Nickel catalysts regeneration

The first process utilizes a bed of nickel catalyst which has been regenerated with hydrogen to reduce the nickel content to metallic form. The finely divided metal then reacts with impurities and retains them in the bed, probably as nickel oxide in the case of oxygen or as physisorbed compounds for other impurities. Periodically, the bed is regenerated at elevated temperature using hydrogen to restore the metallic content. The nickel process can be used and regenerated indefinitely. 

In the presence of low reactive aromatic substrates such as o-tolyl chloride, it has been shown that production of the aromatic zinc occurs only at the potential at which the zinc(II) bipyridine is reduced, i.e. at about —1.4 V/SCE. Furthermore, the nickel(II) complex is also reduced at this potential value. In this case, the formation of either a bi-metallic species, or a cluster (18), intermediary combining Ni(0) and Zn(0) via the bipyridine ligand is suggested. This complex would react with the aromatic chloride to produce the corresponding ArZnCl along with the regeneration of the nickel catalyst. 

This process is characterized by its high C02 retention under pressure and by low steam requirements for regeneration. According to U.S. Patent 3,347,621, a sidestream regenerator is required to remove by-products that build up in the system. Mild steel is suitable in much of the process, but stainless steel is preferred where C02 concentrations are high. The process must be carefully engineered to protect the downstream nickel catalysts from sulfur that may carry-over from the absorber. Likewise, the C02 that is produced must be protected from entrainment of the solvent and contamination with sulfur260. 

Hydrotreating catalysts are usually alumina supported molybdenum based catalysts with cobalt or nickel promotors. By 1990, the demand for hydrotreating catalysts is expected to reach 80,000,000 pounds annually (1). The increased demand for these catalysts and the limitations on the availability and supply of the active metals increase the urgency to develop effective catalyst regeneration techniques. 

Subsequent investigations, including IINS, were carried out to characterize the various resistances of such cokes to controlled after-treatments, such as oxidation or hydrogasification processes, as a basis for determining the feasibility of catalyst reactivation. The presence of metallic contaminants (iron, cobalt, and nickel) was of relevance, not only to the deposition of cokes and the catalytic transformation of the carbon structure, but also to the dynamic processes in the controlled decomposition of the material in catalyst regeneration procedures 50). 

A cyclone outside the moving-bed catalytic colnmn serves to sort only catalyst particles of a desired size among the catalyst particles dropped to the lower portion. A nickel-molybdenum catalyst regenerator with an air injector serves to regenerate the catalyst transferred from the cyclone and the regenerated catalyst is then returned to the moving-bed catalytic cracker [29],... 

In the second reaction, ethylene is reacted with the alkylaluminums to form n-a-olefins and to regenerate triethylaluminum (Figure 2). Although the reaction can be conducted without a catalyst by operating at high temperatures (3, 6), the reaction is normally carried out at lower temperatures in the presence of a nickel, cobalt, or platinum catalyst. Reaction conditions are moderate, 2500 p.s.i. and 200° F. when less than 0.01% of nickel catalyst is used. The catalyst is formed in situ by the addition of a nickel salt. A small amount of alkylaluminum will react with the nickel salt, reducing it to colloidal nickel. 

Chemisorption uptakes of Hj at 298-303 K for alumina supported nickel catalysts were measured. The corresponding nickel surface areas were calculated and subsequently sulfur contents at saturation were determined. The average values were of the same magnitude as the amounts of sulfur that were not desorbed from the catalysts during the TPH treatments. Hence, it may be concluded that the saturation layer of sulfor remains on the catalyst even after regeneration in hydrogen atmosphere. 

Dimethylsulfoxide was found to increase the rate of hydrolysis in esters which were resistant to saponification. Treatment of alkyl toluenesulfonates with sodium naphthalene anion radical in tetrahydrofuran constituted an almost ideal procedure for regenerating the corresponding alcohols. The hydration of nitriles to amides in the presence of nickel catalysts shows an increase in yield with the addition of pyridine. ... 

Reversibility of these poisons depends on process conditions. Sulfur-poisoning of nickel catalysts, for example, is irreversible at lower temperatures. Methanation catalysts beds cannot be regenerated even with... 

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... 

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