, 1635, 1725, 3020, and 3420 (figure not shown). The band at 1078 cm −1 was assigned to the ν (C‐O) (Munkhtsetseg and others 2007). On the other hand, the absorption bands at 1635 and 1725 may be due to carboxyl groups and conjugated ester, respectively (Takenaka and others 2002).…”

“…On the other hand, the absorption bands at 1635 and 1725 may be due to carboxyl groups and conjugated ester, respectively (Takenaka and others 2002). The broad absorption band near 3020 cm −1 is usually assigned to the stretching vibrations of the CH x groups (Munkhtsetseg and others 2007). However, the broad absorption band near 3420 cm −1 is usually assigned to stretching vibrations of hydroxyl groups (Krzton and others 1995).…”

Identification and characterization of a new iridoid compound from two-phase Chemlali olive pomace

“…Although the band at 1,422 cm -1 was attributed to the m (-C=C-H) vibration, while the band at 1,366 cm -1 was due to CH absorption bending vibration of CH 3 groups from aliphatic chain [15]. However, the absorption bands at 1,691 and 1,651 may be due to conjugated COOH and COOR (ester) groups with a, b-unsaturated olefin [16]. On the other hand, the broad absorption band near 3,400-3,000 was usually assigned to stretching vibrations of hydroxyl groups [17,18].…”

FTIR Study of Enriched Bituminous Ukhaa-Khudag Coal

“…Recently used method of using corn starch to suppress coal dust in coal production [2] or to prepare high performance of porous carbon [3] showed promising results of quality improvement. Fourier Transform infrared spectroscopy is widely used to structurally reveal coal characterization [4,5,6], since it can provide crucial information on the molecular structure of organic and inorganic components of coal. The present paper is about earning some information of the structural differences between raw coal and enriched ones (intermediate and final productions) to show qualitatively the coal structural improvement.…”