ARTICLE pubs.acs.org/EF
Mechanism for Removal of Organic Sulfur from Guiding Subbituminous Coal by Electrolysis Shi-Teng Zhong,†,‡ Wei Zhao,*,† Chen Sheng,† Wen-Juan Xu,† Zhi-Min Zong,† and Xian-Yong Wei*,† †
Key Laboratory of Coal Processing and Efficient Utilization (Ministry of Education), China University of Mining and Technology, Xuzhou 221116, Jiangsu, China ‡ Tengzhou Eastern Steel Cord Co., LTD, Tengzhou 277500, Shangdong, China ABSTRACT: Ash in Guiding subbituminous coal (GSBC) was removed by treatment with dilute acids. The treated GSBC (TGSBC) was extracted with isopropanol (IP) to afford IP-extractable fraction (IPEF). TGSBC was sequentially extracted with petroleum ether, carbon disulfide, acetone, and methanol. Octane-1-thiol and thiophene were selected as model compounds (MCs) for organic sulfurs in GSBC. MCs and extracted residue (ER) of TGSBC were electrolyzed in an aqueous NaCl solution. Reaction mixtures from the electrolysis of MCs were extracted with cyclohexane. The electrolyzed extracted residue (EER) was extracted with the same method as TGSBC. The extracts were analyzed with gas chromatography/mass spectrometry (GC/MS). ER and EER were analyzed with Fourier transform infrared (FTIR) spectrometry. Three organic sulfurs were detected in IPEF from TGSBC with GC/MS. FTIR analysis shows that ER electrolysis increased oxygen-containing functional groups but decreased organic sulfurs. Disulfide, sulfoxide, sulfone, and sulfonic acid were detected by GC/MS and FTIR analyses. The mechanism for removal of organic sulfur during GSBC electrolysis was discussed.
1. INTRODUCTION Coal combustion produces sulfur oxides, which are considered as a major source of atmospheric pollutant.1 The methods of desulfurization from coals include physical, chemical, and biological methods. Removal of inorganic sulfur has been found to be successful in many reports,2 but removal of organic sulfur from coals is more difficult. Traditional chemical methods, such as melting alkali treatment, high-temperature gas treatment, and chemical oxidation, can largely remove organic sulfur, but the macromolecular structure and properties of coals were destroyed.38 An electrontransfer process was carried out for the removal of organic sulfur by Borah and Baruah.912 The reactions were mild, but the removal of organic sulfur was very low. The research on efficient, economical, and clean methods for removal of organic sulfur from coals has drawn wide attention. Electrochemical desulfurization (ECD) of coals is a clean and mild approach. It overcomes the shortcomings of traditional physical and chemical methods mentioned above. Lalvani and Pata13 have investigated ECD since the 1970s and achieved good results. Wapner et al.,14 Li et al.,15 and Wang et al.16 investigated the effects of electrolyte, electrolysis voltage, electrolytic time, and coal slurry concentration on organic sulfur removal. Their focus was only on the higher ratio of desulfurization and optimum conditions. However, studies on the mechanism for organic sulfur removal by electrolysis are rare. Li et al.17 reported thermodynamic analysis of the ECD reactions of organic sulfur, but this research lacks experimental basis and cannot reveal a convincing mechanism for removal of organic sulfur. Organic sulfur in coals occurs in various types, including thiols, thioethers, disulfides, thiophenols, thiophenes, and benzothiophenes.18 However, types and amounts of organic sulfur are different in different coals. In order to accurately r 2011 American Chemical Society
understand the mechanism for removal of organic sulfur from Guiding subbituminous coal (GSBC), analysis of the types of organic sulfur in GSBC is very necessary before ECD. In this work, the types of organic sulfur compounds (OSCs) in GSBC were analyzed first. Through the investigation on removal of sulfur from model compounds (MCs) by electrolysis and effect of electrolysis on OSCs in GSBC, we reveal the mechanism for removal of organic sulfur from GSBC to provide a more reliable theory for removal of organic sulfur.
2. EXPERIMENTAL SECTION 2.1. GSBC. GSBC was collected from the Guiding coal mine, Guizhou, China, and it was ground to pass through a 200 mesh sieve (
