Cellulose char structure: a combined analytical Py-GC-MS, FTIR, and NMR study

Abstract

Bulk samples of microcrystalline cellulose were charred in an anaerobic environment, at atmospheric pressure, and temperatures ranging from 190 to 390°C. Curie-point pyrolysis-gas chromatography-mass spectrometry (Cu-Py-GC-MS) was used as an analytical tool for characterization of the resulting chars. Fourier-transform infrared (FTIR) spectroscopy and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy were employed for verification of the results. The abundance of aromatic building blocks (furans, alkylbenzenes, and alkylnaphthalenes) in Cu-Py-GC chromatograms increases with the pretreatment temperature. FTIR and NMR show the breakdown of the pyranose polymer and gradual formation of a new intermediate polymer with an aromatic character which disproportionates further and aromatizes at temperatures above 310°C. A model for the formation of this intermediate polymer is proposed. Cu-Py-GC-MS data are in agreement with the results of FTIR and NMR.