Multiphase Hydrogenation Reactions

M. Reif, Tubular inorganic catalytic membrane reactors Advantages and performance in multiphase hydrogenation reactions, Catal. Today 2003, 79-80, 139-149. 

Figure 5.45 reproduced from Centi, G., Dittmeyer, R., Perathoner, S. and Reif, M. Tubular inorganic catalytic membrane reactors advantages and performance in multiphase hydrogenation reactions. Catalysis Today, Vol. 79-80, pp. 139-149,... 

Metal NPs immobilized in ILs are highly active and recyclable for hydrogenation reactions in multiphase systems (see Scheme 1.2, Table 1.2, and Figure 1.5). 

Multiphase catalytic reactions, such as catalytic hydrogenations and oxidations are important in academic research laboratories and chemical and pharmaceutical industries alike. The reaction times are often long because of poor mixing and interactions between the different phases. The use of gaseous reagents itself may cause various additional problems (see above). As mentioned previously, continuous-flow microreactors ensure higher reaction rates due to an increased surface-to-volume ratio and allow for the careful control of temperature and residence time. 

The use of ionic liquids has been successfully studied in many transition metal-catalyzed hydrogenation reactions, ranging from simple alkene hydrogenation to asymmetric examples. To date, almost all applications have included procedures of multiphase catalysis with the transition-metal complex being immobilized in the ionic liquid by its ionic nature or by means of an ionic (or highly polar) ligand. 

As already shown in paragraph Section 6.2.2, the multiphasic conditions for hydrodechlorination, are also active for hydrogenation reactions, such as was the case of haloaromatic ketones, which could selectively be reduced to the alcohol." This reaction was investigated from the kinetic standpoint,... 

In industrial practice, three-phase catalytic reactors are often used, with gases like such as H2, H2O, NH3 or O2 as reactants. The process can be classified on the basis of these gases as hydrogenation, hydration, amination, oxidation, etc [3]. Among these processes, hydrogenation is by far the most important multiphase catalytic reaction. Recently, liquid- -phase methanol synthesis and the Fischer-Tropsch process were commercialized respectively... 

Hydrogenation reactions may be carried out in bubble column reactors. Often a slurry catalyst may be used which makes it a multiphase reactor. 

An alternative approach, summarised effectively by Figure 5, has been proposed variously. The essential message from this representation is that although typical reactor residence times for multiphase hydrogenations are in the order of minutes to hours, the electronic and chemical interactions are very rapid (micro-seconds and less). This infers that the residence time in the reactor is taken up primarily by getting the reactive species around the vessel and to the active catalyst sites. If the mixing and diffusional distances were made smaller, then by inference the total time for reaction would be shorter. 

The use of iortic hquids has been successfully studied in many transition metal ca lyzed hydrogenation reactions ranging from simple olefin hydrogenation to examples of asymmetric hydrogenation. Almost all apphcations so far include procedures of multiphase catalysis with the transition me l complex being... 

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