Vanadium removal

Kinetics studies of the hydrotreatment (and hydrocracking) of VR has led to the conclusion that most of the metals, sulfur and nitrogen removal takes place during the first 50% of the whole VR conversion [119-123], More than one reactor was needed for HDM and HDS of a Maya VR, when HDT is used as feed pretreatment [119,120], Although vanadium removal appears easier and faster than nickel removal, their kinetics results showed very similar values of the activation energy for the demetallization reactions [122],... 

A cracking catalyst is subjected to two pretreatment steps. The first step effects vanadium removal the second, nickel removal, to prepare the metals on the catalyst for chemical conversion to compounds (chemical treatment step) that can... 

Demet X procedure simply consists of an oxidation at elevated temperature, both the New Demet and the Demet III process has a sulfiding step which transforms the metal oxides to insoluble sulfides. In Demet III the sulfiding step is followed by a partial oxidation step. This oxidation is carefully controlled to produce metal sulfates and sulfides which can be directly removed by washing or be transferred into soluble compounds by the reductive and oxidative washes used in this procedure. In the New Demet process the sulfiding step is followed by chlorination which results in a transformation of the sulfides into washable chlorides. Since vanadium chlorides are volatile, most of the vanadium removal using this procedure occurs in the gas phase. In the Demet X procedure, the vanadium oxides formed are water soluble or can be transformed into water soluble forms by aqueous treatments. In contrast the nickel oxides are insoluble in water. 

In competitive demetallation experiments the same rates do not necessarily hold. Hung and Wei (1980) reported that with both Ni-etio and VO-etio in the feed, the vanadium removal rate was the same as in the individual vanadium run, whereas the nickel removal rate was suppressed to below that of vanadium removal. In a related study using a mixed Ni-T3MPP and VO-etio oil, Webster (1984) reported that VO-etio de-metallated faster than Ni-TMPP and also suppressed the metal removal rate of the latter. This inhibition phenomenon offers a partial explanation as to why in most commercial operations with real feeds vanadium is more reactive than nickel. 

A summary of hydrodemetallation kinetic studies is presented in Table XXVI. The list is not exhaustive but does include a diversity of feedstocks and catalysts. It is apparent that a discrepancy in reaction order rt with respect to total metal (Ni or V) concentration has been observed. Riley (1978) reported first-order kinetics for both nickel and vanadium removal when hydrotreating a Safaniya atmospheric residuum. Demetallation kinetic order of 1.0 to 1.5 depending on reactor configuration has been reported by van Dongen et al. (1980) for vanadium removal. Oleck and Sherry (1977) report a better description of the reaction system is obtained with second-order kinetics for nickel and vanadium removal from Lago-medio (Venezuelan) atmospheric residuum. All studies were conducted on CoMo/A1203 catalysts. 

Most investigations have revealed that vanadium removal rates exceed those of nickel in petroleum residua. Results are summarized in Table XXVI. Cases of V/Ni activity ratios of less than one have been reported less frequently (Inoguchi et al., 1971 Galiasso et al., 1985). These have generally been due to a temperature phenomenon but may also result from unique feedstock or catalyst properties. 

A linear relationship is often observed between vanadium removal and sulfur removal, whereas the relationship between nickel and sulfur removal is linear but of smaller slope (Massagutov et al., 1967). For asphaltene-containing stocks, this phenomenon is interpreted on the basis of heteroatom distribution within the asphaltene micelles (Beuther and Schmid, 1963). Sulfur and vanadium are concentrated on the exterior, whereas nickel is concentrated in the interior. Conversion of the asphaltene generally leads to simultaneous removal of sulfur and vanadium, whereas nickel removal is more difficult. 

Riley (1978) reported that catalyst activity for vanadium removal from Safaniya atmospheric residuum is independent of the Co and Mo loading. 

The natural material catalysts exhibit similar metal removal selectivity patterns as conventional hydrotreating catalysts. Vanadium removal activity is higher than that of nickel and overall activity increases with hydrogen pressure. Thus little change in intrinsic demetallation pathways is indicated with these materials. However, in contrast to CoMo/A1203, the nodule catalysts are only moderately active for HDS and essentially inactive for HDN. 

Figure 4-2 First-order kinetic plots based on the holdup model fot removal reactions (after Paraskox et al. 1). (a) the vanadium removal reaction, (ft) the sulfur removal reaction, (c) the nitrogen removal reaction, (d) the nickel removal reaction.

Kinetics. When the diffusion rate of reactants in a catalyst pore affects the reaction rate, the rate equations can be represented for desulfurization ts and vanadium removal rv, respectively by ... 

Catalyst Deactivation. In the model, the catalyst deactivation is postulated to be caused by the deposition of metals and coke. For convenience the demetallization is represented by vanadium removal and the effect of nickel on deactivation is included in the parameters. The quantities of vanadium Qv and coke Qc accumulated are given with Eqs. ( 1) and ( 2) ... 

The study of the Vanadium deposition profiles in spent catalyst particles from resid hydro-processing confirms that HDM is a sequential reaction. Furthermore, it is shown that the distribution parameter for the deposited Vanadium Qv is constant through the reactor for each catalyst type and that Qv is proportional to the efficiency of the Vanadium removal reaction. 

