Taub Tze'ela, Ruthstein Sharon, Cohen Haim
Department of Chemical Sciences, Ariel University, Ariel 40700, Israel.
Chemistry Department, Faculty of Exact Sciences, Bar Ilan University, Ramat Gan 52900, Israel.
ACS Omega. 2021 Nov 30;6(49):33428-33435. doi: 10.1021/acsomega.1c03965. eCollection 2021 Dec 14.
Coal is intensively used worldwide as a main fuel source. However, it may undergo oxidation processes [i.e., low-temperature oxidation (LTO)] when stored under an air atmosphere in piles post-mining at low temperatures ranging from 300 to 425 K, specifically, a surface gas/solid reaction with molecular oxygen. Therefore, it is of major importance to prevent or appreciably slow down such reactions, which result in a loss in the energy content (calorific value) of coal. Previously, we showed that radicals are formed during the LTO process. In this work, the dependence of radical formation on coal rank as a function of heating (temperature) and the presence of oxygen gas were studied using electron paramagnetic resonance spectroscopy. It was shown that lignite coals are more sensitive than bituminous coals to the atmospheric environment (i.e., molecular oxygen and nitrogen content) and to temperature, as reflected by the formation of surface carbon-centered radicals. Moreover, this is the first publication showing the effects of LTO on micro- and macro-pores by assessing how these structures affect O diffusion. The LTO process blocks the micro-pores, such that radicals form mainly at the surface of the coal macromolecules, in both bituminous and lignite coals.
煤炭在全球范围内被广泛用作主要燃料来源。然而，在开采后低温储存于空气氛围中（温度范围为300至425K）时，煤炭可能会经历氧化过程[即低温氧化（LTO）]，具体而言，是与分子氧发生表面气/固反应。因此，防止或显著减缓此类导致煤炭能量含量（热值）损失的反应至关重要。此前，我们表明在低温氧化过程中会形成自由基。在这项工作中，利用电子顺磁共振光谱研究了自由基形成对煤阶的依赖性，该依赖性是加热（温度）和氧气存在情况的函数。结果表明，褐煤比烟煤对大气环境（即分子氧和氮含量）以及温度更敏感，这通过表面碳中心自由基的形成得以体现。此外，这是首次通过评估这些结构如何影响氧气扩散来展示低温氧化对微孔和大孔影响的出版物。低温氧化过程会堵塞微孔，使得自由基主要在烟煤和褐煤的煤大分子表面形成。
