Pyrolysis behaviors of organic matter (OM) with the same alkyl main chain but different functional groups in the presence of clay minerals

Abstract

Abstract Organic matter (OM)-clay mineral complexes, especially OM-clay interlayer complexes, exist widely in soil, sediment, and source rock. These associations can influence the pyrolytic behaviors of OM. In addition, the nature of OM may also affect pyrolysis due to the variety and complexity of the structure and chemical composition of natural organics. In this study, to investigate the influences of the nature of OM as well as the interface association between OM and clay minerals on the pyrolysis of OM, interlayer clay-OM complexes and clay-OM mixtures were prepared and thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) was adapted to monitor the pyrolytic temperatures and products of these complexes. A series of OM with the same alkyl main chain but different functional groups, i.e., Lauric acid (LA), Dodecylamine (DA), 12-Aminolauric acid (ALA) and Dodecyl trimethyl ammonium bromide (DTAB), was used, and montmorillonite (Mt) was selected as the representative clay mineral. The results showed that Mt decreased the decomposition temperature of the carboxyl groups that contained OM (LA and ALA), promoted the generation of CO2 via the catalysis of the Lewis acid sites of Mt, and delayed the decomposition of DA and DTAB. The interlayer Bronsted acid sites allowed the nitrogen-containing organics to undergo Hoffmann elimination. The pyrolytic behaviors of OM within the interlayers of Mt were more strongly affected than those on the external surface of Mt The pyrolytic performance of OM was closely related to the association ways between OM and clay minerals, the nature of clay minerals, and the nature of OM. The interlayer space was shown to be particularly important for the preservation and catalysis of organics.