Double Bond Equivalent Values Research Articles

Identification of organooxygen compounds in the methanol-soluble portion from the methanolysis of pretreated rice straw with Trichoderma sp. AH

The effect of pretreatment (PT) with Trichoderma sp. AH on the organooxygen compounds (OOCs) in methanol-soluble portions (MSPs) obtained from the methanolysis of raw and pretreated rice straw (RS) was investigated. According to the analyses with a gas chromatograph/mass spectrometer (GC/MS) and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer, molecular masses (MMs) of the OOCs range from 100 to 500 u and are dominant from 300 to 450 u. The relative abundances of detected compounds with MMs from 300 to 350 u in MSP of pretreated RS are higher than those in MSP of raw RS. The predominant compounds in MSPs of raw and pretreated RSs are On (n = 1–10) with double bond equivalent (DBE) values of 1–28 and carbon atom numbers (CANs) of 4–35. The most abundant classes in MSPs of raw and pretreated RSs are O5 and O4, respectively. Besides, N1On (n = 0–9) classes with DBE values of 1–23 and CANs of 4–35 were also identified. These results facilitate understanding the effect of pretreatment with Trichoderma sp. AH on RS conversion and OOC selectivity from the methanolysis of RS and the application of MSP in producing transportation fuel.

Characterization of soluble portions from cellulose, hemicellulose, and lignin methanolysis

Methanolysis of the three biomass components was conducted to afford soluble portions (SPs) and residues. Cellulose has the highest SP yield, followed by hemicellulose and lignin. The relatively volatile or less polar species in the SPs were analyzed with a gas chromatograph/mass spectrometer (GC/MS) and the polar species were identified with a negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). According to analysis with GC/MS, sugars, esters, and phenols are the predominant compounds in cellulose- and hemicellulose-, and lignin-derived SPs, respectively. The analysis with FTICRMS shows that the molecular masses in the SPs range from 100 to 500 u and those in cellulose-/hemicellulose-derived SPs dominate from 250 to 300 u but in lignin-derived SP concentrates from 300 to 350 u. The identified compounds were assigned to On class species with double bond equivalent (DBE) values of 1–14 and carbon atom numbers of 5–35. The most abundant class species in cellulose-, hemicellulose-, and lignin-derived SPs are O5, O5, and O2, respectively. The van Krevelen diagrams of On class species suggest that primary species in lignin-derived SP are mainly located in a relatively narrow region with atomic ratio of O/C 0.0–0.3 and atomic ratio of H/C 1.0–1.3, while those in cellulose- and hemicellulose-derived SPs are principally located in a wider region with atomic ratio of O/C 0.2–0.8 and atomic ratio of H/C 0.8–1.5. The oxygen atom numbers of O4−O10 class species was negatively correlated with the average DBE value, which indicates a cyclic structure or double bond will be generated (opened or saturated) with the removal (addition) of oxygen atoms.

Structural insights of four thermal dissolution products of Dongming lignite by using in-source collision-activated dissociation mass spectrometry

Thermal dissolution (TD) plays an important role in obtaining soluble components from low-rank coals. Characterization of the TD product is essential for both optimization of TD conditions and in-depth understanding of molecular structures in coal that is crucial for the refining processes. In-source collision-activated dissociation (ISCAD) combined with high-resolution mass spectrometry (MS) was employed in this study to analyze four TD products of a low-rank coal obtained by using cyclohexane, acetone, methanol and ethanol as solvents. ISCAD-MS allows the evaluation of distributions of oxygen and nitrogen atoms located within aromatic cores or on alkyl chains based on the abundances of heteroatom-containing precursor ions and fragment ions. In addition, ISCAD-MS can evaluate the abundance of multi-core compounds based on the change of average double bond equivalent value upon fragmentation. These structural details advance the current understanding of the TD products at the molecular level.

