Observation of the Type of Hydrogen Bonds in Coal by FTIR

Abstract

It is hard to distinguish the type of hydrogen bonds formed by hydroxyl groups by normal FTIR methods because of the interference of water in samples. In this work, a method is proposed for the clear observation of the types of hydrogen bonds by FTIR. The method involves the evaporation of water in a vacuum chamber with CaF2 windows (vacuum level, 4 × 10-3 kPa) followed by in situ scanning of the IR spectrum. Five types of hydrogen bonds were found in coal and its extracts. The hydroxyl groups in coal mainly exist as self-associated OH and OH−N hydrogen-bonded pairs. The thermal stability of these hydrogen bonds was investigated by means of in-situ pyrolysis FTIR. It follows the order of OH−ether O > self-associated OH ≈ cyclic OH > OH−N > OH−π.

Identification of basic nitrogen compounds in ethanol-soluble portion from Zhaotong lignite ethanolysis by positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

“…Noncovalent bonds in ZL could also play an important role in the release of BNCs during ethanolysis. Five HBs, including OH-N and OH-p, were observed in coals [40]. Pyridines and quinolines could act as HB acceptors to form HBs with phenolic hydroxyl or carboxyl in ZL.…”

The pyridine vapor adsorption behavior and its influence on suppressing low-temperature cross-linking reactions during slow pyrolysis of lignite

“…In this section, the variation of different types of hydrogen bonds before and after pyridine vapor pretreatment were quantitatively studied based on our previous work, as well as the distribution and reduction of hydrogen bonds in coal. The peak assignments of hydrogen-bonded bands and the half-widths were determined based on the second differential of the spectrum and references or experiential formula [15,[25][26][27][28][29][30][31][32]. The coal spectrum was fitted by Peak Fitting Module included in the origin 7.0SRO.…”

Infrared absorption spectra of coals with different degrees of coalification

“…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.…”

“…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 broad absorption band with maximum near 3250 cm -1 is usually assigned to stretching vibrations of OH groups which are "strongly" bound to the surface of minerals such as montmorillonite (MgO⋅Al 2 O 3 ⋅3SiO 2 ⋅1.5H 2 O) or minerals with water of crystallization (such as vermiculite) [15,16]. The short-wavelength limit of the absorption bands may be due to absorption of OH groups linked by hydrogen bonds with the π electrons of the aromatic ring (OH-π) and appearing in the spectrum near 3500 cm -1 [2,3]. The weak peak near 3545 cm -1 in the spectra of sample IV is due to vibrations of self-associated hydroxyl groups.…”