Experimental Study on the Molecular Hydrogen Release Mechanism during Low-Temperature Oxidation of Coal

Abstract

Although H2 gas is used in coal mines as an important indicator to reflect the state of coal spontaneous combustion, the gas production of H2 at low temperature has been scarcely reported in the literature. In this paper, the modes and release mechanism of molecular hydrogen were investigated for three different coal ranks below 200 °C. Batch reactor tests were performed in combination with chromatographic analysis of the coal oxidation process. The experimental results showed that molecular hydrogen release mainly originated from coal oxidation rather than thermal decomposition of inherent hydrogen-containing groups. The amount of hydrogen released increased with the coal rank. The H2 release process during low-temperature oxidation typically proceeds in two phases, namely H2 slow release (T < 100 °C) and H2 accelerated release (T > 100 °C) phases. Experiments with model compounds revealed aldehyde compounds to noticeably produce H2. Coal plays a positive role in promoting the aldehyde groups to release H2 and CO2, but an opposite trend was observed in the case of CO. As revealed by Fourier transform infrared (FTIR) spectroscopy, the amount of aliphatic structures significantly decreased with the oxidation intensity, and a drastic increase in the aldehyde content was found at temperatures above 120 °C. Additionally, the path for the formation of H2 during low-temperature oxidation of coal was provided.

Oxygen chemisorption and low-temperature oxidation behaviors of sub-bituminous coal

“…In addition, a peak from aldehyde markedly became larger after low-temperature oxidation. It has been reported that the aldehyde group is a functional group that produces not only CO 2 but also H 2 by its oxidation reaction (Wang et al, 2017). This fact is consistent with the H 2 emissions observed in the low-temperature oxidation of coal Q shown in Fig.…”

“…The weight reduction of the coal was almost consistent with the total mass of C and H contained in the emitted gaseous compounds. H 2 emissions in the low-temperature oxidation process of coal was reported by Wang et al (2017), in which the amount of H 2 emissions from sub-bituminous coal was greater than that from bituminous coal at temperatures higher than 373 K.…”

Investigation on Conversion Pathways in Degradative Solvent Extraction of Rice Straw by Using Liquid Membrane-FTIR Spectroscopy

“…The number, sub-peak position, peak width, and their variation ranges were assigned as in Table A1. These values were obtained from previous FTIR analysis of coal and biomass [49,[63][64][65][66][67][68][69][70], and were used to perform peak deconvolution. The band assignment in the OH-stretching region and the nine bands in the oxygen-containing region (anhydride, ester, aldehydes, carboxyl groups, conjugated carbonyl groups, etc.)…”

“…Appendix A Table A1. Peak assignments of IR spectra of the oxygen-containing groups in this study [49,[63][64][65][66][67][68][69][70].…”

Study of the Abnormal CO-Exceedance Phenomenon in the Tailgate Corner of a Low Metamorphic Coal Seam

“…As an organic macromolecular material, coal contains many active components. During the process of coal reacting with O 2 and its subsequent heating, functional groups, such as the ketone group, quinone group, and aldehyde group, are activated and are part of the reaction to produce CO [2]. CO is usually generated in an exponential manner with any increase of temperature [3,4].…”