Fine structural changes of fluid catalytic catalysts and characterization of coke formed resulting from heavy oil devolatilization

Abstract

Coke formation from heavy oil cracking and the associated change in the porous structure of fluid catalytic cracking (FCC) catalysts has been studied using a comprehensive range of techniques, including 2D and 3D imaging and carbon/coke characterization techniques. The carbon/coke formed from heavy oil devolatilization has been investigated with a range of oilto-FCC catalyst ratios (1:3, 1:2, 1:1, 2:1 and 3:1) to simulate the ageing of FCC catalysts in an operating oil refinery. Carbon/coke was formed on all used FCC catalyst samples and was found to generally increase in quantity with the increasing oil-to-FCC catalyst ratios. Coke formation has been correlated with the observed porosity change of the FCC catalyst. Higher quantities of carbon/coke formed on the FCC catalyst due to higher oil-to-FCC catalyst ratios (simulated increase in time on-stream) leads to a decrease of total pore volume and surface area. X-Ray computed tomography (X-Ray CT) studies allowed 3-dimensional imaging of used catalyst particles and showed that the zeolite component of the FCC catalyst remains evenly distributed throughout the FCC particle from the centre to the exterior for pristine and used FCC catalyst particles. This technique showed that while the interior porous structure of the FCC catalyst particle is not affected by the coking, the exterior porous structure is substantially modified for all used FCC catalyst samples. This process of pore collapse and/or clogging at the surface of the particles is likely to have a significant effect on the deactivation of FCC catalysts that is commonly observed. The deeper insight into this process gained through this study is important for understanding how FCC catalysts change with time-onstream and eventually deactivate and may allow for future catalysts to be developed that are more resistant to deactivation.

Tetralin and Decalin H-Donor Effect on Catalytic Upgrading of Heavy Oil Inductively Heated with Steel Balls

“…The X-ray nano-CT image also shows that, while the interior porous structure of the pelleted catalyst is slightly affected by the coking, the exterior is significantly modified by coke formation. This is in agreement with the coke deposition from heavy oil devolatilization by using Fluid Catalytic Cracking (FCC) catalyst reported by Zhang et al [35]. The structural changes in the pellets near the exteriors due to coke deposition leading to pore-mouth blockage is behind the rapid deactivation reflected in the API gravity with TOS shown in Figure 2.…”

“…X-ray nano-CT imaging was used to examine coke deposition within the microstructure of the pelleted spent catalyst in full 3D. This imaging technique was utilized by Lomas et al [34] to study metallurgical coke fracture, and Zhang et al [35] to examine coke deposition resulting from catalytic heavy oil devolatilization. The interior reconstruction of the catalyst structure can be obtained, providing details of the microstructural changes that have taken place after reaction.…”

3‐D X‐ray Nanotomography Reveals Different Carbon Deposition Mechanisms in a Single Catalyst Particle

“…In the first mechanism, at low coke contents, the active site of the catalyst material is covered by coke, which causes catalyst deactivation by preferential blocking of the strongest acid sites. In the second mechanism at high coke contents, pore-clogging causes reduced diffusion in micro-pores [48] (pore sizes < 2 nm [37] ) hindering mass transport of products and feedstock, in turn reducing catalyst efficiency.…”

In-situ microwave-assisted catalytic upgrading of heavy oil: Experimental validation and effect of catalyst pore structure on activity

“…It can be concluded from the previous discussion that the heterogeneity in the sulfur spatial distribution can be attributed in part to the fabrication process of the catalyst pellets/extrudates (granular form) as well as the uneven metal-catalyst dispersion. It is to be noted that the pore sizes in the catalyst are below the resolution currently possible to image directly with hard x-ray tomography [31] , [32] and the sample volumes it is possible to probe by electron microscopy are statistically unrepresentative in this case, and therefore gas adsorption was used to further characterize the pore structure.…”