Characterization of acidic species in ethanol-soluble portion from Zhaotong lignite ethanolysis by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Abstract

Thermal dissolution of Zhaotong lignite in ethanol was conducted in a temperature range of 230 to 350°C for 2h. The maximum yield of the ethanol-soluble portion (ESP) is 64.9% at 305°C. ESP was analyzed with a negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). Molecular mass of ESP ranges from 100 to 500 u with an average peak around m/z 260. According to the assignment of molecular formulae, most of the compounds detected in ESP are oxygen-containing species of types On and OnN1 (n=0–6), especially O1–O4 class acidic species (ASs) with 1–12 double bond equivalent (DBE) values and 8–34 carbon atoms. The maximum condensation degree of aromatic clusters in the ASs is 3 (DBE=10). The average DBE values of On class species are 5 or 6, suggesting that phenols, benzenepolyols, and/or benzoic acids with an aliphatic ring and alkyl chains are characteristic structures. FT-ICR MS proved to be a powerful tool for identifying soluble polar species from coal conversion.