Comparative analysis of petroleum and coal pitches using 1H and 13C NMR spectroscopy

Abstract

Petroleum and coal pitches are known to be among the most important sources of raw materials for the production of carbon materials, including electro-carbon, heat- and chemical-resistant structural products, metal-carbon and carbon-carbon composite materials, graphite electrodes, self-baking anode paste, carbon fibres, blast furnace and cupola coke. The quality of the pitches is determined by the elemental and group composition, as well as their structural and physical-chemical properties. The study of the molecular structure and group composition of the organic components of the pitch and the identification of the effect of the composition on the performance of the products is of great interest for assessing the prediction of the behaviour of pitches during processing and the properties of the products obtained from them. The present work is devoted to the study of the group composition of two petroleum and two coal pitches using high-resolution NMR spectroscopy. The data of the ¹H and ¹³C NMR spectra allow the composition of the pitch product to be estimated without separation into fractions, which, in turn, combined with the accuracy of the method and the recording speed of the ¹H NMR spectra, increases the rapidity of this method of analysis. The combination of ¹N and ¹³C NMR data allows additional information on the correlation of physical parameters and pitch composition to be established. The calculation of the (H ar /H al ) parameter, corresponding to the ratio of the integral intensities of signals of aromatic and aliphatic hydrogen atoms, provides the possibility of using it as a structural characteristic for a particular sample. In order to ensure the correct contribution to the integral intensity of the signals, ¹³C NMR spectra were recorded in a pulse sequence with suppression of the spin-spin proton interaction only for the period of data reading for the purposes of minimising the nuclear Overhauser effect. The relaxation delay between pulses was set to 10 s. The study of petroleum and coal pitches using NMR spectroscopy showed the proton spectra of NMR data to be sufficiently informative and suitable for monitoring the technological process of pitch production.