Styrene, hydrogenation

Acetophenone is separated for hydrogenation to 1-phenylethanol, which is sent to the dehydrator to produce styrene. Hydrogenation is done over a fixed-bed copper-containing catalyst at 115—120°C and pressure of 8100 kPa (80 atm), a 3 1 hydrogen-to-acetophenone ratio, and using a solvent such as ethylbenzene, to give 95% conversion of the acetophenone and 95% selectivity to 1-phenylethanol (186,187). 

Moreover, stable liquid systems made up of nanoparticles coated with a surfactant monolayer and dispersed in an apolar medium could be employed to catalyze reactions involving both apolar substrates (solubilized in the bulk solvent) and polar and amphiphilic substrates (preferentially encapsulated within the reversed micelles or located at the surfactant palisade layer) or could be used as antiwear additives for lubricants. For example, monodisperse nickel boride catalysts were prepared in water/CTAB/hexanol microemulsions and used directly as the catalysts of styrene hydrogenation [215]. 

In a recent development, a new process of preparing borane-terminated isotactic polypropylene (z -PPs) via an in situ chain-transfer reaction was achieved by a styrene/hydrogen consecutive chain-transfer reagent, which avoids the use of a B—H containing chain-transfer agent.74 This has resulted in the utilization of milder polymerization conditions due to the use of the alkylaluminoxane cocatalyst (MAO) (50) (Fig. 33), which cannot normally be used in the presence of a B—H chain-transferring... 

A kinetic analysis of the styrene hydrogenation catalyzed by [Pt2(P205H2)4]4 [66] was indicative of the fact that the dinuclear core of the catalyst was maintained during hydrogenation. However, three speculative mechanisms were in agreement with the kinetic data, which mainly differ in the H2 activation step. This in fact can occur through the formation of two Pt-monohydrides, still connected by a Pt-Pt bond, or through the formation of two independent Pt-monohydrides. The third mechanism involves the dissociation of a phosphine from one Pt center, with subsequent oxidative addition of H2 to produce a Pt-dihy-dride intermediate. 

Ethylbenzene Styrene + Hydrogen The material balance on the flow reactor,... 

H2 and then CO2 pressure were applied, forming a GXL. The fluorinated catalyst then partitioned off of the fluorinated silica support and into the CO2-expanded organic phase. The reaction was assumed to occur in the expanded liquid phase in which reactants (styrene, hydrogen) and catalyst (fluorinated Wilkinson s catalyst) are homogeneously present. After the reaction was completed, the pressure was released and the catalyst then partitioned back onto the silica surface. 

The recyclability of the fluorinated catalyst was investigated. Five consecutive runs were carried out successfully with the same initial fluorinated catalyst/silica. The styrene hydrogenation activity proved to be relatively consistent (TOF from 250-400 h ) for each of the five runs, indicating minimal loss of catalytic activity. 

Dowden and Reynolds (49,50) in further experimental work on the hydrogenation of benzene and styrene with nickel-copper alloys as catalysts, found a similar dependence. The specific activities of the nickel-copper alloy catalysts decreased with increasing copper content to a negligible value at 60% copper and 30-40% copper for benzene and styrene, respectively. Low-temperature specific heat data indicated a sharp fall (1) in the energy density of electron levels N(E) at the Fermi surface, where the d-band of nickel becomes filled at 60 % copper, and (2) from nickel to the binary alloy 80 nickel -)- 20 iron. Further work by these authors (50) on styrene hydrogenation with nickel-iron alloy... 

Reaction of tetranuclear lanthanide octahydrides with styrene provides lanthanide benzylic allyl heptahydride complexes through the insertion of a styrene molecule into one Ln-H bond. The lanthanide benzylic allyl complexes can be considered as the intermediates of styrene hydrogenation. Indeed, both the lanthanide octahydrides and the lanthanide benzylic allyl complexes can catalyze styrene hydrogenation efficiently in the presence of H2 [89]. Lanthanide hydrides react with 1,3-cyclohexadiene to form lanthanide allylic complexes via 1,4-addition [90]. However, these lanthanide hydride clusters can not catalyze the polymerization of styrene and 1,4-cyclohexadiene. 

The use of core-shell impact modifiers combined with styrene-hydrogenated poly butadiene block copolymers in sPS is described by Rohm and Haas [24]. The core of the former type is of polybutadiene or its copolymer, the shell consists predominately of polystyrene. Rohm and Haas found that a synergistic effect is present and that the Izod notched impact strength is higher when both rubber types are used instead of only one. 

If we look at the three panels of data in Figure 21.4, we can begin to appreciate the intractable nature of some of the styrene-hydrogenated rubber-styrene block copolymers. The right panel shows an SBS polymer (not hydrogenated) that is typical in its overall size and styrene content for a commercial polymer. Viscosity is plotted versus shear stress at two testing temperatures (200 and 220 CC) for this SBS polymer, and it serves as our reference point for the center panel. 

TRI-BLOCK COPOLYMER OF STYRENE-HYDROGENATED BUTADIENE-STYRENE [S-BH-S] [6]... 

The resulting TPE can either be used alone or blended with aliphatic oil and polypropylene. In the former case a higher tensile strength and elongation at break are obtained in comparison with the commercially available styrene-hydrogenated butadiene-styrene block copolymers, especially at high temperatures. 

Fig. 12.5. Dependence of the rate of styrene hydrogenation on the Aq of the nickel catalysts listed in Table 12.2. The numbers in the figure correspond to the catalyst numbers in this table. (Redrawn using data from Ref. 129.)...

FIGURE 2, Phenyl acetylene and styrene hydrogenation over Pd/C... 

In the reaction of styrene hydrogenation in toluene, interlayer solvent displacement and clay shrinkage do not occur, as the product ethylbenzene is very similar in character to the solvent molecules. 

Data collected in Table 2 indicate that all Pd-montmorillonite samples were active catalysts in styrene hydrogenation. This is not surprising, since both the sur ce and the internal alkyl... 

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