Structural features of Qingdao petroleum coke from HRTEM lattice fringes: Distributions of length, orientation, stacking, curvature, and a large-scale image-guided 3D atomistic representation

Abstract

Structural features of a green Qingdao petroleum coke (produced at ∼ 500 °C) were investigated by image analysis of high-resolution transmission electron micrographs, XRD, and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). The fringe length distribution was comprised mostly of fringes <20 Å, with a peak at 5–7 Å. The MALDI-TOF MS data also indicated an abundance of low molecular weight material 250–300 Da. The coke had considerable preferential orientation within the field of view of the micrograph. However, the degree of ordering was poor with fringe stacking occurring for ∼20% for the fringes, with a mean of 2.11 fringes. XRD also indicated low ordering as expected for a lower quality, low temperature coke. The poor nanostructure-level order was a result of small fringe lengths, with curvature (present in 42% of the fringe) likely contributing. It is thus a partially ordered system, with order varying over length scales. An image-guided construction strategy capable of controlling the degree of order (utilizing Fringe3D and Vol3D) was used to construct an atomistic structural representation (C3717H1830N54O134S109) incorporating many experimental parameters. The structure was comprised of preferentially orientated molecules, but with the observed limited stacking, incorporating both curvature frequency and extent.