Influence of solvent on the yield and chemical composition of liquid products of hydrothermal liquefaction of Arthrospira platensis as revealed by Fourier transform ion cyclotron resonance mass spectrometry.

Yields of liquid products (bio-oil and residual organics in aqueous solution) of hydrothermal liquefaction (at 300℃ and 60 min) of own cultivated Arthrospira platensis using different solvents have been determined. Nonpolar hexane, moderately polar dichloromethane, and relatively more polar acetonitrile have been used. High-resolution mass spectrometry based on linear quadrupole ion trap and Fourier transform mass spectrometer (LTQ FT) has been used for liquid sample characterization. Concentration of bio-oil in a unit of solvent volume after solvent extraction took the following arrangement: acetonitrile > dichloromethane > hexane. Concentration of residual organics in a unit of aqueous solution after solvent extraction took the following arrangement: hexane >dichloromethane > acetonitrile. Yield of total organics was arranged as follows: hexane > dichloromethane > acetonitrile. Content of carbon in bio-oil was increased and the content of oxygen was decreased with the increasing of solvent polarity. From mass spectrometric analysis it was established that in the positive electrospray ionization (ESI) mode the compounds containing two nitrogen atoms dominate and the considerable portion of the compounds containing single nitrogen atom are also presented for both bio-oil and residual organics samples. In the negative ESI mode the compounds containing four oxygen atoms dominated except bio-oil obtained using hexane where the compounds containing two oxygen atoms dominated. Bio-oil fraction had highly saturated compounds with low double bond equivalent values while the compounds of the residual organics fraction had large double bond equivalent values.

Characterization of nitrogen and sulfur-containing species in Zhaotong lignite and its extracts from ultrasonic extraction

Zhaotong lignite (ZL) was sequentially extracted with cyclohexane, carbon disulfide, methanol, acetone, and isometric carbon disulfide/acetone mixed solvent to afford extracts 1–5 (E1–E5) under ultrasonic radiation at room temperature. In addition, ZL was characterized with solid-state 13C nuclear magnetic resonance (SS 13C NMR), Raman spectrometer and X-ray photoelectron spectrometer (XRPES), while the extracts were analyzed with a gas chromatograph/mass spectrometer along with a positive-ion (PI) and negative-ion (NI) electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (ESIFTICRMS). According to the characterization with SS 13C NMR, aliphatic carbons count for 59.5% of all the organic carbons in ZL, and each aromatic cluster contains 2 or 3 aromatic rings on average. The pyrrolic nitrogen and sulfones are the most abundant nitrogen and sulfur forms, respectively, in ZL based on the analysis with XRPES. ESIFTICRMS resolved thousands of basic and non-basic species, and the molecular masses are mainly concentrated in the range of 350–600 and 300–500 u, respectively. Acidic S1O3 class species with double bond equivalent values of 3–8 and carbon numbers of 6–39 are dominant species and could be attributed to acidic group-substituted thiophenes. Main nitrogen-containing species detected in the PI mode are basic N1O0–3, N2S2, and N2O1–8S1–2. Most of the species were speculated to contain some core structures, such as pyridines, pyrimidines, or pyrazines.

Interpreting Chemical Structures of Compounds in Crude Oil Based on the Tandem Mass Spectra of Standard Compounds Obtained at the Same Normalized Collision Energy

In this study, the tandem mass spectra of 25 standard compounds, obtained at a normalized collision energy of 50, were used to investigate the structures of crude oil. The product ion distributions of these standard compounds were dependent on the number and length of their alkyl side chains. Long alkyl side chains (CnH2n, n ≥ 5) were easily lost during molecular collision, leaving behind methyl groups on the aromatic cores. In contrast, compounds with short interlinking alkyl chains (CnH2n, n ≤ 1) were not significantly fragmented, and a decrease in the double bond equivalent (DBE) value was observed when compounds had saturated rings. Based on the derived observations, the possible structures of S1-class compounds with DBE values of 6, 7, 8, and 9 were suggested. It was also determined that, in the tandem mass spectra of crude oil fractions, (1) a series of peaks separated by CH2 groups were generated from isomers with different numbers of alky side chains, (2) the number of methyl groups left after mol...

