Characterization of petcoke and derived oxygen-functionalized products accompanied by XRD, FT-MIR and SS-NMR

Abstract

This work applies Solid-State Nuclear Magnetic Resonance (SS-NMR) to characterize structural and motional aspects of petcoke and its derived humic-like products from alkaline wet oxidation. Heteronuclear dipolar coupling modulation schemes are used to characterize local mobility and structural heterogeneity of condensed aromatic layers of petcoke and its oxygen-functionalized products. The analytical agreements between heteronuclear H–C dipolar modulated and direct polarization SS-NMR schemes, C/O/H elemental analysis, X-ray diffraction and Fourier-Transform Mid-Infrared (FT-MIR) spectroscopy confirm that alkaline wet oxidation of petcoke provides structural heterogeneity and flexibility in direct correlation to an increase of oxygen content, an increase of O/C ratio, reduction of aromatic stack layers, reduction of crystallite size and increase of C–O, and O–H dipoles within hydrophobic aromatic ring frameworks submitted to multiple oxygen functionalization chemical processes. For the first time, a technique is proposed to distinguish between humic and fulvic acids analogs prepared from petcoke alkaline wet oxidation by means of 13C-CPMAS, 1H- and 13C-DPMAS experiments. Fulvic acid analogs with high non-paramagnetic ash content show 13C profiles only by direct polarization, not by equivalent heteronuclear dipolar coupling polarization-transfer.These analytical techniques propose orthogonality amongst characterizing alkaline wet oxidation methodologies applied to petcoke for valorization into humic-like substances.