Passive vanadium

On non-zeolitic particles in the absence of a vanadium passivator, vanadium (when present at the 0.4 wt% level) makes a greater contribution to contaminant coke and hydrogen yields than nickel at constant surface area and metals loading. Incorporation of a vanadium passivator into the catalyst matrix can greatly alter the selectivity effects of vanadium, and can essentially negate its effect on non-zeolitic particles as in the case of magnesium. 

The relative ease with which VpOr can be reduced to V(III) in aluminosilicates indicate the exiirence of weak metal-surface interactions and the inability of the surface to effectively passivate vanadium. Similarly, V on Kaolin (and metakaolin) exist mostly as the "free oxide and can (in part) be reduced to V(III) species. Therefore, DFCC systems containing metakaolin microspheres (or amorphous aluminosilicates (15)) should not be as effective as sepiolite in passivating metals TTke Ni and V. In fact, DCC mixtures loaded with 5000 ppm Ni-equivalents (that is 0.6% V + 0.38% Ni) are not metals resistant when metakaolin is used as a metals scavenger (1) ... 

A study of the vanadium catalyzed dehydrogenation reaction showed antimony interacts with vanadium and decreases its dehydrogenation activity. Cracking catalyst was contaminated with vanadium in the laboratory, A portion of this contaminated catalyst was then treated with an antimony containing compound to passivate vanadium. The catalysts were evaluated by cracking gas oil. The yield of hydrogen for passivated catalyst averaged fifteen percent less than for the unpassivated catalyst. 

At this point we have an aluminum type sepiolite which shows mild acidity and could be used as a component for FCC catalysts. Then, we have checked if the aluminium containing sepiolite can also passivate vanadium. To do that, two FCC catalysts containing 20% of a REHY zeolite in either 80% of a 23 wt% A1203 containing silica-alumina, or 80% of aluminic sepiolite were prepared. Both samples where impregnated to incipient wetness with a V naphthenate/xylene mixture (15), in order to introduce 6000 ppm of vanadium. Both samples were steam deactivated... 

Catalysts. In industrial practice the composition of catalysts are usuaUy very complex. Tellurium is used in catalysts as a promoter or stmctural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium teUurium molybdate catalyst has successfliUy been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). 

A number of indices relate metal activity to hydrogen and coke production. (These indices predate the use of metal passivation in the FCC process but are still reliable). The most commonly used index is 4 X Nickel + Vanadium. This indicates that nickel is four times as actiw as vanadium in producing hydrogen. Other indices [9] used are ... 

In general, vanadium concentrations above 2,000 ppm on the E-Cat can justify passivation. 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

Occelli, M. L. and Stencel, J. M., "Cracking Metals-Contaminated Oils with Catalysts Containing Metal Scavengers. Part II. The Effect of Aluminuma Particles Addition on Vanadium Passivation." (In preparation)... 

Sepiolite passivates most of the nickel via formation of non interactive silicate-like materials. Heating at high temperatures induces migration of nickel to the interior and of vanadium to the exterior of the catalyst surface. Metal-surface interactions are observed also in Ni-loaded kaolin microspheres however, V on kaolin behaves like bulk V20g with respect to reduction, thus explaining this xlay s inability to passivate V-contaminants. 

DFCC mixtures containing 40% sepiolite and 60% GRZ-1 are equally effective in passivating high (10,000 wtppm) levels of vanadium impurities (1 ). In both cases, metakaolin microspheres do not... 

These results suggest that oxidation state is not solely responsible for catalyst deactivation but that other factors such as V location and mobility may play an important role. Basic alkaline earth oxide passivators such as MgO, admixed to the catalyst, interact strongly with vanadium during the regeneration period. Although the oxidation state of vanadium is essentially unaffected, MgO structurally modifies V as evidenced by a unique X-ray absorption spectrum. 

Understanding the interaction of vanadium with the catalyst is an important step in the development of technology to passivate... 

VANADIUM DEACTIVATION UNDER SIMULATED CONDITIONS. The degree of catalyst deactivation was measured by comparing the activity of the catalyst or catalyst/passivator blend containing 5000 ppm V to that of the corresponding sample with no V added after similar treatment conditions (Table II). For the USY catalyst (catalyst A), steaming with VgO at 1450 F resulted in a 6855 decline in activitjr ... 

Use a vanadium passivator when vanadium level exceeds 3000 ppm on catalyst... 

The passivity of vanadium is referred to on p. 23, and the electrolytic decomposition of anhydrous fused vanadium salts on p. 17. 

Previously proposed mechanisms of the biosynthesis of certain chlorinated compounds have invoked electrophilic bromination of alkenes followed by passive chloride attack [62], Although this mechanism could explain the origin of adjacent brominated and chlorinated carbons, it does not readily account for compounds containing chlorine only. Thus, with the discovery of chloroperoxidase activity of the vanadium enzyme, the origin of specific chlorinated marine natural products can now be addressed. 

Table II, the second example, shows the benefits of metals passivation at a FCCU in a refinery operating to maximize throughput. The FCC catalyst contained 490 ppm nickel and 1200 ppm vanadium, and the unit was operating against both its air blower and gas compressor limits. Hydrogen production was 92 SCF per barrel of FCCU feed with this amount of hydrogen in the gas to the compressor, it was difficult to maintain the compressor governor on control. The high concentration of hydrogen in the fuel gas also affected the steady state operation of the heat control of other processing units.

Metals passivation is an area of active research and development, and several passivation systems have been commercialized. Commercialized systems include addition of elements and combinations of elements to FCC catalysts, such as antimony, antimony plus phosphorus (6,. 14), antimony plus phosphorous plus tin, antimony plus tin, tin (19-21), and bismuth (22, 23). Other commercialized systems include process changes or catalyst changes such as the use of steam or light hydrocarbons as diluents in the reactor (24) and vanadium traps (25). Antimony has been used successfully in conjunction with these systems. Another metals passivation additive, containing ingredients that are proprietary, has also been introduced commercially (26) ... 

Models have been developed to predict cat cracker yields based on operating parameters and feedstock properties (34) These have aided in application and evaluation of metals passivation benefits. Miller and Pawloski (35) reported the use of mathematical models to calculate the benefits of vanadium passivation, and Teran (27) reported the need for FCCU hydrogen modeling and metals tracking to optimize passivation benefits. 

It is the purpose of this paper to investigate and report the use of luminescence techniques to follow the mechanism of metals deposition and passivation in a zeolite when the three vanadium precursors shown in Figure 1 are used. 

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