Fuel 109 (2013) 61–67

Contents lists available at SciVerse ScienceDirect

Fuel

journal homepage: www.elsevier .com/locate / fuel

Organonitrogen compounds identified in degraded wheat straw by oxidationin a sodium hypochlorite aqueous solution

Yao Lu, Xian-Yong Wei ⇑, Zhi-Min Zong, Yong-Chao Lu, Jing-Pei Cao, Xing Fan, Wei Zhao, Liang-Ce Rong,Yun-Peng Zhao, Li Li, Hong-Lei Yan, Yao-Li PengKey Laboratory of Coal Processing and Efficient Utilization (Ministry of Education), China University of Mining & Technology, Xuzhou 221116, Jiangsu, China

h i g h l i g h t s

" NaOCl is an effective oxidant for wheat straw degradation under mild conditions." Thirty-eight ONCs were identified in the extracts from the degraded wheat straw." Sequential extraction is a potential methodology for removing ONCs." CS2 is effective for enriching unsaturated ONCs from the degraded wheat straw.

a r t i c l e i n f o

Article history:Received 8 February 2012Received in revised form 23 November 2012Accepted 20 December 2012Available online 29 January 2013

Keywords:Organonitrogen compoundsWheat strawSodium hypochloriteExtractionGas chromatography/mass spectrometry

0016-2361/$ - see front matter � 2013 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.fuel.2012.12.093

⇑ Corresponding author. Tel.: +86 516 83885951; faE-mail address: wei_xianyong@163.com (X.-Y. We

a b s t r a c t

Wheat straw (WS) was oxidized in a sodium hypochlorite (NaOCl) aqueous solution at 40 �C followed bysequential extraction of the water-soluble fraction (WSF) with petroleum ether, carbon disulfide (CDS),diethyl ether and ethyl acetate (EA). The EA-inextractable solution was acidized and filtrated. The filtra-tion was also sequentially extracted with the same series of solvents. In total, 38 organonitrogen com-pounds (ONCs) were identified by GC/MS analysis from the extracts. The ONCs can be classified intoamides, sulfonamides, amines, an amino acid, nitriles, an isocyanatoethane, chloro(nitro)methanes, anoxime, N-heterocyclic compounds (NHCCs, most of them are pyrrolidones) and a benzohydrazide, indi-cating the diversity of ONCs in WS. NHCCs, amides and nitriles are the most abundant among the ONCs,implying that these types of species might be main existing forms of nitrogen in the oxidized WS andeven in WS itself to some extent. Most of the ONCs, especially amides and pyrrolidones, were enrichedin the CDS-extractable fraction from the WSF because of the strong p–p interaction between C@S bondin CDS and C@O bonds in the ONCs. This investigation provides an effective approach for understandingthe modes of ONC occurrences in WS.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

The fixed nitrogen species in living organisms are essentialparts of the total nitrogen cycle on the Earth [1–3], where it is pres-ent as DNA, RNA, proteins, peptides and amino acids (AAs), etc. Asthe most abundant renewable resource, lignocellulosic biomass(LCBM) plays crucial role in the transformation of inorganic and or-ganic fixed nitrogen and supplies human needs for energy andnutrition.

When LCBM is used as fuel for power generation, NH3, N2O,NOx, HCN and HNCO are emitted to the atmosphere as the maingas-phase nitrogen species (GPNSs) [2–5], leading to acid rain,photochemical smog and greenhouse effects [6,7]. Total contentof organic nitrogen in LCBM is easy to be determined either by

ll rights reserved.

x: +86 516 83884399.i).

the Kjeldahl method or by elemental analysis. However, mostof the investigations did not give the structures and detailedcharacterization of organonitrogen compounds (ONCs) containedin biomass on molecular level, although investigations on theenvironmental effects of organonitrogen species were paid greatattention [8–10].

Combusted LCBM is believed to be one of the largest sourcesof organic aerosol in the atmosphere [11]. Wheat straw (WS) isone of main agricultural wastes with ca. 530 Mt annual globalproduction. However, it does not provide important use andcommercial interests. Furthermore, the combustion of WS inthe field during wheat harvest in rural area of China becomesmore and more serious environmental problem with the emis-sion of large amounts of biomass burning aerosol (BMBA) andGPNSs. Detailed investigations issued on characterization ofONCs in urban air [12] and BMBA [13] have been reported. Ali-phatic and cyclic amides, arylamides, pyridino and amino types

