Nickel catalysts cyclohexane conversion

In the authors laboratory, approximately 3 g. of W-6 Raney nickel catalyst was mixed with 5 ml. of cyclohexene in a test tube. A vigorous reaction took place at once. Mass spectrographic analysis showed a 43 % conversion to cyclohexane (156). 

Figure 2. Product distribution for cyclohexane conversion to either benzene or hydrogenolysis (>90% n-hexane) products over (a) pure nickel on alumina and (b) the same catalyst after treatment with hexamethyldisilane in H2. Reaction conditions are discussed in references (6) and (8).

The effect of nickel content and catalyst preparation on demethyla-tion activity was pursued further. A catalyst of 10.5 wt % nickel, Preparation C, was tested in the fixed bed reactor, after activation in place at 540°F for 2 hours, with the feed at 0.8 LHSV, 150 psig, and a H2-to-methylcyclohexane mole ratio of 6. The temperature was raised over a period of 17 hours to 580°F, other factors held constant, and the effluent analyzed for cyclohexane at various temperatures. The conversion to cyclohexane was low, and only 1.5 wt % cyclohexane was found in the liquid effluent at 580°F. Under somewhat similar conditions, a conversion of over 50% of the methylcyclohexane was obtained with the 26 wt % nickel catalyst. These results suggest that interaction of nickel with the support occurs, and the resulting nickel-aluminate is not active for the demethylation reaction. 

Mesoporous silicates serve as the most suitable host for the gold NPs with the size of 2 mn. The cyclohexane conversion may reach 20-30% at the selectivity to cyclohexanol up to 95%, unlike the commercial nickel naphthenate catalysts (conversion 4%, selectivity 70-85%). 

The reaction involved is very simple and has been well known since Sabatier and Sendeiens reported on their experiments in 1901. They passed hydrogen saturated with benzene vapor at ambient temperature over a nickel catalyst at 180-200°C. At this temperature an almost complete conversion of benzene to cyclohexane was achieved. They made two important observations ... 

The oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone, known as KA-od (ketone—alcohol, cyclohexanone—cyclohexanol cmde mixture), is used for most production (1). The earlier technology that used an oxidation catalyst such as cobalt naphthenate at 180—250°C at low conversions (2) has been improved. Cyclohexanol can be obtained through a boric acid-catalyzed cyclohexane oxidation at 140—180°C with up to 10% conversion (3). Unreacted cyclohexane is recycled and the product mixture is separated by vacuum distillation. The hydrogenation of phenol to a mixture of cyclohexanol and cyclohexanone is usually carried out at elevated temperatures and pressure ia either the Hquid (4) or ia the vapor phase (5) catalyzed by nickel. 

Supported Co, Ni, Ru, Rh, Pd and Pt as well as Raney Ni and Co catalysts were used for the hydrogenation of dodecanenitrile to amines in stirred SS autoclaves both in cyclohexane and without a solvent. The reaction temperature and the hydrogen pressure were varied between 90-140 °C and 10-80 bar, respectively. Over Ni catalysts NH3 and/or a base modifier suppressed the formation of secondary amine. High selectivity (93-98 %) to primary amine was obtained on Raney nickel, Ni/Al203 and Ru/A1203 catalysts at complete nitrile conversion. With respect to the effect of metal supported on alumina the selectivity of dodecylamine decreased in the order Co Ni Ru>Rh>Pd>Pt. The difference between Group VIII metals in selectivity can be explained by the electronic properties of d-band of metals. High selectivity to primary amine was achieved on base modified Raney Ni even in the absence of NH3. 

In the field of hydrocarbon conversions, N. D. Zelinskii and his numerous co-workers have published much important information since 1911. Zelinskii s method for the selective dehydrogenation of cyclohexanes over platinum and palladium was first applied to analytical work (155,351,438,439), but in recent years attempts have been made to use it industrially for the manufacture of aromatics from the cyclohexanes contained in petroleum. In addition, nickel on alumina was used for this purpose by V. I. Komarewsky in 1924 (444) and subsequently by N. I. Shuikin (454,455,456). Hydrogen disproportionation of cyclohexenes over platinum or palladium discovered by N. D. Zelinskii (331,387) is a related field of research. Studies of hydrogen disproportionation are being continued, and their application is being extended to compounds such as alkenyl cyclohexanes. The dehydrocyclization of paraffins was reported by this institute (Kazanskil and Plate) simultaneously with B. L. Moldavskil and co-workers and with Karzhev (1937). The catalysts employed by this school have also been tested for the desulfurization of petroleum and shale oil fractions by hydrogenation under atmospheric pressure. Substantial sulfur removal was achieved by the use of platinum and nickel on alumina (392). 

