Ethane, reactions

SiH3)2C6H4 (H2L) leads to the nickel(iv) complex Ni(dmpe-P,.f, )(L-6V,6V )2. 31P NMR spectroscopic studies of the reaction indicate the presence of the intermediates Ni(dmpe-.P,.P )(dmpe-P)(L-Structural data have confirmed the unusual Ni2Si2 core. Starting from Ni(depe)2 (depe = l,2-bis(diethylphosphino)ethane), reaction with... 

The ethane reaction was studied in a fixed bed continuous-flow reactor made of quartz (100 mm x 27 mm o.d.).Thc reacting gas mixture consisted of 20% C2H6, 40% N2O (or O2) and He as diluent. The flow rate of the reactants was usually 50... 

Figure 5.26. In situ ethane reaction and dynamic ED patterns a) Cu-Ru/C catalyst (room temperature) (Z ) 300 °C with extra rings (c) model of CuRu3 structure observed in dynamic ED. (After Smith et al 1994.)...

The results, presented in Fig. 10, are very similar to those already discussed for ethylene and ethane. Reaction (I), the hydrogenation of cyclopropane, has been shown earlier to be structure insensitive (103a, 103b). The activity pattern of this reaction is reminiscent of cyclohexane dehydrogenation (63). Initially, a small increase in activity is found, followed at 80% Cu by a rapid decline. These results show that reaction (II) is of the hydrogenolysis type and that reaction (I) is hydrogenation of an unsaturated bond. 

The kinetics of the two reactions show that the desirable TML reaction has a higher activation energy than does the undesirable ethane reaction. Therefore the yield of TML is maximized by running the reaction at high temperatures. Of course, an additional and very significant advantage of high-temperature operation is shorter batch times (increased production rate). 

Arnold WA, Ball WP, Roberts AL. Polychlorinated ethane reaction with zerovalent zinc pathways and rate control. J Contam Hydrol 1999 40 183-200. 

Based on the available results, the relative fraction of ethane that reacts by the above reactions is identical regardless of the reactor used. This conclusion is further supported by the findings of this investigation and also by those of Dunkleman and Albright (7) that the overall kinetics of ethane reactions are not affected by the material of construction or by the pretreatment of the reactor even though ethylene and total coke yields are. More discussion of the kinetics of pyrolysis will be reported later in this chapter. 

The pressure dependence of kg/ku at X = 2288 A. can be accounted for by the observation that at this wavelength small amounts of disulfides are formed in the ethane and propane reactions, which were not taken into consideration evaluating the rate constant values. The disulfide can arise (1) from the secondary photolysis of the mercaptan product when the COS pressure is low, and 2) by cracking of hot RSH molecules at low total pressures. From Table III there appears to be a twofold variation in the value of h/kn for the ethane reaction, in going from low COS and total pressure to high COS and total pressure. 

Hydrogen is a significantly less important product than ethane reaction (2) therefore occurs more rapidly than (6), so that the ethyl radicals are essentially jS radicals. First-order initiation and pp combination leads to f-order kinetics, in agreement with experiment. Application of the steady-state treatment gives, for the overall rate of disappearance of butane... 

Transition state theory can also give us some insight into the non-Arrhenius behaviour of rate coefficients as epitomized by Fig. 2.6 for the OH + ethane reaction. Curvature of the Arrhenius plot can arise from a number of factors. 

Figure 3 also shows that the change in selectivity with respect to time was different for the two supported platinum catalysts. For Pt/ri-alumina, essentially complete conversion of TCA to ethane (Reaction 1) was observed for the first 10 h on stream. This was followed by a change in selectivity to primarily DCE, a partially dechlorinated product (Reaction 2) and an accompanying decrease in TCA conversion (Figure 2). 

Figure 4. TOF numbers for the oxidation of ethane. Reaction conditions as in Figure 2.

The qualitative interpretation of the ISM method can be illustrated by Figure 11.18. Figure 11.18a shows the equi-energy curves that pertain to the transfer of H between methyl and methane and ethyl and ethane. The curves nearly overlap, but the slightly weaker C-H bond in ethane is characterized by a smaller force constant and leads to a somewhat smaller barrier. The calculated barriers are 14.6 and 14.3 kcal/mol, respectively. The methyl-ethane reaction, shown in Figure 11.18b, is exothermic and there is a much more substantial shift in the curves. The calculated barrier is 12.4 kcal, compared with the experimental value of 11.5. Thus, the calculation moves the barriers in the right direction, although it does not reproduce the entire effect that is observed experimentally. 

Apparent SMSI effects have also been reported with non-Transition Metal oxide supports.Those obtained with magnesia were almost certainly due to evolution of traces of hydrogen sulfide, or of iron ions, from the bulk at the high temperatures used, but real effects have been seen with silica when very high pre-treatment temperatures were employed the rate of the ethane reaction decreased more quickly than that of hydrogen chemisorption, pointing clearly to the need for multiatomic sites in hydrogenolysis. 

The mechanistic model (of Table II of the previous chapter) was developed by successive approximations. First, only those reactions assumed to be most important were used in the model, and later secondary reaction steps were added until good predictions were obtained of the experimental results. In the previous chapter of the book, the parameters for the various reaction steps are reported. The major reactions for pyrolyses of both ethane and propane are grouped in Table II (1). When ethane is pyrolyzed, the propane reactions are. pf relatively minor importance and eliminating them from the model has little effect on the ethane pyrolysis predictions. When propane is pyrolyzed, however, significantly better predictions result when the ethane reactions are included and the entire set of reactions are employed. 

Figure 6.1 Ethane reactions on Ni catalysts. Relative TOFs [379] [407]. Steam reforming H20/C2H =8, H20/H2=10, 500 t2,1 bar. Hydrogenolysis H2/C2H< =4, N2=75 vol%, 300°C, 1 bar. Reproduced with the permission of Elsevier.

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