Hydrogenation of a-methylstyrene

Farkas and Sherwood (FI, S5) have interpreted several sets of experimental data using a theoretical model in which account is taken of mass transfer across the gas-liquid interface, of mass transfer from the liquid to the catalyst particles, and of the catalytic reaction. The rates of these elementary process steps must be identical in the stationary state, and may, for the catalytic hydrogenation of a-methylstyrene, be expressed by ... 

Models of this type were used successfully in the interpretation of the kinetic data of Maennig and Kolbel as well as of kinetic data obtained for the hydrogenation of a-methylstyrene and cyclohexene. 

Babcock et al. (Bl) examined the hydrogenation of a-methylstyrene catalyzed by palladium and platinum catalysts in a reactor of 1 -in. diameter under countercurrent flow. Flow rates were above 1500 kg/m2-hr for the liquid phase and above 15 kg/m2-hr for the gas, and it was concluded from the experimental results that mass transfer was not of rate-determining influence under these conditions. 

Johnson et al. (J4) investigated the hydrogenation of a-methylstyrene catalyzed by a palladium-alumina catalyst suspended in a stirred reactor. The experimental data have recently been reinterpreted in a paper by Polejes and Hougen (P4), in which the original treatment is extended to take account of variations in catalyst loading, variations in impeller type, and variations of gas-phase composition. Empirical correlations for liquid-side resistance to gas-liquid and liquid-solid mass transfer are presented. 

Johnson et al. (J5) have used the hydrogenation of a-methylstyrene catalyzed by palladium-alumina in powder form in agitated vessels. The physical diffusion of hydrogen through the liquid is the rate-controlling step. The total resistance of this transfer consisted of two separate resistances, one in the liquid adjoining the bubbles and another in the liquid adjoining the suspended solid particles. 

As a second process, the hydrogenation of a-methylstyrene is a standard process for elucidating mass transfer effects in catalyst pellets and in fixed-bed reactors... 

Hanika et al. (62) and Germain et al. (63) observed multiple steady states in the trickle-bed reactors for the hydrogenation of cyklohexane and hydrogenation of a-methylstyrene, respectively. One possible explanation of this effect is an abrupt increase of the reaction rate arising from temperature gradients within the bed and in the gas film surrounding the... 

The hydrogenation of a-methylstyrene was investigated to demonstrate the performance of a packed-bed microreactor with a palladium catalyst supported on activated carbon [324]. The microreactor was operated at 50 °C, and conversions from 20 to 100% were measured. It was determined that the reaction is first order for hydrogen and zero order for a-methylstyrene. Initial reaction rates were close to 0.01 mol/min per reaction channel and were achieved without additional activation of the catalyst. This is in agreement with the literature data on intrinsic kinetics. 

Hydrogenation of a-methylstyrene to cumene in 0.5% and 1% Pd-on-alumina Petroleum hydrocracking, hydrodenit rogenation, hydrodesulfurization, and hydrogenation... 

As an example of the performance of a monolith illustrating these points, the hydrogenation of a-methylstyrene was compared with a trickle-bed reactor and a monolith imder identical reaction conditions... 

Mazzarino and Baldi [27] investigated hydrogenation of a-methylstyrene into cumene, using a ceramic monolith coated with Pd (1% of active metal). They studied the... 

Figure 5 Rates of hydrogenation of a-methylstyrene versus gas flow rate 313 K. (From Ref. 27.)...

Fig. 22.7 Shape-selective inhibition of the hydrogenation of a-methylstyrene on a molecularly imprinted Rh-amine monomer catalyst with different amine inhibitors (A-l-A-7) [62]...

The hydrogenation of a-methylstyrene was studied at 60°C and 50 psia in a 2-inch-diameter reactor packed with Vs-inch catalyst pellets. The reactor was operated with downflow of liquid and gas using 3-ft and... 

In 1977 Sweany and Halpern reported the hydrogenation of a-methylstyrene by (CO)5MnH and proposed that it began with a similar step, the reversible transfer of H" from Mn-H to the olefin (1.14) [49]. They estabUshed reversibility by showing that exchange between (CO)sMnH and a-methylstyrene was faster than the overall reaction. 

The stirred flow reactor is frequently chosen when temperature control is a critical aspect, as in the nitration of aromatic hydrocarbons or glycerine (Biazzi-process). The stirred flow reactor is also chosen when the conversion must take place at a constant composition, as in the copol3rmerization of butadiene and styrene, or when a reaction between two phases has to be carried out, or when a catalyst must be kept in suspension as in the polymerization of ethylene with Ziegler catalyst, the hydrogenation of a-methylstyrene to cumene, and the air oxidation of cumene to acetone and phenol (Hercules-Distillers process). 

Kreutzer et al. [15] demonstrated experimentally using the hydrogenation of a-methylstyrene that at low velocity the mass transfer to the wall indeed increased. So, we again observed that surface tension assists in obtaining high mass transfer. The trick is to use the surface tension in a focused manner in laminar flow, as opposed to trying to fight it in a turbulent environment. 

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