Dehydrogenation endothermic decomposition

The decomposition is endothermic and to dehydrogenate the alcohol, heat must be supplied. However, if oxygen, usually in the form of air, is supplied to the reaction and the process conducted in the presence of certain metallic catalysts, such as finely divided copper or silver, high yields of formaldehyde may be obtained and the reaction made exothermic. It is by this oxidation process that practically all of the formaldehyde is produced. This process, although apparently simple, requires close temperature control and regulation of the extent of reaction to prevent undue losses of raw material. 

In the petrochemical industry the introduction of unsaturations in hydrocarbons is mainly obtained by dehydrogenation. This kind of reaction is less suitable for the functionalization of fine chemicals, because the high temperature necessary for the endothermic reaction can lead to the decomposition of thermally unstable compounds. An alternative reaction consists in the oxidative dehydrogenation, that can be carried out at lower temperatiu es. An example of this kind of reaction is constituted by the synthesis of methacrylic add (MAA, intermediate of methylmethacrylate production) via the oxidative dehydrogenation of isobutyric add (IBA), itself obtained from isobutyraldehyde (by-product of the oxo synthesis of nbutyraldehyde from propylene). This process constitutes one of the economically most interesting routes, alternative to the acetone-cyanohydrin process, which nowadays is the predominant process for the MAA production. 

Catalysts and temperatures conducive to the dehydrogenation of methanol are also conducive to the decomposition of the formaldehyde to hydrogen and carbon monoxide. Furthermore, the reaction is endothermic, and heat must be supplied. 

The dehydrogenation of ethylbenzene is carried out at temperatures up to approx. 600 °C. At higher temperatures, the thermal decomposition of styrene and ethylbenzene increases and reduces the yield. Since dehydrogenation is endothermic, high temperatures and low pressure (less than 1 bar in modem units) favor the reaction (Le Chateliers s principle). In order to lower the partial pressure and prevent carbon deposits or the need for the frequent regeneration of the catalyst, steam is injected into the reactor. In industrial practice, the primary conversion is restricted to limit the formation of undesirable by-products the unconverted ethylbenzene is recycled, to achieve a high styrene yield thus only small amounts... 

HH mixtures have become of greater interest since endothermic fuels (EF) for jet engines were developed [43, 46, 47]. The paradoxical term endothermic fuels relates to a desire to increase a fuel cooling capability due to the dehydrogenation or thermal decomposition of heavy hydrocarbons entering into the fuel composition. 

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