Characteristics and geochemical significance of heteroatom compounds in terrestrial oils by negative-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry

Terrestrial oils and rock extracts from the Nanpu Sag (Huanghua Depression, Bohai Bay Basin, China) were characterized by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and gas chromatography mass spectrometry (GC-MS). Molecular composition of neutral nitrogen and acidic oxygen compounds, mainly by N1, O1, and O2 species were investigated in the samples. Increases in relative abundance and molecular condensation degree of oxygen-containing compounds and a decrease in the carbon number range of N1 species were observed with the changes of kerogen from Type I to III for both the source rock extracts and the relevant oils, which indicates the influence of source input and discrimination potential. We also observed an apparent increase in the condensation degree and a decrease in the carbon number of the N1, O1 and N1O1 species with increasing maturity. The carbon numbers and double bond equivalent (DBE) values of the N1 and N1O1 species in the extracts showed a positive relationship (an approximately linear distribution) during thermal evolution. These results indicate that thermal maturity has a crucial influence on the composition. The relative abundance ratios of N1 and O1 species with specific DBE values and carbon number ranges, C16–20/C21–50-DBE12-N1, C20–24/C25–50-DBE15-N1, C11–15/C16–27-DBE4-O1, DBE12/DBE9-N1, and DBE8–9/DBE4-O1 are proposed as thermal maturity indicators for the evaluation of mature and post-mature source materials. A strong primary migration fractionation effect on the heteroatom compounds was also observed, implying that these compounds can be used as migration auxiliary proxies.

Improvement of organonitrogen compounds in methanol-soluble portion from supercritical methanolysis of pretreated rice straw with Trichoderma sp. AH

The improvement of organonitrogen compounds (ONCs) in methanol-soluble portions (MSPs) obtained from supercritical methanolysis of raw and pretreated rice straw (RS) with Trichoderma sp. AH was investigated. According to detailed analysis with positive-ion ESI FT-ICR MS and GC/MS, the molecular masses (MMs) of ONCs in MSPs of raw and pretreated RS range from 100 to 500u and dominate from 300 to 450u. The relative abundance of ONCs with MMs from 300 to 350 u in MSP of pretreated RS is higher than those in MSP of raw RS. Most of detected ONCs in MSPs of raw and pretreated RS are N2On (n=1–9) species with double bond equivalent values of 2–25 and carbon atom numbers of 4–35. The most abundant ONCs in MSP of pretreated RS are N2O4, while those in MSP of raw RS are N2O5. These results facilitate understanding the effect of pretreatment with Trichoderma sp. AH on the conversion and specificity of ONCs in methanolysis of RS and the application of MSP on production of transportation fuel.

Evolution of Acidic Compounds in Crude Oil during In Situ Combustion

In situ combustion (ISC) process has drawn more and more attention in the development of heavy oil reservoirs as a result of its high recovery efficiency. Although numerous studies have been reported that oil properties exhibit significant changes during the combustion process, the reaction mechanisms and evolution of oil components are still not well understood. In this work, the compounds of produced oils collected from a three-dimensional simulated production model (container) at different duration times after combustion being initiated and the original oil were characterized at the molecular level using gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), and high-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Both aromatic and acidic components were analyzed. The aromatic components showed relatively more stable characteristics than those of acidic components, and no obvious changes in aromatic compound distributions were observed by the positive ion atmospheric pressure photoionization (APPI) FT-ICR MS analysis. Small aliphatic acids were detected in the ISC oils, which were responsible for the high total acid numbers (TANs). The acidic Ox (x = 1–3) compounds, which have major contributions to the increase in TAN, were generated in greater abundances compared to that of the original crude oil. The carbon number distributions of the O1 and O2 classes in the produced oils significantly shifted to a lower carbon number region, with the dominant distribution from 15–40 at the initial state to 10–30 at the longest duration time. The double bond equivalent (DBE) values decreased during the combustion process. The generated acidic O1 components with DBE values less than 4 were also found in negative ion electrospray ionization (ESI) analysis, indicating the oxidation of hydrocarbons to alcohols.

