In the catalytic processing of heavy oils, chemically combined nickel and vanadium present in the oil deposit on the catalyst and markedly influence catalytic behavior. Small quantities of these metals change the selectivity in catalytic cracking, while larger deposits in residual oil desulfurization or hydrocracking cover the catalyst and lower activity. By using a dilute aqueous solution of a complexing agent, such as oxalic acid, dioxane, or acetylacetone, nickel and vanadium oxides can b e removed to obtain a substantial improvement in catalytic activity and/or selectivity. In this work, a number of complexing agents were tested, and their selectivity for removing contaminating metals, catalytic metals, and alumina was studied. A study of the state of vanadium as it exists on the catalyst surface is also reviewed.
HE DEPOSITION ON CATALYSTS of metallic contaminantsTpresent as metallo-organic compounds in petroleum feedstocks is a serious catalytic processing problem. O n cracking catalysts ( 7 ) > such deposition results in a considerable loss of selectivity so that the reaction tends to produce more coke and gas along \vith less of the desired product, gasoline. In residue hydrodesulfurization, the metal deposits do not greatly alter catalyst activity or selectivity (5). However, the abundance of metals in most residues results in a catalyst "blanketing" effect Lvhich completely alters the original surface components and can eventually lead to reactor plugging.. 4 number of approaches to solving the metal contamination problem are evident. Removal of the metallo-organic contaminants from the reactant overcomes the problem, but in many cases this becomes costly or technically difficult to accomplish \vith a high degree of selectivity. Another approach is to allow the contaminants to deposit on the catalyst and then to remove such deposits either chemically or physically without allowing a significant build-up to occur. Although the same limitations of cost and technical difficulty are applicable to this approach? i t is possible to envision a more selective system in jvhich less of the reactant is lost while removing the metals. The work reported in this paper describes some chemical techniques which have been developed for removing certain metallic contaminants from catalysts. It is believed that these can be used effecrively in combination \vith either catalytic cracking or residue hydrodesulfurization to circumvent the metal contamination problems.
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