Raney-nickel coatings

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. 

The metal plates to be coated with Raney nickel were type 304 stainless steel. Plate surfaces were prepared by sand blasting with an iron-free... 

Experiment HGR-12. The catalyst bed for experiment HGR-12 was the same as that used in experiment HGR-10 except that the coat of Raney nickel in HGR-12 was slightly thinner (Figure 4). The objective in ex-... 

The bed of parallel plates coated with Raney nickel catalyst was much more reactive than the bed of precipitated nickel. This was revealed by the generally lower CO concentration in the product gas during operation with the parallel plate bed for example, after 450 hrs stream time, it was 0.01% with the bed of sprayed Raney nickel (experiment HGR-14) and 0.05% with the bed of precipitated nickel catalyst (experiment HGR-13). 

The higher reactivity of the Raney nickel coated plates is also illustrated by the plots of catalyst temperature vs. bed length (Figure 10). The maximum bed temperature (indicative of near-completion of metha-nation) was consistently reached within a shorter distance from the gas inlet, and the slopes of the curves are correspondingly steeper for the more reactive bed of parallel plates coated with Raney nickel. 

Cold rolling, Raney-nickel-coated cathodes, 40 114... 

Raney nickel coatings, 40 113-119 technically applied coatings, 40 112 technoeconomical significance, 40 111-112... 

A 2-1. two-necked round-bottomed flask fitted with a mechanical stirrer and a reflux condenser is charged with 40.0 g. (0.22 mole) of p-cyanobenzenesulfonamide (Note 1), 600 ml. of 75% (v/v) formic acid, and 40 g. of Raney nickel alloy (Note 2). The stirred mixture is heated under reflux for 1 hour (Note 3). The mixture is filtered with suction through a Buchner funnel coated with a filter aid (Note 4), and the residue on the funnel is washed with two 160-ml. portions of 95% ethanol. The combined filtrates are evaporated under reduced pressure with a rotary evaporator (Note 5). The solid residue (Note 6) is heated in 400 ml. of boiling water and freed from a small amount of insoluble material by decantation through a plug of glass wool placed in a filter funnel. The filtrate is chilled in an ice bath and the precipitate is collected by filtration with miction, washed with a small amount of cold water and dried at 50°... 

Lactitol. Lactitol (4-0-/ -D-galactopyranosyl-D-sorbitol), is a synthetic sugar alcohol produced on reduction of lactose, usually using Raney nickel. It can be crystallized as a mono- or di-hydrate. Lactitol is not metabolized by higher animals it is relatively sweet and hence has potential as a non-nutritive sweetener. It is claimed that lactitol reduces the absorption of sucrose, blood and liver cholesterol levels and to be anticariogenic. It has applications in low-calorie foods (jams, marmalade, chocolate, baked goods) it is non-hygroscopic and can be used to coat moisture-sensitive foods, e.g. sweets. 

Electrocatalysis of the Anodic Oxygen Evolution by Raney-Nickel Coatings... 

Microscopic and spectroscopic investigations (SEM and XPS) reveal the relatively fast change of the chemical composition of nickel sulfide coatings upon the onset of cathodic hydrogen evolution (74). Indeed, at 90°C all nickel sulfide phases are reduced to porous nickel within several days to a week s time. They lose some catalytic activity with time with an increase in overvoltage between 0.15 and 0.3 V after continuous operation for 1 year. It is clear that the catalyst after I week is already no longer nickel sulfide but some type of Raney nickel. Thus far the initial catalytic activity of the NiS, coating is of little relevance. The respective results and data are due to be published by the present authors (73). 

Although at least four different technologies [cold rolling, flame spraying, Zn and A1 melt dipping, cathodic deposition of Ni/Zn precursor alloys (76)] have been described, only cold rolling and cathodic deposition of precursor alloys are used for commercial production of Raney-nickel-coated cathodes. 

Fig. 12. Morphology of Raney-nickel-coated cathodes for hydrogen evolution from caustic electrolytes (a) surface of Ni-Zn precursor coatings, (b) surface of Raney-nickel coating prepared by caustic leaching of the Zn content of the precursor, (c) cut through a Raney-nickel coating.

Fig. 13. Schematic of (a) a straight pore, (b) the concentration profile of hydrogen established in the pores of Raney-nickel coating under operation condition (c) calculated distribution of H2 concentration, effective overpotential, and (d) current density in a pore (diameter of 2 nra).

Obviously the contribution of the pore walls—according to the current density distribution—to cathodic hydrogen evolution becomes negligible beyond 10 fim pore depth so that for a perfect, undivided Raney-nickel coating of 100 fim thickness, only 7 to 8% utilization is anticipated. This is the reason why the fissures and cracks, the so-called tertiary structure of the catalyst, formed in Raney-nickel coatings by the leaching process are so important for improving its utilization. 

Fig. 14. Comparison of the current-voltage curves of a smooth nickel cathode and two different Raney-nickel-coated cathodes posessing comparable loading and effective surface (a) smooth nickel. Raney nickel prepared from two different precursors (b) plasma-sprayed NiAh, (c) NiAU cold rolled together with Mond nickel.

Asymmetric hydrogenations have been reported with palladium on silk 123>, palladium on modified cellulose 124> and on modified ion exchange resins 125 >. Also with Raney Nickel modified with amino adds 126> and peptides, 27>. Platinum-carbon catalysts exhibiting shape selectivity have been made by coating them with a thermosetting resin, which is carbonized. In such a way an organic molecular sieve skin is formed over the original catalyst 128>. 

Raney nickel alloy. The stirred mixture is heated under reflux for I hr. The mixture is filtered with suction through a Buchner funnel coated with a filter aid such as Hyflo... 

An interesting coatings application for lecithin is in producing nonpyrophoric Raney nickel (339). The lecithin in this application creates a lipophilic surface on the metal, along with a wax, fat, or organic polymer. 

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