Identification of the structural characteristics of the asphaltenes in the tetrahydrofuran-microwave-extracted portions from two Chinese coals

This work aimed to evaluate the detailed chemical structures of the asphaltenes in the tetrahydrofuran-microwave-extracted portions from two Chinese coals, namely, Shenfu and Zhundong coal (SF, ZD) and to clarify their characteristics on chemical composition at molecular level. Based on the analyses of diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) and Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS), the detailed chemical structure of a series of basic and non-basic nitrogen- and oxygen-containing class species in the asphaltenes were clarified. The results revealed that condensed nitrogen-containing alkylaromatic structures with amidogens (1–3) were the main structure units in N4Oy (y=0–2) class species due to the high double bond equivalent (DBE) values for both the asphaltene from SF (ASF) and the asphaltene from ZD (AZD). Acidic O2–O7 class species with two or three aromatic rings were the main structure units, among which O4 and O2 class species had the highest relative abundances (RAs) in ASF and AZD, respectively. Acidic oxygen-containing components in AZD had narrower range of DBE and carbon number and mainly consisted of aromatic structure units with two rings. On the contrary, the average DBE values of O4–O7 class species in ASF had positive relationship with oxygen atom number which could be attributed to the introduction of phenol groups. The results provided more detailed information on the structural characteristics of polar and aromatic-rich components of mobile phase in coal.

Correlation among Petroleomics Data Obtained with High-Resolution Mass Spectrometry and Elemental and NMR Analyses of Maltene Fractions of Atmospheric Pressure Residues

In this study, maltenes of atmospheric pressure residue oils were fractionated into five fractions and the fractions were examined by elemental analysis, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and 1H nuclear magnetic resonance (NMR) spectroscopy. The obtained data were compared to examine the correlations among the data. The correlation coefficients (R2) were 0.88 and 0.89 respectively between the N and S contents determined by elemental analysis and summed relative abundances of N and S containing compounds observed by FT-ICR MS. Especially, correlation between S content and summed relative abundances of S containing compounds was observed. Further, correlation between %1Hnon-aro determined from NMR data and %Cnon-aro obtained from FT-ICR MS data was observed. %1Hnon-aro was calculated from the relative summed area of peaks in the non-aromatic region (0.5–4.5 ppm) of the NMR spectra. %Cnon-aro values were calculated from double bond equivalence values by assuming linear ...

Characterization of Oxygenates, Nitrogenates, and Sulfonates in Shengli Lignite Extracts by Orbitrap Mass Spectrometry

ABSTRACTA series of carbon disulfide/acetone mixtures were used to extract organic species from Shengli lignite, a Chinese coal. Orbitrap mass spectrometry coupled with electrospray ionization was used to characterize the molecules in the extracts. Heteroatomic species, including oxygenates, nitrogenates, and sulfonates, were determined. Pure carbon disulfide or acetone had the lowest extraction for oxygenates while the mixtures increased the relative abundance of oxygenates. From the value of the double bond equivalence, the compounds with 1 oxygen contained the highest concentrations of aromatics and aliphatics, but compounds with 6 were aliphatic with a double bond equivalence of 3. For compounds containing 2 oxygens, aromatics with one ring were present at the highest concentrations in the 1:1 carbon disulfide:acetone extract. For compounds containing 3, 4, and 5 oxygens, most aromatic species were identified with double bond equivalence values between 4 and 6, showing the presence of an aromatic ring. The results indicated that the solvent mixtures enhanced the extraction of oxygenates from Shengli lignite.

