Research on the influence of sequential isopropanolysis liquefaction on the composition of liquid tars and physicochemical structure evolution of renbei lignite

Abstract

A green and efficient sequential isopropanolysis liquefaction approach was reported to convert lignite into high yield of liquid tars (LTs) as fuels/value-added chemicals in this research, but its influence on the molecular structure composition of LTs and physicochemical structure evolution of lignite still received little attention. The sequential isopropanolysis of RB lignite was performed at 240, 280, and 320 °C in isopropanol for obtaining three LTs (LT240 °C, LT280 °C, and LT320 °C) and three residues (R240 °C, R280 °C, and R320 °C). Among three LTs, phenols represented the highest relative content value, accounting for 72.54, 90.48, and 84.83%, respectively, and mainly can be divided into phenol and (C1–C8)-phenol. There was hydrocarbon, Oy (y = 1–5), NOy (y = 0–2), N2Oy (y = 0–2), N3Oy (y = 0–1), NxSz (x = 0–1, z = 1–2), and SNxOy (x = 1–2, y = 1–2) class species existed in three LTs on the basic of the analysis with quadrupole exactive orbitrap mass spectrometer (QEOTMS). Notably, O1 and O2 class species were the more abundant components in three LTs. The cleavage of C–O bridged bonds should be the main reaction path and the graphitization degree of residues significantly enhanced. The main pyrolysis zone of residues shifted to higher temperature area and the pyrolysis activation energy of stage II increased.