Reaction Types and Kinetics of Methane Generation from Huolinhe Lignite Pyrolysis by TG/MS Experiment and Quantum Chemical Calculations

Abstract

Open system pyrolysis modeling of immature Huolinhe lignite(vitrinite reflectivity,RmO0ax0 of 0.33%) was carried out and an on-line curve for the methane generation rate was obtained using a thermogravimetric analyzer coupled to a quadrupole mass spectrometer(TG/MS) . Five peaks were suitable for curve fitting. A kinetic analysis of these fitted curves indicated that the lowest temperature peak represented desorption of adsorbed methane in coal and the four other peaks were from pyrolytic methane generation. These results indicated four types of reactions as determined by kinetic analysis combined with the structural characterization of coal by 13C-NMR and quantum chemical calculations. From the order of peak fitting,the first type of reaction involves a cleavage of the aliphatic carbons linked to O atoms;the second includes two reactions,a β-secession of short chain aliphatic functional groups and a secondary cracking of long chain aliphatic hydrocarbons that were formed during the primary pyrolysis of coal;the third is a demethylation of methyl-linked aromatic clusters;and the fourth is an aromatization of aliphatic substances within the coal structure and subsequent condensation.