Dehydrogenation exothermic

Styrene is manufactured from ethylbenzene. Ethylbenzene [100-41-4] is produced by alkylation of benzene with ethylene, except for a very small fraction that is recovered from mixed Cg aromatics by superfractionation. Ethylbenzene and styrene units are almost always installed together with matching capacities because nearly all of the ethylbenzene produced commercially is converted to styrene. Alkylation is exothermic and dehydrogenation is endothermic. In a typical ethylbenzene—styrene complex, energy economy is realized by advantageously integrating the energy flows of the two units. A plant intended to produce ethylbenzene exclusively or mostly for the merchant market is also not considered viable because the merchant market is small and sporadic. 

The oxidative propane dehydrogenation is well investigated and also a highly exothermic reaction. In a fixed-bed reactor, steep temperature gradients are ob-servableandtheconversionofpropaneandselectivityofthereactionarestrongly determinedbytemperatureandtotalflowrate[133]. 

Input energy requirements for the process are significantly reduced since the energy released by the exothermic oxidation reactions serves as a driving force for the endothermic dehydrogenation reaction. 

For consistency, an initial well associated with the formation of an adduct of the metal ion with the alkane should be included in Figure 11. The chemical activation associated with the formation of such an adduct is likely to be essential in overcoming intrinsic barriers associated with insertion into C-H bonds. In comparison to larger hydrocarbons, the weaker interaction of ethane with first row group 8-10 metal ions may be insufficient to overcome intrinsic barriers for insertion. This would explain the failure to observe dehydrogenation of ethane by these metal ions, even though the process is known to be exothermic. The well depths could be determined from high pressure equilibria. Studies in our laboratory and elsewhere have indicated the ease with which many of... 

For an endothermic, reversible reaction (such as the dehydrogenation of ethylbenzene), as also shown in Section 5.3 and illustrated in Figure 5.2(b), the rate does not exhibit a maximum with respect to T at constant /, but increases monotonically with increasing T. The rate also decreases with increasing / at constant T, as does the rate of an exothermic reaction. 

Formaldehyde is produced solely from methanol. The process can be air oxidation or simple dehydrogenation. Since the oxidation is exothermic and the dehydrogenation is endothermic, usually a combination is employed where the heat of reaction of oxidation is used for the dehydrogenation. 

These values of A Hr are standard state enthalpies of reaction (aU gases in ideal-gas states) evaluated at 1 atm and 298 K. 7VU values of A are in kilojoules per mole of the first species in the equation. When A Hr is negative, the reaction hberates heat, and we say it is exothermic, while, when A Hr is positive, the reaction absorbs heat, and we say it is endothermic. Tks Table 2-2 indicates, some reactions such as isomerizations do not absorb or liberate much heat, while dehydrogenation reactions are fairly endothermic and oxidation reactions are fairly exothermic. Note, for example, that combustion or total oxidation of ethane is highly exothermic, while partial oxidation of methane to synthesis gas (CO + H2) or ethylene (C2H4) are only slightly exothermic. 

Natural gas instead of pure methane can also be used in condensation reactions.91 When natural gas is dehydrogenated, the C2-C4 alkanes it contain are converted into olefins. The resulting methane-olefin mixture can then without separation be passed through a superacid catalyst, resulting in exothermic alkylative condensation ... 

This process is much faster than the one depicted in Eq. (2.28). Since aromatization of ethylene is exothermic and ethane dehydrogenation and overall aromatization are endothermic, the coupling of the two processes would be energy-efficient. 

The first step is strongly endothermic and is the main hurdle to overcome in the hydrogenation of nitrogen to ammonia. Conversely, the reverse reaction, which is the dehydrogenation of diimide, is strongly exothermic. Therefore we may expect that diimide will have a pronounced tendency to revert to molecular nitrogen. This is in fact so and, at normal temperatures, diimide exists only as a transient intermediate that cannot be isolated. It is extremely reactive and readily transfers hydrogen to carbon-carbon multiple bonds ... 

Membranes coupling endo- and exothermic reaction zones (e.g., hydrogenation-dehydrogenation) Supported liquid membranes (SLM) for homogeneous catalytic processes... 

In some cases, the heat dissipated in an exothermic reaction can be used in an endothermic reaction taking place at the opposite side of the membrane. Typical examples are hydrogenation/dehydrogenation reactions carried out by palladium or Pd-alloy membranes characterized by a 100% theoretical selectivity towards the hydrogen. 

Figure 12.8 Scheme of the combination of a dehydrogenation reaction (endothermic) on one surface of a Pd-based catalytic membrane and a hydrogenation reaction (exothermic) by the diffused hydrogen on the other membrane surface. 

In addition to examples of stoichiometric reactions with alkanes, late transition-metal complexes also seem promising as dehydrogenation catalysts, in view of the many such complexes that catalyze olefin hydrogenation. Olefin hydrogenation is, however, a highly exothermic reaction (AH = ca. -125 kj mol ) and so there is a formidable enthalpic barrier to dehydrogenation. 

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