It has been shown that the suggested. sequential reaction scheme, A - B -< C, fully explains the phenomena observed for Vanadium removal from Kuwait AR at industrially relevant conditions. However, it has also been shown that the A - B reaction controls the Vanadium removal in most of the reactor, and this implies that, in practical terms, the overall HDV reaction can be considered as a simple first order reaction with Qv values as effectiveness factors. 

Figure 4 Vanadium Removal Pseudo TurDover Frequency (atoms V ks nm Versus Time on Stream (hours) - symbols as given in Figure 2...

The S/C and V/C ratios in residual asphaltenes in the products from different nms are plotted in Figs. 3a and 3b. The lowest sulfur and vanadium concentrations in the asphaltenes are noticed for the run conducted with the monomodal macropore catalyst Q. The catalyst R which contains a large proportion of both macro and meso pores ranks next for the removal of sulfur from asphaltenes. Although the conventional bimodal catalyst (S) with a large proportion (> 50%) of micro pores and about 20% macropores shows good activity for removal of sulfur from asphaltenes similar to catalysts R its activity for vanadium removal is poor. 

Another useful comparison is the amount of vanadium "removed" from the equilibrium catalyst. This is somewhat of a misnomer because it represents not only vanadium that has migrated from the equilibrium catalyst to the trap but vanadium that has deposited directly on the trap. Had the trap not been there, all of the vanadium would have deposited on the equilibrium catalyst so it is in essence the amount of vanadium removed. Mathematically it is expressed as ... 

The wt.% vanadium removed varied from approximately 5-25% and correlated well with the amount of trap in inventory (Figure 6). In all cases, the targeted amount of RV4+in inventory was 5%. While much of our laboratory work was done with 10% blends, a 5% blend was chosen for the commercial trials to minimize possible dilution effects. Several units did not attain the 5% level due to previously scheduled turnarounds. In two of the cases where the targeted level was achieved, Trials A and G, vanadium removal exceeded 20%. Interestingly, the partial burn operation, Trial F, was not that much lower than the full bum operations. 

The amount of RV4+ in inventory is a function of time. It stands to reason that the percentage vanadium removed would also vary with time. Figure 7 illustrates this relationship. In general, for the same number of days on the trap, the unit with the greatest % trap in inventory provided the highest vanadium removal. 

Figure 6, Percent Vanadium Removed From E-Cat Commercial Summary.

Vanadium is an element, and as such, is not metabolized. However, in the body, there is an interconversion of two oxidation states of vanadium, the tetravalent form, vanadyl (V+4), and the pentavalent form, vanadate (V+5). Vanadium can reversibly bind to transferrin protein in the blood and then be taken up into erythrocytes. These two factors may affect the biphasic clearance of vanadium that occurs in the blood. Vanadate is considered more toxic than vanadyl, because vanadate is reactive with a number of enzymes and is a potent inhibitor of the Na+K+-ATPase of plasma membranes (Harris et al. 1984 Patterson et al. 1986). There is a slower uptake of vanadyl into erythrocytes compared to the vanadate form. Five minutes after an intravenous administration of radiolabeled vanadate or vandadyl in dogs, 30% of the vanadate dose and 12% of the vanadyl dose is found in erythrocytes (Harris et al. 1984). It is suggested that this difference in uptake is due to the time required for the vanadyl form to be oxidized to vanadate. When V+4 or V+5 is administered intravenously, a balance is reached in which vanadium moves in and out of the cells at a rate that is comparable to the rate of vanadium removal from the blood (Harris et al. 1984). Initially, vanadyl leaves the blood more rapidly than vandate, possibly due to the slower uptake of vanadyl into cells (Harris et al. 1984). Five hours after administration, blood clearance is essentially identical for the two forms. A decrease in glutathione, NADPH, and NADH occurs within an hour after intraperitoneal injection of sodium vanadate in mice (Bruech et al. 1984). It is believed that vanadate requires these cytochrome P-450 components for oxidation to the vanadyl form. A consequence of this action is the diversion of electrons from the monooxygenase system resulting in the inhibition of drug dealkylation (Bruech et al. 1984). 

Naeem, A., Westerhoff, P. and Mustafa, S., Vanadium removal by metal (hydr)oxide adsorbents. Water Res., 41, 1596, 2007. 

Most investigations (10) have revealed that vanadium removal rates exceed those as nickel in petroleum residua. In our case, the values of the rate constants are not comparable since they fit different kinetic orders. Nevertheless the percentages of nickel removal are in all cases lower than those of vanadium removal. 

Nickel and vanadium removed during catalytic processing will constitute a high-grade ore and could supply a substantial amount of the domestic demand for these metals. The U.S. consumption of nickel and vanadium in 1970 was estimated at 155,719 and 5,134 short tons, respectively. Crude oil, based on our estimate, contains up to 60% of the annual U.S. demand for nickel and nine times the annual demand for vanadium. 

Reagents found to have varying capabilities in effecting vanadium removal are given in a descending order of reactivity chlorine sulfuryl chloride > t-butyl hypochlorite > dinitrogen tetroxide > t-butyl hydroperoxide - benzoyl peroxide azobisisobutyronitrile >... 

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