Nickel deactivation

Raney nickel deactivated with piperidine and zinc acetate has been used for semihydrogenation of acetylenic compounds. 

It is well known, even from old literature data (ref. 1) that the presence of metal promotors like molybdenum and chromium in Raney-nickel catalysts increases their activity in hydrogenation reactions. Recently Court et al (ref. 2) reported that Mo, Or and Fe-promoted Raney-nickel catalysts are more active for glucose hydrogenation than unpromoted catalysts. However the effects of metal promotors on the catalytic activity after repeated recycling of the catalyst have not been studied so far. Indeed, catalysts used in industrial operation are recycled many times, stability is then an essential criterion for their selection. From a more fundamental standpoint, the various causes of Raney-nickel deactivation have not been established. This work was intended to address two essential questions pertinent to the stability of Raney-nickel in glucose hydrogenation namely what are the respective activity losses experienced by unpromoted or by molybdenum, chromium and iron-promoted catalysts after recycling and what are the causes for their deactivation ... 

The transfer line between the trap and the GC is made of nickel, deactivated fused silica, or silica-lined stainless steel tubing. Active sites that can interact with the anlaytes are eliminated on these inert materials. The line is... 

The above studies show that oxide and metal promoters influence the rate at which nickel deactivates in the presence of sulfur. Metal-support inter-... 

Reduction of oximes to ketones. Ketoximes can be converted to ketones by hydrogenation catalyzed by Raney nickel (deactivated with acetone) in THF/CH,OH/H,0 or in CHiOH/H,0 containing boric acid to facilitate hydrolysis of the intermediate imine... 

The appHcations of supported metal sulfides are unique with respect to catalyst deactivation phenomena. The catalysts used for processing of petroleum residua accumulate massive amounts of deposits consisting of sulfides formed from the organometaHic constituents of the oil, principally nickel and vanadium (102). These, with coke, cover the catalyst surface and plug the pores. The catalysts are unusual in that they can function with masses of these deposits that are sometimes even more than the mass of the original fresh catalyst. Mass transport is important, as the deposits are typically formed... 

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

A good catalyst is also stable. It must not deactivate at the high temperature levels (1300 to 1400°F) experienced in regenerators. It must also be resistant to contamination. While all catalysts are subject to contamination by certain metals, such as nickel, vanadium, and iron in extremely minute amounts, some are affected much more than others. While metal contaminants deactivate the catalyst slightly, this is not serious. The really important effect of the metals is that they destroy a catalyst s selectivity. The hydrogen and coke yields go up very rapidly, and the gasoline yield goes down. While Zeolite catalysts are not as sensitive to metals as 3A catalysts, they are more sensitive to the carbon level on the catalyst than 3A. Since all commercial catalysts are contaminated to some extent, it has been necessary to set up a measure that will reflect just how badly they are contaminated. 

Two serious drawbacks of this method are the extensive deuterium scrambling around the reaction site and the occasional formation of olefinic side products, which are hard to separate by conventional means. The extent of olefin formation may depend on the nature of the Raney nickel since it is known that desulfurization with deactivated Raney nickel can yield olefins. Best results are obtained when the deuterated Raney nickel is prepared very rapidly and used immediately after preparation. 

The conventional desulfurization of thioketais by Raney nickel does not give olefins (for reviews see ref. 333, 334). However, aged or acetone-deactivated nickel used in ethanol gives considerable amounts of olefins. ... 

Despite all the advantages of this process, one main limitation is the continuous catalyst carry-over by the products, with the need to deactivate it and to dispose of wastes. One way to optimize catalyst consumption and waste disposal was to operate the reaction in a biphasic system. The first difficulty was to choose a good solvent. N,N -Dialkylimidazolium chloroaluminate ionic liquids proved to be the best candidates. These can easily be prepared on an industrial scale, are liquid at the reaction temperature, and are very poorly miscible with the products. They play the roles both of the catalyst solvent and of the co-catalyst, and their Lewis acidities can be adjusted to obtain the best performances. The solubility of butene in these solvents is high enough to stabilize the active nickel species (Table 5.3-3), the nickel... 

