Communication pubs.acs.org/EF
Enrichment and Identification of Condensed Aromatics in a Bio-oil from Degraded Wheat Stalk in Supercritical Ethanol Hua-Mei Yang,†,‡ Wei Zhao,*,†,‡ Yu-Gao Wang,† Dan Liu,†,‡ Jing Zhao,† Xing Fan,† Zhi-Min Zong,† Yao Lu,† and Xian-Yong Wei*,† †
Key Laboratory of Coal Processing and Efficient Utilization (Ministry of Education), China University of Mining & Technology, Xuzhou 221116, Jiangsu, The People’s Republic of China ‡ Key Laboratory of Renewable Energy and Gas Hydrate, Chinese Academy of Sciences, Guangzhou 510640, Guangdong, The People’s Republic of China S Supporting Information *
taken out from the autoclave and filtrated through a membrane filter with a pore size of 0.8 μm, followed by repeated washing of the filter cake with ethanol to extract ethanol-soluble species as completely as possible. The filtrate was distilled using a Büchi R-134 rotary evaporator to afford bio-oil (BO). The BO (4 g) was dissolved in 50 mL of carbon disulfide and then mixed with 12 g of SG under ultrasonic irradiation, followed by solvent removal with the rotary evaporator. The BO−SG mixture was transferred into a 2 cm inner diameter, SG-packed column (height of SG-packed column of 65 cm). The BO was sequentially eluted with PE and MA/PE mixtures to afford fractions F1−1−F4−2. All of the fractions were analyzed with Hewlett-Packard 6890/5973 GC/MS. In total, 54 CAs were detected in F1−1, F4−1, and F4−2, and they can be classified into naphthalene and methyl-substituted naphthalenes (N & MSNs, including mono- and dimethylnaphthalenes), fluorene and methylfluorenes (F & MFs), phenanthrene and methylphenanthrenes (P & MPs), fluoranthene or benzofluorenes (F & BFs), pyrene and methylpyrenes (Py & MPys), biquinolines (BQs), binaphthalenes (BNs), pentacene derivatives (PDs), binaphthofurans (BNFs), and arenofluorenes (AFs, including naphtho- and dibenzofluorenes), as shown in Figures SI-1−SI-6 and Table SI-1 of the Supporting Information. Methyl is the only substituent group for the CAs detected in F1−1, and it is a common group in BO produced in a fix- or cyclone-bed reactor.17−23 The CAs detected in F1−1 are two-ring (i.e., N & MSNs), three-ring (i.e., F & MFs and P & MPs), and four-ring (i.e., F & BFs and Py & MPys) species, while the CAs detected in F4−1 are (i.e., BQs & BNs) and five-ring (i.e., BNFs & AFs) species. PDs are also CAs with five rings and only detected in F4−2. No CAs were detected in other fractions. As exhibited in Figure 2, F1−1, F4−1, and F4−2 account for 7.6, 0.5, and 0.4% of the BO, respectively, and the most abundant CAs are F & MFs and N & MSNs, while the total yield of AFs is almost the same as that of PDs. CAs were also detected from non-catalytically degraded corn stalk in supercritical alkanols24 and from catalytically degraded WS in supercritical ethanol.25 Reported CAs detected in degraded biomass are usually indene, naphthalene, acenaph-
Crop stalks (CSs) are common agricultural wastes in China. The annual yield of CSs in China is ca. 0.7 billion tons,1 but only 1/3 of CSs is used. The problem of dealing with tons of CSs needs to be solved urgently. Part of CSs is piled up along roads, ditches, and even beside houses, which occupies a lot of space and hinders the traffic. During harvest seasons, most of the CSs in China are burned to ensure normal farming.2 CS combustion in the field degrades air quality by emitting soot, carbon monoxide, methane, and other volatile organic compounds and forming aerosol.2−9 Condensed aromatics (CAs) are important parts of aerosol and ubiquitous in the environment.10−12 They are primarily generated from anthropogenic pollution, such as incomplete combustion of oil and biomass in boiler, heating installation, commercial installation, and engine.8,13 CAs associate with inhalable particles, resulting in harm to human health as a result of the teratogenicity, carcinogenicity, and mutagenicity.13−16 They tend to accumulate in aquatic organisms and plants or form more virulent products under effects of photoinduction, bioaccumulation, or biological processes in rivers, lakes, oceans, and soil. Quite a few studies, including volatilization, photo- and chemical oxidation, adsorption to soil particles, leaching, and biodegradation, were focused on seeking solutions to the pollution from CAs.10,13 However, the methods are considered as treatments after CAs enter the