62 Y. Lu et al. / Fuel 109 (2013) 61–67

of ONCs and NHCCs were detected in BMBA [13–15]. Consequentnatural biogenetic problems may arise due to their mutagenicity,carcinogenicity and toxicity [16]. Several NHCCs such as N-het-erocyclic amines (NHCAs) and condensed arenes (CAs) are car-cinogenic and toxic compounds, inducing cancers andmalformations in aquatic animals and human beings [17–19].The ONCs in BMBA as well as GPNSs result in serious environ-mental problems over the world. Furthermore, like CAs, ONCscontained in LCBM may undergo incomplete combustion andbe partially oxidized or just volatilize with smoke to form BMBA.Therefore, it is essential to ascertain the structures of ONCs con-tained in LCBMs as well as their partially oxidized products toevaluate their environmental effects during the LCBMs are usedas fuel. In a recent investigation, several ONCs such as lactams,amides and NHCCs were identified in the products from fastpyrolysis of sewage sludge [20]. The ONCs identified may bequite different from those in the sewage sludge itself becauseof the severe reaction conditions. Fractional extraction with dif-ferent solvents has been successfully used for isolating ONCs incoals [21–23]. Catalytic hydroconversion was found to releaseONCs more selectively and efficiently [24,25]. Therefore, the deg-radation of LCBMs under mild and selective decomposition con-ditions is desired for obtaining more exact compositionalinformation of ONCs. Oxidation is often used as a pretreatmentprocess in the degradation of biomass, especially lignin, in thepapermaking industry and production of bioethanol [26]. Sodiumhypochlorite (NaOCl) is an easy available and strong oxidizingreagent used as bleaching reagent and bactericide, and provedto be effective and selective for coal degradation [27].

In this study, mild oxidation with NaOCl aqueous solutionwas used to degrade WS followed by sequential extraction ofthe resulting water-soluble fraction (WSF) and subsequent anal-yses, especially with gas chromatography/mass spectrometry(GC/MS) to understand the modes of ONCs occurrences in WS.

2. Experimental

2.1. Materials

WS was collected from the field in the vicinity of XuzhouCity, Jiangsu, China. It was washed with fresh water and thendried in sunlight for more than 2 months, chopped into smallpieces, pulverized to pass through an 80-mesh sieve (<180 lm)and followed by desiccation in a vacuum drying oven (VDO) at80 �C for 24 h. Table 1 shows the proximate and ultimate analy-ses of the dried WS sample. Analytical pure NaOCl (6% availablechlorine) aqueous solution was used directly. The strength of theoxidant was determined by iodometric titration with Na2S2O3

aqueous solution. All the organic reagents such as petroleumether (PE), carbon disulfide (CDS), diethyl ether (DEE) and ethylacetate (EA) were also analytical-pure reagents and distilled witha Büchi R-134 rotary evaporator prior to use to remove possiblypresent impurities, especially nitrogen-containing species.

Table 1Proximate and ultimate analyses (wt.%) of WS sample.a

Proximate analysis Ultimate analysis (daf)

Mad Ad Vdaf C H Ob N S

8.0 8.2 70.2 42.3 6.6 50.2 0.3 0.6

a M, moisture; A, ash; V, volatile matter; ad, air-dried base; d, dry base; daf, dryand ash-free base.

b By difference.

2.2. General procedure

As shown in Fig. 1, 10 g WS and 100 mL NaOCl aqueous solution(the mass ratio of WS/NaOCl was ca. 0.79) were added to a 250 mLspherical flask and magnetically stirred at 40 �C for 24 h. Thenreaction mixture was filtrated to afford filter cake 1 (FC1,) and fil-trate 1 (F1). The FC1 was dried in the VDO at 80 �C for 24 h and thenweighed (7.18 g). The F1 was sequentially extracted with PE, CDS,DEE and EA (100 mL of each solvent was used) in a separatory fun-nel to afford extraction solutions ES1–1–ES1–4 and inextractablesolutions IES1–1–IES1–4 correspondingly, and extracts E1–1–E1–4

were obtained by evaporating solvents in ES1–1–ES1–4, respectively.The IES1–4 was acidified with 35% of muriatic acid to pH 2–3 to con-vert ACOONa to ACOOH and filtrated to afford filter cake 2 (FC2)and filtrate 2 (F2). The FC2 was dried in the VDO at 80 �C for 24 hand then weighed (0.01 g). Similar sequential extraction for F2 iso-lation and subsequent solvent evaporation were conducted to af-ford extraction solutions ES2–1–ES2–4, corresponding extracts E2–

1–E2–4 and inextractable solutions IES2–1–IES2–4, as illustrated inFig. 2. The IES2–4 was also evaporated to afford inextractable frac-tion (IEF). The E2–3, E2–4 and IEF were esterified with CH2N2 to af-ford MEE1, MEE2 and MEIEF, respectively. The above experimentswere repeatedly conducted. The mass (mOM in F1) of organic matter(OM) transferred from WS to the F1 was calculated according to thedifference in OM mass between WS (mOM in WS) and FC1 (mOM in

FC1):

mOM in F1 ¼ mOM in WS �mOM in FC1

The yields (YONCs in F1/WS and YONCs in extract/WS) of ONCs enrichedinto organic matter (OM) in the F1 and each extract based on OM inWS were calculated according to mass ratio of the ONCs (mONCs in F1

and mONCs in extract) detected to OM in WS:

YONCs in F1=WS ¼ mONCs in F1=mOM in WS

YONCs in extract=WS ¼ mONCs in extract=mOM in WS

Corresponding contents of nitrogen enriched into the F1 basedon OM in WS (CN in F1/WS) and in OM transferred from WS to theF1 (CN in F1/F1) were calculated according to the following formula:

CNinF1=WS ¼PðMN:mONC in F1=MONCÞ=mOM in WS

CN in F1=F1 ¼PðMN:mONC in F1=MONCÞ=ðmOM in WS �mOM in FC1Þ

where MN, mONC in F1 and MONC denote atomic mass of nitrogen,mass of individual ONC and molecular mass of individual ONC,respectively.

