Metal passivation for anode grade petroleum coke

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing petroleum coke suitable for use in the manufacture of carbon anodes for aluminum production from a petroleum feedstock ("coker feedstock") containing metal impurities.
The methods of the present invention include adding inorganic and/or organometallic compounds of Group 4 and/or Group 13 to the coker feedstock in amounts sufficient to passivate the oxidizing tendencies of the metal impurities inherent in the petroleum coke.
The passivating metal compounds are added into the coker feedstock prior to the completion of the coking process.
The term "passivate" as used herein describes the ability to reduce the oxidizing tendencies of the metal impurities in the coke or anode.
The invention also relates to the petroleum coke composition produced from the methods of the present invention as well as the carbon anodes formed from the resulting coke.
The carbon anodes exhibit improved resistance to oxidation usually caused by the catalytic effects of the metal impurities present in the coke.
The coker feedstock that can be used as the feedstock to the coking process in accordance with the present invention is any such feedstock known in the industry for use in a coking process.
Generally, such feedstocks can be described as atmospheric or vacuum residues with initial boiling points in the range of 340 and 480-C respectively.
The coker feedstock generally has various impurity metals including vanadium and nickel which are of primary significance.
These metal impurities can be present in various concentrations.
Typically, vanadium is present in an amount usually between 1 and 600 ppm, and more typically between 100 and 500 ppm.
Nickel is present in an amount greater than about 1 ppm, usually between 1 and 500 ppm, and more typically between 10 and 230 ppm.
Other metals such as sodium, calcium, and iron may also be present to cause deleterious effects in the anode.
The Group 4 and/or Group 13 metal compounds that can be added to the coker feedstock prior to the completion of the coking process include inorganic compounds, organometallic compounds, or mixtures thereof The term "Group 4 metals" as used herein refers to the elements in Group 4 of the periodic table of elements which includes Ti, Zr, and Hf