Characterization of Oxygen-Containing Species in Methanolysis Products of the Extraction Residue from Xianfeng Lignite with Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract

Methanolysis of an extraction residue (ER) from Xianfeng lignite was carried out to obtain extracts 1−4 (E 1 −E 4 ). The molecular compositions (MCs) of oxygen-containing species (OCSs) in E 1 −E 4 were characterized using negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). In addition, solid-state 13 C nuclear magnetic resonance and X-ray photoelectron spectrometry were used to analyze the carbon types and oxygen functional groups (OFGs) in the ER. The results show that the carbon skeleton structures in the ER are dominated by aliphatic (50.2%) and aromatic (44.9%) carbons. Methylene and methoxy carbons are the most abundant among the aliphatic carbons. Each aromatic cluster contains three rings on average with two substituent groups on each ring. The OFGs in the ER include hydroxy, ether, carbonyl, and carboxyl groups, among which the hydroxy group is the most abundant. The ESI FT-ICR MS analysis shows that the molecular mass distributions of E 1 −E 4 range from 150 to 500 u. The O n (n = 1−6) class species are the predominant OCSs in E 1 −E 4 , with 0−14 double bond equivalent (DBE) values and 9−34 carbon numbers (CNs). The most abundant O n class species in E 1 −E 4 are O 2 , O 2 , O 2 −O 3 , and O 3 , respectively. The OCSs in E 4 contain low abundances of O 1 and O 2 class species but relatively high abundances of O 4 −O 6 class species. In addition, the O n class species in E 4 have narrower ranges of DBE values and CNs than those in E 1 −E 3 . A series of acidic species with different DBE values and CNs are assigned to alkanoic acids, alkanedioic acids, alkanetricarboxylic acids, alkylarenols, alkylarenediols, alkylarenetriols, and alkylarenoic acids. With high resolving power and mass accuracy, ESI FT-ICR MS is an effective technique for characterizing MC of the soluble portion from lignites, which will facilitate producing important chemicals from lignites.

Insight into the structural features of Zhaotong lignite using multiple techniques

“…The assignments of different carbon types were referred to previous studies [8,[31][32][33]. The solid-state 13 C NMR spectra of coals can generally be divided into three main chemical regions: aliphatic carbons (0-90 ppm), aromatic carbons (90-170 ppm), and carbonyl carbons (170-220 ppm).…”

“…XPS has been used to characterize the surface elemental compositions of coals and their residues [8,11,34]. For XPS analysis, the C 1s peak position was set at 284.8 eV and used as reference to position other peaks.…”

“…Coals are too complex to be elaboratively characterized. It is common to understand original structural information on coals with direct characterization tools, such as solid-state 13 C nuclear magnetic resonance (NMR) [6][7][8], Fourier transform infrared (FTIR) spectrometer [9,10], and X-ray photoelectron spectrometer (XPS) [11][12][13]. http Analyses with such tools greatly facilitate the understanding of carbon skeleton structures and functional groups along with oxygen, nitrogen, and sulfur forms in coals.…”

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

“…Bruker software Data Analysis was used for peak detection and molecular formula assignment. Detailed data processing was performed according to the recent investigations [29,[33][34][35][36]. The number of N atom in each molecular formula was limited up to 3 when mass peaks were assigned.…”

“…Meanwhile, electrospray ionization (ESI), a soft ionization technique, can selectively ionize polar molecules. Therefore, FT-ICR MS equipped with an ESI source is useful for analyzing polar species in soluble portions from coals [20,[29][30][31].…”