Evaluation of microwave treatment on coal structure and sulfur species by reductive pyrolysis-mass spectrometry method

• Microwave (MW) treatment has complicated effects on coal matrix.
• Pyrolysis of MW treated coal samples is explored by qualitative organic fragment MS analysis.
• Qualitatively organic sulfur functionality changes of MW treated coal are studied by pyrolysis-MS technique.
• For the first time also quantitative organic sulfur functionality changes in coal are determined by pyrolysis-MS technique.
• MW irradiation is used as pre-treatment for a more optimal desulfurization treatment by PAA.

A comparative study of the effect of microwave irradiation on the determination of organic sulfur forms in high sulfur coal samples of Tabas coal was studied by atmospheric pressure-temperature-programmed reduction (AP-TPR) method coupled on-line with MS. This analytical technique demonstrates the direct effect of microwave irradiation on coal matrix and on sulfur compounds, qualitatively and quantitatively. For the evaluation of the impact of microwave irradiation on sulfur compounds m/z 34 (H2S+) is monitored and on coal matrix the aromatic (benzene m/z = 77 (C6H5+), m/z = 78 (C6H6+), toluene m/z = 92 (C7H8+), m/z = 91 (C7H7+) and xylene m/z = 91 (C7H7+)) and aliphatic fragments ((m/z = 39 (C3H3+), 41 (C3H5+), 43 (C3H7+), and 55 (C4H7+)) are considered. Aromatic sulfur compound structures are more altered than aliphatic ones, as is demonstrated by its evolved H2S peak area and temperature changes. A great peak maximum shift of all aromatic fragments towards higher temperature was noticed, due to the poly cyclic aromatic ring formation as a result of microwave treatment. The microwave treatment used on the coal samples, resulted in coal matrix degradation and changes in terms of physical characteristics and causing a simultaneous degradation of the organic matrix.