2.3. FTIR analysis

All the extracts were analyzed with a Nicolet Magna IR-560Fourier transform infrared (FTIR) spectrometer using KBr pelletmethod. The spectra were recorded by collecting 50 scans at a res-olution of 8 cm�1 in reflectance mode with measuring regions of4000–500 cm�1.

2.4. GC/MS analysis

A Hewlett–Packard 6890/5973 GC/MS system, which isequipped with a HP-5MS capillary column (crosslink 5% PH MEsiloxane, 30 m � 0.32 mm i.d., 0.25 lm film thickness) and a quad-rupole analyzer, was used for analyzing all the extracts. Mass spec-tra were obtained at an electron impact potential of 70 eV. Heliumwas used as the carrier gas. The column was heated first at a rate of5 �C/min from 60 �C to 150 �C and then at a rate of 7 �C/min from150 to 300 �C (and held for 15 min). Both injector and detectortemperatures were set at 300 �C. The mass range scanned was from30 to 500 m/z. The reproducibility of quantitative analysis for the

10 g WS

magnetical agitation followed by filtration

100 mL NaOCl (aq)

FC1

dried and weighed

F1extaction with PE

ES1-1 IES1-1extraction with CDS

ES1-2 IES1-2

ES1-3 IES1-3extraction with EA

extraction with DEE

IES1-4

solvent evaporation

E1-2

solvent evaporation

solvent evaporation

E1-3

solvent evaporation

E1-4

acidification followed by filtration

FC2 F2

GC/MS analysis

dried and weighed to stage 2

E1-1

ES1-4

Fig. 1. Procedure for WS oxidation with NaOCl, subsequent treatment, and product analyses (Stage 1).

F2extaction with PE

ES2-1 IES2-1extraction with CDS

ES2-2 IES2-2

ES2-3 IES2-3extraction with EA

extraction with DEE

ES2-4

E2-2

E2-1

solvent evaporation

solvent evaporation

solvent evaporation

GC/MS analysis

E2-4

MEE2

methyl esterification

MEE1

E2-3methyl esterification

MEIEF

solvent evaporation

IES2-4

IEF

Fig. 2. Subsequent treatment of F2 and product analyses (Stage 2).

10004000

2929 28

50

E1-1

E1-2

E1-3

E1-4

E2-1

E2-2

MEE1

MEE2

3412

1736

1627

Tran

smitt

ance

(%)

Wavenumbers (cm-1)

2270

1402

1217 10

90

838

678

3000 2000

Fig. 3. FTIR spectra of the extracts from F1 and F2.

Y. Lu et al. / Fuel 109 (2013) 61–67 63

ONCs was conducted by duplicated injection of the samples. Thedata were acquired and processed using Chemstation softwarewith the GC/MS system. The ONCs were identified by comparingmass spectra with National Institute of Standards and Technologylibrary data according to fragmentation rules of organic species un-der electron ionization condition. Quantitative analysis was con-ducted using dimethyl phthalate as the external standard.

3. Results and discussion

3.1. FTIR analysis

As shown in Fig. 3, the spectra exhibit several characteristicabsorptions of ONCs around 3412 cm�1 (NAH stretching), 1736–1627 cm�1 (amide I and II bands) and 1402 cm�1 (ANO2 stretch-

ing). The strong absorbance between 3300 and 3600 cm�1 is as-signed to AOH stretching. Another band between 2800 and3000 cm�1 as well as a band around 1400 cm�1 are attributed tostretching and bending of aliphatic CAH, respectively. The sharpabsorbance at 1736 cm�1 is assigned to C@O stretching in ketones,aldehydes and carbonyl groups in esters. The weak bands around1217 cm�1 and 1090 cm�1 are attributed to CAO stretching vibra-tions of carboxylic acids or CAN stretch vibrations by amide II. A

Table 2YONCs in F1/WS (10�5 g g�1, daf) of ONCs detected in the extracts from F1.

