Article pubs.acs.org/EF
Fractional Extraction and Biodepolymerization of Shengli Lignite Jing-Hua Yao, Xian-Yong Wei,* Lei Xiao, Hong-Min Ji, Zhi-Min Zong, and Fang-Jing Liu Key Laboratory of Coal Processing and Efficient Utilization, Ministry of Education, China University of Mining & Technology, Xuzhou, Jiangsu 221116, People’s Republic of China ABSTRACT: Shengli lignite (SL) was sequentially extracted with aqueous NaOH solution, n-hexane, dichloromethane, an azeotropic mixture of benzene and ethanol, and acetone to obtain extracts 1−5 (E1−E5). Each extract was analyzed using a gas chromatograph/mass spectrometer (GC/MS) and then depolymerized by an isolated fungus. Most of E1 cannot be detected by GC/MS perhaps because of strong polarity, and E1 is recognized as humic acids. E2−E5 consist of normal alkanes, arenes, alkanols, phenols, ketones, carboxylic acids, esters, and organonitrogens according to GC/MS analysis. The biodepolymerization (BDP) of E1 is much easier than that of other extracts. According to GC/MS analysis, both 2,4-xylenzo[h]quinoline and methyl 3-(acetoxymethyl)biphenylene-2-carboxylate disappeared, while 3-(1-ethoxyethoxy)butanal, propane-1,2-diyl diformate, 3-phenylbutan-2-ol, and 2-methyl-7-phenyl-1H-indole were produced from the BDP of E1. In comparison to E1 before BDP, the phenoxy moiety in E1 after BDP was significantly reduced according to analysis with a Fourier transform infrared spectrometer, implying that the BDP facilitated the degradation of lignin in SL. This study will provide an important scientific basis for lucubrating bioconversion of lignite.
1. INTRODUCTION Current lignite reserves in China are ca. 130 billion tons, accounting for ca. 13% of total coal reserves in China and 12.4% of world lignite reserves.1−5 However, a high ash yield, high contents of moisture and organo-oxygen species, and a resulting low calorific value, along with the spontaneous combustion characteristic of lignites, make the conventional conversion, including combustion, pyrolysis, or gasification, of lignites a serious potential threat to the environment.6−10 Bioprocess/bioconversion of coals by microorganisms has great advantages over thermochemical conversion, because it takes place at ambient temperature and pressure. Microbial treatment of coals has been considered as a cost-effective and ecofriendly way for converting coals to clean fuels and value-added chemicals.11,12 The capacity of microorganisms to grow on coals and modify physicochemical properties of coals was first reported by Fischer and Fuchs13 in the 1920s, but the systematic studies on coal biosolubilization were not conducted until the 1980s.14−16 Many types of fungi,17,18 bacteria,16,19 and actinomycetes20 were identified and used to depolymerize and solubilize coals.
Alkaline metabolites, microbial chelators and surfactants, and enzymatic attack are generally accepted as the three mechanisms for coal biodegradation.18,20−22 For most bacteria and actinomycetes, alkalinity and chelation are the primary factors in coal depolymerization. For fungi, enzymes play the most important role.11 Coals, especially lignites, still preserve some molecules derived from lignin, which could be susceptible to degradation by some fungal extracellular enzymes, such as ligninase, peroxidase, and laccase.23 It is recognized that the geologically younger lignites and oxidized coals are more susceptible to solubilization by the fungi.24−28 However, very complex organic matter in coals is rather resistive to direct depolymerization by microorganisms, resulting in low conversion and low microbial efficiency. In
Figure 2. Procedure for the sequential extraction of SL and subsequent GC/MS analysis of the extracts. Received: February 19, 2014 Revised: January 29, 2015
Figure 1. Isolated fungus in the Azure-B and PDA-Bavendamm plate media. © XXXX American Chemical Society
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DOI: 10.1021/ef501928d Energy Fuels XXXX, XXX, XXX−XXX
Energy & Fuels
Article
2. MATERIALS AND METHODS
comparison to higher rank coals, lignites have less aromatic condensation but more ether linkages and methoxy groups. Therefore, lignites are much more hydrophilic and more porous.19,30 Even so, lignites are too complicated to be suitable for direct depolymerization by microorganisms. Oxidative pretreatment would improve the biological solubilization of lignites, but some undesired groups would be introduced simultaneously.31,32 In the present investigation, we isolated Shengli lignite (SL) to several extracts by sequential extraction and examined the microbial direct depolymerization of the extracts.
2.1. SL and Solvents. SL was freshly collected from the Shengli Coal Mine, Inner Mongolian Autonomous Region of China. It was pulverized to pass through a 90 mesh sieve (
