Abstract
One of the contaminants in coal is sulphur. The adverse impact of sulfur on coal, such as environmental pollution, degradation of steel quality, and reduction of coal’s thermal value, has led to the attention of sulfur separation methods in recent decades. Leaching (chemical dissolution) is one of the best methods for desulfurising coal, reducing sulfur in coal. In this study, hydrogen peroxide as an oxidising agent on sulfuric acid yield in reducing sulfur types of coal and chemical structure and the organic texture of high sulfur coal was investigated. The experiments were designed using a three-level response surface methodology with four duplicate points and 27 experiments. The independent variables studied were temperature, time, stirring speed and ratio of sulfuric acid to hydrogen peroxide. Dependent variables included reduction percentage of total, pyritic and organic sulfur. This study showed that 99.99% of total sulfur, 30.11% of pyritic sulfur and 69.08% of organic sulfur were reduced. These values were obtained at a temperature of 60°C, time 120 min, stirring speed 200 rpm and 3:1 ratio of sulfuric acid to hydrogen peroxide. Significant changes were observed by infrared spectroscopy (FTIR) of the coal structure before and after desulphurisation. On the other hand, the studies showed no specific changes in the bonds related to the organic coal matrix. The results showed that this method could be used as a secure process for removing inorganic and organic sulfur without destroying the organic coal matrix.
Highlights
This study showed that 99.99% of total sulfur, 30.11% of pyritic sulfur and 69.08% of organic sulfur were reduced
The basis for selecting these parameters is the optimisation of the experiments and placing in the range that gives the most reduction of organic sulfur, this is done according to past research, and the reason for using the response surface method is that using this method can be at least the number of experiments yielded the best and most practical results with the least amount of consumables
Examining the results of experiments and determining the influential factors on reduction sulfur forms of coal, it was found that the combination of sulfuric acid in the presence of hydrogen peroxide as a leaching agent to reduce coal sulfur is effective and by this acidic factor can be the amount significantly of sulfur reduced depending on the type of sulfur and provided a possibility of reducing 99.99% of total sulfur, 30.11% of pyrite sulfur and 69.08% of organic sulfur
Summary
As one of the most important sources of energy worldwide due to its exploitation and utilisation, coal causes increasingly severe ecological problems, especially air pollution. One of the significant causes of pollutant emissions is the sulfur compounds produced by coal combustion. The sulfur contents of coal vary from 0.3% to 0.5% on average. Sulfur contents are more variable and tend to be higher. Sulfur is often present in coal in both organic and inorganic forms, depending on coal [5] [6]. Inorganic sulphur is often found in two forms: disulphide and sulphate [7] [8]. The organic form of sulphur, directly attached to the organic coal matrix, is typically found as thiols, sulphides, disulfides, thiophenes, cyclic sulphides, and organic sulphur removal is one of the most difficult challenges in coal desulphurisation [9] [10]
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