Peak ONC Formula Detected in

E1–1 E1–2 E1–3 E1–4

Nitrile3 2-Hydroxyacetonitrile C2H3NO 1.7 ± 0.26 Succinonitrile C4H4N2 1.6 ± 0.2 3.7 ± 0.412 Glutaronitrile C5H6N2 28.6 ± 1.5 8.3 ± 1.4 3.6 ± 0.416 Benzonitrile C7H5N 87.4 ± 9.5 26.8 ± 3.822 3-Chlorobenzonitrile C7H4ClN 5.3 ± 0.523 4-Hydroxy-3-methoxybenzonitrile C8H7NO2 16.6 ± 4.2

ICE4 1-Chloro-2-isocyanatoethane C3H4ClNO 0.5 ± 0.1

Amide9 2,2-Dichloroacetamide C2H3Cl2NO 15.4 ± 1.8 9.8 ± 1.319 2,2,2-Trichloroacetamide C2H2Cl3NO 11.3 ± 0.8 56.4 ± 4.3 2.3 ± 0.234 Palmitamide C16H33NO 69.3 ± 12.335 Oleamide C18H35NO 96.6 ± 15.636 Stearamide C18H37NO 64.8 ± 11.2

NHCC10 1-Methylpyrrolidin-2-one C5H9NO 10.2 ± 0.6 112 ± 8.4 4.3 ± 0.4 5.5 ± 0.613 Pyrrolidin-2-one C4H7NO 6.5 ± 0.714 1-Methylpyrrolidine-2,5-dione C5H7NO2 4.5 ± 0.3 35.2 ± 2.6 2.9 ± 0.2 5.2 ± 0.520 Oxazolidin-2-one C3H5NO2 5.8 ± 0.5 4.7 ± 0.324 5-Isopropylimidazolidine-2,4-dione C6H10N2O2 3.2 ± 0.528 2-Chloro-6-methylnicotinic acid C7H6ClNO2 2.7 ± 0.333 (E)-3-(2-(Dimethylamino)vinyl)-9H-indeno[2,1-c]pyridin-9-one C16H14N2O 33.1 ± 8.3 5.8 ± 1.4

CNM15 Dichloro(nitro)methane CHCl2NO2 29.6 ± 4.3 106 ± 9.021 Trichloro(nitro)methane CCl3NO2 29.8 ± 5.8

SA29 N,4-Dimethylbenzenesulfonamide C8H11NO2S 18.4 ± 3.4 29.3 ± 4.6

BH30 4-Hydroxy-3,5-dimethoxybenzohydrazide C9H12N2O4 48.7 ± 7.3

Table 3YONCs in F1/WS (10�5 g g�1, daf) of ONCs detected in the extracts from F2.

Peak ONC Formula Detected in

E2–1 E2–2 MEE1 MEE2

Oxime1 (E)-2,3-Dioxobutanal O-methyl oxime C5H7NO3 22.3 ± 3.3

AA2 2-Amino-3-methoxybutanoic acid C5H11NO3 9.1 ± 1.3

NHCC5 2-Chloroquinoline-4-carboxylic acid C10H6ClNO2 3.9 ± 1.37 4-Methyl-1H-imidazole C4H6N2 68.3 ± 7.610 1-Methylpyrrolidin-2-one C5H9NO 0.28 ± 0.04 0.60 ± 0.0214 1-Methylpyrrolidine-2,5-dione C5H7NO2 0.11 ± 0.0117 1-Ethyl-2,3-dihydro-1H-imidazole C5H10N2 3.7 ± 0.818 1H-Imidazole-2-carboxaldehyde C4H4N2O 9.2 ± 1.326 3-Isopropyl-6-methylpiperazine-2,5-dione C8H14N2O2 3.6 ± 0.537 2-(2-(Piperidin-4-yl)pyrimidin-5-yl)benzo[d]oxazole C16H16N4O 5.7 ± 1.3

Nitrile8 Methyl 3-cyanopropanoate C5H7NO2 39.4 ± 7.511 Ethyl 3-cyanopropanoate C6H9NO2 4.9 ± 1.216 Benzonitrile C7H5N 2.1 ± 0.3

Amide19 2,2,2-Trichloroacetamide C2H2ClNO 0.16 ± 0.0231 N-(3-Chlorophenyl)cyclopentanecarboxamide C12H14ClNO 12.3 ± 1.6

CNM21 Trichloro(nitro)methane CCl3NO2 1.9 ± 0.3

Amine25 Methyl 2-amino-3,5-dichlorobenzoate C8H7ClNO2 4.2 ± 0.427 3-(Phenylamino)phenol C12H11NO 5.7 ± 1.132 5-Chloro-4,6-dimethylpyrimidin-2-amine C6H8ClN3 6.8 ± 1.2

SA38 N,4-Dimethyl-N-tosylbenzenesulfonamide C15H17NO4S2 2.3 ± 0.3

64 Y. Lu et al. / Fuel 109 (2013) 61–67

0.5

0.6

0.7

0.8

(wt%

, daf

)

Y. Lu et al. / Fuel 109 (2013) 61–67 65

weak band around 2270 cm�1 can be assigned to nitrile (AC„N)and isonitrile (AN@C) stretchings. Absorbances around 678, 838,1630 and 3100 cm�1 are assigned to aromatic CAH stretching.The significant absorbance around 1627 cm�1 suggests thepresence of amide in E1–2.

0.0

0.1

0.2

0.3

0.4

E1-1 E1-2 E1-3 E1-4 E2-1 E2-2 MEE1 MEE2

Extract

Y ON

Cs

in e

xtra

ct/W

S

Fig. 5. Yields of ONCs enriched in different extracts.

