Dehydrogenation of n-butane

New processes such as isomerization and the dehydrogenation of n-butane will make their appearance. 

Butane is primarily used as a fuel gas within the LPG mixture. Like ethane and propane, the main chemical use of butane is as feedstock for steam cracking units for olefin production. Dehydrogenation of n-butane to butenes and to butadiene is an important route for the production of synthetic rubber. n-Butane is also a starting material for acetic acid and maleic anhydride production (Chapter 6). 

Butadiene is mainly obtained as a byproduct from the steam cracking of hydrocarbons and from catalytic cracking. These two sources account for over 90% of butadiene demand. The remainder comes from dehydrogenation of n-butane or n-butene streams (Chapter 3). The 1998 U.S. production of butadiene was approximately 4 billion pounds, and it was the 36th highest-volume chemical. Worldwide butadiene capacity was nearly 20 billion pounds. 

Because of the high pyrolysis temperature, the C4-fraction contains quantities of vinyl acetylene and ethyl acetylene, the removal of which prior to the recovery of butadiene is necessary in certain cases, particularly if butadiene of low acetylene content is desired. Similar considerations apply to effractions obtained by the dehydrogenation of n-butane and n-butenes. 

Figure 7. Reaction coordinate diagram for the dehydrogenation of n-butane by Ni +. ...

Figure 10. Comparison of experimetnal kinetic energy release distributions to phase-space calculations for (a) dehydrogenation of n-butane by Co+ and (b) loss of methane in reaction of Co+ with isobutane. Data from reference 38.

M.E. Rezac, W.J. Koros and S.J. Miller, Membrane-assisted Dehydrogenation of n-Butane Influence of Membrane Properties on System Performance, 7. Membr. Sci. 93, 193 (1994). 

The dehydrogenation rate was measured at reaction temperatures between 525 and 600°C and butene-l partial pressures of 0.05 to 0.25 bars. The results obtained showed that at temperatures of 575 and 600°C and high partial pressures of butene-1, a rapid decrease in conversion occurred within the first 20 minutes, followed subsequently by a much smaller rate of decrease. Initial reaction rates were measured and these rates were found to increase with reactant concentration up to a maximum of about 0.2 bars butene-l pressure and then to decrease on further increase of reactant partial pressure. These results agree with the data obtained by Carra and Forni (5) for the dehydrogenation of n-butane over a chromia alumina catalyst. 

VO)2P207 is superior for the selective dehydrogenation of n-butane to butene to other crystalline V-P oxides, while few differences exist between the oxidation of butene and butadiene, which are considered reaction intermediates. The abstraction of methylene hydrogen from n-butane is the slowest step. Hence this step determines the overall catalytic activity." 2) Selectivity in forming anhydride from C4 and C5 alkanes, but not in selective oxidation of lower (C2 and C3) or higher (Ce-Cg) alkanes." 3) The number of surface layers involving the catalytic reactions is limited to 2-3 in contrast to Bi-Mo-O catalysts. 

This problem is highlighted in the case of an alumina-supported vanadium catalyst employed for the dehydrogenation of n-butane. The hydrocarbon creates a reducing environment, which results in a reduction in the oxidation state of... 

I 6 Photoelectron Spectroscopy of Catalytic Oxide Materials 63.2.2 Oxidative Dehydrogenation of n-Butane... 

Zaspalis et al. [1991b] and Bitter [1988] utilized alumina membrane reactors containing Pt catalysts to examine dehydrogenation of n-butane to butene and 2-methylbutenes to isoprene, respectively. Both the conversion and selectivity improved by using the membrane reactors. The increase of conversion is about 50% in both cases. Moreover, Suzuki [1987] used stainless steel membranes and Pi or CaA-zeolite layer catalysts to perform dehydrogenation of isobutene and propene to produce propane. 

Dehydrogenation of n-butane preferentially to 1-butene, and isobutane to isobutene Pd-25 Ag 603 60... 