However, attempts to reuse the ionic catalyst solution in consecutive batches failed. While the products could readily be isolated after the reaction by extraction with SCCO2, the active nickel species deactivated rapidly within three to four batch-wise cycles. The fact that no such deactivation was observed in later experiments with the continuous flow apparatus described below (see Figure 5.4-2) clearly indicate the deactivation of the chiral Ni-catalyst being mainly related to the instability of the active species in the absence of substrate. 

The activity of catalyst degrades with time. The loss of activity is primarily due to impurities in the FCC feed, such as nickel, vanadium, and sodium, and to thermal and hydrothermal deactivation mechanisms. To maintain the desired activity, fresh catalyst is continually added to the unit. Fresh catalyst is stored in a fresh catalyst hopper and, in most units, is added automatically to the regenerator via a catalyst loader. 

Contaminant coke is produced by catalytic activity of metals such as nickel, vanadium, and by deactivation of the catalyst caused by organic nitrogen. 

Four pilot plant experiments were conducted at 300 psig and up to 475°C maximum temperature in a 3.07-in. i.d. adiabatic hot gas recycle methanation reactor. Two catalysts were used parallel plates coated with Raney nickel and precipitated nickel pellets. Pressure drop across the parallel plates was about 1/15 that across the bed of pellets. Fresh feed gas containing 75% H2 and 24% CO was fed at up to 3000/hr space velocity. CO concentrations in the product gas ranged from less than 0.1% to 4%. Best performance was achieved with the Raney-nickel-coated plates which yielded 32 mscf CHh/lb Raney nickel during 2307 hrs of operation. Carbon and iron deposition and nickel carbide formation were suspected causes of catalyst deactivation. 

Flame-Sprayed Raney Nickel Plates vs. Pellets of Precipitated Catalyst in a Packed Bed. Experiments HGR-13 and HGR-14 demonstrated that the performance of the plates sprayed with Raney nickel catalyst was significantly better than that of the precipitated nickel catalyst pellets. The sprayed plates yielded higher production of methane per pound of catalyst, longer catalyst life or lower rate of deactivation, lower CO concentration in the product gas, and lower pressure drop across the catalyst bed. 

The initial reactivities of the catalyst beds in experiments HGR-13 and HGR-14 are considered satisfactorily high however, the overall rate of deactivation of the Raney nickel catalyst bed (0.029% /mscf/lb) was... 

Nickel carbide, detected on the catalyst in experiment HGR-14, is another compound suspected of deactivating Raney nickel catalyst. However, the shutdown involved purging with hydrogen while the catalyst... 

The metal surface area at the inlet end of the catalyst bed in experiment HGR-12 was smaller than that at the outlet end this indicates that a decrease in nickel metal sites is part of the deactivation process. Sintering of the nickel is one possible mechanism, but carbon and carbide formation are suspected major causes. Loss of active Raney nickel sites could also conceivably result from diffusion of residual free aluminum from unleached catalyst and subsequent alloying with the free nickel to form an inactive material. 

Nickel catalysts were used in most of the methanation catalytic studies they have a rather wide range of operating temperatures, approximately 260°-538°C. Operation of the catalytic reactors at 482°-538°C will ultimately result in carbon deposition and rapid deactivation of the catalysts (10). Reactions below 260°C will usually result in formation of nickel carbonyl and also in rapid deactivation of the catalysts. The best operating range for most fixed-bed nickel catalysts is 288°-482 °C. Several schemes have been proposed to limit the maximum temperature in adiabatic catalytic reactors to 482°C, and IGT has developed a cold-gas recycle process that utilizes a series of fixed-bed adiabatic catalytic reactors to maintain this temperature control. 

---