3.2. GC/MS analysis

As Figs. S1 and S2 (see Electronic Annex as Supplementary datain the online version of this article) along with Tables 2 and 3 show,in total, 38 ONCs were identified. The ONCs can be classified into anoxime (peak 1), an amino acid (AA, peak 2), nitriles (peaks 3, 6, 8, 11,12, 16, 22 and 23), an isocyanatoethane (ICE, peak 4), NHCCs (peaks5, 7, 10, 13, 14, 17, 18, 20, 24, 26, 28, 32, 33 and 37), amides (peaks 9,19, 31, 34–36), chloro(nitro)methanes (CNMs, peaks 15 and 21),amines (peaks 25 and 27), sulfonamides (SAs, peaks 29 and 38)and a benzohydrazide (BH, peak 30). To the best of our knowledge,no reports were issued on such detailed identification of ONCs fromany biomass or its degradation products. Repeated experiments,including duplicated injection of samples for GC/MS analysis andreproduction of the sample preparation, were conducted. All thedata are expressed as average values. The reproducibility of theGC/MS analysis for the each sample and the relative standard devi-ations for all the ONCs were less than 5%.

As shown in Fig. 4, amides and NHCCs are the most abundantgroup components, while the yields of other group components de-creased in the following order: nitriles > CNMs > SAs > BH > oxi-me > amines = AA > ICE. The amides include twochloroacetamides (peaks 9 and 19), three long-chain fatty acidamides (FAAs, peaks 34–36) with high yields and a carboxamide(peak 31). Most of them except the carboxamide were detectedin E1–2. The NHCCs are a quinoline derivative (peak 5), four imida-zoles (peaks 7, 17, 18 and 24), three lactams (peaks 10, 13 and 14),a piperazinedione derivative (peak 26), two pyridines (peaks 28and 33) and two pyrimidines (peaks 32 and 37). The lactams werereported to be formed via decarboxylation and cyclization of c-and d-amino acids [20]. The nitriles consist of an acetonitrile deriv-ative (peak 3), two alkanedinitriles (peaks 6 and 12), two alkylcyanopropanoates (peaks 8 and 11) and three benzonitriles (peaks16, 22 and 23). Eleven chlorine-containing ONCs (peaks 4, 5, 9, 15,19, 21, 22, 25, 28, 31 and 32) were identified. Most of them mightbe derived from substitution reaction with OCl� from NaOCl andsubsequent hydrolytic reaction. SA 29 could be the product of SA38 via the cleavage of SAN bond during the oxidative degradation.

amides

YO

NC

s in

F1 /

WS (

wt%

, daf

)

0.00nitrilesamines AAsAS I

0.05

0.10

0.15

0.20

0.25

0.30

Group component

YONCs in F1/WS

CN in F1/WS

0.35

Fig. 4. Yields of group components of ONCs

The BH 30 contains a typical structure of basic lignin unit, i.e.,syringyl.

As Fig. 5 displays, most of the ONCs were enriched into E1–2 andall the ONCs in E1–2 shown in Table 2 contain unsaturated bonds(USBs). These facts suggest that CDS is effective for extracting ONCsfrom the F1. Zong et al. first reported the thionation of 1-methyl-pyrrolidin-2-one (MP) with CDS at elevated temperatures and as-cribed the thionation to the strong p–p interaction between C@Sbond in CDS and C@O bond in MP, subsequent cyclization betweenthe C@S and C@O bonds and ring-opening reaction [28]. Similarinteraction between C@S bond in CDS and C@O bond in a seriesof amides and subsequent reactions were also reported [29]. Basedon such an interaction, a series of ONCs were extracted by CDSfrom Tongchuan oil shale [30] and Shengli lignite [31]. Therefore,the effectiveness of CDS for extracting the ONCs from the F1 shouldbe closely related to the intermolecular interaction between CDSand the USBs in the ONCs.

According to quantitative analysis of the extracts shown inFig. 4, CN in F1/WS and YONCs in F1/WS are 0.16% and 1.22%, respectively,while nitrogen content in WS is 0.3% (Table 1), indicating that morethan 50% of nitrogen was transferred into the F1 and ONCs werehighly enriched into the F1 during the oxidative degradation of WS.

3.3. Possible mechanisms for the release of ONCs from WS

NaOCl was reported to be a selective reagent for the oxidationof sp3 and sp2 carbons in coals [32,33]. Active species for NaOCl

CN

in F

1 /W

S (

wt%

, daf

)

NHCCsCNMs BHemixoCE

of the ONCs

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

and corresponding nitrogen contents.

Scheme 1. Possible mechanism for the release of CNMs 15 and 21 from the MMC in WS during oxidation with NaOCl.

