Asphaltene catalytic cracking

Residues containing high levels of heavy metals are not suitable for catalytic cracking units. These feedstocks may be subjected to a demetallization process to reduce their metal contents. For example, the metal content of vacuum residues could be substantially reduced by using a selective organic solvent such as pentane or hexane, which separates the residue into an oil (with a low metal and asphaltene content) and asphalt (with high metal content). Demetallized oils could be processed by direct hydrocatalysis. 

Solvent extraction may also be used to reduce asphaltenes and metals from heavy fractions and residues before using them in catalytic cracking. The organic solvent separates the resids into demetallized oil with lower metal and asphaltene content than the feed, and asphalt with high metal content. Figure 3-2 shows the IFP deasphalting process and Table 3-2 shows the analysis of feed before and after solvent treatment. Solvent extraction is used extensively in the petroleum refining industry. Each process uses its selective solvent, but, the basic principle is the same as above. 

Coking is a severe thermal cracking process designed to handle heavy residues with high asphaltene and metal contents. These residues cannot be fed to catalytic cracking units because their impurities deactivate and poison the catalysts. 

The Asphaltenic Bottom Cracking (ABC) process (Fig. 17) is a proprietary catalytic HDT process for heavy residual oils [118],... 

Figure A, however, does depict the general relationship between API gravity, sulfur, asphaltene and total metal content of crudes in general. Certainly none of these ingredients, especially in such large amounts, could be considered "friendly" for catalysts used in normal catalytic cracking.

This process is a version of the fluid catalytic cracking process that has been adapted to conversion of residua that contain high amounts of metal and asphaltenes (Finneran, 1974 Murphy and Treese, 1979 Johnson, 1982 Feldman et al.,... 

The Demex process is a solvent extraction demetallizing process that separates high metal vacuum residuum into demetallized oil of relatively low metal content and asphaltene of high metal content (Table 8-5) (Houde, 1997). The asphaltene and condensed aromatic contents of the demetallized oil are very low. The demetallized oil is a desirable feedstock for fixed-bed hydrodesulfurization and, in cases where the metals and carbon residues are sufficiently low, is a desirable feedstock for fluid catalytic cracking and hydrocracking units. 

Hydrotreating processes have two definite roles (1) desulfurization to supply low-sulfur fuel oils and (2) pretreatment of feed residua for residuum fluid catalytic cracking processes. The main goal is to remove sulfur, metal, and asphaltene contents from residua and other heavy feedstocks to a desired level. 

The major goal of hydroconversion is the cracking of residua with desulfurization, metal removal, denitrogenation, and asphaltene conversion. The residuum hydroconversion process offers production of kerosene and gas oil, and production of feedstocks for hydrocracking, fluid catalytic cracking, and petrochemical applications. 

The chemical structure of asphaltenes is still not well understood. Ashland Research is currently studying the catalytic cracking of asphaltenes. At the present time these studies have... 

RFCC (resid fluid catalytic cracking) is one of the processes for the conversion of heavy oils in modem refineries. The problem with vacuum residue as FCC feedstock is quick deactivation of catalysts by the coking of asphaltene fractions and the deposition of metals involved in metallorganic polycyclic compounds. Therefore, developing novel zeolites to achieve metal tolerance has long been a goal of catalyst researchers... 

Takeuchi, C. Fukui, Y. Nakamura, M., and Shiroto, Y., Asphaltene Cracking in Catalytic Hydrotreating of Heavy Oils. 1. Processing of Heavy Oils by Catalytic Hydroprocessing and Solvent Deasphalting. Ind. Eng. Chem. Proc. Des. Dev, 1983. 22(2) pp. 236-42. 

Takeuchi et al. (1985) tested the catalytic activity of deposited Ni and V by use of a catalytic metal-free alumina base. These interesting results are shown in Fig. 42. After accumulation of 10wt.% vanadium on the catalyst, the alumina base, with little initial activity, has essentially the same activity for HDM and asphaltene cracking as the catalytic metal-... 

A major problem in the catalytic hydrodesulfurization of residual oils is the deactivation of the catalyst by metal-containing asphaltenic species in the feed. As can be seen from the results of a typical desulfurization experiment presented in Fig. 1, the catalyst shows a rapid initial decline which is attended with a fast build-up of coke on the catalyst. At a relatively low catalyst age 0, as defined in Section IV, a stationary coke level is reached. In contrast, the deposition of the inorganic remnants of the hydro-cracked asphaltenes (mainly vanadium and nickel sulfides) continues and gradually clogs the pores in the outer zone of the catalyst particles, as confirmed by electron microprobe analyses of spent catalyst samples (see Fig. 2). This causes a slow further loss in desulfurization activity over a longer period of time. Ultimately, the catalyst becomes totally inactive for desulfurization because the - still active - inner core has become completely inaccessible to the sulfur-bearing molecules. 

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