Resolution and Identification of Petroleum Sulfonate by Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

In this study, a petroleum sulfonate (PS) and its sulfonating raw oil were directly detected without pre-separation by using negative ion electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), in order to resolve and identify polar heteroatomic compounds in complex PS as well as to study the changes of various compounds from raw oil to PS before and after sulfonation. There were roughly 8500 and 6100 peaks positively resolved by mass spectrometry in PS and raw oil, respectively. Thirteen heteroatom classes in raw oil were identified as follows: N1, N1O1, N1O2, N1O3, N1O4, N1O5, O1, O2, O3, O3S1, O4, O5, and O5S1. As for those in PS, there are 19 classes, including N1, N1O1, N1O1S1, N1O2, N1O2S1, N1O3, N1O3S1, N1O4, N1S1, O1, O1S1, O2, O2S1, O3, O3S1, O4, O4S1, O5, and O5S1. Dominated O3S1, O2, O3, O4, N1O2, and O4S1 classes were classified and discussed in terms of double-bond equivalent (DBE) and carbon numbers. Significant O3S1 class species were centered at a DBE value of 4–10 with a carbon number of 23–34, corresponding to various alkyl aryl sulfonates, such as alkyl benzene and alkyl indanesulfonate. In summary, this paper introduced ESI FT ICR-MS to comprehensively characterize PS at the molecular level.

Insight into the chemical complexity of ethanolysis products from extraction residue of Zhaotong lignite

Ethanolysis of an ethanolyzed residue (ER) from Zhaotong lignite with NaOH was conducted to afford extracts 1–4 (E1–E4). The yields of E1–E4 are 47.1%, 10.6%, 3.0%, and 10.0%, respectively. All the extracts were analyzed with a negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (ESI FTICRMS). In addition, carbon skeleton structures in the ER were determined using a solid-state 13C nuclear magnetic resonance spectrometer. The results suggest that the carbon types in the ER mainly consist of aliphatic (52.3%) and aromatic (42.0%) carbons. CH3– and –CH2– are the major aliphatic carbons. Each aromatic cluster contains one or two aromatic rings on average. According to analysis with FTICRMS, thousands of compounds were detected in the extracts, mainly being oxygen-containing (Ox, x=1–8) class species with double bond equivalent (DBE) values of 1–18 and carbon numbers of 7–37. The most abundant class species in E1–E4 are O2, O2, O3, and O4, respectively. E4 contains low relative contents of O2–O3 class species but high relative contents of O4–O6 class species. The identified Ox class species are mainly ascribed to fatty acids, areneols, and arenecarboxylic acids. Furthermore, nitrogen-containing multiheteroatomic (N1Ox and N2Ox, x=1–8) class species with DBE values of 3–17 and carbon numbers of 13–34 were also identified in the extracts.

Mass spectrometric analyses of biomarkers and oxygen-containing species in petroleum ether-extractable portions from two Chinese coals

Shaerhu subbituminous coal (SSBC) and Mengdong lignite (ML) were extracted with petroleum ether under ultrasonication at room temperature to obtain ESSBC and EML, respectively. The extracts were analyzed with a gas chromatograph/mass spectrometer and a positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer to characterize biomarkers and oxygen-containing species. The biomarkers consist of a homologous series of alkanes and sterenes. The biomarker distributions provide important information on the main origins and microorganism degradation of organic matter in SSBC and ML. Oxygen-containing species, including O2–O4, O2N2, and O1N2 class species, are predominant in the extracts with double bond equivalent (DBE) values of 2–28 and carbon numbers (CNs) of 15–50. The oxygen atoms exist in furan rings, R–O–R′, RCOOR′, and RCOR′ (R and R′ denote an alkyl or aryl group). The species in EML have more varied DBE values and CNs compared with those in ESSBC. Most of the OxN2 (x=1–2) class species have larger DBE values and CNs than the Ox class species, which might be an evidence for more abundant intermolecular associations, such as hydrogen bonds, among the OxN2 class species than among the Ox class species.