66 Y. Lu et al. / Fuel 109 (2013) 61–67

as the oxidant were proposed to be O��2 , Cl��2 and Cl2 generatedaccording to the following reactions [34]:

NaOCl�Naþ þ �OCl2�OCl�O��2 þ Cl��2

Naþ þ Cl��2 �NaClþ Cl�

2Cl� �Cl2

The active species could play important roles in the release ofONCs from WS during oxidation with NaOCl. For example, the pre-cursor of CNMs 15 and 21 could be a macromolecular component(MMC), in which (2,6-dimethoxy-4-(nitromethyl)phenoxy)methylgroup connects to a macromolecular moiety. As Scheme 1 illus-trates, three methoxy groups in 1-, 3- and 5-positions of benzenering (BR) in the MMC facilitates O��2 addition to 4-position of theBR to afford intermediate (IM) 1. Subsequent cleavage of CAC bondconnecting the BR to nitromethyl group occurs to produce IM 2 andnitromethyl radical (NM�). Monochloro(nitro)methane (MCNM) isformed by the reaction of NM. with Cl�. Hydrogen transfer fromthe NM� to oxygen anion in IM 2 followed by the cleavage of OAO�

bond in IM 2 leads to the formation of monochloro(nitro)methylradical (MCNM�) and IM 3 along with AOH. Then, two possiblereactions could occur. The first one is the abstraction of Cl� fromCl2 by the MCNM� and IM 3 to generate CNM 15 and macromolec-ular product 1 (MMP 1). The other is direct abstraction of Cl. by theMCNM� to result in the generation of CNM 15 followed by hydro-gen transfer from CNM 15 to oxygen radical in IM 3 to form di-chloro(nitro)methyl radical (DCNM�) and MMP 2. CNM 21 isderived from the reaction of Cl� with the resulting DCNM�.

Both AAs and amines are ANH2 group-containing species,which can react with either HOCl or NaOCl to produce nitrilesvia sequential substitution, elimination and hydrolysis [35–39].Some nitriles were also identified in degradation products frombiomass [20,40–43] and in an extract from an Erdos coal [44].Therefore, the nitriles identified in the extracts from the F1 couldbe either intrinsic components in WS or derived from the oxidativedegradation of WS with NaOCl. No AOCN group-containing specieswere detected and only one ANCO group-containing component(i.e., ICE 4) was identified, while nitriles are one class of the mostabundant ONCs as displayed in Fig. 4, indicating that the oxidationof ACN group in the nitriles with NaOCl is very difficult under thereaction conditions. In fact, acetonitrile has been widely used as asolvent for ruthenium ion-catalyzed oxidation (RICO) of organicmatter in coals [45,46], an immature asphaltene [47], kerogens[48], soils [49] and meteorites [50], suggesting that ACN group isstable enough during the oxidation.

4. Conclusions

ONCs were significantly enriched into the degraded WS fromthe oxidation in NaOCl aqueous solution under mild conditions.The ONCs identified in the extracts from the degraded WS includean oxime, an AA, nitriles, an ICE, NHCCs, amides, CNMs, amines,SAs and a BH, among which NHCCs, nitriles and amides are themost abundant. CDS is effective for enriching unsaturated ONCsfrom the degraded WS. The combination of oxidation in NaOClaqueous solution under mild conditions with subsequent sequen-tial extraction and GC/MS analysis proved to be an effective ap-proach for understanding the modes of ONC occurrences in WSand provided a useful tool for identifying ONCs in other biomass.

Acknowledgments

This work was subsidized by National Basic Research Programof China (Grant 2012CB215302), the Fund from Natural ScienceFoundation of China for Innovative Research Group (Grant51221462), the Program of the University in Jiangsu Province forGraduate Student’s Innovation in Science Research (GrantCXZZ11_0302), National Natural Science Foundation of China(Grant 21206189), the Fundamental Research Funds for the CentralUniversities (China University of Mining and Technology; Grants2011QNA22 and 2012QNA15), China Postdoctoral Science Founda-tion Funded Project (Grants 2011M500975 and 2012T50501),National Innovation Experiment Program for University Students(Grant 201210290059) and the Priority Academic ProgramDevelopment of Jiangsu Higher Education Institutions.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.fuel.2012.12.093.

References

[1] Chapin III FS, Matson PA, Mooney HA. Principles of Terrestrial EcosystemEcology. New York: Springer, Verlag; 2002.

[2] Hansson KM, Samuelsson J, Tullin C, Åmand LE. Formation of HNCO, HCN andNH3 from the pyrolysis of bark and nitrogen containing model compounds.Combust Flame 2004;137(3):265–77.

[3] Tian FJ, Yu JL, Mckenzie LJ, Hayashi J, Li CZ. Conversion of fuel-N into HCN andNH3 during the pyrolysis and gasification in steam: a comparative study of coaland biomass. Energy Fuels 2007;21(2):517–21.

[4] Matthews E. Nitrogenous fertilizers: global distribution of consumption andassociated emissions of nitrous oxide and ammonia. Global Biogeochem Cy1994;8(4):411–39.

Y. Lu et al. / Fuel 109 (2013) 61–67 67

[5] Bouwman AF, Lee DS, Asman WAH, Dentener FJ, Van der Hoek KW, Olivier JGJ.A global highresolution emission inventory for ammonia. Global BiogeochemCy 1997;11(4):561–87.

