Ethylene to ethane

The depropanizer overhead, Cj and lighter feed is compressed to about 300 psi and then passed over a fixed bed of acetylene removal catalyst, generally palladium on alumina. Because of the very large amount of hydrogen contained in this stream, the operating conditions are critical to selectively hydrogenate the acetylene without degrading the valuable ethylene to ethane. 

However, it was found that the effect on the equilibrium formation of aromatics is not substantial due to thermodynamic considerations. A more favorable effect was found for the reaction between ethylene (formed via cracking during aromatization of propane) and hydrogen. The reverse shift reaction consumes hydrogen and decreases the chances for the reduction of ethylene to ethane byproduct. 

Fig. 2. Pressure fall —AP (Torr) against time t (arbitrary units) in hydrogenation of acetylene on Pt/AhOa catalyst at 110°C and Pst/Pctnt 2. In the initial slow period of the reaction the main product is ethylene, and after the acceleration, further hydrogenation of ethylene to ethane predominates. From G. C. Bond and P. B. Wells, J. CaM. 4, 211 (1965).

We could account for our result by the same mechanism, if the Cp2NbH3-derived system also contains (or generates) a species capable of catalyzing the hydrogenation of ethylene to ethane. 

Some experimental studies (1-7) have demonstrated the possibility of improving the performance of a catalytic reactor through cyclic operation. Eenken et al. (4) reported an improvement of 70% in conversion of ethylene to ethane under periodic operation. In a later article (2), they concluded that periodic operations can be used to eliminate an excessively high local temperature inside the catalytic reactor for a highly exothermic reaction. In our laboratory, Unni et al. (5) showed that under certain conditions of frequency and amplitude associated with the forced concentration cycling of reactants, the rate of oxidation of SC>2 over catalyst can be increased by as much as 30%. Re-... 

Platinum metal is used as a heterogeneous catalyst for the hydrogenation of gaseous ethylene to ethane. 

Hydrogenation of Ethylene to Ethane Porous AI2O3 membranes... 

Shilov and collaborators discovered136 considerable yields of hydrazine and ammonia when dinitrogen reacts with a suspension of freshly prepared VK and Mg11 hydroxides. The magnesium is essential and yields of hydrazine and ammonia depend on temperature, pH, dinitrogen pressure and solvent (Scheme 4). The system has been used to reduce acetylene to ethylene and ethylene to ethane.137 Shilov and collaborators assumed a multinuclear structure for the centre where N2 reduction occurs and suggested the mechanism shown in Scheme 5. 

In general, the ethylene to ethane selectivity is governed by the relative rates of the processes shown in Scheme 3.1. Here, combination of methyl radicals (step 2) is a homogeneous process, but all other steps can be both homogeneous and heterogeneous.294 It was also found that further oxidation of the C2 products (steps 4 and 6) becomes important only with increasing C2 concentration in the system.327... 

A systematic attempt to correlate the catalytic effect of different surfaces with their adsorptive capacity was made by Taylor and his collaborators. Taylor and Burns, for example, investigated the adsorption of hydrogen, carbon dioxide, and ethylene by the six metals nickel, cobalt, palladium, platinum, iron, and copper. All these metals are able to catalyse the hydrogenation of ethylene to ethane, while nickel, cobalt, and palladium also catalyse the reduction of carbon monoxide and of carbon dioxide to methane. 

Mixtures of A1(C2H5)3 and Ti(0-iC3H7)4 will dimerize ethylene to 1-butene but they do not catalyze the isomerization of the 1-butene produced (129). Under the right set of conditions, only small amounts of polyethylene are produced with this latter mixture. On the other hand, solutions of compound 10 or 3 have been found to catalytically convert ethylene to ethane and butadiene (130). 

Problem 8.39 (a) Calculate the heat of hydrogenation, AHh, of acetylene to ethylene if the AHh s to ethane are — 137 kJ/mol for ethylene and —314kJ/mol for acetylene, (b) Use these data to compare the ease of hydrogenation of acetylene to ethylene with that of ethylene to ethane. ... 

Each bend was 25° for acetylene, or 11.9° for the HCH bisector of ethylene, each corresponding to a 42% geometry change from acetylene to ethylene, or ethylene to ethane. The H CC angles were optimized and are shown in parentheses. 

Davis studied the hydrogenation of ethylene to ethane in a catalytic recycle reactor operated at atmospheric pressure (R. J. Davis, Ph.D. Thesis, Stanford University, 1989.) The recycle ratio was large enough so that the reactor approached CSTR behavior. Helium was used as a diluent to adjust the partial pressures of the gases. From the data presented, estimate the orders of the reaction rate with respect to ethylene and dihydrogen and the activation energy of the reaction. 

Figure 8 shows the effect of temperature on the ethylene-to-ethane ratio. It is noted that the ratio increases with increasing temperature. The result is consistent with the result in a conventional reactor. It indicates that ethylene is formed from ethane as a secondary product. The reaction of ethane oxidative dehydrogenation is accelerated with a rise in temperature. 

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