Vapor-phase hydrogenation reaction

Figure 3. Conceptual flow diagram for a typical vapor-phase hydrogenation reaction system.

In contrast to the studies on gas- and vapor-phase hydrogenation reactions utilizing dense Pd-based membrane reactors, dehydrogenation reactions have been consistently observed to benefit from the concept of a membrane reactor. In almost all cases the reaction conversion is increased. This is attributed to the well known favorable effect of equilibrium displacement applied to dehydrogenation reactions which are mostly limited by the equilibrium barrier. 

The foundation for the present industry was laid in 1897 when Sabatier and Senderens illustrated the catalytic effect of nickel in vapor-phase hydrogenation reactions. The earliest technical application, bf- hydrogenation was in the reduction of the double bonds between two carbon atoms for the purpose of converting liquid fats into solid fats, or as it is often called, fat hardening. This industry is now very large. 

Formaldehyde is readily reduced to methanol by hydrogen over many metal and metal oxide catalysts. It is oxidized to formic acid or carbon dioxide and water. The Cannizzaro reaction gives formic acid and methanol. Similarly, a vapor-phase Tischenko reaction is catalyzed by copper (34) and boric acid (38) to produce methyl formate ... 

Finally, selective hydrogenation of the olefinic bond in mesityl oxide is conducted over a fixed-bed catalyst in either the Hquid or vapor phase. In the hquid phase the reaction takes place at 150°C and 0.69 MPa, in the vapor phase the reaction can be conducted at atmospheric pressure and temperatures of 150—170°C. The reaction is highly exothermic and yields 8.37 kJ/mol (65). To prevent temperature mnaways and obtain high selectivity, the conversion per pass is limited in the Hquid phase, and in the vapor phase inert gases often are used to dilute the reactants. The catalysts employed in both vapor- and Hquid-phase processes include nickel (66—76), palladium (77—79), copper (80,81), and rhodium hydride complexes (82). Complete conversion of mesityl oxide can be obtained at selectivities of 95—98%. 

Carbon disulfide is essentially unreactive with water at room temperature, but above about 150°C in the vapor phase some reaction occurs forming carbonyl sulfide (carbon oxysulfide) [463-58-1] and hydrogen sulfide [7783-06-4]. Carbonyl sulfide is an intermediate in the hydrolysis reaction ... 

Silva (1971) used the Berty reactor to execute exploratory measurements on vapor-phase hydrogenation of organic substrates that had little vapor pressure at room temperature. The substrate was measured by weight in a small ceramic boat and put on the catalyst screen beside a few particles of catalyst, also measured by weight. Then the stirring started, and the autoclave was heated to the reaction temperature. Finally the desired hydrogen pressure was applied suddenly and the reaction started. 

Oldenberg and Rase (13) have studied the catalytic vapor phase hydrogenation of pro-pionaldehyde over a commercially supported nickel catalyst. Their data indicate that the mathematical form of the reaction rate at very low conversions and 150 °C can be expressed quite well in the following manner. 

Vapor Phase Hydrogenation of Acetic Anhydride Acetic anhydride was pumped into an evaporator where it was mixed with hydrogen. The temperature of anhydride-hydrogen mixture was raised to the reaction temperature in a preheater zone, made of a 2 feet bed packed with 2 mm glass beads. The reaction took place in a 2 feet catalyst bed packed with 1 m.m. alpha-alumina coated with 0.5% Pd. The effluent was condensed and analyzed by G.C. 

Vapor-phase hydrogenation without a catalyst is impractical the influence of the catalyst on rate and direction of the reaction is by far... 

Vapor-phase hydrogenation results and experimental evidence of this type lead to the conclusion that catalysts on basic supports are suitable for nonsplitting prehydrogenation-type reactions and that acidic supports are best used for splitting catalysts. Activated alumina was found to be the best support because of rapid reduction of tar acids. Especially, alumina precipitated from aluminum salts at constant pH was satisfactory and produced catalysts that could be formed into pellets of high mechanical strength. 

Zinc may be used in place of aluminum in a similar reaction. The method also may be used for the vapor-phase hydrogenation of organo-silicon halides such as methyltrichlorosilane ... 

The ester is then fed directly to the low-pressure, vapor-phase hydrogenation system where it vaporized into an excess of hydrogen in the vaporizer (3) and fed to a fixed-bed reactor (4), containing a copper catalyst. The reaction product is cooled (5) and condensed (6) with the hydrogen being recycled by the centrifugal circulator (7). 

Gas/vapor phase hydrogen-consuming reactions using dense membrane reacimrs... 

Gas/vapor phase hydrogen-generating reactions using dense membrane reactors... 

While some vapor phase hydrogenations of unsaturated aldehydes have shown good initial selectivities, in most cases the reaction selectivity decreases significantly with prolonged reaction time. The vapor phase hydrogenation of crotonaldehyde over a Pt/Ti02 catalyst in the SMSI state, however, showed reasonable selectivities that remained relatively constant over the entire time of the reaction. 0°... 

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