[6] Purvis MRI, Tadulan EL, Tariq AS. NOx control by air staging in a small biomassfuelled underfeed stoker. Int J Energ Res 2000;24(10):917–33.

[7] Ogawa M, Yoshida N. Nitrous oxide emission from the burning of agriculturalresidue. Atmos Environ 2005;39(19):3421–9.

[8] Cornell S, Rendell A, Jickells T. Atmospheric inputs of dissolved organicnitrogen to the oceans. Nature (London) 1995;376(6537):243–6.

[9] Jickells TD. Nutrient biogeochemistry of the coastal zone. Science1998;281(5374):217–22.

[10] Duce RA, LaRoche J, Altieri K, Arrigo KR, Baker AR, Capone DG, et al. Impacts ofatmospheric anthropogenic nitrogen on the open ocean. Science2008;320(5878):893–7.

[11] Simoneit BRT. Biomass burning – a review of organic tracers for smoke fromincomplete combustion. Appl Geochem 2002;17(3):129–62.

[12] Wang X, Gao S, Yang X, Chen H, Chen J, Zhuang G, et al. Evidence for highmolecular weight nitrogen-containing organic salts in urban aerosols. EnvironSci Technol 2010;44(12):4441–6.

[13] Novakov T, Mueller PK, Alcocer AE, Otvos JW. Chemical composition ofPasadena aerosol by particle size and time of day: III. Chemical states offnitrogen and sulfur by photoelectron spectroscopy. J Colloid Interf Sci1972;39(1):225–34.

[14] Cheng Y, Li SM, Leithead A. Chemical characteristics and origins of nitrogen-containing organic compounds in PM2.5 aerosols in the Lower Fraser Valley.Environ Sci Technol 2006;40(19):5846–52.

[15] Laskin A, Smith JS, Laskin J. Molecular characterization of nitrogen-containingorganic compounds in biomass burning aerosols using high-resolution massspectrometry. Environ Sci Technol 2009;43(10):3764–71.

[16] Kaiser JP, Feng Y, Bollag JM. Microbial metabolism of pyridine, quinoline,acridine and their derivatives under aerobic and anaerobic conditions.Microbiol Rev 1996;60(3):483–98.

[17] Knize MG, Kulp KS, Salmon CP, Keating GA, Felton JS. Factors affecting humanheterocyclic amine intake and the metabolism of PhIP. Mutat Res 2002;506–507:153–62.

[18] Sugimura T, Wakabayashi K, Nakagama H, Nagao M. Heterocyclic amines:mutagens/carcinogens produced during cooking of meat and fish. Cancer Sci2004;95(4):290–9.

[19] Burysková B, Hilscherová K, Bláha L, Marsálek B, Holoubek I. Toxicity andmodulations of biomarkers in Xenopus laevis embryos exposed to polycyclicaromatic hydrocarbons and their N-heterocyclic derivatives. Environ Toxicol2006;21(6):590–8.

[20] Cao JP, Zhao XY, Morishita K, Wei XY, Takarada T. Fractionation andidentification of organic nitrogen species from bio-oil produced by fastpyrolysis of sewage sludge. Bioresour Technol 2010;101(19):7648–52.

[21] Wei XY, Wang XH, Zong ZM, Ni ZH, Zhang LF, Ji YF, et al. Identification oforganochlorines and organobromines in coals. Fuel 2004;83(17–18):2435–8.

[22] Zhao XY, Zong ZM, Cao JP, Ma YM, Han L, Liu GF, et al. Difference in chemicalcomposition of carbon disulfide-extractable fraction between vitrinite andinertinite from Shenfu-Dongsheng and Pingshuo coals. Fuel 2008;87(4–5):565–75.

[23] Wei XY, Wang XH, Zong ZM. Extraction of organonitrogen compounds fromfive Chinese coals with methanol. Energy Fuels 2009;23(10):4848–51.

[24] Wei XY, Ni ZH, Xiong YC, Zong ZM, Wang XH, Cai CW, et al. Pd/C-catalyzedrelease of organonitrogen compounds from bituminous coals. Energy Fuels2002;16(2):527–8.

[25] Sun LB, Wei XY, Liu XQ, Zong ZM, Li W. Release of organonitrogen andorganosulfur compounds during hydrotreatment of Pocahontas No. 3 coalresidue over an activated carbon. Energy Fuels 2009;23(10):5284–6.

[26] Taherzadeh MJ, Karimi K. Pretreatment of lignocellulosic wastes to improveethanol and biogas production: a review. Int J Mol Sci 2008;9(9):1621–51.

[27] Yao ZS, Wei XY, Lv J, Liu FJ, Huang YG, Xu JJ, et al. Oxidation of Shenfu coal withRuO4 and NaOCl. Energy Fuels 2010;24(3):1801–8.

[28] Zong ZM, Peng YL, Qin ZH, Liu JZ, Wu L, Wang XH, et al. Reaction of N-methyl-2-pyrrodinone with carbon disulfide. Energy Fuels 2000;14(3):734–5.

