Methanolysis of extraction residue from Xianfeng lignite with NaOH and product characterizations with different spectrometries

• Most of organic matter in ER became soluble portion via methanolysis with NaOH.
• NaOH could promote ER methanolysis and increased the yield of soluble portion.
• Soluble organic species with molecular mass from 100 u to 600 u were identified.
• Polar and involatile species were identified by DARTIS/ITMS and ASAP/TOF-MS.

Extraction residue (ER) from Xianfeng lignite via ultrasonic extraction was subjected to methanolysis in the presence of NaOH at 300 °C for 2 h, and extracts 1–4 (E’1-E’4) from ER methanolysis were acquired by subsequent separation of the resulting soluble portion (SP). NaOH could promote ER methanolysis and hence increased the SP yield. Detailed molecular compositions (MCs) of E’1-E’4 were characterized with Fourier transform infrared spectrometer, gas chromatograph/mass spectrometer (GC/MS), direct analysis in real time ionization source coupled to ion-trap mass spectrometer (DARTIS/ITMS), and atmospheric solid analysis probe/time of flight-mass spectrometer (ASAP/TOF-MS). The results show that the SP is rich in aliphatic moieties, carbonyl and hydroxy groups, and has molecular mass distribution ranging from m/z 100 to 600. According to GC/MS analysis, phenols, especially polymethylphenols, were enriched in E’1 and E’2, whereas almost all the alkanoic acids, alkanedioic acids, benzoic acids, and phenyl-substituted alkanoic acids only appeared in E’4. A series of polar and/or involatile organic species, which are difficult to be detected with GC/MS, were detected with DARTIS/ITMS and ASAP/ TOF-MS. NaOH could play an important role in cleaving ether bonds in ER during methanolysis and thereby enhanced the formation of oxygen-containing organic species. The use of multiple spectrometries provides a promising approach for understanding MC of the SP from coals.