Inge I. Maes

Sulphur group analysis in solid matrices by atmospheric pressure-temperature programmed reduction

The atmospheric pressure-temperature programmed reduction (AP-TPR) has become an established and reliable method amongst the different sulphur characterisation techniques for solid materials, like coal and coal derived products, rubber and clay. The analytical method is based upon the fact that specific sulphur functional groups are hydrogenated at specific temperatures. During the last few years, several adjustments have been made to the hard- and software as well as to the experimental parameters. The changes and the reliability of the method are extensively discussed in this paper.

Interaction of the organic matrix with pyrite during pyrolysis of a high-sulfur bituminous coal

Abstract High-sulfur bituminous coal containing 4.17 wt% of pyritic sulfur and the pyrite concentrate separated from this coal were used to examine the interaction between pyritic sulfur and the organic part of coal during pyrolysis. At 330–500°C, as a result of the reaction of sulfur derived from pyrite decomposition with the coal organic matrix, a significant increase in the organic sulfur in the char is observed, from 1.47 to 3.17 wt%. The enrichment in sulfur is most pronounced between 400 and 450°C, corresponding to the most intensive thermal degradation of this coal. At these temperatures, some of the pyrite is converted to pyrrhotite. The organic sulfur content is a maximum at ∼ 500°C, when all the pyrite is reduced to pyrrhotite. The pyrite in the coal undergoes conversion to troilite via pyrrhotite at lower temperatures than does pure pyrite. Compared with the thermal decomposition of pure pyrite, the pyrite present in coal starts to decompose at a lower temperature (330 vs. 400°C). The conversion to troilite also proceeds to completion at a much lower temperature. This demonstrates that the decomposition of pyrite is markedly affected by the presence of the organic coal substance.

Rank dependence of organic sulfur functionalities in coal

Organic sulfur functionalities were characterized and quantified by atmospheric-pressure temperature-programmed reduction (AP-TPR). Nine coals were chosen to cover the entire rank range from subbituminous coal to anthracite. To be able to study the organic sulfur groups, the vitrinite concentrates were separated from each coal sample. The results confirm the larger amount of sulfide in low-rank coals. The amount of thiophenes generally increases with rank. Nevertheless, sulfur functionality distribution can vary from coal to coal even at the same rank.

Effect of calcium and calcium minerals in coal on its thermal analysis

Abstract The effect of the presence of limestone and dolomite in coal, and calcium in lignite, on atmospheric-pressure temperature-programmed reduction (AP-TPR) analysis was studied. AP-TPR experiments were carried out on a bituminous coal with added limestone and dolomite and on a demineralized lignite. The results showed that both calcium minerals captured the gaseous H 2 S formed under AP-TPR conditions and produced CaS. Consequently the sulfur recovery monitored was too low and the AP-TPR kinetograms were deformed. The study also showed that the influence of dolomite is greater than of limestone. AP-TPR analysis of lignite demineralized and then loaded with calcium ions again showed a clear lowering of sulfur comparable with that of dolomite, but starting at a higher temperature.

Sulfur functionalities and physical characteristics of the Maritza Iztok Basin lignite

Abstract The use of selective functional group modification procedures has been investigated for the determination sulfur forms in low-rank coals. A Bulgarian lignite from the Maritza Iztok Basin was submitted to a variety of chemical treatments. The fresh lignite and residues were studied by atmospheric pressure temperature-programmed reduction (AP-TPR) and sulfur K-edge X-ray absorption near-edge structure (XANES) analysis to investigate the distribution of sulfur forms. The impact on the physical characteristics of the lignite following each treatment was studied by thermal analysis (d.t.a.) and scanning electron microscopy (SEM-EDX). The results have demonstrated the ability of selective procedures to simplify sulfur functionality determination by AP-TPR and have provided a clear insight into the impact of treatments on the thermal characteristics of the lignite.

Reduction of high-sulphur coal in the potassium–liquid ammonia system

Abstract Polish high-sulphur coal was twice subjected to reduction in the potassium–liquid ammonia system. The process was carried out on both raw and demineralised coal. Elemental and spectral analyses of the initial coal and the reduction products were performed. Different forms of sulphur found in the samples were studied by the classical chemical methods and by atmospheric pressure–temperature programmed reduction (AP–TPR). The effect of reduction on particular sulphur compounds is discussed. It was found that reduction in the potassium–liquid ammonia system led to cleavage of C–S bonds, appearance of thiol groups, and the partial removal of pyrite and sulphates from the coal whereas the content of elemental sulphur did not change significantly.

Effect of siderite in coal on reductive pyrolytic analyses

Abstract The effect of the presence of siderite (FeCO 3 ) in coal on the atmospheric pressure–temperature programmed reduction (AP–TPR) analysis of coal is studied. Siderite is added to demineralised Maritza Iztok (lignite) and raw Nowy Wirek (high volatile bituminous) coal before analysis. Results show an extra troilite FeS peak in the AP–TPR profiles for both siderite doped coals. The mechanism of H 2 S capture by siderite is discussed on the base of a model reaction. Additionally, the formation of troilite from the pyrite present in the initial coal during the AP–TPR experiment was monitored by scanning electron microscopy with an energy dispersive X-ray analyser (SEM–EDX). During AP–TPR analysis the evolving H 2 S is captured by FeO or FeCO 3 and FeS is formed. These phenomena disturb the AP–TPR profiles as well as the sulphur recovery.

Study of the sulphur functionalities and physical characteristics of a bulgarian lignite by desulphurization techniques

Abstract A complete knowledge and understanding of the thermal reactivety of sulphur forms in coal is crucial for the development of new, efficient desulphurisation techniques. This contribution reports on seven selective desulphurization treatments of a Bulgarian lignite. The impact of individual treatments on the sulphur distribution was monitored by AP-TPR and XANES techniques. Complementary data concerning the physical impact of the treatments was obtained by DTA and SEM-EDX.

Interpretation of AP-TPR profiles by non-isothermal kinetics

The two peaks in the AP-TPR (Atmospheric Pressure - Temperature Programmed Reduction) spectrum of cystein are resolved and interpreted in terms of the non-isothermal kinetics theory.