[29] Zong ZM, Peng YL, Liu ZG, Zhou SL, Wu L, Wang XH, et al. Convenient synthesisof N-methylpyrrolidine-2-thione and some thioamides. Korean J Chem Eng2003;20(2):235–8.

[30] Cao JP, Zong ZM, Zhao XY, Zhou M, Ma XX, Zhou GJ, et al. Identification ofoctathiocane, organonitrogens and organosulfurs in Tongchuan shale. EnergyFuels 2007;21(2):1193–4.

[31] Ding MJ, Zong ZM, Zong Y, Ou-Yang XD, Huang YG, Zhou L, et al. Isolation andidentification of fatty acid amides from Shengli coal. Energy Fuels2008;22(4):2419–21.

[32] Hyyatsu R, Scott RG, Moore LP, Studier MH. Aromatic units in coal. Nature1975;257(5525):378–80.

[33] Mayo FR. Application of sodium hypochlorite oxidations to the structure ofcoal. Fuel 1977;54(4):273–5.

[34] Qie LM, Wei XY, Li JN, Wei Q, Zong ZM, Lv J, et al. Anthracene oxidation inaqueous sodium hypochlorite solution. Energy Sources, Part A. doi:10.1080/15567036.2011.594855.

[35] Ogata Y, Kimura M, Kondo Y. Photo-promoted hypochlorite oxidation of a-amino acids. Kinetics and irradiation effect for the Strecker degradation. BullChem Soc Jpn 1981;54(7):2057–60.

[36] Hawkins CL, Pattison DI, Davies MJ. Hypochloriteinduced oxidation of aminoacids, peptides and proteins. Amino acids 2003;25(3–4):259–74.

[37] Li J, Blatchley ER. Volatile disinfection byproduct formation resulting fromchlorination of organic-nitrogen precursors in swimming pools. Environ SciTechnol 2007;41(19):6732–9.

[38] Deborde M, von Gunten U. Reactions of chlorine with inorganic and organiccompounds during water treatment-kinetics and mechanisms: a criticalreview. Water Res 2008;42(1–2):13–51.

[39] Bull RJ, Reckhow DA, Li XF, Humpage AR, Joll C, Hrudey SE. Potentialcarcinogenic hazards of non-regulated disinfection by-products:haloquinones, halo-cyclopentene and cyclohexene derivatives, N-alamines,halonitriles, and heterocyclic amines. Toxicology 2011;286(1–3):1–19.

[40] Boon JJ, de Leeuw JW. Amino acid sequence information in proteins andcomplex proteinaceous material revealed by pyrolysis–capillary gaschromatography–low and high resolution mass spectrometry. J Anal ApplPyrol 1987;11:313–27.

[41] Potthast A, Schiene R, Fischer K. Structural investigations of N-modified ligninsby 15N NMR spectroscopy and possible pathways for formation of nitrogencontaining compounds related to lignin. Holzforschung 1996;50(6):554–62.

[42] Cao JP, Zhao XY, Morishita K, Li LY, Xiao XB, Obara R, et al. Triacetonamineformation in a bio-oil from fast pyrolysis of sewage sludge using acetone as theabsorption solvent. Bioresour Technol 2010;101(11):4242–5.

[43] Cao JP, Li LY, Morishita K, Xiao XB, Zhao XY, Wei XY, et al. Nitrogentransformations during fast pyrolysis of sewage sludge. Fuel 2013;104:1–6.

[44] Zong Y, Zong ZM, Ding MJ, Zhou L, Huang YG, Zheng YX, et al. Separation andanalysis of organic compounds in an Erdos coal. Fuel 2009;88(3):469–74.

[45] Stock LM, Wang SH. Ruthenium tetroxide catalysed oxidation of coals: theformation of aliphatic and benzene carboxylic acids. Fuel1986;65(11):1552–62.

[46] Huang YG, Zong ZM, Yao ZS, Zheng YX, Mou J, Liu GF, et al. Ruthenium ion-catalyzed oxidation of Shenfu coal and its residues. Energy Fuels2008;22(3):1799–806.

[47] Peng PA, Fu JM, Sheng GY, Morales-Izquierdo A, Lown EM, Strausz OP.Ruthenium-ions-catalyzed oxidation of an immature asphaltene: structuralfeatures and biomarker distribution. Energy Fuels 1999;13(2):266–77.

[48] Hideyoshi Y, Ryoshi I. An improved ruthenium tetroxide oxidation of marineand lacustrine kerogens: possible origin of low molecular weight acids andbenzenecarboxylic acids. Org Geochem 2005;36(1):83–94.

[49] Anja W, Ludwig H, Wolfgang Z. Insoluble alkyl carbon components in soilsderive mainly from cutin and suberin. Org Geochem 2005;36(4):519–29.

[50] Laurent R, Sylvie D, Francois R. New insight on aliphatic linkages in themacromolecular organic fraction of Orgueil and Murchison meteorites throughruthenium tetroxide oxidation. Geochim Cosmochim Acta2005;69(17):4377–86.