environment. It is urgent and necessary to find a clean way to use CSs and avoid CAs emitting to the environment. In the present investigation, we tried to understand the modes of CA occurrences in wheat stalk (WS) by degradation of the WS in supercritical ethanol, column chromatography of degraded WS, and subsequent analysis of the eluted fractions with gas chromatography/mass spectrometry (GC/MS). The WS was collected from a Xuzhou suburb, Jiangsu province, China. It was pulverized to pass through an 80-mesh sieve and dried in a vacuum oven at 105 °C for 3.5 h. Table 1 shows proximate, ultimate, and chemical analyses of the sample. All of the solvents used in the experiment, including petroleum ether (PE), methyl acetate (MA), and ethanol, are analytical reagents and distilled prior to use. Silica gel (SG, 100−200 mesh) was activated in a vacuum oven at 145 °C for 6 h before use. As Figure 1 shows, 10 g of WS and 300 mL of ethanol were put into a 500 mL stainless-steel, magnetically stirred autoclave. The autoclave was heated to 300 °C within 1 h, kept at that temperature for 0.5 h, and then immediately cooled to room temperature in an ice−water bath. The reaction mixture was © 2012 American Chemical Society
Received: July 25, 2011 Revised: December 14, 2012 Published: December 15, 2012 596
dx.doi.org/10.1021/ef300806c | Energy Fuels 2013, 27, 596−598
Energy & Fuels
Communication
Table 1. Proximate, Ultimate, and Chemical Analyses (wt %) of WS proximate analysis
a
ultimate analysis (daf)
chemical analysis
Mad
Aad
Vdaf
C
H
N
S
Oa
cellulose
hemicellulase
lignin
9.6
7.5
70.2
43.1
4.9
0.4
0.2
36.8
45.1
37.2
17.7
By difference.
the detection of BQs, BNs, PDs, BNFs, and AFs, which were enriched in F4−1 and F4−2, from either non-degraded or degraded biomass were seldom reported, if any. Such highly condensed aromatics (HCAs) could be more toxic if they are released to air to form aerosol during incomplete combustion. Great attention should be paid to their toxicities, including teratogenicity, carcinogenicity, and mutagenicity. On the other hand, most CAs, especially HCAs, are value-added chemicals. For example, pentacene is a promising organic compound and mainly used in the preparation of an organic thin-film transistor in the microelectronic field.27−29 BNs are important precursors for preparing organocatalysts,30 chromatographic supports for chiral separation,31 and liquid crystals.32 BQs are important ligands for ruthenium complexes,33 and their derivatives have good biological activity.34 Separating CAs from degraded CSs could be more promising than from coal tar, which is a nonrenewable resource. In summary, we provided an effective approach for enriching and identifying CAs in the BO from degraded WS in supercritical ethanol. Such an approach facilitates both the understanding of the modes of CA occurrences in CS and subsequent fine separation of the CAs.
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ASSOCIATED CONTENT
S Supporting Information *
Total ion chromatograms (TICs) of F1−1, F4−1, and F4−2 from the BO along with corresponding compounds detected and mass spectra of BQs and BNFs detected in F4−1 along with corresponding library spectra. This material is available free of charge via the Internet at http://pubs.acs.org.
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Figure 1. Experimental procedure.
AUTHOR INFORMATION
Corresponding Author
*Telephone: +86 (516) 83995916 (W.Z.); +86 (516) 83884399 (X.-Y.W.). E-mail:
[email protected] (W.Z.);
[email protected] (X.-Y.W.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was subsidized by the funding from the Natural Science Foundation of China for Innovative Research Group (Grant 50921002), National Basic Research Program of China (Grant 2012CB215302), the Jiangsu Provincial Natural Science Foundation (Grant BK2011225), the Fundamental Research Funds for the Central Universities (Grant 2010LKHX08), the Key Laboratory of Renewable Energy and Gas Hydrate, Chinese Academy of Sciences (Grant y007kb), and the Priority Academic Program Development of Jiangsu Higher Education Institutions.
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Figure 2. Distribution of the fractions and CAs in the BO.
thene, fluorene, anthracene, pyrene, and their alkyl derivatives.16,21−23,26 Similar kinds of CAs were detected in F1−1, but
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