Magnetic Resonance Microimaging Studies of Porous Petroleum Coke

Magnetic resonance microimaging (MRM) is used to characterize petroleum coke formed in the upgrading of Athabasca bitumen. Formation of large coke materials poses processing difficulties, and so the study of the structure and formation mechanism is important. The larger, “peas and beans” coke (approximately spherical, 4.1 mm diameter) possesses significant porosity, and is ideal for MRM. Coke is soaked in cyclohexane, and then 7V-, diffusion-, and density-weighted 1H images are collected with an unprocessed image resolution of 24 μm pixel-1. Scanning electron microscopy indicates that the coke is surrounded by a dense, 100 μm-thick outer shell. MRM shows that this shell is permeable to cyclohexane, and that a significant pore volume is present. The cyclohexane diffusion coefficient (Dmax = 1.4 x 10-9 m2 s-1) is roughly one-half of the Dmax in pure solution indicating that the cyclohexane inside the coke is liquid-like. The MRM images indicate that the coke is formed by an agglomeration mechanism from smaller fluid coke particles (nominal diameter 150 μm), which in turn posess microporosity. MRM shows great promise as a non-destructive, structural and dynamic characterization method for petroleum coke. Strategies to enhance resolution will be presented and discussed.