Deactivation by metals

Careful selection of the deactivation conditions (metals per cycle, regenerator tempeature, % wt steam in can also allow us to distinguish between catalyst deactivation by metals and by hydrothermal effects. (Table VIII.)... 

The deactivation of catalysts used in hydrotreating and hydroconversion of heavy petroleum feedstocks is associated with coking and metals deposition. Deactivation by metals has been thoroughly studied [1], but, little is known about deactivation by carbonaceous deposits. The initial decline in activity has often been attributed to this coke formation [2, 3, 4], However, in a recent study [51 it has been shown that coke deactivation can account for more than 50% of the deactivation in resid upgrading. 

Catalyst Deactivation by Metals and Coke During Hydrodemetallation... 

New Developments in FCC Catalyst Deactivation by Metals Metals Mobility and the Vanadium Mobility Index (VMI)... 

In the MHC mode, the coke deposition on the catalysts is almost constant from the reactor top to the reactor bottom. This means that coke deactivation has the same significance for all catalyst types and is not such a dominant factor. Deactivation by metal deposition is dominant for each catalyst. Therefore demetallization catalysts with a high metal tolerance (higher metal absorption capacity) are essential for the catalyst life in the MHC mode. 

In mild hydrocracking of atmospheric residue for maximum middle distillates production, the metal tolerance of the demetallization catalyst is the most important factor determining the catalyst life. The deactivation by metals is the prevailing mechanism in this mode of operation. 

All heavy crude oil residues have heavy metals such as Ni, V or Fe in their structure. These metals are bonded as organometalic compounds. At high temperatures and for hydrogenation reactions, these compounds are cracked and heavy metals are deposited on the catalyst surface. These metals can also react with hydrogen sulfur from the gas phase to form metal sulfides. The deposition of sulfides of iron, vanadium or nickel leads to irreversible poisoning of the catalyst. This is the difference between catalyst deactivation by metals and deactivation by coke the former leads to an irreversible loss of the catalyst activity. 

Deactivation by metals deposition is also reflected in the measured metals contents of the catalysts. Figures 3 and 4 show electron microprobe measurements of metals as a function of radial position in the catalyst. It is apparent that large amounts of metals are deposited on the outer edge of the catalyst pellets, while the interior contains very little metal. At sufficiently long times on stream, the pores at the outer edge of the catalyst pellets become completely blocked. This phenomena is referred to as pore mouth plugging. When the pores become plugged there is a catastrophic decrease in conversion. 

The catalyst can be reused following regeneration provided that it has not been deactivated by metals such as vanadiirm, nickel, sodium from the feed or iron scale. Deactivated catalysts can contain between 10 and 30% of metal deposits, which may be recovered for economic or environmental reasons. Oxidation of cobalt or nickel sirlfides to sirlfate, during in situ regeneration, can gradually lead to deactivation of the catalyst. 

Deactivation by metals, which is irreversible and whose rate depends on the metals level in the feed... 

The study was focused on three different heavy feedstocks HCO, atmospheric residue from heavy crude oil (ARHCO), and extra-heavy crude oil (EHCO). Their main physical and chemical properties are reported in Table 8.2. The ARHCO was obtained from HCO by fractionation in a 40 L glass column. It can be noticed that all feedstocks are characterized by having high concentration of metals (350-535 wppm Ni + V) and asphaltenes (10-19 wt%), which make them good candidates for studying deactivation by metal deposits. 

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