Imaizumi et al. studied the hydrogenation of l,4-dialkyl-l,3-cyclohexadienes over the nine group VIII (groups 8-10) metals and copper in ethanol at room temperature and atmospheric pressure.122 The selectivity for monoenes formation at 50% conversion increased in the order Os-C, Ir-C < Ru-C, Rh-C, Pt < Pd-C, Raney Fe, Raney Co, Raney Ni, Raney Cu (= 100%). The selectivity for 1,4-addition product increased in the order Os-C, Ir-C < Ru-C, Rh-C, Raney Cu, Raney Fe, Raney Ni < Raney Co, Pd-C, Pt. Extensive formation of 1,4-dialkylbenzenes (more than 50% with the 1,3-dimethyl derivative) was observed over Raney Ni and Pd-C, while they were not formed over Raney Cu, Os-C, and Ir-C. In the hydrogenation of 4-methyl-1,3-pen -tadiene (39) (Scheme 3.15) over group VIII metals in cyclohexane at room temperature and atmospheric pressure, high selectivity to monoenes was obtained with iron, nickel, cobalt, and palladium catalysts where the amounts of the saturate 2-methylpen-... 

Hydrogenation catalysts,such as platinum, palladium, " and nickel. In this case, the reaction is the reverse of double-bond hydrogenation (15-11 and ISIS), and presumably the mechanism is also the reverse, although not much is known.Cyclohexene has been detected as an intermediate in the conversion of cyclohexane to benzene, using Pt. The substrate is heated with the catalyst at 300-350°C. The reactions can often be carried out under milder... 

Cyclohexane is made by the catalytic reduction of benzene w ith hydrogen, usually in a train of several reactors with partial conversion conducted in each. This process uses a nickel or platinum catalyst and requires temperatures of about 200°C, 25-40 atm pressure, and the presence of a cyclohexane recycle diluent to help absorb the exotherm of the hydrogenation (Eq. 19.56). 

The reaction rate remains constant up to high conversion rates (zero order in relation to benzene). Two side reactions must be avoided because they lower the cyclohexane purity. These are conversion to methylcydopentane and hydrocracking. The isomerization equilibrium of cyclohexane to methyicyclopentane corresponds to a conversion of 68 per cent at 200°C, reaching 83 per cent at 300°C. This makes it necessary to select a catalyst that does not favor this reaction. With nickel-based systems, the reaction appears only above 250°C. Moreover, the hydrogen must not contain impurities liable to poison the active phases introduced. 

Once near steady-state activity had been reached (19 hours), the temperature was decreased 15 °F, and the effect of decreased temperature on conversion and selectivity established, Run 4. An estimated activation energy for the conversion of methylcyclohexane is 28 kcal/mole, only 2 kcal less than the approximate value for the nickel-kieselguhr catalyst. The effect of decreased operating pressure is shown by the data of Run 5. Conversion increased, and efficiency to cyclohexane decreased slightly. The same effect was noted previously in fixed bed tests with Preparation A. 

Fig. 4. Cyclohexene selectivity as a function of conversion in the cyclohexane oxidation at 450°C over nickel containing catalysts (a) influence of the metallic substrate A1 (Cl), Ti (C2) and Mg substrate (C3) as well as of the MO/AI2O3 catalyst (C7), respectively (b) influence of the pore length on the selectivity pattern.

It follows, therefore, that contrary to the assertion of Sabatier that metallic cobalt is inferior to nickel in regard to hydrogenating properties, highly disperse cobalt deposited on activated carbon behaves similarly to nickel, not being less effective than nickel as a hydrogenating catalyst. But it should be mentioned that the dehydrogenating capacity of this catalyst was rather low the degree of conversion of cyclohexane to benzene at 300° and a space velocity of 0.2 was for the 4, 2, and 1 % samples within the limits of 25-27.6%. 

The phenol process based on the oxidation of cyclohexane has been operated for a short time by Monsanto in Australia and is of less importance. In this process, a mixture of cyclohexanone and cyclohexanol is dehydrogenated to phenol at 400 °C, using platinum/activated carbon or nickel/cobalt catalysts. The degree of conversion can reach 90 5%. The crude phenol is refined by distillation. A particular disadvantage of this process lies in the difficulty in refining the crude oxidation mixture from cyclohexane oxidation. 

Raney nickel A porous solid catalyst made from an activated alloy of nickel and aluminium. The nickel is the catalytic metal with the aluminium as the structural support It was developed by American mechanical engineer Murray Raney (1885-1966) in 1926 for the hydrogenation of vegetable oil and is now used in hydrogenation reactions in various forms of organic synthesis. It is widely used as an industrial catalyst for the conversion of olefins and acetylenes to paraffins, nitriles, and nifro compounds to amines, and benzene to cyclohexane amongst others. 

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