Characterization of heteroatom-containing species in the soluble portion from the ethanolysis of the extraction residue from Xinghe lignite by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

The extraction residue (ER) from Xinghe lignite was subjected to ethanolysis at 300°C and the yield of ethanol-soluble portion (ESP) is 66.8wt% (daf). The ER was characterized by solid-state 13C nuclear magnetic resonance spectrometry (SS 13C NMRS) and X-ray photoelectron spectrometry (XPS), while non-basic and basic heteroatom-containing species in the ESP were analyzed by negative- and positive-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS), respectively. According to the characterization by SS 13C NMRS, the ER contains 56.6% of aromatic carbon and 37.8% of aliphatic carbon and each aromatic cluster contains 2 aromatic rings on average. The characterization by XPS suggests that OH, pyrrolic nitrogen, thiophene, and sulfoxide are important heteroatom occurrences in the ER. According to the analysis by ESI FTICRMS, the non-basic and basic species distribute in the range of molecular mass from 160 to 450u and 200 to 950u, respectively. The abundant O2 class species among the identified non-basic species could be alkanoic acids, arenediols, and arenoic acids. Non-basic N and NO classes could be pyrroles, indoles, and carbazoles with double bond equivalent (DBE) values from 1 to 16 and carbon numbers (CNs) from 7 to 28. The NOx class species dominate the basic species and span wider DBE values (4–24) and CNs (14–54). Most of these species could be attributed to quinolines (DBE⩾7), acridines (DBE⩾10), and N-heterocyclic aromatics with at least 4 rings like benzoacridine ring (DBE=13). Sulfur in the acidic classes (O3S, S2, and OS2) mainly exists in mercapto group and/or thiophene ring, while the basic OS and O2S classes may have sulfur present in thiophene sulfoxides and thiophene sulfones, respectively.

Molecular composition of urban organic aerosols on clear and hazy days in Beijing: a comparative study using FT-ICR MS

Environmental contextChina has been experiencing severe particulate pollution and frequent haze episodes in recent years. We compare the molecular composition of urban organic aerosols on clear and hazy days in Beijing by high-resolution mass spectrometry. The comparative study shows that oxidation, sulfation and nitrification processes actively involve precursors of anthropogenic origin in the Beijing polluted urban atmosphere. AbstractHaze has frequently affected many cities and threatened human health in China. Detailed knowledge of the chemical composition of secondary organic aerosol provides fundamental information in the study of the formation mechanism of haze and its adverse effects on human health. In our work, dichloromethane and water extracts of ambient aerosols collected on hazy and clear days in Beijing were characterised by negative-ion electrospray ionisation and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Formulae in four elemental compositional groups, namely CHOS, CHONS, CHO and CHON, were identified relying on the ultrahigh resolution and mass accuracy of FT-ICR MS. Significantly more compounds were detected and the peaks were much more intense in the hazy day samples, especially for the CHOS, CHONS and CHON formula groups. Organosulfates (OS) and nitrooxy-organosulfates (nitrooxy OS) were the major forms of CHOS and CHONS formulae respectively, and their numbers more than tripled on the hazy days. Under the severely polluted conditions in Beijing, the compositional distribution of the OS and nitrooxy OS exhibited distinct features such as intense peaks of low double-bond equivalent (DBE) (DBE=0, 1 for OS and DBE=1, 2 for nitrooxy OS) and low degree oxidation, of medium DBE (DBE=2, 3 for OS and DBE=3, 4 for nitrooxy OS), and of high DBE (DBE ≥ 4 for OS and DBE ≥ 5 for nitrooxy OS). The likely respective candidates for these could be aliphatic OS having a low degree of oxidation, biogenic OS and many aromatics and polycyclic aromatic hydrocarbon (PAH)-derived OS. The CHON formulae observed on hazy days were double those on clear days and had higher DBE values and larger O/N ratios. Slightly more CHO compounds were detected in the hazy-day samples and they had higher DBE values and more oxygen atoms. The comparative study suggests that oxidation, sulfation and nitrification processes actively involve precursors of anthropogenic origin in the Beijing polluted urban atmosphere.

