Microstructural Investigation of Coke Deposition in Pelleted Catalyst during Downhole Catalytic Upgrading of Heavy Crude
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Microstructural Investigation of Coke Deposition in Pelleted Catalyst during Downhole Catalytic Upgrading of Heavy Crude Oil Using Porosimetry and X‑ray Computed Tomography Abarasi Hart1 Received: 31 July 2020 / Accepted: 28 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Catalyst pore evolution due to coke and metals (e.g., Ni, V, etc.) deposition from heavy oil catalytic upgrading is studied using nitrogen adsorption–desorption, mercury porosimetry, X-ray computed tomography and Scanning electron microscope (SEM) techniques. These techniques probe the impact of coking on the global pore size distribution and the pore-scale connectivity of pores of different sizes. 24wt% coked NiMo/Al2O3 catalyst was studied. Coke deposition caused active site coverage and pore-mouth blockage making the core pore network inaccessible to reactants as reflected in the nearly loss of total surface area and pore volume observed from porosimetry, while the x-ray computed tomography image shows scanty coke deposits within the microstructure. The SEM image confirmed that pore-mouth blockage due to large coke deposition in the early hours of the upgrading reactions at the outer layer of the catalyst pellets is the major cause of deactivation. The spent catalyst experienced more than 90% drop in surface area with coke deposition on the outer layer of the catalyst far higher than in the centre. Therefore, one of the ways to enhance intra-particle diffusion and limit the impact of coke deposition on the outer layer of the catalyst is either to use nano-catalyst or engineered pore sizes. Graphical Abstract
Keywords Catalytic upgrading · Heavy oil · Coke · Microstructure · Pore structure network · Catalyst deactivation
1 Introduction * Abarasi Hart [email protected]; [email protected] 1
University of Birmingham, School of Chemical Engineering, Edgbaston, Birmingham B15 2TT, UK
In the face of declining reserve of easy to extract light oil and rising demand for fuel, heavy oil and bitumen are seen as potential alternative sources to mitigate the impact of shortage during this transition period to low carbon energy
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sources. However, heavy oil and bitumen need upgrading to match feedstock characteristics of existing refinery. This can be achieved through downhole catalytic upgrading in which the reservoir serves as a chemical reactor propelled by a thermal enhanced oil recovery technique. The application of heterogeneous catalyst in downhole upgrading of heavy oils offers enhanced recovery as well as lower environmental footprint. However, the concept suffers from severe coking arising from the cracking of heavy oil particularly when the catalyst pellets are packed around the horizontal production well, as in the case of Toe-to-Heel Air Injection (THAI) process [1]. The process of catalyst deactivation due to metals (e.g., Ni, V, Fe, etc.) and coke deposition is complex. The deposited coke on the catalyst promotes dehydrogenation activity as the catalyst de
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