The in sim characterization of catalysts was earned out in an apparatus which included a quadiupole mass-spectrometer and a gas chromatograph for TPO and H2 chemisorption measurements. In situ coking was performed by injecting a mixture of He and n-hexane vapor over the reduced catalysts at 500 C, In TPO experiments, ihe coked sample was heated at a rate of 8 C/min in a stream of 2 voL% O2 + 98% He. The amount of CO2 produced was recorded. The chemisorption of H2 was carried out in the same appanitus by a flow method after reduction or caking. The flow rate of carrier gas (Ar) was maintained at 25 ml/min and the volume of H2 injected was 0.062 ml/pulse. Since the partial piessiire of H2 was very low in this system, the hydrogenation of coke was never observed. Isobaric H2 chemisorption measurements with fresh catalysts were carried out in a static adsorption apparatus. Dehydrogenation of n-butane was carried out in a flow micro-rcactor in H2 atmosphere at LHSV = 3 h-l and H2/HC=1. Reaction products were... 

M.E. Rezac, S.J. Miller and W.J. Koros, Membrane assisted dehydrogenation of n-butane using polymer-ceramic composite membranes. The International Congress on Membranes and Membrane Processes, 30 August-3 September 1993, Heidelberg, Germany. 

Catalysts 1 and 2, that are 0.4 and 0.8 % CoNx/y-AbOs, indicate similarly high performances in oxidative dehydrogenation of n-butane. Even at 400°C, the conversion exceeded 40 % (Fig. 1) and yield of olefins reached 25 %. The special feature of this catalyst consists of a high conversion of n-butane yielding mostly light olefins, ethylene and propylene. 90 wt% of olefins formed at 400°C and molar ratio Oj/n-butane of 1.5, were C2-C3 olefins 53 wt.% was ethylene and the rest propylene. 

Dehydrogenation of n-butane was employed to evaluate the activities of the Fresh as well as the regenerated catalysis Before reaction, all samples wpre First, reduced at SSG C for 2 hours in flowing hydrogen. Dehydrogenation reaction conditions were 380°C, 0.1 MPa, H2/n-C4H o (molar ratio) = l and GHSV... 

Table I summarizes the results of previous investigations on catalytic dehydrogenation of n-butane. In this table 2 models were used to correlate dehydrogenation rate data by various investigators one is a power function model, and the other is a Langmuir-Hinshelwood model. The power function model can be obtained by applying the mass action law to describe rate data. Thus, the model presents the dependence of partial...

In their pioneering work Dodd and Watson (3) correlated the dehydrogenation data by Langmuir-Hinshelwood rate models and found that a dual-site surface rate-controlling model is most plausible. Noda and co-workers (21) and more recently Carra and his colleagues (2) obtained essentially the same results as Dodd and Watson (3) for the chromia-alumina catalyzed dehydrogenation of n-butane. As Table I shows, somewhat different values for the orders of power function models are quoted in the references using this method of correlation. 

Combining both the dehydrogenation and hydrogenation rate expressions Lyubarskii (IS) obtained the following power function model to describe the net rate of dehydrogenation of n-butane. 

Three different kinds of rate data were collected for the butane-butene system the dehydrogenation of n-butane with pure n-butane feed, the hydrogenation of butenes without n-butane, and the dehydrogenation or hydrogenation of butane-butenes in the presence of reaction products. We designate these data sets as the dehydrogenation, the hy-... 

Let us examine the case of straightforward dehydrogenation of n-butane. It was assumed that the reaction produces an equilibrium mixture of butenes. The reaction is described by... 

For the dehydrogenation of n-butane our determined value of the thermodynamic equilibrium constant Kwas 0.0133 atm at our reaction temperature of 450°C. Hence we have... 

The differences that still exist between butadiene supply sources, in different geographic areas, are now tending to disappear gradually for economic reasons. Current world availabilities of butadiene essentially originate in the treatment of CA cuts produced by the steam cracking of naphtha or gas oil. Tbe only exception is the United States, where the dehydrogenation of n-butane and n-butenes is still in practice, although... 

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