Catalyst metals removal, effect

Nitrogen and metals are concentrated in the heaviest fraction of the crude oil, i.e., the resid. The main reason for metal removal from refinery streams is the deactivating effect they cause in the catalysts of the other refining processes. In recent times, both HCK... 

The asphaltenes are selectively converted with a low hydrogen consumption decreasing significantly the metal content in the product. Catalyst was tested during a six-month period, processing various heavy feedstocks and showing a stable performance. The yields and product quality reported indicated almost complete conversion of the feed and total metal removal. The net effect of the ABC pretreatment was found to be an increase in catalyst life, higher metal quality of the product oil, and increase distillate yields. 

Evidence for a major mode of catalyst deactivation in this system came from the observation of phosphonium cations (HPR3) in the reaction mixture, which could form through the pro to nation of free PR3 by the acidic dihydride complex. It is not known which species decomposes to release free PR3, but the decomposition pathway is exacerbated by the subsequent reactivity in which protonation of phosphine removes a proton from the metal dihydride, effectively removing a second metal species from the cycle. 

In Section IV, the kinetics and mechanisms of catalytic HDM reactions are presented. Reaction pathways and the interplay of kinetic rate processes and molecular diffusion processes are discussed and compared for demetallation of nickel and vanadium species. Model compound HDM studies are reviewed first to provide fundamental insight into the complex processes occurring with petroleum residua. The effects of feed composition, competitive reactions, and reaction conditions are discussed. Since development of an understanding of the kinetics of metal removal is important from the standpoint of catalyst lifetime, the effect of catalyst properties on reaction kinetics and on the resulting metal deposition profiles in hydroprocessing catalysts are discussed. 

Graded catalyst systems employ two or more catalysts to combine both high metal capacity and high activity. A larger-pore catalyst, designed to maximize metals removal and to provide capacity for metals accumulation, is used in the first reactor bed. This, in effect, provides a metals removal... 

Low levels of SOj in the exhaust gas stream are known to lower the catalytic activity of noble metal-supported catalysts, although this effect is considerably less compared to base metal catalysts [19]. Iwamoto et al. [20] observed a sUght decrease of NO removal activity of the Cu- M-5 for NO reduction by C3H5 upon the addition of SOj to the feed gas stream. The conversion of NO at 300°C, however, completely recovered to the initial state upon termination of the SO2 feed. They suggested that the loss of the removal activity of the catalyst is probably due to the alteration of the copper ionic state on the catalyst surface but provided no evidence in support of this hypothesis. 

Two relatively recent advancements that have increased the utility of the P-K reaction include (1) allowing the reaction to run with catalytic amounts of transition metal and (2) making the transformation asymmetric. Several metals beside Co will catalyze the P-K reaction, including Rh, Ir, Fe, Ru, Group 6 metals, and Ti. Much of the work in catalyst development has focused on use of Rh(I) and Ru(II) complexes, which seem to be most effective. Many Rh precatalysts have been used, such as Rh3(CO)12, Wilkinson s catalyst, and complexes 103 and 104. AgOTf is often used in conjunction with the last three catalysts to remove Cl, which then produces more catalytically active cationic Rh(I) species. 

Operation. The preheated gas stream is passed through a catalyst bed, where the catalyst initiates and promotes the oxidation of the organic without being permanently altered. The catalyst is normally an active material, such as platiniun, copper chromite, chromium, or nickel, on an inert substrate, such as honeycomb-shaped ceramic. For the catalyst to be effective, the active sites upon which the organic gas molecules react must be accessible. The buildup of polymerized material or reaction with certain metal particulates will prevent contact between active sites and the gas. A catalyst can be reactivated by removing such a coating. 

The action of nickel is so much more powerful than that of alumina that the dehydrating action of the latter is practically eliminated when catalysts containing mixtures of reduced nickel and alumina are used. In fact, the alumina apparently only acts as a support for the active metal. However, comparative measurements have shown that the oxides of aluminium, iron, magnesium, and calcium may act as strong promoters for nickel catalysts. This effect has been explained as a mechanical effect, viz., the development of a large surface by which relatively more active metal is effectively exposed.10 When only small amounts of oxide are present the effect is predominantly that of support. The increased addition of oxide may increase the catalytic activity up to a certain point beyond which it only serves to dilute the catalyst and reduce its selectivity. Other explanations of the promoter action postulate the removal of catalyst poisons by the oxide, or regeneration of the active metallic catalyst by oxidations and reductions.20... 

Metal Free Transition metal catalysts are highly effective for C—H bond activation. However, transition metal complexes are not only expensive, but also difficult to remove from the reaction products, resulting in toxicity concerns. DDQ is a well-known oxidant in organic chemistry [33]. For many years, it has been used for the oxidation of alcohols to ketones and aromatization. The first intermolecular C—C bond formation was realized by DDQ-mediated Mukaiyama-type aldol reactions [34], The reactions of electron-rich benzyl ethers and silyl enol ethers afforded 3-alkoxy-3-phenylpropionyl derivatives at ambient temperature with moderate to excellent yields (Equation 11.12). 

It is possible that adsorption of A/-containing compounds reduces the electrophilic character of the catalyst (by removing traces of acids or poisoning metal ions). For this reason hydrogenolysis occurs via an 8 2-like mechanism instead of the faster S l. Additional evidence is that oxidic or unreduced catalysts give the best selectivity in debenzylation [9]. It has also been found that for O-benzyl systems palladium oxide was much more effective than palladium metal whereas no such effect was observed with /V-benzyl systems [66]. 

Alkaline earth and rare earth metal cocation effects are reported in this paper for copper ion-exchanged ZSM-5 zeolites used for the catalytic decomposition of nitric oxide in 02- free, 02- rich, and wet streams. Severe steaming (20% H2O) of Na-ZSM-5 at temperatures above 6(X)°C leads to partial vitreous glass formation and dealumination. Unpromoted Cu-ZSM-5 catalysts suffer drastic loss of NO decomposition activity in wet gas streams at 500°C. Activity is partially recovered in dry gas. Copper migration out of the zeolite channels leading to CuO formation has been identified by STEM DX. In Ce/Cu-ZSM-5 catalysts the wet gas activity is greatly improved. CuO particle formation is less extensive and the dry gas activity is largely recovered upon removal of the water vapor. 

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