Characterization of bio-oils from the alkanolyses of sweet sorghum stalk by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Bio-oils (BOs) obtained from sweet sorghum stalk (SSS) methanolysis (BOm) and ethanolysis (BOe) at 300°C for 30min were analyzed with an electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (ESI FT-ICR MS). In negative-ion mode, the predominant compounds in BOm and BOe are On (n=1–10) class species with double bond equivalent (DBE) values of 1–14 and carbon atom numbers (CANs) of 5–35. The most abundant class species in BOm and BOe are O4 and O3, respectively. According to the distribution of On class species and the van Krevelen diagram, lignin-derived compounds are the main acidic species in the BOs. In addition, N1On (n=0–10) class species with DBE values of 1–14 and CANs of 7–35 were also identified. In positive-ion mode, most of detected compounds in BOm and BOe are N2On (n=1–6) class species with DBE values of 1–19 and CANs of 10–40, in which N2O2–N2O4 class species with DBE=8–12 and CAN=19–28 are the most abundant. These results facilitate understanding thermochemical behavior of SSS.

Analysis of extractable basic nitrogen compounds in Buliangou subbituminous coal by positive-ion ESI FT-ICR MS

Buliangou subbituminous coal (BSBC) was sequentially extracted with carbon disulfide, methanol, and acetone under ultrasonic irradiation to afford extracts 1–3 (E1–E3). All the extracts were analyzed with a positive-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). In total, 11.11% of organic matter in BSBC was extracted with the three solvents. According to analysis with positive-ion ESI FT-ICR MS, the molecular masses of basic nitrogen compounds (BNCs) in E1–E3 range from 200 to 600u and dominate from 250 to 450u. The BNCs detected are mainly N1Ox (x=0–2) and N2Oy (y=0 and 1) with 4–25 of double bond equivalent (DBE) values and 12–38 of carbon numbers (CNs). The BNCs in E2 have lower DBE values (4–16) and CNs (14–28). According to DBE distributions, molecular core structures of most N1Ox classes should be aromatic rings, including benzene, pyridine, quinoline, and acridine rings. Moreover, core structures of most N1Ox moieties connected with an amino group or condensed with a pyrrole ring are characteristic structures for N2Oy classes in E1–E3. In addition, a small amount of amines (DBE<4) were also identified in the extracts. Positive-ion ESI FT-ICR MS proved to be a powerful tool for identifying extractable BNCs in coals.

Investigation on compositional and structural features of Xianfeng lignite through sequential thermal dissolution

Xianfeng lignite (XL) was subjected to sequential thermal dissolution (TD) in cyclohexane at 200–320°C. The yields of soluble portions (SPs) decreased with raising temperature from 200 to 260°C, but then increased with further raising the temperature. The SPs were analyzed with a Fourier transform infrared spectrometer, gas chromatograph/mass spectrometer, and atmospheric pressure solid analysis probe/time-of-flight mass spectrometer (ASAP/TOF-MS). The results show that cyclohexane is effective for thermally extracting inherent hydrocarbons in XL without breaking the covalent bonds. Intermolecular interactions such as hydrogen bonds, π–hydrogen bonds, and π–π interactions can be destroyed at higher temperatures and thereby release arenes and arenols trapped in the capsule structure of XL. According to ASAP/TOF-MS analysis, the molecular mass of organic species in the SPs is smaller than 550 u and SPs from different TD temperatures have different molecular mass distributions. The organic species detected with ASAP/TOF-MS have double bond equivalent values ranging from 0 to 11 and carbon numbers from 3 to 35. A series of arenes and alkylarenols were also confirmed by ASAP/TOF-MS analysis.