The Comparison of Oxygen and Sulfur Species Formed by Coal Oxidation with O₂/Na₂CO₃ or Peroxyacetic Acid Solution. XPS Studies

Abstract

Oxidation of coals of different rank and containing different amounts of sulfur was carried out using O 2 /Na 2 CO 3 . The surface chemical state of some elements (C, O, S) and their content was studied by X-ray photoelectron spectroscopy and compared to those of coal samples oxidized with peroxyacetic acid solution. The extent of surface oxidation depended on the rank of coal, bulk oxygen content of the starting sample, and the type of oxidizing agent. The oxidizing process led to the increase of the amount of oxidized forms of sulfurssulfoxides and sulfones. The changes in the amount of oxygen-containing species were also discussed.

Macroscale Superlubricity Accomplished by Sb2O3-MSH/C Under High Temperature

“…The worn surface is mainly composed of C, O, and Sb elements with the elemental concentration (at.%) of 24.7, 62.2, and 7.6%, which is in agreement with the TEM results: an outer carbon layer, an inner Sb 2 O 3 layer. The amorphous carbon layer in Figure 10j is made up of C-C, C-O, and COO − as the C 1s peak can be fitted by three peaks at 284.8, 286.1, and 288.6 eV (Grzybek et al, 2004;Morent et al, 2008;Cai and Zhang, 2013;Samanta et al, 2019). The C-C bond only accounted for 66.1%, which indicates the oxidation reaction takes place in the process of high temperature friction resulting in about third of C atoms being bonded with O atoms to form C-O and O-C=O groups.…”

Studies on the Low-Temp Oxidation of Coal Containing Organic Sulfur and the Corresponding Model Compounds

“…The two results are therefore close, with the ratio in the XPS results being slightly smaller than that of the chemical analysis results. The reasons for this phenomenon are that, on the one hand, as a surface analysis technology, XPS only detects the molecular layer 2–20 in the surface [37], so there is a gap between it and bulk analysis results; on the other hand, the “particle effect” of pyrite might weaken the XPS signal.…”

“…The conclusions can be drawn by making a comparison of XPS test results of the XF sample before and after oxidation: the sulfur peak intensity and area of the oxidized sample are higher than the original one, which shows sulfur element enrichment on the surface of coal during oxidation, which is consistent with Graybek’s conclusions. This may be due to the expansion of pores on the oxidized sample surface, which enables sulfur compounds to migrate to the surface [37]. Another reason is the oxidation makes C elements on the surface be consumed via gasification, while less S element is consumed, then the content of coal surface S is relatively increased [22].…”

“…Pietrzak and Grzybek did series of oxidation experiments using different rank coals by using O 2 /Na 2 CO 3 , PPA, and their XPS results showed that the oxidation sequence of the organic sulfur in coal is: sulphide → sulfoxide → sulfone. They also found the sulfur enrichment on the surface of coal during oxidation is probably due to the opening and expansion of coal pores [23,37,38].…”

Recent advances in beneficiation for low rank coals

“…Pietrzak and Wachowska [72,73] found that the loss of sulfur in the solid oxidation products was the highest for the coal samples oxidized with HNO 3 and peroxyacetic acid, and the organically bound sulfur in high sulfur coals was converted to oxidized forms, sulfones (-SO 2 ) and sulfoxides (S = O) under peroxyacetic acid oxidation. The effect of oxidation process on the sulfur and oxygen compounds of coal samples is usually different and depends on the oxidation method and the degree of coalification [74][75][76]. Mild oxidants like oxygen in gaseous mixtures at temperature of 125°C lead to an obvious reduction of pyritic sulfur content.…”